Purpose: Bcl-2 is expressed in the majority of cases of small cell lung cancer (SCLC) and may contribute to chemotherapeutic resistance. Bcl-2 suppression by G3139 (oblimersen sodium), a phosphorothioate oligonucleotide complementary to the bcl-2 mRNA, has the potential to enhance the antitumor efficacy of standard cytotoxic chemotherapy. A dose-finding study was performed evaluating the combination of G3139, carboplatin, and etoposide in patients with previously untreated extensive stage SCLC.
Patients and methods: Sixteen patients were treated in three consecutive cohorts. Cohort 1 (n=5) received G3139 5 mg/kg/d on days 1 to 8 of a 21 day cycle, with carboplatin area under the curve (AUC)=6 on day 6, and etoposide 80 mg/m2/d on days 6 to 8. In cohort 2 (n=4), carboplatin dose was reduced to AUC=5. In cohort 3 (n=7), G3139 dose was escalated to 7 mg/kg/d. G3139 plasma concentrations and Bcl-2 protein levels in peripheral blood mononuclear cells were evaluated.
Results: Two of three assessable patients in cohort 1 experienced cycle 1 dose-limiting toxicity (grade 4 neutropenia). No cycle 1 dose-limited toxicity was observed in cohorts 2 or 3. Of 14 patients assessable for response, partial response was documented in 12 patients (86%), and stable disease in two. Median time to progression was 5.9 months. Carboplatin and etoposide administration did not appear to alter G3139 pharmacokinetics. No evidence of Bcl-2 suppression in peripheral blood mononuclear cells was observed.
Conclusion: The combination of G3139, carboplatin, and etoposide is well tolerated and results in an encouraging response rate and time to progression in patients with extensive stage SCLC.