In vitro pharmacodynamic evaluation of VP-16-213 and implications for chemotherapy.

VP-16-213 (Etoposide) is an active antineoplastic agent which has undergone extensive evaluation of clinical dose escalation. To corroborate a putative dose-response relationship, we studied, in a modified clonogenic assay, various doses and durations of exposure. VP-16-213 at doses of 0.01, 0.05, 0.10, 0.50, 1.0, 5.0, and 10.0 micrograms/ml, each with exposure durations of 1, 3, 18, and 30 h, was studied in vitro against two human tumor cell lines, MOLT and 9812. The doses and durations of exposure were chosen to approximate some of the pharmacokinetic values achievable in either standard-dose or high-dose clinical studies. The results, summarized as linear regression lines, demonstrate with statistical significance (p less than 0.03) that there is correlation between dose and cytotoxicity and between dose X duration of exposure (representing the area under the concentration-time curve) and cytotoxicity. Our in vitro data thus support the concept of intensive use of VP-16-213 to maximize antitumor activity. However, how best to accomplish the manipulation of dose and duration of exposure is not yet clear and will be the subject of future clinical investigations.