Trial in progress: Phase 1a/b study of PF-07284890 (brain-penetrant BRAF inhibitor) with/without binimetinib in patients with BRAF V600-mutant solid tumors.

Abstract

TPS3152 Background: BRAF inhibitors have transformed treatment (Tx) for patients (pts) with BRAF V600-mutant cancers, but long-term efficacy is limited by disease progression in the brain, due to poor brain penetration. PF-07284890 is a potent, selective, highly brain-penetrant, small-molecule inhibitor of BRAF V600 mutations. This first in human study will assess the PK, safety, and preliminary clinical activity of PF-07284890, as monotherapy and in combination with binimetinib (MEK inhibitor), in pts with BRAF V600-mutated advanced solid tumors with/without brain metastases. Methods: Phase 1a/1b open-label, multicenter, dose-finding study (NCT04543188). Pts will be ≥18 y with a histologically confirmed advanced/metastatic solid tumor including primary brain tumor (PBT), confirmed BRAF V600 mutation, and presence/absence of brain involvement. Pts will have disease progression despite prior Tx without alternative Tx options. Pts with brain metastasis/PBT > 4 cm and/or symptomatic brain disease will be excluded initially, but allowed based on emerging PK. Phase 1a is a dose escalation study of PF-07284890 (monotherapy and combination). ̃35 pts will be enrolled to determine maximum tolerated dose (MTD) and/or recommended dose for expansion (RDE) of PF-07284890 (monotherapy and combination). Cohorts of 2-4 pts will be treated at each dose level of PF-07284890 until MTD/RDE determination (PF-07284890 starting dose: 50 mg QD; binimetinib 45 mg BID). Bayesian Logistic Regression Model will be used to inform dose level decisions. At least 6 pts each for monotherapy and combination will be treated at MTD/RDE. Phase 1a primary endpoints: Cycle 1 dose-limiting toxicities; MTD/RDE; AEs; lab abnormalities; and dose interruptions, modifications and discontinuations due to AEs. Secondary endpoints include PK parameters and overall response (RECIST; overall and intracranial; RANO for PBT). Phase 1b is a dose expansion and drug-drug interaction study to further evaluate PF-07284890 + binimetinib. Cohorts 1-4 (̃40 pts each) will enroll pts based on tumor type, brain involvement (asymptomatic/symptomatic), and prior Tx. Cohort 5 (̃20 pts) will include pts with any solid tumor including leptomeningeal metastases. Cohort 6 (̃10 pts) will assess the effect of PF-07284890 + binimetinib on CYP3A activity using midazolam as a substrate. Phase 1b primary endpoint: overall response (RECIST; overall and intracranial; RANO for PBT). Secondary endpoints: duration of response; progression-free survival; disease control rate; time to response; overall survival; AEs; lab abnormalities; and dose interruptions, modifications and discontinuations due to AEs; and PK parameters. For both Phase 1a and 1b, Tx will continue until disease progression, unacceptable toxicity or patient refusal. Study began enrolling pts in January 2021 and is ongoing. Clinical trial information: NCT04543188.