Synergistic combination effect of the PCA-1/ALKBH3 inhibitor HUHS015 on prostate cancer drugs in vitro and in vivo.

Prostate cancer antigen-1/ALKBH3, a DNA/RNA demethylase of 3-methylcytosine, 1-methyladenine (1-meA), and 6-meA, was found in prostate cancer as an important prognostic factor. Additionally, 1-meA has been associated with other cancers. The ALKBH3 inhibitor HUHS015 was found to be effective against prostate cancer both in vitro and in vivo. Herein, we investigated the effect of HUHS015 in combination with drugs for prostate cancer approved in Japan (including bicalutamide, cisplatin, mitoxantrone, prednisolone, ifosfamide, tegafur/uracil, docetaxel, dacarbazine, and estramustine) by treating DU145 cells with around IC50 value concentrations of these drugs for 3 days. Additionally, the cells were observed for additional 9 days after drug removal. Combination treatment with dacarbazine, estramustine, tegafur/uracil, and HUHS015 showed a slight additive effect after 3 days. After drug washout of them and mitoxantrone, the combined effects and levels were enhanced and sustained, although the effects of each treatment alone declined. HUHS015 combined with cisplatin or docetaxel elicited synergistic and sustained effects. In vivo, combining HUHS015 and docetaxel, the first chemotherapeutic agent for castration-resistant prostate cancer, showed notable effects in the DU145 xenograft model. In conclusion, HUHS015 exhibited a synergistic effect with docetaxel and drugs acting on DNA in vitro, even after drug removal. Since cancer chemotherapy is typically administered during rest periods due to its high toxicity, combining it with an ALKBH3 inhibitor could be a promising strategy for enhancing cancer treatment, as it can elicit an additive effect during treatment, allowing dosage reduction, and synergistically sustain the effect after drug washout during rest periods.