Assessment of two dosing schedules of GSK1363089 (GSK089), a dual MET/VEGFR2 inhibitor, in metastatic gastric cancer (GC): Interim results of a multicenter phase II study

Abstract

4502 Background: GSK089 is an oral, small-molecule inhibitor of cMET and VEGFR2/KDR, and has potent antitumor activity in cMET-amplified cell lines and xenografts. cMET is reportedly amplified, overexpressed and/or activated in GC, making it an attractive therapeutic target. This phase II study examines the safety and efficacy of 2 dosing schedules of GSK089 as a single agent in patients (pts) with metastatic GC. Methods: Pts with distal esophagus, GE junction or stomach adenocarcinoma, 0–2 prior chemotherapy regimens, adequate organ function, measurable disease, and ECOG PS 0–2 are sequentially enrolled in 2 cohorts: 1) Intermittent 5 days on/9 off - GSK089 240 mg/d on D1–5 repeated every 14 days, and 2) Daily - 80 mg/d. Primary study endpoint (response) is assessed every 8 weeks. cMET amplification by FISH (≥2 copies of cMET per copy of chromosome 7) is not an entry criterion, but is determined on archival tissue for all pts. Pre- and on-treatment tumor biopsies in select pts and plasma samples in all pts are analyzed for GSK089 effects on direct and downstream drug targets. GSK089 pharmacokinetics (PK) are also evaluated. Results: As of 12/19/08, enrollment to the 5 on/9 off cohort is complete with 41 evaluable pts, and 14 evaluable pts have enrolled on the daily cohort. cMET amplification was seen in 3/43 (7%) pts tested; all 3 were in 5 on/9 off cohort. Best response of stable disease (SD), was noted in 6/41 (15%) pts in the 5 on/9 off cohort (none were cMET-amplified), with 2 pts SD >6 months, 1 ongoing; and in 3/14 (21%) pts in the daily cohort. Among all-enrolled pts (48 pts in 5 on/9 off, 16 pts in daily cohort), LFT abnormalities (9%), fatigue (5%), and venous thromboembolism (3%) were the most common GSK089 related grade 3- 4 adverse events (AE). Only 1 possibly related grade 5 AE, death due to unknown cause, was noted. Conclusions: GSK089 is well tolerated on both dosing schedules. cMET amplification in metastatic GC is rare. Single agent GSK089 demonstrates minimal antitumor activity in a cMET-unselected gastric population on the 5 on/9 off schedule. Enrollment on the daily dosing schedule continues, now with mandatory pre- and on-treatment biopsies to better define cMET pathway and target inhibition with GSK089. No significant financial relationships to disclose.