Abstract 2360: Targeting of microRNA let-7b-5p-mediated aberrant AR signaling inhibits the growth and proliferation of preneoplastic and preinvasive stages of triple-negative breast cancer
Authors: Leslie Faye T. Cando, Zhenlin Ju, Leslie Michelle M. Dalmacio, Preethi H. Gunaratne, Jing Wang, Anjana Bhardwaj, Isabelle Bedrosian
Journal: Cancer Research (2025)

Abstract Background: In search for targets for triple-negative breast cancer (TNBC) prevention, we analyzed molecular changes that occur early in the tumorigenic process. We hypothesize that the early loss of microRNA let-7b-5p, and subsequent upregulation of its target gene androgen receptor (AR), promotes the growth and proliferation of preneoplastic and preinvasive lesions. And while targeting AR has been studied in the therapeutic setting for breast cancer, it may also have potential use in preventing disease progression. Methods: TNBC patient samples included tumors and histologically normal tissue adjacent (&amp;lt;2 cm) and distant (&amp;gt;2 cm) from tumor. Sublines of MCF10A TNBC progression model corresponding to preneoplastic lesions MCF10.NeoT (hyperplasia) and MCF10.AT1 (atypical hyperplasia), and preinvasive tumor MCF10.DCIS (ductal carcinoma in situ) were used to study the effect of let-7b rescue and AR inhibition on proliferation, survival, or migration as measured by MTT, colony formation, and scratch assays. Let-7b gene targets were identified by cross-referencing the RNA sequencing data of MCF10A panel for upregulated genes that are predicted targets of let-7b. QPCR and RNA sequencing were used to measure AR and let-7b expression. Results: In TNBC patients, let-7b expression is reduced by 68-74% in tumors compared to adjacent (p=0.015) and distant normal tissues (p=0.048)—confirming previous results in the MCF10A model, where let-7b expression is reduced from normal-like to AT1 by 35% and to DCIS by 65% (p&amp;lt;0.05). Let-7b rescue results in 15-32% lower proliferation (p&amp;lt;0.0001), 6-9% reduction in migration (p&amp;lt;0.003), and a 25% (p=0.076), 66% (p&amp;lt;0.0001), and 55% (p=0.030) decrease in colony formation compared to scramble control in NeoT, AT1, and DCIS cells, respectively. After screening potential let-7b targets, we selected AR for validation. As expected of the inverse regulation by let-7b, AR increases in the MCF10A model, with a notable 23-fold increase in DCIS as compared to normal-like (p&amp;lt;0.0001), and similarly in TNBC patient tumors compared to normal tissue controls (p=0.018). Furthermore, we validated AR as a direct target with let-7b overexpression causing AR downregulation by 67% in NeoT (p=0.001), 86% in AT1 (p&amp;lt;0.0001), and 15% in DCIS (p=0.011). Finally, treatment with AR inhibitor enzalutamide reduced DHT-dependent AR mediated proliferation by 29-41% (p&amp;lt;0.0001) and colony formation by 82-95% (p&amp;lt;0.0001) as compared to DHT only control at a minimal concentration of 25µM in AT1 and DCIS. Conclusions: Let-7b-5p, which acts as a tumor suppressor microRNA, is lost early in tumorigenesis of TNBC, with resulting upregulation of AR. Inhibiting the AR signaling pathway impacts cellular growth and proliferation of preneoplastic and preinvasive cancer cells, suggesting a potential opportunity for TNBC prevention. Citation Format: Leslie Faye T. Cando, Zhenlin Ju, Leslie Michelle M. Dalmacio, Preethi H. Gunaratne, Jing Wang, Anjana Bhardwaj, Isabelle Bedrosian. Targeting of microRNA let-7b-5p-mediated aberrant AR signaling inhibits the growth and proliferation of preneoplastic and preinvasive stages of triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2360.