Phase I/II study to assess safety, pharmacokinetics, and efficacy of the oral MEK 1/2 inhibitor GSK1120212 (GSK212) dosed in combination with the oral BRAF inhibitor GSK2118436 (GSK436).

Abstract

CRA8503 Background: In preclinical models, the BRAF/MEK inhibitor (i) combination GSK436/GSK212 has demonstrated enhanced activity against BRAF-mutant cancer cells compared to either drug alone, delayed emergence of GSK436 resistance, and prevented proliferative skin lesions attributable to BRAFi exposure. Methods: Eligible patients (pts) had BRAF V600 mutation positive solid tumors. Part 1: pharmacokinetic (PK) drug-drug interaction (DDI) study. Part 2: Dose escalation of continuous daily dosing of the combination followed by expansion cohorts; Part 3: Randomized phase II trial in untreated stage IV melanoma. Results: 45 pts have received ≥ 1 dose of GSK212 + GSK436, including 43 melanoma (all BRAFi naïve), 1 NSCLC and 1 salivary duct carcinoma. PK results of 7 pts in Part 1 showed no effect of GSK212 on single dose of GSK436. There was no clinically meaningful DDI between GSK436 and GSK212 after repeat dosing of the combination (Part 2). GSK436 was dosed 75-150 mg BID in combination with GSK212 1.0, 1.5, 2.0 mg QD. The recommended dose was 2 mg QD GSK212 in combination with 150 mg BID GSK436. At 1.5 mg GSK212, there was one DLT, a recurrent grade (G) 2 neutrophilic panniculitis. The only G4 adverse event (AE) was a sepsis-like syndrome with fever/hypotension. G3 AEs included generalized rash (n=2, 4%) and neutropenia (n=2, 4%). Skin toxicity ≥ G2 occurred in 9 (20%) pts; of these, G2 rash (n=4, 8%) and G2 macular rash (n=1, 2%). No cutaneous squamous cell carcinoma (SCC) or hyperproliferative skin lesions have occurred at any dose level. Other common G2 toxicities were pyrexia (n=5, 11%), vomiting (n=2, 4%) and fatigue (n=2, 4%). Of 16 evaluable pts in Part 2, 13 pts had PR and 3 SD for an ORR of 81% (95% CI 54.4%-96.0%) and all but 2 pts remain on study. In 10 evaluable pts who received 150 mg BID GSK436 + ≥1 mg QD GSK212, 9 pts had PR and 1 SD. Conclusions: GSK212 at 2 mg QD combines safely with GSK436 150 mg BID, no SCC thus far and decreased frequency of rash compared to previous trials of single agent GSK436 and GSK212, respectively. The preliminary anti-tumor activity warrants further investigation; the randomized phase II trial (Part 3) is accruing.