Perturbation of in vitro drug resistance in human lymphatic neoplasms by combinations of putative inhibitors of protein kinase C

Fresh specimens of human lymphatic neoplasms were tested with the differential staining cytotoxicity assay. Cells from relapsed patients with acute lymphoblastic leukemia (ALL) were significantly more resistant to vincristine, dexamethasone, and doxorubicin in the assay than were cells from previously untreated patients. The putative C kinase inhibitors verapamil (V), imipramine (I), lidocaine (L), tamoxifen (T), chlorpromazine (C), and haloperidol (H) were then tested singly, in combination with each other (VILTCH, ITCH, and VL), and in combination with vincristine. At concentrations judged to be clinically achievable, VILTCH itself was occasionally toxic to ALL and chronic lymphocytic leukemia. The VILTCH combination clearly potentiated the cytotoxic activity of vincristine in five of eight ALL specimens from relapsed patients and potentiated vincristine in 18 of 30 chronic lymphocytic leukemia specimens. It also potentiated vincristine in two of six specimens of multiple myeloma and five of six specimens of non-Hodgkin's lymphoma. The VILTCH combination had no significant effects in fresh cultures of normal human lymphocytes. The most active drugs in the VILTCH combination appeared to be verapamil and lidocaine. We conclude that the differential staining cytotoxicity assay is a useful tool to study the circumvention of clinically acquired drug resistance. While the mechanism of the observed enhancement of the cytotoxic effects of vincristine is not known, it is possible that combinations of putative C kinase inhibitors may reduce drug resistance in human lymphatic neoplasms.

Selective enhancement by menadiol of in vitro drug activity in human lymphatic neoplasms

The effect of menadiol (vitamin K3) on fresh specimens of human lymphatic neoplasms (HLN) was tested by means of the differential staining cytotoxicity assay. Menadiol was tested alone and in combination with standard antineoplastic agents. Drug effects were then compared with the effects of the same drugs in normal human lymphocytes and in fresh specimens of human non-small cell lung cancer. By itself, menadiol was moderately toxic to HLN, but not to normal lymphocytes or non-small cell lung cancer. Menadiol, menadione, and two structurally related congeners were equitoxic to HLN cells, but sodium metabisulfite (present in menadiol solutions as a preservative) was nontoxic. Menadiol increased the cytotoxic effects of a number of standard agents in HLN but not in normal lymphocytes. Cell survival times with mechlorethamine, vincristine, and dexamethasone were converted from a range characteristic of drug resistance (ie, range observed in relapsed patients) to a range characteristic of drug sensitivity (ie, range observed in untreated patients) in the presence of menadiol. These effects occurred at a concentration (2.0 micrograms/ml; 4.7 microM) of menadiol which is probably clinically achievable and which did not deplete intracellular glutathione. Menadiol should receive clinical testing as a chemosensitizing agent in HLN.

Laboratory detection of primary and acquired drug resistance in human lymphatic neoplasms

We tested the ability of the differential staining cytotoxicity (DiSC) assay to discriminate between sensitive and resistant cell populations in human lymphatic neoplasms. First, the in vitro activity spectra of the most important drugs paralleled the known clinical activity spectra of the same agents. Second, there were highly significant correlations between in vitro chemosensitivity and the results of clinical chemotherapy. Third, specimens from previously untreated patients were significantly more sensitive to the most important drugs than were specimens from patients who had previously received chemotherapy. Finally, metachronous assays performed on specimens from the same patients showed little change in chemosensitivity if there had been no intervening chemotherapy between the times that the first and second assays were performed. However, if the patients had received intervening chemotherapy between the times of the first and second assays, the specimens in the second assays tended to be significantly more resistant than were the specimens in the first assays. These data indicate that the DiSC assay may be of value in the design of strategies to circumvent drug resistance in human lymphatic neoplasms.