THE INFLUENCE OF STORAGE ON CYTOTOXIC DRUG ACTIVITY IN AN ATP-BASED CHEMOSENSITIVITY ASSAY

The use of viability assays to assess the effect of antineoplastic age nts on cell lines and tumor cells is an important investigative tool a nd may have clinical relevance. Such assays require very small quantit ies of drugs and it is the practice of many laboratories to freeze ali quots of drugs for use in these assays as required. We have investigat ed the stability of 11 different agents in an ATP-based chemosensitivi ty assay which is being evaluated for clinical use. The results show t hat most drugs maintain their biological activity well when frozen at -20 degrees C for periods up to 24 months, or occasionally at room tem perature. However, 4-hydroperoxycyclophosphamide and mitomycin C are e xceptions to this rule, and should not be kept frozen for more than 2- 3 months. Cisplatin is unstable when frozen and then thawed, but maint ained activity at room temperature for at least 6 months. Since biolog ical activity may not correlate completely with chemical stability, fu rther studies on the effect of storage are required, but it seems unli kely that the appropriate use of frozen aliquots is a major source of error in tumor chemosensitivity assays.