Abstract P6-21-04: Targeting PI3Kβ alone and in combination with chemotherapy or immunotherapy in tumors with PTEN loss

Background: PTEN functions as a negative regulator of the phosphatidylinositol 3-kinase (PI3K)/AKT/mTOR pathway to promote balanced cell proliferation, survival and differentiation. PTEN loss occurs across a variety of cancer subtypes; PTEN-deficient tumors are dependent on PI3Kβ activity, making PI3Kβ a compelling target. We evaluated the efficacy of PI3Kβ inhibitor AZD8186 as a single agent and in combination with standard chemotherapy and immune checkpoint inhibitors focused on tumors with loss of PTEN function.

Methods: In vitro, cell proliferation assays were performed to determine the half maximal inhibitory concentration (IC50) after 3 days of treatment and to test the effects in combination with standard chemotherapy. Colony formation assays were performed to confirm efficacy of AZD8186 in PTEN-deficient cell lines. Western blot analysis was performed to assess PTEN protein expression and to evaluate effects of AZD8186 on PI3K signaling. In vivo, antitumor efficacy of AZD8186 as a single agent as well as in combination with paclitaxel and anti-PD1 was evaluated.

Results: AZD8186 inhibited the cell proliferation of three of ten TNBC cell lines in vitro; PTEN loss was significantly correlated with AZD8186 sensitivity (p= 0.008). Colony formation assay confirmed sensitivity of PTEN-deficient cell lines to AZD8186. AZD8186 inhibited PI3K signaling with decreased expression of pAKT, pGSK3β, pPRAS40 and pS6. AZD8186 treatment of PTEN-deficient cell lines, MDA-MB-436 and MDA-MB-468, resulted in increased apoptosis. Cell proliferation assays demonstrated additive effect of the combination of paclitaxel with AZD8186. AZD8186 significantly enhanced antitumor activity of paclitaxel in MDA-MB-436 and MDA-MB-468 cell-line-derived xenografts, with disease stabilization in the latter. In syngeneic models, AZD8186 enhanced antitumor efficacy of anti-PD1 antibodies in PTEN-deficient BP murine melanoma xenograft (p=0.0073), but not in PTEN-wildtype colon carcinoma, CT26.

Conclusion: AZD8186 has single agent efficacy in PTEN-deficient triple negative breast cancer cell lines in vitro, with modest single agent efficacy in vivo. AZD8186 enhanced the antitumor efficacy of paclitaxel and of Anti-PD1 antibodies in vivo. Further study is needed to determine optimal combination therapies for PTEN-deficient solid tumors.

Citation Format: Owusu-Brackett N, Zhao M, Akcakanat A, Evans KW, Yuca E, Tapia C, Ileana-Dumbrava E, Janku F, Meric-Bernstam F. Targeting PI3Kβ alone and in combination with chemotherapy or immunotherapy in tumors with PTEN loss [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 P6-21-04.

Abstract P6-20-11: The stapled peptide ALRN-6924, a dual inhibitor of MDMX and MDM2, enhances antitumor efficacy of paclitaxel and Nab-paclitaxel in TP53 wild-type MCF-7 breast cancer models

Background: MDMX and MDM2 are endogenous inhibitors of the p53 tumor suppressor protein. MDMX levels are frequently elevated in luminal breast cancer, which generally expresses wild-type p53. ALRN-6924, an α-helical stapled peptide, is the first and only dual inhibitor of MDMX and MDM2 currently in clinical trials for solid tumors and hematological malignancies. We sought to determine the antitumor efficacy of the combination of ALRN-6924 with taxanes in models of human breast cancer.

Methods: Sulforhodamine B colorimetric assay was used to assess the cytotoxicity of the combination of ALRN-6924 with taxanes in vitro. Athymic nude mice were implanted with MCF-7 tumors and treated for four weeks with ALRN-6924 alone and in combination with paclitaxel in cremaphor (Taxol®, study #1) or a nanoparticle-albumin-bound (nab) formulation (Abraxane®, study #2). In study #1, ALRN-6924 (5, 10 mg/kg) was dosed twice weekly and paclitaxel (10, 15 mg/kg) was dosed weekly, with paclitaxel administered 6 h prior to ALRN-6924. In study #2, ALRN-6924 alone (5 mg/kg) was dosed twice weekly while nab-paclitaxel (15 mg/kg) was administered weekly in combination at -24h, -6h, 0h, +6h, or +24h relative to ALRN-6924 administration.

Results: ALRN-6924 was found to have synergistic activity with paclitaxel in both MCF-7 and ZR-75-1 cell lines in vitro (Combination index: 0.874 and 0.323 respectively). In in vivo study #1, the combination of ALRN-6924 and paclitaxel significantly inhibited MCF-7 tumor growth compared to either agent alone (p<0.005). Paclitaxel 15 mg/kg + ALRN-6924 5 mg/kg resulted in the greatest tumor inhibition with average tumor size decreased by 13% at four weeks versus the starting size.

In study #2, the combination of nab-paclitaxel with ALRN-6924 administered -6h to +24h relative to nab-paclitaxel resulted in improved efficacy over either single agent and a significant increase in the number of tumor regressions (up to 6/10 with 3 consecutive measurements <50% of starting volume) compared to nab-paclitaxel alone (1/10, p<0.005). When ALRN-6924 was administered 24h prior to nab-paclitaxel, there was a marked decrease in efficacy and no tumor regressions were observed.

In both studies, drug treatments were well tolerated with no significant weight loss in mice.

Conclusion: The significant increase in efficacy observed with ALRN-6924 in combination with paclitaxel supports further evaluation in patients with breast cancer.

Citation Format: Pairawan SS, Yuca E, Evans K, Annis A, Narasimhan N, Sutton D, Carvajal LA, Ren J-G, Santiago S, Guerlavais V, Akcakanat A, Tapia C, Illeana Dumbrava EE, Aivado M, Meric-Bernstam F. The stapled peptide ALRN-6924, a dual inhibitor of MDMX and MDM2, enhances antitumor efficacy of paclitaxel and Nab-paclitaxel in TP53 wild-type MCF-7 breast cancer models [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 P6-20-11.

Vertical inhibition of the PI3K/Akt/mTOR pathway is synergistic in breast cancer

Deregulation and activation of the phosphoinositide 3-kinase (PI3K)/Akt/mammalian (or mechanistic) target of rapamycin (mTOR) pathway have a major role in proliferation and cell survival in breast cancer. However, as single agents, mTOR inhibitors have had modest antitumor efficacy. In this study, we evaluated the effects of vertical inhibition of mTOR and Akt in breast cancer cell lines and xenografts. We assessed the effects of mTOR inhibitor rapamycin and Akt inhibitor MK-2206, given as single drugs or in combination, on cell signaling, cell proliferation and apoptosis in a panel of cancer cell lines in vitro. The antitumor efficacy was tested in vivo. We demonstrated that MK-2206 inhibited Akt phosphorylation, cell proliferation and apoptosis in a dose-dependent manner in breast cancer cell lines. Rapamycin inhibited S6 phosphorylation and cell proliferation, and resulted in lower levels of apoptosis induction. Furthermore, the combination treatment inhibited phosphorylation of Akt and S6, synergistically inhibited proliferation and induced apoptosis with a higher efficacy. In vivo combination inhibited tumor growth more than either agent alone. Our data suggest that a combination of Akt and mTOR inhibitors have greater antitumor activity in breast cancer cells, which may be a viable approach to treat patients.

Open-label randomized clinical trial of standard neoadjuvant chemotherapy with paclitaxel followed by FEC versus the combination of paclitaxel and everolimus followed by FEC in women with triple receptor-negative breast cancer†

BACKGROUND

Everolimus synergistically enhances taxane-induced cytotoxicity in breast cancer cells in vitro and in vivo in addition to demonstrating a direct antiproliferative activity. We aim to determine pharmacodynamics changes and response of adding everolimus to standard neoadjuvant chemotherapy in triple-negative breast cancer (TNBC).

PATIENTS AND METHODS

Phase II study in patients with primary TNBC randomized to T-FEC (paclitaxel 80 mg/m(2) i.v. weekly for 12 weeks, followed by 5-fluorouracil 500 mg/m(2), epirubicin 100 mg/m(2), and cyclophosphamide 500 mg/m(2) every 3 weeks for four cycles) versus TR-FEC (paclitaxel 80 mg/m(2) i.v. and everolimus 30 mg PO weekly for 12 weeks, followed by FEC). Tumor samples were collected to assess molecular changes in the PI3K/AKT/mTOR pathway, at baseline, 48 h, 12 weeks, and at surgery by reverse phase protein arrays (RPPA). Clinical end points included 12-week clinical response rate (12-week RR), pathological complete response (pCR), and toxicity.

RESULTS

Sixty-two patients were registered, and 50 were randomized, 27 received T-FEC, and 23 received TR-FEC. Median age was 48 (range 31-75). There was downregulation of the mTOR pathway at 48 h in the TR-FEC arm. Twelve-week RR by ultrasound were 29.6% versus 47.8%, (P = 0.075), and pCR were 25.9% versus 30.4% (P = 0.76) for T-FEC and TR-FEC, respectively. mTOR downregulation at 48 h did not correlate with 12-week RR in the TR-FEC group (P = 0.58). Main NCI grade 3/4 toxicities included anemia, neutropenia, rash/desquamation, and vomiting in both arms. There was one case of grade 3 pneumonitis in the TR-FEC arm. No grade 3/4 stomatitis occurred.

CONCLUSION

The addition of everolimus to paclitaxel was well tolerated. Everolimus downregulated mTOR signaling but downregulation of mTOR at 48 h did not correlate with 12-week RR in the TR-FEC group.

CLINICAL TRIAL NUMBER

NCT00499603.

Abstract P1-07-06: Effect of biospecimen variables on proteomic biomarker assessment in breast cancer

Background: PI3K/Akt/mTOR signaling is being actively pursued as a therapeutic target. We sought to determine how tumor heterogeneity and biospecimen variables affect assessment of PI3K/Akt/mTOR pathway activation.

Methods: Intraoperative image-guided core-needle biopsies (CNB) of primary breast tumors were prospectively collected in 53 patients with invasive breast cancer. After surgery, specimens were collected from the center and periphery of the excised tumor. CNB, central and peripheral surgical specimens were assessed with reverse phase proteomic arrays (RPPA), H&E and immunohistochemistry (IHC).

Results: The expression of standard of care markers ER, PR, and HER2 by RPPA correlated well between biospecimen types. Overall, there was a significant correlation between the expression of 132 (86%) of 154 different markers in the center and periphery; the correlation was significantly higher for smaller tumors, and with shorter cold ischemia time. Expression of many investigational prognostic markers and druggable targets on CNB correlated with expression in the surgical specimen (average of center and periphery), while others, such as EGFR and c-MET, had a weak correlation. Of 154 RPPA markers, 132 (86%) were not statistically different between the center and periphery, and 97 (67%) were not different between the CNB and the surgical specimen. On analysis of the PI3K/AKT/mTOR pathway, pAkt S473 and PTEN had a significant correlation between central and peripheral specimens, and between CNB and surgical specimens. However, pAkt S473, pS6 S235/236 and pS6 240/244 levels were higher in CNB than the central specimens both by RPPA and by IHC. When patients were classified by RPPA PI3K pathway activation score, there was a moderate agreement between classification on the CNB and central specimens (Cohen's Kappa 0.539). However 9 of 20 tumors classified as having PI3K activation on CNB were classified as not having pathway activation on central specimens.

Conclusions: There is remarkable homogeneity in expression of biomarkers within a tumor. However, proteomic markers are differentially expressed by biospecimen type and other preanalytic variables. PI3K pathway activation is greater in CNB compared to surgical samples.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-07-06.

Abstract P1-03-01: Generation of a Novel In Vivo Model of Patient-Derived Chemoresistant Breast Cancers

Background: Breast cancer patients who have significant residual cancer after neoadjuvant chemotherapy (NCT) are at high risk of relapse. There is a pressing need to identify novel therapeutics that can be offered to these patients. In vivo models available to test new agents are limited. We hypothesized that tumors from patients with poor response to NCT can be transplanted into nude mice to establish xenografts, providing a novel in vivo model to study therapies for chemoresistant tumors. Materials and Methods: After informed consent, excess tumor was taken from the mastectomy specimens from six patients who had either disease progression during NCT or significant residual disease after NCT. On surgical pathologic evaluation, average tumor size was 8.6 ± 3.2 cm (range 4.5-12 cm), and average number of positive lymph nodes was 6.2 ± 6.8 (range 0-18). Patients had RECIST criteria of partial response (n=2), stable disease (n= 1) or progressive disease (n=3). For each patient, tumors were implanted subcutaneously into the flanks of five nude mice. Tumors were passaged to successive generations when they reached 1.5 cm in diameter. In vivo tumor growth and the ability to serially passage tumors were assessed. Patient and tumor characteristics, and patient outcomes were evaluated.

Results: Three patients had ER+HER2- tumors and three had ER-HER2- tumors. Serially transplanted xenografts were established from all six patients (100%); see Figure 1. Within each group of five mice implanted with the human tumors, 60 ± 26% developed tumor. Time to tumor size of 1.5 cm diameter was 4.2 ± 2.6 months (range 1.5-7.8 months). Two mice also developed tumors at a location distant from the implantation site (Met). These tumors were separately engrafted, also with 100% take, reaching 1.5 cm diameter at 1.5 and 1.7 months. Of the six patients, one had metastatic disease at surgery and underwent palliative mastectomy. Of the other five patients, four (80%) developed metastatic disease 4-8.4 months after surgery. Mice developed passagable tumors at least 2 months before the donor patients developed distant recurrence. The one patient who remains distant disease-free had the longest time to tumor passage (8.4 months).

Figure 1. Time to passage of tumor to next generation of mice. Flank tumors xenografts were derived from patients with chemoresistant breast cancers. When tumors reach 1.5 cm in diameter, they are passaged to the next generation of 5 mice. X-axis depicts time to reach 1.5 cm with each passage.

Discussion: Patients with progression or significant residual disease after NCT are at very high risk of distant relapse. Their chemoresistant tumors can be used to create serially transplantable xenografts. This in vivo model of chemoresistant breast cancer may be utilized to allow individualization of additional adjuvant or metastatic breast cancer treatment.

Rapamycin-regulated gene expression signature determines prognosis in breast cancer

Abstract #3072

Background: Mammalian target of rapamycin (mTOR) is a serine/threonine kinase involved in multiple intracellular signaling pathways promoting tumor growth. mTOR is aberrantly activated in a significant portion of breast cancers and is a promising target for treatment. Rapamycin and its analogues are in clinical trials for breast cancer treatment. Patterns of gene expression (metagenes) may also be used to simulate a biologic process or effects of a drug treatment. In this study, we tested the hypothesis that the gene-expression signature regulated by rapamycin could predict disease outcome for patients with breast cancer.
 Methods: MDA-MB-468 breast cancer cell line is triple negative and PTEN null. Sensitivity of MDA-MB-468 breast cancer cell line to rapamycin was determined by in vitro growth assays and in vivo tumor studies. Total RNA was extracted from cell lines treated with rapamycin or DMSO for 24 hours and xenografts treated with DMSO or rapamycin for 1 or 22 days. Total RNA was used for expression profiling and hybridized to Affymetrix HG-U133 Plus 2.0 arrays. We used two well-described primary breast cancer datasets of 251 (Miller et al, Proc. Natl. Acad. Sci. USA 2005;102:13550) and 286 (Wang et al, Lancet. 2005;365:671) patients from the public domain and assessed the prognostic capability of rapamycin-regulated gene expression signatures.
 Results: Colony formation and sulforhodazine B (IC50 < 1 nM) assays, and xenograft animals showed that MDA-MB-468 cells were sensitive to treatment with rapamycin. The comparison of in vitro and in vivo gene expression data identified a 31-gene expression signature that was up- regulated by rapamycin treatment in vitro as well as in vivo (FDR of 0.1). From the 31 genes on HG-U133 Plus 2.0 array, 20 that were included on HG-U133A array were used for analysis. In the Miller dataset, rapamycin metagene index (RMI) did not correlate with tumor size or lymph node status. High (0.75 percentile) RMI was significantly associated with longer survival (P=0.015). On multivariate analysis, RMI (P=0.029), tumor size (P=0.015) and lymph node status (P=0.001) were prognostic. In the Wang dataset, RMI predicted time to disease relapse (P=0.009).
 Conclusion: Rapamycin-regulated gene expression signature predicts clinical outcome in breast cancer. This supports the central role of mTOR signaling in breast cancer biology and provides further impetus to pursue mTOR-targeted therapies for breast cancer treatment.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 3072.

mTOR modulates cellular fat metabolism by regulating stearoyl-CoA desaturase 1 transcription

Abstract #6030

mTOR (mammalian target of rapamycin) signaling is a central regulator of cell growth and proliferation. Rapamycin and its analogues have been shown to inhibit breast cancer cell growth in preclinical models, and are actively being pursued in clinical trials. We performed a high-throughput microarray polysome analysis to identify novel genes whose expression was regulated by rapamycin at the level of transcription or translation. In three breast cancer cell lines representing different breast cancer subtypes, we found a significant decline in polysome-associated mRNA for stearoyl-CoA desaturase 1 (SCD1), the rate-limiting enzyme in monounsaturated fatty acid synthesis. Insulin and insulin-like growth factor, both activators of mTOR, increase SCD1 expression. Rapamycin and PI3K inhibitors decrease SCD1 protein, as does mTOR siRNA. Quantitative RT-PCR of total, polysomal and monosomal RNA, northern analysis and stability studies demonstrate that rapamycin regulates SCD1 at the level of transcription. Furthermore, rapamycin inhibits the SCD1 promoter activation by mevinolin, an inhibitor of cholesterol biosynthesis. We demonstrate that mTOR regulates SCD1 expression. This establishes a novel link between cell signaling and cancer cell fat metabolism. In doing so, we also present SCD1 as a potential marker of response to treatment by mTOR inhibitors.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6030.