A phase I study of AMN107 alone and in combination with imatinib in patients (pts) with imatinib-resistant gastrointestinal stromal tumors (GIST)

Abstract

9545 Background: Although imatinib induces durable clinical benefit in pts with metastatic GIST, resistance may emerge. AMN107 is a novel agent rationally designed to inhibit the PDGFR, KIT and Bcr-Abl tyrosine kinases. It has been shown to inhibit the proliferation of both imatinib-sensitive and imatinib-resistant GIST cells in vitro. Methods: Cohorts of imatinib-resistant GIST pts with radiological progressive disease (PD) were treated with AMN107 alone (400 mg p.o. bid) or with escalating doses of AMN107 (200 mg qd, 400 mg qd, or 400 mg bid) in combination with imatinib (400 mg p.o. bid). Pharmacokinetic (PK) analyses were performed for both AMN107 and imatinib. Serial tumor assessments included CT and 18FDG-PET scans. Results: As of 30 November 2005, 30 pts (13 women and 17 men), median age 51 yr (range 24–83) received AMN107 alone (n=18) or in combination up to 400 mg qd with imatinib (n=12) for 7 to 98 days (median 49 days). This study continues to accrue. Serious adverse events (SAE’s) reported in four patients deemed related to disease included abdominal pain, peritonitis and anemia. Grade 1/2 drug-related adverse events included hyperbilirubinemia, myalgias, peripheral edema and skin rash. Dose-limiting toxicity (Grade 3 elevated bilirubin) was reported in one pt on AMN107 alone. Efficacy data available for 18 patients show that three patients experienced progressive disease and 15 patients had stable disease, although the duration of follow-up was short. PK results in a limited number of patients showed that the effect of imatinib co-administration on AMN107 PK appears to be minimal, while AMN107 increases imatinib exposure on the average by 50%. Conclusions: AMN107 alone or in combination with imatinib has acceptable tolerability in patients with imatinib-resistant GIST. These initial data suggest there may be relevant activity of AMN107 alone and in combination with imatinib in imatinib-resistant metastatic GIST patients. [Table: see text]