A bioassay for cyclophosphamide in blood, lung and tumour.

A bioassay has been developed to detect and quantify the concentration of cytotoxic metabolites of cyclophosphamide (CY) in blood, tumour, and lungs of mice. Extracts were made of blood or solid tissues taken from mice given CY and these were used to treat log phase Chinese Hamster V79 cells in culture for up to 24 h. The amount of cell killing was tested by colony formation 7 days later. The effects of incubation time, CY dose, and the time of tissue sampling after CY injection were investigated. The bioassay could detect cytotoxic metabolites in blood after doses as low as 10 mg kg-1 CY given i.p. The half life of these metabolites in blood after giving 400 mg kg-1 i.p. decreased over a 2 h period from 14 to 9 min. The method was then modified to define the pharmacokinetics of CY metabolites in two different types of tumour and in lung. The half life of the cytotoxic metabolites in the lung was longer than in blood, falling from 35 to 11 min over a 2 h period. In tumours, the half lives were longer again, i.e. approximately 61 min. The maximum metabolite levels achieved were similar in the two tumour types, although these differed markedly in their therapeutic response to CY. The bioassay for CY is a relatively simple and rapid procedure, and the extension of its application from body fluids to solid tissues makes it a useful tool in experimental pharmacokinetic studies.