Discovery of a Novel Ubenimex Derivative as a First-in-Class Dual CD13/Proteasome Inhibitor for the Treatment of Cancer

The CD13 inhibitor ubenimex is used as an adjuvant drug with chemotherapy for the treatment of cancer due to its function as an immunoenhancer, but it has limitations in its cytotoxic efficacy. The proteasome inhibitor ixazomib is a landmark drug in the treatment of multiple myeloma with a high anti-cancer activity. Herein, we conjugated the pharmacophore of ubenimex and the boric acid of ixazomib to obtain a dual CD13 and proteasome inhibitor 7 (BC-05). BC-05 exhibited potent inhibitory activity on both human CD13 (IC(50) = 0.13 μM) and the 20S proteasome (IC(50) = 1.39 μM). Although BC-05 displayed lower anti-proliferative activity than that of ixazomib in vitro, an advantage was established in the in vivo anti-cancer efficacy and prolongation of survival time, which may be due to its anti-metastatic and immune-stimulating activity. A pharmacokinetic study revealed that BC-05 is a potentially orally active agent with an F% value of 24.9%. Moreover, BC-05 showed more favorable safety profiles than those of ixazomib in preliminary toxicity studies. Overall, the results indicate that BC-05 is a promising drug candidate for the treatment of multiple myeloma.