Acquired drug resistance in human lung carcinoma xenografts.

The development of resistance to vincristine and dactinomycin has been investigated in a human epidermoid lung xenograft line grown in nude mice. With 1 mg/kg BW vincristine and 0.5 mg/kg BW dactinomycin per passage, resistance of the solid tumors was visible already at the second transplantation. The vincristine-resistant subline showed cross-resistance to dactinomycin and doxorubicin, and the dactinomycin-resistant subline only to vincristine. To determine whether multidrug resistance genes were overexpressed in the resistant sublines, slot blots were performed using the cDNA probe pcDR 1.5. Slightly elevated RNA levels could be detected in the vincristine-resistant subline and in the dactinomycin-resistant subline.