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A Positive Feedback Loop Between TGFβ and Androgen Receptor Supports Triple-negative Breast Cancer Anoikis Resistance.

ABSTRACT: Triple-negative breast cancer (TNBC) is an aggressive subtype with peak recurrence as metastatic disease within the first few years of diagnosis. Androgen receptor (AR) expression is increased in anchorage-independent cells in TNBC preclinical models. Both AR knockdown and inhibition lead to reduced TNBC invasion in vitro, reduced tumorigenicity, and less recurrence in vivo in preclinical models. Transforming growth factor β (TGFβ) pathway gene signatures also increased during anchorage-independent survival both in vitro and in vivo in preclinical models and in circulating tumor cells (CTCs) from patients during emergence of chemo resistant disease. We hypothesized that a positive loop between AR and TGFβ signaling facilitates TNBC anchorage-independent survival. We find that multiple components of the TGFβ pathway, including TGFβ1 and 3, as well as pathway activity measured by nuclear localization and transcriptional activity of phosphorylated Smad3, are enhanced in anchorage-independent conditions. Further, exogenous TGFβ increased AR protein while TGFβ inhibition decreased AR and TNBC viability, particularly under anchorage-independent culture conditions. ChIP-seq experiments revealed AR binding to TGFB1 and SMAD3 regulatory regions in MDA-MB-453 cells. In clinical datasets, TGFB3 and AR positively correlate and high expression of both genes together corresponded to significantly worse recurrence-free and overall survival in both ER-negative and basal-like breast cancer. Finally, inhibiting both AR and TGFβ decreased cell survival, particularly under anchorage-independent conditions. These findings warrant further investigations into whether combined inhibition of AR and TGFβ pathways might decrease metastatic recurrence rates and mortality from TNBC.

SUBMITTER: Rosas E

PROVIDER: S-EPMC7806239 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Triple-negative breast cancer (TNBC) is an aggressive subtype with few treatment options for chemo-resistant disease. In both preclinical models and patient circulating tumor cells, androgen receptor (AR) expression is increased in anchorage independent TNBC. The AR inhibitor enzalutamide (Enza) leads to reduced TNBC growth in soft agar, invasion, mammosphere formation in vitro, and reduced tumorigenicity and recurrence when combined with chemotherapy in vivo pre-clinical models. Transforming growth factor β (TGFβ) pathway gene signatures are also increased during TNBC anchorage independent survival both in vitro and in vivo in pre-clinical models and CTC from patients during relapse while on chemotherapy. We hypothesized that a positive loop between AR and TGFβ signaling facilitates TNBC anchorage independent survival (anoikis resistance). We previously published that AR protein levels and transcriptional activity increased during anchorage independent conditions and we now find that that multiple components of the TGFβ pathway, including TGFβ1 and 3, as well as pathway activity, as measured by nuclear localization and transcriptional activity of pSmad3, are enhanced in anchorage independent conditions. Indeed, exogenous TGFβ increased AR protein and TGFβ inhibition decreased AR and TNBC viability, particularly under anchorage independent culture conditions. ChIP-Seq experiments revealed AR binding to genomic regions near the TGFB1 and SMAD3. TGFB3 and AR expression were positively correlated in clinical datasets and high levels of co-expression correspond to significantly worse recurrence-free and overall survival in both ER- and basal-like breast cancer. Finally, combining Enza with a TGFβ inhibitor decreased cell survival more than either drug alone, particularly under anchorage independent conditions, where the effect was more than additive. These findings warrant further investigations into whether combined inhibition of AR and TGFβ pathways might decrease metastatic recurrence rates and mortality from TNBC.

Project description:IntroductionOverexpression of the androgen receptor (AR) characterizes a distinct molecular subset of triple negative breast carcinomas (TNBC). The role of AR as a prognostic/predictive biomarker in TNBC is controversial, but increasing evidence suggests that this subset may respond to therapeutic agents targeting AR. Evaluation of AR has not been standardized, and criteria for selection of patients for antiandrogen therapy remain controversial. In this study we determine the appropriate threshold of AR immunoreactivity to define AR positive (AR+) TNBC, describe the clinicopathologic features of AR+ TNBC, and discuss the utility of AR positivity as a prognostic and predictive marker in TNBC.Materials and methods135 invasive TNBC processed in accordance with ASCO/CAP guidelines, were immunostained for AR. Clinicopathologic features of AR+ TNBC were analyzed and compared to AR negative (AR-) TNBC. Patients' age, tumor size, tumor grade, lymph node status, proliferation rate, immunopositivity for EGFR, CK5/6, Ki-67, and disease free survival (DFS) were evaluated statistically.ResultsA 1% cutpoint was confirmed as the appropriate threshold for AR positivity. Using this cutpoint 41% of 135 TNBC were AR+. AR+ TNBC occurred in older women, were larger, had lower mean proliferation rate and increased incidence of axillary metastasis than AR- TNBC. 76% of TNBC with apocrine morphology were AR+. A subset of AR+TNBC expressed basal markers (EGFR and CK5/6). A prognostic model was created.SummaryAR identifies a heterogeneous group of TNBC. Additional evaluation of EGFR expression allowed us to stratify TNBCs into 3 risk groups with significant differences in DFS and therapeutic implications: low-risk (AR+ EGFR-) which represents the LAR molecular subtype with the best prognosis and may benefit the most from anti-androgen therapies; high-risk (AR- EGFR+) which represents the basal molecular subtype with the worst prognosis and may benefit the most from chemotherapy regimens; intermediate-risk (AR+EGFR+ and AR-EGFR-) TNBC with an intermediate prognosis. Prospective trials are required to further validate this prognostic and predictive grouping.

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A Positive Feedback Loop Between TGFβ and Androgen Receptor Supports Triple-negative Breast Cancer Anoikis Resistance.

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