RAF, a core signaling component of the MAPK kinase cascade, is often mutated in various cancers, including melanoma, lung, and colorectal cancers. The approved inhibitors were focused on targeting the BRAFV600E mutation that results in constitutive activation of kinase signaling through the monomeric protein (Class I). However, these inhibitors also paradoxically activate kinase signaling of RAF dimers, resulting in increased MAPK signaling in normal tissues. Recently, significant attention has turned to targeting RAF alterations that activate dimeric signaling (class II and III BRAF and NRAS). However, the discovery of a potent and selective inhibitor with biopharmaceutical properties suitable to sustain robust target inhibition in the clinical setting has proven challenging. Herein, we report the discovery of exarafenib (15), a highly potent and selective inhibitor that intercepts the RAF protein in the dimer compatible αC-helix-IN conformation and demonstrates anti-tumor efficacy in preclinical models with BRAF class I, II, and III and NRAS alterations.

Background: MAPK activating mutations are common in melanoma, with 40% of cases attributed to oncogenic BRAF mutations and 20-25% NRAS mutations. Secondary MAPK activation is a known resistance mechanism to approved BRAF inhibitors in BRAFV600 melanoma. While BRAF inhibitors are approved for Class I BRAFV600 melanomas, patients with dimer-driven BRAF Class II/III and RAF1-dependent NRAS activated melanomas lack approved targeted therapy. Development of next-gen pan-RAF inhibitors targeting all RAF proteins and mutant dimers remains a priority. Emerging clinical data from pan-RAF inhibitors combined with MEK inhibitors suggests increased benefit for MAPK-altered melanoma patients. Exarafenib (KIN-2787) is a clinical stage, novel, highly selective pan-RAF inhibitor designed to be effective in RAF-dependent cancers.Methods: KIN-2787 was evaluated using enzyme assays across the human kinome and activity against oncogenic RAF alterations were validated in BaF3 cells. MAPK pathway suppression and cell growth inhibition were assessed across a panel of human tumor cell lines. Combination dose matrices were performed with KIN-2787 and binimetinib (bini) to evaluate synergistic cell growth inhibition. Extended cell growth studies were performed by Incucyte. In vivo KIN-2787 efficacy was evaluated in cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) models of human BRAF and NRAS mutant cancer.Results: Exarafenib demonstrated exceptional kinome selectivity with minimal off-target kinases significantly inhibited relative to BRAF. Exarafenib potently inhibited a broad panel of oncogenic BRAF mutations in biochemical and BaF3 cell assays. Functional MAPK signaling and viability studies in human tumor cell lines highlighted exarafenib activity in BRAF and NRAS mutant melanoma with minimal activity in normal (BRAF WT) cells. Synergy with the MEK inhibitor bini was determined and the exarafenib + bini combination durably inhibited growth in NRAS mutant melanoma cell lines. In line with cellular studies, treatment with exarafenib demonstrated significant tumor growth inhibition at 30 mg/kg BID in CDX and PDX models of human NRAS mutant melanoma. 10 mg/kg BID exarafenib combined with a clinically relevant dose of bini resulted in combination benefit and durable suppression of the MAPK pathway, relative to either agent alone.Conclusions: The superior kinome selectivity of exarafenib and its activity across multiple RAF-dependent melanoma models position it as a potentially class-leading pan-RAF inhibitor. In addition to efficacy in BRAF mutant tumors, these data support use of exarafenib in combination therapy with MEK inhibitors in NRAS mutant melanoma. A Ph I dose escalation clinical trial evaluating the safety and efficacy of exarafenib in monotherapy and in combination with binimetinib is ongoing (NCT04913285). Citation Format: Tim S. Wang, Catherine Lee, Paul Severson, Robert J. Pelham, Richard Williams, Nichol L. G. Miller. Exarafenib (KIN-2787) is a potent, selective pan-RAF inhibitor with activity in preclinical models of BRAF class II/III mutant and NRAS mutant melanoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4927.

Abstract Background: MAPK activating mutations are common in melanoma, with 40% of cases attributed to oncogenic BRAF mutations and 20-25% NRAS mutations. Secondary MAPK activation is a known resistance mechanism to approved BRAF inhibitors in BRAFV600 melanoma. While BRAF inhibitors are approved for Class I BRAFV600 melanomas, patients with dimer-driven BRAF Class II/III and RAF1-dependent NRAS activated melanomas lack approved targeted therapy. Development of next-gen pan-RAF inhibitors targeting all RAF proteins and mutant dimers remains a priority. Emerging clinical data from pan-RAF inhibitors combined with MEK inhibitors suggests increased benefit for MAPK-altered melanoma patients. Exarafenib (KIN-2787) is a clinical stage, novel, highly selective pan-RAF inhibitor designed to be effective in RAF-dependent cancers.Methods: KIN-2787 was evaluated using enzyme assays across the human kinome and activity against oncogenic RAF alterations were validated in BaF3 cells. MAPK pathway suppression and cell growth inhibition were assessed across a panel of human tumor cell lines. Combination dose matrices were performed with KIN-2787 and binimetinib (bini) to evaluate synergistic cell growth inhibition. Extended cell growth studies were performed by Incucyte. In vivo KIN-2787 efficacy was evaluated in cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) models of human BRAF and NRAS mutant cancer.Results: Exarafenib demonstrated exceptional kinome selectivity with minimal off-target kinases significantly inhibited relative to BRAF. Exarafenib potently inhibited a broad panel of oncogenic BRAF mutations in biochemical and BaF3 cell assays. Functional MAPK signaling and viability studies in human tumor cell lines highlighted exarafenib activity in BRAF and NRAS mutant melanoma with minimal activity in normal (BRAF WT) cells. Synergy with the MEK inhibitor bini was determined and the exarafenib + bini combination durably inhibited growth in NRAS mutant melanoma cell lines. In line with cellular studies, treatment with exarafenib demonstrated significant tumor growth inhibition at 30 mg/kg BID in CDX and PDX models of human NRAS mutant melanoma. 10 mg/kg BID exarafenib combined with a clinically relevant dose of bini resulted in combination benefit and durable suppression of the MAPK pathway, relative to either agent alone.Conclusions: The superior kinome selectivity of exarafenib and its activity across multiple RAF-dependent melanoma models position it as a potentially class-leading pan-RAF inhibitor. In addition to efficacy in BRAF mutant tumors, these data support use of exarafenib in combination therapy with MEK inhibitors in NRAS mutant melanoma. A Ph I dose escalation clinical trial evaluating the safety and efficacy of exarafenib in monotherapy and in combination with binimetinib is ongoing (NCT04913285). Citation Format: Tim S. Wang, Catherine Lee, Paul Severson, Robert J. Pelham, Richard Williams, Nichol L. G. Miller. Exarafenib (KIN-2787) is a potent, selective pan-RAF inhibitor with activity in preclinical models of BRAF class II/III mutant and NRAS mutant melanoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4927.

Abstract Background: In the US in 2021, invasive melanoma will account for an estimated 106,000 new cases and > 7,000 deaths. Somatic mutations that activate the MAPK signaling pathway are a leading cause of melanoma with 50% harboring oncogenic BRAF alterations and another 20% with activating NRAS mutations. Of note, NRAS mutant melanoma has been shown to be dependent upon RAF signaling via CRAF dimers for downstream activation of MEK/ERK. While targeted therapies are approved for V600 (Class I, monomer-driven) BRAF mutant melanoma, no approved targeted therapy exists for patients with melanoma driven by Class II or Class III dimer-dependent BRAF alterations or NRAS mutations. KIN-2787 is a novel, orally available, potent, and selective pan-RAF inhibitor designed to be effective in RAF-dependent cancers, including all classes of BRAF alterations, by targeting mutant BRAF monomers and RAF dimers, regardless of isoform. Methods: KIN-2787 activity was assessed by suppression of downstream MAPK pathway signaling and subsequent cell growth inhibition in a panel of human melanoma cell lines. In vivo KIN-2787 efficacy was evaluated in BRAF and NRAS mutant melanoma cell- and patient-derived xenograft models. Results: KIN-2787 cellular activity was measured by inhibition of ERK phosphorylation across a panel of melanoma cell lines, including those harboring Class I BRAF alterations, Class II and III BRAF alterations, NRAS mutations, KRAS mutations, and wild type RAF/RAS. In contrast to vemurafenib, an approved BRAF inhibitor with activity limited to Class I BRAF alterations, KIN-2787 was active across all classes of BRAF mutant melanoma cells (EC50 values < 100 nM). NRAS and KRAS mutant cell lines were moderately responsive to KIN-2787 inhibition. Melanoma cells expressing wild type RAS/RAF were the least sensitive to MAPK pathway inhibition by KIN-2787. KIN-2787 also inhibited cell proliferation in BRAF and NRAS mutant melanoma in 2D and 3D cell cultures. Daily KIN-2787 treatment resulted in significant tumor growth inhibition in human melanoma xenograft models bearing Class I, II and III BRAF alterations as well as NRAS mutations and was associated with MAPK pathway suppression. Additionally, KIN-2787 was efficacious in a pre-/post-treatment melanoma PDX pair in which the original tumor was Class I BRAF V600E but acquired a Class II BRAF kinase domain duplication upon progression on dabrafenib + trametinib. Details from the above findings will be presented at the meeting. Conclusions: KIN-2787 is a next-generation, pan-RAF inhibitor with in vitro and in vivo activity against human melanoma driven by BRAF and/or NRAS mutations. Data supports KIN-2787 use in acquired BRAF dimer-dependent resistance to BRAF+MEK inhibitor therapy. A Phase I dose escalation and expansion clinical trial evaluating the safety and efficacy of KIN-2787 is ongoing (NCT04913285). Citation Format: Nichol L. G. Miller, Tim S. Wang, Paul Severson, Ping Jiang, Michelle Perez, Noel Timple, Toufike Kanouni, Aleksandra Franovic, Eric S. Martin, Eric Murphy. Antitumor activity of KIN-2787, a next-generation pan-RAF inhibitor, in preclinical models of human RAF/RAS mutant melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2674.

Abstract Overcoming checkpoints to cell cycle control is the basis for tumorigenesis and malignant growth. Therefore, models that recapitulate clinically relevant cell cycle deregulation enhance our understanding of defined tumors subsets. Specifically, pancreatic ductal adenocarcinomas (PDAs) frequently delete the 9p21 locus which contains the cyclin dependent kinase (CDK) inhibitors CDKN2A (p16, p14) and CDKN2B (p15), as well as methylthioadenosine phosphorylase (MTAP), a metabolic gene required for methionine salvage from methylthioadenosine. No model currently exists that accurately represents loss of the entire locus in a relevant disease context. Moreover, the contribution of MTAP to tumor progression remains largely unknown. Therefore, we have developed a novel genetically engineered mouse model (GEMM) of PDA which combines loss of the orthologous murine 9p21 region (4qC4) with activated KRAS [Pdx-Cre; LSL-KrasG12D; 9p21L/L (K9C)], which results in rapid adenocarcinoma formation and subsequent mortality in mice homozygous for 9p21 deletion. Single-cell RNA sequencing revealed a remarkable level of inter- and intra-tumoral heterogeneity, including a significant immune and stromal component that contribute to tumor growth and progression. Additionally, K9C derived cell lines are responsive to Pfizer's first-in class CDK2/4/6 selective inhibitor while displaying de novo resistance to CDK4/6 inhibitor Palbociclib. Allograft and single-cell RNA sequencing experiments corroborated these findings and implicate Myc in contributing to CDK2/4/6i sensitivity. Furthermore, phenotypic-based screens revealed synthetic-lethal hits with 9p21 loss, indicating ample opportunities for combination strategies in this select patient population. Thus, we show that the K9C model recapitulates salient aspects of PDA and is amenable to novel therapeutic intervention strategies that may aid in improving the outcomes of patients with this precise genetic background. *All procedures performed on animals were in accordance with regulations and established guidelines and were reviewed and approved by an Institutional Animal Care and use committee Citation Format: Christina Adams, Lynn Wang, Tim S. Wang, Nichol Miller, Elizabeth McMillan, Monica Ramstetter, John Chionis, Koleen Eisele, Jonathan Almaden, Timothy Affolter, Smitha Pillai, Todd VanArsdale, Chris Dillon, Stephen G. Dann. A novel mouse model of pancreatic cancer reveals new insights into cell cycle deregulation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2960.