Abstract B61: c-Myc is regulated and therapeutically targetable via the miR-1207-3p/FNDC1/FN1/AR pathway in aggressive prostate cancer in men of African ancestry

Abstract

Abstract Prostate cancer is the 2nd most common cancer in the world for men. For reasons still unclear, aggressive PCa disproportionately affects males of African ancestry (MoAA). Incidence and mortality rates are highest in MoAA as they have consistently shown a 2.3-3.0-fold higher risk of mortality compared to Caucasian men (CM). This aggressiveness of PCa may be due to specific biologic factors. Located downstream of c-Myc at chromosome 8q24 is PVT1, which encodes miR-1207-3p. Studies have shown that PVT1/MYC cooperation is a fundamental feature in all cancers with 8q24 amplification, and 98% of the 8q24 amplicons contained concurrent amplification of the MYC and PVT1 loci. Moreover, MYC has been linked to PCa aggressiveness and has been reported to be downstream of AR in some PCa. However, the mechanisms regulating c-MYC have never been studied in MoAA. We recently demonstrated that miR-1207-3p directly binds to FNDC1 to regulate a novel FNDC1/FN1/AR pathway upregulated in metastatic prostate cancer (PCa). However, the mechanisms regulating c-Myc in PCa remain unclear, and the relevance of our novel and clinically significant miR-1207-3p molecular pathway in PCa in MoAA is unknown. The aim of this study was to determine if c-Myc is regulated and therapeutically targetable via the miR-1207-3p/FNDC1/FN1/AR pathway in aggressive PCa in MoAA. We used qPCR, immunoblotting, RNA pulldown, proliferation, migration, and apoptosis assays to evaluate miR-1207-3p regulation of c-Myc in aggressive PCa in MoAA. Also, miR-1207-3p, FNDC1, FN1, AR, and c-Myc expression was analyzed in prostate tissues (normal = 21; benign = 41; tumor = 26) of patients who received prostatectomy or transrectal ultrasound-guided biopsies at the University College Hospital, Ibadan, Nigeria, a sub-Saharan Black African population. Seventeen patients had tumor tissues with Gleason score ≥ 8. Tissues were collected in compliance with Institutional Review Board-approved protocols. ANOVA, student's t-test, and Tukey post-hoc tests were used for statistical analysis. Prostate tissue analysis revealed that underexpression of miR-1207-3p and the overexpression of FNDC1, FN1, AR, and c-Myc is significantly associated with aggressive PCa in MoAA. Also, miR-1207-3p was underexpressed while FNDC1 and c-MYC were overexpressed in tumors with Gleason score ≥8 in comparison to those with Gleason score <8. Thus, miR-1207-3p and FNDC1 may be useful for risk stratification in PCa in MoAA. Next, we observed that our novel synthetic biotinylated miR-1207-3p duplex (NB1207, patent pending) significantly inhibited c-Myc protein expression in 7 PCa cell lines when compared with a biotinylated scramble duplex (NB-1, patent pending). RNA pulldown assay determined that c-Myc is not a direct molecular target of miR-1207-3p. However, siRNAs against FNDC1, FN1, and AR revealed significant suppression of c-Myc expression by >75% in the MoAA-derived indolent E006AA PCa cell line and the MoAA-derived aggressive/castration-resistant E006AA-hT PCa cell line, indicating that c-Myc is downstream of AR. c-Myc expression is higher in the E006AA-hT PCa cell line when compared to the E006AA PCa cell line, suggesting that c-Myc is associated with aggressive PCa. Moreover, NB1207 significantly inhibited migration and induced apoptosis in E006AA and E006AA-hT PCa cell lines. Next, we compared the efficacy of NB1207 in inhibiting proliferation to the commercially available drugs for treatment of CPRC (enzalutamide and abiraterone). NB1207 inhibited proliferation in the CRPC cell line E006AA-hT by nearly 50% while enzalutamide and abiraterone had no effect. In conclusion, miR-1207-3p regulates c-Myc expression via the miR-1207-3p/FNDC1/FN1/AR pathway in aggressive PCa in MoAA. miR-1207-3p may be a biomarker for risk stratification in PCa in MoAA. NB1207 has potential for therapeutic targeting of c-Myc for treatment of aggressive PCa in MoAA. Citation Format: Dibash K. Das, Akintunde T. Orunmuyi, Gabriel Olabiyi Ogun, S. Adekola Adebayo, A. Ayo Salako, Adeodat Ilboudo, Cuong Bach, E. O. Olapade-Olaopa, Olorunseun O. Ogunwobi. c-Myc is regulated and therapeutically targetable via the miR-1207-3p/FNDC1/FN1/AR pathway in aggressive prostate cancer in men of African ancestry [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr B61.