Reversal of multidrug resistance by novel cyclosporin A analogues and the cyclopeptolide SDZ 214-103 biosynthesized in vitro

It was shown that cyclopeptolide SDZ 214-103 (10 microM) is more active in rhodamine-123 accumulation in actinomycin-D-resistant human lymphoma cells CCRF/ACTD400 than cyclosporin A (10 microM), but equipotent in the doxorubicin-resistant Friend erythroleukemia cell line F4-6/ADR. In F4-6/ADR cells, the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cytotoxicity assay showed comparable cytotoxic effects of doxorubicin at various concentrations in the presence of SDZ 214-103 and cyclosporin A. For the other novel cyclosporin A analogues minor multidrug-resistance-modulating potency was demonstrated. At equipotent modulating doses of verapamil (10 microM) and cyclosporin A (10 microM) in the MTT assay regarding doxorubicin cytotoxicity, cyclosporin A was efficient in the rhodamine-123-uptake assay while verapamil was not active when identical incubation times were used.