Phase I and Pharmacological Study of the Novel Topoisomerase I Inhibitor 7-Ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11) Administered as a Ninety-Minute Infusion Every 3 Weeks¹

7-Ethyl-10-[4-(1-piperidino)-1-piperidino]carbonyloxycamptothecin (CPT-11; Irinotecan), a semisynthetic analogue of camptothecin (CPT) with broad preclinical antitumor activity, has demonstrated impressive activity in phase II trials in Japan in advanced small and non-small cell lung, colorectal, cervical, and ovarian carcinomas, as well as in refractory lymphomas and leukemias. In this phase I and pharmacological study, 90-min infusions of CPT-11 were administered every 3 weeks at doses ranging from 100 to 345 mg/m² to patients with solid malignancies. Acute, severe, and refractory vomiting, diarrhea, and/or abdominal cramps associated with flushing, warmth, and diaphoresis occurred in the immediate posttreatment period at the 240-mg/m² dose level in several patients who were not treated with premedications. The characteristics and temporal nature of these toxicities, the prompt resolution of symptoms following treatment with diphenhydramine, and the successful use of a premedication regimen consisting of ondansetron and diphenhydramine in preventing these acute effects suggest that vasoactive substances are involved in the mediation of these acute toxicities. With the routine use of these premedications, there was no single toxicity type that limited the escalation of CPT-11 doses. Instead, a constellation of severe hematological and gastrointestinal effects precluded the repetitive administration of CPT-11 at doses above 240 mg/m², the maximum tolerated dose and recommended phase II dose on this Schedule. Major responses were observed in patients with advanced colorectal, cervical, and renal cancers. The disposition of total CPT-11 in plasma was fit by a biexponential kinetic model with renal elimination accounting for 37 ± 4% (SE) of total drug disposition. The C_max for the active metabolite of CPT-11, 7-ethyl-10-hydroxycamptothecin (SN-38), was achieved at 2.2 ± 0.1 h after treatment, and mean residence times for both CPT-11 and SN-38 were long, 9.1 and 10.0 h, respectively. Compared with topotecan, another CPT analogue under development, a larger proportion of total drug exposure was accounted for by the active lactone (closed-ring) forms of CPT-11 and SN-38; areas under the time-versus concentration curve for their respective lactone were 44 and 50% of areas under the time-versus concentration curve for total CPT-11 and SN-38. Although intermittent dosing schedules appear to be superior to single dosing schedules for CPT and some CPT analogues in preclinical tumor models, the maintenance of biologically relevant concentrations of SN-38 for relatively long durations may negate the potential pharmacological benefits of intermittent and continuous administration schedules for CPT-11. The clinical activity observed with CPT-11 on the single dosing schedule and the lack of severe diarrhea after repetitive dosing at the maximum tolerated dose, which has been problematic on intermittent schedules, suggest that the single dosing schedule should be evaluated further in the phase II setting and in the development of combination chemotherapy regimens, particularly those containing both CPT-11 and 5-fluorouracil in which diarrhea is a significant concern.