CHIDER CHIANG

Quinocarmycin monocitrate is a novel antitumor antibiotic isolated from Streptomyces melanovinaceus. We have utilized a human tumor clonogenic assay to test the antitumor activity of this drug against carcinoma of the lung and to compare its activity with those of mitomycin C or cisplatin, which are components of the clinically effective regimens in therapy for this disease. The overall in vitro response rate (defined as less than 50% survival of tumor colony forming units) for quinocarmycin at 0.1 and 1.0 microgram/ml continuous exposure was 42% and 72%, respectively, which was superior to that of other drugs. Quinocarmycin and other antitumor drugs do not have identical spectra of antitumor activities in vitro, suggesting that this compound with good in vitro activity should be further developed for clinical trials.

To assess the influence of different schedules of drug exposure in human tumor clonogenic assay on in vitro cytotoxicity of antitumor drugs, the in vitro sensitivities of a human carcinoma cell line, PC-9, to various antitumor drugs were measured by using two different procedures: exposure was either by pulse for 1 h prior to plating or continuous throughout the period of growth in agar. Marked differences between the two procedures in testing actinomycin D, etoposide, 5-fluorouracil, vinblastine and vindesine but not in adriamycin, daunomycin, melphalan, nimustine and ranomustine were observed. The former and the latter were classified as schedule dependent drugs and a schedule independent drugs, respectively. In this study, the schedule dependency of in vitro drug response appears to be related mainly to time-dependency and partially to other factors, such as stability during culture in medium.