Abstract CT178: Phase 1 trial of PF-07799933 (ARRY-440), a next-generation BRAF inhibitor, for BRAF-mutant cancers

Abstract BACKGROUND Approved BRAF inhibitors (BRAFi) have transformed the treatment of BRAF V600-mutant cancers. However, clinical benefit is limited by BRAF dimer-promoting resistance mutations, toxicity from paradoxical activation of signaling in BRAF wild-type cells, and poor brain penetration. Further, current RAF inhibitors are ineffective against non-V600 BRAF mutants. Next-generation agents that cause pan-RAF inhibition may more broadly target BRAF mutants but are limited by a narrow therapeutic index. PF-07799933 (ARRY-440) is a brain-penetrant BRAF-selective monomer/dimer inhibitor that spares ARAF and CRAF. METHODS We characterized PF-07799933 in patient (pt) -derived BRAF-mutant cancer cells in vitro and in vivo. We investigated PF-07799933 in pts with refractory BRAF-mutant solid tumors using a novel first-in-patient phase 1 design that enabled flexible, rapid dose escalation based on safety and pharmacokinetics (PK) assessments. RESULTS PF-07799933 inhibited signaling in vitro, disrupted BRAF-containing homo- and heterodimers, and caused less paradoxical signaling than approved agents. PF-07799933 alone and in combination with binimetinib inhibited tumor growth systemically and in the brain in mouse xenografts harboring de novo and acquired BRAF dimer-forming mutations. As of August 24, 2023 data cutoff, 30 pts with BRAF-mutant cancers started PF-07799933 treatment at 50 mg QD-450 mg BID as monotherapy (60%) or combination with binimetinib (27%) or cetuximab (all colorectal cancer CRC) (13%). Tumor types were melanoma (mel) (43%), CRC (17%), primary brain (PBT) (13%), thyroid (10%), and other (n=1/3% each). BRAF mutations were class I (V600E) (73%), Class II (13%), and class III (13%). All BRAF V600E+ cancer pts were previously treated with ≥1 approved BRAFi and all BRAF V600E+ mel pts also were previously treated with ≥1 immune checkpoint inhibitor. PF-07799933 was well-tolerated as monotherapy or combination. There were no DLTs and the MTD was not reached. Treatment-emergent adverse events (TEAEs) in ≥3 pts for monotherapy were fatigue (any grade 44%/grade ≥3 0%), headache (28%/0%), vision blurred (22%/6%), and lipase increased (16%/0%). The most common TEAEs for combination were peripheral edema (33%/0%), acneiform rash, diarrhea, and fatigue (each 28%/0%). The AE profile was consistent with less paradoxical signaling activation. PK-guided dose escalation enabled PF-07799933 efficacious concentrations to be reached by dose level 3 (225 mg BID), together with multiple confirmed responses in BRAF V600E+ cancer pts (n=4/7 at 225 mg BID ± binimetinib, includes 1 complete response CR in a BRAF V600E+ PBT pt) systemically, in the brain, and all after failure of approved BRAF inhibitors. A 5th confirmed response (2nd BRAF V600E+ PBT pt) occurred after data cutoff. This includes, to our knowledge, the first evidence of efficacy in a BRAF V600E+ pt with a dimerizing BRAF splice variant. A BRAF G466E+ (class III) adenoid cystic carcinoma pt had a molecular CR in ctDNA. CONCLUSION PF-07799933 treatment was associated with anti-tumor activity against BRAF V600- and non-V600-mutant cancers preclinically and in treatment-refractory pts. The novel, rapid PK-informed dose escalation design provides a new paradigm for accelerating testing of next-generation targeted therapies early in clinical development. TRIAL REGISTRATION NUMBER NCT05355701 Citation Format: Rona Yaeger, Meredith McKean, Rizwan Haq, Joseph T. Beck, Matthew H. Taylor, Jonathan Cohen, Daniel Bowles, Shirish M. Gadgeel, Catalin Mihalcioiu, Kyriakos P. Papadopoulos, Eli L. Diamond, Keren B. Sturtz, Gang Feng, Stefanie K. Drescher, Micaela B. Reddy, Bhaswati Sengupta, Arnab K. Maity, Suzy A. Brown, Anurag Singh, Eric N. Brown, Brian R. Baer, Jim Wong, Tung-Chung Mou, Wen I. Wu, Dean Kahn, Sunyana Gadal, Neal Rosen, John J. Gaudino, Patrice A. Lee, Dylan P. Hartley, Stephen Michael Rothenberg. Phase 1 trial of PF-07799933 (ARRY-440), a next-generation BRAF inhibitor, for BRAF-mutant cancers abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr CT178.