A Phase I-II study of sequential administration of topotecan and oral etoposide (toposiomerase I and II inhibitors) in the treatment of patients with small cell lung carcinoma

Background: Topotecan (9-dimethylaminomethyl-10-hydroxycampthothecin) is a new topoisomerase I inhibitor with promising efficacy in the treatment of patients with small cell lung carcinoma (SCLC). Combination with a topoisomerase II inhibitor may potentate the therapeutic effect of topotecan, although there has been conflicting preclinical information on the combination. The objectives of this study were to establish the maximum tolerated dose and to determine the efficacy of the sequential combination of intravenous topotecan and oral etoposide in the treatment of patients with SCLC.

Methods: Patients with histologically confirmed, limited or extensive stage SCLC were eligible. The dose escalation scheme of three cohorts (six patients per cohort) started at intravenous topotecan 0.5 mg/m(2) per day for 5 days and oral etoposide 50 mg twice daily for 7 days (21-day cycles). Subsequent dose levels involved escalation of topotecan to 0.75 mg/m(2) per day and 1.0 mg/m(2) per day for 5 days. A Phase II study was conducted at one dose level below the maximum tolerated dose. The authors alternated the drug sequence with each consecutive cycle and compared the hematologic toxicity between the two sequences.

Results: Thirty-six patients (21 patients with limited disease and 15 patients with extensive disease) received a total of 173 courses of sequential combination chemotherapy (topotecan --> etoposide, 88 courses; etoposide --> topotecan, 85 courses). The authors identified dose levels for the Phase II study as follows: topotecan, 0.75 mg/m(2) per day for 5 days; and etoposide, 50 mg twice daily for 7 days. The dose-limiting toxicity was neutropenia. At this dose level, the incidence of Grade 3-4 neutropenia and the incidence of Grade 3-4 thrombocytopenia were 25% and 10.9%, respectively. Two patients died from neutropenic sepsis. There was no significant difference in hematologic toxicities between the two sequences. Complete and partial response rates were 5.6% and 55.6%, respectively (limited disease, 9.5% and 66.75%; extensive disease, 0% and 40%, respectively). The median progression free survival was 31.9 weeks (limited disease, 36.1 weeks; extensive disease, 28.9 weeks; 95% confidence interval, 25.6-36.0 weeks), and the median overall survival was 52.4 weeks (limited disease, 54.9 weeks; extensive disease, 30.1 weeks; 95% confidence interval, 39.6-57.7 weeks).

Conclusions: Combination therapy with topoisomerase I and II inhibitors is a safe and effective regimen for patients with SCLC. Future research on this combination should focus on an oral regimen for patients with extensive disease and poor tolerance to cisplatin. The authors recommend an oral dosage of topotecan at 1.2 mg/m(2) per day (equivalent to intravenous topotecan at 0.75 mg/m(2) per day) for 5 days followed by etoposide 50 mg twice daily for 7 days.