Abstract A121: Targeting <i>TMPRSS2-ERG</i> Fusion-Driven Prostate Cancer using Novel HBS-α-Helicomimics

Abstract Prostate cancer (PCa), a leading malignancy among men, is characterized by the frequent occurrence of TMPRSS2-ERG gene fusion, found in over 50% of Indian and Caucasian patients. This fusion juxtaposes the 5′ untranslated region of the androgen receptor (AR)-responsive TMPRSS2 gene with the coding region of ERG, resulting in androgen-driven upregulation of the ERG transcription factor. Moreover, patients harboring TMPRSS2-ERG fusion show association with advanced tumor stage, higher Gleason scores, and metastasis, suggesting its role in cancer progression. Despite its prevalence, pharmacological targeting of ERG remains a daunting task as majority of the treatment strategies are focused on disrupting ERG’s interaction with its cofactors and/or transcriptional regulators. To address these caveats, we developed HBS-α-helicomimic, a novel class of chemically engineered, α-helix mimicking polypeptide designed to specifically bind to the ETS consensus DNA motif, thereby blocking ERG-DNA interaction. The non-biodegradable N-terminal HBS-turns and thermally stable helical backbone of these helicomimics were rationally designed for enhanced in vivo stability, bioavailability, and DNA affinity. Through lead optimization, two helicomimics with the highest DNA sequence selectivity and binding affinity were identified for functional validation. Mechanistic studies, including co-immunoprecipitation (Co-IP), confirmed that these helicomimics disrupt ERG binding and its interactions with key partners such as AR in ERG-positive PCa cell lines. Additionally, luciferase-based promoter-reporter assay demonstrated a marked reduction in ERG transcriptional activity upon helicomimics treatment. Given the overlapping cistrome of ERG and AR, we performed chromatin immunoprecipitation-PCR (ChIP-PCR) and found that the helicomimics disrupts ERG occupancy at its target gene, leading to decrease in its oncogenic potential. Finally, cell-based functional assays showed marked reduction in cell proliferative, migratory, and invasive potential of ERG-expressing PCa cells. Collectively, our findings establish HBS-α-helicomimics as a transformative therapeutic strategy that directly impedes oncogenic function of ERG, offering a novel and promising therapeutic avenue for the treatment of TMPRSS2-ERG driven prostate cancer. Citation Format: Sushmita Kundu, Lalnunfela Varte, Shifali Mahajan, Erode N Prabhakaran, Bushra Ateeq. Targeting TMPRSS2-ERG Fusion-Driven Prostate Cancer using Novel HBS-α-Helicomimics [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2025 Oct 22-26; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2025;24(10 Suppl):Abstract nr A121.