Abstract SP139: HER2 targeted therapy: Determinants of response and mechanisms of resistance

HER2-positive (+) breast cancer (BC), accounting for 15-20% of all BCs, is characterized by overexpression, mostly via gene amplification, of HER2. HER2 is a key member of the HER family of 4 tyrosine kinase receptors. Multiple clinically available HER2-targeted therapies, including monoclonal antibodies, tyrosine kinase inhibitors (TKIs), and antibody-drug conjugates have revolutionized the outcome of patients with HER2+ BC. Despite these effective therapies, intrinsic and acquired resistance still occurs, posing a major challenge in the clinical management of this disease. A better understanding of the determinants of response and mechanisms of resistance may help develop personalized treatment approaches and new strategies to overcome resistance. Tumors that are truly addicted to HER2, clinically reflected especially under chemotherapy-sparing HER2-targeted therapy regimens, are associated with high and homogeneous levels of HER2 gene amplification, protein, and activity. Even in these HER2-addicted tumors, the efficacy of anti-HER2 therapy can be jeopardized by deregulations in the downstream PI3K pathway (e.g., PIK3CA mutations), which can lead to constitutive activation of the PI3K/AKT pathway and resistance. Given the functional redundancy of signaling from multiple HER receptor dimers and compensatory signaling within the pathway, dual anti-HER2 therapy has proven superior to single agents in achieving a more comprehensive blockade of the entire HER receptor layer and in anti-tumor efficacy. Further, in the HER2+ tumors that co-express ER, an unblocked, re-expressed and/or reactivated ER signaling can provide alternative proliferative and survival signals to evade sustained HER2 blockade, thus underscoring the need for concurrent blockade of HER2 and ER signaling. Nevertheless, effective inhibition of HER2 might prove challenging in some cases due to molecular masking of the HER receptors (e.g., mucins) or due to the de novo presence or acquisition of genetic, epigenetic or post-translational alterations in HER2 itself, including activating HER2 mutations (e.g., L755S), and p95HER2. We recently reported that acquired resistance to HER2-targeted therapy, especially TKIs, is mediated by the common HER2 L755S mutation, the clinical importance of which is underscored by the observation that this and other HER mutations are further enriched in the metastatic lesions compared to primary HER2+ tumors. On the other hand, when HER2 does remain effectively inhibited under potent HER2-targeted therapy, resistance can arise due to the upregulation of alternative escape pathways that transmit proliferative stimuli. These include activation of other receptor tyrosine kinases (e.g., AXL, FGFR), other downstream/intracellular signaling (e.g., SRC, YES1), or metabolic pathways (e.g., FASN and mevalonate pathways). Our recent data suggest that the mevalonate pathway offers an escape mechanism by providing alternative signaling through the YAP/TAZ-mTORC1-survivin axis to activate a transcriptional program that promotes resistant cell proliferation and survival, which can be overcome using inhibitors of mevalonate pathway (e.g., statins). Importantly, activation of the key cell cycle regulator cyclin D1/CDK4 complex has been shown to mediate resistance to HER2-targeted therapy and that CDK4/6 inhibitors, at least partly by also inhibiting mTORC1 activity, can overcome this resistance. Finally, the role of tumor microenvironment, including host immune components (e.g., TILs) and extracellular matrix components signaling via integrins, have been shown to play a role in modulating tumor response to treatment and in resistance. Together, these findings suggest new strategies to enhance sensitivity and overcome resistance to HER2-targeted therapy, some of which are already under clinical development.

Citation Format: R Schiff, J Veeraraghavan, C De Angelis, C Osborne, MF Rimawi. HER2 targeted therapy: Determinants of response and mechanisms of resistance [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr SP139.

A combinatorial biomarker predicts pathologic complete response to neoadjuvant lapatinib and trastuzumab without chemotherapy in patients with HER2+ breast cancer

BACKGROUND

HER2-positive (+) breast cancers, defined by HER2 overexpression and/or amplification, are often addicted to HER2 to maintain their malignant phenotype. Yet, some HER2+ tumors do not benefit from anti-HER2 therapy. We hypothesize that HER2 amplification levels and PI3K pathway activation are key determinants of response to HER2-targeted treatments without chemotherapy.

PATIENTS AND METHODS

Baseline HER2+ tumors from patients treated with neoadjuvant lapatinib plus trastuzumab [with endocrine therapy for estrogen receptor (ER)+ tumors] in TBCRC006 (NCT00548184) were evaluated in a central laboratory for HER2 amplification by fluorescence in situ hybridization (FISH) (n = 56). HER2 copy number (CN) and FISH ratios, and PI3K pathway status, defined by PIK3CA mutations or PTEN levels by immunohistochemistry were available for 41 tumors. Results were correlated with pathologic complete response (pCR; no residual invasive tumor in breast).

RESULTS

Thirteen of the 56 patients (23%) achieved pCR. None of the 11 patients with HER2 ratio <4 and/or CN <10 achieved pCR, whereas 13/45 patients (29%) with HER2 ratio ≥4 and/or CN ≥10 attained pCR (P = 0.0513). Of the 18 patients with tumors expressing high PTEN or wild-type (WT) PIK3CA (intact PI3K pathway), 7 (39%) achieved pCR, compared with 1/23 (4%) with PI3K pathway alterations (P = 0.0133). Seven of the 16 patients (44%) with HER2 ratio ≥4 and intact PI3K pathway achieved pCR, whereas only 1/25 (4%) patients not meeting these criteria achieved pCR (P = 0.0031).

CONCLUSIONS

Our findings suggest that there is a clinical subtype in breast cancer with high HER2 amplification and intact PI3K pathway that is especially sensitive to HER2-targeted therapies without chemotherapy. A combination of HER2 FISH ratio and PI3K pathway status warrants validation to identify patients who may be treated with HER2-targeted therapy without chemotherapy.

Abstract P6-17-12: Neratinib in combination with trastuzumab is superior to each alone and to pertuzumab plus trastuzumab in HER2-positive in vivo breast cancer models

Background: Lapatinib (L) plus trastuzumab (T) alone or with endocrine therapy for HER2+/ER+ tumors but without chemotherapy, yielded complete tumor eradication in xenograft models. In neoadjuvant trials (NCT00548184, 00999804, 01973660), a substantial number of patients achieved pathologic complete response with this same strategy. The irreversible pan-HER inhibitor neratinib (N) has been recently approved by the FDA for early stage HER2+ breast cancer and has shown greater potency compared to L in the preclinical setting. However, the therapeutic efficacy of N in combination with T (N+T) and how it compares to pertuzumab (P) +T (without chemotherapy) has not been well studied.

We hypothesize that dual HER2 inhibition using N+T will be highly efficacious and more effective than P+T due to more complete blockade of the HER pathway. Here, we evaluate the therapeutic efficacy of N, P, and T, either alone or in combination, with a primary focus on comparing N+T vs. P+T in established cell line- and patient-derived xenograft (PDX) models.

Methods: Athymic nude and SCID/Beige mice bearing BT474-AZ cell line (ER+/HER2+), and BCM-3963 PDX tumors (ER-/HER2+, wild-type PIK3CA), respectively were randomized to vehicle, N (20mg/kg, 5 days/week), T (10mg/kg, twice a week), P (6mg/kg, once a week), N+T, or P+T, with simultaneous estrogen (E2) deprivation (ED) in BT474-AZ model. Treatment response was assessed by biweekly tumor measurements. Study endpoints included time to tumor regression (TTR) and progression (TTP) (tumor halving/doubling over baseline, respectively), and the rate and time of complete response (CR and TCR, respectively). Results were analyzed using survival analysis (Kaplan-Meier estimates) and generalized Wilcoxon tests.

Results: In the BT474-AZ model, mice treated with E2+vehicle and ED+vehicle showed steady tumor growth, with a median TTP of 8 and 25 days, respectively. While tumor regression was observed in 100% of mice treated with N, P, T, N+T, and P+T, tumors treated with N+T regressed faster compared to P (p&lt;0.001), T (p=0.004), and P+T (p=0.044). Further, N+T was superior to N (p=0.018) and T (p=0.007) alone in achieving accelerated CR. In the BCM-3963 model, tumors treated with vehicle, T, P, and P+T continued to grow with a median TTP of 11, 16, 19, and 17 days, respectively. In contrast, CR was achieved in 100% of N and N+T treated mice. Importantly, combining N with T accelerated the attainment of CR compared to N alone (p=0.026). Molecular and pathologic analysis of short-term treated tumors in both models to evaluate alterations in HER signaling, cell proliferation, and apoptosis is ongoing.

Model/TreatmentN of miceMedian TTP (Days)Median TTR (Days)Median TCR (Days)CR (%)BT474-AZ     E2+Vehicle98--0ED+Vehicle1025--0ED+N13-214100ED+T12-519100ED+P12-185492ED+N+T13-210100ED+P+T14-414100BCM-3963     Vehicle1511--0N15-417100T1416--0P1319--0N+T19-614100P+T1617--0

Conclusions: Our findings establish the preclinical efficacy of combining N with T for HER2+ breast cancer and warrant further clinical testing to investigate the efficacy of N+T without chemotherapy in the neoadjuvant setting for patients with HER2+ breast cancer.

Citation Format: Veeraraghavan J, Sethunath V, Qin L, Shea MJ, Mitchell T, De Angelis C, Nanda S, Diala I, Lalani AS, Hilsenbeck SG, Rimawi MF, Osborne CK, Schiff R. Neratinib in combination with trastuzumab is superior to each alone and to pertuzumab plus trastuzumab in HER2-positive in vivo 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 P6-17-12.

Abstract P3-06-03: Dual p38/NLK kinase inhibitor as potential novel therapeutic agent for tamoxifen-resistant luminal breast cancer

Background: Tamoxifen is the most commonly used endocrine agent for estrogen receptor (ER) positive breast cancer (also known as luminal breast cancer). However, approximately half of the patients develop resistance after initial response to tamoxifen. To date, no effective targeted therapy exists to overcome it. We previously identified the role of nemo-like kinase (NLK), a serine-threonine kinase that functions in stress response and neurite outgrowth, in breast endocrine resistance. In addition, activation of p38 MAPK has been reported to modulate ER signaling and promote endocrine resistance. We identified a highly selective dual p38 and NLK kinase inhibitor (PNKI) through analysis of public kinase profiling datasets, and evaluated its therapeutic effect in endocrine-resistant breast cancers using in vitro and in preclinical mouse models. Experimental design and methods: To determine the in vitro therapeutic window of PNKI, we treated an acquired tamoxifen-resistant cell line (MCF7-TamR) and a benign breast epithelial cell line (MCF10A) with gradually increasing doses of PNKI. To determine the effect of PNKI on tamoxifen-resistant breast cancer cells, we treated primary tamoxifen-resistant breast cancer cell line BT483, and MDAMB415, together with acquired tamoxifen-resistant line MCF7 TamR, T47D TamR, and ZR-75-B TamR, with 0.5 uM PNKI in the presence of different doses of Tamoxifen. To evaluate the therapeutic effect of PNKI in a T47D-derived xenograft tumor model with acquired tamoxifen resistance, we administered PNKI alone or in combination with Fulvestrant, the second-line endocrine therapy agent, or with Everolimus, the mTOR inhibitor that could improve patient outcomes in several clinical trials. Mice bearing xenografts were randomized into six treatment groups (Vehicle, PNKI, Fulvestrant, Fulvestrant+PNKI, Everolimus, Everolimus+PNKI). Tumor growth was tracked closely. The tumors harvested two weeks after treatments started were profiled with Reverse Phase Protein Array (RPPA) to assess the early signaling changes after treatments. The therapeutic effect of PNKI were also evaluated in a patient-derived xenograft (PDX) model of de novo endocrine resistant breast cancer. Mice bearing the PDX tumors were randomized to four treatment groups (Vehicle, PNKI, Everolimus, Everolimus+PNKI) and tumor growth curve was measured timely. Results: PNKI showed an in vitro therapeutic window at 0.1-1μM for MCF7-TamR cells. Breast cancer cell lines with either de novo or acquired Tamoxifen resistance became more sensitive to tamoxifen when treated with 0.5uM PNKI. The concomitant treatment of PNKI and Everolimus results in significant decreased tumor burden and prolonged progression free survival in the both T47D-TamR xenograft tumors and re-transplanted de novo endocrine-resistant PDX tumors compared to other treatments. RPPA data of T47D-TamR tumors harvested following 2-week treatments revealed that several key survival signaling in breast cancer are repressed only when PNKI are combined with Everolimus. Conclusion: The dual p38 and NLK inhibitor (PNKI) exhibited potential therapeutic value as adjuvant agent to the mTOR inhibitor everolimus for acquired or de novo tamoxifen-resistant luminal breast cancers.

Citation Format: Wang X, Cao X, Veeraraghavan J, Qin L, Kim J-A, Tan Y, Hilsenbeck SG, Schiff R, Wang X. Dual p38/NLK kinase inhibitor as potential novel therapeutic agent for tamoxifen-resistant luminal 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 P3-06-03.

Abstract P4-04-03: Hyperactive FOXA1 activates super-enhancer-engaged HIF2α/EPAS1 to promote endocrine-resistant metastatic ER-positive breast cancer

Background: We have recently reported that acquired endocrine resistance (Endo-R) in multiple ER+ breast cancer (BC) Endo-R cell models is driven by high levels of FOXA1 (High-FOXA1), via gene amplification and/or overexpression (OE), leading to coordinated reprogramming of the FOXA1 genomic binding (cistrome) and transcriptome. Forced FOXA1 OE in parental (P) cells induced similar transcriptional reprogramming leading to Endo-R and metastasis. Recent clinical data showing enrichment of FOXA1 amplification in ER+ metastases further support the clinical importance of our findings. However, the molecular components and the mechanism of High-FOXA1-induced transcriptional reprogramming in Endo-R and metastasis are unknown.

Methods: High-FOXA1-containing MCF7 tamoxifen-resistant (TamR) and P/FOXA1-OE cells were used in this study. An integrative multi-OMICS approach was employed to analyze transcriptome (RNA-seq), FOXA1 cistrome, and histone H3K27 acetylation (ac) (ChIP-seq). Intersection of High-FOXA1-induced transcriptome and distinct FOXA1 cistrome-predicted genes defined a High-FOXA1 core gene signature (CGS). Gene Set Enrichment Analysis (GSEA) and Gene Ontology (GO) were used for functional annotation. Cell growth and migration/invasion were measured by a bright-field automated cell counter and Transwell insert system. Altered gene expression was measured by RT-qPCR. High-FOXA1 signaling inhibition included gene knockdown (siRNA) or pharmacologic blockade (the EPAS1 inhibitor PT2385). The predictive role of EPAS1 and the associated gene signature were analyzed using publicly available BC datasets.

Results: FOXA1 OE reprogrammed the FOXA1 cistrome in P cells to resemble that of the TamR cells. The FOXA1 cistrome was significantly correlated with the deposition of H3K27ac in TamR vs. P cells (P&lt;2.2e-16). Similarly, the differentially expressed genes in TamR vs. P cells were enriched for FOXA1 binding at enhancers demarcated by H3K27ac (P=8e-125). The FOXA1-CGS was linked to multiple metastasis-related GO terms including “hypoxia response”, enriched for the cancer secretome gene set (P=4.1e-16), and highly represented in the Endo-R transcriptome across our multiple cell models (MCF7, 600MPE, and CAMA1) (P&lt;0.01). Integrative analysis of H3K27ac-defined super-enhancers (SEs) and altered cistrome/transcriptome upon High-FOXA1 nominated EPAS1, a hypoxia-inducible transcription factor (TF), as a top candidate of SE-activated TFs amplifying High-FOXA1 signaling. EPAS1 blockade markedly repressed the secretome genes (e.g., IL8 and S100P) and cell migration and invasion in TamR cells. Primary ER+ tumors (TCGA) with high EPAS1 are enriched for a cancer secretome gene set (P=3e-4). High EPAS1 predicts poor distant metastasis-free survival in ER+ BC treated with endocrine therapy (P=.034).

Conclusions: High-FOXA1 induces transcriptional reprogramming by coordinating histone enhancer marks to activate EPAS1 via an SE mechanism, which in turn mediates transcriptional reprogramming, partly via inducing a pro-metastatic secretome, to promote Endo-R and metastasis. Targeting the High-FOXA1/EPAS1 axis to block transcriptional reprogramming may offer a new therapeutic strategy to prevent and treat Endo-R metastatic ER+ BC.

Citation Format: Fu X, Pereira R, De Angelis C, Veeraraghavan J, Shea MJ, Nanda S, Feng Q, Jeselsohn R, O'Malley BW, Brown M, Osborne CK, Schiff R. Hyperactive FOXA1 activates super-enhancer-engaged HIF2α/EPAS1 to promote endocrine-resistant metastatic ER-positive 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 P4-04-03.

Abstract P4-03-04: Targeting the mevalonate pathway in HER2-positive breast cancer to overcome resistance to anti-HER2 therapy

Background: Despite the advent of HER2-targeted therapies for HER2+ breast cancer (BC), including the monoclonal antibody trastuzumab (T) either alone or in combinations, resistance still poses a major clinical challenge. Using our broad panel of HER2+ cell lines made resistant (R) to T alone (TR), and to lapatinib plus T (LTR), we observed that in resistant models where HER2 remains inhibited, especially the LTR derivative, the mevalonate (MVA) pathway is activated and provides an alternative proliferative signal, including the activation of mTOR, to drive resistance. While these resistant cell models were hypersensitive to the widely-used cholesterol-lowering statins, the role of other MVA pathway inhibitors such as zoledronic acid (ZA), which is in clinical use to treat bone metastasis, in overcoming resistance to HER2-targeted therapy has not been explored. Based on recent reports and our preliminary data using reverse phase protein array (RPPA) analysis, the YAP/TAZ transcription factor (TF) emerged as a potential mediator of MVA pathway signaling to mTOR. Here, we investigated the therapeutic efficacy of additional MVA pathway inhibitors and the role of YAP/TAZ in mediating resistance to HER2-targeted therapy.

Methods: HER2+ SKBR3 and AU565 BC cells and their LTR derivatives were used. Changes in cell growth upon genetic and pharmacologic inhibition of the MVA pathway were quantified by methylene blue staining. Luciferase reporter assays and western blots (WB) measured changes in total and phosphorylated (S127 and S381/inactive) YAP protein levels to examine activity of the YAP/TAZ TF complex. To validate the function of YAP/TAZ in resistance, we performed YAP/TAZ knockdown (siRNA), overexpression of dominant-active YAP constructs (S381A, S381/127A), and qRT-PCR assessment of YAP/TAZ target gene expression.

Results: ZA, like simvastatin (Sim), selectively inhibited the growth of resistant cells in a dose-dependent manner. This inhibition was rescued by geranyl geranyl pyrophosphate (GGPP), a downstream metabolite, but not by MVA, an upstream metabolite, indicating the on-target effect of ZA. Further, ZA and Sim combination showed a synergistic growth-inhibitory effect in R but not in parental (P) cells. YAP/TAZ luciferase reporter assays and phosphorylated YAP and total TAZ levels by WB, confirmed the increased activity of YAP/TAZ in R models, which was selectively inhibited by Sim or ZA and was rescued by the corresponding downstream metabolites. YAP/TAZ knockdown selectively inhibited resistant cell growth and mTOR signaling in R vs. P cells, and dominant-active YAP/TAZ rescued the mTOR inhibition by Sim. YAP/TAZ inhibition by siRNA or by Sim significantly decreased the expression of YAP/TAZ target gene survivin in R vs. P cells, and the Sim inhibition was rescued by MVA.

Conclusions: The MVA pathway plays a critical role in mediating resistance to anti-HER2 therapy, which was overcome by Sim and ZA either alone or in combination. Given the synergistic effect of Sim and ZA, their combination may offer a therapeutic strategy to overcome HER2-targeted therapy resistance. Our results also reveal the role of YAP/TAZ in MVA pathway-mediated HER2-targeted therapy resistance, which could suggest new biomarkers and therapeutic targets.

Citation Format: Sethunath V, Hu H, De Angelis C, Veeraraghavan J, Qin L, Rimawi MF, Osborne KC, Schiff R. Targeting the mevalonate pathway in HER2-positive breast cancer to overcome resistance to anti-HER2 therapy [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 P4-03-04.

Abstract P4-03-05: AP-1 as a potential mediator of resistance to the cyclin-dependent kinase (CDK) 4/6-inhibitor palbociclib in ER-positive endocrine-resistant breast cancer

Background: The CDK4/6-inhibitor palbociclib (Palbo) in combination with endocrine therapy (ET) substantially improves progression-free survival compared to ET alone. However, almost all initial responders eventually develop resistance and relapse. Delineating the early adaptive signaling and the mechanisms underlying resistance to CDK4/6 inhibition is therefore crucial to identify new biomarkers and therapeutic targets to enhance the efficacy of Palbo and improve patient outcome.

Materials and Methods: MCF7 parental (P) cells and derivative lines made resistant (R) to tamoxifen (TamR), estrogen deprivation (EDR), or fulvestrant (FulR) were used. The MCF7P line and its endocrine-R (EndoR) derivatives were exposed to increasing concentrations of Palbo to generate acquired Palbo-R (PDR) models. The proteomic/signaling profiles of P and EndoR cells upon short-term Palbo treatment and as PDR develops were determined using reverse-phase protein arrays (RPPA). Transcriptional activity of the activator protein-1 (AP-1) transcription factor (TF) was measured by luciferase reporter assay. Global AP-1 blockade was achieved using a pINDUCER system to express doxycycline (Dox)-inducible dominant-negative (DN) c-Jun that lacks the transcriptional activation domain. Cell growth and colony formation were assessed using methylene blue staining and clonogenic assays, respectively. Levels of phosphorylated (p)-RB and CDK2 were assessed by Western Blot.

Results: In P and all EndoR cell models, Palbo inhibited cell growth and colony formation in a dose-dependent manner, though the inhibitory effect was greater in the EndoR cells compared to P cells [IC50 value of P cells &gt;3 times that of EndoR lines (p&lt;0.001); clonogenic % inhibition at 100nM = 54 in P and &gt;85 in EndoR lines (p&lt;0.001)]. Across the P and all EndoR models, short-term Palbo treatment resulted in increased levels of several membrane and intracellular signaling molecules, TFs, and enzymes. Among these, the AP-1 TF components c-Jun and p-c-Jun showed the highest increase across all models, with the utmost change observed in the TamR model (Fold-change = 4.4, 4.0 for total and p-c-Jun, respectively). Since we also observed that acquired resistance to Palbo in the TamR model was associated with higher AP-1 transcriptional activity and increased total and p-c-Fos levels, we assessed the efficacy of combining Palbo with AP-1 blockade in the TamR model. In two independent TamR clones ectopically expressing inducible DN-c-Jun, AP-1 blockade (+Dox) in combination with Palbo was highly effective in inhibiting cell growth and reducing p-RB and CDK2 levels compared to single agent treatments. In addition, in both the TamR/DN-c-Jun-expressing clones, the combination of Palbo, AP-1 blockade, and fulvestrant resulted in cell death and a significantly greater cell growth inhibition compared to any dual or mono treatments.

Conclusion: Our results suggest activation of AP-1 as a potential mechanism of resistance to Palbo in ER+ EndoR models. Transcriptomic profiling of the Palbo-sensitive and R cells, currently underway, will provide an in-depth understanding of the role of AP-1 as well as other key targets and associated molecular mechanisms in Palbo resistance.

Citation Format: De Angelis C, Nardone A, Cataldo ML, Veeraraghavan J, Fu X, Giuliano M, Malorni L, Jeselsohn R, Osborne KC, Schiff R. AP-1 as a potential mediator of resistance to the cyclin-dependent kinase (CDK) 4/6-inhibitor palbociclib in ER-positive endocrine-resistant 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 P4-03-05.

Abstract PD2-05: Evaluating the role of recurrent ESR1-CCDC170 in breast cancer endocrine resistance

Background

Recurrent gene fusions resulting from chromosome translocations are critical genetic aberrations causing cancer. In our previous study, we identified recurrent rearrangements between ESR1 and its neighbor, CCDC170, in 6-8% of luminal B tumors. Luminal B subtype is a more aggressive ER+ breast cancer, with a higher risk of early relapse after endocrine therapy. These rearrangements enable the expression of N-terminally truncated CCDC170 (ΔCCDC170) under ESR1 promoter. Consistent with the behavior of luminal B tumors, ectopic ΔCCDC170 expression in ER+ breast cancer cells, led to markedly increased cell motility, invasion, anchorage-independent growth, and reduced endocrine sensitivity in vitro, as well as enhanced xenograft growth in vivo. In the present study, we studied the role of ESR1-CCDC170 in breast cancer endocrine resistance in vivo and explored the potential mechanism.

Methods

To study endocrine resistance in vivo, we transplanted T47D cells stably overexpressing (OE) control (empty) construct or 2 ΔCCDC170 fusion variants (E2-E7 and E2-E10) bilaterally to 4-6 week old female athymic nude mice (supplemented with 17β-estradiol pellets). The tumor growth was monitored biweekly and tumor volume was measured by the formula 1/2(length × width2). When the tumors reach 150–200 mm3, mice were randomly allocated to vehicle or tamoxifen (tam) treatment groups. For ERE luciferase assay, cells were co-transfected with ERE luciferase reporter (ERE-TK-Luc) and pCMV β-galactosidase. The luciferase levels were measured and normalized to β-gal activity. For immunoblot analysis, T47D OE cells were estrogen-deprived, serum-starved, and treated with vehicle, estrogen (E2) or tam. Reverse Phase Protein Array (RPPA) analysis was performed using ∼200 validated antibodies against an array of key signaling molecules in cancer.

Results

Our in vivo endocrine sensitivity study showed that, while T47D vector control tumors mostly regressed after tam treatment, the regression of E2-E7 tumors was significantly slower. Moreover, E2-E10 tumors continued to grow despite tam treatment. These observations suggest that ΔCCDC170 may render the T47D xenografts less sensitive to tam in vivo. Kaplan–Meier analysis revealed a significantly worse progression-free survival (defined by tumor doubling time) for E2-E7 (p&lt;0.01) and E2-E10 (p&lt;0.001) tumors treated with tam compared to control tumors. ΔCCDC170 expression in T47D cells enhanced the ER transcriptional activity in the presence of E2 but not tam, suggesting that the fusion-mediated endocrine-sensitivity changes is unlikely due to restoration of classic ER activity. Immunoblot analysis of T47D OE cells revealed hyperactive growth factor signaling even after serum withdrawal, which was not significantly affected by tam treatment. Preliminary RPPA analysis revealed upregulation of key signaling molecules in T47D cells expressing ΔCCDC170, such as Her3, AMPK, Akt, Erk, c-Myc, and Src-3.

Conclusion

These data suggest a potential role of ESR1-CCDC170 in mediating breast cancer endocrine resistance, presumably due to hyperactive growth factor signaling endowed by this fusion. Further studies are required to elucidate the role of endogenous ESR1-CCDC170 in breast cancer endocrine resistance, and discover the precise engaged mechanisms.

Citation Format: Hu Y, Veeraraghavan J, Wang X, Tan Y, Kim J, Schiff R, Wang X-S. Evaluating the role of recurrent ESR1-CCDC170 in breast cancer endocrine resistance. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr PD2-05.

Abstract P2-07-02: Low-LET γ-Radiation Induced Protein S-Nitrosylation Regulates Tumor Invasion and Metastatic Transcriptional Response

Local-regional radiotherapy is one of the major therapeutic means in the management of breast cancer. However, besides the therapeutic effect, studies have shown that irradiation promotes malignant behavior of cancer cells both in vitro and in vivo by activating several tumor invasion and metastatic molecules. In this regard, ascertaining the molecular alterations contributing to this radiation-induced response is imperative. Accordingly, we investigated the role of radiation-induced NO-dependent nitrosylation in the transcription of invasion and metastatic genes in human breast adenocarcinoma cells. Human MCF-7 cells either mock irradiated, exposed to 2Gy (IR), treated with L-NAME (NOS inhibition) or BAY-11-7082 (phosphorylation inhibition) and then exposed to 2Gy, were examined for modulations in the transcriptional response of 93 tumor invasion and metastasis signaling genes. Cells treated with β-estradiol and mock-irradiated MDA-MB-231 cells were used as positive controls. Compared to mock irradiated cells, real time QPCR profiling revealed that 20 of 29 IR-induced genes including Birc3, Casp8, Ctgf, Ctsk, Htatip2, Kras, Map2k7, Mgat5, Mta2, Nme1, Nme2, Nme4, Pax5, Pten, Runx1, Serpinb5, Syk, Timp1, Timp2 and Timp4 were completely suppressed with NOS inhibition. Conversely, as opposed to NOS inhibition, IR-induced phosphorylation inhibition either failed to suppress or further induced the expression of these IR-induced genes. Furthermore, β-estradiol treatment revealed upregulation of 16 of these 20 IR-induced nitrosylation-dependent molecules and serves as a positive control for the study. More importantly, the highly metastatic, MDA-MB-231 cell line showed a robust induction in the expression of 15 of these 20 IR-induced nitrosylation-dependent genes. Taken together, these data imply that IR induces the expression of tumor invasion and metastatic genes and more importantly, may regulate the radiation-activated invasion and metastatic phenotype in breast adenocarcinoma cells.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P2-07-02.

Abstract P6-14-14: Concerted Anti-Tumor/Radiosentizing Effect of Epigallocatechin Gallate, Resveratrol and Genistein by Targeting Tumor Invasion and Metastasis Molecules in Human Breast Cancer Cells

Accomplishing the desired anti-tumor efficacy with individual dietary phytochemicals is clinically unachievable. This is due to the existence of converging and diverging pathways spanning the complex metabolic networks in cancer cells. This complexity demands the development of a multi-component approach with physiological doses of phytochemicals that could be used as “deliverable” anti-cancer agent. To address this concern, we investigated the synergistic efficacy of Genistein (GEN), Epigallocatechin gallate (EGCG) and Resveratrol (RES) in mitigating cancer progression. Human breast adenocarcinoma cells (MCF-7 and MDA-MB-231) were treated with physiological concentration of GEN, EGCG, RES, individually or all three together (GER). In parallel cultures cells were treated with GER and either exposed to radiation (2Gy;IR) or treated with β-estradiol (≥2E, positive control). The trated cells were examined after 24h. In MCF-7 cells, QPCR profiling of 93 tumor invasion and metastasis molecules revealed that EGCG, RES and GEN significantly (≥2 fold) induced 23, 36, 22 genes and completely suppressed 61, 40 and 64 genes respectively as stand-alone compounds. Conversely, GER completely knocked down the transcription of 82 genes, while another 9 genes were maintained at baseline level. More importantly, GER significantly inhibited 75 and 63 genes in ≥2E and IR exposed MCF-7 cells. Interestingly, in highly metastatic MDA-MB-231 cells, EGCG, RES, GEN significantly induced 17, 19, 2 genes and completely suppressed 41, 26 and 57 genes respectively as stand-alone compounds. Conversely, GER completely suppressed 67 genes while another 17 genes were maintained at baseline level. To that end, GER significantly inhibited 57 and 59 genes and maintained 16 genes at basal level in ≥2E and IR exposed MCF-7 cells. Taken together, these data evidently exhibit the potential synergestic effect of EGCG, GEN and RES in mitigating breast cancer progression as opposed to their stand alone effect. More importantly, these data strongly suggests that GER potentiates synergistic radiosensitization in these cells and this GER influenced radiosensitization may involve selective targeting of tumor invasion and metastatic transcription.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P6-14-14.

Curcumin-altered p53-response genes regulate radiosensitivity in p53-mutant Ewing's sarcoma cells

AIM

Curcumin has been demonstrated to have antitumor effects including radiosensitization by modulating many molecular targets including p53. Herein, we investigated the radiosensitizing effect of curcumin in p53 mutant Ewing's sarcoma (ES) cells.

MATERIALS AND METHODS

Cells exposed to radiation with or without curcumin were examined for transcriptional and translational levels of p53 downstream targets and its influence in regulated apoptosis, DNA fragmentation, cell survival and clonal expansion.

RESULTS

Curcumin significantly caused radiation induced expression of p21 and Bax, and reduced BclXl, Mcl1 with only marginal Bcl2 modulation. As a positive control to the study, both transcriptional and translational levels of p53 remained unchanged after radiation with/without curcumin. Conversely, curcumin caused radiation-induced apoptosis and DNA fragmentation. Consistently, curcumin enhanced radiation-induced cytotoxicity and clonal expansion.

CONCLUSION

These results suggest that curcumin potentially radiosensitizes p53-mutant ES cells by regulating IR-modulated p53-response genes. However, the curcumin-associated p53-independent regulation of downstream targets remains to be explored.