Fibroblast Activation Protein α Activated Tripeptide Bufadienolide Antitumor Prodrug with Reduced Cardiotoxicity

Bufadienolides are the major pharmacologic constituents of traditional Chinese medicine Chan'su, which is frequently used clinically for cancer treatment in China. Motivated by reducing or avoiding the cardiac toxicity of bufadienolides, we have designed, synthesized, and evaluated the fibroblast activation protein alpha (FAP alpha) activated tripeptide arenobufagin prodrugs with the purpose of improving the safety of arenobufagin (a representative bufadienolide). Among these FAP alpha-activated prodrugs, 3f exhibited the best hydrolytic efficiency by recombinant human FAP alpha (rhFAP alpha) and was activated in tumors. The LD50 of 3f was 6.5-fold higher than that of arenobufagin. We also observed that there are nonapparent changes in echocardiography, pathological section of cardiac muscle, and the lactate dehydrogenase activities (LDH) in 3f-treatment tumor-bearing mice, even when the dose reached 3 times the amount of parent drug arenobufagin that was used. Compound 3f also exhibits significant antitumor activity in vitro and in vivo. The improved safety profile and favorable anticancer properties of 3f warrant further studies of the potential clinical implications. Our study suggests that FAP alpha prodrug strategy is an effective approach for successful increasing the therapeutic window of bufadienolides.