Phase I clinical and plasma and cellular pharmacological study of topotecan without and with granulocyte...

Topotecan, a semisynthetic water-soluble analogue of camptothecin, inhibits human topoisomerase I (topo I). We performed a Phase I clinical and plasma pharmacological study of topotecan administered by 24-h continuous infusion without and with granulocyte colony-stimulating factor (G-CSF). We also measured topo I-DNA complexes in peripheral blood mononuclear cells (PBMCs) in an attempt to correlate formation of topo I-DNA complexes in patients treated with topotecan with toxicity and/or response. One hundred four courses of topotecan at doses of 2.5-15.0 mg/m2 were administered to 44 patients with solid tumors. The maximum tolerated dose without G-CSF was 10.0 mg/m2; granulocytopenia was the dose-limiting toxic effect. The maximum tolerated dose could not be increased with G-CSF because of severe thrombocytopenia. Plasma pharmacology was obtained in 11 patients treated at 12.5 mg/m2 and 15.0 mg/m2. The topotecan lactone end-infusion plasma levels correlated strongly with the area under the curve. Lactone elimination was biexponential with a mean t1/2alpha of 28 min and a t1/2beta of 3.8 h at 12.5 mg/m2. Topo I-DNA complexes were measured before and after treatment in PBMCs from seven patients. Pretopotecan topo I-DNA complexes were available on two additional patients treated at 15 mg/m2. The mean increase in topo I-DNA complexes at the end of the topotecan infusion was 1.25 times the pretreatment value. There was a statistically significant relationship (P = 0.02) between lack of disease progression and the level of topo I-DNA complexes measured in PBMCs before therapy. For Phase II studies of minimally treated adults with solid tumors, the recommended topotecan starting dose administered by 24-h continuous infusion is 10 mg/m2 without G-CSF.