GTP-bound State Research Articles

Abstract B071: Preclinical evaluation of RM-042, an orally bioavailable inhibitor of GTP-RAS, in models of pancreatic ductal adenocarcinoma

Abstract Approximately 95% of pancreatic ductal adenocarcinoma (PDAC) cases are driven by activating mutations in KRAS, accounting for over 45,000 deaths per year in the United States. In KRAS-mutant cells, KRAS protein exists predominantly in an active, GTP-bound state, leading to excessive oncogenic signaling via RAF/MEK/ERK and other effector pathways. After decades of anticipation, the first therapeutic inhibitors of this oncoprotein target a specific mutant allele (KRASG12C) and have shown promising results in this rare subset of human PDAC patients (1-2% of cases). While these encouraging clinical results bolster support for targeting RAS in human PDAC, most patients harbor KRASG12D and KRASG12V mutations and remain unserved by targeted therapies. Here we report preclinical studies of RM-042, a first-in-class, potent, oral, small molecule inhibitor of GTP-bound RAS proteins, designed to treat cancers driven by a variety of RAS mutations. RMC-6236, a clinical candidate and RM-042, a tool compound, both act through non-covalent binding to an abundant intracellular chaperone protein, cyclophilin A (CypA), resulting in a binary complex that engages GTP-bound RAS to form a high-affinity, RAS-selective tri-complex that sterically inhibits RAS binding to effectors. We examined the anti-tumor activity of RM-042 in two complementary preclinical model systems of PDAC. Using primary human PDAC explant cultures (tissue slices cultured intact in optimized media for up to one week), we found that RM-042 potently inhibits phospho-ERK expression (a marker of KRAS/RAF/MEK pathway activity), in a concentration-dependent manner. Loss of pERK expression in tumors was also associated with reduced viability, and altered stromal content. Pilot studies in the K-rasLSL.G12D/+, p53LSL.R172H/+, Pdx1Cretg/+ (KPC) mouse model of PDAC found that RM-042 induced tumor stabilizations and regressions associated with loss of pERK expression, and alterations in apoptosis and proliferation, at tolerated doses. Ongoing studies will determine the duration of tumor responses and assess the mechanisms by which RM-042 may impact both epithelial and stromal cell populations. Together, these studies provide complementary evidence from in vivo murine and ex vivo human models for anti-tumor activity in response to GTP-Ras inhibition, supporting the inclusion of PDAC patients in future clinical trials of RMC-6236. Citation Format: Urszula N. Wasko, Stephen A. Sastra, Carmine F. Palermo, David Wildes, Mallika Singh, Kenneth P. Olive. Preclinical evaluation of RM-042, an orally bioavailable inhibitor of GTP-RAS, in models of pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B071.

A novel protein RASON encoded by a lncRNA controls oncogenic RAS signaling in KRAS mutant cancers

Mutations of the RAS oncogene are found in around 30% of all human cancers yet direct targeting of RAS is still considered clinically impractical except for the KRASG12C mutant. Here we report that RAS-ON (RASON), a novel protein encoded by the long intergenic non-protein coding RNA 00673 (LINC00673), is a positive regulator of oncogenic RAS signaling. RASON is aberrantly overexpressed in pancreatic ductal adenocarcinoma (PDAC) patients, and it promotes proliferation of human PDAC cell lines in vitro and tumor growth in vivo. CRISPR/Cas9-mediated knockout of Rason in mouse embryonic fibroblasts inhibits KRAS-mediated tumor transformation. Genetic deletion of Rason abolishes oncogenic KRAS-driven pancreatic and lung cancer tumorigenesis in LSL-KrasG12D; Trp53R172H/+ mice. Mechanistically, RASON directly binds to KRASG12D/V and inhibits both intrinsic and GTPase activating protein (GAP)-mediated GTP hydrolysis, thus sustaining KRASG12D/V in the GTP-bound hyperactive state. Therapeutically, deprivation of RASON sensitizes KRAS mutant pancreatic cancer cells and patient-derived organoids to EGFR inhibitors. Our findings identify RASON as a critical regulator of oncogenic KRAS signaling and a promising therapeutic target for KRAS mutant cancers.

LRRK2 phosphorylation of Rab GTPases in Parkinson's disease.

Rab GTPases comprise a large family of conserved GTPases that are critical regulators of the secretory and endocytic pathways. The human genome encodes ~ 65 Rabs that localize to discrete membrane compartments and, when in their GTP-bound state, bind to effector proteins to carry out diverse functions. Activating mutations in LRRK2 kinase cause Parkinson's disease, and subsets of Rab GTPases are important LRRK2 substrates. LRRK2 phosphorylates a conserved threonine residue that is essential for Rab interaction with guanine nucleotide exchange factors, effectors, and GDI that recycles Rabs between membrane compartments. This brief review will highlight new findings related to LRRK2-mediated phosphorylation of Rab GTPases and its consequences. Remarkably, Rab phosphorylation flips a switch on Rab effector selection with dominant consequences for cell pathophysiology.

Recruitment of Irgb6 to the membrane is a direct trigger for membrane deformation.

Irgb6 is a member of interferon γ-induced immunity related GTPase (IRG), and one of twenty “effector” IRGs, which coordinately attack parasitophorous vacuole membrane (PVM), causing death of intracellular pathogen. Although Irgb6 plays a pivotal role as a pioneer in the process of PVM disruption, the direct effect of Irgb6 on membrane remained to be elucidated. Here, we utilized artificial lipid membranes to reconstitute Irgb6-membrane interaction in vitro, and revealed that Irgb6 directly deformed the membranes. Liposomes incubated with recombinant Irgb6 were drastically deformed generating massive tubular protrusions in the absence of guanine nucleotide, or with GMP-PNP. Liposome deformation was abolished by incubating with Irgb6-K275A/R371A, point mutations at membrane targeting residues. The membrane tubules generated by Irgb6 were mostly disappeared by the addition of GTP or GDP, which are caused by detachment of Irgb6 from membrane. Binding of Irgb6 to the membrane, which was reconstituted in vitro using lipid monolayer, was stimulated at GTP-bound state. Irgb6 GTPase activity was stimulated by the presence of liposomes more than eightfold. Irgb6 GTPase activity in the absence of membrane was also slightly stimulated, by lowering ionic strength, or by increasing protein concentration, indicating synergistic stimulation of the GTPase activity. These results suggest that membrane targeting of Irgb6 and resulting membrane deformation does not require GTP, but converting into GTP-bound state is crucial for detaching Irgb6 from the membrane, which might coincident with local membrane disruption.

Small GTPase FoSec4-Mediated Protein Secretion Is Important for Polarized Growth, Reproduction and Pathogenicity in the Banana Fusarium Wilt Fungus Fusarium odoratissimum.

Apical secretion at hyphal tips is important for the growth and development of filamentous fungi. In this study, we analyzed the role of the Rab GTPases FoSec4 involved in the secretion of the banana wilt fungal pathogen Fusarium odoratissimum. We found that the deletion of FoSEC4 affects the activity of extracellular hydrolases and protein secretion, indicating that FoSec4 plays an important role in the regulation of protein secretion in F. odoratissimum. As a typical Rab GTPase, Sec4 participates in the Rab cycle through the conversion between the active GTP-bound state and the inactive GDP-bound state, which is regulated by guanine nucleate exchange factors (GEFs) and GTPase-activating proteins (GAPs). We further found that FoSec2 can interact with dominant-negative FoSec4 (GDP-bound and nucleotide-free form, FoSec4DN), and that FoGyp5 can interact with dominant active FoSec4 (GTP-bound and constitutively active form, FoSec4CA). We evaluated the biofunctions of FoSec4, FoSec2 and FoGyp5, and found that FoSec4 is involved in the regulation of vegetative growth, reproduction, pathogenicity and the environmental stress response of F. odoratissimum, and that FocSec2 and FoGyp5 perform biofunctions consistent with FoSec4, indicating that FoSec2 and FoGyp5 may work as the GEF and the GAP, respectively, of FoSec4 in F. odoratissimum. We further found that the amino-terminal region and Sec2 domain are essential for the biological functions of FoSec2, while the carboxyl-terminal region and Tre-2/Bub2/Cdc16 (TBC) domain are essential for the biological functions of FoGyp5. In addition, FoSec4 mainly accumulated at the hyphal tips and partially colocalized with Spitzenkörper; however, FoGyp5 accumulated at the periphery of Spitzenkörper, suggesting that FoGyp5 may recognize and inactivate FoSec4 at a specific location in hyphal tips.

Abstract P1082: Activation And Phosphorylation Of Rap1b In The Human Megakaryocytic Leukemia Cell Line DAMI

In platelet-producing megakaryocytes, the signaling protein Rap1b mediates both activation of integrins for cell adhesion and activation of the transcription factor ERK leading to gene expression changes. As a small G-protein, Rap1b acts as a molecular switch with an inactive GDP-bound state and an active GTP-bound state. Additionally, the association of Rap1b within the inner side of the plasma membrane is dictated by cAMP-dependent protein kinase (PKA) phosphorylation. In an unphosphorylated state, Rap1b is attached to the plasma membrane via a lipid anchor. Upon phosphorylation, Rap1b detaches from the membrane and is cytosolic. We hypothesize the location of active Rap1b, dictated by the guanine nucleotide bound (GDP/GTP) and its phosphorylation status, determines which signaling pathways Rap1b contributes to in megakaryocytes. To evaluate this hypothesis, we first need to optimize methods to detect Rap1b activation (GTP binding) and phosphorylation. Using the megakaryocyte cell line (DAMI), we over-expressed green fluorescent protein (GFP)-tagged Rap1b and treated with reagents to stimulate activation or phosphorylation and then use pull-down assays with the Rap binding domain (RBD) to capture activated Rap1b or pan phospho S/T antibodies, respectively. In addition, the activation of downstream proteins like ERK were evaluated in DAMI cells overexpressing GFP-tagged Rap1b phosphorylation mutants. Overall, this work seeks to determine how the spatial distribution of Rap1b, dictated by phosphorylation influences cellular processes.

Structure of the MRAS–SHOC2–PP1C phosphatase complex

RAS–MAPK signalling is fundamental for cell proliferation and is altered in most human cancers1–3. However, our mechanistic understanding of how RAS signals through RAF is still incomplete. Although studies revealed snapshots for autoinhibited and active RAF–MEK1–14-3-3 complexes4, the intermediate steps that lead to RAF activation remain unclear. The MRAS–SHOC2–PP1C holophosphatase dephosphorylates RAF at serine 259, resulting in the partial displacement of 14-3-3 and RAF–RAS association3,5,6. MRAS, SHOC2 and PP1C are mutated in rasopathies—developmental syndromes caused by aberrant MAPK pathway activation6–14—and SHOC2 itself has emerged as potential target in receptor tyrosine kinase (RTK)–RAS-driven tumours15–18. Despite its importance, structural understanding of the SHOC2 holophosphatase is lacking. Here we determine, using X-ray crystallography, the structure of the MRAS–SHOC2–PP1C complex. SHOC2 bridges PP1C and MRAS through its concave surface and enables reciprocal interactions between all three subunits. Biophysical characterization indicates a cooperative assembly driven by the MRAS GTP-bound active state, an observation that is extendible to other RAS isoforms. Our findings support the concept of a RAS-driven and multi-molecular model for RAF activation in which individual RAS–GTP molecules recruit RAF–14-3-3 and SHOC2–PP1C to produce downstream pathway activation. Importantly, we find that rasopathy and cancer mutations reside at protein–protein interfaces within the holophosphatase, resulting in enhanced affinities and function. Collectively, our findings shed light on a fundamental mechanism of RAS biology and on mechanisms of clinically observed enhanced RAS–MAPK signalling, therefore providing the structural basis for therapeutic interventions.

Abstract 2918: Comprehensive survey of KRas4B membrane interaction and orientation

Abstract Three RAS genes encode four Ras proteins, HRas, NRas, and KRas splice variants, KRas4A and KRas4B. In human cancers, KRAS oncogene is highly expressed (85%) as compared to other RAS oncogenes, NRAS (11%) and HRAS (4%). Oncogenic Ras leads to aberrant cell proliferation signaling, primarily through the MAPK (Raf/MEK/ERK) pathway. At the plasma membrane, nanoclustered Ras proteins promote Raf activation, mediating the downstream signaling pathway. Among the Ras isoforms, KRas4B in the membrane has been studied extensively due to its higher level of mutations in cancer. Although a number of experimental studies have focused on KRas4B subcellular localization and their nanocluster formation at the signaling platform, the mechanistic details of the membrane anchorage and the membrane orientation of KRas4B at atomic resolution are still unknown. Here, comprehensive computational studies were performed for KRas4B at the anionic lipid bilayers, composed of the phospholipids, PS and PA, and the phosphoinositides, PIP2, PI4P, and PI5P. Wild-type and two oncogenic mutants, G12D and G12V KRas4B in the GTP- and GDP-bound states were considered. The lysine rich HVR was post-translationally modified with the farnesyl and methyl groups. Previous studies showed that wild-type KRas4B-GDP interacts weakly and nonspecifically with anionic phospholipids, while oncogenic mutations alter selective anionic lipid binding toward anionic lipids, PA, PI3P, PI4P, and PI5P. Our studies indicate that the membrane interaction of KRas4B is highly sensitive depending on the types of nucleotides, mutational states, and anionic lipids enriched the lipid bilayer. While the GTP-bound spontaneously inserts its prenyl group into the hydrophobic core of the bilayer, the occurrence of spontaneous insertion is reduced in the GDP-bound form. The distance of GTP-bound catalytic domain from the bilayer surface is longer than the GDP-bound form. The HVR is sequestered by the GDP-bound catalytic domain, which causes the catalytic domain to be occluded and increases the membrane interaction by the catalytic domain. In contrast, the GTP-bound catalytic domain releases its HVR and liberates from the membrane interaction. The occlusion of catalytic domain is less prevalent in the GTP-bound state. KRas4BG12D/G12V-GTP exhibits the active-state orientation, exposing its effector binding site for recruiting the effectors. While PA and PIP2 support the active-state orientation, the PIP4 enriched bilayer prevents the spontaneous prenyl insertion resulting in the occlusion of catalytic domain. Our results underscore the importance of detailed structural mechanisms of KRas4B membrane interaction and orientation, elucidating vital mechanistic role of KRas4B, a key membrane-anchored protein in cancer. Funded by Frederick National Laboratory for Cancer Research, National Institutes of Health, under contract HHSN261201500003I. Citation Format: Hyunbum Jang, Mingzhen Zhang, Vadim Gaponenko, Ruth Nussinov. Comprehensive survey of KRas4B membrane interaction and orientation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2918.

Abstract 4029: Combination of KRASG12C(ON) and SHP2 inhibitors overcomes adaptive resistance and enhances anti-tumor immunity

Abstract Oncogenic mutations in KRAS are frequent in non-small cell lung cancer and have been associated with poor prognosis. The recent development and approval of KRASG12C mutant-specific inhibitors could change the clinical practice of lung cancer patients harboring KRASG12C mutations. However, early clinical data indicate the development of acquired resistance after initial responses. All of the KRASG12C inhibitors being tested in clinical trials to date target GDP-bound KRAS (OFF state), which makes them vulnerable to upstream pathway reactivation, as this will increase KRAS in a GTP-bound (ON) state and therefore reduce drug efficacy. In this study we use a covalent tri-complex KRASG12C(ON) inhibitor which targets KRASG12C in the active state. In vitro, the KRASG12C(ON) inhibitor RM-029 exhibited higher efficacy than the KRASG12C(OFF) inhibitor MRTX849 (adagrasib). However, treatment with RM-029 also showed adaptive RAS pathway reactivation after 24 hours of treatment, which can be blocked using the SHP2 inhibitor RMC-4550, suggesting that pathway reactivation is mediated by signaling from RTKs to RAS proteins. In vivo, KRASG12C(ON) treatment led to strong regression of KRASG12C tumors and addition of a SHP2 inhibitor significantly increased anti-tumor responses. Single treatments with KRASG12C(ON) or SHP2 inhibitors led to complete responses in some animals and immunological memory in an immune responsive KRASG12C lung tumor model, with all tumors showing complete responses when the inhibitors were combined. Consistent with this finding, both KRASG12C(ON) and SHP2 inhibition resulted in a profound remodeling of the lung tumor microenvironment (TME), with increased infiltration and activation of T cells accompanied by a reduction of tumor-promoting myeloid cells. Interestingly, similar changes were obtained in an immune evasive KRASG12C lung cancer model. Besides acting upstream RAS, SHP2 has also specific roles in immune cells, including regulation of T cell function. As comparison, responses to SOS1 inhibition, which acts only upstream RAS, have also been analyzed. Overall, our preclinical results show that the anti-tumor activity of the combination of KRASG12C(ON) with SHP2 inhibition is the result of different mechanisms. First, a KRASG12C(ON) inhibitor potently inhibits oncogenic RAS and addition of a SHP2 inhibitor blocks RAS pathway reactivation increasing tumor responses. Second, both inhibitors have beneficial effects in the TME which can be potentiated when combined. Finally, addition of a SHP2 inhibitor could potentially overcome intrinsic resistant populations by directly targeting cells resistant to G12C inhibition and/or by increasing anti-tumor immunity. Citation Format: Panayiotis Anastasiou, Edurne Mugarza, Jesse Boumelha, Sareena Rana, Christopher Moore, Miriam Molina-Arcas, Julian Downward. Combination of KRASG12C(ON) and SHP2 inhibitors overcomes adaptive resistance and enhances anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4029.

Abstract 2681: Novel and selective inhibitors of KRASG12D

Abstract RAS proteins are family of small GTP-binding proteins that play a major role in regulating cellular responses such as proliferation, differentiation, migration, and cell growth. RAS proteins function as molecular switches, cycling between inactive (GDP-bound) and active (GTP-bound) states, which relay cellular signals in response to extracellular stimuli. Aberrant RAS signaling plays a role in up to 30% of all human cancers, with the highest incidence occurring in carcinomas of the pancreas (63–90%), colon (36–50%), and lung (19–30%). Targeting the inactive, GDP bound KRASG12C has been a promising approach for generating novel anti RAS therapies, which is validated by the approval of AMG 510 (Lumakras) by the FDA. It is also known that KRASG12D also retains GTPase activity. Consequently, KRASG12D is one of the most important chemotherapeutic drug targets. KRASG12D is commonly observed in pancreatic cancer. Here we describe preclinical profile of a potent, selective, in-vivo tool compound, VRTX144. VRTX144 was potent in HPAC cell line, representing pancreatic adenocarcinoma, and a panel of KRASG12D mutated cell lines. It was found to be several folds less active in non-KRASG12D mutant cell lines. In vitro combination strategies with other targeted therapies such as EGFR, SHP2 and CDK4/6 inhibitor is also being investigated. VRTX144 exhibited low propensity for metabolism in microsomes, and has high protein bound. VRTX144 was found to have no adverse effect in hERG upto 10 uM. Citation Format: Prashant Kashinath Bhavar, Uday Kumar Surampudi, Partha Pratim Sarma, Mahesh Mohan Shidore, Anuj Ramesh Kshirsagar. Novel and selective inhibitors of KRASG12D [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2681.

Abstract 5443: BPI-421286: A highly potent small molecule inhibitor targeting KRASG12C mutation

Abstract KRAS is a GTP-binding protein that links receptor tyrosine kinase activation to intracellular signaling. Mutation of KRAS favors the GTP-bound active state and constitutive activation of downstream effects. KRASG12C mutation has been identified as an oncogenic driver of tumorigenesis, which is found in approximately 14% of lung cancer, 4% of colorectal (CRC), and 1-3% of other solid tumors. Herein, we report BPI-421286, a highly potent and selective covalent small molecular KRASG12C inhibitor. In vitro, BPI-421286 showed a high Kinact/Ki value (256,000 M-1 s-1), and inhibited KRAS-GTP/GDP exchange with a lower IC50 (55 nM). In cell-based assays, BPI-421286 suppressed proliferation of KRASG12C mutant cell lines with sub-nanomolar potency, but did not affect cell lines with wide type or non-G12C KRAS mutations. BPI-421286 also inhibited phospho-ERK in MIA PaCa-2 cell with a low IC50 value (2.9 nM). In vivo, daily oral administration of 3-100 mg/kg BPI-421286 led to tumor growth suppression or regression in multiple KRASG12C mutant xenograft or PDX models of NSCLC, CRC and PDAC. The in vivo PKPD in MIA PaCa-2 xenograft model showed that durable pERK inhibition can be achieved without continuous drug exposure, featuring BPI-421286 as a covalent, non-reversible KRAS inhibitor. Combining BPI-421286 with several targeted agents, including a SHP2 inhibitor BPI-442096 and a CDK4/6 inhibitor BPI-16350, demonstrated enhanced tumor growth inhibition compared to either agent alone. Notably, for the acquired resistance mutations that are clinically observed after KRASG12C inhibitor treatment, such as G12C/H95D, G12C/H95Q, G12C/R68S and G12C/Y96C, BPI-421286 also exhibited strong inhibitory activities, suggesting that BPI-421286 could overcome the acquired resistance of currently approved KRASG12C inhibitors. Taken together, BPI-421286 is a highly potent and selective KRASG12C inhibitor, with favorable ADME properties and wide therapeutic index in pre-clinical toxicology studies. BPI-421286 is currently in Phase 1 clinical study. Citation Format: Xiaoguan Zhu, Yuan Lu, Jing Guo, Dan Yan, Boyan Li, Xiaoping Chen, Haibo Chen, Hong Lan, Hao Wu, Lieming Ding, Jiabing Wang. BPI-421286: A highly potent small molecule inhibitor targeting KRASG12C mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5443.

Abstract 2675: Discovery of potent CNS-penetrant covalent KRAS G12C inhibitors

Abstract The RAS family of GTPases, which include KRAS, NRAS, and HRAS, are key regulators of cellular signaling, acting as molecular switches downstream of receptor tyrosine kinases (RTKs) and as key regulators of the RAS/MAPK pathway. RAS cycles between inactive (GDP) and active (GTP) states to regulate the activity of the RAS/MAPK pathway. In many cancers, activating KRAS mutations enable KRAS to persist in the active GTP-bound state, resulting in hyperactive RAS/MAPK pathway signaling that drives cell growth and survival. The KRAS G12C mutation occurs in 14% of lung adenocarcinoma, a cancer type that frequently metastasizes to the brain (40%). To address the high prevalence of KRAS G12C mutant CNS metastases in lung adenocarcinoma, we are developing CNS-penetrant covalent KRAS G12C inhibitors (“ERAS G12Ci’s”) to treat both CNS and systemic disease. ERAS G12Ci’s rapidly form covalent adducts with the KRAS G12C protein in its inactive GDP state and exhibit low nanomolar IC50’s in a nucleotide exchange assay. ERAS G12Ci’s demonstrate high selectivity in a cell-based proteome selectivity assay and inhibit the growth of RAS Initiative KRAS G12C mutant cells, and not RAS Initiative KRAS WT cells. ERAS G12Ci’s potently inhibit cell proliferation in 3-dimensional Cell-Titer Glo (3D-CTG) assays in KRAS G12C mutant lung and pancreatic cell lines (NCI-H1373, NCI-H2122, and MIA PaCa-2). Mechanistically, ERAS G12Ci’s blocked RAS-RAF complex formation and inhibited ERK1/2 phosphorylation. This in vitro activity translates in vivo where ERAS G12Ci’s induce pharmacodynamic modulation in the pancreatic cancer MIA PaCa-2 model. ERAS G12Ci’s significantly inhibit tumor growth in NCI-H1373 and NCI-H2122 CDX lung adenocarcinoma and MIA PaCa-2 PDAC models. No meaningful body weight loss or clinical adverse events were observed with any of these compounds. Human efflux transporter substrate assessments indicate that ERAS G12Ci’s are either not substrates or weak/modest substrates of P-gp, a crucial efflux transporter that can limit CNS penetration. In rat CNS studies, these inhibitors exhibit good CNS penetration performance as measured by brain-to-plasma partition coefficients, which are comparable to those of approved CNS-active small molecule inhibitors. Daily oral administration demonstrates dose-dependent tumor regression in intracranial and intra-carotid injection (ICA) KRAS G12C CDX models. We are optimizing multiple covalent CNS-penetrant KRAS G12C inhibitors that exhibit both CNS and systemic activity in vivo. Citation Format: Jae Hyun Bae, Erin D. Lew, Jun Feng, Marcos Gonzalez-Lopez, Joanne Oh, Patrick Fagan, Matt Salie, Nick Isley, Richard Lam, Adriana Irimia, Robin Nevarez, Bingzhen Lin, Taylor Congdon, Jingchuan Zhang, Dawei Xuan, Ping Chen, Jean-Michel Vernier, Robert Shoemaker. Discovery of potent CNS-penetrant covalent KRAS G12C inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2675.

Abstract 2671: ERAS-601, a potent allosteric inhibitor of SHP2, demonstrates anti-tumor activity in RAS/MAPK-driven tumor models

Abstract SHP2 is a non-receptor protein tyrosine phosphatase (PTP) encoded by the PTPN11 gene. SHP2 transduces upstream receptor tyrosine kinase (RTK) signaling to the RAS/MAPK pathway via its phosphatase-mediated regulation of guanine nucleotide exchange factors (GEFs). The modulation of GEF activity impacts the rate at which KRAS cycles from the inactive GDP-bound state to the active GTP-bound state. ERAS-601 is a potent, selective small molecule allosteric inhibitor of SHP2. ERAS-601 potently inhibits the wild type SHP2 protein with a biochemical IC50 of 4.6 nM. ERAS-601 is a selective SHP2 inhibitor and demonstrates no appreciable inhibition against any off-target kinase or phosphatase across panels of 300 kinases and 12 phosphatases. ERAS-601 inhibits the loading of active GTP-bound oncogenic RAS and inhibits RAS/MAPK pathway signaling as measured by pERK1/2 inhibition and DUSP6 mRNA. ERAS-601 demonstrates anti-proliferative activity across a panel of human cancer cell line models with oncogenic alterations in the RAS/MAPK pathway. In a mouse in vivo study, ERAS-601 achieves substantial systemic exposure and demonstrates inhibition of ERK1/2 phosphorylation and DUSP6 mRNA levels in the NCI-H358 xenograft model. ERAS-601 also inhibits tumor growth in multiple RAS/MAPK-driven CDX and PDX models that harbor EGFR, KRAS, BRAF Class III, and NF1LOF mutations. ERAS-601 is a potent and selective allosteric SHP2 inhibitor that demonstrates anti-tumor activity in vitro and in vivo and is currently being studied as a monotherapy in an ongoing Phase 1 clinical study in patients with advanced or metastatic solid tumors (FLAGSHP-1, NCT04670679). Citation Format: Leenus Martin, Roopal Patel, Jingchuan Zhang, Jennifer Yang, Robin Nevarez, Taylor Congdon, Les Brail, Robert Shoemaker. ERAS-601, a potent allosteric inhibitor of SHP2, demonstrates anti-tumor activity in RAS/MAPK-driven tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2671.

Abstract 2919: The structural basis of BCR-ABL recruitment of GRB2 in chronic myelogenous leukemia

Abstract Philadelphia chromosomes 9 and 22 encode BCR and ABL1 genes, respectively. Translocation mutation of two chromosomes generates the fused BCR-ABL1 gene. The resulting fused gene encodes the chimeric BCR-ABL oncoprotein with constitutively enhanced and dysregulated tyrosine activity to disturb different cell signaling. Ras/MAPK is a significant pathway in mediating cell proliferation and its hyperactivation is responsible for malignant transformation in cancer. Autophosphorylation Y177 (pY177) of BCR protein stimulates the direct binding of an adaptor protein GRB2, which is involved in Ras/MAPK pathway. In BCR-ABL-associated Ras/MAPK signaling pathway, BCR-ABL can target GRB2 through the interaction of its pY motif with GRB2 SH2 domain, followed by SOS recruitment to the plasma membrane by GRB2. The resulting BCR-ABL/GRB2/SOS assembly stimulates the transformation of inactive GDP-bound form of Ras to the active GTP-bound state, which causes the constitutive activation of the downstream components of Raf/MEK/ERK. Despite a number of biophysical experiments have showed that BCR-ABL is able to recruit GRB2, the molecular-level understanding of how the two proteins interact with each other remains to be elucidated. In this work, we used molecular modeling and molecular dynamics (MD) simulations to study the structural basis for the binding between BCR-ABL and GRB2 SH2 domain to explain CML oncogenesis at the atomic level. Different pY/Y-peptide-SH2 complex models have been constructed and their binding specificity and affinity were compared. Simulation results showed that phosphorylated BCR (pBCR) specifically binds to GRB2 SH2 domain through its five-residue 176FpYVNV180 motif. GRB2 SH2 domain contains two binding pockets: the pY-binding pocket for the phosphate recognition and the specificity pocket for the selection of Asn. pY177 triggers the binding through the interaction in pY-binding pocket. The interaction in specificity pocket determines the binding specificity, which is regulated by N179 in pBCR and W121 in EF loop of GRB2 SH2 domain. In addition, the interaction in the specificity pocket experiences conformation selection for both the bound motif in pBCR and GRB2 SH2 domain; the binding motif adopts type I β-turn conformation and the specificity pocket of GRB2 SH2 domain displays the closed conformation. This specific binding mode between pBCR and GRB2 SH2 domain is similar with that between phosphorylated EGFR (pEGFR) and GRB2 SH2 domain. Residues adjacent to the pY and Arg residue at the +2 position C-terminal to pY in the binding motifs influence the binding affinity of a pY-peptide to GRB2 SH2 domain, explaining why pBCR shows stronger affinity to GRB2 SH2 domain than pEGFR. Our study supports the BCR-ABL oncoprotein recruitment of GRB2 for the induction of CML through Ras/MAPK pathway and provides deeply understanding of the specific interaction of the pY motif with GRB2 SH2 domain at atomic level. Citation Format: Yonglan Liu, Hyunbum Jang, Mingzhen Zhang, Chung-Jung Tsai, Ryan Maloney, Ruth Nussinov. The structural basis of BCR-ABL recruitment of GRB2 in chronic myelogenous leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2919.

Abstract 3345: ERAS-601, a potent inhibitor of SHP2, synergistically enhances the activity of a FLT3 inhibitor, gilteritinib, in FLT3-mutated AML tumor models

Abstract ERAS-601 is a potent, small molecule allosteric inhibitor of wildtype SHP2, a non-receptor protein tyrosine phosphatase (PTP) encoded by the PTPN11 gene. ERAS-601 inhibits wildtype SHP2 biochemically with an IC50 of 4.6 nM and demonstrates selectivity across panels of 300 kinases and 12 phosphatases. SHP2 mediates upstream receptor tyrosine kinase (RTK) signaling via its phosphatase-mediated regulation of guanine nucleotide exchange factors (GEFs). ERAS-601 inhibits the SHP2 dependent cycling of KRAS from the inactive GDP-bound state to the active GTP-bound state and demonstrates anti-proliferative activity in FLT3-mutated human cancer cells. Gilteritinib is a second-generation FLT3 inhibitor and has demonstrated clinical activity, but emerging resistance limits the benefit of monotherapy. Here, we explored the combination of gilteritinib with ERAS-601 in FLT3 mutated AML nonclinical models. The combination of ERAS-601 with gilteritinib inhibits the oncogenic RAS/MAPK signaling as measured by pERK1/2 and synergistically inhibits the cellular viability of FLT3-mutated AML cells in vitro. The combination of ERAS-601 with gilteritinib achieves a more durable tumor growth inhibition than the respective gilteritinib and ERAS-601 monotherapies in vivo. These preclinical data support the clinical development of ERAS-601 in combination with gilteritinib in FLT3-altered AML. Citation Format: Leenus Martin, Roopal Patel, Jingchuan Zhang, Robin Nevarez, Taylor Congdon, Les Brail, Robert Shoemaker. ERAS-601, a potent inhibitor of SHP2, synergistically enhances the activity of a FLT3 inhibitor, gilteritinib, in FLT3-mutated AML tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3345.

Abstract 2670: ERAS-601, a potent allosteric inhibitor of SHP2, synergistically enhances the efficacy of sotorasib/adagrasib and cetuximab in NSCLC, CRC, and HNSCC tumor models

Abstract ERAS-601 is a potent, small molecule allosteric inhibitor of wildtype SHP2, a non-receptor protein tyrosine phosphatase (PTP) encoded by the PTPN11 gene. ERAS-601 inhibits wild type SHP2 biochemically with an IC50 of 4.6 nM and demonstrates selectivity across panels of 300 kinases and 12 phosphatases. SHP2 mediates upstream receptor tyrosine kinase (RTK) signaling via its phosphatase-mediated regulation of guanine nucleotide exchange factors (GEFs). ERAS-601 inhibits the SHP2 dependent cycling of KRAS from the inactive GDP-bound state to the active GTP-bound state and demonstrates anti-proliferative activity in KRASG12C and EGFR amplified cell lines. The combination of upstream blockade of RAS-GTP cycling by ERAS-601 with inhibition of KRASG12C by a selective KRASG12C inhibitor synergistically inhibits cellular proliferation in multiple KRASG12C mutated human cancer cell lines. The combinations of ERAS-601 with KRASG12C inhibitors achieve tumor growth inhibition that is superior to the respective ERAS-601 and KRASG12C monotherapies in NSCLC and CRC CDX and PDX tumor models. Similarly, the combination of ERAS-601 with an EGFR antibody, cetuximab, inhibits oncogenic RAS/MAPK signaling as measured by pERK1/2 and enhances the anti-proliferative activity of cetuximab in RAS/RAF wild type CRC and HPV-negative HNSCC cell lines. The combination of ERAS-601 with cetuximab achieves tumor growth inhibition that is superior to respective ERAS-601 and cetuximab monotherapies in RAS/RAF wild type CRC and HPV-negative HNSCC CDX and PDX tumor models. These nonclinical data support the clinical development of ERAS-601 in combination with a KRASG12C inhibitor in NSCLC and CRC tumors, and ERAS-601 in combination with cetuximab in RAS/RAF wild type CRC as well as HPV-negative HNSCC tumors. Both combinations are being studied in ongoing clinical studies (HERKULES-2, NCT04959981; FLAGSHP-1, NCT04670679). Citation Format: Leenus Martin, Roopal Patel, Jingchuan Zhang, Robin Nevarez, Taylor Congdon, Les Brail, Robert Shoemaker. ERAS-601, a potent allosteric inhibitor of SHP2, synergistically enhances the efficacy of sotorasib/adagrasib and cetuximab in NSCLC, CRC, and HNSCC tumor models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2670.

The RAL Enigma: Distinct Roles of RALA and RALB in Cancer.

RALA and RALB are highly homologous small G proteins belonging to the RAS superfamily. Like other small GTPases, the RALs are molecular switches that can be toggled between inactive GDP-bound and active GTP-bound states to regulate diverse and critical cellular functions such as vesicle trafficking, filopodia formation, mitochondrial fission, and cytokinesis. The RAL paralogs are activated and inactivated by a shared set of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) and utilize similar sets of downstream effectors. In addition to their important roles in normal cell biology, the RALs are known to be critical mediators of cancer cell survival, invasion, migration, and metastasis. However, despite their substantial similarities, the RALs often display striking functional disparities in cancer. RALA and RALB can have redundant, unique, or even antagonistic functions depending on cancer type. The molecular basis for these discrepancies remains an important unanswered question in the field of cancer biology. In this review we examine the functions of the RAL paralogs in normal cellular physiology and cancer biology with special consideration provided to situations where the roles of RALA and RALB are non-redundant.

Rab39 and its effector UACA regulate basolateral exosome release from polarized epithelial cells.

Exosomes are small extracellular vesicles that originate from the intraluminal vesicles of multivesicular bodies (MVBs). We previously reported that polarized Madin-Darby canine kidney (MDCK) epithelial cells secrete two types of exosomes, apical and basolateral exosomes, from different MVBs. However, how these MVBs are selectively targeted to the apical or basolateral membrane remained unknown. Here, we analyze members of the Rab family small GTPases and show that different sets of Rabs mediate asymmetrical exosome release. Rab27, the best-known regulator of MVB transport for exosome release, is specifically but partially involved in apical exosome release, and Rab37, a close homolog of Rab27, is an additional apical exosome regulator. By contrast, Rab39 functions as a specific regulator of basolateral exosome release. Mechanistically, Rab39 interacts with its effector UACA, and UACA then recruits Lyspersin, a component of BLOC-1-related complex (BORC). Our findings suggest that the Rab39-UACA-BORC complex specifically mediates basolateral exosome release.

Autopromotion of K-Ras4B Feedback Activation Through an SOS-Mediated Long-Range Allosteric Effect.

The Ras-specific guanine nucleotide exchange factors Son of Sevenless (SOS) regulates Ras activation by converting inactive GDP-bound to active GTP-bound states. The catalytic activity of Ras is further allosterically regulated by GTP−Ras bound to a distal site through a positive feedback loop. To address the mechanism underlying the long-range allosteric activation of the catalytic K-Ras4B by an additional allosteric GTP–Ras through SOS, we employed molecular dynamics simulation of the K-Ras4BG13D•SOScat complex with and without an allosteric GTP-bound K-Ras4BG13D. We found that the binding of an allosteric GTP−K-Ras4BG13D enhanced the affinity between the catalytic K-Ras4BG13D and SOScat, forming a more stable conformational state. The peeling away of the switch I from the nucleotide binding site facilitated the dissociation of GDP, thereby contributing to the increased nucleotide exchange rate. The community networks further showed stronger edge connection upon allosteric GTP−K-Ras4BG13D binding, which represented an increased interaction between catalytic K-Ras4BG13D and SOScat. Moreover, GTP−K-Ras4BG13D binding transmitted allosteric signaling pathways though the Cdc25 domain of SOS that enhanced the allosteric regulatory from the K-Ras4BG13D allosteric site to the catalytic site. This study may provide an in-depth mechanism for abnormal activation and allosteric regulation of K-Ras4BG13D.

Direct Targeting KRAS Mutation in Non-Small Cell Lung Cancer: Focus on Resistance.

KRAS is the most frequently mutated oncogene in non-small cell lung cancers (NSCLC), with a frequency of around 30%, and encoding a GTPAse that cycles between active form (GTP-bound) to inactive form (GDP-bound). The KRAS mutations favor the active form with inhibition of GTPAse activity. KRAS mutations are often with poor response of EGFR targeted therapies. KRAS mutations are good predictive factor for immunotherapy. The lack of success with direct targeting of KRAS proteins, downstream inhibition of KRAS effector pathways, and other strategies contributed to a focus on developing mutation-specific KRAS inhibitors. KRAS p.G12C mutation is one of the most frequent KRAS mutation in NSCLC, especially in current and former smokers (over 40%), which occurs among approximately 12-14% of NSCLC tumors. The mutated cysteine resides next to a pocket (P2) of the switch II region, and P2 is present only in the inactive GDP-bound KRAS. Small molecules such as sotorasib are now the first targeted drugs for KRAS G12C mutation, preventing conversion of the mutant protein to GTP-bound active state. Little is known about primary or acquired resistance. Acquired resistance does occur and may be due to genetic alterations in the nucleotide exchange function or adaptative mechanisms in either downstream pathways or in newly expressed KRAS G12C mutation.