Critical requirement of SOS1 RAS-GEF function for mitochondrial dynamics, metabolism, and redox homeostasis

SOS1 Inhibition Enhances the Efficacy of KRASG12C Inhibitors and Delays Resistance in Lung Adenocarcinoma

The clinical effectiveness of KRASG12C inhibitors (G12Ci) is limited both by intrinsic and acquired resistance, necessitating the development of combination approaches. Here, we identified targeting proximal receptor tyrosine kinase signaling using the SOS1 inhibitor (SOS1i) BI-3406 as a strategy to improve responses to G12Ci treatment. SOS1i enhanced the efficacy of G12Ci and limited rebound receptor tyrosine kinase/ERK signaling to overcome intrinsic/adaptive resistance, but this effect was modulated by SOS2 protein levels. G12Ci drug-tolerant persister (DTP) cells showed up to a 3-fold enrichment of tumor-initiating cells (TIC), suggestive of a sanctuary population of G12Ci-resistant cells. SOS1i resensitized DTPs to G12Ci and inhibited G12C-induced TIC enrichment. Co-mutation of the tumor suppressor KEAP1 limited the clinical effectiveness of G12Ci, and KEAP1 and STK11 deletion increased TIC frequency and accelerated the development of acquired resistance to G12Ci, consistent with clinical G12Ci resistance seen with these co-mutations. Treatment with SOS1i both delayed acquired G12Ci resistance and limited the total number of resistant colonies regardless of KEAP1 and STK11 mutational status. Together, these data suggest that targeting SOS1 could be an effective strategy to both enhance G12Ci efficacy and prevent G12Ci resistance regardless of co-mutations. Significance: The SOS1 inhibitor BI-3406 both inhibits intrinsic/adaptive resistance and targets drug tolerant persister cells to limit the development of acquired resistance to clinical KRASG12C inhibitors in lung adenocarcinoma cells.

Polyphyllin VII Promotes Apoptosis in Breast Cancer by Inhibiting MAPK/ERK Signaling Pathway through Downregulation of SOS1

Polyphyllin VII is a biologically active herbal monomer extracted from the traditional Chinese herbal medicine Chonglou. Many studies have demonstrated the anticancer activity of polyphyllin VII against various types of cancers, such as colon, liver, and lung cancer, but its effect on breast cancer has not been elucidated. In this study, we demonstrate that polyphyllin VII inhibited proliferation, increased production of intracellular reactive oxygen species, and decreased mitochondrial membrane potential in breast cancer cells. Notably, polyphyllin VII also induced apoptosis via the mitochondrial pathway. Transcriptome sequencing was used to analyze the targets of PPVII in regulating breast cancer cells. Mechanistic studies showed that polyphyllin VII downregulated Son of Sevenless1 (SOS1) and inhibited the MAPK/ERK pathway. Furthermore, PPVII exerted strong antitumor effects in vivo in nude mice injected with breast cancer cells. Our results suggest that PPVII may promote apoptosis through regulating the SOS1/MAPK/ERK pathway, making it a possible candidate target for the treatment of breast cancer.

Current advances and development strategies of targeting son of sevenless 1 (SOS1) in drug discovery

The Son of Sevenless 1 (SOS1) guanine nucleotide exchange factor, prevalent across eukaryotic species, plays a pivotal role in facilitating the attachment of RAS protein to GTP, thereby regulating the activation of intracellular RAS proteins. This regulation is part of a feedback mechanism involving SOS1, which allows both activators and inhibitors of SOS1 to exert control over downstream signaling pathways, demonstrating potential anti-tumor effects. Predominantly, small molecule modulators that target SOS1 focus on a hydrophobic pocket within the CDC25 protein domain. The effectiveness of these modulators largely depends on their ability to interact with specific amino acids, notably Phe890 and Tyr884. This interaction is crucial for influencing the protein-protein interaction (PPI) between RAS and the catalytic domain of SOS1. Currently, most small molecule modulators targeting SOS1 are in the preclinical research phase, with a few advancing to clinical trials. This progression raises safety concerns, making the assurance of drug safety a primary consideration alongside the enhancement of efficacy in the development of SOS1 modulators. This review encapsulates recent advancements in the chemical categorization of SOS1 inhibitors and activators. It delves into the evolution of small molecule modulation targeting SOS1 and offers perspectives on the design of future generations of selective SOS1 small molecule modulators.

Discovery of Five SOS2 Fragment Hits with Binding Modes Determined by SOS2 X-Ray Cocrystallography

SOS1 and SOS2 are guanine nucleotide exchange factors that mediate RTK-stimulated RAS activation. Selective SOS1:KRAS PPI inhibitors are currently under clinical investigation, whereas there are no reports to date of SOS2:KRAS PPI inhibitors. SOS2 activity is implicated in MAPK rebound when divergent SOS1 mutant cell lines are treated with the SOS1 inhibitor BI-3406; therefore, SOS2:KRAS inhibitors are of therapeutic interest. In this report, we detail a fragment-based screening strategy to identify X-ray cocrystal structures of five diverse fragment hits bound to SOS2.

SOS1 inhibition enhances the efficacy of and delays resistance to G12C inhibitors in lung adenocarcinoma

Clinical effectiveness of KRAS G12C inhibitors (G12Cis) is limited both by intrinsic and acquired resistance, necessitating the development of combination approaches. We found that targeting proximal receptor tyrosine kinase (RTK) signaling using the SOS1 inhibitor (SOS1i) BI-3406 both enhanced the potency of and delayed resistance to G12Ci treatment, but the extent of SOS1i effectiveness was modulated by both SOS2 expression and the specific mutational landscape. SOS1i enhanced the efficacy of G12Ci and limited rebound RTK/ERK signaling to overcome intrinsic/adaptive resistance, but this effect was modulated by SOS2 protein levels. Survival of drug-tolerant persister (DTP) cells within the heterogeneous tumor population and/or acquired mutations that reactivate RTK/RAS signaling can lead to outgrowth of tumor initiating cells (TICs) that drive therapeutic resistance. G12Ci drug tolerant persister cells showed a 2-3-fold enrichment of TICs, suggesting that these could be a sanctuary population of G12Ci resistant cells. SOS1i re-sensitized DTPs to G12Ci and inhibited G12C-induced TIC enrichment. Co-mutation of the tumor suppressor KEAP1 limits the clinical effectiveness of G12Cis, and KEAP1 and STK11 deletion increased TIC frequency and accelerated the development of acquired resistance to G12Ci in situ. SOS1i both delayed acquired G12Ci resistance and limited the total number of resistant colonies regardless of KEAP1 and STK11 mutational status. These data suggest that SOS1i could be an effective strategy to both enhance G12Ci efficacy and prevent G12Ci resistance regardless of co-mutations.

Critical requirement of SOS1 for tumor development and microenvironment modulation in KRASG12D-driven lung adenocarcinoma

The impact of genetic ablation of SOS1 or SOS2 is evaluated in a murine model of KRASG12D-driven lung adenocarcinoma (LUAD). SOS2 ablation shows some protection during early stages but only SOS1 ablation causes significant, specific long term increase of survival/lifespan of the KRASG12D mice associated to markedly reduced tumor burden and reduced populations of cancer-associated fibroblasts, macrophages and T-lymphocytes in the lung tumor microenvironment (TME). SOS1 ablation also causes specific shrinkage and regression of LUAD tumoral masses and components of the TME in pre-established KRASG12D LUAD tumors. The critical requirement of SOS1 for KRASG12D-driven LUAD is further confirmed by means of intravenous tail injection of KRASG12D tumor cells into SOS1KO/KRASWT mice, or of SOS1-less, KRASG12D tumor cells into wildtype mice. In silico analyses of human lung cancer databases support also the dominant role of SOS1 regarding tumor development and survival in LUAD patients. Our data indicate that SOS1 is critically required for development of KRASG12D-driven LUAD and confirm the validity of this RAS-GEF activator as an actionable therapeutic target in KRAS mutant LUAD.

LC-MS/MS based metabolomics and proteomics reveal candidate biomarkers and molecular mechanism of early IgA nephropathy

BACKGROUND

Immunoglobulin A nephropathy (IgAN), a globally common primary chronic glomerulopathy, is one of the leading causes of end-stage renal disease. However, the underlying mechanisms of IgAN have yet to be demonstrated. There were no adequate and reliable plasma biomarkers for clinical diagnosis, especially at the early stage. In the present study, integrative proteomics and metabolomics were aimed at exploring the mechanism of IgAN and identifying potential biomarkers.

METHODS

Plasma from IgAN and healthy individuals were collected and analyzed in a randomized controlled manner. Data-independent acquisition quantification proteomics and mass spectrometry based untargeted metabolomics techniques were used to profile the differentially expressed proteins (DEPs) and differentially abundant metabolites (DAMs) between two groups and identify potential biomarkers for IgAN from health at the early stage. Disease-related pathways were screened out by clustering and function enrichment analyses of DEPs and DAMs. And the potential biomarkers for IgAN were identified through the machine learning approach. Additionally, an independent cohort was used to validate the priority candidates by enzyme-linked immunosorbent assay (ELISA).

RESULTS

Proteomic and metabolomic analyses of IgAN plasma showed that the complement and the immune system were activated, while the energy and amino acid metabolism were disordered in the IgAN patients. PRKAR2A, IL6ST, SOS1, and palmitoleic acid have been identified as potential biomarkers. Based on the AUC value for the training and test sets, the classification performance was 0.994 and 0.977, respectively. The AUC of the external validation of the four biomarkers was 0.91.

CONCLUSION

In this study, we combined proteomics and metabolomics techniques to analyze the plasma of IgAN patients and healthy individuals, constructing a biomarker panel, which could provide new insights and provide potential novel molecular diagnoses for IgAN.

Effects of Noonan Syndrome-Germline Mutations on Mitochondria and Energy Metabolism

Noonan syndrome (NS) and related Noonan syndrome with multiple lentigines (NSML) contribute to the pathogenesis of human diseases in the RASopathy family. This family of genetic disorders constitute one of the largest groups of developmental disorders with variable penetrance and severity, associated with distinctive congenital disabilities, including facial features, cardiopathies, growth and skeletal abnormalities, developmental delay/mental retardation, and tumor predisposition. NS was first clinically described decades ago, and several genes have since been identified, providing a molecular foundation to understand their physiopathology and identify targets for therapeutic strategies. These genes encode proteins that participate in, or regulate, RAS/MAPK signalling. The RAS pathway regulates cellular metabolism by controlling mitochondrial homeostasis, dynamics, and energy production; however, little is known about the role of mitochondrial metabolism in NS and NSML. This manuscript comprehensively reviews the most frequently mutated genes responsible for NS and NSML, covering their role in the current knowledge of cellular signalling pathways, and focuses on the pathophysiological outcomes on mitochondria and energy metabolism.

Critical Requirement of SOS1 for Development of BCR/ABL-Driven Chronic Myelogenous Leukemia

Simple Summary

The p210^BCR/ABL oncoprotein is necessary and sufficient to trigger chronic myelogenous leukemia (CML) in mice. Our prior in vitro studies showing that the ABL-mediated phosphorylation of SOS1 promotes RAC activation and contributes to BCR-ABL leukemogenesis suggested the significant role of SOS1 in the development of CML. To provide direct in vivo experimental evidence of the specific contribution of SOS1 to the development of CML, here, we analyzed the effect of the direct genetic ablation of SOS1 or SOS2 on the genesis of p210^BCR/ABL -driven CML in mice. Our data showed that direct SOS1 genetic ablation causes the significant suppression of all the pathological hallmarks typical of CML, demonstrating that SOS1 deficiency is protective against CML development and identifying this cellular GEF as a relevant, novel therapeutic target for the clinical treatment of this hematological malignancy.

Abstract

We showed previously that the ABL-mediated phosphorylation of SOS1 promotes RAC activation and contributes to BCR-ABL leukemogenesis, suggesting the relevant role of SOS1 in the pathogenesis of CML. To try and obtain direct experimental evidence of the specific mechanistic implication of SOS1 in CML development, here, we combined a murine model of CML driven by a p210^BCR/ABL transgene with our tamoxifen-inducible SOS1/2-KO system in order to investigate the phenotypic impact of the direct genetic ablation of SOS1 or SOS2 on the pathogenesis of CML. Our observations showed that, in contrast to control animals expressing normal levels of SOS1 and SOS2 or to single SOS2-KO mice, p210^BCR/ABL transgenic mice devoid of SOS1 presented significantly extended survival curves and also displayed an almost complete disappearance of the typical hematological alterations and splenomegaly constituting the hallmarks of CML. SOS1 ablation also resulted in a specific reduction in the proliferation and the total number of colony-forming units arising from the population of bone marrow stem/progenitor cells from p210^BCR/ABL transgenic mice. The specific blockade of CML development caused by SOS1 ablation in p210^BCR/ABL mice indicates that SOS1 is critically required for CML pathogenesis and supports the consideration of this cellular GEF as a novel, alternative bona fide therapeutic target for CML treatment in the clinic.

Oxidative Stress in Arterial Hypertension (HTN): The Nuclear Factor Erythroid Factor 2-Related Factor 2 (Nrf2) Pathway, Implications and Future Perspectives

Arterial hypertension (HTN) is one of the most prevalent entities globally, characterized by increased incidence and heterogeneous pathophysiology. Among possible etiologies, oxidative stress (OS) is currently extensively studied, with emerging evidence showing its involvement in endothelial dysfunction and in different cardiovascular diseases (CVD) such as HTN, as well as its potential as a therapeutic target. While there is a clear physiological equilibrium between reactive oxygen species (ROS) and antioxidants essential for many cellular functions, excessive levels of ROS lead to vascular cell impairment with decreased nitric oxide (NO) availability and vasoconstriction, which promotes HTN. On the other hand, transcription factors such as nuclear factor erythroid factor 2-related factor 2 (Nrf2) mediate antioxidant response pathways and maintain cellular reduction-oxidation homeostasis, exerting protective effects. In this review, we describe the relationship between OS and hypertension-induced endothelial dysfunction and the involvement and therapeutic potential of Nrf2 in HTN.

Inhibition of KDM5A attenuates cisplatin-induced hearing loss via regulation of the MAPK/AKT pathway

The study aimed to investigate the potential role of lysine-specific demethylase 5A (KDM5A) in cisplatin-induced ototoxicity. The effect of the KDM5A inhibitor CPI-455 was assessed by apoptosis assay, immunofluorescence, flow cytometry, seahorse respirometry assay, and auditory brainstem response test. RNA sequencing, qRT-PCR, and CUT&Tag assays were used to explore the mechanism underlying CPI-455-induced protection. Our results demonstrated that the expression of KDM5A was increased in cisplatin-injured cochlear hair cells compared with controls. CPI-455 treatment markedly declined KDM5A and elevated H3K4 trimethylation levels in cisplatin-injured cochlear hair cells. Moreover, CPI-455 effectively prevented the death of hair cells and spiral ganglion neurons and increased the number of ribbon synapses in a cisplatin-induced ototoxicity mouse model both in vitro and in vivo. In HEI-OC1 cells, KDM5A knockdown reduced reactive oxygen species accumulation and improved mitochondrial membrane potential and oxidative phosphorylation under cisplatin-induced stress. Mechanistically, through transcriptomics and epigenomics analyses, a set of apoptosis-related genes, including Sos1, Sos2, and Map3k3, were regulated by CPI-455. Altogether, our findings indicate that inhibition of KDM5A may represent an effective epigenetic therapeutic target for preventing cisplatin-induced hearing loss.

Proteasome inhibition induces macrophage apoptosis via mitochondrial dysfunction

Dysfunction of the ubiquitin-proteasome system has been linked to the pathogenesis of a variety of diseases. Proteasome inhibition not only exerts antitumor effects but also affects inflammatory signaling pathways. MG132, a proteasome inhibitor, has been shown to induce tumor cell apoptosis. However, its role in the induction of macrophage apoptosis remains unknown. In our study, we investigated the mechanism of the proapoptotic effects of MG132 in macrophages. Our data showed that MG132 treatment induced mitochondrial reactive oxygen species (ROS) generation and loss of mitochondrial membrane potential in macrophages. We found that proteasome inhibition induced a significant increase in the apoptosis rate, as evidenced by cleavage of caspase-3 and cleavage of poly(ADP-ribose) polymerase (PARP). Moreover, (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenyl-phosphonium chloride (Mito-TEMPO) attenuated MG132-induced apoptosis. In conclusion, proteasome inhibition by MG132 can induce macrophage apoptosis by promoting the production of ROS and mitochondrial dysfunction.

SOS2 Comes to the Fore: Differential Functionalities in Physiology and Pathology

The SOS family of Ras-GEFs encompasses two highly homologous and widely expressed members, SOS1 and SOS2. Despite their similar structures and expression patterns, early studies of constitutive KO mice showing that SOS1-KO mutants were embryonic lethal while SOS2-KO mice were viable led to initially viewing SOS1 as the main Ras-GEF linking external stimuli to downstream RAS signaling, while obviating the functional significance of SOS2. Subsequently, different genetic and/or pharmacological ablation tools defined more precisely the functional specificity/redundancy of the SOS1/2 GEFs. Interestingly, the defective phenotypes observed in concomitantly ablated SOS1/2-DKO contexts are frequently much stronger than in single SOS1-KO scenarios and undetectable in single SOS2-KO cells, demonstrating functional redundancy between them and suggesting an ancillary role of SOS2 in the absence of SOS1. Preferential SOS1 role was also demonstrated in different RASopathies and tumors. Conversely, specific SOS2 functions, including a critical role in regulation of the RAS-PI3K/AKT signaling axis in keratinocytes and KRAS-driven tumor lines or in control of epidermal stem cell homeostasis, were also reported. Specific SOS2 mutations were also identified in some RASopathies and cancer forms. The relevance/specificity of the newly uncovered functional roles suggests that SOS2 should join SOS1 for consideration as a relevant biomarker/therapy target.