A phase II study of obatoclax mesylate, a Bcl-2 antagonist, plus topotecan in relapsed small cell lung cancer

INTRODUCTION

We previously reported data on the safety, tolerability, and recommended phase II dose of obatoclax mesylate in conjunction with topotecan in patients with advanced solid tumor malignancies. Preliminary efficacy data suggested activity in patients with recurrent small cell lung cancer (SCLC). Based on these data, we performed a phase II study of obatoclax mesylate plus topotecan in patients with relapsed SCLC to assess efficacy.

METHODS

This was an open-label, single-arm, phase II extension of obatoclax mesylate plus topotecan in patients with relapsed SCLC. Obatoclax mesylate was given intravenously (IV) at a dose of 14mg/m(2) on days 1 and 3 with IV topotecan at 1.25mg/m(2) on days 1-5 of an every 3-week cycle. The primary end-point of this study was overall response rate.

RESULTS

Nine patients with recurrent SCLC were enrolled into the first stage of the study. Patients received a median of 2 cycles of treatment. All patients were evaluable for the primary end-point of overall response. There were no partial or complete responses. Five patients (56%) had stable disease. The remaining four patients (44%) developed progressive disease. The most common grade 3 or 4 adverse events included thrombocytopenia (22%), anemia (11%), neutropenia (11%), and ataxia (11%).

CONCLUSION

Obatoclax mesylate added to topotecan does not exceed the historic response rate seen with topotecan alone in patients with relapsed SCLC following the first-line platinum-based therapy.

Phase I/II study of AT-101 with topotecan in relapsed and refractory small cell lung cancer

INTRODUCTION

AT-101 is an oral, pan Bcl-2 family protein inhibitor that has demonstrated activity in small cell lung cancer (SCLC) models. A phase I/II study was conducted combining AT-101 with topotecan in relapsed and refractory SCLC.

METHODS

An open-labeled multicenter phase I/II study was conducted of oral AT-101 with intravenous topotecan in patients with SCLC who had progressed on prior platinum-containing chemotherapy. The phase II portion was a two-stage design, and two cohorts of patients, sensitive relapsed and refractory, were analyzed. Primary endpoint in the two-stage phase II portion was response rate; secondary endpoints were duration of response and time to progression.

RESULTS

Thirty-six patients were enrolled. The most common toxicities were hematologic, as would be expected with topotecan and AT-101. The recommended phase II dose was 40 mg AT-101 days 1 to 5 with topotecan 1.25 mg/m(2) days 1 to 5 on a 21-day cycle. In the sensitive-relapsed cohort (n = 18), there were 0 complete response (CR), three partial response (PR), 10 stable disease (SD), and four progressive disease (PD). In the refractory cohort (n = 12), there were 0 CR/PR, five SD, and five PD. The study did not meet its prespecified endpoints to continue enrollment in the second stage of the phase II study. Median time to progression in the sensitive-relapsed cohort was 17.4 weeks and 11.7 weeks in the refractory cohort.

CONCLUSIONS

AT-101 can be safely combined with topotecan at a reduced dose of 1.25 mg/m(2). The response rates observed did not meet the criteria for additional enrollment; however, many patients had a best response of SD and the median time to progression in both cohorts was favorable. Additional trials of AT-101 in SCLC are ongoing.