Development of BLX-3030, a potent and selective inhibitor of CDK9 for the treatment of NMYC-driven NEPCS.

Abstract

e17067 Background: Cell lineage reprogramming in cancer cells is a major mechanism for cancers to develop drug resistance and escape targeted therapy. The use of new potent targeted therapies in prostate cancers has led to the development of highly aggressive cancers, including neuroendocrine prostate cancer (NEPC).Gene amplification of N-MYC and C-MYC oncogenes leads to its overexpression in NEPC and mCRPC patients. This overexpression is highly prevalent in these lethal subtypes of cancers, detected in 2% of all Prostate Cancers (PCa) and over 10-17% of mCRPC patients. N-MYC is a transcriptional target of CDK9, which acts as an oncogenic driver, sufficient to transform human-derived prostate cancer cells to take on NEPC phenotypic changes. This results in a more aggressive disease identified in late-stage human PCa patients. Additionally, N-MYC and C-MYC are required for tumor drug resistance and its downregulation, through CDK9 inhibition, lowers tumor growth. Our efforts have demonstrated that targeting both N-MYC and C-MYC as a driver of NEPC and mCRPC with a highly selective CDK9 inhibitor (BLX-3030) is a viable approach for therapeutic intervention of mCRPC and NEPC. Methods: We employed our AI/ML driven FIELDS fragment-based design strategies, in vitro including FACS/apoptosis, cell migration, live cell imaging, immunofluorescent and in vivo tumor models, 7-day tox, PK, selectivity, and ADME-Tox and in vitro safety and secondary pharmacological assays. Results: We discovered and synthesized a series of novel small molecule CDK9 agents that reversibly bind to CDK9, competitively block the ATP site with an IC50 of < 5 nM, and elicit pharmacological responses in N-MYC, C-MYC, and other prostate cancer cells in vitro and in vivo. We detected the expression of CDK9 and N-MYC in PC-3, DU-145, LNCaP, LASCPC-01, NCI-H660, and 22RV1 cell lines. BLX-3030 exhibited potent cellular efficacy in PC cells (IC50 of 22 to 590 nM) and in N-MYC expressed cells (IC50 of 76, 470, and 132 nM), respectively. BLX-3030 reduced pCDK9, C-MYC, Mcl-1, N-MYC and its downstream RNA Pol II (Ser-2) and pAR (Ser-81) in a dose dependent manner. Additionally, we performed FACS/apoptosis, cell migration, and live cell imaging, including immunofluorescence. We also conducted three separate in vivo efficacy mouse models (LASCPC-01, 22RV1, and C4-2) which demonstrated > 70% TGI. Several in vitro ADME-Tox, hERG, P450, safety panel screen, in vivo MTD and dose range finding experiments in SD rats and beagle dogs will also be presented. Conclusions: In summary, a series of BLX-3030 and its analogs display a potency in MYC-driven PCa, with ideal PK properties in rodent, canine species ranging 28-82 % F, with low clearance, and > 3.0 hr half-life. Within this profile, BLX-3030 was selected as a candidate that had the appropriate developable properties. Our plans for IND enabling studies and future clinical trials will also be discussed.