Clofazimine treatment modulates key non-coding RNAs associated with tumor progression and drug resistance in lethal Prostate Cancer

Prostate cancer (PCa) is the most commonly diagnosed cancer and the second-leading cause of cancer death among men in the United States, representing 24.3% of all new cancer cases in the US Metastatic castration-resistant prostate cancer (mCRPC) is a lethal variant of prostate cancer that is associated with increased aggressiveness, cancer stemness, morbidity, and the risk of developing into taxane drug-resistant PCa. As taxanes are currently the first-line chemotherapeutic agents for mCRPC, there is a critical need to develop novel agents for the treatment of mCRPC. Clofazimine (CLF) is a potential immunomodulator drug that is FDA-approved for the treatment of leprosy.

Recently, using a phenotype-based high-throughput drug screening, we demonstrated the in vitro (cell lines), in vivo (mouse xenograft models), and ex vivo (patient-derived primary tumor cells) efficacy of CLF in drug-resistant forms of chronic myeloid leukemia and multiple myeloma.

In this study, we demonstrate that CLF is effective as a single agent and in combination with docetaxel (DTX) in a panel of PCa cell lines representing the diversity of CRPC patients. The response to CLF in the PCa cell lines was quantified using in vitro cytotoxicity assays, caspase 3/7 activity assay for apoptosis, cell cycle analysis, and aldehyde dehydrogenase activity assay for cancer stemness. We show that following CLF treatment, cellular pathways associated with apoptosis and ER stress were up-regulated, providing additional understanding of the mechanism of action of CLF in PCa cells. Further, we also found that CLF reduces ALDH activity, which is a marker for cancer cell stemness, a subtype of cancer cells that are associated with the aggressiveness of the cancer.

Finally, drug-induced changes were investigated using whole transcriptome (next-generation RNA sequencing) analysis, where CLF treatment was found to modulate the expression of several non-coding RNAs that are associated with tumor cell proliferation, cell migration, and PCa drug resistance. Western Blotting was performed to validate the dysregulation of proteins associated with cell death and apoptosis, as well as the top dysregulated pathways in mCRPC following treatment with CLF.

Our results support the preclinical development of CLF as a combination therapy candidate against aggressive forms of Prostate Cancer and provide additional insights into its mechanism of action.