Son Of Sevenless Homolog Research Articles

KRASG 12C-inhibitor-based combination therapies for pancreatic cancer: insights from drug screening.

Pancreatic ductal adenocarcinoma (PDAC) has limited treatment options, emphasizing the urgent need for effective therapies. The predominant driver in PDAC is mutated KRAS proto-oncogene, KRA, present in 90% of patients. The emergence of direct KRAS inhibitors presents a promising avenue for treatment, particularly those targeting the KRASG12C mutated allele, which show encouraging results in clinical trials. However, the development of resistance necessitates exploring potent combination therapies. Our objective was to identify effective KRASG12C-inhibitor combination therapies through unbiased drug screening. Results revealed synergistic effects with son of sevenless homolog 1 (SOS1) inhibitors, tyrosine-protein phosphatase non-receptor type 11 (PTPN11)/Src homology region 2 domain-containing phosphatase-2 (SHP2) inhibitors, and broad-spectrum multi-kinase inhibitors. Validation in a novel and unique KRASG12C-mutated patient-derived organoid model confirmed the described hits from the screening experiment. Our findings propose strategies to enhance KRASG12C-inhibitor efficacy, guiding clinical trial design and molecular tumor boards.

The SOS1 Inhibitor MRTX0902 Blocks KRAS Activation and Demonstrates Antitumor Activity in Cancers Dependent on KRAS Nucleotide Loading.

KRAS is the most frequently mutated oncogene in human cancer and facilitates uncontrolled growth through hyperactivation of the receptor tyrosine kinase (RTK)/mitogen-activated protein kinase (MAPK) pathway. The Son of Sevenless homolog 1 (SOS1) protein functions as a guanine nucleotide exchange factor (GEF) for the RAS subfamily of small GTPases and represents a druggable target in the pathway. Using a structure-based drug discovery approach, MRTX0902 was identified as a selective and potent SOS1 inhibitor that disrupts the KRAS:SOS1 protein-protein interaction to prevent SOS1-mediated nucleotide exchange on KRAS and translates into an anti-proliferative effect in cancer cell lines with genetic alterations of the KRAS-MAPK pathway. MRTX0902 augmented the antitumor activity of the KRAS G12C inhibitor adagrasib when dosed in combination in eight out of 12 KRAS G12C-mutant human non-small cell lung cancer and colorectal cancer xenograft models. Pharmacogenomic profiling in preclinical models identified cell cycle genes and the SOS2 homolog as genetic co-dependencies and implicated tumor suppressor genes (NF1 and PTEN) in resistance following combination treatment. Lastly, combined vertical inhibition of RTK/MAPK pathway signaling by MRTX0902 with inhibitors of EGFR or RAF/MEK led to greater downregulation of pathway signaling and improved antitumor responses in KRAS-MAPK pathway-mutant models. These studies demonstrate the potential clinical application of dual inhibition of SOS1 and KRAS G12C and additional SOS1 combination strategies that will aide in the understanding of SOS1 and RTK/MAPK biology in targeted cancer therapy.

FBL Promotes LPS-Induced Neuroinflammation by Activating the NF-κB Signaling Pathway.

Neuroinflammation occurs in response to central nervous system (CNS) injury, infection, stimulation by toxins, or autoimmunity. We previously analyzed the downstream molecular changes in HT22 cells (mouse hippocampal neurons) upon lipopolysaccharide (LPS) stimulation. We detected elevated expression of Fibrillarin (FBL), a nucleolar methyltransferase, but the associated proinflammatory mechanism was not systematically elucidated. The aim of this study was to investigate the underlying mechanisms by which FBL affects neuroinflammation. RT-real-time PCR, Western blotting and immunofluorescence were used to assess the mRNA and protein expression of FBL in HT22 cells stimulated with LPS, as well as the cellular localization and fluorescence intensity of FBL. BAY-293 (a son of sevenless homolog 1 (SOS1) inhibitor), SR11302 (an activator protein-1 (AP-1) inhibitor) and KRA-533 (a KRAS agonist) were used to determine the molecular mechanisms underlying the effect of FBL. AP-1 was predicted to be the target protein of FBL by molecular docking analysis, and validation was performed with T-5224 (an AP-1 inhibitor). In addition, the downstream signaling pathways of FBL were identified by transcriptome sequencing and verified by RT-real-time PCR. LPS induced FBL mRNA and protein expression in HT22 cells. In-depth mechanistic studies revealed that when we inhibited c-Fos, AP-1, and SOS1, FBL expression decreased, whereas FBL expression increased when KRAS agonists were used. In addition, the transcript levels of inflammatory genes in the NF-kB signaling pathway (including CD14, MYD88, TNF, TRADD, and NFKB1) were elevated after the overexpression of FBL. LPS induced the expression of FBL in HT22 cells through the RAS/MAPK signaling pathway, and FBL further activated the NF-kB signaling pathway, which promoted the expression of relevant inflammatory genes and the release of cytokines. The present study reveals the mechanism by which FBL promotes neuroinflammation and offers a potential target for the treatment of neuroinflammation.

Abstract 7268: The SOS1 inhibitor MRTX0902 demonstrates activity across cancer models with mutations in proximal components of the RAS-MAPK pathway

Abstract Genetic alterations in the RAS-MAPK pathway are one of the most frequent causes of human cancers. While targeted therapies are approved for patients harboring mutations in KRAS G12C in advanced or metastatic non-small cell lung cancer, there remains a need for an effective therapy for cancers characterized by additional RAS-MAPK pathway mutations across cancer types. Previous studies have shown that genetic or pharmacological inhibition of Son of Sevenless homolog 1 (SOS1) demonstrates antiproliferative activity in cancer cells addicted to KRAS signaling, including cell lines with oncogenic mutations in KRAS, SOS1, PTPN11, or EGFR or a loss-of-function mutation in NF1. These genetic alterations each function to increase SOS1-mediated GTP-loading of KRAS and increase signaling flux through the MAPK pathway. Inhibition of SOS1 by MRTX0902 is anticipated to shift the tumor cell equilibrium of KRAS towards the inactive GDP-bound KRAS, leading to MAPK pathway inhibition. MRTX0902 is a selective inhibitor of SOS1 under evaluation in clinical trials for the treatment of advanced, unresectable, or metastatic cancers with mutations in the KRAS-MAPK pathway. In the present studies, we have shown that MRTX0902 demonstrates single-agent anti-proliferative activity and modulates ERK1/2 phosphorylation (pERK) across a panel of human tumor cell lines harboring oncogenic mutations in SOS1, PTPN11, BRAF (class III) and NF1. Furthermore, oral administration of MRTX0902 as a monotherapy in preclinical human tumor cell-derived xenograft models harboring these oncogenic mutations results in significant tumor growth inhibition. Additionally, combination with the RAF/MEK clamp avutometinib demonstrated greater antitumor activity versus either monotherapy treatment. These data support the clinical utility of MRTX0902 as a single agent or combination partner of avutometinib for the treatment of human cancers harboring oncogenic mutations implicated in dysregulation of RAS-dependent signaling including SOS1, PTPN11, NF1, and BRAF (class III). Citation Format: Niranjan Sudhakar, Larry Yan, Fadia Qiryaqos, Jade Laguer, David Briere, Allan Hebbert, Andrew Calinisan, Silvia Coma, Jonathan Pachter, James G. Christensen, Peter Olson, Shilpi Khare. The SOS1 inhibitor MRTX0902 demonstrates activity across cancer models with mutations in proximal components of the RAS-MAPK pathway [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 7268.

Discovery of LHF418 as a new potent SOS1 PROTAC degrader

Son of sevenless homolog 1 (SOS1) plays a pivotal role as a molecular switch in the conversion of GDP-bound inactive KRAS to its active GTP-bound form, making SOS1 a promising therapeutic target for KRAS-driven cancers. While the most advanced SOS1 inhibitor has processed to phase I clinical trial, the exploration of novel SOS1 targeting strategies with distinct modes of action remains required. By employing proteolysis targeting chimera (PROTAC) technology, we obtained a series of new SOS1 degraders. The representative compound LHF418 potently induced SOS1 degradation with a DC50 value of 209.4 nM and a Dmax value of over 80 %. Mechanistic studies have illuminated that compound LHF418 induced the formation of ternary complex involving SOS1-PROTAC-cereblon (CRBN) and triggered SOS1 protein degradation in a CRBN- and proteasome-dependent manner. In addition, compound LHF418 effectively inhibited KRAS-RAF-ERK signalling, leading to the suppression of colony formation in KRAS-driven cancer cells. Overall, compound LHF418 represents a new lead compound in the developing novel and potent therapy for the treatment of KRAS-driven cancers.

Cereblon-based Bifunctional Degrader of SOS1, BTX-6654, Targets Multiple KRAS Mutations and Inhibits Tumor Growth.

Mutations within the oncogene KRAS drive an estimated 25% of all cancers. Only allele-specific KRAS G12C inhibitors are currently available and are associated with the emergence of acquired resistance, partly due to upstream pathway reactivation. Given its upstream role in the activation of KRAS, son of sevenless homolog 1 (SOS1), has emerged as an attractive therapeutic target. Agents that target SOS1 for degradation could represent a potential pan-KRAS modality that may be capable of circumventing certain acquired resistance mechanisms. Here, we report the development of two SOS1 cereblon-based bifunctional degraders, BTX-6654 and BTX-7312, cereblon-based bifunctional SOS1 degraders. Both compounds exhibited potent target-dependent and -specific SOS1 degradation. BTX-6654 and BTX-7312 reduced downstream signaling markers, pERK and pS6, and displayed antiproliferative activity in cells harboring various KRAS mutations. In two KRAS G12C xenograft models, BTX-6654 degraded SOS1 in a dose-dependent manner correlating with tumor growth inhibition, additionally exhibiting synergy with KRAS and MEK inhibitors. Altogether, BTX-6654 provided preclinical proof of concept for single-agent and combination use of bifunctional SOS1 degraders in KRAS-driven cancers.

From bench to bedside: current development and emerging trend of KRAS-targeted therapy.

Kirsten rat sarcoma 2 viral oncogene homolog (KRAS) is the most frequently mutated oncogene in human cancers with mutations predominantly occurring in codon 12. These mutations disrupt the normal function of KRAS by interfering with GTP hydrolysis and nucleotide exchange activity, making it prone to the GTP-bound active state, thus leading to sustained activation of downstream pathways. Despite decades of research, there has been no progress in the KRAS drug discovery until the groundbreaking discovery of covalently targeting the KRASG12C mutation in 2013, which led to revolutionary changes in KRAS-targeted therapy. So far, two small molecule inhibitors sotorasib and adagrasib targeting KRASG12C have received accelerated approval for the treatment of non-small cell lung cancer (NSCLC) harboring KRASG12C mutations. In recent years, rapid progress hasbeen achieved in the KRAS-targeted therapy field, especially the exploration of KRASG12C covalent inhibitors in other KRASG12C-positive malignancies, novel KRAS inhibitors beyond KRASG12C mutation or pan-KRAS inhibitors, and approaches to indirectly targeting KRAS. In this review, we provide a comprehensive overview of the molecular and mutational characteristics of KRAS and summarize the development and current status of covalent inhibitors targeting the KRASG12C mutation. We also discuss emerging promising KRAS-targeted therapeutic strategies, with a focus on mutation-specific and direct pan-KRAS inhibitors and indirect KRAS inhibitors through targeting the RAS activation-associated proteins Src homology-2 domain-containing phosphatase 2 (SHP2) and son of sevenless homolog 1 (SOS1), and shed light on current challenges and opportunities for drug discovery in this field.

Impact of trifluoromethyl and sulfonyl groups on the biological activity of novel aryl-urea derivatives: synthesis, in-vitro, in-silico and SAR studies

We designed and prepared a novel series of urea derivatives with/without sulfonyl group in their structures to investigate the impact of the sulfonyl group on the biological activity of the evaluated compounds. Antibacterial investigations indicated that derivatives 7, 8, 9, and 11 had the most antibacterial property of all the compounds examined, their minimum inhibitory concentrations (MICs) determined against B. mycoides, E. coli, and C. albicans, with compound 8 being the most active at a MIC value of 4.88 µg/mL. Anti-cancer activity has been tested against eight human cancer cell lines; A549, HCT116, PC3, A431, HePG2, HOS, PACA2 and BJ1. Compounds 7, 8 and 9 emerged IC50 values better than Doxorubicin as a reference drug. Compounds 7 and 8 showed IC50 = 44.4 and 22.4 μM respectively against PACA2 compared to Doxorubicin (IC50 = 52.1 μM). Compound 9 showed IC50 = 17.8, 12.4, and 17.6 μM against HCT116, HePG2, and HOS, respectively. qRT-PCR revealed the down-regulation of PALB2 in compounds 7 and 15 treated PACA2 cells. Also, the down-regulation of BRCA1 and BRCA2 was shown in compound 7 treated PC3 cells. As regard A549 cells, compound 8 decreased the expression level of EGFR and KRAS genes. While compounds 7 and 9 down-regulated TP53 and FASN in HCT116 cells. Molecular docking was done against Escherichia coli enoyl reductase and human Son of sevenless homolog 1 (SOS1) and the results showed the promising inhibition of the studied proteins.

Soloxolone Methyl Reduces the Stimulatory Effect of Leptin on the Aggressive Phenotype of Murine Neuro2a Neuroblastoma Cells via the MAPK/ERK1/2 Pathway.

Despite the proven tumorigenic effect of leptin on epithelial-derived cancers, its impact on the aggressiveness of neural crest-derived cancers, notably neuroblastoma, remains largely unexplored. In our study, for the first time, transcriptome analysis of neuroblastoma tissue demonstrated that the level of leptin is elevated in neuroblastoma patients along with the severity of the disease and is inversely correlated with patient survival. The treatment of murine Neuro2a neuroblastoma cells with leptin significantly stimulated their proliferation and motility and reduced cell adhesion, thus rendering the phenotype of neuroblastoma cells more aggressive. Given the proven efficacy of cyanoenone-bearing semisynthetic triterpenoids in inhibiting the growth of neuroblastoma and preventing obesity in vivo, the effect of soloxolone methyl (SM) on leptin-stimulated Neuro2a cells was further investigated. We found that SM effectively abolished leptin-induced proliferation of Neuro2a cells by inducing G1/S cell cycle arrest and restored their adhesiveness to extracellular matrix (ECM) proteins to near control levels through the upregulation of vimentin, zonula occludens protein 1 (ZO-1), cell adhesion molecule L1 (L1cam), and neural cell adhesion molecule 1 (Ncam1). Moreover, SM significantly suppressed the leptin-associated phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and ribosomal protein S6 kinase A1 (p90RSK), which are key kinases that ensure the survival and proliferation of cancer cells. Further molecular modeling studies demonstrated that the inhibitory effect of SM on the mitogen-activated protein kinase (MAPK)/ERK1/2 signaling pathway can be mediated by its direct interaction with ERK2 and its upstream regulators, son of sevenless homolog 1 (SOS) and mitogen-activated protein kinase kinase 1 (MEK1). Taken together, our findings in murine Neuro2a cells provide novel evidence of the stimulatory effect of leptin on the aggressiveness of neuroblastoma, which requires further detailed studies in human neuroblastoma cells and relevant animal models. The obtained results indicate that SM can be considered a promising drug candidate capable of reducing the impact of adipokines on tumor progression.

Design of Orally-bioavailable Tetra-cyclic phthalazine SOS1 inhibitors with high selectivity against EGFR

KRAS mutations (G12C, G12D, etc.) are implicated in the oncogenesis and progression of many deadliest cancers. Son of sevenless homolog 1 (SOS1) is a crucial regulator of KRAS to modulate KRAS from inactive to active states. We previously discovered tetra-cyclic quinazolines as an improved scaffold for inhibiting SOS1-KRAS interaction. In this work, we report the design of tetra-cyclic phthalazine derivatives for selectively inhibiting SOS1 against EGFR. The lead compound 6c displayed remarkable activity to inhibit the proliferation of KRAS(G12C)-mutant pancreas cells. 6c showed a favorable pharmacokinetic profile in vivo, with a bioavailability of 65.8% and exhibited potent tumor suppression in pancreas tumor xenograft models. These intriguing results suggested that 6c has the potential to be developed as a drug candidate for KRAS-driven tumors.

Abstract 3499: Inhibition of SOS1 by MRTX0902 augments the anti-tumor response of the targeted EGFR inhibitor osimertinib in NSCLC

Abstract Osimertinib is a third generation, irreversible epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor recommended as a first line therapy in patients with advanced non-small lung cancer (NSCLC) characterized by EGFR activating mutations (exon 19 deletions and exon 21 L858R) and the resistance associated exon 20 T790M mutation, which is present in approximately 40-55% of patients following treatment with first generation EGFR-targeting inhibitors. Unfortunately, osimertinib monotherapy inevitably leads to both EGFR-dependent and EGFR-independent resistance mechanisms that reactivate RTK/MAPK pathway signaling. Thus, exploration of new combination strategies that target RTK/MAPK-mediated bypass of EGFR dependence may circumvent or delay therapeutic resistance are a key research focus. Preclinically, it has been shown that EGFR-mutant NSCLC cell lines are sensitive to inhibition of an upstream node of the MAPK pathway, the Son of Sevenless homolog 1 (SOS1) protein, which functions as a guanine nucleotide exchange factor (GEF) for the RAS subfamily of small GTPases. MRTX0902 is a selective and potent SOS1 inhibitor currently in Phase 1 clinical trials and functions by disrupting the KRAS/SOS1 protein-protein interaction to prevent SOS1-mediated nucleotide exchange on KRAS, ultimately leading to downregulation of KRAS-MAPK pathway signaling. Here we demonstrate that dual inhibition of SOS1 and mutant EGFR by osimertinib results in greater anchorage-independent (3D) cell death and further downregulation of MAPK and PI3K/AKT pathway signaling compared to single agent osimertinib treatment. In our current study, we characterized the anti-tumor effects of SOS1 inhibition by MRTX0902 as a monotherapy and in combination with osimertinib in EGFR mutant models of NSCLC. While single agent MRTX0902 treatment effectively inhibited EGFR mutant cell survival, combination treatment of MRTX0902 with osimertinib resulted in (1) deeper and sustained inhibition of MAPK and PI3K/AKT pathway signaling, (2) enhanced inhibition of 3D cell viability and increased apoptosis, and (3) increased anti-tumor efficacy compared to osimertinib monotherapy in EGFR mutant CDX models in vivo. These studies uncover the potential clinical application of combined vertical inhibition of RTK/MAPK pathway signaling by osimertinib and MRTX0902 and ultimately aide in the understanding of EGFR and RAS biology in targeted cancer therapy. Citation Format: Shilpi Khare, Niranjan Sudhakar, Jade Laguer, David M. Briere, Larry Yan, Allan Hebbert, Andrew Calinisan, Lars D. Engstrom, Fadia Qiryaqos, Peter Olson, James G. Christensen, Jacob R. Haling. Inhibition of SOS1 by MRTX0902 augments the anti-tumor response of the targeted EGFR inhibitor osimertinib in NSCLC [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 3499.

SOS1-inspired hydrocarbon-stapled peptide as a pan-Ras inhibitor

Blocking the interaction between Ras and Son of Sevenless homolog 1 (SOS1) has been an attractive therapeutic strategy for treating cancers involving oncogenic Ras mutations. K-Ras mutation is the most common in Ras-driven cancers, accounting for 86%, with N-Ras mutation and H-Ras mutation accounting for 11% and 3%, respectively. Here, we report the design and synthesis of a series of hydrocarbon-stapled peptides to mimic the alpha-helix of SOS1 as pan-Ras inhibitors. Among these stapled peptides, SSOSH-5 was identified to maintain a well-constrained alpha-helical structure and bind to H-Ras with high affinity. SSOSH-5 was furthermore validated to bind with Ras similarly to the parent linear peptide through structural modeling analysis. This optimized stapled peptide was proven to be capable of effectively inhibiting the proliferation of pan-Ras–mutated cancer cells and inducing apoptosis in a dose-dependent manner by modulating downstream kinase signaling. Of note, SSOSH-5 exhibited a high capability of crossing cell membranes and strong proteolytic resistance. We demonstrated that the peptide stapling strategy is a feasible approach for developing peptide-based pan-Ras inhibitors. Furthermore, we expect that SSOSH-5 can be further characterized and optimized for the treatment of Ras-driven cancers.

Design and Structural Optimization of Orally Bioavailable SOS1 Inhibitors for the Treatment of KRAS-Driven Carcinoma.

KRAS mutations (G12C, G12D, etc.) are implicated in the oncogenesis and progression of many refractory cancers. Son of sevenless homolog 1 (SOS1) is a key regulator of KRAS to modulate KRAS from inactive to active states. Herein, we disclosed efficacy-improving tetra-cyclic quinazoline derivatives as an enhanced scaffold for inhibiting the SOS1-KRAS interaction. Compound 37, which conjugated 1-carbonitrile-cyclopropane to tetra-cyclic quinazoline, showed a twofold higher oral drug exposure and 2.5-fold longer half-life than BI-3406 in CD-1 mouse plasma. In a Mia-paca-2 xenograft model, 37 administrated alone inhibited tumor growth by 71%. Preclinical investigations demonstrated that 37 had a limited inhibition of CYP and hERG. Overall, our studies showed that 37 was a promising drug candidate for treatment of KRAS-driven cancer.

SOS1 regulates HCC cell epithelial-mesenchymal transition via the PI3K/AKT/mTOR pathway

The influence of son of sevenless homolog 1 (SOS1) on invasion and metastasis of hepatocellular carcinoma (HCC) cells was investigated. HCC cells were transfected with siRNA and lentivirus to achieve SOS1 knock down/overexpression and changes in RNA and protein levels analyzed by q-PCR and Western blotting (WB). Transwell assay was utilized to assess variations in cell invasion and migration in vitro and by a lung metastasis model of liver cancer in vivo. High expression of SOS1 was observed in most human liver cancers, which indicated a worse prognosis. SOS1 knockout in HepG2 cells significantly decreased cell invasion and migration. SOS1 knockout also reduced the number of metastatic foci in a lung metastasis model of HCC established in nude mice. SOS1 knockout inhibited the epithelial-mesenchymal transition (EMT) in HepG2 cells as well as the PI3K/AKT/mTOR pathway. Overexpression of SOS1 in Huh7 cells had the opposite effect. To conclude, SOS1 may induce the EMT by the activation of the PI3K/AKT/mTOR pathway, thereby enhancing invasion, migration and metastasis of HCC cells. These findings may expose SOS1 as a new HCC therapeutic target.

Chemically modified MIR143-3p exhibited anti-cancer effects by impairing the KRAS network in colorectal cancer cells

Kirsten rat sarcoma virus (KRAS) mutations are frequently detected in many cancers and are major driver genes. Therefore, KRAS inhibitors have been the subject of extensive research. We developed chemically modified MIR143-3p (MIR143#12), which exhibits higher anticancer activity and nuclease resistance than other commercial inhibitors. MIR143#12 potently suppressed cell growth in colorectal and pancreatic cancer cell lines via apoptosis induced by repression of the entire rat sarcoma virus (RAS) network, which was achieved by silencing KRAS, Son of sevenless homolog 1 (SOS1), AKT, and extracellular signal-regulated kinase (ERK). We investigated the mechanistic advantages of MIR143#12 in various KRAS mutant colorectal cancer cell lines. Its effects were stronger than those of knockdown of KRAS alone in colon cancer cells because silencing of KRAS by small interfering RNA (siRNA) did not decrease the protein expression levels of AKT or ERKs. The KRAS mRNA recruitment system, called the “positive circuit” under effector signaling pathways, may contribute to insensitivity of KRAS mutant cancers to MIR143#12 and siRNAs. In an in vivo study, we newly demonstrated that MIR143#12 induced neoangiogenesis in the tumor microenvironment with growth suppression. Based on the present results, it is crucial to down-regulate not only KRAS but also the entire KRAS signaling network, which may be accomplished by MIR143#12.

Abstract LB193: Chemical genomics identify novel druggable nodes and resistance pathways in the presence of concomitant SOS1 and KRAS inhibition

Abstract KRAS is the most frequently mutated oncogene in human cancer and facilitates uncontrolled growth through hyperactivation of the MAPK pathway. Recent data has consistently demonstrated co-dependencies of mutant-KRAS with extrinsic proteins that augment GTP-loading. Son of Sevenless homolog 1 (SOS1) is the most proximal of these proteins to KRAS and functions as a guanine nucleotide exchange factor (GEF) for the RAS subfamily of small GTPases, thus representing a highly sought-after druggable target. Utilizing a structure-based drug discovery approach, we identified a selective and potent SOS1 inhibitor, MRTX0902, that functions by disrupting the KRAS/SOS1 protein-protein interaction, ultimately preventing SOS1-mediated nucleotide exchange on KRAS. MRTX0902 enhances the anti-tumor activity of the KRASG12C inhibitor adagrasib across multiple KRASG12C-mutant preclinical models; however, it is anticipated that deeper pharmacological inhibition of KRAS signaling may give rise to novel combination targets and additional adaptive resistance mechanisms. To identify additional vulnerabilities and combination strategies, we conducted drug-anchored CRISPR screens in two KRASG12C xenograft models in the presence of MRTX0902 and adagrasib in vitro and in vivo. Interestingly, we found that the SOS1 homolog, SOS2, only emerges as a co-dependency under selective pressure of combination treatment and likely compensates for the inhibition of SOS1. Furthermore, multiple components from the PIK3CA/mTOR signaling pathway, PRMT5, and other non-vertical signal transduction pathways were uncovered and identified as genetic co-dependencies that emerged under selective pressure. Conversely, tumor suppressor genes including TSC1/2, PTEN, NF1, KEAP1 and TP53 along with phosphatases PTPN12 and PTPN14 enhanced tumor growth when knocked out providing a catalogue of putative resistance genes and mechanisms. Lastly, we utilized small molecule inhibitors of putative therapeutic targets identified from our CRISPR screens to validate genetic co-dependencies across in vitro and in vivo translational models. These studies uncover the potential utility of additional drug partners for the MRTX0902 and adagrasib combination and aide in the understanding of SOS and RAS biology in targeted cancer therapy. Citation Format: Shilpi Khare, Niranjan Sudhakar, David M. Briere, Larry Yan, Lars D. Engstrom, Jade Laguer, James Medwid, Laura Vegar, Darin Vanderpool, Matthew A. Marx, John M. Ketcham, James G. Christensen, Peter Olson, Jacob R. Haling. Chemical genomics identify novel druggable nodes and resistance pathways in the presence of concomitant SOS1 and KRAS inhibition [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 LB193.

MiR-148b-3p, as a tumor suppressor, targets son of sevenless homolog 1 to regulate the malignant progression in human osteosarcoma

ABSTRACT Osteosarcoma (OS) is a malignant tumor that occurs in children and adolescents. Previous studies reported a low expression of miR-148b-3p in OS, but its biological function in OS remains obscure. This study aimed to explore the role of miR-148b-3p in OS progression. Herein, the expression of miR-148b-3p and son of sevenless homolog 1 (SOS1) both in OS tissues and cells were examined using quantitative real-time polymerase chain reaction and Western blotting assay. miR-148b-3p mimic or inhibitor, pcDH-SOS1 plasmid or si-SOS1 and agomir-miR-148b-3p were constructed for cell transfection. In vitro, the biological effect of miR-148b-3p was determined employing MTT, EdU, colony formation, flow cytometry, transwell and wound healing assay, separately. The target relationship between SOS1 3’-untranslated region (3’-UTR) and miR-148b-3p was analyzed using dual-luciferase reporter gene. In vivo, the inhibition of agomir-miR-148b-3p in mice was evaluated via a xenograft mouse model. miR-148b-3p was noticeably low-expressed in OS tissues and cells, and miR-148b-3p over-expression in OS cells suppressed the growth, migration and invasion, induced apoptosis. The effect of miR-148b-3p-inhibitor on cell biological behavior is opposite to that of miR-148b-3p over-expression. Conversely, The expression of SOS1 was significant higher in OS tissues and cells, miR-148b-3p targeted and was negatively associated with the expression level of SOS1. In addition, the anti-tumor effect of miR-148b-3p was reversed by SOS1. Importantly, we demonstrated that the tumor growth of stably over-expressed miR-148b-3p human MG-63 cells was obviously reduced in tumor-bearing mice. These data highlighted that miR-148b-3p might be as a promising therapeutic target for OS.

Hypomagnesemia and seizures in a patient with an SOS1 mutation

Noonan syndrome (NS) is an autosomal dominant multisystem disorder. The son of sevenless homolog 1 (symbolized SOS1) gene encodes a guanine nucleotide exchange factor (GEF) for Ras proteins.[1] Genetic disorders in which the SOS1 mutation has been confirmed include NS. Missense mutations in SOS1 account for roughly 10% of NS.[2]

Abstract P470: Disrupted HRAS/GRB2 Signaling In Induced-cardiomyocytes Derived From Patients With Noonan Syndrome Carrying SOS1 Gene Mutation

Background: Noonan syndrome (NS), a dominant autosomal genetic disorder that prevents normal development, and exhibits cardiac defects, which is estimated to appear in 50% to 90% of patients. Son of sevenless homolog 1 (SOS1) gene mutation has been identified as a major gene causing NS and attributes to the development of cardiomyopathy and congenital heart defects. SOS1 is a guanine nucleotide exchange factor for RAS and is known to interact with growth factor receptor-bound protein 2 (GRB2). Recently, we have generated induced pluripotent stem cells (iPSCs)-derived cardiomyocytes (iCMCs) from cardiac fibroblasts obtained from a NS patient carrying SOS1 gene variant 1654A>G. Hypothesis: Since NS is known to have aberrant RAS-MAPK signaling, we hypothesize that iCMCs derived from NS patient (NS-iCMCs) may have atypical RAS signaling leading to the development of cardiomyopathy. Methods and Results: We have compared the normal skin fibroblast-derived iPSCs (N-iPSCs) and N-iCMCs with NS patient-derived induced NS-iPSCs and NS-iCMCs. Our qRT-PCR results showed that the mRNA expressions of signaling molecules HRAS, GRB2 and SOS1 were significantly decreased in NS-iCMCs compared with N-iCMCs (Figure A), and further confirmed through the protein expression by Western immunoblotting (Figure B). These results were in association with a significantly decreased mRNA and protein expressions of cardiac transcription factor GATA4, and structural proteins alpha sarcomeric actinin-2 (ACTN2), cardiac troponin T (TNNT2) and tropomyosin alpha-1 (TPM1) in NS-iCMCs compared with N-iCMCs. Further studies are underway to explore the difference in the guanine nucleotide exchange factor (GEF) activity and ERK activation between NS-iCMCs and N-iCMCs. Conclusion: Our current findings clearly indicate that the SOS1-associated signaling molecules HRAS and GRB2 were disrupted in NS-iCMCs, which may result in the development of cardiomyopathy in NS patients.

SOS1 promotes epithelial-mesenchymal transition of Epithelial Ovarian Cancer(EOC) cells through AKT independent NF-κB signaling pathway

We aimed to explore the role and mechanism of SOS1 (Son of sevenless homolog 1) in malignant behaviors of epithelial ovarian cancer (EOC) cells Hey with high metastatic potential. Firstly, compared with Hey-WT (wild type) and Hey-NT (none targeted) cells, Hey-SOS1i cells showed decreased polarities, disorders in cytoskeleton arrangement. Numbers of transwell migrated, invaded, intravasation cells and extravasated cells were decreased significantly. Hey-NT cells and Hey-SOS1i cells were employed to establish a peritoneal dissemination model in nude mice. Hey-SOS1i cells formed less implantation metastatic foci in the abdominal cavity than Hey-NT cells, especially on the intestine and diaphragm in the 5th week after the tumor cells were injected intraperitoneally. SOS1 knockdown in Hey cells resulted in increased E-cadherin and decreased Vimentin, N-cadherin, MMP2, and MMP9, together with reduced Snail and activation of NF-κB pathway. Together, these results suggest SOS1 might induce EMT through activating AKT independent NF-κB pathway and the transcriptive activity of Snail, and subsequently regulate the cytoskeleton reprogramming and cell motility of Hey, one of EOC cells with high metastatic potential. This may provide some new targets for the treatment of ovarian cancer with high metastatic potential.