Broad targeting of triptolide to resistance and sensitization for cancer therapy.

Cancer cell resistance to current anticancer therapeutics as well as the side effects are still obstacles to successful cancer therapy. Hence, the development of novel anticancer agents or therapeutics is of vital significance, and especially rational adjuvant therapies containing low-cost natural products with multiple targets have attracted great interests. Triptolide, the main biocomponent of Tripterygium wilfordii Hook F, is restricted in clinical applications mainly due to its severe systemic toxicities, although it has shown strong antitumor activities in preclinical studies. Mounting evidence suggests that triptolide at low doses as an adjuvant therapeutic agent circumvents resistance to current anticancer therapies, enhances the anticancer effectiveness, and relieves toxicities of both triptolide and anticancer therapies. Furthermore, several unique antitumor targets of triptolide make it superior to other therapeutics. The molecular mechanisms of triptolide-induced anti-resistance and sensitization effects include changes in ATP-binding cassette transporters, induction of apoptosis pathways, increase in tumor suppressors and decrease in oncogenic factors, and interactions with the RNA polymerase II complex; targeting cancer stem cells and tumor-microenvironment-mediated resistance are also involved. Besides, some synthetic derivatives and novel delivery systems of triptolide are also developed to enhance the water-solubility and reduce the toxicity, which will also be discussed.