Lacidipine and josamycin: two new multidrug resistance modulators.

In this paper we report the results obtained treating a multidrug resistant (MDR) murine erythroleukemia cell line with daunomycin (DNM) in association with two new modulators characterized by a favourable therapeutic index, lacidipine (LCD), a dihydropyridine calcium antagonist, and josamycin (JSM), a macrolide antibiotic. LCD and JSM exhibited a greater MDR reversal activity than verapamil (VRP) and erythromycin (ERY) respectively. The accumulation of DNM in the DRTL cells exposed to modulators was similar to that of the parental cell line FLC. In the case of LCD, it was possible to ascertain that at a very low concentration this molecule can circumvent MDR without modifying DNM accumulation, suggesting that multiple different determinants may be responsible for MDR other than P-170 in this cell line.