A simple, small scale cytotoxicity test, and its uses in drug metabolism studies

A small scale method is described, for the estimation of drug toxicity against cells in culture. The usefulness of this test is illustrated by reference to the results of a study of the microsomal activation of cyclophosphamide. Firstly, it is shown that the microsomal activation of drugs, in this case cyclophosphamide, can easily be demonstrated, in vitro , using this technique. It is also shown that the small scale of the test allows measurements of cytotoxicity to be made on drug metabolites separated by thin layer chromatography, and therefore available in only microgramme quantities. The identification of a number of cytotoxic metabolites of cyclophosphamide is described. An adaptation of the method is described which allows thin layer plates to be “scanned” for cytotoxicity and which has been useful for demonstrating the presence, on the plates, of toxic metabolites of cyclophosphamide which might otherwise have been missed. The importance of cytotoxicity testing is discussed in relation to the formulation of theories of drug activation in general, and that of cyclophosphamide in particular.