RAF Inhibitors Research Articles

Elucidating the Morphogenic and Signaling Roles of Defined Growth Factors Controlling Human Endothelial Cell Lumen Formation Versus Sprouting Behavior

Five growth factors [ie, insulin, fibroblast growth factor-2 (FGF-2), stem cell factor, IL-3, and stromal-derived factor 1α] in combination are necessary for human endothelial cells (ECs) to undergo tube morphogenesis, a process requiring both lumen formation and sprouting behavior. This study investigated why these factors are required by subdividing the factors into 4 separate groups: insulin-only, insulinand FGF-2, no FGF-2 (all factors but without FGF-2), and all factors. The study found that the insulin-only condition failed to support EC morphogenesis or survival, the insulinand FGF-2 condition supported primarily EC lumen formation, and the no FGF-2 condition supported EC sprouting behavior. By comparison, the all-factors condition more strongly stimulated both EC lumen formation and sprouting behavior, and signaling analysis revealed prolonged stimulation of multiple promorphogenic signals coupled with inhibition of proregressive signals. Pharmacologic inhibition of Jak kinases more selectively blocked EC sprouting behavior, whereas inhibition of Raf, phosphatidylinositol 3-kinase, and Akt kinases showed selective blockade of lumen formation. Inhibition of Src family kinases and Notch led to increased sprouting coupled to decreased lumen formation, whereas inhibition of Pak, Mek, and mammalian target of rapamycin kinases blocked both sprouting and lumen formation. These findings reveal novel downstream biological and signaling activities of defined factors that are required for the assembly of human EC-lined capillary tube networks.

Differentiating Benign from Malignant Thyroid Tumors by Kinase Activity Profiling and Dabrafenib BRAF V600E Targeting.

Differentiated non-medullary thyroid cancer (NMTC) can be effectively treated by surgery followed by radioactive iodide therapy. However, a small subset of patients shows recurrence due to a loss of iodide transport, a phenotype frequently associated with BRAF V600E mutations. In theory, this should enable the use of existing targeted therapies specifically designed for BRAF V600E mutations. However, in practice, generic or specific drugs aimed at molecular targets identified by next generation sequencing (NGS) are not always beneficial. Detailed kinase profiling may provide additional information to help improve therapy success rates. In this study, we therefore investigated whether serine/threonine kinase (STK) activity profiling can accurately classify benign thyroid lesions and NMTC. We also determined whether dabrafenib (BRAF V600E-specific inhibitor), as well as sorafenib and regorafenib (RAF inhibitors), can differentiate BRAF V600E from non-BRAF V600E thyroid tumors. Using 21 benign and 34 malignant frozen thyroid tumor samples, we analyzed serine/threonine kinase activity using PamChip®peptide microarrays. An STK kinase activity classifier successfully differentiated malignant (26/34; 76%) from benign tumors (16/21; 76%). Of the kinases analyzed, PKC (theta) and PKD1 in particular, showed differential activity in benign and malignant tumors, while oncocytic neoplasia or Graves' disease contributed to erroneous classifications. Ex vivo BRAF V600E-specific dabrafenib kinase inhibition identified 6/92 analyzed peptides, capable of differentiating BRAF V600E-mutant from non-BRAF V600E papillary thyroid cancers (PTCs), an effect not seen with the generic inhibitors sorafenib and regorafenib. In conclusion, STK activity profiling differentiates benign from malignant thyroid tumors and generates unbiased hypotheses regarding differentially active kinases. This approach can serve as a model to select novel kinase inhibitors based on tissue analysis of recurrent thyroid and other cancers.

BRAFΔβ3-αC in-frame deletion mutants differ in their dimerization propensity, HSP90 dependence, and druggability.

In-frame BRAF exon 12 deletions are increasingly identified in various tumor types. The resultant BRAFΔβ3-αC oncoproteins usually lack five amino acids in the β3-αC helix linker and sometimes contain de novo insertions. The dimerization status of BRAFΔβ3-αC oncoproteins, their precise pathomechanism, and their direct druggability by RAF inhibitors (RAFi) has been under debate. Here, we functionally characterize BRAFΔLNVTAP>F and two novel mutants, BRAFdelinsFS and BRAFΔLNVT>F, and compare them with other BRAFΔβ3-αC oncoproteins. We show that BRAFΔβ3-αC oncoproteins not only form stable homodimers and large multiprotein complexes but also require dimerization. Nevertheless, details matter as aromatic amino acids at the deletion junction of some BRAFΔβ3-αC oncoproteins, e.g., BRAFΔLNVTAP>F, increase their stability and dimerization propensity while conferring resistance to monomer-favoring RAFi such as dabrafenib or HSP 90/CDC37 inhibition. In contrast, dimer-favoring inhibitors such as naporafenib inhibit all BRAFΔβ3-αC mutants in cell lines and patient-derived organoids, suggesting that tumors driven by such oncoproteins are vulnerable to these compounds.

Protomer selectivity of type II RAF inhibitors within the RAS/RAF complex

RAF dimer inhibitors offer therapeutic potential in RAF- and RAS-driven cancers. The utility of such drugs is predicated on their capacity to occupy both RAF protomers in the RAS-RAF signaling complex. Here we describe a method to conditionally quantify drug-target occupancy at selected RAF protomers within an active RAS-RAF complex in cells. RAF target engagement can be measured in the presence or absence of any mutant KRAS allele, enabling the high-affinity state of RAF dimer inhibitors to be quantified in the cellular milieu. The intracellular protomer selectivity of clinical-stage type II RAF inhibitors revealed that ARAF protomer engagement, but not engagement of BRAF or CRAF, is commensurate with inhibition of MAPK signaling in various mutant RAS cell lines. Our results support a fundamental role for ARAF in mutant RAS signaling and reveal poor ARAF protomer vulnerability for a cohort of RAF inhibitors undergoing clinical evaluation.

Combined RAF and MEK Inhibition to Treat Activated Non-V600 BRAF-Altered Advanced Cancers.

Cancers with non-V600 BRAF-activating alterations have no matched therapy. Preclinical data suggest that these tumors depend on ERK signaling; however, clinical response to MEK/ERK inhibitors has overall been low. We hypothesized that a narrow therapeutic index, driven by ERK inhibition in healthy (wild-type) tissues, limits the efficacy of these inhibitors. As these mutants signal as activated dimers, we further hypothesized that RAF inhibitors given concurrently would improve the therapeutic index by opposing ERK inhibition in normal tissues and not activate ERK in the already activated tumor. Using cell lines and patient-derived xenografts, we evaluated the effect of RAF inhibition, alone and in combination with MEK/ERK inhibitors. We then undertook a phase I/II clinical trial of a higher dose of the MEK inhibitor binimetinib combined with the RAF inhibitor encorafenib in patients with advanced cancer with activating non-V600 BRAF alterations. RAF inhibition led to modest inhibition of signaling and growth in activated non-V600 BRAF preclinical models and allowed higher dose of MEK/ERK inhibitors in vivo for more profound tumor regression. Fifteen patients received binimetinib 60 mg twice daily plus encorafenib 450 mg daily (6 gastrointestinal primaries, 6 genitourinary primaries, 3 melanoma, and 2 lung cancer; 7 BRAF mutations and 8 BRAF fusions). Treatment was well tolerated without dose-limiting toxicities. One patient had a confirmed partial response, 8 had stable disease, and 6 had radiographic or clinical progression as best response. On-treatment biopsies revealed incomplete ERK pathway inhibition. Combined RAF and MEK inhibition does not sufficiently inhibit activated non-V600 BRAF-mutant tumors in patients.

A target map of clinical combination therapies in oncology: an analysis of clinicaltrials.gov

Combination therapies have taken center stage for cancer treatment, however, there is a lack of a comprehensive portrait to quantitatively map the current clinical combination progress. This study aims to capture clinical combination therapies of the validated FDA-approved new oncology drugs by a macro data analysis and to summarize combination mechanisms and strategies in the context of the existing literature. A total of 72 new molecular entities or new therapeutic biological products for cancer treatment approved by the FDA from 2017 to 2021 were identified, and the data on their related 3334 trials were retrieved from the database of ClinicalTrials.gov. Moreover, these sampled clinical trials were refined by activity status and combination relevance and labeled with the relevant clinical arms and drug combinations, as well as drug targets and target pairs. Combination therapies are increasingly prevalent in clinical trials of new oncology drugs. From retrospective work, existing clinical combination therapies in oncology are driven by different patterns (i.e., rational design and industry trends). The former can be represented by mechanism-based or structure-based combinations, such as targeting different domains of HER2 protein or in-series co-targeting in RAF plus MEK inhibitors. The latter is an empirically driven strategy, including redundant combinations in hot targets, such as PD-1/PD-L1, PI3K, CDK4/6, and PARP. Because of an explosion in the number of clinical trials and the resultant shortage of available patients, it is essential to rationally design drug combinations.

A Combination of Conformation-Specific RAF Inhibitors Overcome Drug Resistance Brought about by RAF Overexpression.

Cancer cells often adapt to targeted therapies, yet the molecular mechanisms underlying adaptive resistance remain only partially understood. Here, we explore a mechanism of RAS/RAF/MEK/ERK (MAPK) pathway reactivation through the upregulation of RAF isoform (RAFs) abundance. Using computational modeling and in vitro experiments, we show that the upregulation of RAFs changes the concentration range of paradoxical pathway activation upon treatment with conformation-specific RAF inhibitors. Additionally, our data indicate that the signaling output upon loss or downregulation of one RAF isoform can be compensated by overexpression of other RAF isoforms. We furthermore demonstrate that, while single RAF inhibitors cannot efficiently inhibit ERK reactivation caused by RAF overexpression, a combination of two structurally distinct RAF inhibitors synergizes to robustly suppress pathway reactivation.

Raf/MEK/ERK Signaling Pathway Is Involved in the Inhibition of Glioma Cell Proliferation and Invasion in the Ketogenic Microenvironment.

A high-fat, low-carbohydrate ketogenic diet has been used to treat malignant glioma, in which the Raf/MEK/ERK signaling pathway is overactivated. However, whether the Raf/MEK/ERK signaling pathway is involved in the therapeutic effect of ketone bodies remains unknown. In this study, we investigated the effects of a major ketone body, 3-hydroxybutyric acid (3-HBA), on the proliferation and metastasis of malignant glioblastoma cells and the underlying mechanism. Two human malignant glioblastoma cell lines (U87 and U251) were treated with different concentrations of 3-HBA with or without the Raf inhibitor PAF C-16 for 24 h. Cell proliferation, cell cycle, cell invasion, and phospholipase D1 (PLD1) activity were determined. Protein and gene expression levels of Raf/MEK/ERK signaling pathway members were examined. 3-HBA significantly decreased cell proliferation, invasion, and intracellular PLD1 activity in both U87 and U251 glioblastoma cell lines. 3-HBA treatment significantly increased the proportion of cells in the G1 phase and decreased the proportion of cells in S phase in U87 cells. In the U251 line, the proportion of treated cells in S phase was increased and proportion of cells in G2 was decreased. 3-HBA treatment also significantly decreased the protein expression levels of Raf, MEK, p-MEK, ERK, p-ERK, and PLD1 while increasing p53 expression; an effect that was similar to treatment with the Raf inhibitor. Co-treatment of 3-HBA with the Raf inhibitor further enhanced the effects of the 3-HBA in both cell lines. We confirmed that a ketogenic microenvironment can inhibit glioma cell proliferation and invasion by downregulating the expression of PLD1 through the Raf/MEK/ERK signaling pathway.

Targeting RAF Isoforms and Tumor Microenvironments in RAS or BRAF Mutant Colorectal Cancers with SJ-C1044 for Anti-Tumor Activity.

Colorectal cancer (CRC) is a significant global health issue characterized by a high prevalence of KRAS gene mutations. The RAS/MAPK pathway, involving KRAS, plays a crucial role in CRC progression. Although some RAS inhibitors have been approved, their efficacy in CRC is limited. To overcome these limitations, pan-RAF inhibitors targeting A-Raf, B-Raf, and C-Raf have emerged as promising therapeutic strategies. However, resistance to RAF inhibition and the presence of an immunosuppressive tumor microenvironment (TME) pose additional obstacles to effective therapy. Here, we evaluated the potential of a novel pan-RAF inhibitor, SJ-C1044, for targeting mutant KRAS-mediated signaling and inhibiting CRC cell proliferation. Notably, SJ-C1044 also exhibited inhibitory effects on immunokinases, specifically, CSF1R, VEGFR2, and TIE2, which play crucial roles in immune suppression. SJ-C1044 demonstrated potent antitumor activity in xenograft models of CRC harboring KRAS or BRAF mutations. Importantly, treatment with SJ-C1044 resulted in increased infiltration of T cells and reduced presence of tumor-associated macrophages and regulatory T cells within the TME. Thus, SJ-C1044 shows immunomodulatory potential and the ability to enhance antitumor responses. The study underscores the therapeutic potential of SJ-C1044 as a novel pan-RAF inhibitor capable of targeting oncogenic signaling pathways and overcoming immune suppression in CRC.

The combination of osimertinib with Raf inhibitor overcomes osimertinib resistance induced by KRAS amplification in EGFR-mutated lung cancer cells

Osimertinib is a third-generation epidermal growth factor receptor (EGFR)1 tyrosine kinase inhibitor (TKI) approved for the treatment of EGFR-positive patients exhibiting a T790 M resistance mutation after treatment with an earlier generation of EGFR TKIs. However, resistance to osimertinib inevitably develops despite its efficacy, and the resistance mechanisms are complex and not fully understood. We established cell lines with acquired resistance to osimertinib from gefitinib- or erlotinib-resistant NSCLC cells using a dose-escalation method, and found that they had upregulated levels of phosphorylated ERK1/2. Targeted next-generation sequencing of 143 genes was performed, and interestingly, amplification of KRAS was observed in osimertinib-resistant cells. Transfection of siRNA against the KRAS gene notably reduced the activation of ERK1/2 and AKT and significantly enhanced the induction of apoptosis by osimertinib treatment in osimertinib-resistant cells. LY3009120, a RAF inhibitor, showed a significant synergistic effect with osimertinib on apoptotic cell death in osimertinib-resistant cells. Combined treatment with osimertinib and LY3009120 also demonstrated remarkable synergistic anti-tumor activity in mouse xenografts of these cells. This could be a potential new treatment option for KRAS amplification-induced osimertinib failure.

Analysis of RAS and drug induced homo- and heterodimerization of RAF and KSR1 proteins in living cells using split Nanoluc luciferase

The dimerization of RAF kinases represents a key event in their activation cycle and in RAS/ERK pathway activation. Genetic, biochemical and structural approaches provided key insights into this process defining RAF signaling output and the clinical efficacy of RAF inhibitors (RAFi). However, methods reporting the dynamics of RAF dimerization in living cells and in real time are still in their infancy. Recently, split luciferase systems have been developed for the detection of protein–protein-interactions (PPIs), incl. proof-of-concept studies demonstrating the heterodimerization of the BRAF and RAF1 isoforms. Due to their small size, the Nanoluc luciferase moieties LgBiT and SmBiT, which reconstitute a light emitting holoenzyme upon fusion partner promoted interaction, appear as well-suited to study RAF dimerization. Here, we provide an extensive analysis of the suitability of the Nanoluc system to study the homo- and heterodimerization of BRAF, RAF1 and the related KSR1 pseudokinase. We show that KRASG12V promotes the homo- and heterodimerization of BRAF, while considerable KSR1 homo- and KSR1/BRAF heterodimerization already occurs in the absence of this active GTPase and requires a salt bridge between the CC-SAM domain of KSR1 and the BRAF-specific region. We demonstrate that loss-of-function mutations impairing key steps of the RAF activation cycle can be used as calibrators to gauge the dynamics of heterodimerization. This approach identified the RAS-binding domains and the C-terminal 14–3-3 binding motifs as particularly critical for the reconstitution of RAF mediated LgBiT/SmBiT reconstitution, while the dimer interface was less important for dimerization but essential for downstream signaling. We show for the first time that BRAFV600E, the most common BRAF oncoprotein whose dimerization status is controversially portrayed in the literature, forms homodimers in living cells more efficiently than its wildtype counterpart. Of note, Nanoluc activity reconstituted by BRAFV600E homodimers is highly sensitive to the paradox-breaking RAFi PLX8394, indicating a dynamic and specific PPI. We report the effects of eleven ERK pathway inhibitors on RAF dimerization, incl. third-generation compounds that are less-defined in terms of their dimer promoting abilities. We identify Naporafenib as a potent and long-lasting dimerizer and show that the split Nanoluc approach discriminates between type I, I1/2 and II RAFi.Ah1kwifp3aoZnF_eXdbERzVideo

TRLS-13. NOVEL PAN-RAF INHIBITOR BELVARAFENIB AS A PROMISING TARGETED THERAPY FOR BRAF-ALTERED PEDIATRIC LOW-GRADE GLIOMAS

Abstract In recent years targeted therapy has improved the outcome of childhood cancer patients. The second most common pediatric cancers are central nervous system (CNS) tumors, particularly low-grade gliomas (LGGs). Approximately 15-20% of pediatric LGGs cases present with oncogenic mutations that alter the RAS/mitogen-activated protein kinase (MAPK) signaling pathway by the B-RAF kinase constitutive activation. Only five RAF inhibitors are FDA-approved as cancer treatments and with limited-to-no data for pediatric patients. The lack of pediatric data results from limited access to childhood clinical trials, although there has been an increase in clinical trials for RAF inhibitors and combinations for children. However, there is a pressing need for alternative therapeutic approaches for pediatric patients with BRAF-altered LGGs. Hence, this study proposes a type II pan-RAF inhibitor called Belvarafenib (BEV) as a potential therapeutic candidate. Belvarafenib has shown viability effects at 500fM to 5nM in a PRKAR2B/BRAF fusion patient-derived cell line with a calculated cytotoxic concentration 50 (CC50) of 2nM. The expression of apoptotic markers will be measured to characterize the mechanism of cell death through BEV’s direct stimulation of the MAPK signaling or via an alternative pathway. Understanding the allosteric properties of the RAF inhibitor Belvarafenib enables the opportunity to have effective and well-tolerated alternative therapies for BRAF-altered tumors in children. Thus, this preliminary study intends to profile the effectivity of Belvarafenib in cell culture and help design in vivo experiments with the potential to establish clinical trials in combination with other potential therapeutic agents.

LGG-04. CLINICALLY RELEVANT MODELING OF FUSION-DRIVEN PEDIATRIC LOW GRADE GLIOMAS USING DROSOPHILA MELANOGASTER

Abstract Pediatric low-grade gliomas (PLGGs) are the most common brain tumors in children, with varying degrees of brain invasion. Recent whole-genome sequencing has identified a rare gene fusion involving RAF1, a RAF isoform. Unlike other RAF fusions, RAF1 fusions are resistant to existing RAF inhibitors. Therefore, aside from surgical resection with adjuvant chemotherapy and radiation therapy, there are few targeted therapeutic alternatives for RAF1-fusion-driven PLGGs. Despite the prevalence and challenges this disease presented, our understanding of PLGGs was limited by a lack of genetic models. We ultimately picked Drosophila melanogaster as our model organism due to the conservation of major signaling pathways between flies and humans. Furthermore, this connection between humans and flies, coupled with other technical advantages associated with this model organism, like short generation cycle and its powerful genetic toolbox, makes Drosophila melanogaster an ideal organism to study the genesis and progression of PLGGs. With the help of the GAL4/UAS system, we established four fusion-driven PLGG fly genetic models and found that glial overexpression of QKI-RAF1, a fusion gene in pilocytic astrocytomas, induces an invasion-like phenotype with aberrant glial migration. This migration defect was suppressed by glial overexpression of repulsive guidance signaling receptors Robo2 or PlexA/B, indicating the dysregulation of repulsive guidance signaling pathways. Immunostaining coupled with quantitative analysis revealed that Robo2 expression is downregulated in migrating tumor cells in flies, which is recapitulated in mouse astrocytes overexpressing QKI-RAF1 and PLGG patients with RAF fusions. We further broaden our findings by profiling the tumor transcriptomes, revealing potential downstream effectors, including the G protein-coupled receptor GPR180/CG9304, and inhibition of which suppresses tumor invasion in flies. Taken together, we present the PLGG fly model system, leading to the discovery of Robo2, Plexins, and GPR180/CG9304 as potential therapeutic targets.

RAF-inhibitor rechallenge therapy in BRAF aberrated pan-cancers: RE-RAFFLE study.

3105 Background: Prior studies have demonstrated clinical benefit with rechallenging the RAF pathway in melanoma with prior exposure to BRAF inhibitors. Purpose of this study was to explore antitumor activity and outcomes of BRAF aberrated solid tumors retreated with RAF inhibitors (RAFi). Methods: Between January 2010 and November 2022, 44 pts with BRAF alterations [ V600E (42); V600K (1); K601Q (1)] who received RAFi as monotherapy or in combination were rechallenged with a second RAFi with or without other therapies at a single tertiary cancer center. All received therapy as part of standard of care or investigational (INV) regimens. Primary objectives: objective response rate (ORR), overall survival (OS) and progression-free survival (PFS) on rechallenge. Results: Median age: 54.5 (25-76) with predominantly Caucasian pts (36; 82%) and males (26; 59%). Tumor types: melanoma (16; 36%), colon (10; 23%), thyroid (4; 9%); brain (4; 9%) and others (10; 23%). Median treatment duration was 7 months (m) for first RAFi (RAF1i) and 2.8m with second RAFi (RAF2i) while median time to RAF2i was 3.3m. Best ORR to rechallenge with RAF2i was partial response (PR) (8; 18.1%), stable disease (SD) (16; 36%) and progressive disease (PD) (20; 45.4%) with 5 PR + 6 SD >6m. PRs were seen in thyroid (1 anaplastic; 2 papillary), 1 ovarian, 2 melanoma, 1 cholangiocarcinoma and 1 anaplastic astrocytoma with median duration of response for 2.5m. Of the 36 pts who discontinued RAF1i due to PD, 14% responded (6 PR) to RAF2i. Among 16 pts who had CR or PR on RAF1i, 5 pts had PR with RAF2i. In RAF2i group, of all pts achieving PR ( n = 8), 5 pts had other intervening therapies prior to RAF2i (immunotherapy [IO]; kinase inhibitors; chemotherapy; INV) while 3 had no interim therapies and both factors did not have significant impact on survival for RAF2i ( p=0.2). 5 responders received combination with MEKi, while 1 had MEKi + IO and 2 had monotherapy. ORR did not significantly differ between combination and monotherapy group in RAF 2i ( p=0.056). At median follow up of 20m, median OS and PFS from rechallenge was 15.5m and 2.7m. 9 pts had genomic testing post RAF1i (3 tumor;7 blood) with no new acquired aberrations and persistence of BRAF V600E mutation. Independent prognostic factors for survival at rechallenge compared to RAF1i included inferior outcomes with male gender (HR: 3.05; p=0.0089), presence of metastatic sites (HR: 3.12; p=0.036), ECOG (1 vs. 0 or 2; HR: 3.50; p<0.001) while rechallenge with combination RAF2i had a worse survival impact compared to RAF2i monotherapy (PFS: 11.6m vs 2.7m; HR: 3.6; p=0.00145). These findings need to be cautiously inferenced due to small sample size. Conclusions: Rechallenge with RAFi(s) resulted in a clinically meaningful benefit in >50% pts on efficacy (>6m in 25%) and survival outcomes. Further prospective studies are warranted to validate these findings and expand re-challenging targeted therapy options in tumor-agnostic BRAF-aberrated cancers.

Characterizing non-small cell lung cancer driven by mutations in ARAF and CRAF family members.

e15085 Background: Cancer genome screening is becoming standard clinical practice, but the number of actionable mutations detected is limited. To expand on our previous report of the possibility that ARAF S214C and CRAF S257L located in the conserved region 2 (CR2) were actionable driver mutations, we investigated responses to targeted therapies in mouse models and the prevalence of these alterations across many cancer types represented in a large real-world database of molecularly profiled patient tumors. Methods: Conditional transgenic mice that expressed human ARAF S214C or CRAF S257L in their lungs were established and treated with sorafenib or trametinib. Activation of the MAPK pathway following sorafenib or trametinib treatment was assessed in vitro by phospho-ERK IHC. DNA sequencing (592-gene or whole exome) was performed for patient samples submitted to Caris Life Sciences (Phoenix, AZ), and the prevalence of ARAF/CRAF variants was determined for each cancer type. Results: Both ARAF S214C and CRAF S257L dimerized to activate the MAPK pathway. Although a low concentration of sorafenib promoted ERK phosphorylation, a high concentration of sorafenib inhibited ERK phosphorylation. Transgenic mice rapidly developed lung adenocarcinoma when the mutant proteins were expressed. Sorafenib treatment induced tumor necrosis in both ARAF- and CRAF-mutated tumors, and 3 months of sorafenib treatment prolonged the survival of CRAF-mutant mice. Pan-tumor analysis of real-world patient samples revealed that ARAF and CRAF mutations in CR2 were found in 0.125% and 0.234% of tumors, respectively. ARAF mutations in CR2 were found in 0.415% of cholangiocarcinoma, 0.132% of colorectal cancer, and 0.173% of non-small cell lung cancer (NSCLC). CRAF mutations in CR2 were found in 0.509% of colorectal cancer, 0.502% of gastric cancer, 0.303% of NSCLC, and 0.978% of melanoma. The most prevalent CR2 mutations were ARAF S214F and CRAF S257L. Conclusions: Our in vitro results suggest ARAF S214C and CRAF S257L mutations are rare driver mutations that may be effectively treated with RAF inhibitors and warrant further investigation. [Table: see text]

The analysis of BRAF fusions characteristics in Chinese solid tumor patients.

e15073 Background: BRAF encodes a RAF kinase, which signal downstream of RAS and activate the MAPK pathway, and has emerged as a major oncogenic driver and a potential therapy target. BRAF V600E base substitution is an approved target for the BRAF inhibitors in solid tumors. BRAF gene fusions represent a different mechanism of BRAF activation. BRAF fusions have shown responses to MEK inhibitors and non-specific RAF inhibitors (eg, sorafenib) in Melanoma (NCCN). We sought to analysis of BRAF fusions characteristics in Chinese solid tumor patients to explore the possibility of therapeutic intervention in solid tumors. Methods: We comprehensively characterized BRAF fusions from next-generation sequencing (NGS) data from May 2019 to January 2023 in 80083 various solid tumors. Considering the characteristics of the receptor tyrosine kinase, we focused on the BRAF fusions which contain the kinase domain. Results: A total of 164 unique cases (70.1% (115/164) glioma and 29.9% (49/164) non-glioma with BRAF fusions) were identified. The non-glioma cohort consisted up mainly lung tumors (49%, 24/49), colorectal tumors (18.4%, 9/49), pancreatic tumors (10.2%,5/49), melanoma (9.2%, 4/49) and biliary tumors (4.1%, 2/49). In the glioma cohort, the median age of the 115 patients was 12 with a range of 0–66; 43 (37.4%) of the patients were female and 72 (62.6%) were male. On the other hand, the median age was 64 with a range of 33–82; 23 (46.9%) of the patients were female and 26 (53.10%) were male in the non-glioma cohort. In the glioma cohort, 82.4% of the partners were KIAA1549. However, the most common fusion partners were AGK (14.04%), TRIM24(14.0%), SND1(12.28%), TPK1(8.77%) in the non-glioma cohort. These BRAF fusions comprised 49 unique 5′ fusion partners, of which 51% (25) were known and 49.0% (24) were novel. 14 novel partners were TMEM176B, HMBOX1, SEMA3E, LOC441204, PDE4D, DENND2A, STIM1, TNS3, PRRC2B, BCR, MET, COL4A3BP, TPM4, ZBTB16 and 10 novel partners were intergenic region. 130 patients with BRAF fusions could be evaluated for concurrent mutations. Of interest is that no KRAS and BRAF V600E mutations were identified in the 130 cases. Conclusions: BRAF fusions were detected in 0.2% (164/80083) of Chinese solid tumor patients. 70.1% of BRAF fusion positive cases were diagnosed with glioma and 29.9% were diagnosed with non-glioma. 14 novel BRAF fusion partners were discovered. BRAF fusion is an important driver genomic alteration and occur in a mutually exclusive pattern with other activating mutations in the MAP kinase signaling pathway. BRAF fusion targeted therapies should be further explored in solid tumors.

A randomized trial of consolidation-targeted adjuvant therapy with encorafenib and cetuximab versus usual care for patients with stage II/III BRAF V600E colon cancer: Alliance for Clinical Trials in Oncology A022004.

TPS3641 Background: Patients with mismatch repair proficient (pMMR) BRAF V600E mutant high-risk stage II (T4) or stage III colon cancer have a substantial risk of recurrence despite standard adjuvant therapy. In patients with metastatic BRAF V600E mutant colorectal cancer, the combination of the RAF inhibitor encorafenib and the EGFR inhibitor cetuximab has been shown to improve overall and progression-free survival compared to standard therapy after at least one prior line of therapy. This study will evaluate if this combination improves disease-free survival (DFS) in patients with resected BRAF V600E mutant pMMR/microsatellite stable (MSS) high-risk stage II (T4) or stage III colon cancer after standard adjuvant therapy. Methods: The study has a seamless phase II/III design, enrolling a maximum of 394 patients. BRAF mutation status can be determined locally or submitted for central testing in trial pre-screening. Eligible patients will be randomized 1:1 to usual surveillance versus 6 months of treatment with encorafenib (300mg oral daily) plus cetuximab (500mg/m2 intravenous every 14 days). Stratification factors are adjuvant chemotherapy regimen (FOLFOX versus CAPOX), duration of adjuvant therapy (3 months versus > 3 months), tumor stage (T4N0 versus T1-3N1 versus T4N1/TanyN2), and ctDNA marker status (detectable versus undetectable) at randomization. Adjuvant therapy must be completed at most 8 weeks prior to registration. For the phase II component, in the ctDNA detectable cohort, the primary endpoint will be ctDNA clearance rate at 6 months, and, in the ctDNA undetectable cohort, the primary endpoint will be 6-month ctDNA recurrence-free survival, where events consist of death, recurrence, or ctDNA positivity. The primary endpoint of the phase III component is DFS, and secondary endpoints are overall survival, adverse events, and alternative DFS calculated from the date of primary resection, rather than date of study randomization. Patient reported symptoms (PRO-CTCAE) will be collected and analyzed as an exploratory endpoint, and serial blood banking will support future correlative studies. The trial will proceed to the phase III portion if either of the two endpoints in the phase II cohorts is statistically superior in patients receiving encorafenib plus cetuximab. The phase III study sample size will provide 80% power at a one-sided α of 0.05 to detect an approximately 10% improvement in the three-year DFS rate, assuming 68% in the control arm. Two interim analyses will be performed for DFS endpoint. Support: U10CA180821, U10CA180882; https://acknowledgments.alliancefound.org . U10CA180820 (ECOG-ACRIN); U10CA180868 (NRG); U10CA180888 (SWOG); Pfizer, Eli Lilly; Clinicaltrials.gov ID: NCT05710406. Clinical trial information: NCT05710406 .

Phase 1 study of the pan-RAF inhibitor tovorafenib in patients with advanced solid tumors followed by dose expansion in patients with metastatic melanoma

PurposeGenomic alterations of BRAF and NRAS are oncogenic drivers in malignant melanoma and other solid tumors. Tovorafenib is an investigational, oral, selective, CNS-penetrant, small molecule, type II pan‑RAF inhibitor. This first-in-human phase 1 study explored the safety and antitumor activity of tovorafenib.MethodsThis two-part study in adult patients with relapsed or refractory advanced solid tumors included a dose escalation phase and a dose expansion phase including molecularly defined cohorts of patients with melanoma. Primary objectives were to evaluate the safety of tovorafenib administered once every other day (Q2D) or once weekly (QW), and to determine the maximum-tolerated and recommended phase 2 dose (RP2D) on these schedules. Secondary objectives included evaluation of antitumor activity and tovorafenib pharmacokinetics.ResultsTovorafenib was administered to 149 patients (Q2D n = 110, QW n = 39). The RP2D of tovorafenib was defined as 200 mg Q2D or 600 mg QW. In the dose expansion phase, 58 (73%) of 80 patients in Q2D cohorts and 9 (47%) of 19 in the QW cohort had grade ≥ 3 adverse events. The most common of these overall were anemia (14 patients, 14%) and maculo-papular rash (8 patients, 8%). Responses were seen in 10 (15%) of 68 evaluable patients in the Q2D expansion phase, including in 8 of 16 (50%) patients with BRAF mutation-positive melanoma naïve to RAF and MEK inhibitors. In the QW dose expansion phase, there were no responses in 17 evaluable patients with NRAS mutation-positive melanoma naïve to RAF and MEK inhibitors; 9 patients (53%) had a best response of stable disease. QW dose administration was associated with minimal accumulation of tovorafenib in systemic circulation in the dose range of 400–800 mg.ConclusionsThe safety profile of both schedules was acceptable, with QW dosing at the RP2D of 600 mg QW preferred for future clinical studies. Antitumor activity of tovorafenib in BRAF-mutated melanoma was promising and justifies continued clinical development across multiple settings.ClinicalTrials.gov identifierNCT01425008.

SH3 domain-binding kinase 1 promotes proliferation and inhibits apoptosis of cervical cancer via activating the Wnt/β-catenin and Raf/ERK1/2 signaling pathways.

SH3 domain-binding kinase 1 (SBK1), is a member of the serine/threonine protein kinases family, and was confirmed to be upregulated in cervical cancer in our previous study. Nonetheless, the role of SBK1 in regulating cancer occurrence and development is unclear. In this study, the stable SBK1-knockdown and -overexpressed cell models were constructed by plasmid transfection technology. Cell viability and growth were assessed through CCK-8, colony formation, and BrdU methods. Cell cycle and apoptosis were analyzed by flow cytometry. The JC-1 staining assay was used to explore mitochondrial membrane potential. The scratch and Transwell assays were used to evaluate the cell metastatic ability. The nude mice models were utilized to explore the SBK1 expression affecting tumor growth in vivo. Our research indicated a high expression of SBK1 both in tissues and cells of cervical cancer. The proliferative, migratory, as well as invasive capacities of cervical cancer cells, were suppressed, and apoptosis was enhanced after SBK1 silence, whereas SBK1 upregulation led to opposite results. In addition, Wnt/β-catenin and Raf/ERK1/2 pathways were activated by SBK1 upregulation. Furthermore, downregulation of c-Raf or β-catenin, reversed the proliferation promotion and apoptosis inhibition effects in SBK1-overexpressed cells. The same results were observed with the use of the specific Raf inhibitor. SBK1 overexpression also contributed to tumor growth in vivo. Overall, SBK1 played a vital role in cervical tumorigenesis via activating the Wnt/β-catenin and Raf/ERK1/2 pathways.

Abstract B025: The RAF/MEK clamp avutometinib (VS-6766) enhances antitumor efficacy of KRAS G12C and G12D inhibitors through vertical inhibition of RAS, RAF and MEK. </title>

Abstract KRAS is the most frequently mutated RAS family member. Within non-small cell lung cancer (NSCLC), G12C is the most prevalent KRAS mutation (~13%) and the KRAS G12C inhibitors (G12Ci) sotorasib and adagrasib are now FDA approved. However, it has been shown that simultaneous targeting of multiple nodes in the MAPK pathway may be optimal for deeper and more durable responses. Furthermore, acquired mutations in the MAPK pathway occur clinically upon progression on sotorasib or adagrasib, altogether supporting the need for clinical combinations with G12Ci. Based on the clinical success of G12Ci, several KRAS G12D inhibitors (G12Di) are now being developed as G12D is the most prevalent KRAS mutation across human cancers including pancreatic (~28%) and colorectal (~11%) cancers. Avutometinib (VS-6766; avuto) is a RAF/MEK clamp that potently inhibits MEK kinase activity and induces a dominant negative RAF-MEK complex preventing phosphorylation of MEK by ARAF, BRAF and CRAF. This unique mechanism allows avuto to block MEK signaling without the compensatory re-activation of MEK that appears to limit the efficacy of MEK-only inhibitors. Here, we tested whether addition of avuto to G12Ci or G12Di could improve MAPK pathway blockade and anti-tumor efficacy. Avuto was synergistic with sotorasib and adagrasib in reducing viability of a panel of KRAS G12C cancer cell lines in 3D culture, and the combination of avuto + G12Ci showed improved depth and duration of MAPK pathway inhibition, stronger inhibition of cell cycle/proliferation markers and stronger activation of pro-apoptotic markers relative to G12Ci alone. In mouse models, avuto enhanced efficacy of G12Ci in KRAS G12C NSCLC xenograft models. Furthermore, avuto potentiated G12Ci efficacy in a KRAS(+/G12C);p53null NSCLC GEMM model with avuto + G12Ci combination inducing complete response in 25% of the mice. To evaluate efficacy of avuto against KRAS mutations that have been observed clinically upon acquired resistance to G12Ci, proliferation of Ba/F3 cells expressing these mutations was assessed. While avuto potently inhibited (IC50 < 15 nM) proliferation of cells bearing KRAS G12C/R68S, G12C/H95D or G12C/Y96C mutations, adagrasib showed diminished potency (IC50 ≥ 85 nM) against all 3 of these mutations and sotorasib showed diminished potency (IC50 ≥ 150 nM) against G12C/R68S and G12C/Y96C. Accordingly, avuto strongly inhibited tumor growth of an in vivo model expressing KRAS G12C/Y96D, while sotorasib was ineffective. Similarly, avuto was found to be synergistic with the G12Di MRTX1133 in reducing viability of a panel of KRAS G12D cancer cell lines, and avuto enhanced anti-tumor efficacy of MRTX1133 in KRAS G12D colorectal (CR3300) and pancreatic (PA1252) cancer PDX models. These results support ongoing clinical studies of avutometinib in combination with sotorasib (NCT05074810) and adagrasib (NCT05375994) for patients with KRAS G12C NSCLC. Additionally, these preclinical data support combination of avutometinib with a G12D inhibitor for patients with KRAS G12D colorectal or pancreatic cancers. Citation Format: Silvia Coma, Monica Musteanu, Cristina Caffarra, Alessia Mira, Enrico Patrucco, Julien Dilly, Andrew J. Aguirre, Mariano Barbacid, Chiara Ambrogio, Jonathan A. Pachter. The RAF/MEK clamp avutometinib (VS-6766) enhances antitumor efficacy of KRAS G12C and G12D inhibitors through vertical inhibition of RAS, RAF and MEK. </title> [abstract]. In: Proceedings of the AACR Special Conference: Targeting RAS; 2023 Mar 5-8; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Res 2023;21(5_Suppl):Abstract nr B025.