Occurrence of a multidrug-resistant phenotype in human lung xenografts.

The intrinsic sensitivity of a panel of 8 human epidermoid lung cancer xenografts to vincristine and actinomycin D has been examined and the cross-resistance patterns of the most vincristine-resistant and vincristine-sensitive tumour line were tested to a variety of other drugs, including radiation. The results demonstrate that xenograft lines derived from human lung tumours not previously treated with chemotherapy exhibit a similar general pattern of cross-resistance to the drugs vincristine, actinomycin D and adriamycin as is observed in human cell lines and in animal models selected for resistance to these drugs. It is also shown that intrinsic resistance to vincristine can be partially overcome by verapamil. This may indicate a potential role of this substance in circumventing clinically observed drug resistance.