Nanoformulations of anticancer thiosemicarbazones to reduce methemoglobin formation and improve anticancer activity

Triapine is a promising anticancer thiosemicarbazone which was investigated in multiple clinical trials, where it was active against leukemia but not against solid cancers. This is probably based on insufficient drug levels in the tumor due to a short plasma half-life. Therefore, we encapsulated Triapine into polymeric nanoparticles and remote-loaded liposomes to improve the drug pharmacokinetics as well as targeted delivery. However, burst release of Triapine from both nanoformulations was observed, making the synthesis of two novel Triapine derivatives necessary in order to improve the remote-loading properties. Indeed, the encapsulation efficiency increased and for one derivative also the desired continuous drug release was in line with a strongly reduced cytotoxic activity against cancer cells. In vivo studies of this most promising formulation demonstrated a significant increase in survival of the animals compared to the free drug. Finally, we investigated drug-induced methemoglobin formation, a frequently observed side effect of thiosemicarbazones, which was completely prevented by the liposomal formulation. Triapine and two derivatives were encapsulated into polymeric nanoparticles as well as liposomes. The most stable formulation showed strongly reduced methemoglobin formation and improved anticancer activity.