A Study of Pimitespib in Combination With Imatinib in Patients With GIST (CHAPTER-GIST-101)

Pimitespib will be administered orally in 5 consecutive days followed by 2 days off treatment (QD 5) on an empty stomach at least 1 hour before or 2 hours after a meal. The doses in the Dose Escalation Part will be 80, 120 (starting dose), and 160 mg. The doses used in Arm A will be MTD or recommended dose (RD) based on the information, including the safety and the pharmacokinetics (PK) data in the Dose Escalation Part. In Expansion Part-B, pimitespib will be administered with the starting dose of 160 mg daily.

Imatinib will be administered orally, after a meal and large glass of water QD. The doses in Dose Escalation Part will be 400 mg or 300 mg (De-escalation). The doses used in Expansion Part-A will be MTD or RD based on information, including the safety and PK data in the Dose Escalation Part. In Expansion Part-B, imatinib will be administered post after pimitespib discontinuation with the starting dose of 400 mg daily.

Sunitinib will be administered orally QD with a starting dose of 50 mg, on a schedule of 4 weeks on treatment followed by 2 weeks off, and will be taken with or without a meal in Expansion Part-C.