3576 Background: Obatoclax (Ob) is a small-molecule antagonist of all the Bcl-2 prosurvival proteins. In vitro it enhances the effects of the drugs cisplatin and etoposide. Bcl-2 family proteins are frequently expressed in SCLC, and SCLC cell lines are sensitive to Ob.
METHODS
This study was designed to find the maximal tolerated doses (MTD) of oOb when given on a 21 day (D) cycle together with carboplatin (AUC 5 D1) and etoposide (100 mg/m2 D1-3), in separate dose escalations using Ob as a 3-hr infusion D1-3 and as a 24-hr infusion D1-3. Eligible patients had ES-SCLC, measurable disease, ≤1 prior therapy, ECOG PS ≤1, and adequate hematological, renal and hepatic function. 3- 6 patients were enrolled into ascending dose cohorts with standard DLT rules evaluating safety in C1 to determine dose escalation.
RESULTS
24 patients were enrolled into 5 dosing cohorts (14 males; median age 67). A total of 66 cycles (C) have been administered to date. There were no DLTs in the initial cohorts using Ob 15 mg over 3 hr or Ob 30 mg over 24 hr. Two DLTs occurred in the Ob 30 mg over 3 hr cohort - both due to myelosuppression in previously treated patients. As a result, the trial was amended to exclude previously treated patients. 5 previously untreated patients receiving Ob 30 over 3 hr had no DLTs. There were no DLTs in the Ob 45 mg over 24 hr cohort but 2 patients in the Ob 24-hr infusion cohorts had infusion pump malfunctions while at home. There were 2 DLTs in the Ob 45 mg over 3 hr cohort (somnolence, euphoria, & disorientation) establishing MTD of Ob 30 mg over 3 hr daily x 3. After C2 the 6 previously untreated patients on Ob 24-hr infusion cohorts had 3 PRs, 1 SD, 1 PD, and 1 Unk; the 2 previously treated patients had PRs. After C2 all 7 previously-untreated patients at 15 or 30 mg in the 3-hr infusion cohorts have PR; the 3 previously treated patients had SD.
CONCLUSIONS
Ob can be combined with carboplatin and etoposide using either a 3-hr or a 24-hr infusion, and both regimens are associated with high early response rates in ES-SCLC, perhaps due to inhibition of mcl-1. Due to practical issues with the 24-hr infusion arm, the 3-hr 30 mg MTD dose will be utilized in a randomized phase II versus carboplatin and etoposide alone. [Table: see text].