Pharmacokinetic-driven phase I study of DCC-2618 a pan-KIT and PDGFR inhibitor in patients (pts) with gastrointestinal stromal tumor (GIST) and other solid tumors.

Abstract

2515 Background: DCC-2618 is a potent switch control inhibitor of KIT and PDGFR kinases active in a broad range of mutations. GIST is an important disease to achieve a proof-of-concept due to the heterogeneity of KIT resistance mutations, which emerge on treatment with approved KIT inhibitors. Methods: This was a PK-guided dose escalation study of oral DCC-2618 (QD or BID q28 days) in advanced solid tumors. FDG-PET scans were used to assess changes in FDG uptake in GIST pts after 3 wks of therapy. Next generation sequencing (NGS) of plasma cell-free (cf) DNA was performed throughout the study to assess and quantify KIT and other molecular alterations in drug targets and potential mechanisms of resistance. Results: 38 pts were enrolled (30 GIST; 4 glioma; 1 mastocytosis, 3 other carcinoma) to 8 dose levels: BID doses: 20 (4 pts), 30 (4), 50 (5), 100 (6), 150 (6) and 200 mg (3); QD doses: 100 (5) and 150 mg (4). Safety of evaluable pts is as follows: G3 or G4 adverse effects (regardless of attribution and occurring in > 1 pt) included anemia (5), lipase increase (4), hypertension (2). Two of the G3/4 lipase increase at 100 mg BID and 200 mg BID were DLTs. All G3/4 lipase increase were asymptomatic. G1/2 AEs (considered at least possibly related to DCC-2618) and occurring in ≥15% (n > 5) of pts include fatigue (12), alopecia & lipase increase (7), weight decrease (6). Starting with 50 mg BID dose level, trough concentrations of total drug exceeded the IC90 of the least sentivitive KIT mutations. Plasma concentrations > 5μM were achieved starting at 100 mg BID and the selection of the expansion phase dose is being finalized. Of 18 pts with KIT mutant GIST assessed by FDG PET, 14 (78%) had partial metabolic response per EORTC criteria. RANO/RECIST partial responses (PRs) were reported in 3 patients (1 GBM with PDGFRA/KIT amplifications and 2 GIST with Ex 11 & 17 / Ex 11 & 18 mutations, respectively). NGS of plasma cfDNA revealed 44 KIT mutations in baseline samples from 19 of 21 pts with GIST. Conclusions: DCC-2618 is well tolerated with encouraging preliminary activity in GIST pts with a broad spectrum of mutations and prior therapies. PR was also seen in a pt with GBM with PDGFRA/KIT amplifications. Clinical trial information: NCT02571036.