Abstract 6398: Functional characterization of Androgen Receptor splice variants in breast cancer invasion and metastasis
Authors: Srivastava Tryambak Pratap , Dhar Ruby , Srivastava Anurag , Deo SVS , Parshad Rajinder , Karmakar Subhradip 
Published: June 2022

Introduction: A growing body of evidence suggests the prognostic and therapeutic value of Androgen Receptors (AR) in Breast Cancer (BrCa), particularly Triple Negative BrCa (TNBC). The splice variants of AR (ARVs); notably full-length AR (AR-fl) of ~110 kDa and a C-terminally Ligand Binding Domain (LBD) truncated AR isoform (AR-V7) of ~67 kDa are present in a variety of tissues. The ligand-independent AR-V7 is constitutively expressed and confers castration resistance in prostate cancer. With the irrefutable role of ARVs in BrCa, we evaluated their expression profile in cell lines with their prevalence and clinicopathological correlation in BrCa patients from India.

Methods: Breast Cancer cell lines MDA-MB-231, MCF7, and MDA-MB-453 were procured from American Type Culture Collection. Thirty-eight de novo cases of Breast Cancer undergoing surgical intervention at a tertiary healthcare center in India were recruited. Tumor and adjacent benign tissue were collected after informed consent. The ARVs expression at transcriptomic and proteomic levels was evaluated by qRT-PCR and western blotting & Immunohistochemistry (IHC) respectively. For functional annotation, ARVs were knocked down in vitro using differently targeting siRNAs facilitated by Lipofectamine 3000 based transfection. There was a strong complementarity observed in western blotting and IHC.

Results: All the ARVs were significantly higher in MDA-MB-453 followed by MCF7 and MDA-MB-231 cells. The expression ratio of AR-V7 versus AR-fl is, however, elevated in highly aggressive TNBC cell line MDA-MB-231.

67% of patients recruited were immunostained positive for AR (n=38). A majority of patients were of Luminal phenotype (37%) expressing both the prominent ARVs. One-third of the TNBC fraction were AR positive. Following the TNBC cell line, a subset of patients' samples also exhibited a substantial upregulation of AR-V7 compared to AR-fl. These patients had poor prognoses and aggressive features. The siRNA knockdown of all the ARVs resulted in decreased invasion and Epithelial-mesenchymal transition (EMT). Interestingly knocking down of ARVs barring AR-V7, restored invasiveness suggesting the compensatory behavior of AR-V7.

Conclusion: Our work demonstrates the presence of ARVs in BrCa with a particular focus on the AR-V7. The LBD truncated AR-V7 potentiates the growth in BrCa cell lines and patients. This study further encourages the ARVs expression screening with AR positive BrCa for a prognostic biomarker of aggressive phenotype and therapeutic resistance.

Citation Format: Tryambak Pratap Srivastava, Ruby Dhar, Anurag Srivastava, SVS Deo, Rajinder Parshad, Subhradip Karmakar. Functional characterization of Androgen Receptor splice variants in breast cancer invasion and metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6398.