The usefulness of human tumor cell lines in the study of chemosensitivity. A study of malignant melanomas.

The chemosensitivity of human melanoma cells has been studied before and after continuous in vitro culture. Altogether, nine cell lines were studied, two derived from patients' biopsies, and seven from xenografts in athymic mice. The sensitivity to the agents DTIC (Dacarbazine), CCNU (Lomustine), procarbazine, vinblastine, abrin and ricin was assayed. Furthermore, in five cases the chemosensitivity of the cell lines was compared to that of tumors obtained by injecting the cell lines into athymic mice. In all cases the sensitivity was measured in an in vitro soft agar assay. Upon cultivation in vitro, two of the cell lines, one derived from a patient's metastasis and one from a xenograft in athymic mice, showed marked increases in sensitivity to some of the drugs, whereas sensitivity to other drugs showed little or no change. For the other cell lines small, but definite increases or decreases in chemosensitivity were observed. Permanent cultures showed the same chemosensitivity as early subcultures. The tumors formed by injecting the cell lines into athymic mice showed moderate changes in chemosensitivity, as compared to the cell lines in vitro. The data indicate that considerable changes in chemosensitivity may occur when cells are brought from in vitro to in vitro conditions and vice versa and that such changes may be highly specific. Therefore, although cell lines may be useful in some respects, they should be used with caution in attempts to evaluate quantitatively the sensitivity of human tumors to cancerostatic drugs.