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A four-day tumour chemosensitivity assay of potential use in predicting tumour response to cytotoxic drugs has been developed for haematological cancers. The method comprised isolation of white cells from peripheral blood or bone marrow aspirates, drug exposure and incubation for 4 days. Drug-induced tumour cell kill was assessed by differential staining of live and dead cells such that the former could be morphologically identified. Tumour cell viability was subsequently calculated by reference to an internal standard of fixed duck red blood cells. Over 30 drugs have been tested in vitro, all of which have shown a dose response relationship in vitro and given a good scatter of sensitivities from patient to patient within the concentration ranges tested. In 27 cases where the in vitro chemosensitivity could be compared with the in vivo response, there were 7 true positive comparisons (sensitive in vitro and in vivo), 17 true negative comparisons (resistant both in vitro and in vivo) and 3 false positive comparisons (sensitive in vitro, resistant in vivo). A result was obtained in 38 of 50 samples received, comprising 16 of 18 chronic lymphocytic leukaemias, 11 of 20 acute lymphoblastic leukaemias, 5 of 5 acute myeloid leukaemias and 6 of 7 myelomas. The assay appears to show considerable promise as a tumour chemosensitivity test and warrants wider investigations.

Extensive research into mechanisms of cytotoxic drug resistance and subsequent clinical trials of drug resistance modifiers have produced few encouraging results. In this report, we analyze 4,400+ ex vivo Differential Staining Cytotoxicity (DiSC) assay drug response results from patients with chronic lymphocytic leukemia (CLL) to investigate the development of drug resistance during treatment. Patients were untreated (n = 216) or previously treated with various cytotoxic agents (n = 188). Data was processed to identify ex vivo resistance (or sensitivity) induced by treating patients with prednisolone, chlorambucil, cyclophosphamide, anthracycline, or fludarabine. Induced resistance was apparently not associated with any one known mechanism. Treatment with chlorambucil induced a 10-fold sensitivity to steroids; cyclophosphamide induced greater resistance to anthracyclines than alkylating agents; anthracyclines induced greatest resistance to chlorambucil, cisplatin, carboplatin, and cladribine. Patients previously treated with at least two regimens were only 2.16-fold more resistant to CLL drugs than untreated patients, but had significantly reduced survival (median survival, 7.9 months compared with 61.1 months for untreated patients). These results suggest that chlorambucil and/or an antimetabolite should be administered before cyclophosphamide or anthracyclines to delay the onset of extensive pleiotropic drug resistance. Because individual differences in drug sensitivity are considerable, specific guidance could be obtained from ex vivo assay results. Furthermore, as a model for investigating drug resistance mechanisms, fresh CLL lymphocytes represent a useful alternative to drug-resistant cell lines.