Abstract P2-06-04: Enhancing abiraterone acetate efficacy in androgen receptor-positive triple negative breast cancer: Chk1 as a potential target

Purpose: Our aim was to identify predictive factors of abiraterone acetate (AA) efficacy and putative new druggable targets in androgen receptor (AR)-positive triple-negative breast cancer (TNBC) treated in the UCBG 2012-1 trial. Material and methods: We defined AA response as either complete or partial response, or stable disease at 6 months. Using Ampliseq, we sequenced 91 general and breast cancerassociated genes from the tumor DNA samples. We analyzed transcriptomes from the extracted RNA samples on a Nanostring platform and performed immunohistochemistry (IHC) on tumor samples using tissue microarrays. We assessed AA and CHK1 inhibitors (GDC-0575 and AZD7762) efficacies, either alone or in combination, on cell lines grown in vitro and in vivo. Results: Classical IHC apocrine markers, including AR, FOXA1, GGT1 and GCDFP15, allowed identifying AA responders and non-responders. All responders have clear apocrine features. Transcriptome analysis revealed that 31 genes were differentially expressed in the two subgroups, 9 of them being linked to proliferation and DNA damage repair. One of the most significant differences was the overexpression in non-responders of CHEK1, a gene encoding Chk1, a protein kinase that can be blocked by specific inhibitors. In vitro, AA and Chk1 inhibitor combination showed additive or slightly synergistic effect on cell viability, cell cycle, apoptosis and accumulation of DNA damages. In vivo, orthotopic xenograft experiments confirmed the efficacy of this combination therapy. Conclusions: This study suggests that apocrine features can be helpful in the identification of AA-responders. We identified Chk1 as a putative drug target in AR-positive TNBCs. Citation Format: Grellety T, Callens C, Richard E, Pulido M, Goncalves A, Gestraud P, MacGrogan G, Bonnefoi H, Cardinaud B. Enhancing abiraterone acetate efficacy in androgen receptor-positive triple negative breast cancer: Chk1 as a potential target [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 P2-06-04.