Ras Downstream Signaling Research Articles

Key Signaling Pathways Engaged in Cancer Management: Current Update

<P>Background: Till today cancer is still challenging to treat and needs more active therapeutic approaches. Participation of complex multi-pathway cell propagation instrument is a noteworthy issue in creating active anticancer therapeutic methodologies. Immune evasions, metabolic modifications, imperfect apoptotic component, modification in upstream or downstream RAS signaling, altered nuclear factor kappa B actions, imbalanced autophagy design and distortedly controlled angiogenesis are distinguishing features of cancer. </P><P> Methods: On the basis of systemic research and analysis of the current online available database, we analyzed and reported about the key signaling pathway engaged with cancer development outlining the effectiveness of different therapeutic measures and targets that have been created or are being researched to obstruct the cancer development. </P><P> Results: A number of signaling pathways, for example, resistant, metabolism, apoptosis, RAS protein, nuclear factor kappa B, autophagy, and angiogenesis have been perceived as targets for drug treatment to control the advancement, development and administration of cancer. </P><P> Conclusion: A noteworthy challenge for future medication advancement is to detail a synthesis treatment influencing distinctive targets to enhance the treatment of cancer.</P>

Anti-leukemic effects of simvastatin on NRASG12D mutant acute myeloid leukemia cells.

The statins are a group of therapeutic drugs widely used for lowering plasma cholesterol level, while it has also been reported to induce cell death in human acute myeloid leukemia (AML) cells. To determine antitumor activity triggered by simvastatin, four AML cell lines-U937, KG1, THP1 (NRASG12D mutant) and HL60 (NRASQ61L mutant)-were cultured with simvastatin and cell viability was assessed using the CellTiter-Glo reagent. For understanding mechanism of antitumor activity, immunoblot analysis for pAkt (Ser473), Akt, pMEK, MEK, pERK (Thr202/Tyr204) and ERK (Thr202/Tyr204) was performed. Apoptotic cell population was calculated using the Annexin V-FITC assay, and cell cycle state was assessed by flow cytometry. Simvastatin showed different cytotoxic effect among AML cells, of which NRASG12D mutant THP1 was the most statin sensitive cell line (IC50 values: 1.96uM in HL60, 7.87uM in KG1, 0.83uM in THP1 and 1.37uM in U937). Western blot analysis revealed that Ras downstream signaling molecules including Akt, MEK, and ERK1/2 were markedly inhibited in THP1 cells compared to other AML cells when exposed to simvastatin. In addition, only in THP1 cells, increased apoptosis and cell cycle arrest by simvastatin was observed. The combination of simvastatin and MEK inhibitor AZD6244 synergistically reduced THP1 cell proliferation compared to simvastatin alone and AZD6244 alone (IC50 values: 0.88 uM in simvastatin, 0.32 uM in AZD6244, and 0.23 uM in combination of simvastatin and AZD6244). Simvastatin exhibited anti-leukemic effect in human AML cells in vitro, especially at NRASG12D mutant AML cell line.

Abstract 1791: RADIL regulates RAS downstream signaling

Abstract RAS proteins regulate a variety of cellular processes including cell survival, proliferation, and differentiation. RAS genes are among the most frequently mutated oncogenes in human malignancies. To date, there are no successful anti-cancer drugs in the clinic that target RAS proteins or their pathways. Therefore, it is imperative to identify and characterize new components that regulate RAS activity or mediates its downstream signaling. Recently, we identified a series of proteins that are associated with HRAS using a combination of immunoprecipitation and mass spectrometry. We first focused on RADIL, a gene product with Ras-Association (RA) and DIL domains. RADIL is known to be a downstream effector of RAP1, inhibiting RhoA signaling in the regulation of cell survival, adhesion, and migration. We demonstrated that RADIL interacted with all three isoforms of RAS, including H, N, and KRAS. Interestingly, constitutively active HRAS (HRASG12V) was strongly associated with RADIL whereas dominant negative HRAS (HRASS17N) displayed a compromised association with RADIL, suggesting that RADIL may be required for RAS activation. We also found that Radil Knockout cells had weakened ERK phosphorylation whereas induced expression of RADIL promoted ERK phosphorylation, suggesting that RADIL is required for the RAS-MEK-ERK signaling cascade in vitro. Taken together, our current studies strongly suggest that RADIL may be important for regulating RAS signaling. Citation Format: Byeong Hyeok Choi, Ziyue Kou, Mark R. Philips, Wei Dai. RADIL regulates RAS downstream signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1791.

Abstract 4822: Targeting RAS and downstream signaling in high-grade serous ovarian carcinoma with novel RAS inhibitors

Abstract High grade serous ovarian carcinoma (HGSOC), which accounts for 70-80% of ovarian cancer deaths, is characterized by TP53 mutations and about half of these tumors present defects in homologous recombination DNA repair pathway genes. PARP inhibitors have now become FDA-approved for the treatment of recurrent and BRCA-associated ovarian cancer. Despite providing a major advance in ovarian cancer treatment in recent years, resistance to PARP inhibitors is often encountered and new treatment strategies must be devised. Oncogenic RAS and constitutively active RAS signaling regulate multiple downstream cascades to increase cell proliferation, survival, and malignant transformation. Despite the absence of RAS mutations, upregulation in the RAS pathway is prevalent in HGSOC, suggesting that these represent key, yet under-explored, inhibition targets for the treatment of ovarian cancer. Further bolstering the importance of RAS pathway inhibition are reports on cytotoxic synergistic effects for the combination of MEK and PARP inhibitors in ovarian cancer. The development of inhibitors directly targeting RAS has been hindered by the lack of suitable surfaces on the protein for small molecule binding and its high affinity for GTP binding. We developed a novel series of indene derivatives that showed highly selective growth inhibitory activity in tumor cells harboring constitutively active RAS vs. cells with low levels of active RAS. Chemical optimization led to a series of compounds that potently and selectively inhibit RAS-dependent tumor cell growth by blocking GTP binding to RAS. Here we examined the effects of RAS inhibition by two novel compounds, MCI-059 and MCI-062, in a panel of HGSOC cell lines with variable baseline levels of active RAS. We observed potent growth inhibitory activity for these novel inhibitors in most of the 15 ovarian cancer cell lines tested (IC50s ~25nM and 7nM for MCI-059 and MCI-062, respectively), with the lesser sensitivity in OV-90 cells correlating with its lowest basal levels of active RAS measured by a pull down assay using GST-RAF1-RBD/ glutathione agarose beads. Time-course experiments revealed that MCI-062 induces apoptosis beginning at 18-24 hours. Furthermore, both MCI-059 and MCI-062 inhibited: i) RAS-RAF1-RBD binding in GTPγS loaded recombinant human KRAS; ii) RAS-RAF1-RBD binding in OVCAR8 and SKOV3ip cells under normal culture growth conditions or under serum starvation followed by EGF-stimulation; iii) EGF-stimulated activation of the RAF-MEK-ERK and PI3K-AKT cascades in OVCAR-8 and SKOV3ip cells. We also confirmed that MCI-062 decreases several components of the RAS downstream signaling pathway via RPPA analysis. In summary, our results demonstrate that MCI-059 and MCI-062 inhibit HGSOC cell growth by blocking RAS-effector interactions, and support further evaluation of our novel RAS inhibitors for the treatment of ovarian cancer. Citation Format: Tyler E. Mattox, Tiffany S. Norton, Adam B. Keeton, Antonio B. Ward, Yulia Y. Maxuitenko, Kristy L. Berry, Bing Zhu, Alla Musiyenko, Elaine Gavin, Veronica Ramirez-Alcantara, Xi Chen, Jacob Valiyaveettil, Jennifer Scalici, Rodney P. Rocconi, Gary A. Piazza, Luciana Madeira da Silva. Targeting RAS and downstream signaling in high-grade serous ovarian carcinoma with novel RAS inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4822.

A Potent Isoprenylcysteine Carboxylmethyltransferase (ICMT) Inhibitor Improves Survival in Ras-Driven Acute Myeloid Leukemia.

Blockade of Ras activity by inhibiting its post-translational methylation catalyzed by isoprenylcysteine carboxylmethyltransferase (ICMT) has been suggested as a promising antitumor strategy. However, the paucity of inhibitors has precluded the clinical validation of this approach. In this work we report a potent ICMT inhibitor, compound 3 [UCM-1336, IC50 = 2 μM], which is selective against the other enzymes involved in the post-translational modifications of Ras. Compound 3 significantly impairs the membrane association of the four Ras isoforms, leading to a decrease of Ras activity and to inhibition of Ras downstream signaling pathways. In addition, it induces cell death in a variety of Ras-mutated tumor cell lines and increases survival in an in vivo model of acute myeloid leukemia. Because ICMT inhibition impairs the activity of the four Ras isoforms regardless of its activating mutation, compound 3 surmounts many of the common limitations of available Ras inhibitors described so far. In addition, these results validate ICMT as a valuable target for the treatment of Ras-driven tumors.

156 Conditional expression of oncogenic KrasG12Dand HrasG12V alleles in mouse keratinocytes reveals a dose dependent requirement for tumor formation

The goal of the current study is to compare the tumor initiating properties of conditionally expressed endogenous KrasG12D and HrasG12V mutant alleles in primary mouse keratinocytes. Primary keratinocytes were isolated from the LSL-HrasG12Dand LSL -KrasG12D C57BL/6J mouse models that carry mutant alleles that are conditionally expressed when a Lox-STOP-Lox segment is excised by Cre recombinase adenovirus treatment. Keratinocyte cultures expressing two mutant alleles of HrasG12D (HRAS Homo) were compared with cultures expressing only one mutant allele of HrasG12D (HRAS Het) or one mutant allele of KrasG12D (KRAS Het) or one mutant allele of each (HKRAS Het). Endpoints evaluated were signal transduction pathways, gene expression, and the ability to form squamous papillomas in vivo when orthotopically transplanted on the skin of nude mice. Upon treatment with Cre, HRAS homo, HRAS Het and KRAS Het keratinocytes replicate the resistance to calcium-induced differentiation that we previously reported using v-rasHa retroviral transduction. HRAS Homo, HRAS Het, and KRAS Het keratinocytes demonstrate an upregulation of the simple epithelia keratin 8 and a downregulation of suprabasal keratins 1 and 10 through changes in both mRNA and protein expression. Furthermore, transcripts for ligands for the epidermal growth factor receptor (EGFR) are also elevated as is the phosphorylation of EGFR protein. In vivo, 100% of nude mice grafted with HRAS Homo and HKRAS Het keratinocytes developed squamous papillomas, whereas those with KRAS Het and HRAS Het keratinocytes did not form tumors. This result suggests that the HrasG12Dmutant allele may have a dose dependent influence or that wild-type Hras and Kras alleles may possess a tumor suppressing effect. We are currently exploring differences in the activation of RAS downstream signaling pathways and gene expression among the four genotypes to explain the differential ability to form tumors in vivo.

A role for the unfolded protein response stress sensor ERN1 in regulating the response to MEK inhibitors in KRAS mutant colon cancers

BackgroundMutations in KRAS are frequent in human cancer, yet effective targeted therapeutics for these cancers are still lacking. Attempts to drug the MEK kinases downstream of KRAS have had limited success in clinical trials. Understanding the specific genomic vulnerabilities of KRAS-driven cancers may uncover novel patient-tailored treatment options.MethodsWe first searched for synthetic lethal (SL) genetic interactions with mutant RAS in yeast with the ultimate aim to identify novel cancer-specific targets for therapy. Our method used selective ploidy ablation, which enables replication of cancer-specific gene expression changes in the yeast gene disruption library. Second, we used a genome-wide CRISPR/Cas9-based genetic screen in KRAS mutant human colon cancer cells to understand the mechanistic connection between the synthetic lethal interaction discovered in yeast and downstream RAS signaling in human cells.ResultsWe identify loss of the endoplasmic reticulum (ER) stress sensor IRE1 as synthetic lethal with activated RAS mutants in yeast. In KRAS mutant colorectal cancer cell lines, genetic ablation of the human ortholog of IRE1, ERN1, does not affect growth but sensitizes to MEK inhibition. However, an ERN1 kinase inhibitor failed to show synergy with MEK inhibition, suggesting that a non-kinase function of ERN1 confers MEK inhibitor resistance. To investigate how ERN1 modulates MEK inhibitor responses, we performed genetic screens in ERN1 knockout KRAS mutant colon cancer cells to identify genes whose inactivation confers resistance to MEK inhibition. This genetic screen identified multiple negative regulators of JUN N-terminal kinase (JNK) /JUN signaling. Consistently, compounds targeting JNK/MAPK8 or TAK1/MAP3K7, which relay signals from ERN1 to JUN, display synergy with MEK inhibition.ConclusionsWe identify the ERN1-JNK-JUN pathway as a novel regulator of MEK inhibitor response in KRAS mutant colon cancer. The notion that multiple signaling pathways can activate JUN may explain why KRAS mutant tumor cells are traditionally seen as highly refractory to MEK inhibitor therapy. Our findings emphasize the need for the development of new therapeutics targeting JUN activating kinases, TAK1 and JNK, to sensitize KRAS mutant cancer cells to MEK inhibitors.

Simultaneous Inhibition of MEK and Hh Signaling Reduces Pancreatic Cancer Metastasis

Pancreatic cancer, mostly pancreatic ductal adenocarcinoma (PDAC), is one of the most lethal cancer types, with an estimated 44,330 death in 2018 in the US alone. While targeted therapies and immune checkpoint inhibitors have significantly improved treatment options for patients with lung cancer and renal cell carcinomas, little progress has been made in pancreatic cancer, with a dismal 5-year survival rate currently at ~8%. Upon diagnosis, the majority of pancreatic cancer cases (~80%) are already metastatic. Thus, identifying ways to reduce pancreatic cancer metastasis is an unmet medical need. Furthermore, pancreatic cancer is notorious resistant to chemotherapy. While Kirsten RAt Sarcoma virus oncogene (K-RAS) mutation is the major driver for pancreatic cancer, specific inhibition of RAS signaling has been very challenging, and combination therapy is thought to be promising. In this study, we report that combination of hedgehog (Hh) and Mitogen-activated Protein/Extracellular Signal-regulated Kinase Kinase (MEK) signaling inhibitors reduces pancreatic cancer metastasis in mouse models. In mouse models of pancreatic cancer metastasis using human pancreatic cancer cells, we found that Hh target gene Gli1 is up-regulated during pancreatic cancer metastasis. Specific inhibition of smoothened signaling significantly altered the gene expression profile of the tumor microenvironment but had no significant effects on cancer metastasis. By combining Hh signaling inhibitor BMS833923 with RAS downstream MEK signaling inhibitor AZD6244, we observed reduced number of metastatic nodules in several mouse models for pancreatic cancer metastasis. These two inhibitors also decreased cell proliferation significantly and reduced CD45+ cells (particularly Ly6G+CD11b+ cells). We demonstrated that depleting Ly6G+ CD11b+ cells is sufficient to reduce cancer cell proliferation and the number of metastatic nodules. In vitro, Ly6G+ CD11b+ cells can stimulate cancer cell proliferation, and this effect is sensitive to MEK and Hh inhibition. Our studies may help design novel therapeutic strategies to mitigate pancreatic cancer metastasis.

KRAS targeting antibody synergizes anti-cancer activity of gemcitabine against pancreatic cancer

Pancreatic cancer exhibits an oncogenic KRAS mutation rate of ∼90%. Despite research and drug development efforts focused on KRAS, no targeted therapy has been clinically approved for the treatment of pancreatic cancer with KRAS mutation. Also, the efficacy of gemcitabine is poor due to rapidly acquired resistance. We developed RT11-i antibody, which directly targets the intracellularly activated GTP-bound form of oncogenic RAS mutants. Here, we investigated the combined effects of RT11-i and gemcitabine in vitro and in vivo, and the mechanism involved. RT11-i significantly sensitized pancreatic cancer cells to gemcitabine. Also, the co-treatment synergistically inhibited angiogenesis, migration, and invasion, and showed synergistic anticancer activity by inhibiting the RAF/MEK/ERK or PI3K/AKT pathways. Furthermore, co-treatment inhibited endothelial barrier disruption in tumor vessels, which is a critical step in vascular leakiness of metastasis, and improved vessel structural stability. Importantly, co-treatment significantly suppressed tumor growth in an orthotopic tumor model. Taken together, our findings show that RT11-i synergistically increased the antitumor activity of gemcitabine by inhibiting RAS downstream signaling, which suggests RT11-i and gemcitabine be viewed a potential combination treatment option for pancreatic cancer patients with KRAS mutation.

Pulmonary hypertension associated with neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1), also known as von Recklinghausen disease, is a frequent autosomal dominant genetic disorder with a prevalence of 1 in 3000. Pulmonary hypertension (PH) associated with NF1 (PH-NF1) is a rare but severe complication of NF1 and is classified as Group 5 PH, defined as "PH with unclear and/or multifactorial mechanisms". A literature review in PubMed on the association between NF1 and PH identified 18 articles describing 31 cases. PH-NF1 was characterised by a female predominance, an advanced age at diagnosis, an association with parenchymal lung disease in two out of three cases and poor long-term prognosis. NF1 is generally associated with interstitial lung disease but some cases of severe PH without parenchymal lung disease suggest that there could be a specific pulmonary vascular disease. There is no data available on the efficacy of specific pulmonary arterial hypertension treatment in PH-NF1. Therefore, these patients should be evaluated in expert PH centres and referred for lung transplantation at an early stage. As these patients have an increased risk of malignancy, careful assessment of the post-transplant malignancy risk prior to listing for transplantation is necessary. Clinical trials are needed to evaluate promising treatments targeting the RAS-downstream signalling pathways.

Abstract 929: Discovery of novel covalent KRASG12C inhibitors that display high potency and selectivity in vitro and in vivo

Abstract Activating mutations in KRAS have a high prevalence in human cancer. The codon 12 glycine to cysteine missense mutation (KRASG12C) is among the most common KRAS mutations, present in non-small cell lung adenocarcinoma (~15 %), colorectal adenocarcinoma (~3 %), and pancreatic adenocarcinoma (~1 %). KRASG12C was previously identified as potentially druggable by allele-specific covalent targeting of cysteine 12 near the allosteric switch II pocket (S-IIP). Building on this early work, we recently described the ARS-853 series of S-IIP KRASG12C inhibitors that covalently react with the GDP-bound state of KRASG12C, trapping KRASG12C in this inactive state. In cells, ARS-853 series compounds profoundly deplete the signaling competent GTP-bound state of KRASG12C, thereby inhibiting downstream RAS signaling. However, this series of covalent KRASG12C inhibitors exhibited modest cellular potency and/or poor pharmacokinetic properties, making them unsuitable for further evaluation of covalent KRASG12C inhibition in animal models. We now describe in further detail the discovery and characterization of a new series of structurally distinct quinazoline based S-IIP KRASG12C inhibitors with substantially improved potency and pharmacologic properties that overcome limitations of the ARS-853 series. Through structure-guided medicinal chemistry optimization we identified compound ARS-1620, a potent, orally bioavailable covalent inhibitor of KRASG12C. The co-crystal structure of ARS-1620 covalently bound to KRASG12C reveals a distinct binding mode and additional interactions, compared to ARS-853. ARS-1620 rapidly engages KRASG12C, depletes KRASG12C-GTP in tumor cell lines, and inhibits downstream RAS signaling in a dose-dependent manner. The compound potently inhibits the growth of cell lines harboring the KRASG12C mutation with little or no effect on control cell lines. ARS-1620 demonstrates robust dose-dependent efficacy with once daily oral administration across a panel of KRASG12C-positive mouse cell line (CDX) and patient-derived (PDX) tumor xenograft models, with no response observed at all doses tested in KRASG12C-negative tumor models. The anti-tumor activity of ARS-1620 correlates with target engagement in the tumors as well as with inhibition of downstream RAS signaling. The in vivo efficacy and mutant selectivity observed with ARS-1620 across a wide range of KRASG12C mouse tumor models provides the first in vivo evidence that the S-IIP targeted approach may be a promising therapeutic strategy for patients with KRASG12C mutant cancers. Citation Format: Liansheng Li, Matthew R. Janes, Jingchuan Zhang, Rasmus Hansen, Ulf Peters, Xin Guo, Yuching Chen, Anjali Babbar, Sarah J. Firdaus, Jun Feng, Jeffrey H. Chen, Shuangwei Li, Shisheng Li, Carol Thach, Yuan Liu, Ata Zarieh, Jeff M. Kucharski, Tao Wu, Ke Yu, Yi Wang, Yvonne Yao, Xiaohu Deng, Patrick P. Zarrinkar, Dashyant Dhanak, Matthew V. Lorenzi, Dana Hu-Lowe, Pingda Ren, Yi Liu. Discovery of novel covalent KRASG12C inhibitors that display high potency and selectivity in vitro and in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 929.

Abstract 3993: Efficacy of SHP2 phosphatase inhibition in cancers with nucleotide-cycling oncogenic RAS, NF1 loss and RAS-GTP-dependent oncogenic BRAF

Abstract Oncogenic alterations in the RAS-RAF-MEK-ERK pathway, including mutant forms of KRAS, BRAF, and loss of the tumor suppressor and RAS GTPase-activating protein (GAP) NF1, drive the growth of a wide spectrum of cancers. While BRAF and MEK inhibitors are efficacious against BRAFV600E-driven cancers, effective targeted therapies are lacking for most cancers driven by other pathway alterations, including oncogenic KRAS, NF1 loss, and non-V600E oncogenic BRAF. Here, we show that targeting the PTPN11/SHP2 phosphatase with a novel small molecule allosteric inhibitor is effective in human cancer models bearing nucleotide-cycling oncogenic RAS (e.g. KRASG12C), NF1 loss, or RAS-GTP dependent oncogenic BRAF (e.g. class 3 BRAF mutants). SHP2 inhibitor treatment decreases oncogenic RAS-RAF-MEK-ERK signaling and cancer growth by disrupting SOS1-mediated RAS-GTP loading. Our findings illuminate a critical function for SHP2 in promoting oncogenic RAS activation and downstream signaling in cancers with nucleotide-cycling oncogenic RAS, RAS-GTP dependent oncogenic BRAF, and NF1 loss. SHP2 inhibition is a promising molecular therapeutic strategy for patients with cancers bearing these oncogenic drivers. Citation Format: Trever G. Bivona, Robert Nichols, Franziska Haderk, Carlos Stahlhut,Christopher Schulze, Golzar Hemmati, David Wildes. Efficacy of SHP2 phosphatase inhibition in cancers with nucleotide-cycling oncogenic RAS, NF1 loss and RAS-GTP-dependent oncogenic BRAF [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3993.

Oncogenic KRAS and p53 Loss Drive Gastric Tumorigenesis in Mice That Can Be Attenuated by E-Cadherin Expression.

Gastric adenocarcinoma is the third leading cause of cancer-related death worldwide, but no models exist to readily investigate distant metastases that are mainly responsible for mortality in this disease. Here we report the development of a genetically engineered mouse model of gastric adenocarcinoma tumorigenesis based on KrasG12D expression plus inactivation of E-cadherin (Cdh1) and p53 in the gastric parietal cell lineage. Intestinal and diffuse gastric tumors arise rapidly in this model that displays a median survival of 76 days. Tumors occur throughout the stomach, with metastases documented in lymph nodes, lung, and liver. Mice otherwise identical but retaining one wild-type Cdh1 allele exhibited longer survival with only 20% penetrance of invasive tumors and no apparent lung or liver metastases. Notably, increased RAS activity and downstream MAPK signaling was observed in stomachs only when E-cadherin was absent. This model offers a valuable tool to investigate gastric adenocarcinoma subtypes where RAS/MAPK pathway activation and E-cadherin attenuation are common. Cancer Res; 77(19); 5349-59. ©2017 AACR.

Abstract 1362: Argonaute 2 controls RAS activation in mouse embryonic fibroblasts

Abstract The RAS gene family is among the most commonly mutated genes within cancer, and while much research has elucidated the major downstream pathways, including MAPK and PI3K, little progress has been made in successfully targeting mutant RAS in cancer. We recently identified an interaction between the N terminal domain of Argonaute 2 (AGO2), a core component of RNA-induced silencing complex (RISC), and the Switch II domain of KRAS. Furthermore, this interaction was found in all cell lines tested, expressing either wild-type (WT) or mutant KRAS. We found that stable knockdown of AGO2 in KRAS dependent cell lines lead to a decrease in KRAS protein expression with a subsequent decrease in cellular proliferation. Conversely, the overexpression of AGO2 in these cells lead to both an increase in KRAS expression and oncogenesis. In addition, this interaction inhibits the RNAi function of AGO2 by preventing microRNA unwinding in the presence of oncogenic KRAS compared to WT-KRAS. Despite a clear association between mutant KRAS and AGO2 mediating increased KRAS mediated oncogenesis, the precise function of this interaction remains unclear in normal physiology. In order to better assess the endogenous function of the KRAS-AGO2 interaction, we analyzed two mouse embryonic fibroblast cell lines (NIH 3T3 and MEF) with complete knockout of AGO2. Utilizing a Raf-1 RAS binding domain (RBD) pulldown method, we assessed activated WT-RAS levels in AGO2 null NIH 3T3 and MEF cells. We found that knockout of AGO2 lead to an increase in WT RAS-GTP activation compared to normal control cells. Immunoblot analysis also indicates that AGO2 null fibroblasts lead to increase in RAS downstream signaling through the MAPK/ERK and PI3K/AKT pathways. Furthermore, rescue of AGO2 knockout using full length mouse AGO2 decreased wild type RAS activation and its downstream signaling. Taken together, these observations suggest that the AGO2 interaction may suppress WT-KRAS activation, leading to maintenance of RAS-GDP levels. Using RNA-seq, proteome and microRNA analysis, we have begun to identify the pathways that may be involved in RAS activation in AGO2 null cells. Early analyses indicate that AGO2 controls WT-KRAS levels and activity through multiple mechanisms, laying the foundation for a better understanding of the RAS-AGO2 interaction in normal physiology. Citation Format: Ronald F. Siebenaler, Sunita Shankar, Vijaya L. Dommeti, Malay Mody, Arul Chinnaiyan. Argonaute 2 controls RAS activation in mouse embryonic fibroblasts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1362. doi:10.1158/1538-7445.AM2017-1362

PI3K and MEK Inhibition in Hypodiploid Acute Lymphoblastic Leukemia

Introduction: Hypodiploid acute lymphoblastic leukemia (ALL) is a rare, high-risk subtype of B-ALL associated with poor outcome. Genomic analysis of over 130 Hypodiploid ALL patients defined the distinct genomic landscape of this disease, defining two principal subtypes including Ras-activating alterations and IKZF3 loss in near haploid tumors (24-31 chromosomes) and mutation of TP53 coupled with homozygous IKZF2 loss in low hypodiploid tumors (32-39 chromosomes). New therapies are needed to improve outcome of this disease, necessitating preclinical studies in hypodiploid tumors in vitro, ex vivo and in vivo.Hypothesis: The observation of frequent Ras pathway activating mutations in hypodiploid ALL tumors, as well as increased phosphorylation of downstream Ras signaling targets, suggests that these tumors may be susceptible to PI3K/MEK inhibition. Ras signaling target activation was observed in hypodiploid tumors irrespective of mutational status. Here we used cell lines and representative xenograft models to explore the therapeutic efficacy of inhibiting PI3K/MAPK signaling in hypodiploid ALL.Methods: The near haploid cell lines NALM-16 and MHH-CALL-2 and eight patient-derived xenograft (PDX) models (four near haploid and four low hypodiploid) were selected for preclinical studies. Xenografts were representative of the most common genomic lesions observed in hypodiploid ALL patients, including deletion of NF1, PAG1 and IKZF3 in near haploid and mutation of TP53 and IKZF2 deletion in low hypodiploid (Holmfeldt et al. Nat Genet 2013; Mullighan et al. Blood 2015). Next-gen sequencing of xenograft and diagnosis tumor DNA confirmed the presence of key genetic alterations in the xenografts. A lentiviral vector was used for stable expression of luciferase in xenograft tumors for in vivo disease burden monitoring. Cell lines were treated in vitro with PI3K, mTOR, MEK, CDK4/6 and BET inhibitors either as single agents, inhibitor combinations or combined with chemotherapeutic agents. Xenografts were treated ex vivo with single agents and in vivo with PI3K and MEK inhibitors with or without chemotherapy.Results: NALM-16 and MHH-CALL-2 cell lines were most sensitive to PI3K, mTOR and BET inhibitors with IC50 values in the sub-micromolar range (Fig. 1).Treatment of xenografts ex vivo showed near haploid and low hypodiploid tumors to be four-fold more sensitive to pan-PI3K inhibitors and PI3K/mTOR dual inhibitors compared to PI3K α and d isoform-specific inhibitors. Near haploid and low hypodiploid xenografts were sensitive to MEK and BET inhibition ex vivo, but MEK inhibitors showed weak activity in the near haploid cell lines. Treatment with CDK4/6 inhibitors either as single agents or in combination with MEK inhibitors revealed minimal efficacy. Changes in cell signaling upon treatment was assayed by phosphoflow (Fig. 2). Akt and Erk1/2 phosphorylation was variable between tumors, whereas 4E-BP1 and S6 phosphorylation was consistently elevated, suggesting strong signaling through mTOR pathways. Pan-PI3K and PI3K/mTOR dual inhibitors showed potent activity against hypodiploid ALL tumors in vitro and ex vivo, however PI3K inhibition alone was insufficient to eliminate tumors in vivo. Substantial weight loss in mice treated with PI3K/mTOR dual inhibitors limited prolonged study in vivo. MAPK inhibition showed activity in both near haploid and low hypodiploid tumors ex vivo and displayed a modest reduction in tumor growth as a single agent in vivo. Combining the MEK inhibitor GDC-0973 with dexamethasone treatment increased efficacy, but induced significantly more weight loss than either monotherapy.Conclusion: Treatment of hypodiploid cell lines and xenografts in vitro and ex vivo, respectively, with PI3K and MEK inhibitors showed promising results, however the anti-tumor effect in vivo appeared mostly cytostatic and inhibitors were not sufficient as single agents to kill the tumor cells. MEK inhibitors showed stronger activity than PI3K inhibitors on xenografts in vivo and ex vivo, but this was not significantly increased when combined with dexamethasone treatment. The notable resistance of hypodiploid cells to dexamethasone may underlie this limited efficacy in addition to the increase in GDC-0973 clearance observed upon combination. Our findings also highlight the need to consider the PK properties of agents in the preclinical setting, particularly in combinations. [Display omitted] [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Statins improve NASH via inhibition of RhoA and Ras.

Nonalcoholic steatohepatitis (NASH), especially as part of the metabolic syndrome (MS), is an increasing burden in Western countries. Statins are already used in MS and seem to be beneficial in liver diseases. The aim of this study was to investigate the molecular mechanisms underlying pleiotropic effects on small GTPases of statins in NASH. NASH within MS was induced in 12-wk-old apoE-/- mice after 7 wk of Western diet (NASH mice). Small GTPases were inhibited by activated simvastatin (SMV), NSC23766 (NSC), or Clostridium sordellii lethal toxin (LT) by using subcutaneous osmotic minipumps. Hepatic steatosis, inflammation, and fibrosis were assessed by histology, Western blot, and RT-PCR measurements of cholesterol and hydroxyproline content. SMV treatment significantly decreased hepatic inflammation and fibrosis, but had no significant effect on steatosis and hepatic cholesterol content in NASH. SMV blunted fibrosis due to inhibition of both RhoA/Rho kinase and Ras/ERK pathways. Interestingly, inhibition of RAC1 and Ras (by LT) failed to decrease fibrosis to the same extent. Inhibition of RAC1 (by NSC) showed no significant effect at all. Inhibition of RhoA and Ras downstream signaling by statins is responsible for the beneficial hepatic effects in NASH.

SIRT2 deletion enhances KRAS-induced tumorigenesis in vivo by regulating K147 acetylation status.

The observation that cellular transformation depends on breaching a crucial KRAS activity threshold, along with the finding that only a small percentage of cellsharboring KRAS mutations are transformed, support the idea that additional, not fully uncovered, regulatory mechanisms may contribute to KRAS activation. Here we report that KrasG12D mice lacking Sirt2 show an aggressive tumorigenic phenotype as compared to KrasG12D mice. This phenotype includes increased proliferation, KRAS acetylation, and activation of RAS downstream signaling markers. Mechanistically, KRAS K147 is identified as a novel SIRT2-specific deacetylation target by mass spectrometry, whereas its acetylation status directly regulates KRAS activity, ultimately exerting an impact on cellular behavior as revealed by cell proliferation, colony formation, and tumor growth. Given the significance of KRAS activity as a driver in tumorigenesis, identification of K147 acetylation as a novel post-translational modification directed by SIRT2 in vivo may provide a better understanding of the mechanistic link regarding the crosstalk between non-genetic and genetic factors in KRAS driven tumors.

Overexpression of PDGFRA cooperates with loss of NF1 and p53 to accelerate the molecular pathogenesis of malignant peripheral nerve sheath tumors

Malignant peripheral nerve sheath tumors (MPNSTs) are aggressive, frequently metastatic sarcomas that are associated with neurofibromatosis type 1 (NF1), a prominent inherited genetic disease in humans. Although loss of the NF1 gene predisposes to MPNST induction, relatively long tumor latency in NF1 patients suggests that additional genetic or epigenetic abnormalities are needed for the development of these nerve sheath malignancies. To study the molecular pathways contributing to the formation of MPNSTs in NF1 patients, we used a zebrafish tumor model defined by nf1 loss in a p53-deficient background together with the overexpression of either wild-type or constitutively activated PDGFRA (platelet-derived growth factor receptor-α) under control of the sox10 neural crest-specific promoter. Here we demonstrate the accelerated onset and increased penetrance of MPNST formation in fish overexpressing both the wild-type and the mutant PDGFRA transgenes in cells of neural crest origin. Interestingly, overexpression of the wild-type PDGFRA was even more potent in promoting transformation than the mutant PDGFRA, which is important because ~78% of human MPNSTs have expression of wild-type PDGFRA, whereas only 5% harbor activating mutations of the gene encoding this receptor. Further analysis revealed the induction of cellular senescence in zebrafish embryos overexpressing mutant, but not wild-type, PDGFRA, suggesting a mechanism through which the oncogenic activity of the mutant receptor is tempered by the activation of premature cellular senescence in an NF1-deficient background. Taken together, our study suggests a model in which overexpression of wild-type PDGFRA associated with NF1 deficiency leads to aberrant activation of downstream RAS signaling and thus contributes importantly to MPNST development—a prediction supported by the ability of the kinase inhibitor sunitinib alone and in combination with the MEK inhibitor trametinib to retard MPNST progression in transgenic fish overexpressing the wild-type receptor.

Targeted therapy: RAS mimetic revealed.

The small-molecule inhibitor rigosertib acts as a RAS mimetic — by disrupting the association of RAS with RAF and other effector proteins, it inactivates RAS downstream signalling.

KRAS Mutant Pancreatic Cancer: No Lone Path to an Effective Treatment.

Pancreatic ductal adenocarcinoma (PDAC) is among the deadliest cancers with a dismal 7% 5-year survival rate and is projected to become the second leading cause of cancer-related deaths by 2020. KRAS is mutated in 95% of PDACs and is a well-validated driver of PDAC growth and maintenance. However, despite comprehensive efforts, an effective anti-RAS drug has yet to reach the clinic. Different paths to inhibiting RAS signaling are currently under investigation in the hope of finding a successful treatment. Recently, direct RAS binding molecules have been discovered, challenging the perception that RAS is an “undruggable” protein. Other strategies currently being pursued take an indirect approach, targeting proteins that facilitate RAS membrane association or downstream effector signaling. Unbiased genetic screens have identified synthetic lethal interactors of mutant RAS. Most recently, metabolic targets in pathways related to glycolytic signaling, glutamine utilization, autophagy, and macropinocytosis are also being explored. Harnessing the patient’s immune system to fight their cancer is an additional exciting route that is being considered. The “best” path to inhibiting KRAS has yet to be determined, with each having promise as well as potential pitfalls. We will summarize the state-of-the-art for each direction, focusing on efforts directed toward the development of therapeutics for pancreatic cancer patients with mutated KRAS.