Combination Of MEK Inhibitors Research Articles

Reshaping the Tumor Microenvironment of KRASG12D Pancreatic Ductal Adenocarcinoma with Combined SOS1 and MEK Inhibition for Improved Immunotherapy Response.

Combination of SOS1 and MEK inhibitors increase T cell infiltration while blunting pro-immune myeloid cell maturation and highlights the need for combining KRAS cancer-targeted therapy with myeloid activation to enhance and prolong anti-tumor effects.

A Practical Review of Encorafenib and Binimetinib Therapy Management in Patients with BRAF V600E-Mutant Metastatic Non-Small Cell Lung Cancer.

According to current guidelines, targeted therapy with a combination of BRAF plus MEK inhibitors is the preferred first-line treatment for patients with BRAF V600E-mutant metastatic non-small cell lung cancer (NSCLC). In the open-label, single-arm, phase2 PHAROS trial (NCT03915951), the combination of encorafenib, a potent BRAF inhibitor, and binimetinib, a potent MEK inhibitor, demonstrated durable antitumor activity with a manageable safety profile in this patient population. On the basis of the results of this study, the combination of encorafenib plus binimetinib was approved by the US Food and Drug Administration on October 11, 2023, for patients with BRAF V600E-mutant metastatic NSCLC. In this review, we summarize the efficacy and safety of encorafenib plus binimetinib from the PHAROS study. In addition, we discuss strategies to manage adverse reactions with this combination therapy with the intent of minimizing unnecessary treatment discontinuations in these patients.

Targeted therapy in BRAFmutated aggressive papillary craniopharyngioma: a case report and overview of the literature.

Papillary craniopharyngiomas harbor the BRAF V600E mutation, which paves the way for using BRAF inhibitor molecules to treat tumors refractory to standard therapies. Single case reports confirmed the efficacy of targeted therapy. However, most reports were limited by the short follow-up. We describe the long-term course of a patient treated with dual-agent BRAF and MEK inhibitors and review the available literature. A 75-year-old male patient had recurrence of a papillary craniopharyngioma after transsphenoidal surgery and Gamma Knife radiosurgery. Review of the pathologic specimen confirmed the presence of the BRAF V600E mutation. Because of the few therapeutic options, we decided to initiate BRAF/MEK inhibitor combined therapy for six months. Rapid reduction of the tumor occurred, but three months after quitting combined medical therapy the tumor recurred. BRAF/MEK inhibitor therapy was resumed and the tumor again showed a marked reduction. The second course was maintained for 20months and the tumor showed another recurrence within three months, which, again, responded to a third course of targeted therapy. Our study confirms the excellent response of papillary craniopharyngioma to combined BRAF and MEK inhibitors. However, rapid tumor recurrence is the rule when medical therapy is stopped. Resistance to a second and third course of targeted therapy did not occur, suggesting that tumor mutations affecting the response to drugs seems an uncommon event in papillary craniopharyngioma. The exact role of targeted therapy in the treatment algorithm of papillary craniopharyngiomas has still to be refined.

Genetics-guided therapy in neuroendocrine carcinoma: response to BRAF- and MEK-inhibitors.

Metastatic neuroendocrine carcinoma (NEC) is associated with short survival. Other than platinum-based chemotherapy, there is no clear standard regimen. Current guidelines suggest that combination treatment with BRAF-inhibitors should be considered for patients with BRAF V600E-mutated NEC. However, since only eight such patients have been reported in the literature, our object was to confirm the validity of this recommendation. This was a single-center retrospective cohort study conducted at Uppsala University Hospital. The included patients 1) had a histopathologically confirmed diagnosis of NEC, 2) were diagnosed between January 1st, 2018 and December 31st, 2023, 3) had tumor tissue genetically screened by a broad next-generation sequencing (NGS) panel, and 4) showed a tumor mutation for which there is a currently available targeted therapy. We screened 48 patients diagnosed with NEC between January 1st, 2018 and December 31st, 2023. Twelve had been analyzed with a broad NGS-panel, and two had a targetable mutation. Both these patients harbored a BRAF V600E-mutated colon-NEC and were treated with BRAF- and MEK-inhibitors dabrafenib and trametinib in second-line. At first radiological evaluation (RECIST 1.1), both patients had a reduction of tumor size, which decreased by 31 and 40%. Both had short response periods, and their overall survival was 12 and 9 months. BRAF-mutated NEC is sensitive to treatment with BRAF- and MEK-inhibitor combination. These results further support that DNA sequencing should be considered as standard of care in NECs to screen for potential treatment targets.

Abstract 3864: Role of NK/TAM cross-talk on T-CD8+ recruitment and efficacy of chemoimmunotherapy and MEKi combination in "cold" tumors

Abstract In patients with non-small cell lung cancer (NSCLC), double platinum-based chemotherapy (cisplatin or carboplatin and pemetrexed) combined with the anti-PD-1 antibody has shown significant clinical benefit and has become the standard of care. In the context of so-called "cold" tumors, the immunogenic capacities of chemotherapies increase danger signals (type I IFNs, CXCL9/10) and favor both infiltration of NK/T-CD8+ cells and response to anti-PD-1. Despite the therapeutic progress represented by this new combination, some patients have limited benefit from chemo-immunotherapy, suggesting that in these patients, the immunogenic capacities of chemotherapy are limited. Recently, we were able to show that KRAS oncogene signaling restricts the ability of the cisplatin/pemetrexed doublet to induce the chemokine CXCL10, lymphocyte recruitment and sensitize to PD-L1 blockade. Thus, the addition of a MEK inhibitor (MEKi) to the chemo-immunotherapy combination restores an immunogenic signal through CXCL10, enabling T-CD8+ to infiltrate the tumor more extensively, making it more sensitive to immunotherapy. Here, we unravel the essential role of NK cells in the immunological and antitumoral effect of chemo-immunotherapy plus MEKi combination in the LLC1 preclinical lung cancer model. We showed that chemo/MEKi combination favors NK cell recruitment and activation in tumor bed through both CXCL10 and NKG2D-ligand (Rae1, Mult1). Then, IFNγ-producing NK cells trigger tumor associated macrophage switch from M2 toward M1 phenotype and amplify T-CD8+ cells recruitment through CXCL9 production by macrophages. Thus, NK cell depletion, CXCR3, CXCL9 or NKG2D-neutralization restrained chemo/MEKi therapeutic efficacy. However, IFNγ also triggers NKG2A-ligand expression (Qa-1b, HLA-E in human) which restrained NK cell activation and CD8+ T cell recruitment. Thus reducing the NKG2A pathway, by using Qa-1b-/- LLC1 cells, enhances chemo-immunotherapy/MEKi anti-tumor efficacy. Similar results were obtained in preclinical “cold” CT26 colon cancer model treated by chemo-immunotherapy. Our results underline a new role for NK cell activation to trigger TAM2/TAM1 switch, CXCL9 expression and amplify CD8 T cell recruitment in “cold” tumor. In a context of resistance to chemo-immunotherapy, MEKi or ICI targeting NK cells could be an interesting way to amplify the anti-tumor immune response by modulating both TAMs biology and the recruitment of CD8+ T cells. Citation Format: Lisa Nuttin, Charlène Latour, Solène Revy, Romain Aucagne, Guilhem Lalle, François Ghiringhelli, Emeric Limagne. Role of NK/TAM cross-talk on T-CD8+ recruitment and efficacy of chemoimmunotherapy and MEKi combination in "cold" tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3864.

Abstract 4652: Combined inhibition of MCL-1 and MEK reduces tumor growth in a triple-negative/inflammatory breast cancer, MEK-resistant xenograft mouse model

Abstract Background: Triple-negative breast cancer (TNBC) and inflammatory breast cancer (IBC) are highly aggressive subtypes of invasive breast cancer. Our previous work showed that the MEK inhibitor (MEKi) selumetinib (AZD6244) prevents lung metastasis in a xenograft model. However, clinical studies have shown that MEKi’s as single agents have only modest activity against solid tumors. Using a genome-wide synthetic lethal siRNA screening, we identified myeloid cell leukemia-1 (MCL1) as a potential contributor to selumetinib resistance. MCL-1 is an anti-apoptotic protein associated with cell immortalization, transformation, and chemoresistance in numerous cancers. We hypothesized that MCL-1 promotes MEKi resistance in TNBC/IBC and inhibition of MCL-1 in the presence of AZD6244 overcomes this MEKi resistance. Methods & Results: To understand MCL1’s role in MEKi resistance, we established two AZD6244 -resistant TNBC/IBC cell lines: MDA-MB-231-R and SUM149-R. These cells showed increased cell viability, colony formation, migration, cells in G1 phase, CD44+CD24low, mammosphere count, anchorage-independent growth and high MCL-1 expression. MCL-1’s biological role was evaluated by transient and stably knock down (KD) of MCL-1 in the resistant cells which showed decreased cell viability, colony formation, and increased apoptosis. To understand the mechanism mediating apoptosis, we examined the expression of MCL-1’s binding partners in the MCL-1-KD-R cells in the presence of AZD6244. These cells showed a high expression of the PUMA, NOXA, BAK, and BAX in the presence of AZD6244. Further, we treated resistant cells with MEKi AZD6244 and an MCL-1i (AZD5991) that confirmed restoration of MEK sensitivity in both resistant cell lines, resulting in decreased cell viability, colony formation and increased apoptosis. We compared tumor formation capability between SUM149 parental and SUM149 resistant cells by injecting them in nu/nu mice and observed a time-dependent increase (avg. 4-fold) in tumor growth with SUM149-R cells compared to parental cells (P≤0.0001). Moreover, IHC analysis showed high expression of MCL-1 (P≤0.01), Ki67 (ns), CD44 (P≤0.0001), and ALDHA1 (P≤0.0001) in the mammary gland tumor tissues of SUM149-R-injected mice compared to SUM149-P-injected mice. Next, we evaluated the therapeutic effect of AZD6244 in mice harboring SUM149-R - MCL-1-deficient tumors. AZD6244 treatment significantly reduced tumor development in mice harboring SUM149-R - MCL-1-KD tumors compared to control mice (P<0.0001), suggesting that MCL-1 mediates MEK resistance in triple-negative/inflammatory breast cancer. Conclusion: Our results suggest that MCL-1 is important for inducing acquired MEK resistance and combining an MCL-1i with a MEKi could improve treatment outcomes of patients with TNBC or IBC who have developed resistance to single-agent MEKi. Citation Format: Mohd Mughees, Alex Tan, Lakesla Iles, Michael White, Debu Tripathy, Savitri Krishnamurthy, Jian Wang, Wendy A. Woodward, Geoffrey Bartholomeusz, Chandra Bartholomeusz. Combined inhibition of MCL-1 and MEK reduces tumor growth in a triple-negative/inflammatory breast cancer, MEK-resistant xenograft mouse model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4652.

Abstract 2899: Combined inhibition of RAF, MEK and FAK increases PDAC responsiveness to cytotoxic- and immune therapy

Abstract Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy with poor response rate to therapy. An immune suppressive tumor microenvironment (TME) and oncogenic mutations in KRAS have been implicated as drivers of resistance to both conventional and immune therapies. As such, targeting RAS/MAPK signaling is an attractive strategy. However, RAS/MAPK inhibition has not yet shown clinical efficacy for PDAC, likely due to rapid acquisition of resistance in PDAC cells. Tumor intrinsic mechanisms of resistance to RAS/MAPK have been studied, however, the unique PDAC TME may also be a key driver in resistance. Previous studies have shown that FAK inhibition can reprogram the PDAC TME and delay PDAC progression in animal models. Herein, we found that long-term FAK inhibitor treatment led to hyperactivation of the RAS/MAPK pathway in both genetically engineered mouse models and in post-treatment PDAC tissues from FAK inhibitor clinical trials. Concomitant inhibition of both FAK (VS-4718) and RAF/MEK (avutometinib) signaling dramatically suppressed tumor growth, leading to increased survival across multiple PDAC mouse models. The mechanisms of synergy include both changes in tumor-intrinsic signaling and modulation of tumor/stroma interactions that drive avutometinib resistance. In the TME, we found that cancer associated fibroblasts (CAFs) can impair the downregulation of cMyc by RAF/MEK inhibition in PDAC cells. This resulted in de-novo resistance to RAF/MEK inhibition in fibrotic conditions. By contrast, FAK inhibitors reprogramed CAFs to suppress the production of key growth factors, including FGF1, that drove resistance to RAF/MEK inhibition. While combined FAK and RAF/MEK inhibition only led to disease stasis, the addition of chemotherapy to the combination led to tumor regression and improved long-term survival in PDAC mouse models. Analysis of tumor immunity showed that the combination of FAK and RAF/MEK inhibition improved anti-tumor immunity and improved priming of T cell responses, which was further improved with the addition of chemotherapy. These findings led to testing of FAK (defactinib) plus RAF/MEK (avutometinib) inhibition in combination with gemcitabine and nab-paclitaxel in advanced front-line pancreatic cancer patients (RAMP 205; NCT05669482). Finally, we tested whether addition of immunotherapy could enhance the efficacy of FAKi + RAF/MEKi + chemotherapy and found that addition of either PD-1 or CTLA4/PD-1 blockade led to long term disease control in PDAC animal models. Together, these studies identified FAK inhibition as a novel approach to overcome both tumor intrinsic and stromal-derived resistance to RAS/MAPK inhibition and showed that this combination can be exploited to increase the efficacy of cytotoxic and immunotherapy approaches. Citation Format: Xiuting Liu, John Baer, Brett Knolhoff, Graham Hogg, Faiz Ahmad, Silvia Coma, Jonathan Pachter, Kian Lim, David DeNardo. Combined inhibition of RAF, MEK and FAK increases PDAC responsiveness to cytotoxic- and immune therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2899.

Abstract 4127: Combined inhibition of RAF, MEK, and FAK attenuates melanoma brain metastases and prolongs survival in preclinical models

Abstract Despite promising results from recent FDA-approved therapies, many advanced melanoma patients develop resistance to both immunotherapy and targeted therapy. A common resistance mechanism to targeted therapy is upregulation of the PI3K/AKT signaling pathway, which has also been shown to promote the development of melanoma brain metastases. Historically, AKT inhibitors have failed in the clinic due to their limited efficacy or intolerable toxicity. Proteomic analysis comparing non-metastatic vs brain metastatic primary tumors in mice revealed focal adhesion kinase (FAK) as an AKT1 specific effector and a potential alternative therapeutic target. FAK is a non-receptor tyrosine kinase that localizes primarily to focal adhesions to regulate cell migration. To determine whether targeting FAK alone or in combination with the RAF/MEK inhibitor avutometinib reduces brain metastases and prolongs survival, we utilized both autochthonous and syngeneic melanoma mouse models. Mice with either subcutaneous tumors or established brain metastases were treated with FAK inhibitor, RAF/MEK inhibitor, or the combination of FAK and RAF/MEK inhibitors. Each cohort was assessed for tumor onset, growth, metastasis, and survival. Our results show that combined RAF/MEK/FAK inhibition significantly delays tumor onset, causes regression of established tumors, prevents the development of brain metastases, promotes the regression of established brain metastases, and prolongs survival. In addition, patient-derived BRAF V600E melanoma xenograft mouse models resistant to the BRAF inhibitor dabrafenib and the MEK inhibitor trametinib, were sensitive to combined RAF/MEK/FAK blockade. The addition of the BRAF inhibitor encorafenib to these models further enhanced the effect on tumor growth. These results support the initiation of a clinical trial evaluating the efficacy of the RAF/MEK inhibitor avutometinib in combination with the FAK inhibitor defactinib in patients with brain metastases from cutaneous melanoma. Additionally, we are assessing non-canonical roles of FAK in modulating the tumor microenvironment to determine whether avutometinib and defactinib also enhance the efficacy of immune checkpoint inhibition in this disease. Citation Format: Karly A. Stanley, Jared D. Almazan, Tursun Turapov, David A. Kircher, Gennie L. Parkman, MiKaela N. Field, Katie M. Culver, Christopher M. Stehn, Silvia Coma, Jonathan A. Pachter, Howard Colman, Sheri L. Holmen. Combined inhibition of RAF, MEK, and FAK attenuates melanoma brain metastases and prolongs survival in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4127.

Abstract 2089: A pro-oncogenic RAS-GTP:RAN-GAP complex facilitates nuclear protein export and has clinical implications

Abstract The majority of RAS oncogenic activity is thought to be mediated by its canonical signaling, mainly via RAS-GTP interactions with its effectors RAF and PI3K at the plasma membrane, which respectively activate MEK/ERK and AKT/mTOR pathways. However, in this study, we have identified a new, fundamental, pro-oncogenic, non-canonical activity of RAS-GTP that increases the Exportin 1 (XPO1)-dependent export of nuclear proteins into the cytoplasm and is independent of RAF/MEK and PI3K/AKT signaling. The nuclear protein export machinery is known to depend on a trimeric protein complex composed of RAN-GTP:XPO1:nuclear protein cargo. Unexpectedly, we have found that RAS-GTP forms a stable complex with RAN GTPase-Activating Protein 1 (RAN-GAP) at the nuclear envelope, which facilitates the release of nuclear protein cargo by increasing the hydrolysis of RAN-GTP to RAN-GDP. We have determined that RAS-GTP and RAN-GAP form this complex in primary human lung tumors, patient derived xenografts, and human lung cancer cell lines. Interestingly, the RAS-GTP:RAN-GAP complex is found at the nuclear envelope and in the cytoplasm, but not at the plasma membrane. The RAS-dependent step mediated by the RAS-GTP:RAN-GAP complex acts downstream of XPO1 by increasing RAN-GTP hydrolysis, which promotes protein cargo release. Our fundamental findings have important clinical implications. For example, in human lung cancer models that harbor a KRAS-G12C mutation, the combined inhibition of MEK and PI3K (MEKi + PI3Ki) does not inhibit tumor growth to the same degree as a KRAS-G12C inhibitor. Remarkably, adding an XPO1 inhibitor to MEKi + PI3Ki inhibits tumor growth to the same degree as the KRAS-G12C inhibitor. One critical pro-oncogenic target of the RAS-GTP:RAN-GAP complex is nuclear export of the EZH2 methyltransferase, whose increase in the cytoplasm leads to a direct methylation of the cytoplasmic DLC1 tumor suppressor protein, leading to ubiquitin-dependent proteasomal degradation of DLC1 protein. Analysis of a KRAS mutant cell line from which the DLC1 gene has been disrupted by CRISPR-Cas9 technology indicates that DLC1 makes an important contribution to the growth inhibition by inhibitors that reduce nuclear protein export. These findings establish nuclear protein export as a critical, pro-oncogenic, non-canonical RAS function that is mediated by the RAS-GTP:RAN-GAP complex and provide a mechanistic explanation for poor clinical responses to combined inhibition of MEK and PI3K, which do not regulate the nuclear protein activity identified in this study. Citation Format: Brajendra K. Tripathi, Nicole H. Hirsh, David Hansen, Xiaolan Qian, Marian E. Durkin, Dunrui Wang, Alex G. Papageorge, Ross Lake, Yvonne A. Evrard, Adam Marcus, Suresh S. Ramalingam, Mary Dasso, Karen Vousden, James H. Doroshow, Kylie J. Walters, Douglas R. Lowy. A pro-oncogenic RAS-GTP:RAN-GAP complex facilitates nuclear protein export and has clinical implications [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 2089.

Abstract 1099: Combined MEK and RET inhibition overcomes resistance to single agent RET inhibition in medullary thyroid cancer

Abstract Medullary thyroid carcinoma (MTC) is a rare neuroendocrine cancer, caused by activating mutations in the RET proto-oncogene, contributing to 13% of all thyroid cancer mortalities. Patients with metastatic MTC treated with RET inhibitors (RETi) can develop resistance through mechanisms currently being investigated. We aim to understand the molecular mechanisms of acquired resistance to RETi and develop novel combination therapies to circumvent resistance to these drugs. We used TT, an MTC cell line, to develop vandetanib-resistant (VanR) lines, at two independent sites, the Medical College of Wisconsin (MCW) and the Pediatric Oncology Branch (POB) at the NCI. We applied a multiomic approach to investigate the mechanisms of resistance, including Spectral karyotyping (SKY) and multiplex interphase Fluorescence in situ Hybridization (miFISH) to study the karyotype, ploidy, and heterogeneity at a single-cell level. Whole exome and RNA-sequencing was done to identify genetic alterations such as acquired mutations, copy number variations, and gene expression changes. In parallel, we performed genome-wide CRISPR gene knockout (KO) in TT cells treated with selpercatinib or vehicle to develop potential synergistic targeted combination therapy with RETi. Additionally, we performed a cytotoxicity screening using the Mechanism Interrogation Plate (MIPE6.0) library containing 2803 investigational drugs, novel agents, and FDA-approved drugs with known mechanisms of action. SKY and miFISH results showed that, for the parental TT_POB cell line, there were 4 copies of chromosome 10 (location of the RET gene), whereas there were 3 copies in TT_POB VanR. This was associated with an increase in the RET variant allele frequency, indicating a loss of heterozygosity of the wildtype allele as a mechanism of resistance, which was confirmed by whole exome sequencing. For TT_MCW VanR, we identified a new RET solvent front (G810S), as well as an increased copy number of RET with an increase in expression. CRISPR KO demonstrated that the knockout of NF1 led to resistance and survival to selpercatinib treatment. The MIPE6.0 screening confirmed resistance to RETi in TT_MCW VanR and sensitivity to multiple MEK inhibitors. In vivo testing in a xenograft mouse model confirmed the synergistic/additive activity of combined selpercatinib with trametinib, a MEK inhibitor. In conclusion, using a multiomic approach, we show that resistance to RETi occurs by an adaptive increase in RET signaling through secondary mutations in RET, and an increase in expression or dose of the mutant RET allele. These genetic events are associated with an activation of RAS signaling, in VanR cell lines, through the ERK/MAPK pathway. Furthermore, we demonstrate that the combination of RET and ERK/MAPK inhibition is synergistic against RET-mutant MTC. Future plans include translating our findings through clinical trials at the NCI. Citation Format: Arwa Fallatah, Abdelrahman Rahmy, Sophia Khan, Hsien-chao Chou, Kerstin Heselmeyer-Haddad, Darawalee Wangsa, David Milewski, Yong Kim, Robert Hawley, Young Song, Xiaohu Zhang, Craig Thomas, Jun S. Wei, Jong-In Park, John Glod, Javed Khan. Combined MEK and RET inhibition overcomes resistance to single agent RET inhibition in medullary thyroid cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1099.

Abstract 5847: Characterizing mechanisms of BRAF/MEK inhibitor resistance in BRAF V600 mutant colorectal cancer vs. melanoma

Abstract Background: BRAF V600 mutations comprise ~80% of all oncogenic BRAF mutations in metastatic colorectal cancer (mCRC). While most cancers with BRAF V600 mutations can be effectively treated with combined BRAF and MEK inhibition, BRAF V600 mutant mCRC acquire resistance through EGFR-mediated signaling. The profound difference in response rates to BRAF/MEK inhibitors in BRAF V600 mutant mCRC (12%) vs. melanoma (63-68%) is not sufficiently explained by increased EGFR signaling in CRC. Therefore, we sought to characterize the differences that exist between BRAF V600 mutant CRC and melanomas that could explain the differential sensitivity to BRAF/MEK inhibition and identify more effective treatments for BRAF V600 mutant CRC. Methods: We assessed cell survival by clonogenic assay in the presence of small molecule inhibitors. In parallel, we mined TCGA RNAseq data to calculate the MAPK Pathway Activity Score (MPAS). RTK expression was assessed in TCGA data from patients with BRAF V600 mutant CRC vs. melanoma. We developed cells with acquired resistance to BRAF+MEK inhibitors (Encorafenib+Binimetinib; E+B) by culturing cells in increasing concentrations of drug over several months. RNA-sequencing and analysis was performed on parental and resistant cells treated with vehicle control or BRAF+MEK inhibitors. Results: When comparing the efficacy of BRAF+MEK inhibitors across BRAF V600 mutant cells, we found that BRAF V600 mutant CRC cell lines (n=2) were less sensitive than melanoma cell lines (n=2). MPAS scores were significantly lower in BRAF V600 mutant CRC (n=46) vs. melanoma (n=188) tumors. We interrogated protein array data from the DepMap and identified increased activation of several RTKs (EGFR, HER2, HER3) in BRAF V600 CRC (n=8) vs. melanoma (n=39) cell lines. Similarly, we established resistant HT29 (BRAF V600 CRC) cells and observed sustained MAPK pathway activity despite a lack of difference in EGFR activity in the presence of BRAF+MEK inhibitor treatment. Both HT29 parental and resistant cells showed re-establishment of MAPK signaling after 72 hours. Resistant SkMel28 (BRAF V600 melanoma) cells showed increased pERK levels compared to resistant HT29 cells. RNAseq revealed increased expression of multiple RTKs (PDGFRB, ERBB2, ERBB3) and ligands/growth factors for multiple RTKs (FGF3, PDGFA, HB-EGF) in resistant HT29 cells. Shp2 is a protein tyrosine phosphatase that regulates signaling of multiple RTKs to activate the MAPK pathway. Accordingly, we assessed the efficacy of an inhibitor of Shp2 (TNO155) overcoming MAPKi resistance in BRAF V600 CRC cells. We confirmed that E+B+TNO155 more effectively inhibited cell growth and MAPK pathway activity in BRAF V600 CRC cell lines (n=2) in vitro. Conclusion: Together, these data identify key, actionable drivers of MAPK inhibitor resistance in CRC and highlight Shp2 as a potential therapeutic target for BRAF V600 CRC. Citation Format: Jennifer Maxwell, Emmanuelle Rousselle, Lucy An, April Rose. Characterizing mechanisms of BRAF/MEK inhibitor resistance in BRAF V600 mutant colorectal cancer vs. melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5847.

Abstract 3581: IGFR1 and MEK inhibition synergize to mediate anti-tumor activity in adrenocortical carcinoma

Abstract Adrenocortical carcinoma (ACC) is an aggressive and rare endocrine malignancy with limited treatment options and poor prognosis. IGF2, the ligand for IGFR1, is highly expressed in ACC. However, linsitinib, an IGFR1 inhibitor, failed to improve overall survival over placebo in a randomized, phase 3 clinical trial of metastatic ACC. We hypothesized that combination therapy with IGFR1 inhibition may have greater anti-tumor efficacy in ACC than IGFR1 inhibition alone. To test this hypothesis, we performed high-throughput cell toxicity screening of 2803 clinical-stage compounds with linsitinib in an ACC cell line. MAPK inhibitors were among the top screening hits. MEK inhibitors were chosen for further evaluation given the safety, tolerability, and broad clinical activity of these FDA-approved agents. IGFR1 and MEK inhibitors were strongly synergistic in cytotoxicity across ACC cell lines, ACC organoid short-term cultures derived from surgical tissue resections (PDOs), and PDX-derived organoids (PDXOs). Genetic depletion of IGF2 significantly inhibited growth with cobimetinib and genetic depletion of MEK1 inhibited growth with linsitinib in ACC cell lines. Combination IGFR1 and MEK inhibition downregulated ERK phosphorylation and increased apoptosis compared to either IGFR1 or MEK inhibition alone. Linsitinib combined with cobimetinib significantly reduced tumor growth compared to either linsitinib or cobimetinib alone in an ACC xenograft model. Our study provides preclinical support for testing the combination of IGFR1 and MEK inhibition in patients with ACC. Citation Format: Suresh Kumar, Nai-Yun Sun, Yasuhiro Arakawa, Diana Varghese, Chuong D. Hoang, Jonathan M. Hernandez, Yves Pommier, Craig Thomas, Jaydira Del Rivero, Nitin Roper. IGFR1 and MEK inhibition synergize to mediate anti-tumor activity in adrenocortical carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3581.

Abstract 6555: scRNAseq and TCR repertoire analysis identifies immune correlates of response to combined BRAF/MEK/PD1 inhibition in a phase 2 trial

Abstract Background: Our recent clinical trial of combined BRAF, MEK, and PD-1 inhibition showed a 24% response rate in BRAF V600E mutant colon cancer (PMID: 36702949). Analysis of epithelial single-cell RNA sequencing data showed an increase in interferon-stimulated genes (ISG) and inhibition of the MAPK pathway in responders. MAPK inhibition in organoids also induced ISGs. These data suggest a synergy between MAPK inhibition and induction of immune responses. Methods: We analyzed over 100,000 immune and stromal cells from 23 paired scRNAseq profiles of pre- and day 15 on-treatment tumor biopsies. Progression free survival greater than 6 months was defined as a clinical response. We performed traditional differentially expressed gene and gene program analyses, and tracked TCR repertoire in tumor and blood. We developed a novel approach based on supervised clustering (PMID: 34675423) to identify fine-grained cell subtypes associated with response. We applied supervised clustering separately to T and myeloid cells, and tested the association of each cluster’s abundance with response. Results: We applied supervised clustering to T cells and identified a CD74+IFNG+ CD8 T cell cluster that increased in only responders (p=0.0078). In the myeloid compartment, we identified two populations of CXCL10+ macrophages: one whose abundance increased in all patients and a CCL3+CCL4+ activation state expanded (p=0.01) only in responders. Pathway analysis of the expanded populations suggests an enrichment of ISGs in both CD74+IFNG+ CD8 T cells and CXCL10+CCL3+CCL4+ macrophages, with specific enrichment of interferon-gamma responsive genes GBP1 and GBP4 in the macrophages. T cell analysis yielded two responders with marked clonal expansion within the CXCL13+ population, which likely represent tumor-specific T cells. Within the blood, these CXCL13+ clonotypes underwent a short-lived burst at day 15, yet represented only a minor population. We saw concomitant expansion of both CXCL13+ CD4 and CD8 populations within patients, suggesting CXCL13+ CD4s might provide help to the CXCL13+ CD8 T cells. The same two responders had increased stem-like TCF7+PD1+ CD8 T cells previously implicated in immunotherapy response and an increase in CCL19+ fibroblasts associated with stem-immunity hubs. Conclusions: Our analysis of pre- and on-therapy biopsy scRNAseq data from our clinical trial of MAPK and PD-1 inhibition found expansion of ISG enriched CD74+IFNG+ CD8 T cells and CXCL10+CCL3+CCL4+ macrophages in responders. Both populations are enriched in ISGs: this coordinated expansion may result from a shared, interferon-rich microenvironment. Ongoing work will explore this hypothesis using spatial transcriptomics to identify these activated cells and their microenvironments. Ethics approval "This study was approved by the DF/HCC IRB as protocol 18-144 (see also ClinicalTrials.gov NCT03668431). Citation Format: Hongcheng Yao, Vjola Jorgji, Alexander L. Tang, David Lieb, Sherry X. Chao, Daniel J. Stein, Maxwell Spurrell, Liad Elmelech, Jun Tian, Moshe Sade-Feldman, Karin Pelka, Ryan B. Corcoran, Nir Hacohen, Ilya Korsunsky, Jonathan Chen. scRNAseq and TCR repertoire analysis identifies immune correlates of response to combined BRAF/MEK/PD1 inhibition in a phase 2 trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6555.

Abstract 1925: Wild-type RAS signaling is an essential therapeutic target in RAS-mutated cancers

Abstract Single-agent targeting of RAS-mutated cancers using RAF/MEK/ERK or PI3K/AKT pathway inhibitors is ineffective; blocking one pathway relieves negative feedback control of RTK signaling and hyperactivates parallel effector pathways. While combined MEK and PI3K inhibition is effective in preclinical models, toxicity of this combination prevents its clinical use. Alternative strategies for treating RAS-mutated cancers are essential. Therapeutics directly targeting mutated RAS proteins have the potential to spare normal cellular function thereby lessening overall toxicity. Unfortunately, direct RAS inhibition as a monotherapy does not fully block RAS effector signaling. RAS proteins show differential activation of RAF and PI3K pathways: KRAS potently activates RAF but poorly activates PI3K, whereas HRAS effectively activates PI3K but poorly activates RAF. Further, mutant RAS inhibition relieves negative feedback controls leading to rapid hyperactivation of RTK−WT RAS signaling. A more comprehensive understanding of the interplay between mutant RAS and RTK−WT RAS signaling is essential to developing rational therapeutic approaches to treat RAS-mutated cancers. We found that WT RAS enhanced mutant RAS-driven transformation by activating RAS effectors poorly engaged by mutated RAS. Further, inhibition of RAS effectors activated poorly by mutant RAS synergized with and limited resistance to mutant HRAS and KRAS inhibitors. The mutant HRAS inhibitor tipifarnib blocked PI3K signaling and synergized with MEK inhibitors in HRAS-mutated cancer cell lines; covalent KRASG12C inhibitors blocked MEK signaling and synergized with PI3K inhibitors in KRASG12C- mutated cell lines. Synergy between inhibitors of mutant RAS and RAS effectors was dependent on intact RTK/WT RAS signaling and was lost in both RASless or SOSless MEFs. Dual knock-out of WT RAS isoforms in KRAS- and HRAS-mutated cancer cell lines reduced PI3K signaling in KRAS-mutant cell lines and MAPK signaling in HRAS-mutant cell lines and reduced proliferation, confirming our findings in MEF cells. Overall, our data highlight the critical role of WT RAS isoforms in supporting mutant RAS signaling and should be considered when designing combination therapies in RAS-mutated cancers. Citation Format: Nancy E. Sealover, Bridget Finniff, Jacob Hughes, Hyun Lee, Robert L. Kortum. Wild-type RAS signaling is an essential therapeutic target in RAS-mutated cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1925.

Abstract 5265: Targeting mtDNA dynamics enhances immunogenicity and sensitizes KRAS mutant cancers to PD-1 blockade

Abstract Mitochondrial DNA (mtDNA) can stimulate an innate immune response that potentiates the efficacy of cancer immunotherapy. However, mtDNA-targeting therapy has not been developed to enhance this innate immune system in specific cancer subtypes efficiently. Here we discover that mtDNA is enriched in KRAS mutant tumors where the DNA sensor machinery cGAS-STING signaling is primed for innate immune activation. Intriguingly, MEK inhibitor induces cytosolic mtDNA release to potently activate the cGAS-STING signaling, which in turn induces PRKN-mediated mitophagy in response to mitochondrial stress in KRAS mutant cancer cells. During the process of mitophagy, PRKN, as an E3 ubiquitin ligase, degrades BAX protein and attenuates mitochondrial pore formation, which is essential for mtDNA efflux upon MEK inhibition. Combined MEK and mitophagy inhibitors efficiently stimulate type I IFNs in both mtDNA- and STING-dependent manners, and this combination enhances the efficacy of PD-1 blockade in Kras mutant murine syngeneic tumors. In the clinic, PRKN is associated with a ‘cold tumor’ phenotype among KRAS mutant tumors. Together, targeting mtDNA dynamics by co-inhibition of MEK and mitophagy represents a promising strategy to convert ‘cold to hot tumor’ in mtDNA-enriched KRAS mutant cancers. Citation Format: Kosuke Tanaka, Yasuki Adachi, Miyuki Yoshiya, Takuya Owari, Tomoko Yamamori-Morita, Akihiro Ohashi, Susumu Kobayashi, Shohei Koyama, Hiroyoshi Nishikawa. Targeting mtDNA dynamics enhances immunogenicity and sensitizes KRAS mutant cancers to PD-1 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5265.

Anaplastic thyroid cancer spheroids as preclinical models to test therapeutics

Anaplastic thyroid cancer (ATC) is the most aggressive thyroid cancer. Despite advances in tissue culture techniques, a robust model for ATC spheroid culture is yet to be developed. In this study, we created an efficient and cost-effective 3D tumor spheroids culture system from human ATC cells and existing cell lines that better mimic patient tumors and that can enhance our understanding of in vivo treatment response. We found that patient-derived ATC cells and cell lines can readily form spheroids in culture with a unique morphology, size, and cytoskeletal organization. We observed both cohesive (dense and solid structures) and discohesive (irregularly shaped structures) spheroids within the same culture condition across different cell lines. BRAFWT ATC spheroids grew in a cohesive pattern, while BRAFV600E-mutant ATC spheroids had a discohesive organization. In the patient-derived BRAFV600E-mutant ATC spheroids, we observed both growth patterns, but mostly the discohesive type. Histologically, ATC spheroids had a similar morphology to the patient’s tumor through H&E staining and proliferation marker staining. Moreover, RNA sequencing analysis revealed that the gene expression profile of tumor cells derived from the spheroids closely matched parental patient tumor-derived cells in comparison to monolayer cultures. In addition, treatment response to combined BRAF and MEK inhibition in BRAFV600E-mutant ATC spheroids exhibited a similar sensitivity to the patient clinical response. Our study provides a robust and novel ex vivo spheroid model system that can be used in both established ATC cell lines and patient-derived tumor samples to better understand the biology of ATC and to test therapeutics.

Targeting MEK in non-small cell lung cancer

The mitogen-activated protein kinase (MAPK or MEK) pathway modulates tumor cell survival and proliferation in non-small cell lung cancer (NSCLC). Unlike RAS or EGFR, activating mutations in MEK are exceedingly rare in NSCLC. Instead, enhanced activation of the MEK pathway is often linked to increased signaling by upstream oncogenic driver mutations. Thus far, MEK inhibitor monotherapy has shown little promise. However, treatment strategies involving MEK inhibition in combination with other targeted therapies in other oncogene-driven NSCLC has proven to be encouraging. For example, MEK inhibition - when combined with BRAF inhibition, - has shown strong anti-tumor activity in BRAF V600 mutated NSCLC. In this review, recent data on MEK inhibitor strategies in NSCLC are summarized. Furthermore, ongoing early phase trials investigating MEK inhibitor combination therapy with immunotherapy, chemotherapy and other oncogene drivers are highlighted. These and other studies could help inform future rational combination strategies of MEK-ERK inhibition in oncogene-driven NSCLC.

A Review of Current and Pipeline Drugs for Treatment of Melanoma.

Malignant melanoma is the most aggressive form of skin cancer. Standard treatment options include surgery, radiation therapy, systemic chemotherapy, targeted therapy, and immunotherapy. Combining these modalities often yields better responses. Surgery is suitable for localized cases, sometimes involving lymph node dissection and biopsy, to assess the spread of the disease. Radiation therapy may be sometimes used as a standalone treatment or following surgical excision. Systemic chemotherapy, while having low response rates, is utilized as part of combination treatments or when other methods fail. The development of resistance to systemic chemotherapies and associated side effects have prompted further research and clinical trials for novel approaches. In the case of advanced-stage melanoma, a comprehensive approach may be necessary, incorporating targeted therapies and immunotherapies that demonstrate significant antitumor activity. Targeted therapies, including inhibitors targeting BRAF, MEK, c-KIT, and NRAS, are designed to block the specific molecules responsible for tumor growth. These therapies show promise, particularly in patients with corresponding mutations. Combination therapy, including BRAF and MEK inhibitors, has been evidenced to improve progression-free survival; however, concerns about resistance and cutaneous toxicities highlight the need for close monitoring. Immunotherapies, leveraging tumor-infiltrating lymphocytes and CAR T cells, enhance immune responses. Lifileucel, an FDA-approved tumor-infiltrating lymphocyte therapy, has demonstrated improved response rates in advanced-stage melanoma. Ongoing trials continue to explore the efficacy of CAR T-cell therapy for advanced melanoma. Checkpoint inhibitors targeting CTLA-4 and PD-1 have enhanced outcomes. Emerging IL-2 therapies boost dendritic cells, enhancing anticancer immunity. Oncolytic virus therapy, approved for advanced melanoma, augments treatment efficacy in combination approaches. While immunotherapy has significantly advanced melanoma treatment, its success varies, prompting research into new drugs and factors influencing outcomes. This review provides insights into current melanoma treatments and recent therapeutic advances.

Abstract A026: EGF/EGFR signaling in priming for resistance to BRAF/MEK inhibitors in melanoma

Abstract Targeted therapies kill cancer cells very efficiently. However, the effectiveness of targeted therapies is limited by the eventual emergence of resistance, arising from a small subset of cells capable of surviving therapy. Our work has shown genetically homogeneous cells, in distinct transcriptomic states, are capable of surviving combination BRAF and MEK inhibition. In the presence of targeted therapies these rare cells transform into resistant cells, we therefore call these cells ‘primed’ for resistance. Our research has focused on characterizing these primed cells, however, the mechanisms of survival remain unknown. Since primed cells overexpress receptor tyrosine kinases (RTKs), which are associated with growth and survival, we tested if overexpression of the RTK EGFR could explain priming and subsequent resistance. While melanoma cells in which we artificially overexpressed EGFR had no significant increase in resistance, EGFR overexpressing cells in the presence of exogenous EGF are highly resistant to combination BRAF/MEK inhibition. While EGF is not overexpressed in primed cells, preliminary data suggests that while most cells reduce EGF expression in the presence of BRAF/MEK inhibition, primed cells maintain their baseline expression, potentially maintaining EGF/EGFR signaling in these colonies. We are therefore testing if EGF/EGFR signaling is necessary in vitro by knocking out EGF or EGFR. Furthermore, to test if EGF/EGFR signaling can create a primed state, we used flow cytometry to determine expression of the prime cell marker NT5E. In cells with confirmed EGFR overexpression we observed an increased fraction of NT5E overexpressing cells, suggesting that EGF/EGFR signaling could initiate aspects of primeness beyond simple survival. Further research will determine if EGF/EGFR signaling can initiate an overall primed transcriptional state. The heritability of any primeness as a consequence of EGF/EGFR signaling will inform us if this signaling is a potential cause of priming or a mechanism by which paracrine signaling and/or stromal protection can eventually result in independent resistance. Citation Format: Robert J. Vander Velde, Sydney M. Shaffer. EGF/EGFR signaling in priming for resistance to BRAF/MEK inhibitors in melanoma [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Translating Cancer Evolution and Data Science: The Next Frontier; 2023 Dec 3-6; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_2):Abstract nr A026.

A phase 1 trial of combined MEK, STAT3 and PD-1 inhibition in metastatic pancreatic ductal adenocarcinoma (PDAC).

TPS713 Background: PDAC is characterized by its innate and acquired resistance to both MAPK pathway inhibition and immune checkpoint (e.g. PD-1/PD-L1) inhibition (ICI) via multiple mechanisms. In preclinical models of PDAC, combined MEK and STAT3 inhibition (MEKi+STAT3i) uncovers stromal plasticity by attenuating cancer-associated fibroblasts (CAF) with IL-6/CXCL1-secretory phenotypes while enriching for Ly6a/CD34-expressing CAF phenotypes with mesenchymal stem cell-like features. This remodeling of CAF heterogeneity is associated with a striking attenuation in and reprogramming of tumor-associated macrophages (TAMs) as well as enhanced trafficking of CD8 T cells, which exhibit a distinct effector and anti-apoptotic transcriptional program. The addition of MEKi+STAT3i to PD-1 blockade overcomes ICI resistance by significantly enhancing the recruitment, degranulating capacity, and functional cytotoxicity of CD8+ T-cells, thereby augmenting antitumor responses and dramatically improving survival in these models. Furthermore, a patient with refractory PDAC treated off-label with this combination achieved a meaningful response. Based on this strong rationale, a phase 1 trial was initiated to test the combination of MEKi+STAT3 and PD1 inhibition in patients with metastatic PDAC. Methods: NCT05440942 is an open-label, prospective, single-institution phase 1 trial testing the safety, preliminary efficacy, and biomarkers of response to the combination of trametinib (MEKi), ruxolitinib (JAK2/STAT3 inhibitor) and retifanlimab (PD-1 inhibitor) in patients with metastatic PDAC. Patients with metastatic PDAC who have had disease progression on at least one line of prior therapy, with good organ function, preserved performance status, and without major intercurrent illness are eligible. Patients must have an accessible lesion for biopsy and must be willing to undergo this research biopsy at baseline and on treatment. Part 1 of the study is a dose-escalation phase with 3 dose levels and a target dose of trametinib 2mg orally daily, ruxolitinib 15mg orally twice daily, and retifanlimab 500mg intravenously every 28 days. The dose escalation is being done using the novel Bayesian keyboard design and 9-15 patients will be treated to get to the potential maximum tolerated dose (MTD). Dose level 1 has been completed without any dose-limiting toxicities seen. Part 2 is an expansion phase which will accrue an additional 20 patients. All patients in part 1 and 2 will have core-needle biopsies pre-treatment and after 4 weeks. Serial blood samples will be collected at baseline and on treatment. Biopsies are being analyzed by multiparameter immune profiling using mass cytometry and bulk RNA sequencing; blood is being analyzed for circulating tumor DNA and immune profiling. These results will be correlated with clinical response to therapy to determine biomarkers of response and resistance. Clinical trial information: NCT05440942 .