[Search for new MDR modifier possessing taxane skeleton].

Among new taxoids, taxuspines A-H and J-T, and known taxoids containing taxol and taxol-type compounds with an N-acylphenylisoserine group at C-13 and an oxetane ring at C-4 and C-5 isolated from stems and leaves of the Japanese yew Taxus cuspidata Sieb. et Zucc., two non-taxol-type compounds remarkably reduced CaCl2-induced depolymerization of microtubules. Furthermore, seven non-taxol-type compounds increased cellular accumulation of vincristine in multidrug-resistant(MDR) tumor cells as potent as verapamil, while taxol and taxol-type compounds did not show such an activity. In addition, the non-taxol-type compounds enhancing vincristine accumulation inhibited competitively binding of azidopine to P-glycoprotein. These results suggest that some non-taxol-type taxoids may be useful for overcoming MDR in tumor cells.