Abstract 1625: c-Myc inhibition in prostate cancer cell lines

Abstract

Abstract The proto-oncogene c-Myc is a transcription factor that is upregulated in several human cancers. Despite its key role, therapeutic targeting of c-Myc remains a challenge because of a disordered protein tertiary structure. The basic helical structure and zipper protein of c-Myc forms an obligate heterodimer with its partner MAX to function as a transcription factor. An attractive strategy is to inhibit MYC/MAX dimerization to decrease c-Myc transcriptional function. Several methods have been described to inhibit MYC/MAX dimerization including small molecular inhibitors and proteomimetics. We used NOD SCID gamma mice (NGS mice) that are immunodeficient, non-obese diabetic laboratory mice (Jackson Laboratories, Cat Number J000077451) carrying patient-derived xenograft (PDX) following implantation of grade IV adenocarcinoma of the prostate from a patient into the flanks of each mouse. For maximum tolerable dose studies, we used C57BL/6 wild type mice (Jackson Laboratories, Cat Number J000664). We performed a maximum dose tolerability study with the drug 3JC48-3 up to 100 mg/kg to determine limiting toxicity. We monitored the rate of growth for 2 weeks and measured the final volume of the tumors. Immunoprecipitation studies were performed using the prostate cancer cell line, PC-3, that were treated with the drug 3JC48-3 at different doses (0, 5, 10, and 20uM) for 24 hours and subsequently lysed. We found 3JC48-3 decreases prostate cancer growth and viability in a dose-dependent fashion in vitro. We confirmed the inhibition of MYC/MAX dimerization by 3JC48-3 using immunoprecipitation experiments. Normal mice and mice with patient-derived prostate cancer xenografts (PDX) tolerated intraperitoneal injections of 3JC48-3 up to 100 mg/kg body weight without dose-limiting toxicity. Preliminary results in these PDX mouse models suggest that 3JC48-3 may be effective in decreasing the rate of tumor growth. Our study demonstrates that 3JC48-3 is a potent MYC/MAX heterodimerization inhibitor that decreases prostate cancer growth and viability in association with upregulation of both PrKD1 expression and kinase activity. In addition, 3JC48-3 is well tolerated in prostate cancer PDX mice models and may be a candidate drug for further preclinical development. Citation Format: Carlos Riveros, Victor Chalfant, Sanjeev Shukla, Teruko Osumi, KC Balaji. c-Myc inhibition in prostate cancer cell lines [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 1625.