Abstract 1232: Development of novel therapeutic splice-switching oligonucleotides targeting oncogenic RNA isoforms driving race-related aggressive prostate cancer

Abstract Background: Age-adjusted incidence and mortality rates for prostate cancer (PCa) among African American (AA) men are 1.6- and 2.4-fold greater, respectively, than among white men. More aggressive characteristics of AA PCa account for a significant component of the PCa disparity, in addition to social determinants of health. Previous work from our laboratory and others have identified deregulation of the androgen receptor (AR) and epidermal growth factor receptor (EGFR) pathways in AA versus white PCa. Thus, there is an urgent need to develop a novel therapeutic strategy capable of inhibiting oncogenic AR and EGFR RNA isoforms enriched for in AA PCa. Methods: We have designed and synthesized novel chemically modified splice switching oligonucleotides (SSOs) to: 1) correct aberrant splicing leading to production of AR-V7 (AR-V7 SSO), an AR variant that lacks the ligand binding domain, is constitutively active and associates with castration-resistant PCa, poorer clinical outcomes and resistance to androgen ablation/AR inhibition therapies, 2) drive production of AR45 (AR45 SSO), an AR variant that has a unique, non-functional transactivation domain and acts in a dominant-negative manner and 3) drive production of inhibitory or dominant-negative EGFR isoforms (EGFR-TM or EGFR-TK SSOs), lacking the transmembrane or tyrosine kinase domain, respectively. Results: Transfection of a panel of PCa cell lines derived from AA and white patients with AR-V7 SSO decreases AR-V7 RNA and protein in a dose-dependent manner. Preliminary data suggests this biochemical response correlates with a biologically significant phenotype, as AR-V7 SSO also decreases proliferation, proliferation in the presence of enzalutamide and colony forming ability of PCa cells. Following transfection of PCa cell lines with AR45 SSO, an increase in AR45 RNA is seen and simultaneous decreases in wild type AR RNA and AR-V7 RNA are seen. In addition, modulation of AR signaling is detected, with decreases in RNAs corresponding to AR-induced target genes and increases in RNAs corresponding to AR-repressed target genes. Transfection of PCa cell lines with EGFR-TM or EGFR-TK SSOs increase RNA corresponding to these isoforms in a dose-dependent manner. Furthermore, a decrease in phosphorylated EGFR protein is detected. Further studies to examine the effects of these SSOs on transactivation activity, signaling and PCa cell biology and the therapeutic efficacy of these SSOs in AA and white PCa patient-derived explants are underway. Conclusions: These studies suggest that SSOs can be developed to modulate AR and EGFR signaling. Such SSOs could represent a novel therapeutic strategy with the potential to reduce PCa disparities for AA men and improve outcomes for men of all races with aggressive disease driven by these mechanisms. Citation Format: Jennifer A. Freedman, Timothy Robinson, Bonnie LaCroix, Brendon Patierno, Daniel George, Bruce Sullenger, Steven Patierno. Development of novel therapeutic splice-switching oligonucleotides targeting oncogenic RNA isoforms driving race-related aggressive prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1232. doi:10.1158/1538-7445.AM2017-1232