Acquisition of multiple drug resistance by CCRF-CEM cells selected for different degrees of resistance to vincristine.

We studied the acquisition of multiple drug resistance to several "natural product" drugs by cultured human leukemic lymphoblasts selected for increasing resistance to vincristine (VCR). Three apparent types of cross-resistance patterns could be distinguished: specific, pleiotropic, and mixed. Cross-resistance to vindesine developed in parallel with VCR resistance, appearing at the lowest levels of VCR resistance (approximately fivefold). Vinblastine resistance did not become noticeable until VCR resistance was higher (approximately equal to 50-100-fold). Cross-resistance resistance to three other tubulin-binding agents developed in a different pattern, however. While cross-resistance to maytansine was seen in cells of intermediate (approximately equal to 50-fold) resistance to VCR, colchicine cross-resistance occurred only in cells that were highly resistant to VCR (approximately equal to 500-fold). Even at the highest level of VCR resistance (approximately equal to 600-fold), complete sensitivity to podophyllotoxin was retained. Conversely, cross-resistance to the epipodophyllotoxins , teniposide and etoposide, semisynthetic derivatives of podophyllotoxin, was seen in cells that were greater than 50-fold resistant to VCR. The same pattern obtained for the anthracyclines, doxorubicin and daunorubicin. We conclude that resistance to low concentrations of VCR does not uniformly confer cross-resistance to other classes of natural product drugs.