Intermittent dosing of RMC-4630, a potent, selective inhibitor of SHP2, combined with the MEK inhibitor cobimetinib, in a phase 1b/2 clinical trial for advanced solid tumors with activating mutations of RAS signaling

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 has been 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.

Targeting KRAS and SHP2 signaling pathways for immunomodulation and improving treatment outcomes in solid tumors

Historically, KRAS has been considered 'undruggable' inspite of being one of the most frequently altered oncogenic proteins in solid tumors, primarily due to the paucity of pharmacologically 'druggable' pockets within the mutant isoforms. However, pioneering developments in drug design capable of targeting the mutant KRAS isoforms especially KRASG12C-mutant cancers, have opened the doors for emergence of combination therapies comprising of a plethora of inhibitors targeting different signaling pathways. SHP2 signaling pathway, primarily known for activation of intracellular signaling pathways such as KRAS has come up as a potential target for such combination therapies as it emerged to be the signaling protein connecting KRAS and the immune signaling pathways and providing the link for understanding the overlapping regions of RAS/ERK/MAPK signaling cascade. Thus, SHP2 inhibitors having potent tumoricidal activity as well as role in immunomodulation have generated keen interest in researchers to explore its potential as combination therapy in KRAS mutant solid tumors. However, the excitement with these combination therapies need to overcome challenges thrown up by drug resistance and enhanced toxicity. In this review, we will discuss KRAS and SHP2 signaling pathways and their roles in immunomodulation and regulation of tumor microenvironment and also analyze the positive effects and drawbacks of the different combination therapies targeted at these signaling pathways along with their present and future potential to treat solid tumors.

SHP2 clinical phenotype, cancer, or RASopathies, can be predicted by mutant conformational propensities

SHP2 phosphatase promotes full activation of the RTK-dependent Ras/MAPK pathway. Its mutations can drive cancer and RASopathies, a group of neurodevelopmental disorders (NDDs). Here we ask how same residue mutations in SHP2 can lead to both cancer and NDD phenotypes, and whether we can predict what the outcome will be. We collected and analyzed mutation data from the literature and cancer databases and performed molecular dynamics simulations of SHP2 mutants. We show that both cancer and Noonan syndrome (NS, a RASopathy) mutations favor catalysis-prone conformations. As to cancer versus RASopathies, we demonstrate that cancer mutations are more likely to accelerate SHP2 activation than the NS mutations at the same genomic loci, in line with NMR data for K-Ras4B more aggressive mutations. The compiled experimental data and dynamic features of SHP2 mutants lead us to propose that different from strong oncogenic mutations, SHP2 activation by NS mutations is less likely to induce a transition of the ensemble from the SHP2 inactive state to the active state. Strong signaling promotes cell proliferation, a hallmark of cancer. Weak, or moderate signals are associated with differentiation. In embryonic neural cells, dysregulated differentiation is connected to NDDs. Our innovative work offers structural guidelines for identifying and correlating mutations with clinical outcomes, and an explanation for why bearers of RASopathy mutations may have a higher probability of cancer. Finally, we propose a drug strategy against SHP2 variants-promoting cancer and RASopathies.

CDK4/6 inhibition enhances SHP2 inhibitor efficacy and is dependent upon RB function in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are highly aggressive soft tissue sarcomas with limited treatment options, and new effective therapeutic strategies are desperately needed. We observe antiproliferative potency of genetic depletion of PTPN11 or pharmacological inhibition using the SHP2 inhibitor (SHP2i) TNO155. Our studies into the signaling response to SHP2i reveal that resistance to TNO155 is partially mediated by reduced RB function, and we therefore test the addition of a CDK4/6 inhibitor (CDK4/6i) to enhance RB activity and improve TNO155 efficacy. In combination, TNO155 attenuates the adaptive response to CDK4/6i, potentiates its antiproliferative effects, and converges on enhancement of RB activity, with greater suppression of cell cycle and inhibitor-of-apoptosis proteins, leading to deeper and more durable antitumor activity in in vitro and in vivo patient-derived models of MPNST, relative to either single agent. Overall, our study provides timely evidence to support the clinical advancement of this combination strategy in patients with MPNST and other tumors driven by loss of NF1.

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.

Small molecular inhibitors for KRAS-mutant cancers

Three rat sarcoma (RAS) gene isoforms, KRAS, NRAS, and HRAS, constitute the most mutated family of small GTPases in cancer. While the development of targeted immunotherapies has led to a substantial improvement in the overall survival of patients with non-KRAS-mutant cancer, patients with RAS-mutant cancers have an overall poorer prognosis owing to the high aggressiveness of RAS-mutant tumors. KRAS mutations are strongly implicated in lung, pancreatic, and colorectal cancers. However, RAS mutations exhibit diverse patterns of isoforms, substitutions, and positions in different types of cancers. Despite being considered "undruggable", recent advances in the use of allele-specific covalent inhibitors against the most common mutant form of RAS in non-small-cell lung cancer have led to the development of effective pharmacological interventions against RAS-mutant cancer. Sotorasib (AMG510) has been approved by the FDA as a second-line treatment for patients with KRAS-G12C mutant NSCLC who have received at least one prior systemic therapy. Other KRAS inhibitors are on the way to block KRAS-mutant cancers. In this review, we summarize the progress and promise of small-molecule inhibitors in clinical trials, including direct inhibitors of KRAS, pan-RAS inhibitors, inhibitors of RAS effector signaling, and immune checkpoint inhibitors or combinations with RAS inhibitors, to improve the prognosis of tumors with RAS mutations.

CDK4/6 inhibition enhances SHP2 inhibitor efficacy and is dependent upon restoration of RB function in malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNST) are highly aggressive soft tissue sarcomas with limited treatment options, and novel effective therapeutic strategies are desperately needed. We observe anti-proliferative efficacy of genetic depletion or pharmacological inhibition using the clinically available SHP2 inhibitor (SHP2i) TNO155. Our studies into the signaling response to SHP2i reveal that resistance to TNO155 is partially mediated by reduced RB function, and we therefore test the addition of a CDK4/6 inhibitor (CDK4/6i) to enhance RB activity and improve TNO155 efficacy. In combination, TNO155 attenuates the adaptive response to CDK4/6i, potentiates its anti-proliferative effects, and converges on enhancement of RB activity, with greater suppression of cell cycle and inhibitor-of-apoptosis proteins, leading to deeper and more durable anti-tumor activity in in vitro and in vivo patient-derived models of MPNST, relative to either single agent. Overall, our study provides timely evidence to support the clinical advancement of this combination strategy in patients with MPNST and other tumors driven by loss of NF1.

AZD4625 is a Potent and Selective Inhibitor of KRASG12C

AZD4625 is a potent, selective, and orally bioavailable inhibitor of oncogenic KRASG12C as demonstrated in cellular assays and in vivo in preclinical cell line-derived and patient-derived xenograft models. In vitro and cellular assays have shown selective binding and inhibition of the KRASG12C mutant isoform, which carries a glycine to cysteine mutation at residue 12, with no binding and inhibition of wild-type RAS or isoforms carrying non-KRASG12C mutations. The pharmacology of AZD4625 shows that it has the potential to provide therapeutic benefit to patients with KRASG12C mutant cancer as either a monotherapy treatment or in combination with other targeted drug agents.

More to the RAS Story: KRASG12C Inhibition, Resistance Mechanisms, and Moving Beyond KRASG12C

Despite the discovery of RAS oncogenes in human tumor DNA 40 years ago, the development of effective targeted therapies directed against RAS has lagged behind those more successful advancements in the field of therapeutic tyrosine kinase inhibitors targeting other oncogenes such as EGFR, ALK, and ROS1. The discoveries that (1) malignant RAS oncogenes differ from their wild-type counterparts by only a single amino acid change and (2) covalent inhibition of the cysteine residue at codon 12 of KRAS^G12C in its inactive GDP-bound state resulted in effective inhibition of oncogenic RAS signaling and have catalyzed a dramatic shift in mindset toward KRAS-driven cancers. Although the development of allele-selective KRAS^G12C inhibitors has changed a treatment paradigm, the clinical activity of these agents is more modest than tyrosine kinase inhibitors targeting other oncogene-driven cancers. Heterogeneous resistance mechanisms generally result in the restoration of RAS/mitogen-activated protein kinase pathway signaling. Many approaches are being evaluated to overcome this resistance, with many combinatorial clinical trials ongoing. Furthermore, because KRAS^G12D and KRAS^G12V are more prevalent than KRAS^G12C, there remains an unmet need for additional therapeutic strategies for these patients. Thus, our current translational standing could be described as "the end of the beginning," with additional discovery and research innovation needed to address the enormous disease burden imposed by RAS-mutant cancers. Here, we describe the development of KRAS^G12C inhibitors, the challenges of resistance to these inhibitors, strategies to mitigate that resistance, and new approaches being taken to address other RAS-mutant cancers.

Small-Molecule Inhibitors and Degraders Targeting KRAS-Driven Cancers

Drug resistance continues to be a major problem associated with cancer treatment. One of the primary causes of anticancer drug resistance is the frequently mutated RAS gene. In particular, considerable efforts have been made to treat KRAS-induced cancers by directly and indirectly controlling the activity of KRAS. However, the RAS protein is still one of the most prominent targets for drugs in cancer treatment. Recently, novel targeted protein degradation (TPD) strategies, such as proteolysis-targeting chimeras, have been developed to render "undruggable" targets druggable and overcome drug resistance and mutation problems. In this study, we discuss small-molecule inhibitors, TPD-based small-molecule chemicals for targeting RAS pathway proteins, and their potential applications for treating KRAS-mutant cancers. Novel TPD strategies are expected to serve as promising therapeutic methods for treating tumor patients with KRAS mutations.

If Virchow and Ehrlich Had Dreamt Together: What the Future Holds for KRAS-Mutant Lung Cancer

Non-small-cell lung cancer (NSCLC) with Kirsten rat sarcoma (KRAS) mutations has notoriously challenged oncologists and researchers for three notable reasons: (1) the historical assumption that KRAS is "undruggable", (2) the disease heterogeneity and (3) the shaping of the tumor microenvironment by KRAS downstream effector functions. Better insights into KRAS structural biochemistry allowed researchers to develop direct KRAS(G12C) inhibitors, which have shown early signs of clinical activity in NSCLC patients and have recently led to an FDA breakthrough designation for AMG-510. Following the approval of immune checkpoint inhibitors for PDL1-positive NSCLC, this could fuel yet another major paradigm shift in the treatment of advanced lung cancer. Here, we review advances in our understanding of the biology of direct KRAS inhibition and project future opportunities and challenges of dual KRAS and immune checkpoint inhibition. This strategy is supported by preclinical models which show that KRAS(G12C) inhibitors can turn some immunologically "cold" tumors into "hot" ones and therefore could benefit patients whose tumors harbor subtype-defining STK11/LKB1 co-mutations. Forty years after the discovery of KRAS as a transforming oncogene, we are on the verge of approval of the first KRAS-targeted drug combinations, thus therapeutically unifying Paul Ehrlich's century-old "magic bullet" vision with Rudolf Virchow's cancer inflammation theory.

Mechanisms of Resistance to KRASG12C Inhibitors

KRAS is one of the most common human oncogenes, but concerted efforts to produce direct inhibitors have largely failed, earning KRAS the title of "undruggable". Recent efforts to produce subtype specific inhibitors have been more successful, and several KRASG12C inhibitors have reached clinical trials, including adagrasib and sotorasib, which have shown early evidence of efficacy in patients. Lessons from other inhibitors of the RAS pathway suggest that the effect of these drugs will be limited in vivo by the development of drug resistance, and pre-clinical studies of G12C inhibitors have identified evidence of this. In this review we discuss the current evidence for G12C inhibitors, the mechanisms of resistance to G12C inhibitors and potential approaches to overcome them. We discuss possible targets of combination therapy, including SHP2, receptor tyrosine kinases, downstream effectors and PD1/PDL1, and review the ongoing clinical trials investigating these inhibitors.