Sos-mediated cross-activation of wild-type Ras by oncogenic Ras is essential for tumorigenesis

Design, synthesis, and bioevaluation of SOS1 PROTACs derived from pyrido[2,3-d]pyrimidin-7-one-based SOS1 inhibitor

Oncogenic KRAS mutations drive an approximately 25 % of all human cancers. Son of Sevenless 1 (SOS1), a critical guanine nucleotide exchange factor, catalyzes the activation of KRAS. Targeting SOS1 degradation has engaged as a promising therapeutic strategy for KRAS-mutant cancers. Herein, we designed and synthesized a series of novel CRBN-recruiting SOS1 PROTACs using the pyrido[2,3-d]pyrimidin-7-one-based SOS1 inhibitor as the warhead. One representative compound 11o effectively induced the degradation of SOS1 in three different KRAS-mutant cancer cell lines with DC50 values ranging from 1.85 to 7.53 nM. Mechanism studies demonstrated that 11o-induced SOS1 degradation was dependent on CRBN and proteasome. Moreover, 11o inhibited the phosphorylation of ERK and displayed potent anti-proliferative activities against SW620, A549 and DLD-1 cells. Further optimization of 11o may provide us promising SOS1 degraders with favorable drug-like properties for developing new chemotherapies targeting KRAS-driven cancers.

State-of-the-art and upcoming trends in RAS-directed therapies in gastrointestinal malignancies

PURPOSE OF REVIEW

Overall, the review underscores the evolving landscape of KRAS-targeted therapy and the potential for these approaches to improve outcomes for patients with gastrointestinal malignancies. It highlights the importance of ongoing research and clinical trials in advancing precision medicine strategies for KRAS-driven cancers. This review provides a comprehensive overview of the RAS signaling pathway and its significance in gastrointestinal malignancies.

RECENT FINDINGS

The introduction of KRAS inhibitor represents a significant advancement in the treatment landscape for KRAS-mutant cancers. In this review, we discuss upcoming trends in KRAS-targeted therapy, including the development of mutant-specific direct KRAS inhibitors like MRTX1133 and pan-RAS inhibitors such as RMC-6236. It also explores indirect RAS inhibitors targeting upstream and downstream components of the RAS pathway. Additionally, the review examines other upcoming strategies like combination therapies, such as CDK4/6 and ERK MAPK inhibitors, as well as adoptive cell therapy and cancer vaccines targeting KRAS-mutant cancers.

SUMMARY

Targeting RAS has become an important strategy in treating gastrointestinal cancer. These findings in this review underscore the importance of a multidisciplinary approach, integrating advances in molecular profiling, targeted therapy, immunotherapy, and clinical research to optimize treatment strategies for patients with KRAS-mutant gastrointestinal malignancies.

Identifying Potential SOS1 Inhibitors via Virtual Screening of Multiple Small Molecule Libraries against KRAS-SOS1 Interaction

The RAS-MAPK signaling pathway, crucial for cell proliferation and differentiation, involves key proteins KRAS and SOS1. Mutations in the KRAS and SOS1 genes are implicated in various cancer types, including pancreatic, lung, and juvenile myelomonocytic leukemia. There is considerable interest in identifying inhibitors targeting KRAS and SOS1 to explore potential therapeutic strategies for cancer treatment. In this study, advanced in silico techniques were employed to screen small molecule libraries at this interface, leading to the identification of promising lead compounds as potential SOS1 inhibitors. Comparative analysis of the average binding free energies of these predicted potent compounds with known SOS1 small molecule inhibitors revealed that the identified compounds display similar or even superior predicted binding affinities compared to the known inhibitors. These findings offer valuable insights into the potential of these compounds as candidates for further development as effective anti-cancer agents.

Targeting guanine nucleotide exchange factors for novel cancer drug discovery

INTRODUCTION

Guanine nucleotide exchange factors (GEFs) regulate the activation of small GTPases (G proteins) of the Ras superfamily proteins controlling cellular functions. Ras superfamily proteins act as 'molecular switches' that are turned 'ON' by guanine exchange. There are five major groups of Ras family GTPases: Ras, Ran, Rho, Rab and Arf, with a variety of different GEFs regulating their GTP loading. GEFs have been implicated in various diseases including cancer. This makes GEFs attractive targets to modulate signaling networks controlled by small GTPases.

AREAS COVERED

In this review, the roles and mechanisms of GEFs in malignancy are outlined. The mechanism of guanine exchange activity by GEFs on a small GTPase is illustrated. Then, some examples of GEFs that are significant in cancer are presented with a discussion on recent progress in therapeutic targeting efforts using a variety of approaches.

EXPERT OPINION

Recently, GEFs have emerged as potential therapeutic targets for novel cancer drug development. Targeting small GTPases is challenging; thus, targeting their activation by GEFs is a promising strategy. Most GEF-targeted drugs are still in preclinical development. A deeper biological understanding of the underlying mechanisms of GEF activity and utilizing advanced technology are necessary to enhance drug discovery for GEFs in cancer.

Biological and targeting differences between the rare KRAS A146T and canonical KRAS mutants in gastric cancer models

BACKGROUND

Gastric cancer (GC) is the third leading cause of cancer-related death worldwide, with a poor prognosis for patients with advanced disease. Since the oncogenic role of KRAS mutants has been poorly investigated in GC, this study aims to biochemically and biologically characterize different KRAS-mutated models and unravel differences among KRAS mutants in response to therapy.

METHODS

Taking advantage of a proprietary, molecularly annotated platform of more than 200 GC PDXs (patient-derived xenografts), we identified KRAS-mutated PDXs, from which primary cell lines were established. The different mutants were challenged with KRAS downstream inhibitors in in vitro and in vivo experiments.

RESULTS

Cells expressing the rare KRAS A146T mutant showed lower RAS-GTP levels compared to those bearing the canonical G12/13D mutations. Nevertheless, all the KRAS-mutated cells displayed KRAS addiction. Surprisingly, even if the GEF SOS1 is considered critical for the activation of KRAS A146T mutants, its abrogation did not significantly affect cell viability. From the pharmacologic point of view, Trametinib monotherapy was more effective in A146T than in G12D-mutated models, suggesting a vulnerability to MEK inhibition. However, in the presence of mutations in the PI3K pathway, more frequently co-occurrent in A146T models, the association of Trametinib and the AKT inhibitor MK-2206 was required to optimize the response.

CONCLUSION

A deeper genomic and biological characterization of KRAS mutants might sustain the development of more efficient and long-lasting therapeutic options for patients harbouring KRAS-driven GC.

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.

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.

Stereoselective Amine Synthesis Mediated by a Zirconocene Hydride to Accelerate a Drug Discovery Program

Chiral amine synthesis remains a significant challenge in accelerating the design cycle of drug discovery programs. A zirconium hydride, due to its high oxophilicity and lower reactivity, gave highly chemo- and stereoselective reductions of sulfinyl ketimines. The development of this zirconocene-mediated reduction helped to accelerate our drug discovery efforts and is applicable to several motifs commonly used in medicinal chemistry. Computational investigation supported a cyclic half-chair transition state to rationalize the high selectivity in benzyl systems.

SOS2 modulates the threshold of EGFR signaling to regulate osimertinib efficacy and resistance in lung adenocarcinoma

Son of sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic receptor tyrosine kinase (RTK)-dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR tyrosine kinase inhibitor (EGFR-TKI) osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion (SOS2KO ) sensitized EGFR-mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit phosphatidylinositol 3-kinase (PI3K)/AKT pathway activation, oncogenic transformation, and survival. Bypassing RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR-TKIs; SOS2KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET-driven bypass model, SOS2KO inhibited hepatocyte growth factor (HGF)-stimulated PI3K signaling to block HGF-driven osimertinib resistance. Using a long-term in situ resistance assay, most osimertinib-resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT-dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2KO cultures that became osimertinib resistant primarily underwent non-RTK-dependent epithelial-mesenchymal transition (EMT). Since bypassing RTK reactivation and/or tertiary EGFR mutations represent most osimertinib-resistant cancers, these data suggest that targeting proximal RTK signaling, here exemplified by SOS2 deletion, has the potential to delay the development osimertinib resistance and enhance overall clinical responses for patients with EGFR-mutated LUAD.

A Potent SOS1 PROTAC Degrader with Synergistic Efficacy in Combination with KRASG12C Inhibitor

AMG510, as the first approved inhibitor for KRASG12C mutation, has shown promising efficacy in nonsmall-cell lung cancer and colorectal cancer harboring KRASG12C mutation. However, the moderate response rate and the rapid emergence of acquired resistance limit the therapeutic potential of AMG510, highlighting the need for the development of combination strategies. Here, we observed the suppression of RAS-MAPK signaling induced by AMG510 was prolonged and enhanced by SOS1 knockdown. Thus, we design, synthesize, and characterize a potent and specific SOS1 degrader 23. Compound 23 showed efficient SOS1 degradation in KRAS-driven cancer cells and achieved significant antiproliferative potency. Importantly, the combination of 23 with AMG510 suppressed RAS signaling feedback activation, showing synergistic effects against KRASG12C mutant cells in vitro and in vivo. Our findings demonstrated that KRASG12C inhibition plus SOS1 degradation as a potential therapeutic strategy to improve antitumor response and overcome acquired resistance to KRASG12C inhibitor.

Inhibition of the RAF/MEK/ERK Signaling Cascade in Pancreatic Cancer: Recent Advances and Future Perspectives

Pancreatic cancer represents a formidable challenge in oncology, primarily due to its aggressive nature and limited therapeutic options. The prognosis of patients with pancreatic ductal adenocarcinoma (PDAC), the main form of pancreatic cancer, remains disappointingly poor with a 5-year overall survival of only 5%. Almost 95% of PDAC patients harbor Kirsten rat sarcoma virus (KRAS) oncogenic mutations. KRAS activates downstream intracellular pathways, most notably the rapidly accelerated fibrosarcoma (RAF)/mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) signaling axis. Dysregulation of the RAF/MEK/ERK pathway is a crucial feature of pancreatic cancer and therefore its main components, RAF, MEK and ERK kinases, have been targeted pharmacologically, largely by small-molecule inhibitors. The recent advances in the development of inhibitors not only directly targeting the RAF/MEK/ERK pathway but also indirectly through inhibition of its regulators, such as Src homology-containing protein tyrosine phosphatase 2 (SHP2) and Son of sevenless homolog 1 (SOS1), provide new therapeutic opportunities. Moreover, the discovery of allele-specific small-molecule inhibitors against mutant KRAS variants has brought excitement for successful innovations in the battle against pancreatic cancer. Herein, we review the recent advances in targeted therapy and combinatorial strategies with focus on the current preclinical and clinical approaches, providing critical insight, underscoring the potential of these efforts and supporting their promise to improve the lives of patients with PDAC.

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.

Studying early structural changes in SOS1 mediated KRAS activation mechanism

KRAS activation is known to be modulated by a guanine nucleotide exchange factor (GEF), namely, Son of Sevenless1 (SOS1). SOS1 facilitates the exchange of GDP to GTP thereby leading to activation of KRAS. The binding of GDP/GTP to KRAS at the REM/allosteric site of SOS1 regulates the activation of KRAS at CDC25/catalytic site by facilitating its exchange. Different aspects of the allosteric activation of KRAS through SOS1 are still being explored. To understand the SOS1 mediated activation of KRAS, molecular dynamics simulations for a total of nine SOS1 complexes (KRAS-SOS1-KRAS) were performed. These nine systems comprised different combinations of KRAS-bound nucleotides (GTP/GDP) at REM and CDC25 sites of SOS1. Various conformational and thermodynamic parameters were analyzed for these simulation systems. MMPBSA free energy analysis revealed that binding at CDC25 site of SOS1 was significantly low for GDP-bound KRAS as compared to that of GTP-bound KRAS. It was observed that presence of either GDP/GTP bound KRAS at the REM site of SOS1 affected the activation related changes in the KRAS present at CDC25 site. The conformational changes at the catalytic site of SOS1 resulting from GDP/GTP-bound KRAS at the allosteric changes may hint at KRAS activation through different pathways (slow/fast/rare). The allosteric effect on activation of KRAS at CDC25 site may be due to conformations adopted by switch-I, switch-II, beta2 regions of KRAS at REM site. The effect of structural rearrangements occurring at allosteric KRAS may have led to increased interactions between SOS1 and KRAS at both the sites. The SOS1 residues involved in these important interactions with KRAS at the REM site were R694, S732 and K735. Whereas the ones interacting with KRAS at CDC25 site were S807, W809 and K814. This may suggest the crucial role of these residues in guiding the allosteric activation of KRAS at CDC25 site. The conformational shifts observed in the switch-I, switch-II and alpha3 regions of KRAS at CDC25 site may be attributed to be a part of allosteric activation. The binding affinities, interacting residues and conformational dynamics may provide an insight into development of inhibitors targeting the SOS1 mediated KRAS activation.

Inhibition of Son of Sevenless Homologue 1 (SOS1): Promising therapeutic treatment for KRAS-mutant cancers

Kristen rat sarcoma (KRAS) is one of the most common oncogenes in human cancers. As a guanine nucleotide exchange factor, Son of Sevenless Homologue 1 (SOS1) represents a potential therapeutic concept for the treatment of KRAS-mutant cancers because of its activation on KRAS and downstream signaling pathways. In this review, we provide a comprehensive overview of the structure, biological function, and regulation of SOS1. We also focus on the recent advances in SOS1 inhibitors and emphasize their binding modes, structure-activity relationships and pharmacological activities. We hope that this publication can provide a comprehensive compendium on the rational design of SOS1 inhibitors.

Targeting KRAS in Pancreatic Ductal Adenocarcinoma: The Long Road to Cure

Pancreatic ductal adenocarcinoma (PDAC) remains an important cause of cancer-related mortality, and it is expected to play an even bigger part in cancer burden in the years to come. Despite concerted efforts from scientists and physicians, patients have experienced little improvement in survival over the past decades, possibly because of the non-specific nature of the tested treatment modalities. Recently, the discovery of potentially targetable molecular alterations has paved the way for the personalized treatment of PDAC. Indeed, the central piece in the molecular framework of PDAC is starting to be unveiled. KRAS mutations are seen in 90% of PDACs, and multiple studies have demonstrated their pivotal role in pancreatic carcinogenesis. Recent investigations have shed light on the differences in prognosis as well as therapeutic implications of the different KRAS mutations and disentangled the relationship between KRAS and effectors of downstream and parallel signaling pathways. Additionally, the recognition of other mechanisms involving KRAS-mediated pathogenesis, such as KRAS dosing and allelic imbalance, has contributed to broadening the current knowledge regarding this molecular alteration. Finally, KRAS G12C inhibitors have been recently tested in patients with pancreatic cancer with relative success, and inhibitors of KRAS harboring other mutations are under clinical development. These drugs currently represent a true hope for a meaningful leap forward in this dreadful disease.

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.

Prognostic and therapeutic impact of the KRAS G12C mutation in colorectal cancer

KRAS G12C mutations are critical in the pathogenesis of multiple cancer types, including non-small cell lung (NSCLC), pancreatic ductal adenocarcinoma (PDAC), and colorectal (CRC) cancers. As such, they have increasingly become a target of novel therapies in the management of these malignancies. However, the therapeutic success of KRAS G12C inhibitors to date has been far more limited in CRC and PDAC than NSCLC. In this review, we briefly summarize the biochemistry of KRAS targeting and treatment resistance, highlight differences in the epidemiology of various G12C-mutated cancers, and provide an overview of the published data on KRAS G12C inhibitors for various indications. We conclude with a summary of ongoing clinical trials in G12C-mutant CRC and a discussion of future directions in the management of this disease. KRAS G12C mutation, targeted therapies, colorectal cancer, non-small cell lung cancer, pancreatic cancer, drug development.

Proteomic Mapping of the Interactome of KRAS Mutants Identifies New Features of RAS Signalling Networks and the Mechanism of Action of Sotorasib

RAS proteins are key regulators of cell signalling and control different cell functions including cell proliferation, differentiation, and cell death. Point mutations in the genes of this family are common, particularly in KRAS. These mutations were thought to cause the constitutive activation of KRAS, but recent findings showed that some mutants can cycle between active and inactive states. This observation, together with the development of covalent KRASG12C inhibitors, has led to the arrival of KRAS inhibitors in the clinic. However, most patients develop resistance to these targeted therapies, and we lack effective treatments for other KRAS mutants. To accelerate the development of RAS targeting therapies, we need to fully characterise the molecular mechanisms governing KRAS signalling networks and determine what differentiates the signalling downstream of the KRAS mutants. Here we have used affinity purification mass-spectrometry proteomics to characterise the interactome of KRAS wild-type and three KRAS mutants. Bioinformatic analysis associated with experimental validation allows us to map the signalling network mediated by the different KRAS proteins. Using this approach, we characterised how the interactome of KRAS wild-type and mutants is regulated by the clinically approved KRASG12C inhibitor Sotorasib. In addition, we identified novel crosstalks between KRAS and its effector pathways including the AKT and JAK-STAT signalling modules.

SOS2 regulates the threshold of mutant EGFR-dependent oncogenesis

Son of Sevenless 1 and 2 (SOS1 and SOS2) are RAS guanine nucleotide exchange factors (RasGEFs) that mediate physiologic and pathologic RTK-dependent RAS activation. Here, we show that SOS2 modulates the threshold of epidermal growth factor receptor (EGFR) signaling to regulate the efficacy of and resistance to the EGFR-TKI osimertinib in lung adenocarcinoma (LUAD). SOS2 deletion sensitized EGFR-mutated cells to perturbations in EGFR signaling caused by reduced serum and/or osimertinib treatment to inhibit PI3K/AKT pathway activation, oncogenic transformation, and survival. Bypass RTK reactivation of PI3K/AKT signaling represents a common resistance mechanism to EGFR-TKIs; SOS2 KO reduced PI3K/AKT reactivation to limit osimertinib resistance. In a forced HGF/MET-driven bypass model, SOS2 KO inhibited HGF-stimulated PI3K signaling to block HGF-driven osimertinib resistance. Using a long term in situ resistance assay, a majority of osimertinib resistant cultures exhibited a hybrid epithelial/mesenchymal phenotype associated with reactivated RTK/AKT signaling. In contrast, RTK/AKT-dependent osimertinib resistance was markedly reduced by SOS2 deletion; the few SOS2 KO cultures that became osimertinib resistant primarily underwent non-RTK dependent EMT. Since bypass RTK reactivation and/or tertiary EGFR mutations represent the majority of osimertinib-resistant cancers, these data suggest that targeting SOS2 has the potential to eliminate the majority of osimertinib resistance.

Lipid raft protein flotillin-1 is important for the interaction between SOS1 and H-Ras/K-Ras, leading to Ras activation

Ras mutations have been frequently observed in human cancer. Although there is a high degree of similarity between Ras isomers, they display preferential coupling in specific cancer types. The binding of Ras to the plasma membrane is essential for its activation and biological functions. The present study elucidated Ras isoform-specific interactions with the membrane and their role in Ras-mediated biological activities. We investigated the role of a lipid raft protein flotillin-1 (Flot-1) in the activations of Ras. We found that Flot-1 was co-localized with H-Ras, but not with N-Ras, in lipid rafts of MDA-MB-231 human breast cells. The amino-terminal hydrophobic domain (1-38) of Flot-1 interacted with the hypervariable region of H-Ras. The epidermal growth factor-stimulated activation of H-Ras required Flot-1 which was not necessary for that of N-Ras in breast cancer cells. Flot-1 interacted with son of sevenless (SOS)-1, which promotes the conversion of Ras-bound GDP to GTP. Notably, Flot-1 was crucial for the interaction between SOS1 and H-Ras/K-Ras in breast and pancreatic cancer cells. Stable knockdown of Flot-1 reduced the in vivo metastasis in a mouse xenograft model with human breast carcinoma cells. A tissue microarray composed of 61 human pancreatic cancer samples showed higher levels of Flot-1 expression in pancreatic tumor tissues compared to normal tissues, and a correlation between K-Ras and Flot-1. Taken together, our findings suggest that Flot-1 may serve as a membrane platform for the interaction of SOS1 with H-Ras/K-Ras in human cancer cells, presenting Flot-1 as a potential target for Ras-driven cancers.

Development of Son of Sevenless Homologue 1 (SOS1) Modulators To Treat Cancers by Regulating RAS Signaling

Son of sevenless homologue 1 (SOS1) protein is universally expressed in cells and plays an important role in the RAS signaling pathway. Specifically, this protein interacts with RAS in response to upstream stimuli to promote guanine nucleotide exchange in RAS and activates the downstream signaling pathways. Thus, targeting SOS1 is a new approach for treating RAS-driven cancers. In this Perspective, we briefly summarize the structural and functional aspects of SOS1 and focus on recent advances in the discovery of activators, inhibitors, and PROTACs that target SOS1. This review aims to provide a timely and updated overview on the strategies for targeting SOS1 in cancer therapy.

Discovery of a Potent, Cooperative, and Selective SOS1 PROTAC ZZ151 with In Vivo Antitumor Efficacy in KRAS-Mutant Cancers

The linker moiety of a proteolysis-targeting chimera (PROTAC) molecule plays a critical role in modulating the degradation activity, target selectivity, and physico-chemical properties. However, the basics and underlying mechanisms of chemical modifications of the linker structure causing dramatic changes in the PROTAC degradation activity warrant further investigation. Herein, we report the design and characterization of a highly potent and selective SOS1 PROTAC ZZ151. After systematically modifying the linker length and composition, we observed that subtle modification of just one atom of the linker moiety of ZZ151 resulted in remarkable changes in the formation of the ternary complex and thus dramatically affected the degradation activities. ZZ151 quickly, specifically, and effectively induced SOS1 degradation; displayed potent antiproliferation activities against a broad panel of KRAS mutant-driven cancer cells; and showed superior anticancer activities in the KRAS^G12D- and ^G12V-mutant xenografts in mice. ZZ151 is a promising lead for developing new chemotherapies targeting KRAS mutants.

A multi-organoid platform identifies CIART as a key factor for SARS-CoV-2 infection

COVID-19 is a systemic disease involving multiple organs. We previously established a platform to derive organoids and cells from human pluripotent stem cells to model SARS-CoV-2 infection and perform drug screens^1,2. This provided insight into cellular tropism and the host response, yet the molecular mechanisms regulating SARS-CoV-2 infection remain poorly defined. Here we systematically examined changes in transcript profiles caused by SARS-CoV-2 infection at different multiplicities of infection for lung airway organoids, lung alveolar organoids and cardiomyocytes, and identified several genes that are generally implicated in controlling SARS-CoV-2 infection, including CIART, the circadian-associated repressor of transcription. Lung airway organoids, lung alveolar organoids and cardiomyocytes derived from isogenic CIART^-/- human pluripotent stem cells were significantly resistant to SARS-CoV-2 infection, independently of viral entry. Single-cell RNA-sequencing analysis further validated the decreased levels of SARS-CoV-2 infection in ciliated-like cells of lung airway organoids. CUT&RUN, ATAC-seq and RNA-sequencing analyses showed that CIART controls SARS-CoV-2 infection at least in part through the regulation of NR4A1, a gene also identified from the multi-organoid analysis. Finally, transcriptional profiling and pharmacological inhibition led to the discovery that the Retinoid X Receptor pathway regulates SARS-CoV-2 infection downstream of CIART and NR4A1. The multi-organoid platform identified the role of circadian-clock regulation in SARS-CoV-2 infection, which provides potential therapeutic targets for protection against COVID-19 across organ systems.

Design, Synthesis, and Bioevaluation of Pyrido[2,3-d]pyrimidin-7-ones as Potent SOS1 Inhibitors

The use of small molecular modulators to target the guanine nucleotide exchange factor SOS1 has been demonstrated to be a promising strategy for the treatment of various KRAS-driven cancers. In the present study, we designed and synthesized a series of new SOS1 inhibitors with the pyrido[2,3-d]pyrimidin-7-one scaffold. One representative compound 8u showed comparable activities to the reported SOS1 inhibitor BI-3406 in both the biochemical assay and the 3-D cell growth inhibition assay. Compound 8u obtained good cellular activities against a panel of KRAS G12-mutated cancer cell lines and inhibited downstream ERK and AKT activation in MIA PaCa-2 and AsPC-1 cells. In addition, it displayed synergistic antiproliferative effects when used in combination with KRAS G12C or G12D inhibitors. Further modifications of the new compounds may give us a promising SOS1 inhibitor with favorable druglike properties for use in the treatment of KRAS-mutated patients.

Targeting RAS mutants in malignancies: successes, failures, and reasons for hope

RAS genes are the most frequently mutated oncogenes and play critical roles in the development and progression of malignancies. The mutation, isoform (KRAS, HRAS, and NRAS), position, and type of substitution vary depending on the tissue types. Despite decades of developing RAS-targeted therapies, only small subsets of these inhibitors are clinically effective, such as the allele-specific inhibitors against KRASG12C . Targeting the remaining RAS mutants would require further experimental elucidation of RAS signal transduction, RAS-altered metabolism, and the associated immune microenvironment. This study reviews the mechanisms and efficacy of novel targeted therapies for different RAS mutants, including KRAS allele-specific inhibitors, combination therapies, immunotherapies, and metabolism-associated therapies.

Multiplexed screens identify RAS paralogues HRAS and NRAS as suppressors of KRAS-driven lung cancer growth

Oncogenic KRAS mutations occur in approximately 30% of lung adenocarcinoma. Despite several decades of effort, oncogenic KRAS-driven lung cancer remains difficult to treat, and our understanding of the regulators of RAS signalling is incomplete. Here to uncover the impact of diverse KRAS-interacting proteins on lung cancer growth, we combined multiplexed somatic CRISPR/Cas9-based genome editing in genetically engineered mouse models with tumour barcoding and high-throughput barcode sequencing. Through a series of CRISPR/Cas9 screens in autochthonous lung cancer models, we show that HRAS and NRAS are suppressors of KRASG12D-driven tumour growth in vivo and confirm these effects in oncogenic KRAS-driven human lung cancer cell lines. Mechanistically, RAS paralogues interact with oncogenic KRAS, suppress KRAS-KRAS interactions, and reduce downstream ERK signalling. Furthermore, HRAS and NRAS mutations identified in oncogenic KRAS-driven human tumours partially abolished this effect. By comparing the tumour-suppressive effects of HRAS and NRAS in oncogenic KRAS- and oncogenic BRAF-driven lung cancer models, we confirm that RAS paralogues are specific suppressors of KRAS-driven lung cancer in vivo. Our study outlines a technological avenue to uncover positive and negative regulators of oncogenic KRAS-driven cancer in a multiplexed manner in vivo and highlights the role RAS paralogue imbalance in oncogenic KRAS-driven lung cancer.

Development of SOS1 Inhibitor-Based Degraders to Target KRAS-Mutant Colorectal Cancer

Direct blockade of KRAS driver mutations in colorectal cancer (CRC) has been challenging. Targeting SOS1, a guanine nucleotide exchange factor, has arisen as an attractive approach for KRAS-mutant CRC. Here, we describe the development of novel SOS1 degraders and their activity in patient-derived CRC organoids (PDO). The design of these degraders as proteolysis-targeting chimera was based on the crystal structures of cereblon and SOS1. The synthesis used the 6- and 7-OH groups of a quinazoline core as anchor points to connect lenalidomide. Fifteen compounds were screened for SOS1 degradation. P7 was found to have up to 92% SOS1 degradation in both CRC cell lines and PDOs with excellent specificity. SOS1 degrader P7 demonstrated superior activity in inhibiting CRC PDO growth with an IC₅₀ 5 times lower than that of SOS1 inhibitor BI3406. In summary, we developed new SOS1 degraders and demonstrated SOS1 degradation as a feasible therapeutic strategy for KRAS-mutant CRC.

Targeting KRASp.G12C Mutation in Advanced Non-Small Cell Lung Cancer: a New Era Has Begun

OPINION STATEMENT

KRASp.G12C mutation occurs in 12% of newly diagnosed advanced NSCLC and has recently emerged as a positive predictive biomarker for the selection of advanced NSCLC patients who may respond to novel KRASp.G12C inhibitors. The recent discovery of a new binding pocket under the effector region of KRAS G12C oncoprotein has made direct pharmacological inhibition of the KRASp.G12 mutation possible, leading to the clinical development of a new series of direct selective inhibitors, with a potential major impact on patients' survival and quality of life. Promising efficacy and tolerability data emerging from the early phase CodeBreak trial have already supported the regulatory approval of sotorasib as first in class targeted treatment for the second-line treatment of KRASp.G12C-positive NSCLC population, following immunotherapy-based first-line therapies, while the randomized phase III CodeBreak 200 clinical study has recently confirmed a significant superiority of sotorasib over docetaxel in terms of progression-free survival and quality of life. However, KRAS mutant NSCLC is a high heterogeneous disease characterized by a high rate of co-mutations, most frequently involving P53, STK11, and KEAP1 genes, which significantly modulate the composition of the tumor microenvironment and consequently affect clinical responses to both immunotherapy and targeted inhibitors now available in clinical practice. Both pre-clinical and clinical translational series have recently revealed a wide spectrum of resistance mechanisms occurring under selective KRASG12C inhibitors, including both on-target and off-target molecular alterations as well as morphological switching, negatively affecting the antitumor activity of these drugs when used as single agent therapies. The understanding of such biological background along with the emergence of pre-clinical data provided a strong rational to investigate different combination strategies, including the inhibition of SHP2, SOS1, and KRAS G12C downstream effectors, as well as the addition of immunotherapy and/or chemotherapy to targeted therapy. The preliminary results of these trials have recently suggested a promising activity of SHP2 inhibitors in the front-line setting, while toxicity issues limited the concurrent administration of immune-checkpoint inhibitors and sotorasib. The identification of predictive genomic/immunological biomarkers will be crucial to understand how to optimally sequencing/combining different drugs and ultimately personalize treatment strategies under clinical investigation, to definitively increase the survival outcomes of KRASp.G12C mutant advanced NSCLC patients.

Targeting KRAS in Pancreatic Cancer

Pancreatic cancer is mainly driven by mutations in the KRAS oncogene. While this cancer has shown remarkable therapy resistance, new approaches to inhibit mutated KRAS, KRAS activators and effectors show promise in breaking this therapeutic deadlock. Here, we review these innovations in therapies that target RAS signaling in pancreatic cancer from a clinical point of view. A number of promising approaches are currently in clinical trials or in clinical development. We focus on small-molecule drugs but also discuss immunotherapies and tumor vaccines.

Light at the end of the tunnel: Clinical features and therapeutic prospects of KRAS mutant subtypes in non-small-cell lung cancer

Lung cancer is one of the most common causes of cancer-related deaths, and non-small-cell lung cancer (NSCLC) accounts for approximately 85% of all lung cancer cases. Kirsten rat sarcoma virus (KRAS), one of the three subtypes of the RAS family, is the most common oncogene involved in human cancers and encodes the key signaling proteins in tumors. Oncogenic KRAS mutations are considered the initiating factors in 30% of NSCLC cases, accounting for the largest proportion of NSCLC cases associated with driver mutations. Because effective inhibition of the related functions of KRAS with traditional small-molecule inhibitors is difficult, the KRAS protein is called an “undruggable target.” However, in recent years, the discovery of a common mutation in the KRAS gene, glycine 12 mutated to cysteine (G12C), has led to the design and synthesis of covalent inhibitors that offer novel strategies for effective targeting of KRAS. In this review, we have summarized the structure, function, and signal transduction pathways of KRAS and discussed the available treatment strategies and potential treatment prospects of KRAS mutation subtypes (especially G12C, G12V, and G12D) in NSCLC, thus providing a reference for selecting KRAS mutation subtypes for the treatment of NSCLC.

Pan-KRAS inhibitors suppress proliferation through feedback regulation in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is currently one of the most lethal cancers worldwide. Several basic studies have confirmed that Kirsten rat sarcoma virus (KRAS) is a key driver gene for the occurrence of PDAC, and KRAS mutations have also been found in most patients in clinical studies. In this study, two pan-KRAS inhibitors, BI-2852 and BAY-293, were chosen as chemical probes to investigate their antitumor potency in PDAC. Their inhibitory effects on KRAS activation were validated in vitro and their antiproliferative potency in PDAC cell lines were profiled, with half-maximal inhibitory concentration (IC50) values of approximately 1 μM, demonstrating the therapeutic potential of pan-KRAS inhibitors in the treatment of PDAC. However, feedback regulation in the KRAS pathway weakened inhibitor activity, which was observed by a 50 times difference in BAY-293 from in vitro activity. Furthermore, pan-KRAS inhibitors effectively inhibited cell proliferation in 3D organoids cultured from PDAC patient samples; however, there were some variations between individuals. These results provide a sufficient theoretical foundation for KRAS as a clinical therapeutic target and for the application of pan-KRAS inhibitors in the treatment of PDAC, with important scientific significance in translational medicine.

Inhibition of KRAS, MEK and PI3K Demonstrate Synergistic Anti-Tumor Effects in Pancreatic Ductal Adenocarcinoma Cell Lines

Kirsten rat sarcoma virus (KRAS) mutations are widespread in pancreatic ductal adenocarcinoma (PDAC) and contribute significantly to tumor initiation, progression, tumor relapse/resistance, and prognosis of patients. Although inhibitors against KRAS mutations have been developed, this therapeutic approach is not routinely used in PDAC patients. We investigated the anti-tumor efficacy of two KRAS inhibitors BI-3406 (KRAS::SOS1 inhibitor) and sotorasib (KRAS G12C inhibitor) alone or in combination with MEK1/2 inhibitor trametinib and/or PI3K inhibitor buparlisib in seven PDAC cell lines. Whole transcriptomic analysis of combined inhibition and control groups were comparatively analyzed to explore the corresponding mechanisms of inhibitor combination. Both KRAS inhibitors and corresponding combinations exhibited cytotoxicity against specific PDAC cell lines. BI-3406 enhance the efficacy of trametinib and buparlisib in BXPC-3, ASPC-1 and MIA PACA-2, but not in CAPAN-1, while sotorasib enhances the efficacy of trametinib and buparlisib only in MIA PACA-2. The whole transcriptomic analysis demonstrates that the two triple-inhibitor combinations exert antitumor effects by affecting related cell functions, such as affecting the immune system, cell adhesion, cell migration, and cytokine binding. As well as directly involved in RAF/MEK/ERK pathway and PI3K/AKT pathway affect cell survival. Our current study confirmed inhibition of KRAS and its downstream pathways as a potential novel therapy for PDAC and provides fundamental data for in vivo evaluations.

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.

Design and Discovery of MRTX0902, a Potent, Selective, Brain-Penetrant, and Orally Bioavailable Inhibitor of the SOS1:KRAS Protein-Protein Interaction

SOS1 is one of the major guanine nucleotide exchange factors that regulates the ability of KRAS to cycle through its “on” and “off” states. Disrupting the SOS1:KRAS^G12C protein–protein interaction (PPI) can increase the proportion of GDP-loaded KRAS^G12C, providing a strong mechanistic rationale for combining inhibitors of the SOS1:KRAS complex with inhibitors like MRTX849 that target GDP-loaded KRAS^G12C. In this report, we detail the design and discovery of MRTX0902—a potent, selective, brain-penetrant, and orally bioavailable SOS1 binder that disrupts the SOS1:KRAS^G12C PPI. Oral administration of MRTX0902 in combination with MRTX849 results in a significant increase in antitumor activity relative to that of either single agent, including tumor regressions in a subset of animals in the MIA PaCa-2 tumor mouse xenograft model.

Conformational Dynamics Allows Sampling of an "Active-like" State by Oncogenic K-Ras-GDP

Mutations in K-Ras GTPase replacing Gly12 with either Asp or Val are common in cancer. These mutations decelerate intrinsic and catalyzed GTP hydrolysis, leading to accumulation of K-Ras-GTP in cells. Signaling cascades initiated by K-Ras-GTP promote cell proliferation, survival, and invasion. Despite functional differences between the most frequent G12D mutation and the most aggressive and chemotherapy resistant G12V mutation, their long-suspected distinct structural features remain elusive. Using NMR, X-ray structures, and computational methods, we found that oncogenic mutants of K-Ras4B, the predominant splice variant of K-Ras, exhibit distinct conformational dynamics when GDP-bound, visiting the "active-like" conformational state similar to the one observed in GTP-bound K-Ras. This behavior distinguishes G12V from wild type and G12D K-Ras4B-GDP. The likely reason is hydrophobic interactions between the aliphatic sidechain of V12 and the Switch II region of K-Ras4B^G12V-GDP, which are distinct in K-Ras4B^G12D-GDP. In the X-ray structures, crystal contacts reduce the dynamics of the sidechain at position 12 by stabilizing the Switch I region of the protein. This explains why structural differences between G12V and G12D K-Ras have yet not been reported. Together, our results suggest a previously unknown mechanism of K-Ras activation. This mechanism relies on conformational dynamics caused by specific oncogenic mutations in the GDP-bound state. Our findings also imply that the therapeutic strategies decreasing the level of K-Ras-GTP by interfering with nucleotide exchange or by expediting GTP hydrolysis may work differently in different oncogenic mutants.

Enhanced BRAF engagement by NRAS mutants capable of promoting melanoma initiation

A distinct profile of NRAS mutants is observed in each tumor type. It is unclear whether these profiles are determined by mutagenic events or functional differences between NRAS oncoproteins. Here, we establish functional hallmarks of NRAS mutants enriched in human melanoma. We generate eight conditional, knock-in mouse models and show that rare melanoma mutants (NRAS G12D, G13D, G13R, Q61H, and Q61P) are poor drivers of spontaneous melanoma formation, whereas common melanoma mutants (NRAS Q61R, Q61K, or Q61L) induce rapid tumor onset with high penetrance. Molecular dynamics simulations, combined with cell-based protein-protein interaction studies, reveal that melanomagenic NRAS mutants form intramolecular contacts that enhance BRAF binding affinity, BRAF-CRAF heterodimer formation, and MAPK > ERK signaling. Along with the allelic series of conditional mouse models we describe, these results establish a mechanistic basis for the enrichment of specific NRAS mutants in human melanoma.

Emerging RAS-directed therapies for cancer

RAS oncogenes are the most commonly mutated oncogenes in human cancer, and RAS-mutant cancers represent a major burden of human disease. Though these oncogenes were discovered decades ago, recent years have seen major advances in understanding of their structure and function, including the therapeutic and prognostic significance of diverse isoforms. Targeting of these mutations has proven difficult, despite some successes with inhibition of RAS effector signalling. More recently, direct RAS inhibition has been achieved in a trial setting. While this has yet to be translated to everyday clinical practice, this development carries much promise. This review summarizes the diverse approaches that have been taken to RAS inhibition and then focuses on the most recent developments in direct inhibition of KRAS(G12C).

Daily Practice Assessment of KRAS Status in NSCLC Patients: A New Challenge for the Thoracic Pathologist Is Right around the Corner

Simple Summary

RAS mutation is the most frequent oncogenic alteration in human cancers and KRAS is the most frequently mutated, notably in non-small cell lung carcinomas (NSCLC). Various attempts to inhibit KRAS in the past were unsuccessful in these latter tumors. However, recently, several small molecules (AMG510, MRTX849, JNJ-74699157, and LY3499446) have been developed to specifically target KRAS G12C-mutated tumors, which seems promising for patient treatment and should soon be administered in daily practice for non-squamous (NS)-NSCLC. In this context, it will be mandatory to systematically assess the KRAS status in routine clinical practice, at least in advanced NS-NSCLC, leading to new challenges for thoracic oncologists.

Abstract

KRAS mutations are among the most frequent genomic alterations identified in non-squamous non-small cell lung carcinomas (NS-NSCLC), notably in lung adenocarcinomas. In most cases, these mutations are mutually exclusive, with different genomic alterations currently known to be sensitive to therapies targeting EGFR, ALK, BRAF, ROS1, and NTRK. Recently, several promising clinical trials targeting KRAS mutations, particularly for KRAS G12C-mutated NSCLC, have established new hope for better treatment of patients. In parallel, other studies have shown that NSCLC harboring co-mutations in KRAS and STK11 or KEAP1 have demonstrated primary resistance to immune checkpoint inhibitors. Thus, the assessment of the KRAS status in advanced-stage NS-NSCLC has become essential to setting up an optimal therapeutic strategy in these patients. This stimulated the development of new algorithms for the management of NSCLC samples in pathology laboratories and conditioned reorganization of optimal health care of lung cancer patients by the thoracic pathologists. This review addresses the recent data concerning the detection of KRAS mutations in NSCLC and focuses on the new challenges facing pathologists in daily practice for KRAS status assessment.

Targeting KRAS Mutant in Non-Small Cell Lung Cancer: Novel Insights Into Therapeutic Strategies

Although KRAS-activating mutations represent the most common oncogenic driver in non-small cell lung cancer (NSCLC), various attempts to inhibit KRAS failed in the past decade. KRAS mutations are associated with a poor prognosis and a poor response to standard therapeutic regimen. The recent development of new therapeutic agents (i.e., adagrasib, sotorasib) that target specifically KRAS G12C in its GDP-bound state has evidenced an unprecedented success in the treatment of this subgroup of patients. Despite providing pre-clinical and clinical efficacy, several mechanisms of acquired resistance to KRAS G12C inhibitors have been reported. In this setting, combined therapeutic strategies including inhibition of either SHP2, SOS1 or downstream effectors of KRAS G12C seem particularly interesting to overcome acquired resistance. In this review, we will discuss the novel therapeutic strategies targeting KRAS G12C and promising approaches of combined therapy to overcome acquired resistance to KRAS G12C inhibitors.

Discovery of the First-in-Class Agonist-Based SOS1 PROTACs Effective in Human Cancer Cells Harboring Various KRAS Mutations

Regulating SOS1 functions may result in targeted pan-KRAS therapies. Small-molecule SOS1 inhibitors showed promising anticancer potential, and the most advanced inhibitor BI 1701963 is currently under phase I clinical studies. SOS1 agonists provide new opportunities to treat cancer; however, the underlying mechanisms still warrant investigation. We here report the discovery of the first SOS1 PROTACs designed uniquely by connecting a VHL ligand to the reported SOS1 agonist, ensuring that the observed inhibitory activity results from degraders. The best compound 9d induced SOS1 degradation in various KRAS-driven cancer cells and displayed superior antiproliferation activity compared to the agonist itself. Tumor xenograft study clearly showed the promising antitumor potency of 9d against human lung cancer. This study provides good evidence of using agonists to design SOS1 PROTACs and demonstrates that targeted SOS1 degradation represents an effective therapeutic strategy for overcoming KRAS-driven cancers.

Targeting KRAS G12C mutation in lung adenocarcinoma

Lung cancer continues to be a major cause of cancer related death globally. Therapies targeting driver mutations have significantly extended the survival of patients whose lung cancer cells harbor these mutations. Patients with KRAS mutations, however, lacked specific targeted therapy until the recent FDA approval of sotorasib, a specific inhibitor of KRAS G12C mutant protein. We will discuss the efficacy and toxicities of the novel KRAS G12C inhibitors as well as other indirect strategies for targeting oncogenic KRAS mutations. We will review the limited literature on acquired resistance to these inhibitors and the novel combinatorial treatment strategies that are being tested currently in clinical trials.

Targeting RAS oncogenesis with SOS1 inhibitors

RAS proteins play major roles in many human cancers, but programs to develop direct RAS inhibitors so far have only been successful for the oncogenic KRAS mutant G12C. As an alternative approach, inhibitors for the RAS guanine nucleotide exchange factor SOS1 have been investigated by several academic groups and companies, and major progress has been achieved in recent years in the optimization of small molecule activators and inhibitors of SOS1. Here, we review the discovery and development of small molecule modulators of SOS1 and their molecular binding modes and modes of action. As targeting the RAS pathway is expected to result in the development of resistance mechanisms, SOS1 inhibitors will most likely be best applied in vertical combination approaches where two nodes of the RAS signaling pathway are hit simultaneously. We summarize the current understanding of which combination partners may be most beneficial for patients with RAS driven tumors.

Targeting KRAS in Lung Cancer Beyond KRAS G12C Inhibitors: The Immune Regulatory Role of KRAS and Novel Therapeutic Strategies

Approximately 20% of lung adenocarcinomas harbor KRAS mutations, an oncogene that drives tumorigenesis and has the ability to alter the immune system and the tumor immune microenvironment. While KRAS was considered “undruggable” for decades, specific KRAS G12C covalent inhibitors have recently emerged, although their promising results are limited to a subset of patients. Several other drugs targeting KRAS activation and downstream signaling pathways are currently under investigation in early-phase clinical trials. In addition, KRAS mutations can co-exist with other mutations in significant genes in cancer (e.g., STK11 and KEAP1) which induces tumor heterogeneity and promotes different responses to therapies. This review describes the molecular characterization of KRAS mutant lung cancers from a biologic perspective to its clinical implications. We aim to summarize the tumor heterogeneity of KRAS mutant lung cancers and its immune-regulatory role, to report the efficacy achieved with current immunotherapies, and to overview the therapeutic approaches targeting KRAS mutations besides KRAS G12C inhibitors.

A novel 10-gene immune-related lncRNA signature model for the prognosis of colorectal cancer

BACKGROUND

The tumor immune microenvironment of colorectal cancer (CRC) affects tumor development, prognosis and immunotherapy strategies. Recently, immune-related lncRNA were shown to play vital roles in the tumor immune microenvironment. The objective of this study was to identify lncRNAs involved in the immune response, tumorigenesis and progression of CRC and to establish an immune-related lncRNA signature for predicting the prognosis of CRC.

METHODS

We used data retrieved from the cancer genome atlas (TCGA) dataset to construct a 10-gene immune-related lncRNA pair (IRLP) signature model using a method based on the ranking and comparison of paired gene expression in CRC. The clinical prognosis, immune checkpoints and lncRNA-protein networks were analyzed to evaluate the signature.

RESULTS

The signature was closely associated with overall survival of CRC patients (p < 0.001 in both of the training and validating cohorts) and the 3-year AUC values for the training and validating cohorts were 0.884 and 0.739, respectively. And, there were positive correlations between the signature and age (p = 0.048), clinical stage (p < 0.01), T stage (p < 0.01), N stage (p < 0.001) and M stage (p < 0.01). In addition, the signature model appeared to be highly relevant to some checkpoints, including CD160, TNFSF15, HHLA2, IDO2 and KIR3DL1. Further, molecular functional analysis and lncRNA-protein networks were applied to understand the molecular mechanisms underlying the carcinogenic effect and progression.

CONCLUSION

The 10-gene IRLP signature model is an independent prognostic factor for CRC patient and can be utilized for the development of immunotherapy.

Cytotoxic activity of KRAS inhibitors in combination with chemotherapeutics

INTRODUCTION

KRAS is the most frequently mutated oncogenic driver in pancreatic, lung, and colon cancer. Recently, KRAS inhibitors in clinical use show promising activity but most responses are partial and drug resistance develops. The use of therapeutics in combination with KRAS inhibitors are expected to improve outcomes.

AREAS COVERED

This review describes the KRAS G12C mutation-specific inhibitors and the SOS1-targeting inhibitors that reduce the GTP-loading of wildtype and mutated KRAS. Both types of compounds reduce tumor cell proliferation in vitro and in vivo. The combinations of the various KRAS inhibitors with downstream signaling effectors, modulators of KRAS-associated metabolic alterations and chemotherapeutics are summarized.

EXPERT OPINION

The clinical potency of mutated KRAS-specific inhibitors needs to be improved by suitable drug combinations. Inhibition of downstream signaling cascades increases toxicity and other combinations exploited comprise G12C-directed inhibitors with SOS1 inhibitors, glucose/glutamine metabolic modulators, classical chemotherapeutics, and others. The most suitable inhibitor combinations corroborated in preclinical development await clinical verification.

Structure-based inhibitor design of mutant RAS proteins-a paradigm shift

As a member of small GTPase family, KRAS protein is a key physiological modulator of various cellular activities including proliferation. However, mutations of KRAS present in numerous cancer types, most frequently in pancreatic (> 60%), colorectal (> 40%), and lung cancers, drive oncogenic processes through overactivation of proliferation. The G12C mutation of KRAS protein is especially abundant in the case of these types of malignancies. Despite its key importance in human disease, KRAS was assumed to be non-druggable for a long time since the protein seemingly lacks potential drug-binding pockets except the nucleotide-binding site, which is difficult to be targeted due to the high affinity of KRAS for both GDP and GTP. Recently, a new approach broke the ice and provided evidence that upon covalent targeting of the G12C mutant KRAS, a highly dynamic pocket was revealed. This novel targeting is especially important since it serves with an inherent solution for drug selectivity. Based on these results, various structure-based drug design projects have been launched to develop selective KRAS mutant inhibitors. In addition to the covalent modification strategy mostly applicable for G12C mutation, different innovative solutions have been suggested for the other frequently occurring oncogenic G12 mutants. Here we summarize the latest advances of this field, provide perspectives for novel approaches, and highlight the special properties of KRAS, which might issue some new challenges.

Innovative dual system approach for selective eradication of cancer cells using viral-based delivery of natural bacterial toxin-antitoxin system

The inactivation of p53, a tumor suppressor, and the activation of the RAS oncogene are the most frequent genetic alterations in cancer. We have shown that a unique E. coli MazF-MazE toxin–antitoxin (TA) system can be used for selective and effective eradication of RAS-mutated cancer cells. This out of the box strategy holds great promise for effective cancer treatment and management. We provide proof of concept for a novel platform to selectively eradicate cancer cells using an adenoviral delivery system based on the adjusted natural bacterial system. We generated adenoviral vectors carrying the mazF toxin (pAdEasy-Py4-SV40mP-mCherry-MazF) and the antitoxin mazE (pAdEasy-RGC-SV40mP-MazE-IRES-GFP) under the regulation of RAS and p53, resp. The control vector carries the toxin without the RAS-responsive element (pAdEasy-ΔPy4-SV40mP-mCherry-MazF). In vitro, the mazF-mazE TA system (Py4-SV40mP-mCherry-MazF+RGC-SV40mP-MazE-IRES-GFP) induced massive, dose-dependent cell death, at 69% compared to 19% for the control vector, in a co-infected HCT116 cell line. In vivo, the system caused significant tumor growth inhibition of HCT116 (KRAS^mut/p53^mut) tumors at 73 and 65% compared to PBS and ΔPY4 control groups, resp. In addition, we demonstrate 65% tumor growth inhibition in HCT116 (KRAS^mut/p53^wt) cells, compared to the other two control groups, indicating a contribution of the antitoxin in blocking system leakage in WT RAS cells. These data provide evidence of the feasibility of using mutations in the p53 and RAS pathway to efficiently kill cancer cells. The platform, through its combination of the antitoxin (mazE) with the toxin (mazF), provides effective protection of normal cells from basal low activity or leakage of mazF.

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.

Oncogenic KRAS engages an RSK1/NF1 pathway to inhibit wild-type RAS signaling in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy with limited treatment options. Although activating mutations of the KRAS GTPase are the predominant dependency present in >90% of PDAC patients, targeting KRAS mutants directly has been challenging in PDAC. Similarly, strategies targeting known KRAS downstream effectors have had limited clinical success due to feedback mechanisms, alternate pathways, and dose-limiting toxicities in normal tissues. Therefore, identifying additional functionally relevant KRAS interactions in PDAC may allow for a better understanding of feedback mechanisms and unveil potential therapeutic targets. Here, we used proximity labeling to identify protein interactors of active KRAS in PDAC cells. We expressed fusions of wild-type (WT) (BirA-KRAS4B), mutant (BirA-KRAS4B^G12D), and nontransforming cytosolic double mutant (BirA-KRAS4B^G12D/C185S) KRAS with the BirA biotin ligase in murine PDAC cells. Mass spectrometry analysis revealed that RSK1 selectively interacts with membrane-bound KRAS^G12D, and we demonstrate that this interaction requires NF1 and SPRED2. We find that membrane RSK1 mediates negative feedback on WT RAS signaling and impedes the proliferation of pancreatic cancer cells upon the ablation of mutant KRAS. Our findings link NF1 to the membrane-localized functions of RSK1 and highlight a role for WT RAS signaling in promoting adaptive resistance to mutant KRAS-specific inhibitors in PDAC.

Targeting BRAF and RAS in Colorectal Cancer

Simple Summary

In colorectal cancer, mutations of the KRAS and BRAF genes are quite common and can contribute to the activation of cell signaling pathways that lead to cell proliferation and differentiation. These processes promote cancer growth, and in some cases, they may cause cells to develop resistance to certain types of treatment, notably EGFR inhibitors. We summarize recent knowledge regarding the effects of KRAS and BRAF mutations in the setting of colorectal cancer and discuss the new therapies under development.

Abstract

Colorectal cancer (CRC) is still one of the most frequent forms of cancer in the world in terms of incidence. Around 40% of CRC patients carry a mutation of the Kirsten rat sarcoma (KRAS) gene, while 10% have a mutation in the B-Raf proto-oncogene serine/threonine kinase (BRAF) gene. These mutations are responsible for dysregulation of the mitogen-associated protein kinase (MAPK) pathway, leading to the proliferation, differentiation, angiogenesis, and resistance to apoptosis of cells. Activation of the MAPK pathway results in adaptive therapeutic resistance, rendering EGFR inhibitors ineffective. This review aims to highlight the recent findings that have improved our understanding of KRAS and BRAF mutations in colorectal cancer and to describe new targeted therapies, used alone or in combination.