Preclinical development of the class I selective histone deacetylase inhibitor OKI-179 for the treatment of solid tumors

Histone deacetylases (HDACs) play critical roles in epigenomic regulation and histone acetylation is dysregulated in many human cancers. While HDAC inhibitors are active in T-cell lymphomas, poor isoform selectivity, narrow therapeutic indices and a deficiency of reliable biomarkers may contribute to the lack of efficacy in solid tumors. In this article, we report the discovery and preclinical development of the novel, orally bioavailable, class I-selective HDAC inhibitor, OKI-179. OKI-179 and its cell active predecessor OKI-005 are thioester prodrugs of the active metabolite OKI-006, a unique congener of the natural product HDAC inhibitor largazole. OKI-006, OKI-005 and subsequently OKI-179, were developed through a lead candidate optimization program designed to enhance physiochemical properties without eroding potency and selectivity relative to largazole. OKI-005 displays anti-proliferative activity in vitro with induction of apoptosis and increased histone acetylation, consistent with target engagement. OKI-179 demonstrated anti-tumor activity in preclinical cancer models with a favorable pharmacokinetic profile and on-target pharmacodynamic effects. Based on its potency, desirable class I HDAC inhibition profile, oral bioavailability, and efficacy against a broad range of solid tumors, OKI-179 is currently being evaluated in a first-in-human phase I clinical trial with plans for continued clinical development in solid tumor and hematologic malignancies.

WEE1 Inhibition in Combination With Targeted Agents and Standard Chemotherapy in Preclinical Models of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal cancer with high incidences of p53 mutations. AZD1775 (adavosertib, previously MK-1775) is a small molecule WEE1 inhibitor that abrogates the G2M checkpoint and can potentially synergize with DNA damaging therapies commonly used in PDAC treatment. The purpose of this study was to identify combination partners for AZD1775, including standard chemotherapy or targeted agents, in PDAC preclinical models. Low powered preliminary screens demonstrated that two of the four PDX models responded better to the combinations of AZD1775 with irinotecan or capecitabine than to either single agent. Following the screens, two full powered PDAC PDX models of differing p53 status were tested with the combinations of AZD1775 and irinotecan or capecitabine. The combinations of AZD1775 and SN38 or 5-FU were also tested on PDAC cell lines. Cellular proliferation was measured using an IncuCyte Live Cell Imager and apoptosis was measured using a Caspase-Glo 3/7 assay. Flow cytometry was conducted to measure alterations in cell cycle distribution. Western blot analysis was used to determine the effects of the drug combinations on downstream effectors. In PDX models with mutated p53 status, there was significant tumor growth inhibition from the combination of AZD1775 with irinotecan or capecitabine (P ≤ 0.03), while PDX models with wild type p53 did not show anti-tumor synergy from the same combinations (P ≥ 0.08). The combination of AZD1775 with SN38 or 5-FU significantly decreased proliferation in all PDAC cell lines, and enhanced apoptosis in multiple cell lines. Cell cycle distribution was disrupted from the combination of AZD1775 with SN38 or 5-FU which was recorded as G2M arrest and decreased G1 phase. AZD1775 inhibited phospho-CDC2 and increased the expression of γH2AX that was either maintained or enhanced after combination with SN38 or 5-FU. The combination of AZD1775 with irinotecan/SN38 or capecitabine/5-FU showed anti-tumor effects in vivo and in vitro in PDAC models. These results support further investigation for these combination strategies to enhance outcomes for PDAC patients.

RX-5902, a novel β-catenin modulator, potentiates the efficacy of immune checkpoint inhibitors in preclinical models of triple-negative breast Cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype with limited systemic treatment options. RX-5902 is a novel anti-cancer agent that inhibits phosphorylated-p68 and thus attenuates nuclear β-catenin signaling. The purpose of this study was to evaluate the ability of β-catenin signaling blockade to enhance the efficacy of anti-CTLA-4 and anti-PD-1 immune checkpoint blockade in immunocompetent, preclinical models of TNBC.

METHODS

Treatment with RX-5902, anti-PD-1, anti-CTLA-4 or the combination was investigated in BALB/c mice injected with the 4 T1 TNBC cell line. Humanized BALB/c-Rag2nullIl2rγnullSIRPαNOD (hu-CB-BRGS) mice transplanted with a human immune system were implanted with MDA-MB-231 cells. Mice were randomized into treatment groups according to human hematopoietic chimerism and treated with RX-5902, anti-PD-1 or the combination. At sacrifice, bone marrow, lymph nodes, spleen and tumors were harvested for flow cytometry analysis of human immune cells.

RESULTS

The addition of RX-5902 to CTLA-4 or PD-1 inhibitors resulted in decreased tumor growth in the 4 T1 and human immune system and MDA-MB-231 xenograft models. Immunologic analyses demonstrated a significant increase in the number of activated T cells in tumor infiltrating lymphocytes (TILs) with RX-5902 treatment compared to vehicle (p < 0.05). In the RX-5902/nivolumab combination group, there was a significant increase in the percentage of CD4+ T cells in TILs and increased systemic granzyme B production (p < 0.01).

CONCLUSIONS

Conclusions: RX-5902 enhanced the efficacy of nivolumab in a humanized, preclinical model of TNBC. Several changes in immunologic profiles were noted in mice treated with RX-5902 and the combination, including an increase in activated TILs and a decrease in human myeloid populations, that are often associated with immunosuppression in a tumor microenvironment. RX-5902 also was shown to potentiate the effects of checkpoint inhibitors of CTLA4 and the PD-1 inhibitor in the 4 T-1 murine TNBC model. These findings indicate that RX-5902 may have important immunomodulatory, as well as anti-tumor activity, in TNBC when combined with a checkpoint inhibitor.

Preclinical and Dose-Finding Phase I Trial Results of Combined Treatment with a TORC1/2 Inhibitor (TAK-228) and Aurora A Kinase Inhibitor (Alisertib) in Solid Tumors

PURPOSE

The purpose of this study was to evaluate the rational combination of TORC1/2 inhibitor TAK-228 and Aurora A kinase inhibitor alisertib in preclinical models of triple-negative breast cancer (TNBC) and to conduct a phase I dose escalation trial in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

TNBC cell lines and patient-derived xenograft (PDX) models were treated with alisertib, TAK-228, or the combination and evaluated for changes in proliferation, cell cycle, mTOR pathway modulation, and terminal cellular fate, including apoptosis and senescence. A phase I clinical trial was conducted in patients with advanced solid tumors treated with escalating doses of alisertib and TAK-228 using a 3+3 design to determine the maximum tolerated dose (MTD).

RESULTS

The combination of TAK-228 and alisertib resulted in decreased proliferation and cell-cycle arrest in TNBC cell lines. Treatment of TNBC PDX models resulted in significant tumor growth inhibition and increased apoptosis with the combination. In the phase I dose escalation study, 18 patients with refractory solid tumors were enrolled. The MTD was alisertib 30 mg b.i.d. days 1 to 7 of a 21-day cycle and TAK-228 2 mg daily, continuous dosing. The most common treatment-related adverse events were neutropenia, fatigue, nausea, rash, mucositis, and alopecia.

CONCLUSIONS

The addition of TAK-228 to alisertib potentiates the antitumor activity of alisertib in vivo, resulting in increased cell death and apoptosis. The combination is tolerable in patients with advanced solid tumors and should be evaluated further in expansion cohorts with additional pharmacodynamic assessment.

Wee1 Inhibition Enhances the Anti-Tumor Effects of Capecitabine in Preclinical Models of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype defined by lack of hormone receptor expression and non-amplified HER2. Adavosertib (AZD1775) is a potent, small-molecule, ATP-competitive inhibitor of the Wee1 kinase that potentiates the activity of many DNA-damaging chemotherapeutics and is currently in clinical development for multiple indications. The purpose of this study was to investigate the combination of AZD1775 and capecitabine/5FU in preclinical TNBC models. TNBC cell lines were treated with AZD1775 and 5FU and cellular proliferation was assessed in real-time using IncuCyte^® Live Cell Analysis. Apoptosis was assessed via the Caspase-Glo 3/7 assay system. Western blotting was used to assess changes in expression of downstream effectors. TNBC patient-derived xenograft (PDX) models were treated with AZD1775, capecitabine, or the combination and assessed for tumor growth inhibition. From the initial PDX screen, two of the four TNBC PDX models demonstrated a better response in the combination treatment than either of the single agents. As confirmation, two PDX models were expanded for statistical comparison. Both PDX models demonstrated a significant growth inhibition in the combination versus either of the single agents. (TNBC012, p < 0.05 combo vs. adavosertib or capecitabine, TNBC013, p < 0.01 combo vs. adavosertib or capecitabine.) An enhanced anti-proliferative effect was observed in the adavosertib/5FU combination treatment as measured by live cell analysis. An increase in apoptosis was observed in two of the four cell lines in the combination when compared to single-agent treatment. Treatment with adavosertib as a single agent resulted in a decrease in p-CDC2 in a dose-dependent manner that was also observed in the combination treatment. An increase in γH2AX in two of the four cell lines tested was also observed. No significant changes were observed in Bcl-xL following treatment in any of the cell lines. The combination of adavosertib and capecitabine/5FU demonstrated enhanced combination effects both in vitro and in vivo in preclinical models of TNBC. These results support the clinical investigation of this combination in patients with TNBC, including those with brain metastasis given the CNS penetration of both agents.

Abstract P1-19-25: Wee1 inhibition enhances the anti-tumor effects of capecitabine in preclinical models of triple negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype defined by lack of hormone receptor expression and non-amplified HER2. TNBC accounts for approximately 15% of breast cancer cases, however, is associated with an increased risk of cancer recurrence, brain metastasis, and death due to metastatic breast cancer. Mutations in p53 are common in TNBC, occurring in approximately 85% of tumors. While a number of promising targeted therapies are on the horizon in TNBC including immunotherapy, there remains an unmet need for active targeted therapies where chemotherapy remains the standard treatment for metastatic disease and results in a median survival of 12-18 months. Adavosertib (AZD1775) is a potent, small molecule, ATP-competitive inhibitor of the Wee1 kinase that potentiates the activity of many DNA-damaging chemotherapeutics and is currently in clinical development for multiple indications. AZD1775 potentiates the activity of DNA-damaging and antimetabolite chemotherapeutics in preclinical models without TP53-deficiency, possibly due to baseline replicative stress or compromised DNA repair proficiency. A previous unbiased screen of CTEP compounds in TNBC PDX models demonstrated that the combination of adavosertib and capecitabine/5FU had greater anti-proliferative effects than either of the single agents. The purpose of this study was to further investigate the combination of adavosertib and capecitabine/5FU in preclinical TNBC models. Methods: HCC1937, CAL51, MDA-MB-231 and MDA-MB-468 cells were plated in 96-well plates and exposed to increasing concentrations of adavosertib, 5FU, or the combination. Cellular proliferation was assessed in real-time using IncuCyte® Live Cell Analysis. Apoptosis was assessed via the Caspase-Glo 3/7 assay system. Western blotting was used to assess changes in expression of CDC2, phospho-CDC2, H2AX, and Bcl-xL. TNBC PDX models CU_TNBC_012 and CU_TNBC_013 were treated with vehicle, adavosertib, capecitabine, or the combination and assessed for tumor growth inhibition. Results: From the initial PDX screen, two of the four TNBC PDX models demonstrated a better response in the combination treatment than either of the single agents. As confirmation, two PDX models were expanded for statistical comparison. Both PDX models demonstrated a significant growth inhibition in the combination versus either of the single agents. (TNBC012, p&lt;0.05 combo vs adavosertib or capecitabine, TNBC013, p&lt;0.01 combo vs adavosertib or capecitabine ). An enhanced antiproliferative effect was observed in the adavosertib/5FU combination treatment as measured by live cell analysis. An increase in apoptosis was observed in two of the four cell lines in the combination when compared to single agent treatment. Treatment with single agent adavosertib resulted in an increase in p-cdc2 in a dose dependent manner that was also observed in the combination treatment. Similar results were observed with γH2AX in two of the four cell lines tested. No significant changes were observed in Bcl-xL following treatment in any of the cell lines. Conclusions: The combination of adavosertib and capecitabine/5-FU demonstrated enhanced combination effects both in vitro and in vivo in preclinical models of TNBC. These results support the clinical investigation of this combination in patients with TNBC, including those with brain metastasis given the CNS penetration of both agents.

Citation Format: Todd M Pitts, Dennis M Simmons, Kyrie Dailey, Stacey M Bagby, Sarah J Hartman, Betelehem W Yacob, Brian Gittleman, John J Tentler, Diana Cittely, D. Ryan Ormond, Wells A Messersmith, S Gail Eckhardt, Jennifer R Diamond. Wee1 inhibition enhances the anti-tumor effects of capecitabine in preclinical models of triple negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-19-25.

First-in-Class Phosphorylated-p68 Inhibitor RX-5902 Inhibits β-Catenin Signaling and Demonstrates Antitumor Activity in Triple-Negative Breast Cancer

RX-5902 is a first-in-class anticancer agent targeting phosphorylated-p68 and attenuating nuclear shuttling of β-catenin. The purpose of this study was to evaluate the efficacy of RX-5902 in preclinical models of triple-negative breast cancer (TNBC) and to explore effects on β-catenin expression. A panel of 18 TNBC cell lines was exposed to RX-5902, and changes in proliferation, apoptosis, cellular ploidy, and effector protein expression were assessed. Gene expression profiling was used in sensitive and resistant cell lines with pathway analysis to explore pathways associated with sensitivity to RX-5902. The activity of RX-5902 was confirmed in vivo in cell line and patient-derived tumor xenograft (PDX) models. RX-5902 demonstrated potent antiproliferative activity in vitro against TNBC cell lines with an average IC₅₀ of 56 nmol/L in sensitive cell lines. RX-5902 treatment resulted in the induction of apoptosis, G₂-M cell-cycle arrest, and aneuploidy in a subset of cell lines. RX-5902 was active in vivo against TNBC PDX models, and treatment resulted in a decrease in nuclear β-catenin. RX-5902 exhibited dose-proportional pharmacokinetics and plasma and tumor tissue in nude mice. Pathway analysis demonstrated an increase in the epithelial-to-mesenchymal transformation (EMT), TGFβ, and Wnt/β-catenin pathways associated with sensitivity to RX-5902. RX-5902 is active against in vitro and in vivo preclinical models of TNBC. Target engagement was confirmed with decreases in nuclear β-catenin and MCL-1 observed, confirming the proposed mechanism of action. This study supports the continued investigation of RX-5902 in TNBC and combinations with immunotherapy.

Abstract P2-06-15: Rational combination of Wee1 and BCL-2 inhibition in preclinical models of triple-negative breast cancer

Background:

Triple-negative breast cancer (TNBC) is an aggressive subtype distinguished by its lack of expression of receptors for estrogen, progesterone, and normal human epidermal growth factor 2 expression. TNBC is difficult to treat and is associated with a high risk of recurrence and mortality. In order to effectively treat TNBC, alternative therapeutic targets need to be identified. Wee1 is a tyrosine kinase that phosphorylates CDC2 to pause the cell cycle at the G2 checkpoint as a means to delay mitosis while DNA damage undergoes repair. Inactivation of Wee1 via adavosertib (AZD1775, MK1775), a highly selective inhibitor of Wee1, allows CDC25 to dephosphorylate the CDC2/cyclin B complex resulting in premature initiation of mitosis and, ultimately, mitotic catastrophe and apoptosis. An unbiased screen of adovosertib in combination with other targeted compounds in TNBC patient-derived xenograft (PDX) models demonstrated that the combination of adavosertib and navitoclax, an inhibitor of anti-apoptotic BCL-2 and BCL-XL proteins, had greater efficacy than the single agents alone. The purpose of this study was to investigate the combination of adavosertib and navitoclax in preclinical TNBC models, both in vitro and in vivo.

Methods:

HCC1937, CAL51, MDA-MB-231 and MDA-MB-468 cells were plated in 96-well plates and exposed to increasing concentrations of adavosertib (125nM – 1000nM), navitoclax (2500nM – 10000nM), or the combination. Cellular proliferation was assessed in real-time using IncuCyte Live Cell Analysis, followed by endpoint sulforhodamine B (SRB) assay. Combination effects were analyzed using Calcusyn to determine combination indexes (CI). Apoptosis was assessed via the Caspase 3/7 assay. Western blotting was used to assess changes in expression of CDC2, phospho-CDC2, and BCL2. TNBC PDX models CU_TNBC_013 and CU_TNBC_014 were treated with vehicle, adavosertib (50mg/kg), navitoclax (100mg/kg), or the combination and assessed for tumor growth inhibition.

Results:

The combination of adavosertib and navitoclax resulted in greater antiproliferative effects in vitro compared to either single agent (p&lt; 0.05). This effect was classified as synergistic with CI values &lt;1. We observed a significant increase in apoptosis with the combination treatment as measured by Caspase 3/7 (p &lt;0.005). The combination of adavosertib and navitoclax treatment resulted in a decrease in phospo-CDC2, and BCL2 in cell lines. In vivo, the combination treatment resulted in greater tumor growth inhibition as compared to adavosertib or navitoclax alone in the CU_TNBC_013 and CU_TNBC_014 PDX models.

Conclusions:

The combination of adavosertib and navitoclax is active in preclinical TNBC models and induces apoptosis and tumor growth inhibition. This data supports the continued development of this combination in TNBC with investigation of potential selective markers.

Citation Format: Simmons DM, Tse TE, Dailey K, Hartman SJ, Bagsby S, Pitts TM, Tentler JJ, Diamond JR. Rational combination of Wee1 and BCL-2 inhibition in preclinical models of triple-negative breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-06-15.

Inhibition of MERTK Promotes Suppression of Tumor Growth in BRAF Mutant and BRAF Wild-Type Melanoma

Molecularly-targeted agents have improved outcomes for a subset of patients with BRAF-mutated melanoma, but treatment of resistant and BRAF wild-type tumors remains a challenge. The MERTK receptor tyrosine kinase is aberrantly expressed in melanoma and can contribute to oncogenic phenotypes. Here we report the effect of treatment with a MERTK-selective small molecule inhibitor, UNC2025, in preclinical models of melanoma. In melanoma cell lines, treatment with UNC2025 potently inhibited phosphorylation of MERTK and downstream signaling, induced cell death, and decreased colony formation. In patient-derived melanoma xenograft models, treatment with UNC2025 blocked or significantly reduced tumor growth. Importantly, UNC2025 had similar biochemical and functional effects in both BRAF-mutated and BRAF wild-type models and irrespective of NRAS mutational status, implicating MERTK inhibition as a potential therapeutic strategy in tumors that are not amenable to BRAF-targeting and for which there are limited treatment options. In BRAF-mutated cell lines, combined treatment with UNC2025 and the BRAF inhibitor vemurafenib provided effective inhibition of oncogenic signaling through ERK, AKT, and STAT6, increased induction of cell death, and decreased colony-forming potential. Similarly, in NRAS-mutated cell lines, addition of UNC2025 to cobimetinib therapy increased cell death and decreased colony-forming potential. In a BRAF-mutated patient-derived xenograft, treatment with combined UNC2025 and vemurafenib was well-tolerated and significantly decreased tumor growth compared with vemurafenib alone. These data support the use of UNC2025 for treatment of melanoma, irrespective of BRAF or NRAS mutational status, and suggest a role for MERTK and targeted combination therapy in BRAF and NRAS-mutated melanoma.

BRAF fusions identified in melanomas have variable treatment responses and phenotypes

Oncogenic BRAF fusions have emerged as an alternate mechanism for BRAF activation in melanomas and other cancers. A number of BRAF fusions with different 5' gene partners and BRAF exon breakpoints have been described, but the effects of different partners and breakpoints on cancer phenotypes and treatment responses has not been well characterized. Targeted RNA sequencing was used to screen 60 melanoma patient-derived xenograft (PDX) models for BRAF fusions. We identified three unique BRAF fusions, including a novel SEPT3-BRAF fusion, occurring in four tumors (4/60, 6.7%), all of which were "pan-negative" (lacking other common mutations) (4/18, 22.2%). The BRAF fusion PDX models showed variable growth rates and responses to MAPK inhibitors in vivo. Overexpression of BRAF fusions identified in our study, as well as other BRAF fusions previously identified in melanomas, resulted in a high degree of variability in 2D proliferation and 3D invasion between the different fusions. While exogenously expressed BRAF fusions all responded to MAPK inhibition in vitro, we observed potential differences in signaling and feedback mechanisms. In summary, BRAF fusions are actionable therapeutic targets, however there are significant differences in phenotypes, treatment responses, and signaling which may be clinically relevant.

A phase II clinical trial of the Aurora and angiogenic kinase inhibitor ENMD-2076 for previously treated, advanced, or metastatic triple-negative breast cancer

Background

Triple-negative breast cancer (TNBC) remains an aggressive breast cancer subtype with limited treatment options. ENMD-2076 is a small-molecule inhibitor of Aurora and angiogenic kinases with proapoptotic and antiproliferative activity in preclinical models of TNBC.

Methods

This dual-institution, single-arm, two-stage, phase II clinical trial enrolled patients with locally advanced or metastatic TNBC previously treated with one to three prior lines of chemotherapy in the advanced setting. Patients were treated with ENMD-2076 250 mg orally once daily with continuous dosing in 4-week cycles until disease progression or unacceptable toxicity occurred. The primary endpoint was 6-month clinical benefit rate (CBR), and secondary endpoints included progression-free survival, pharmacokinetic profile, safety, and biologic correlates in archival and fresh serial tumor biopsies in a subset of patients.

Results

Forty-one patients were enrolled. The 6-month CBR was 16.7% (95% CI, 6–32.8%) and included two partial responses. The 4-month CBR was 27.8% (95% CI, 14–45.2%), and the average duration of benefit was 6.5 cycles. Common adverse events included hypertension, fatigue, diarrhea, and nausea. Treatment with ENMD-2076 resulted in a decrease in cellular proliferation and microvessel density and an increase in p53 and p73 expression, consistent with preclinical observations.

Conclusions

Single-agent ENMD-2076 treatment resulted in partial response or clinical benefit lasting more than 6 months in 16.7% of patients with pretreated, advanced, or metastatic TNBC. These results support the development of predictive biomarkers using archival and fresh tumor tissue, as well as consideration of mechanism-based combination strategies.

Trial registration

ClinicalTrials.gov, NCT01639248. Registered on July 12, 2012.

Antitumor activity of the aurora a selective kinase inhibitor, alisertib, against preclinical models of colorectal cancer

Background

The Aurora kinases are a family of serine/threonine kinases comprised of Aurora A, B, and C which execute critical steps in mitotic and meiotic progression. Alisertib (MLN8237) is an investigational Aurora A selective inhibitor that has demonstrated activity against a wide variety of tumor types in vitro and in vivo, including CRC.

Results

CRC cell lines demonstrated varying sensitivity to alisertib with IC₅₀ values ranging from 0.06 to > 5 umol/L. Following exposure to alisertib we observed a decrease in pAurora A, B and C in four CRC cell lines. We also observed an increase in p53 and p21 in a sensitive p53 wildtype cell line in contrast to the p53 mutant cell line or the resistant cell lines. The addition of alisertib to standard CRC treatments demonstrated improvement over single agent arms; however, the benefit was largely less than additive, but not antagonistic.

Methods

Forty-seven CRC cell lines were exposed to alisertib and IC₅₀s were calculated. Twenty-one PDX models were treated with alisertib and the Tumor Growth Inhibition Index was assessed. Additionally, 5 KRAS wildtype and mutant PDX models were treated with alisertib as single agent or in combination with cetuximab or irinotecan, respectively.

Conclusion

Alisertib demonstrated anti-proliferative effects against CRC cell lines and PDX models. Our data suggest that the addition of alisertib to standard therapies in colorectal cancer if pursued clinically, will require further investigation of patient selection strategies and these combinations may facilitate future clinical studies.

Abstract P5-21-16: Preclinical studies of RX-5902, a beta-catenin modulator in triple negative breast cancer

Background: RX-5902 (Supinoxin) is a novel anti-cancer compound that targets phosphorylated p68 RNA helicase, a member of the DEAD box family of helicases, affecting upstream and downstream molecules in the Wnt canonical pathway. As a single agent, RX-5902 exhibits strong growth inhibition in both in vitro and in vivo settings. Specifically, RX-5902 enhances survival and tumor growth inhibition in numerous xenograft models, including ovarian, renal and breast. We have previously shown RX-5902 inhibits cell growth in a dose-dependent fashion in the triple-negative breast cancer (TNBC) xenograft MDA-MB231. In the current study, we have expanded our investigation of the therapeutic potential of RX-5902 against TNBC using both in vitro and in vivo preclinical models.

Methods: RX-5902 was provided by Rexahn, Inc. (Rockville, MD). Cell proliferation was measured using the Cell-Titer Glo luminescent cell viability assay (Promega). Apoptosis was assessed using Incucyte Caspase 3/7 Green apoptosis assay (Essenbioscience). Immunoblots of MDA-MB-231 cell line were probed for ß-catenin (Cell Signaling). Syngeneic 4T1 murine TNBC mice were obtained from Sippr-BK Laboratory Animal Co (Shanghai, China) and tumor volumes were measured twice a week. When the mean tumor volumes reached ˜90 mm3, mice were randomized and treated with vehicle or RX-5902 PO daily alone or in combination with anti-CTLA4 or anti-PD-1 BIW for 3 weeks. Tumor growth inhibition (TGI) was calculated at Day 25.

Results: A panel of 18 TNBC cell lines were treated with RX-5902 and effects on cell proliferation were measured by the Cell Titer-Glo assay. Using 100nM as a cutoff, 14 sensitive lines and 4 resistant lines were identified, with an average IC50 of 56 nM in the sensitive lines. Of these, we chose 2 sensitive lines (MDA-MB-231, HCC1806) and 2 resistant lines (MDA-MB-436 and CAL-120) and assessed induction of apoptosis by the Incucyte caspase activity assay. Robust induction of apoptosis was observed in both sensitive lines (N=3). These lines were then subjected to cell cycle analysis by flow cytometry, which revealed a pronounced G2/M cell cycle arrest and aneuploidy following exposure to RX-5902. Western blot analysis of the MDA-MB-231 cell line showed decreases in the Wnt pathway-related protein nuclear ß-catenin in doses ranging from 20 nM to 200 nM. Finally, the therapeutic efficacy of RX-5902 was assessed as a single agent and in combination with two immune-oncology agents in the treatment of the TNBC 4T1 animal model. RX-5902 as a single agent showed dose dependency in the 4T1 model, and when given in combination with either anti-CTLA4 or anti-PD1 showed an additive effect (p&lt;0.001). All the treatments were well-tolerated and no severe body weight loss was observed in this study.

Conclusions: RX-5902 showed efficacy against several in vitro and in vivo preclinical models of TNBC. RX-5902 resulted in G2/M arrest and induced apoptosis in sensitive TNBC cell lines and decreases in nuclear beta-catenin. In vivo, RX-5902 demonstrated additive anti-tumor effects when combined with either anti-CTLA4 or anti-PD1 immunotherapies. Together, these finding indicate that RX-5902 may have important clinical implications for the treatment of TNBC. A phase 2a clinical study in metastatic TNBC is ongoing..training_cert

Citation Format: Tentler JJ, Frank JG, Kim DJ, George C, Lee YB, Ely B, Tan AC, Kim J, Pitts TM, Capasso A, Dailey KL, Eckhardt G, Diamond JR. Preclinical studies of RX-5902, a beta-catenin modulator in triple negative breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-21-16.

Abstract PD3-16: Clinical safety and efficacy of the aurora and angiogenic kinase inhibitor ENMD-2076 in previously treated, locally advanced or metastatic triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype defined by the lack of expression of the estrogen and progesterone receptors and lack of HER2 over-expression. ENMD-2076 is an orally bioavailable small molecule inhibitor of Aurora and angiogenic kinases with pro-apoptotic and antiproliferative activity in preclinical models of TNBC.

Methods: This two institution, single-arm, two-stage, phase II clinical trial enrolled patients with locally advanced or metastatic TNBC refractory to 1-3 prior lines of chemotherapy in the advanced setting. Patients had ECOG PS ≤ 1, measureable disease by RECIST 1.1 and no evidence of brain metastasis. Patients were treated with ENMD-2076 250 mg PO daily with continuous dosing in 4-week cycles until disease progression or unacceptable toxicity occurred. The primary end point was 6-month clinical benefit rate (6-CBR) and secondary endpoints included time to progression (TTP), PK profile, safety and biologic correlatives in archival and fresh serial tumor biopsies in a subset of patients.

Results: Between July 2012 and October 2016, 41 patients were enrolled (median age 54; range 30-73; female 40; male 1). Patients received a mean 1.7 prior lines of chemotherapy for locally advanced unresectable or metastatic disease and 80.5% received prior neoadjuvant or adjuvant chemotherapy (N=33). Thirty-six patients were evaluable per protocol for the primary efficacy analysis. Five patients (12.2%) were not included in the efficacy analysis due to: adverse events (AE) leading to discontinuation prior to objective efficacy assessment (N=3), not meeting eligibility criteria on day 1 (N=1) and withdraw of consent in cycle 1 (N=1). The study proceeded to the second stage of enrollment based on observing three 6-CBR events in Stage 1 (N=18 patients). The 6-CBR in the overall trial was 16.7% (95% exact CI: 6%-32.8%; 2 patients with PR and 4 patients with SD &gt; 6 mos). The median duration of response or clinical benefit in these patients was 32 weeks (8 cycles). 4-CBR was 27.8% (95% exact CI: 14%-45.2%). Dose reduction occurred in 8 patients (20%) for fatigue, hypertension and proteinuria. The most common grade 3 treatment-related adverse events were hypertension (37.5%) and fatigue (10%). One patient experienced grade 4 hypertension. Analysis of serial tumor biopsies prior to and following 2 weeks of ENMD-2076 (N=8 patients), demonstrated a treatment-induced decrease in cellular proliferation (Ki-67) and microvessel density (CD34) as assessed by IHC. Immunofluorescence performed on a subset of samples demonstrated an increase in p53-family member expression following treatment, consistent with changes observed in preclinical TNBC patient-derived tumor xenograft models.

Conclusions: ENMD-2076 has durable clinical activity in a subset of patients with pretreated, advanced or metastatic triple-negative breast cancer. Predictive biomarker development using archival and fresh tumor tissue is underway. Exploration of lower doses of ENMD-2076 in future clinical trials may improve tolerability.

Citation Format: Diamond JR, Eckhardt SG, Pitts TM, van Bokhoven A, Aisner D, Gustafson DL, Capasso A, Elias AD, Storniolo AM, Schneider BP, Gao D, Tentler JJ, Borges VF, Miller KD. Clinical safety and efficacy of the aurora and angiogenic kinase inhibitor ENMD-2076 in previously treated, locally advanced or metastatic triple-negative breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr PD3-16.

Antitumor activity of the polo-like kinase inhibitor, TAK-960, against preclinical models of colorectal cancer

BACKGROUND

Polo-like kinase 1 (Plk1) is a serine/threonine kinase that is a key regulator of multiple stages of mitotic progression. Plk1 is upregulated in many tumor types including colorectal cancer (CRC) and portends a poor prognosis. TAK-960 is an ATP-competitive Plk1 inhibitor that has demonstrated efficacy across a broad range of cancer cell lines, including CRC. In this study, we investigated the activity of TAK-960 against a large collection of CRC models including 55 cell lines and 18 patient-derived xenografts.

METHODS

Fifty-five CRC cell lines and 18 PDX models were exposed to TAK-960 and evaluated for proliferation (IC50) and Tumor Growth Inhibition Index, respectively. Additionally, 2 KRAS wild type and 2 KRAS mutant PDX models were treated with TAK-960 as single agent or in combination with cetuximab or irinotecan. TAK-960 mechanism of action was elucidated through immunoblotting and cell cycle analysis.

RESULTS

CRC cell lines demonstrated a variable anti-proliferative response to TAK-960 with IC50 values ranging from 0.001 to > 0.75 μmol/L. Anti-proliferative effects were sustained after removal of drug. Following TAK-960 treatment a highly variable accumulation of mitotic (indicating cell cycle arrest) and apoptotic markers was observed. Cell cycle analysis demonstrated that TAK-960 treatment induced G2/M arrest and polyploidy. Six out of the eighteen PDX models responded to single agent TAK-960 therapy (TGII< 20). The addition of TAK-960 to standard of care chemotherapy resulted in largely additive antitumor effects.

CONCLUSION

TAK-960 is an active anti-proliferative agent against CRC cell lines and PDX models. Collectively, these data suggest that TAK-960 may be of therapeutic benefit alone or in combination with other agents, although future work should focus on the development of predictive biomarkers and hypothesis-driven rational combinations.

Abstract B175: Rational combination of mTOR and Aurora kinase A inhibition in preclinical models of triple-negative breast cancer

Background: Alisertib is a highly selective inhibitor of Aurora kinase A and has antiproliferative and proapoptotic activity in a subset of triple-negative breast cancer (TNBC) cell lines and patient-derived tumor xenograft (PDX) models. Cellular senescence and increased expression of genes in the PI3K/AKT/mTOR pathway has been observed in TNBC models following treatment with alisertib that demonstrate de novo or acquired resistance. The purpose of this study was to investigate the combination of alisertib and the TORC1/2 inhibitor TAK-228 in preclinical TNBC models. Methods: MDA-MB-468, HCC1187, HCC1937, CAL51, and BT20 cells were plated in 96 well plates and exposed to increasing concentrations of alisertib (25nM-125nM), TAK-228 (25nM-125nM), or the combination and proliferation was assessed using the Cell Titer-Glo (CTG) assay. Apoptosis was assessed using long-term live cell microscopy and caspase 3/7 staining. Western blotting was used to assess changes in pS6, p4EBP1, and survivin expression. TNBC p53 wildtype CAL51 cells were transfected with the fluorescent ubiquitin cell cycle indicator (FUCCI) reporters and exposed to increasing concentrations of alisertib, TAK-228, or the combination to evaluate the effect on cell cycle progression, growth, and apoptosis. TNBC PDX models CU_TNBC_004 and CU_TNBC_007 were treated with vehicle, alisertib (30mg/kg), TAK-228 (0.5mg/kg), or the combination and assessed for tumor growth inhibition and translational markers by immunofluorescence (IF) and senescence-associated- ß-galactosidase (SA-ß-gal) staining. Results: A combination effect was observed for alisertib and TAK-228 in vitro with a decrease in cellular proliferation with the combination as measured by CTG. We observed an increase in cell death with the combination, as opposed to cell cycle arrest with single-agent treatment. Alisertib treatment was associated with an increase in survivin not observed with combination treatment. TAK-228 treatment was associated with a decrease in pS6 and p4EBP1 as a single agent or in combination. The combination of TAK-228 and alisertib resulted in greater tumor growth inhibition in vivo as compared to either single agent alone, accompanied by an increase in apoptosis as measured by BAX and DR5 expression and a decrease in senescence as evaluated by SA-ß-gal and phenotypic changes. Single agents in the CAL51 FUCCI system resulted in a dose-dependent effect on cell cycle progression and apoptosis by live cell microscopy. The combination, however, led to a complete block of cell growth and simultaneous apoptosis, leading to no expansion of cells after treatment and a gradual loss of the cell population. Conclusions: The combination of alisertib and TAK-228 in vitro and in vivo in TNBC models resulted in greater antiproliferative and proapoptotic activity. This combination is currently being investigated in a phase I dose escalation trial in patients with advanced solid tumors with a planned expansion cohort in metastatic TNBC to further evaluate the mechanism of the combination (NCT02719691).

Citation Format: Jennifer R. Diamond, James D. Orth, Anastasia Ionkina, Kyrie Dailey, Todd M. Pitts, Anna Capasso, Joshua M. Marcus, Russell T. Burke, Sarah L. Davis, Jiyhe Kim, Aik-Choon Tan, Sue G. Eckhardt, John J. Tentler. Rational combination of mTOR and Aurora kinase A inhibition in preclinical models of triple-negative breast cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B175.

Abstract A083: A phase Ib study of the combination of MLN0128 (dual TORC1/2 inhibitor) and MLN8237 (Aurora A inhibitor, alisertib) in patients with advanced solid tumors

Background: MLN0128 is an oral inhibitor of mTOR kinase and mTORC1/2 signaling. Alisertib is an oral inhibitor of Aurora A kinase. Senescence and upregulation of genes in the PI3K/AKT/mTor pathway have been observed in triple-negative breast cancer (TNBC) patient-derived xenograft models treated with alisertib, with greater tumor growth inhibition demonstrated in combination with MLN0128 as compared to each agent alone. An investigator-initiated trial was developed to evaluate the combination of MLN0128 and alisertib in patients with advanced solid tumors, followed by an expansion cohort in metastatic TNBC and other selected cancers. The goals of this ongoing study are to evaluate safety, tolerability, pharmacokinetics (PK) and preliminary efficacy of the combination. Results of dose escalation are presented here. Methods: Patients with advanced solid tumors refractory to standard therapy were treated orally at escalating doses with the combination of MLN0128 daily on a continuous schedule and alisertib twice daily (BID) on days 1-7 of a 21-day cycle. Dose escalation was conducted according to a standard 3+3 design. Key eligibility criteria included HgbA1c &lt;7%, fasting serum glucose &lt;130mg/dL and fasting triglycerides &lt;300mg/dL, normal cardiac function, no condition with potential to cause excessive daytime sleepiness (including chronic hypoxia) and no risk of malabsorption of oral medications. PK assessments were performed at various time points after single-agent and combination dosing. Results: A total of 16 patients with refractory cancers were enrolled in dose escalation. No dose-limiting toxicity (DLT) was observed in dose level 1 (MLN0128 1mg/alisertib 30mg) or dose level 2 (2mg/30mg). At the third dose level (2mg/40mg) 2 of 7 patients experienced a DLT (grade 3 fatigue/confusion and grade 2 GERD/nausea leading to study discontinuation). In an alternate dose level cohort evaluating MLN0128 3mg and alisertib 30mg, 2 of 2 patients experienced a DLT of grade 3 fatigue. The maximum tolerated dose (MTD) of the combination was determined to be MLN0128 2mg daily and alisertib 30mg BID. Most common adverse events (AEs) of any grade included alopecia, diarrhea, fatigue and rash in 19% each and nausea in 31% of patients. Most common Grade 3 AEs included fatigue (19%) and decreased neutrophil count (31%). Dose modification was required in 56% of patients, most often due to neutropenia. Median time on study was 3 cycles (range 1-15) at data cutoff. Best response of stable disease was observed in 5 patients (31%), with prolonged stable disease noted in a patient with ER+/HER2- breast cancer (15 cycles) and a patient with castrate-resistant prostate cancer (10 cycles). PK assessments indicate no significant drug interaction between agents. Cmax was 24.7 (± 13.6) ng/mL for MLN0128 and 1049 (±363) ng/mL for alisertib at combination MTD doses. MLN0128 AUC was 128.2 (±72.7) ng/mLxhr and alisertib AUC0-8 was 6119 (±2331) ng/mlxhr at these doses. Conclusions: MLN0128 2mg daily on a continuous schedule and alisertib 30mg BID days 1-7 of a 21-day cycle is the MTD of the drug combination. An expansion cohort in patients with TNBC and other selected cancers is currently enrolling at this dose. Functional imaging and serial tumor biopsies are being integrated into this cohort to assess the pharmacodynamic interactions of the combination.

Citation Format: S. Lindsey Davis, Elaine T. Lam, Bradley R. Corr, Cindy L. O'Bryant, Ashley Glode, Nichole Adler, Todd M. Pitts, John J. Tentler, Anna Capasso, Kyrie Dailey, Natalie J. Serkova, Colin D. Weekes, Daniel L. Gustafson, Christopher H. Lieu, Wells A. Messersmith, Stephen Leong, S. Gail Eckhardt, Jennifer R. Diamond. A phase Ib study of the combination of MLN0128 (dual TORC1/2 inhibitor) and MLN8237 (Aurora A inhibitor, alisertib) in patients with advanced solid tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A083.

ALK Inhibitor Response in Melanomas Expressing EML4-ALK Fusions and Alternate ALK Isoforms

Oncogenic ALK fusions occur in several types of cancer and can be effectively treated with ALK inhibitors; however, ALK fusions and treatment response have not been characterized in malignant melanomas. Recently, a novel isoform of ALK (ALKATI ) was reported in 11% of melanomas but the response of melanomas expressing ALKATI to ALK inhibition has not been well characterized. We analyzed 45 melanoma patient-derived xenograft models for ALK mRNA and protein expression. ALK expression was identified in 11 of 45 (24.4%) melanomas. Ten melanomas express wild-type (wt) ALK and/or ALKATI and one mucosal melanoma expresses multiple novel EML4-ALK fusion variants. Melanoma cells expressing different ALK variants were tested for response to ALK inhibitors. Whereas the melanoma expressing EML4-ALK were sensitive to ALK inhibitors in vitro and in vivo, the melanomas expressing wt ALK or ALKATI were not sensitive to ALK inhibitors. In addition, a patient with mucosal melanoma expressing ALKATI was treated with an ALK/ROS1/TRK inhibitor (entrectinib) on a phase I trial but did not respond. Our results demonstrate ALK fusions occur in malignant melanomas and respond to targeted therapy, whereas melanomas expressing ALKATI do not respond to ALK inhibitors. Targeting ALK fusions is an effective therapeutic option for a subset of melanoma patients, but additional clinical studies are needed to determine the efficacy of targeted therapies in melanomas expressing wt ALK or ALKATIMol Cancer Ther; 17(1); 222-31. ©2017 AACR.

Abstract 1662: Development and validation of humanized mice models implanted with patient derived colorectal cancer xenografts

Introduction: Agents that reverse T cell inhibitory signals have reinvigorated the strategy of cancer immunotherapy and are leading to robust clinical responses. In colorectal cancer (CRC), objective responses to single-agent therapy with anti-PD-1/PD-L1 antibodies have largely been restricted to the small proportion of CRC patients with microsatellite unstable (MSI-high) disease. Although there are additional subsets of advanced CRC patients that are responsive to immune checkpoint inhibition in combination with tumor-targeted agents, preclinical models have been hampered by their immune-compromised status. In order to gain a better biological understanding of the context of immune responses and facilitate preclinical evaluation of combination strategies incorporating cancer immunotherapy, we developed a “hematopoietic” humanized mouse model utilizing patient-derived CRC xenografts with the intent of leveraging this model for the development of rational combinations.

Methods: BRG.NODSirpalfa newborn pups were humanized through transplantation of 1x105 CD34+ cells purified from umbilical cord blood. Mice were evaluated for chimerism at 8 and 12 weeks. At 16 weeks, tumor tissue from established PDX models was implanted on the right and left flanks of humanized mice. When the average tumor size reached a volume of ~150-300 mm3, the mice were randomized into vehicle or nivolumab (30 mg/kg twice weekly i.p.) treatment groups according to %chimerism. Mice were monitored for signs of toxicity and tumor size was evaluated twice weekly by caliper measurements (tumor volume= (length × width2) × 0.52). At the end of the treatment, mice were euthanized while sera, lymph nodes, spleen, bone marrow and tumors were collected for immunological assessment.

Results: As preliminary proof-of-concept, we successfully established 3 humanized CRC PDX models and one breast cancer cell line (MDA-MB-231). In one of the CRC (MSI-high) and in the breast model we observed tumor growth inhibition in the treated groups vs control. We detected differences in PD-1 expression among treated versus control mice, with lower expression in the nivolumab-treated groups. We also observed an increased number of TILs, CD8+ T cells and greater numbers of T cells in the lymph nodes of treated mice, suggesting T cell expansion. Mice were highly chimeric with high TILs whereas responder tumors exhibited an increase of CD44 high IFN+ T cells, high CD8% and a higher effector memory% (HLADR+, CD45RO+).

Conclusions: Humanized PDX models were successfully established and tumor engraftment occurred in all humanized mice with nivolumab-treated mice demonstrating the development of lymph nodes that were populated by activated T cells. These preliminary results demonstrate that human immunity and PD-1 expressing T cells exist in these models and provide the basis for planned immunotherapy combination studies.

Citation Format: Anna Capasso, Julie Lang, Todd M. Pitts, Sarah Lindsey Davis, Christopher Lieu, Scott Kopetz, Stacey Bagby, Paul Francoeur, John J. Tentler, Jill Slansky, Roberta Pelanda, Gail Eckhardt. Development and validation of humanized mice models implanted with patient derived colorectal cancer xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1662. doi:10.1158/1538-7445.AM2017-1662

HDAC and PD-1 inhibition in humanized triple-negative breast cancer xenografts

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Background: There is great interest in investigating immune checkpoint inhibition in combination with novel agents, however, preclinical studies are limited by the lack of immune-competent human cancer cell line xenograft models. We developed a “hematopoietic” humanized mouse model to address this unmet need. HDAC inhibitors (HDACi) induce T-cell chemokine expression and enhance response to PD1 inhibitors in lung cancer models. We evaluated the combination of OKI-179, a novel Class I HDACi and nivolumab in our humanized mouse model. Methods: BRGS newborn pups were transplanted with CD34+ cells purified from umbilical cord blood. At 16 weeks, MDA-MB-231 cells were implanted in the flanks of the mice. When the average tumor size reached ~150-300 mm3, the mice were randomized into vehicle, nivolumab, OKI-179, or the combination treatment according to % chimerism. At the end of the treatment, mice were euthanized and tissues were collected for further analysis. Results: We observed a statistically significant improvement in tumor growth inhibition with the combination of OKI-179 and nivolumab (%TGI = 77%) as compared to single agent nivolumab (45%TGI). Nivolumab treatment led to a significant decrease in PD-1 expression on T cells. We also observed an increased number of TILs (CD8+ T cells) and T cells in the lymph nodes of treated mice suggesting T cell expansion. All mice were highly chimeric and responding tumors exhibited an increase in CD44 high IFN+ T cells. We observed a higher CD8% and a higher effector memory % (HLADR+, CD45RO+) in these mice. Conclusions: We successfully established a humanized TNBC human cancer cell line xenograft model, with tumor engraftment occurred in all humanized mice. Mice treated with nivolumab demonstrating the development of lymph nodes that were populated by activated T cells. The combo resulted in superior tumor growth inhibition. These preliminary results demonstrate that human immunity and PD-1 expressing T cells exist in these models and provide the basis for planned immunotherapy combination studies.

Efficacy and Molecular Mechanisms of Differentiated Response to the Aurora and Angiogenic Kinase Inhibitor ENMD-2076 in Preclinical Models of p53-Mutated Triple-Negative Breast Cancer

Purpose

Triple-negative breast cancer (TNBC) is a subtype associated with poor prognosis and for which there are limited therapeutic options. The purpose of this study was to evaluate the efficacy of ENMD-2076 in p53-mutated TNBC patient-derived xenograft (PDX) models and describe patterns of terminal cell fate in models demonstrating sensitivity, intrinsic resistance, and acquired resistance to ENMD-2076.

Experimental design

p53-mutated, TNBC PDX models were treated with ENMD-2076 and evaluated for mechanisms of sensitivity or resistance to treatment. Correlative tissue testing was performed on tumor tissue to assess for markers of proliferation, apoptosis, senescence, and pathways of resistance after treatment and at the time of acquired resistance.

Results

Sensitivity to ENMD-2076 200 mg/kg daily was associated with induction of apoptosis while models exhibiting intrinsic or acquired resistance to treatment presented with a senescent phenotype. Response to ENMD-2076 was accompanied by an increase in p53 and p73 levels, even within the background of mutant p53. Treatment with ENMD-2076 resulted in a decrease in pAurA and an increase in pHH3. We observed a TNBC subtype switch from the luminal androgen receptor to the basal-like subtype at acquired resistance.

Conclusion

ENMD-2076 has antitumor activity in preclinical models of p53-mutated TNBC. Increased levels of p53 and p73 correlated with sensitivity whereas senescence was associated with resistance to ENMD-2076. The novel finding of a TNBC subtype switch at time of acquired resistance may provide mechanistic insights into the biologic effects of selective pressure of anticancer treatments on TNBC. ENMD-2076 is currently being evaluated in a Phase 2 clinical trial in patients with metastatic, previously treated TNBC where these biologic correlates can be further explored.

Rational combination therapy in young vs older patients with advanced colorectal cancer (CRC)

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Background: Although CRC is rare in young adults, the incidence has increased recently and patients present more commonly with Stage III or IV disease which may reflect differing biology. Prior analyses revealed a statistically significant increase in the risk of death in young patients with metastatic CRC compared to older patients. Methods: To assess age-dependent genetic changes, DNA and RNA from younger ( < 40) and older ( > 65) CRC were isolated, and whole exome and transcriptome sequencing analysis from 4699 FFPE CRC clinical specimens were performed. Hybridization capture was performed on up to 3,769 exons from 403 cancer-related genes and 47 introns of 19 genes commonly rearranged in cancer. Samples were sequenced to high (average 688X) uniform coverage. CRC PDXs were injected into athymic nude mice and randomized into vehicle control, refametinib (MEKi), OMP-18R5 (monoclonal Ab against FZD 1, 2, 5, 7, and 8), or the combination and treated for at least 28 days. Results: Gene alteration rates in the younger and older cohorts were similar in a majority of the genes analyzed. Alterations in CTNNB1 [p < 0.001, False Discovery Rate (FDR) = 0.07] and MLH1 (p < 0.001, FDR = 0.017) were found to be more common in younger patients. Older patients were more likely to have alterations in APC (p < 0.01, FDR < 0.01) and FAM123B (p < 0.01, FDR = 0.03). The CTNNB1 data provided support to explore the WNT pathway as a potential target for younger patients. Therefore, we conducted an in vivo study of MEKi and OMP-18R5 to assess efficacy in molecularly defined young CRC PDX models. In a young PDX models, we observed enhanced combination effects with tumor growth inhibition index (treated/control) of 13% in the combination arm (compared to tumor growth of 150 %, and 116%, respectively with MEKi and OMP-18R5 alone). Interestingly, in this PDX models, RNA sequencing data showed baseline enrichment in the WNT and mTOR pathway, not observed in the older PDX models. Conclusions: The combination of refametinib and OMP-18R5 showed enhanced antitumor activity in combination compared to the single agent arms. Studies investigating predictive biomarkers of response are currently underway.

Development and Maintenance of a Preclinical Patient Derived Tumor Xenograft Model for the Investigation of Novel Anti-Cancer Therapies

Patient derived tumor xenograft (PDTX) models provide a necessary platform in facilitating anti-cancer drug development prior to human trials. Human tumor pieces are injected subcutaneously into athymic nude mice (immunocompromised, T cell deficient) to create a bank of tumors and subsequently are passaged into different generations of mice in order to maintain these tumors from patients. Importantly, cellular heterogeneity of the original tumor is closely emulated in this model, which provides a more clinically relevant model for evaluation of drug efficacy studies (single agent and combination), biomarker analysis, resistant pathways and cancer stem cell biology. Some limitations of the PDTX model include the replacement of the human stroma with mouse stroma after the first generation in mice, inability to investigate treatment effects on metastasis due to the subcutaneous injections of the tumors, and the lack of evaluation of immunotherapies due to the use of immunocompromised mice. However, even with these limitations, the PDTX model provides a powerful preclinical platform in the drug discovery process.

Abstract PR03: Characterizing the immune context of responses to immunotherapy in humanized patient derived xenograft models of CRC

Introduction: Inhibiting the activity of the epidermal growth factor receptor (EGFR) with monoclonal antibodies has been utilized as a therapeutic strategy for patients with metastatic colorectal cancer (CRC), leading to improved clinical results alone and in combination with standard chemotherapy. Many systematic reviews and metanalyses were performed to better understand the role of EGFR inhibition in CRC, revealing that KRAS exon 2 mutations and furthermore exons 3 and 4 and NRAS exons 2, 3, and 4 were predictive of non-responsiveness to these agents. Concurrent with these results has been the development of immunotherapy targeting immune regulatory checkpoints such as CTLA-4 and PD-1 that have initiated a new era in the treatment of cancer. In order to gain a better biological understanding of the context of immune responses and facilitate preclinical evaluation of cancer immunotherapy, we developed a hematopoietic humanized mouse model utilizing patient-derived CRC xenograft tumor models to assess immune therapy for RAS mutant CRC. Not only could evaluation of humanized RAS mutant PDX models provide additional information on the potential for clinical activity of immune therapies, but could also improve the understanding of immune responses to RAS mutant cancers. We therefore hypothesize that humanized RAS mutant colorectal PDX models can be used to evaluate the preclinical activity of immune targeted agents for treatment of RAS mutant colorectal cancer.

Methods: Humanized BRG mice developed from the BALB/cRag2-/-IL2Rγc-/- (BRG) strain which is known to accept human hematopoietic stem cells, have been used to enhance engraftment. BRG newborn pups were humanized through transplantation of approximately 1x105 CD34+ cells purified from umbilical cord blood. The mice were evaluated for chimerism at 8 and 12 weeks. At 14 weeks, tumor tissue from established PDX models were implanted on the right and left flank of humanized mice. The tumor was selected among a cluster within the “immune-enriched” subtype (C2) based upon the RNAseq characterization of the models. When the average tumor size reached a volume of approximately ~150-300 mm3, the mice were randomized into either vehicle or nivolumab treatment groups. Mice were monitored daily for signs of toxicity and weighed twice weekly. They were treated with nivolumab (30 mg/kg) twice a week by intraperitoneal injection for 15 days. Tumor size was evaluated twice weekly by caliper measurements using the following equation: tumor volume= (length × width2) × 0.52. At the end of the treatment, mice were euthanized while sera, lymph nodes, spleen, bone marrow and tumors were collected for further investigation.

Results: Humanized RAS mutant CRC PDX models were successfully established in vivo. While no differences were observed in tumor growth among the control and treated arms, we were able to detect differences in PD1 expression among treated versus control mice, with lower expression in the nivolumab treated group. We also observed higher numbers of T cells in the lymph nodes of nivolumab treated mice, suggesting T cell expansion. Interestingly, we also observed an increase of T cells in the spleen and blood and late occupancy of T cells in the bone marrow. Two of the treated mice exhibited identifiable TILs that were comprised of a majority of CD4+ T cells with an activated phenotype (CD69+).

Conclusions: Humanized KRAS mutant CRC PDX models were successfully established and tumor engraftment occurred in all humanized mice with nivolumab-treated mice demonstrating the development of lymph nodes that were populated by activated T cells. These preliminary results demonstrate that human immunity and PD-1 expressing T cells exist in these models and provide the basis for planned immunotherapy combination studies.

This abstract is also being presented as Poster A23.

Citation Format: Anna Capasso, Julie Lang, Todd M. Pitts, S. Lindsey Davis, Chris H. Lieu, Stacey M. Bagby, Aik Choon Tan, John J. Tentler, Jill E. Slansky, Roberta Pelanda, S. Gail Eckhardt. Characterizing the immune context of responses to immunotherapy in humanized patient derived xenograft models of CRC. [abstract]. In: Proceedings of the AACR Special Conference: Patient-Derived Cancer Models: Present and Future Applications from Basic Science to the Clinic; Feb 11-14, 2016; New Orleans, LA. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(16_Suppl):Abstract nr PR03.

Antitumor activity of a potent MEK inhibitor, TAK-733, against colorectal cancer cell lines and patient derived xenografts

BACKGROUND

CRC is a significant cause of cancer mortality, and new therapies are needed for patients with advanced disease. TAK-733 is a highly potent and selective investigational novel MEK allosteric site inhibitor.

MATERIALS AND METHODS

In a preclinical study of TAK-733, a panel of CRC cell lines were exposed to varying concentrations of the agent for 72 hours followed by a sulforhodamine B assay. Twenty patient-derived colorectal cancer xenografts were then treated with TAK-733 in vivo. Tumor growth inhibition index (TGII) was assessed to evaluate the sensitivity of the CRC explants to TAK-733 while linear regression was utilized to investigate the predictive effects of genotype on the TGII of explants.

RESULTS

Fifty-four CRC cell lines were exposed to TAK-733, while 42 cell lines were deemed sensitive across a broad range of mutations. Eighty-two percent of the cell lines within the sensitive subset were BRAF or KRAS/NRAS mutant, whereas 80% of the cell lines within the sensitive subset were PIK3CA WT. Twenty patient-derived human tumor CRC explants were then treated with TAK-733. In total, 15 primary human tumor explants were found to be sensitive to TAK-733 (TGII ≤ 20%), including 9 primary human tumor explants that exhibited tumor regression (TGII > 100%). Explants with a BRAF/KRAS/NRAS mutant and PIK3CA wild-type genotype demonstrated increased sensitivity to TAK-733 with a median TGII of -6%. MEK-response gene signatures also correlated with responsiveness to TAK-733 in KRAS-mutant CRC.

CONCLUSIONS

The MEK inhibitor TAK-733 demonstrated robust antitumor activity against CRC cell lines and patient-derived tumor explants. While the preclinical activity observed in this study was considerable, single-agent efficacy in the clinic has been limited in CRC, supporting the use of these models in an iterative manner to elucidate resistance mechanisms that can guide rational combination strategies.

An integrated bioinformatics analysis to dissect kinase dependency in triple negative breast cancer

BACKGROUND

Triple-Negative Breast Cancer (TNBC) is an aggressive disease with a poor prognosis. Clinically, TNBC patients have limited treatment options besides chemotherapy. The goal of this study was to determine the kinase dependency in TNBC cell lines and to predict compounds that could inhibit these kinases using integrative bioinformatics analysis.

RESULTS

We integrated publicly available gene expression data, high-throughput pharmacological profiling data, and quantitative in vitro kinase binding data to determine the kinase dependency in 12 TNBC cell lines. We employed Kinase Addiction Ranker (KAR), a novel bioinformatics approach, which integrated these data sources to dissect kinase dependency in TNBC cell lines. We then used the kinase dependency predicted by KAR for each TNBC cell line to query K-Map for compounds targeting these kinases. We validated our predictions using published and new experimental data.

CONCLUSIONS

In summary, we implemented an integrative bioinformatics analysis that determines kinase dependency in TNBC. Our analysis revealed candidate kinases as potential targets in TNBC for further pharmacological and biological studies.

Abstract C34: Senescence as a mechanism of resistance to the Aurora kinase and angiokinase inhibitor, ENMD-2076, in p53 mutated triple-negative breast cancer (TNBC) models

Background: Despite advances in targeted therapies for cancer, TNBC remains an aggressive breast cancer subtype with limited treatment options. Mutations in p53 are common in TNBC, however, the exact contribution of individual p53 mutations to response to therapy and mechanisms of acquired resistance are unknown. The purpose of this study was to characterize the activity of ENMD-2076, a multi-target Aurora kinase A and angiokinase inhibitor, against p53 mutated TNBC patient-derived tumor xenografts (PDX) and to identify differences in molecular pathways determining cellular fate in sensitive and resistant models.

Methods: TNBC PDX models harboring different p53 mutations were used for ENMD-2076 treatment studies. Athymic nude mice were injected with tumor tissue and tumor volumes were measured twice a week. When the mean tumor volumes reached 150 mm3, mice were randomized and treated with vehicle control or ENMD-2076 200 mg/kg by oral gavage daily. A subset of animals were sacrificed at Day 4, 30, and at the time of acquired resistance for correlative tissue testing which included: immunofluorescence (IF) for p53, p73, BCL2, BAX, p16, phospho Aurora A (pAA) and phospho histone H3 (pHH3); immunohistochemistry (IHC) for cleaved caspase 3 (CC3) and Ki67; H&E and staining for senescence associated beta-galactosidase (SA -βgal) activity. Tumor growth inhibition (TGI) was calculated at Day 30 and sensitive models were treated until resistance when additional correlative tissue samples were obtained.

Results: ENMD-2076 had significant anti-tumor activity against the CU_002 and CU_005 TNBC PDX models (TGI 71.3%, p value &lt;0.0001; TGI 66.1% p value &lt; 0.0002, respectfully). The CU_004 TNBC PDX model was intrinsically resistant to ENMD-2076 treatment (TGI 37%, p value 0.07). In the two sensitive PDX models, we observed an increase in p53, p73, BAX and the apoptotic marker CC3. This was accompanied by a decrease in the anti-apoptotic protein BCL2 and the proliferation marker Ki67 following treatment at Day 30. Consistent with Aurora kinase A inhibition, we detected an increase in pAA and a decrease in pHH3 expression in both sensitive and resistant PDTX models following treatment at Day 4 and Day 30. At the time of acquired resistance, defined by at least doubling of tumor volumes from the maximal response, we observed loss of p73, p53, and BAX expression and an increase in p16 staining and SA β-gal activity consistent with senescence. These findings were also observed following treatment with ENMD-2076 in the intrinsically resistant CU_004 model.

Conclusions: ENMD-2076 has pro-apoptotic anti-cancer activity in a subset of p53 mutated TNBC PDX models. Sensitivity was associated with the induction of p73, which may mediate the response in the absence of functional p53. Intrinsic and acquired resistance to ENMD-2076 in TNBC PTX models was associated with loss of p73 expression and an increase in markers associated with senescence, including p16 expression and SA β-gal activity. These data support the role of senescence as a potential mechanism of resistance to Aurora kinase inhibitors in p53 mutated TNBC and support the continued development of combination therapies including with inhibitors of pathways that mediate senescence.

Citation Format: Anastasia A. Ionkina, S. Gail Eckhardt, Todd M. Pitts, Carol Sartorius, Peter Kabos, Jiyhe Kim, Aik Choon Tan, John J. Tentler, Jennifer R. Diamond. Senescence as a mechanism of resistance to the Aurora kinase and angiokinase inhibitor, ENMD-2076, in p53 mutated triple-negative breast cancer (TNBC) models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C34.

Combined inhibition of MEK and Aurora A kinase in KRAS/PIK3CA double-mutant colorectal cancer models

Aurora A kinase and MEK inhibitors induce different, and potentially complementary, effects on the cell cycle of malignant cells, suggesting a rational basis for utilizing these agents in combination. In this work, the combination of an Aurora A kinase and MEK inhibitor was evaluated in pre-clinical colorectal cancer models, with a focus on identifying a subpopulation in which it might be most effective. Increased synergistic activity of the drug combination was identified in colorectal cancer cell lines with concomitant KRAS and PIK3CA mutations. Anti-proliferative effects were observed upon treatment of these double-mutant cell lines with the drug combination, and tumor growth inhibition was observed in double-mutant human tumor xenografts, though effects were variable within this subset. Additional evaluation suggests that degree of G2/M delay and p53 mutation status affect apoptotic activity induced by combination therapy with an Aurora A kinase and MEK inhibitor in KRAS and PIK3CA mutant colorectal cancer. Overall, in vitro and in vivo testing was unable to identify a subset of colorectal cancer that was consistently responsive to the combination of a MEK and Aurora A kinase inhibitor.

p53 Family Members Regulate Phenotypic Response to Aurora Kinase A Inhibition in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive disease with a poor prognosis. Advances in the treatment of TNBC have been hampered by the lack of novel effective targeted therapies. The primary goal of this study was to evaluate the efficacy of targeting Aurora kinase A (AurA), a key regulator of mitosis, in TNBC models. A secondary objective was to determine the role of the p53 family of transcriptional regulators, commonly mutated in TNBC, in determining the phenotypic response to the AurA inhibitor alisertib (MLN8237). Alisertib exhibited potent antiproliferative and proapoptotic activity in a subset of TNBC models. The induction of apoptosis in response to alisertib exposure was dependent on p53 and p73 activity. In the absence of functional p53 or p73, there was a shift in the phenotypic response following alisertib exposure from apoptosis to cellular senescence. In addition, senescence was observed in patient-derived tumor xenografts with acquired resistance to alisertib treatment. AurA inhibitors are a promising class of novel therapeutics in TNBC. The role of p53 and p73 in mediating the phenotypic response to antimitotic agents in TNBC may be harnessed to develop an effective biomarker selection strategy in this difficult to target disease.

Dual pharmacological targeting of the MAP kinase and PI3K/mTOR pathway in preclinical models of colorectal cancer

BACKGROUND

The activation of the MAPK and PI3K/AKT/mTOR pathways is implicated in the majority of cancers. Activating mutations in both of these pathways has been described in colorectal cancer (CRC), thus indicating their potential as therapeutic targets. This study evaluated the combination of a PI3K/mTOR inhibitor (PF-04691502/PF-502) in combination with a MEK inhibitor (PD-0325901/PD-901) in CRC cell lines and patient-derived CRC tumor xenograft models (PDTX).

MATERIALS AND METHODS

The anti-proliferative effects of PF-502 and PD-901 were assessed as single agents and in combination against a panel of CRC cell lines with various molecular backgrounds. Synergy was evaluated using the Bliss Additivity method. In selected cell lines, we investigated the combination effects on downstream effectors by immunoblotting. The combination was then evaluated in several fully genetically annotated CRC PDTX models.

RESULTS

The in vitro experiments demonstrated a wide range of IC50 values for both agents against a cell line panel. The combination of PF-502 and PD-901 demonstrated synergistic anti-proliferative activity with Bliss values in the additive range. As expected, p-AKT and p-ERK were downregulated by PF-502 and PD-901, respectively. In PDTX models, following a 30-day exposure to PF-502, PD-901 or the combination, the combination demonstrated enhanced reduction in tumor growth as compared to either single agent regardless of KRAS or PI3K mutational status.

CONCLUSIONS

The combination of a PI3K/mTOR and a MEK inhibitor demonstrated enhanced anti-proliferative effects against CRC cell lines and PDTX models.

Antitumor activity of the MEK inhibitor TAK-733 against melanoma cell lines and patient-derived tumor explants

The goal of this study was to investigate the activity of the selective MEK1/2 inhibitor TAK-733 in both melanoma cell lines and patient-derived melanoma xenograft models. In vitro cell proliferation assays using the sulforhodamine B assay were conducted to determine TAK-733 potency and melanoma responsiveness. In vivo murine modeling with eleven patient-derived melanoma explants evaluated daily dosing of TAK-733 at 25 or 10 mg/kg. Immunoblotting was performed to evaluate on-target activity and downstream inhibition by TAK-733 in both in vitro and in vivo studies. TAK-733 demonstrated broad activity in most melanoma cell lines with relative resistance observed at IC50 > 0.1 μmol/L in vitro. TAK-733 also exhibited activity in 10 out of 11 patient-derived explants with tumor growth inhibition ranging from 0% to 100% (P < 0.001-0.03). Interestingly, BRAF(V600E) and NRAS mutational status did not correlate with responsiveness to TAK-733. Pharmacodynamically, pERK was suppressed in sensitive cell lines and tumor explants, confirming TAK-733-mediated inhibition of MEK1/2, although the demonstration of similar effects in the relatively resistant cell lines and tumor explants suggests that escape pathways are contributing to melanoma survival and proliferation. These data demonstrate that TAK-733 exhibits robust tumor growth inhibition and regression against human melanoma cell lines and patient-derived xenograft models, suggesting that further clinical development in melanoma is of scientific interest. Particularly interesting is the activity in BRAF wild-type models, where current approved therapy such as vemurafenib has been reported not to be active.

Triple-negative breast cancer: bridging the gap from cancer genomics to predictive biomarkers

Triple-negative breast cancer (TNBC) represents a challenge clinically due to a lack of response to hormonal and HER2-targeted agents coupled with an aggressive disease course. As the biology of this breast cancer subtype is better understood, it is clear that TNBC is a heterogeneous disease and one targeted therapy is unlikely to be active in all patients. Biomarkers predictive of response to treatment are thus of great importance in TNBC. This review outlines studies evaluating biomarkers predictive of response to neoadjuvant chemotherapy and to targeted therapies in the advanced setting. The development of validated biomarkers in conjunction with novel targeted therapies represents an opportunity to improve patient outcomes in TNBC.

Abstract P2-09-06: The role of p53 family tumor suppressors in mediating response to aurora kinase inhibition in triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype defined by the lack of expression of the estrogen and progesterone receptors and lack of HER2 over-expression. TNBC carries an increased risk of developing distant metastatic disease and cancer-related death. TNBC is heterogeneous in its underlying biology, however, mutations in p53 are found in approximately 80% of tumors. The purpose of this study was to utilize TNBC cell line models to investigate the role of p53 and p73 in mediating sensitivity to MLN8237, a selective Aurora kinase A inhibitor, in the setting of mutant or wildtype p53. Additionally, we used p53 and p73 knock-down models to determine the role of p53 and p73 in mediating induction of apoptosis and cellular senescence in response to Aurora kinase inhibition.

Methods: Eighteen TNBC cell lines were exposed to MLN8237 and the effects on proliferation, apoptosis, and cell cycle distribution were evaluated. Proliferation was assessed using an SRB assay, apoptosis was analyzed using a caspase 3/7 assay and cell cycle was measured using flow cytometry. Proliferation was confirmed using a cell counting technique to control for an increase in cell size following MLN8237 exposure. The p53 wildtype TNBC cell line CAL51 was transduced with several clones of shRNA constructs targeting p53 and p73 with &gt; 80% knockdown by RT-PCR. These clones were exposed to escalating doses of MLN8237 and the effect on proliferation was determined using an SRB assay and the effect on cellular senescence was determined using a senescence associated beta-galactosidase (SA b-gal) assay.

Results: In vitro exposure to MLN8237 resulted in robust inhibition of proliferation in TNBC cell lines which was associated with dose-dependent G2/M cell cycle arrest and induction of caspase-dependent apoptosis in a subset of sensitive cell lines. Knock-down of p53 and p73 in the CAL51 cell line resulted in an increase in the absolute 50% inhibitory concentration (IC50) calculated from the SRB proliferation assay curves from 0.04 μM to &gt; 2 μM, 1.8 μM, &gt; 2 μM and 1.5 μM in the CAL51scr, CAL51p5310, CAL51p5312, CAL51p7326, CAL51p7355, respectively. The sensitive p53 mutated MDA-MB-468 cell line (IC50 40 nM) and the sensitive p53 wild-type CAL51 cell line (IC50 45 nM) were selected for further experimentation. Exposure to MLN8237 at concentrations of 50 nM and 100 nM for 7 days resulted in induction of cellular senescence as detected by the SA b-gal assay in the CAL51 p53 wild-type cell line, but not in the MDA-MB-468 cell line where induction of apoptosis at 48 hours was observed using the caspase 3/7 assay. In the CAL51 p73 knock-down clones, induction of cellular senescence was not observed following exposure to MLN8237.

Conclusions: MLN8237 exhibited robust anticancer activity towards preclinical models of p53 mutated and p53 wild-type TNBC, supporting future clinical investigation of Aurora kinase inhibitors in TNBC. In p53 wild-type TNBC, both p53 and p73 mediate sensitivity to MLN8237 and p73 is essential for induction of cellular senescence following exposure to MLN8237. Biomarkers predictive of response to MLN8237 in p53 mutated TNBC are being developed.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-09-06.

Abstract A286: The role of p53 family tumor suppressors in mediating response to the Aurora and angiogenic kinase inhibitor ENMD-2076 in triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype defined by the lack of expression of ER, PR and HER2 over-expression. TNBC is heterogeneous in its biology, however, mutations in p53 are found in approximately 80% of tumors. The purpose of this study was to utilize TNBC cell line models to investigate the role of p53 and p73 in mediating sensitivity to ENMD-2076, a selective Aurora kinase A inhibitor (AurKi). p53 and p73 knockdown (KD) models were developed to determine their role in mediating induction of apoptosis and senescence in response to AurK inhibition. Additionally, the effects of combining ENMD-2076 with the p53 modulator nutlin-3 were assessed.

Methods: TNBC cell lines, MDA-MB-468 (p53 mut) and CAL51 (p53 WT) were transduced with shRNA constructs targeting p53 and p73 with &gt; 80% knockdown as determined by RT-PCR. These clones were exposed to escalating doses of ENMD-2076 and the effect on proliferation was determined using an SRB assay. Proliferation was assessed using an SRB assay, and confirmed using a direct cell counting to control for increase in cell size following ENMD-2076 exposure. In the CAL51 KD lines, the effects of ENMD-2076 treatment on cellular senescence were determined using a senescence associated beta-galactosidase (SA β-gal) assay. Combination studies with nutlin-3 in MDA-MB-468 and HCC1937 were assessed by SRB and synergy measured using Calcusyn software.

Results: KD of p53 and p73 in the MDA-MB-468p5310, MDA-MB-468p7355 cell lines resulted in an increase in the IC50 from 0.625 μM to 1.5 μM compared to scrambled. KD of CAL51 p53 and p73 increased from 0.16 µM to 0.41 µM, and 1.3 µM, in the CAL51scr, CAL51p5310, CAL51p7326, respectively. The sensitive MDA-MB-468 cell line (IC50 40 nM) and the sensitive CAL51 cell line (IC50 45 nM) were selected for further experimentation. Exposure to ENMD-2076 at concentrations of 0.5 μM and 1 μM for varying time points resulted in induction of senescence in the CAL51 cell line, but not in the MDA-MB-468 cell line, where induction of apoptosis at 48 hours was observed. In CAL51 p53 and p73 KD clones, induction of senescence was observed following exposure to ENMD-2076. Combination treatment with nutlin-3 showed synergistic activity.

Conclusions: ENMD-2076 exhibited robust anticancer activity towards preclinical models of TNBC, in both p53 mutated and p53 WT cell lines, supporting future clinical investigation of AurKi in TNBC. In p53 WT TNBC, both p53 and p73 mediate sensitivity to ENMD-2076 and p73 is essential for induction of senescence following exposure to ENMD-2076. Synergistic anticancer activity of ENMD-2076 and nutlin reinforces the role of p53 in Aurora kinase inhibition of TNBC. Biomarkers predictive of response to ENMD-2076 in p53 mutated TNBC are being developed. These results with p53 KD cell lines are currently being confirmed in vivo.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A286.

Citation Format: Anastasia A. Ionkina, John J. Tentler, Timothy P. Newton, Kelsey L. Brunkow, Jared S. Johnson, Aik Choon Tan, Todd M. Pitts, S. Gail Eckhardt, Jennifer R. Diamond. The role of p53 family tumor suppressors in mediating response to the Aurora and angiogenic kinase inhibitor ENMD-2076 in triple-negative breast cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A286.

Overcoming IGF1R/IR resistance through inhibition of MEK signaling in colorectal cancer models

PURPOSE

Results from clinical trials involving resistance to molecularly targeted therapies have revealed the importance of rational single-agent and combination treatment strategies. In this study, we tested the efficacy of a type 1 insulin-like growth factor receptor (IGF1R)/insulin receptor (IR) tyrosine kinase inhibitor, OSI-906, in combination with a mitogen-activated protein (MAP)-ERK kinase (MEK) 1/2 inhibitor based on evidence that the MAP kinase pathway was upregulated in colorectal cancer cell lines that were resistant to OSI-906.

EXPERIMENTAL DESIGN

The antiproliferative effects of OSI-906 and the MEK 1/2 inhibitor U0126 were analyzed both as single agents and in combination in 13 colorectal cancer cell lines in vitro. Apoptosis, downstream effector proteins, and cell cycle were also assessed. In addition, the efficacy of OSI-906 combined with the MEK 1/2 inhibitor selumetinib (AZD6244, ARRY-142886) was evaluated in vivo using human colorectal cancer xenograft models.

RESULTS

The combination of OSI-906 and U0126 resulted in synergistic effects in 11 of 13 colorectal cancer cell lines tested. This synergy was variably associated with apoptosis or cell-cycle arrest in addition to molecular effects on prosurvival pathways. The synergy was also reflected in the in vivo xenograft studies following treatment with the combination of OSI-906 and selumetinib.

CONCLUSIONS

Results from this study demonstrate synergistic antiproliferative effects in response to the combination of OSI-906 with an MEK 1/2 inhibitor in colorectal cancer cell line models both in vitro and in vivo, which supports the rational combination of OSI-906 with an MEK inhibitor in patients with colorectal cancer. Clin Cancer Res; 19(22); 6219-29. ©2013 AACR.

Rational combination of a MEK inhibitor, selumetinib, and the Wnt/calcium pathway modulator, cyclosporin A, in preclinical models of colorectal cancer

PURPOSE

The mitogen-activated protein kinase (MAPK) pathway is a crucial regulator of cell proliferation, survival, and resistance to apoptosis. MEK inhibitors are being explored as a treatment option for patients with KRAS-mutant colorectal cancer who are not candidates for EGFR-directed therapies. Initial clinical results of MEK inhibitors have yielded limited single-agent activity in colorectal cancer, indicating that rational combination strategies are needed.

EXPERIMENTAL DESIGN

In this study, we conducted unbiased gene set enrichment analysis and synthetic lethality screens with selumetinib, which identified the noncanonical Wnt/Ca++ signaling pathway as a potential mediator of resistance to the MEK1/2 inhibitor selumetinib. To test this, we used shRNA constructs against relevant WNT receptors and ligands resulting in increased responsiveness to selumetinib in colorectal cancer cell lines. Further, we evaluated the rational combination of selumetinib and WNT pathway modulators and showed synergistic antiproliferative effects in in vitro and in vivo models of colorectal cancer.

RESULTS

Importantly, this combination not only showed tumor growth inhibition but also tumor regression in the more clinically relevant patient-derived tumor explant (PDTX) models of colorectal cancer. In mechanistic studies, we observed a trend toward increased markers of apoptosis in response to the combination of MEK and WntCa(++) inhibitors, which may explain the observed synergistic antitumor effects.

CONCLUSIONS

These results strengthen the hypothesis that targeting both the MEK and Wnt pathways may be a clinically effective rational combination strategy for patients with metastatic colorectal cancer.

Abstract 1006: A novel class I histone deacetylase (HDAC) inhibitor, paragazole, demonstrates antiproliferative and proapoptotic effects in triple-negative breast cancer models

Introduction: Triple-negative breast cancer (TNBC) is a clinically aggressive breast cancer subtype which lacks estrogen receptor expression. Histone deacetylase (HDAC) inhibitors have previously been shown to induce estrogen receptor expression in TNBC models. Paragazole is a selective class I HDAC inhibitor (HDACs 1, 2, and 3) currently in preclinical development. In this project, we explored the antiproliferative and proapoptotic activity of paragazole and investigated the combination of paragazole and chemotherapy in a panel of breast cancer cell lines.

Methods: Breast cancer cell lines were exposed to varying sub-micromolar concentrations of paragazole alone and in combination with carboplatin, paclitaxel, and gemcitabine. Proliferation was assessed using an SRB assay and analyzed using the Calcusyn program, whereby synergy was defined as a Combination Index of less than 1. Cell cycle analysis was performed using flow cytometry and apoptosis was analyzed using a caspase 3/7 assay. Baseline HDAC expression was measured by RT-PCR and RNA-Seq was used pre- and post-treatment in a subset of 2 sensitive and 2 resistant cell lines.

Results: Exposure to paragazole resulted in a decrease in cell proliferation at submicromolar concentrations with more robust antiproliferative activity observed in the TNBC cell lines compared to the estrogen receptor positive cell lines. An increase in apoptosis that was maximal at 24-48 hours was observed with single agent paragazole in a subset of sensitive TNBC cell lines. The combinations of paragazole with either paclitaxel, gemcitabine, or carboplatin all resulted in additive or synergistic growth inhibition. Expression of HDAC 1 was higher in the sensitive TNBC cell lines than in the resistant lines. Exposure to paragazole led to an increase in CARM1 mediated estrogen receptor expression.

Discussion: These in vitro results demonstrate that paragazole has antiproliferative and proapototic activity against TNBC cell lines and may potentiate the activity of chemotherapy. These data support confirmation of the findings using in vivo models and the investigation of paragazole in combination with anti-estrogen agents such as tamoxifen and fulvestrant.

Citation Format: David P. Astling, John J. Tentler, Benjamin R. Cross, Timothy P. Newton, Todd M. Pitts, Eric Gunther, Xuedong Liu, S. Gail Eckhardt, Jennifer R. Diamond. A novel class I histone deacetylase (HDAC) inhibitor, paragazole, demonstrates antiproliferative and proapoptotic effects in triple-negative breast cancer models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1006. doi:10.1158/1538-7445.AM2013-1006

MERTK receptor tyrosine kinase is a therapeutic target in melanoma

Metastatic melanoma is one of the most aggressive forms of cutaneous cancers. Although recent therapeutic advances have prolonged patient survival, the prognosis remains dismal. C-MER proto-oncogene tyrosine kinase (MERTK) is a receptor tyrosine kinase with oncogenic properties that is often overexpressed or activated in various malignancies. Using both protein immunohistochemistry and microarray analyses, we demonstrate that MERTK expression correlates with disease progression. MERTK expression was highest in metastatic melanomas, followed by primary melanomas, while the lowest expression was observed in nevi. Additionally, over half of melanoma cell lines overexpressed MERTK compared with normal human melanocytes; however, overexpression did not correlate with mutations in BRAF or RAS. Stimulation of melanoma cells with the MERTK ligand GAS6 resulted in the activation of several downstream signaling pathways including MAPK/ERK, PI3K/AKT, and JAK/STAT. MERTK inhibition via shRNA reduced MERTK-mediated downstream signaling, reduced colony formation by up to 59%, and diminished tumor volume by 60% in a human melanoma murine xenograft model. Treatment of melanoma cells with UNC1062, a novel MERTK-selective small-molecule tyrosine kinase inhibitor, reduced activation of MERTK-mediated downstream signaling, induced apoptosis in culture, reduced colony formation in soft agar, and inhibited invasion of melanoma cells. This work establishes MERTK as a therapeutic target in melanoma and provides a rationale for the continued development of MERTK-targeted therapies.

Abstract 3037: Mer receptor tyrosine kinase is a novel therapeutic target in melanoma

Metastatic melanoma is one of the most aggressive forms of cutaneous cancers. While recent therapeutic advances have prolonged patient survival, prognosis remains dismal. Mer is a receptor tyrosine kinase with oncogenic properties that is often overexpressed or activated in various malignancies. Using both protein immunohistochemistry and microarray analyses, we demonstrate that Mer expression correlates with disease progression. Mer expression was highest in metastatic melanomas followed by primary melanomas whereas the lowest expression was observed in nevi. In addition, over 50% of melanoma cell lines overexpressed Mer compared to normal human melanocytes, however overexpression did not correlate with mutations in BRAF or RAS. Stimulation of melanoma cells with the Mer ligand Gas6 resulted in activation of several downstream signaling pathways including MAPK/ERK, PI3K/Akt, and Jak/STAT. Mer inhibition via shRNA reduced Mer-mediated downstream signaling, reduced colony formation by up to 59% (p&lt;0.05) and diminished tumor volume by 60% (p&lt;0.05) in a human melanoma xenograft murine model. Treatment of melanoma cells with UNC1062, a novel Mer-selective small molecule tyrosine kinase inhibitor, reduced activation of Mer-mediated downstream signaling, induced apoptosis in culture, reduced colony formation in soft agar and inhibited invasion of melanoma cells. In addition, Mer inhibition synergized with mutant BRAF inhibition in signaling and apoptosis assays. This work establishes Mer as a therapeutic target in melanoma and provides rationale for the continued development of Mer-targeted therapies.

Citation Format: Jennifer Schlegel, Maria Sambade, Susan Sather, Stergios Moschos, Aik-Choon Tan, Amanda Winges, Deborah DeRyckere, Craig C. Carson, Dimitri G. Trembath, John J. Tentler, Gail Eckhardt, Pei-Fen Kuan, Ronald L. Hamilton, Lyn M. Duncan, C. Ryan Miller, Nana Nikolaishvili-Feinberg, Bentley R. Midkiff, Xiaodong Wang, Jing Liu, Weihe Zhang, Chao Yang, Stephen V. Frye, H. Shelton Earp, Janiel Shields, Douglas K. Graham. Mer receptor tyrosine kinase is a novel therapeutic target in melanoma. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3037. doi:10.1158/1538-7445.AM2013-3037

Association of the epithelial-to-mesenchymal transition phenotype with responsiveness to the p21-activated kinase inhibitor, PF-3758309, in colon cancer models

The p21-activated kinase (PAK) family of serine/threonine kinases, which are overexpressed in several cancer types, are critical mediators of cell survival, motility, mitosis, transcription, and translation. In the study presented here, we utilized a panel of colorectal cancer (CRC) cell lines to identify potential biomarkers of sensitivity or resistance that may be used to individualize therapy to the PAK inhibitor PF-03758309. We observed a wide range of proliferative responses in the CRC cell lines exposed to PF-03758309, this response was recapitulated in other phenotypic assays such as anchorage-independent growth, three-dimensional (3D) tumor spheroid formation, and migration. Interestingly, we observed that cells most sensitive to PF-03758309 exhibited up-regulation of genes associated with a mesenchymal phenotype (CALD1, VIM, ZEB1) and cells more resistant had an up-regulation of genes associated with an epithelial phenotype (CLDN2, CDH1, CLDN3, CDH17) allowing us to derive an epithelial-to-mesenchymal transition (EMT) gene signature for this agent. We assessed the functional role of EMT-associated genes in mediating responsiveness to PF-3758309, by targeting known genes and transcriptional regulators of EMT. We observed that suppression of genes associated with the mesenchymal phenotype conferred resistance to PF-3758309, in vitro and in vivo. These results indicate that PAK inhibition is associated with a unique response phenotype in CRC and that further studies should be conducted to facilitate both patient selection and rational combination strategies with these agents.

Role of ubiquitin ligases and the proteasome in oncogenesis: novel targets for anticancer therapies

The ubiquitin proteasome system (UPS) regulates the ubiquitination, and thus degradation and turnover, of many proteins vital to cellular regulation and function. The UPS comprises a sequential series of enzymatic processes using four key enzyme families: E1 (ubiquitin-activating enzymes), E2 (ubiquitin-carrier proteins), E3 (ubiquitin-protein ligases), and E4 (ubiquitin chain assembly factors). Because the UPS is a crucial regulator of the cell cycle, and abnormal cell-cycle control can lead to oncogenesis, aberrancies within the UPS pathway can result in a malignant cellular phenotype and thus has become an attractive target for novel anticancer agents. This article will provide an overall review of the mechanics of the UPS, describe aberrancies leading to cancer, and give an overview of current drug therapies selectively targeting the UPS.

CtBP1 is expressed in melanoma and represses the transcription of p16INK4a and Brca1

Carboxyl-terminal binding protein 1 (CtBP1) has been shown to suppress the transcription of several tumor suppressors in vitro. Paradoxically, a previous report showed that CtBP1 mRNA was down-regulated in melanoma. Using immunostaining, we found that a large percentage of human melanomas were positive for CtBP1 protein. Further, we demonstrated that CtBP1 expression in melanoma cells contributes to cell proliferation and genome instability, two aspects promoting melanoma initiation and progression. Breast Cancer Susceptibility Gene 1(Brca1), a core protein in DNA damage repair, was repressed by CtBP1 in melanoma cells. Consistently, Brca1 loss was found in human malignant melanoma tissues inversely correlated with CtBP1 expression levels. Additionally, the inhibitor of cyclin-dependent protein kinases (CDKs), p16INK4a, whose loss has been related to the pathogenesis of melanoma, was repressed by CtBP1 as well. Our findings suggest an important role of CtBP1 in the transcriptional control of p16INK4a and Brca1, with CtBP1 over-expression potentially contributing to increased proliferation and DNA damage in melanoma.

Predictive biomarkers of sensitivity to the aurora and angiogenic kinase inhibitor ENMD-2076 in preclinical breast cancer models

PURPOSE

The Aurora kinases are a family of conserved serine-threonine kinases with key roles in mitotic cell division. As with other promising anticancer targets, patient selection strategies to identify a responsive subtype will likely be required for successful clinical development of Aurora kinase inhibitors. The purpose of this study was to evaluate the antitumor activity of the Aurora and angiogenic kinase inhibitor ENMD-2076 against preclinical models of breast cancer with identification of candidate predictive biomarkers.

EXPERIMENTAL DESIGN

Twenty-nine breast cancer cell lines were exposed to ENMD-2076 and the effects on proliferation, apoptosis, and cell-cycle distribution were evaluated. In vitro activity was confirmed in MDA-MB-468 and MDA-MB-231 triple-negative breast cancer xenografts. Systematic gene expression analysis was used to identify up- and downregulated pathways in the sensitive and resistant cell lines, including within the triple-negative breast cancer subset.

RESULTS

ENMD-2076 showed antiproliferative activity against breast cancer cell lines, with more robust activity against cell lines lacking estrogen receptor expression and those without increased HER2 expression. Within the triple-negative breast cancer subset, cell lines with a p53 mutation and increased p53 expression were more sensitive to the cytotoxic and proapoptotic effects of ENMD-2076 exposure than cell lines with decreased p53 expression.

CONCLUSIONS

ENMD-2076 exhibited robust anticancer activity against models of triple-negative breast cancer and the candidate predictive biomarkers identified in this study may be useful in selecting patients for Aurora kinase inhibitors in the future.

ATM and MET kinases are synthetic lethal with nongenotoxic activation of p53

The p53 tumor suppressor orchestrates alternative stress responses including cell cycle arrest and apoptosis, but the mechanisms defining cell fate upon p53 activation are poorly understood. Several small-molecule activators of p53 have been developed, including Nutlin-3, but their therapeutic potential is limited by the fact that they induce reversible cell cycle arrest in most cancer cell types. We report here the results of a genome-wide short hairpin RNA screen for genes that are lethal in combination with p53 activation by Nutlin-3, which showed that the ATM and MET kinases govern cell fate choice upon p53 activation. Genetic or pharmacological interference with ATM or MET activity converts the cellular response from cell cycle arrest into apoptosis in diverse cancer cell types without affecting expression of key p53 target genes. ATM and MET inhibitors also enable Nutlin-3 to kill tumor spheroids. These results identify new pathways controlling the cellular response to p53 activation and aid in the design of p53-based therapies.

Preclinical activity of the rational combination of selumetinib (AZD6244) in combination with vorinostat in KRAS-mutant colorectal cancer models

PURPOSE

Despite the availability of several active combination regimens for advanced colorectal cancer (CRC), the 5-year survival rate remains poor at less than 10%, supporting the development of novel therapeutic approaches. In this study, we focused on the preclinical assessment of a rationally based combination against KRAS-mutated CRC by testing the combination of the MEK inhibitor, selumetinib, and vorinostat, a histone deacetylase (HDAC) inhibitor.

EXPERIMENTAL DESIGN

Transcriptional profiling and gene set enrichment analysis (baseline and posttreatment) of CRC cell lines provided the rationale for the combination. The activity of selumetinib and vorinostat against the KRAS-mutant SW620 and SW480 CRC cell lines was studied in vitro and in vivo. The effects of this combination on tumor phenotype were assessed using monolayer and 3-dimensional cultures, flow cytometry, apoptosis, and cell migration. In vivo, tumor growth inhibition, (18)F-fluoro-deoxy-glucose positron emission tomography (FDG-PET), and proton nuclear magnetic resonance were carried out to evaluate the growth inhibitory and metabolic responses, respectively, in CRC xenografts.

RESULTS

In vitro, treatment with selumetinib and vorinostat resulted in a synergistic inhibition of proliferation and spheroid formation in both CRC cell lines. This inhibition was associated with an increase in apoptosis, cell-cycle arrest in G(1), and reduced cellular migration and VEGF-A secretion. In vivo, the combination resulted in additive tumor growth inhibition. The metabolic response to selumetinib and vorinostat consisted of significant inhibition of membrane phospholipids; no significant changes in glucose uptake or metabolism were observed in any of the treatment groups.

CONCLUSION

These data indicate that the rationally based combination of the mitogen-activated protein kinase/extracellular signal-regulated kinase inhibitor, selumetinib, with the HDAC inhibitor vorinostat results in synergistic antiproliferative activity against KRAS-mutant CRC cell lines in vitro. In vivo, the combination showed additive effects that were associated with metabolic changes in phospholipid turnover, but not on FDG-PET, indicating that the former is a more sensitive endpoint of the combination effects.

P3-01-08: In Vitro and In Vivo Antitumor Activity of the Aurora and Angiogenic Kinase Inhibitor ENMD-2076 in Triple-Negative Breast Cancer Models

Background

Triple-negative breast cancer (TNBC) is an aggressive biologic subtype which lacks effective targeted anti-cancer agents and is characterized by a high mitotic index and dependence on angiogenesis. ENMD-2076 is a novel orally bioavailable Aurora and angiogenic kinase inhibitor currently in clinical development with favorable pharmacokinetics and a manageable toxicity profile. The purpose of this study was to use TNBC cell line-based in vitro and in vivo models to demonstrate the antitumor activity of ENMD-2076 towards this breast cancer subtype compared to the luminal and HER2−amplified subtypes. Additionally, we used baseline gene expression profiling and pathway analysis to explore molecular predictors of responsiveness to ENMD-2076 in TNBC.

Methods: Twenty-five breast cancer cell lines were exposed to ENMD-2076 and the effects on proliferation, apoptosis, and cell cycle distribution were evaluated. Proliferation was assessed using an SRB assay, apoptosis was analyzed using a caspase 3/7 assay and cell cycle was measured using flow cytometry. In vitro activity of ENMD-2076 was confirmed in 3-D cell culture and in MDA-MB-231 and MDA-MB-468 triple-negative breast cancer xenograft models and immunohistochemical analysis was performed for phosphor-histone H3 (pHH3). Gene array and gene set enrichment analysis (GSEA) was used to identify pathways differentially regulated in the sensitive and resistance cell lines, including within the triple-negative breast cancer subset.

Results: In vitro exposure to ENMD-2076 resulted in robust inhibition of proliferation in TNBC cell lines which was associated with a G2 cell cycle arrest and induction of caspase-dependent apoptosis. Of the TNBC cell lines screened, 1 of 10 had a mean IC50 value &gt; 5 μmol/L and 7 of 10 had a mean IC50 ≤ 1 μmol/L (Fisher's exact test, p-value = 0.009). In comparison, only 1 luminal (ER+) and one UER2-amplified breast cancer cell line had an IC50 value &lt; 1, whereas 7 and 5 resistant lines were luminal and HER2−amplified, respectively (Fisher's exact test, p-values = 0.02 and 0.11 for ER and HER2 status, respectively). ENMD-2076 exhibited antitumor activity towards MDA-MD-231 and MDA-MB-468 xenograft models of TNBC with statistically significant tumor growth inhibition compared to vehicle control (p&lt; 0.05 and p&lt; 0.01, respectively). A trend towards an increase in pHH3 staining cells in the MDA-MB-231 ENMD-2076 treated group compared to the vehicle control group was observed; however, this was not statistically significant (104.7 ± 36.2 positive cells/mm2 in treated vs. 79.9 ± 34.5 in control). Using significance of analysis of microarrays (SAM) analysis and GSEA, we identified Ran, a member of the mitotic spindle regulation pathway as upregulated in sensitive TNBC cell lines (p = 0.017). Interestingly, AURKA, the main target of ENMD-2076, is a core gene in this pathway.

Conclusions: ENMD-2076 exhibited robust anticancer activity towards preclinical models of TNBC, supporting future clinical investigations of this agent in TNBC with an emphasis on the continued development of biomarkers predictive of response in this breast cancer subset.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P3-01-08.

Abstract B245: Synergistic antiproliferative effects of the P21-activated kinase (PAK) inhibitor, PF-03758309, and standard-of-care agents in colorectal cancer models

Background: The p21-activated kinase (PAK) family of serine/threonine kinases is overexpressed in multiple cancer types including breast, ovarian, colorectal, thyroid, and pancreatic. The two groups of PAK proteins, Group I (PAK 1–3) and Group II (PAK 4–6), are critical mediators of cell survival, motility, mitosis, transcription, and translation. The goal of this study was to assess the efficacy of a PAK inhibitor, PF-03758309, with irinotecan in colorectal cancer (CRC).

Methods: A panel of 27 colorectal cancer (CRC) cell lines were exposed to increasing doses of PF-03758309 (0.015–1 μM) for 72 hours and analyzed for inhibition of proliferation using the sulforhodamine B (SRB) assay. Cell lines were designated sensitive (S), intermediate (I), or resistant (R) based on IC50's &lt; 0.125 μM, ≥ 0.125 and ≤ 1 μM, or &gt; 1 μM, respectively. Two sensitive and two resistant cell lines were exposed to three different concentrations of either the PAKi, irinotecan or all possible combinations. Proliferation was assessed by the SRB assay and synergy was calculated using the Calcusyn software. Apoptosis was also assessed using the luminescent Caspase 3/7 assay. Athymic nude mice were injected with primary patient derived explants. Once the tumors reached 200–300mm3 the mice were dosed with PF-03758309, irinotecan, or cetuximab or the combination. Tumors were measured twice weekly and growth curves were analyzed.

Results: Synergy was observed in both PF-03758309 sensitive and resistant cell lines, though the greatest synergy was seen in one of the more sensitive lines. Apoptosis was also increased in the combination when compared to the single agents. Of the explants treated, one of them demonstrated a synergistic/super-additive effect when dosed with the combination of irinotecan. One of the explants also demonstrated an added benefit with the combination of PF-03758309 and cetuximab. Further investigation into the differential sensitivities seen with PF-03758309 revealed that the more resistant CRC cell lines had higher expression of MDR1. When this was modulated either by shRNA knockdown or by addition of verapamil, we saw a shift to a more sensitive phenotype.

Conclusions: The combination of the PAKi, PF-03758309 with irinotecan resulted in synergistic anti-proliferative effectsand apoptosis in CRC cell lines regardless of sensitivity. Similar effects were observed in patient-derived CRC explants with PF-03758309 and standard of care agents.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B245.

Abstract B178: Molecular determinants of response to the investigational small molecule inhibitor of Nedd8-activating enzyme (NAE) MLN4924 in melanoma cell lines and patient-derived tumor explant models

Background: The ubiquitin proteasome system (UPS) regulates the ubiquitination, and thus degradation and turnover, of many proteins vital to proper functioning of the cell. Recent studies have shown that the UPS is more complex than previously thought, and its role in cell cycle regulation, signal transduction, DNA replication, and thus the evolution of the malignant phenotype of many cancers, is now well appreciated. The proteasome inhibitor bortezomib has provided validation of interfering with the UPS for clinical benefit in cancer patients and has provided the impetus for the development of new drugs that target the UPS more specifically. MLN4924 (Millennium Pharmaceuticals, Inc.) is an investigational first-in-class small molecule inhibitor of the key enzyme in the Nedd8 conjugation pathway, NAE. Inhibition of NAE results in in S-phase arrest, DNA re-replication and apoptosis. In this study, we used both in vitro and in vivo models of melanoma to assess the preclinical efficacy of MLN4924 in conjunction with gene array and gene set enrichment analysis (GSEA) to identify differentially expressed genes and pathways as potential molecular determinants of response to this novel compound.

Methods & Results: A panel of thirty-six melanoma cell lines was exposed to MLN4924 and IC50s were determined using the CellTiter Glo method. The cell lines were then classified as sensitive (S) or resistant (R) based on an IC50&lt;0.03μM or &gt;2.59μM, respectively. The most extreme S and R lines were also grown as subcutaneous flank xenograft tumors in nude mice to confirm in vitro responses to MLN4924. Additionally, twelve patient-derived melanoma tumors were implanted in mice and both the cell line and explant xenograft mice were treated s.c. with MLN4924 at 90mg/kg. The compound was well-tolerated and no significant weight loss or lethality was observed. Tumors were measured three times weekly by caliper and tumor growth inhibition (TGI) was analyzed. Of the explant models, five responded favorably to MLN4924, with TGI&gt;50%, with one model exhibiting tumor regression. Pharmacodynamic studies were also performed on melanoma explant tumors from mice exposed to a single dose of MLN4924 which were then harvested over a seven point time course ranging from 30 min to 24 hr post-drug. Immunoblotting of these tumors revealed rapid increases in the levels of caspase 3 as well as phospho-Chk-1 at 1 hr and decreases in neddylated cullin levels beginning at 8 hr, consistent with the known mode of action of MLN4924. Affymetrix 1.0 ST gene array analysis was performed on 6 S and 6 R cell lines in order to identify differentially expressed genes that could be used as predictive biomarkers. GSEA and KEGG pathway analysis of this data identified several DNA repair pathways as being enriched in the S lines while ABC drug transporter pathways were enriched in the R lines.

Conclusion: MLN4924 demonstrated strong antitumor activity in a subset of melanoma cell lines and patient-derived explants. Based on these preclinical results, MLN4924 demonstrates promising data supportive of further patient-selective clinical development in melanoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr B178.

Abstract C182: Antitumor efficacy of the investigational MEK inhibitor TAK-733 against melanoma cell lines and human-derived tumor explant models

Background: Sixty-percent of melanomas express mutant BRAF oncoproteins, which result in constitutive activation of the Rasmitogen activated protein kinase (MAPK) pathway and thus abnormal growth and ultimately a malignant phenotype. It has also been demonstrated that many melanomas are dependent on the MAPK pathway for survival and proliferation. MEK is a seronine/threonine kinase that is part of the BRAF downstream signaling cascade and is responsible for the phosphorylation of ERK1/2. Interestingly, ERK1/2 appear to be the sole target of the MEK protein kinase. Without ERK1/2 nuclear translocation, the inappropriate nuclear signaling responsible for the malignant phenotype is inhibited. The development of BRAF inhibitors has provided an exciting new treatment option for BRAF mutated melanoma, but unfortunately many patients have relapsed due to downstream alternative pathway activation. Investigational drug TAK-733 (Millennium Pharmaceuticals, Inc) is a potent, novel, selective, non-ATP competitive, allosteric inhibitor of MEK 1/2. With molecular inhibition downstream of BRAF, CRAF, COT, or NRAS mutations, tumor growth would theoretically be slowed or suppressed altogether. We explored the preclinical efficacy of TAK-733 in both in vitro and in vivo models of melanoma. Based on these translational results, TAK-733 demonstrates promising pre-clinical data supportive of further clinical development.

Methods & Results: 36 melanoma cell lines were exposed to TAK-733 and the IC50 was determined using the SRB method. The cell lines were then classified as sensitive (S) or resistant (R) based on an IC50&lt;0.01uM or IC50&gt;0.1uM, respectively. BRAF status was obtained on all cell lines and did not correlate with responsiveness to TAK-733. Immunoblotting for effector proteins was performed on both S and R cell lines after 72 hrs of treatment with TAK-733. Phospho-ERK was suppressed in both S and R cell lines, confirming TAK-733-mediated inhibition of MEK 1/2. The evidence of MEK inhibition in the relatively resistant cell lines suggests other escape pathways are also contributing to melanoma survival and proliferation. There was no evidence of up-regulation of known MAPK-associated alternative pathways involving PI3 kinase or phospho-S6. Ten patient-derived melanoma tumors (5 V600E BRAF mutant, 2 wild-type BRAF, 3 unknown) were implanted into nude mice and treated daily via oral gavage with TAK-733 10mg/kg or 25mg/kg daily. The tumors were measured three times weekly and tumor growth inhibition (TGI) was analyzed. Nine explants, regardless of BRAF status, showed statistically significant TGI, ranging 87–97%, when compared to controls. One of the ten explants (BRAF V600E mutant) was resistant to TAK-733 with a TGI of 23%. Additionally, in one sensitive explant (BRAF wild type), treatment with TAK-733 was stopped, re-growth to 1533 mm3 was allowed, and subsequent re-treatment with TAK-733 induced tumor shrinkage to &lt;50mm3. The compound was well-tolerated and no significant weight loss or lethality was observed.

Conclusion: These data demonstrate that TAK-733 exhibited robust tumor growth inhibition and regression in human melanoma cell lines and human melanoma explant models in mice. Based on these results, TAK-733 demonstrates promising preclinical data supportive of further clinical development in melanoma.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr C182.

Mapping of ESE-1 subdomains required to initiate mammary epithelial cell transformation via a cytoplasmic mechanism

BACKGROUND

The ETS family transcription factor ESE-1 is often overexpressed in human breast cancer. ESE-1 initiates transformation of MCF-12A cells via a non-transcriptional, cytoplasmic process that is mediated by a unique 40-amino acid serine and aspartic acid rich (SAR) subdomain, whereas, ESE-1's nuclear transcriptional property is required to maintain the transformed phenotype of MCF7, ZR-75-1 and T47D breast cancer cells.

RESULTS

To map the minimal functional nuclear localization (NLS) and nuclear export (NES) signals, we fused in-frame putative NLS and NES motifs between GFP and the SAR domain. Using these GFP constructs as reporters of subcellular localization, we mapped a single NLS to six basic amino acids (242 HGKRRR 247) in the AT-hook and two CRM1-dependent NES motifs, one to the pointed domain (NES1: 102 LCNCALEELRL 112) and another to the DNA binding domain (DBD), (NES2: 275 LWEFIRDILI 284). Moreover, analysis of a putative NLS located in the DBD (316 GQKKKNSN 323) by a similar GFP-SAR reporter or by internal deletion of the DBD, revealed this sequence to lack NLS activity. To assess the role of NES2 in regulating ESE-1 subcellular localization and subsequent transformation potency, we site-specifically mutagenized NES2, within full-length GFP-ESE-1 and GFP-NES2-SAR reporter constructs. These studies show that site-specific mutation of NES2 completely abrogates ESE-1 transforming activity. Furthermore, we show that exclusive cytoplasmic targeting of the SAR domain is sufficient to initiate transformation, and we report that an intact SAR domain is required, since block mutagenesis reveals that an intact SAR domain is necessary to maintain its full transforming potency. Finally, using a monoclonal antibody targeting the SAR domain, we demonstrate that the SAR domain contains a region accessible for protein - protein interactions.

CONCLUSIONS

These data highlight that ESE-1 contains NLS and NES signals that play a critical role in regulating its subcellular localization and function, and that an intact SAR domain mediates MEC transformation exclusively in the cytoplasm, via a novel nontranscriptional mechanism, whereby the SAR motif is accessible for ligand and/or protein interactions. These findings are significant, since they provide novel molecular insights into the functions of ETS transcription factors in mammary cell transformation.