Channing J. Der - US grants

A considerable body of experimental evidence has implicated an important role for the cellular ras oncogenes in human carcinogenesis. Recently, the human Krev-1 gene has been shown to suppress the transforming activity of oncogenic ras. Surprisingly, the Krev-1 protein shares significant sequence homology (50%) with human ras proteins. Thus, while Krev-1 and ras share significant structural and biochemical properties, differences must exist to account for their divergent biological activities. The biochemical basis for Krev-1 suppressing activity is not known. The overall goal of this proposal is to characterize the structural and biochemical properties of the Krev-1 protein, and to determine which properties are important for Krev-1 suppression of oncogenic ras activity. The approaches outlined in this proposal are based on information derived from structure-function studies of the ras oncogene proteins. For these studies, structural mutations have been introduced into Krev-1 sequences corresponding to functional domains in ras to delineate the biochemical similarities and differences between these two proteins. Additionally, chimeric proteins have been generated between Krev-1 and H-ras to identify the Krev-1 domains responsible for its dominant suppressing activity. Furthermore, since there are strong structural and functional similarities between Krev-1 and oncogenic ras, the possibility that Krev-1 is a proto- oncogene protein will also be evaluated. Finally, since oncogenic ras is frequently associated with human carcinomas, the ability of Krev-1 to antagonize ras transforming activity in cells of epithelial origin will be evaluated. Although the mechanism of ras suppression by Krev-1 is not known, the strong structural similarities with ras proteins suggest the possibility that Krev-1 may antagonize the activity of oncogenic ras by competing for common target or regulatory proteins. Alternatively, Krev-1 may modulate a negative growth regulatory pathway which indirectly antagonizes the positive growth regulatory pathway modulated by oncogenic ras. The studies outlined in this proposal will generate important information for distinguishing between these two possibilities and provide a biochemical basis for the Krev-1 suppression of oncogenic ras activity.

Although a strong association between ras activation and human carcinogenesis has been established, both the mechanism of oncogenic ras transformation and its contribution to the malignant process remain to be determined. The overall goal of the proposed research is the identification of the structural and biochemical properties of the ras proteins that are important for neoplastic transformation. The interaction between ras and other cellular components that may regulate ras biological activity will also be emphasized. The general approach will entail the generation of structural and functional mutants of the human ras proteins. Chimeric proteins will also be constructed between H-ras and ras-related proteins. These ras-related proteins will include the recently identified Krev-1 protein, which suppresses oncogenic ras transforming activity. The biological activities of these mutant ras proteins will be characterized by a variety of in vitro biological assays. Additional in vitro cell transformation systems will also be established to address the involvement of oncogenic ras in the transformation of cells of epithelial origin. Overall, these approaches should generate useful information for identifying the properties of the oncogenic ras that are responsible for the malignant transformation and altered differentiation.

Substantial experimental evidence now implicates a strong involvement of oncogenic human ras proteins in human carcinogenesis. Unexpectedly, the three human ras proteins represent only a small branch of a larger superfamily of ras-related proteins. Over the past several years, molecular, biochemical and genetic approaches have identified over 30 distinct members of the ras superfamily. The strong structural and biochemical similarities between ras and ras-related proteins suggest the possibility that they may also be candidates for oncogene proteins. The brisk pace at which new members have been identified suggests that the spectrum of ras-related proteins will be quite extensive, and their functions diverse. While ras is believed to be involved in signal transduction, these related proteins are likely to be involved in regulation of a diverse range of cellular functions in eukaryotic cells. In particular, the members of the rab protein branch are believed to be involved in the regulation of vesicular trafficking of protein through the endocytic and exocytic pathways of eukaryotic cells. Our interest in rab proteins is two-fold. First, we are interested in the study of rab proteins as naturally occurring, nontransforming variants of the ras oncogene proteins as an approach for defining the properties of ras proteins critical for oncogenesis. Second, we are interested in establishing a regulatory role for rab proteins in intracellular transport. We will use our extensive knowledge of ras protein structure and biochemistry as a strong foundation to characterize the structural, biochemical, and functional properties of rab proteins. The specific aims of this proposal are (1) to determine the structural and biochemical properties of rab proteins which distinguish them from the ras oncogene proteins, (2) to determine the posttranslational modifications and amino acid sequences that determine the unique subcellular localization of each rab protein, (3) to evaluate the role of rab proteins in regulating intracellular transport processes, and (4) to determine whether rab proteins are potential oncogene proteins, or alternatively, can function to antagonize ras transforming function. This last aim will also address the role of the unique rab and ras subcellular associations in determining their unique functions. The observations that both exocytic and endocytic events are triggered by ras proteins suggest functional similarities between ras and rab proteins, and suggest that aberrant forms of rab may perturb transport processes thereby contributing to malignant growth potential. Since intracellular transport processes are fundamental to the maintenance of cell homeostasis, disruptions in these functions may exert profound effects on intracellular processes controlling cell proliferation. The information from our studies will both provide a better understanding of ras oncogene function and extend our understanding of the involvement of related GTP-binding regulatory proteins in cellular processes such as signal transduction and intracellular transport.

DESCRIPTION (provided by applicant): There is now substantial and compelling evidence implicating aberrant Rho GTPase function in malignant cancer cell progression and growth. Like Ras, the Ras-related Rho GTPases function as regulated molecular switches activated by diverse extracellular signals that control actin cytoskeletal organization, gene expression, and G1 cell cycle progression. In light of their critical involvement in key cellular processes of normal cells, it is not surprising that the aberrant activation of Rho family proteins (e.g., Racl, RhoA, and Cdc42) contributes to the uncontrolled proliferation, invasion, and metastatic properties of cancer cells. One important outcome of our previous studies was the demonstrated requirement for Rho GTPase function in the transforming activity of Ras and other oncoproteins, as well as in tumor suppressor function. Thus, in contrast to direct mutational activation of Ras, Rho GTPases are activated indirectly in cancer, by perturbations in oncoprotein or tumor suppressor function. Therefore, an emphasis of our studies has been the delineation of the mechanisms by which Rho GTPases are aberrantly deregulated by oncoproteins or tumor suppressors. In the current proposal, we extend this goal with studies that evaluate the involvement of novel members of the Rho family of GTPases (Rnd3, Wrch-1, and Chp) or their activators (Asef) in oncogenesis by Ras and by other oncoproteins (Wnt and beta-catenin) or tumor suppressors (APC). We propose four specific aims to evaluate (1) the involvement of Rnd3 inactivation of RhoA in Ras transformation, (2) the contribution of Wrch-1 to Wnt transformation, (3) the involvement of Chp in Ras and Wnt transformation, and (4) the role of Asef deregulation of Rac in APC tumor suppressor or beta-catenin function. Additional issues that we will address include the regulation of Rho GTPase activity at the level of gene expression, in addition to regulation by GDP/GTP cycling, as well as the possibility that certain Rho GTPases are important therapeutic targets for farnesyltransferase inhibitors that are currently under evaluation as novel anti-cancer drugs in phase II-III clinical trials. The long-term goals of our studies are to validate Rho GTPases as important targets for anti-cancer drug discovery and to delineate their mechanisms of regulation and signaling to define approaches to block their function.

Our understanding of how Ras proteins function as molecular switches that relay signals initiated at the cell surface by extracellular stimuli that control cell growth and differentiation has increased considerably during the past year. Both the key regulators of Ras activity (GAPs and GEFs) and the essential downstream components of the Ras signal transduction pathway have now been identified. However, while a detailed picture of Ras-mediated signaling has now been defined, the precise role of each component and how the information is relayed from component to component remains to be elucidated. The overall goals of this proposal are (1) to determine the role of upstream activators (GEFs) and downstream mediators of Ras signal transduction in Ras-mediated transformation, and (2) to determine whether two Ras-related proteins (TC21 and R-Ras) also utilize these same components for signal transduction and for triggering malignant transformation. The specific aims of this proposal are (1) to determine if Ras GEFs (CDC25 and SOS1) are also activators of other members of the Ras superfamily of proteins, (2) to establish the role of the mitogen-activated protein (MAP kinase cascade of serine/threonine kinases (MEKs and MAPKs) in Ras transformation, (3) to establish the role of the Ras-related TC21/R-RasB protein in human carcinogenesis, (4) to establish whether the Ras-related R-Ras protein is functionally distinct from TC21 and whether its activities are regulated by Bcl-2, and (5) to determine if CAAX-based peptidomimetics are specific inhibitors of Ras prenylation and transformation, and whether they also function as inhibitors of TC21 and R-Ras transformation. Our increased understanding of how Ras proteins mediate signaling pathways that control normal cell growth and differentiation, and how oncogenic Ras proteins perturb these pathways, will have two important implications for cancer biology. First, the deregulated function of other components of the Ras signal transduction pathway (e.g., Ras GEFs), in the absence of Ras mutations, may also be important in cancer. Second, any essential components of Ras signaling (e.g., the MEK/MAPK serine/threonine kinases) may represent novel targets for rational drug design. The studies that we have proposed will provide further insight into both possibilities.

Transformation by Ras oncogene proteins requires their modification (prenylation) by a farnesyl isoprenoid lipid. Therefore, specific inhibitors of the farnesyl transferase (FTase) enzyme responsible for this modification may represent novel anti-cancer chemotherapeutic agents. The overall goal of this Program (#3) will be to establish the biochemical basis for the ability of FTase inhibitors to inhibit both Ras transformation and the Ras signal transduction pathways that are responsible for this transformation. This proposal represents a logical extension of our previous studies on protein prenylation, Ras signal transduction and oncogene transformation. Recent studies with FTase inhibitors by ourselves and others have suggested that normal cells are insensitive to the inhibitory activity of such compounds and that the observed reversal of Ras transformation may be due to a more complex mechanism than simply to antagonizing oncogenic Ras function. Therefore, it is clear that the specific biochemical and biological consequences of FTase inhibitor action remain to be determined. We propose six specific aims to accomplish three primary goals. First, we will test FTase inhibitors (developed by Program #1 and initially characterized by Program #2) for their ability to specifically and efficaciously antagonize Ras signal transduction and transformation (Specific Aims 1, 2 and 3). Second, we will determine if other prenylated proteins are also perturbed by treatment with FTase inhibitors (Specific #4). These studies will emphasize the analysis of Ras-related proteins that influence cell growth. Third, we will utilize these inhibitors to address the role of Ras in specific cellular processes (e.g., differentiation, radioresistance) (Specific Aims 5 and 6). Because of the complex and distinct roles that Ras plays in different systems (growth, differentiation, apoptosis), understanding the consequences of FTase inhibition in the intact animal will require the study of diverse cell types. Candidate FTase inhibitors that perform well in these assays will be tested in an animal model system by Program #2. Feedback provided by us to Programs #1 and #2 at each step of the process will enable the design and synthesis of improved candidates for testing. Thus, while our primary goal will be to complement the studies in Programs #1 and #2 to achieve FTase inhibitors that will be clinically useful in human cancers, our studies are designed to accomplish this goal by providing a better understanding of the role and mechanism of prenylation in protein function and of the role of Ras in normal cell function.

DESCRIPTION: (provided by applicant) The two primary goals of our previous proposal were to determine the contribution of multiple Ras-mediated effector signaling pathways to transformation and to determine whether different Ras signaling events are important for oncogenic Ras transformation of fibroblasts versus epithelial cells. In our continuation of these studies, we extend these analyses to emphasize two additional themes. First, we will evaluate the role of a novel effector pathway in Ras transformation We have identified Tiami as a novel effector of Ras. Tiami in turn can activation the Rac small GTPase. Rac has been shown to mediate Ras regulation of the p38 and JNK MAPK pathways. Therefore, we will assess the roles of these MAPK cascades as key components of Raf-independent signaling pathways important for Ras transformation. Second, the least understood aspect of Ras signaling involves the gene targets important for Ras-mediated oncogenesis. We describe studies to begin a delineation of the genes whose expression is deregulated by oncogenic Ras. Four specific aims are proposed to accomplish these goals. First, we will characterize the role of Tiami as a critical effector of Ras transformation, and whether Tiami links Ras with Rac and p38/JNK signaling. Second, we will evaluate the distinct and opposing roles of the p38 and JNK MAPK cascades in Ras transformation, and determine whether these MAPKs mediate Ras regulation of gene expression. Third, we will determine the role of specific Ras-mediated signaling pathways involved in transformation of ROSE rat ovarian epithelial cells and define the gene targets that promote Ras transformation. Finally, we will employ microarray analyses to delineate the gene targets important for Ras transformation (in cooperation with telomerase and SV4O T antigen) of primary human embryonic kidney and mammary epithelial cells. These studies will evaluate our hypothesis that oncogenic Ras transformation of epithelial cells is critically dependent on activation of Raf-independent effector signaling pathways, in part, by deregulating the expression and function of key target genes.

DESCRIPTION: (Adapted from the investigator's abstract) The leukemia-associated Rho guanine nucleotide exchange factor (LARG) was recently identified as a fusion partner of the mixed lineage leukemia (MLL) protein in acute myeloid leukemia. LARG is a novel member of the rapidly expanding Dbl family of oncoproteins that promote malignant transformation by activating Ras-related Rho family GTPases. Like other Dbl family proteins, LARG contains a Dbl homology (DH) domain that functions as a guanine nucleotide exchange factor and activator of Rho GTPases. The DH domain is followed by a pleckstrin homology (PH) domain that presumably regulates DH domain function. LARG also contains a regulator of G-protein signaling (RGS) domain, suggesting that it may link G protein-coupled receptor signaling to Rho GTPases. Our preliminary studies determined that LARG is an activator of RhoA and can cause transformation of NIH 3T3 mouse fibroblasts. We have proposed four specific aims to perform detailed structure-function analyses of LARG. Specific aim 1 will determine the roles of the DH and PH domains in mediating LARG activation of RhoA. In particular, whether the PH domain regulates DH domain function in a phosphatidylinositol 3-kinase dependent fashion will be determined. Specific aim 2 will evaluate the role of the RGS domain in linking LARG with G protein coupled receptor signaling. This includes a determination of which heterotrimeric G alpha subunit(s) is regulated by the RGS domain and which G alpha subunit(s) in turn regulates LARG DH domain activation. Specific aim 3 will determine if the tumor-associated MLL-LARG fusion protein is an aberrantly activated form of LARG and can promote growth transformation of epithelial cells and lL-3 independent growth of 32D myeloid cells. Finally, Specific Aim 4 will involve a determination of the crystal structure of the DH/PH domains of LARG complexed with its GTPase target, RhoA, and the determination of the structural basis for DH domain recognition of GTPases. Although the number of Dbl family oncoproteins continue to increase at a rapid pace, to date, LARG is the only functional Dbl protein found to be mutated in human cancer. Our studies will provide a comprehensive, structural, biochemical, and biological analysis of LARG function and assess a role for aberrant LARG activation of RhoA in AML development.

Mutations in Ras are associated with 50% of colorectal carcinomas, indicating the importance of aben'ant Ras activation in tumor development and progression. Recently, mutations in B-Raf, the downstream target of Ras, have been identified in 10% of colorectal carcinomas. The presence of B-Raf mutations in tumors distinct from those with Ras mutations indicates that these mutations are genetically equivalent, such that either one confers a similar advantage. These data support the critical contribution of the Raf>MEK>ERK mitogen-activated protein kinase cascade in Ras-mediated oncogenesis. CmTently, pharmacologic inhibitors of two kinases in this cascade, Raf and MEK, have been developed and are under evaluation in clinical trials. Such target-based drugs are believed to represent the key future direction for anti-cancer drug discovery. However, one major complication that has slowed the clinical development of target-based anti-cancer drugs (e.g., epidermal growth factor receptor inhibitors) is continued uncertainty regarding whether aberrant activation of the target alone is sufficient to define the patient population that will be responsive to these drugs. This uncertainty is based, in part, on the fact that the presence of an altered target may simply have a correlative, rather than a causal, role in oncogenesis. Based on observations in preclinical models, this will also be a concern for efforts to evaluate the clinical efficacy of anti-Ras therapies. It is likely that Ras mutation status alone will not be sufficient to define the subset of colorectal cancers that will be responsive to inhibitors of Ras signaling, specifically to inhibitors of the Raf and MEK protein kinases. Instead, we hypothesize that other approaches, such as microarray gene profiling, will be needed to determine the subsets of Ras mutation positive colorectal cancers that will be responsive to anti-Raf or anti-MEK therapy. Therefore, the broad goal of this project will be to determine whether a group of patients with colorectal carcinomas that harbor mutated Ras show gene expression profiles that may have clinical relevance in predicting sensitivity to anti-Ras and anti-Raf/MEK therapeutic strategies.

DESCRIPTION (provided by applicant): The importance of the Ras small GTPases in normal cell physiology and the aberrant behavior of cancer cells is well-established. Ras functions'as a signaling node that regulates normal cell proliferation, differentiation and survival. The diverse cellular roles of Ras are mediated through Ras regulation of multiple, functionally distinct, downstream signaling networks, with the Raf-MEK-ERK mitogen-activated protein kinase (MARK) cascade the best understood. The mutational activation of Ras results in persistent, deregulated signaling that promotes the aberrant growth and behavior of malignant cancer cells. Consequently, there is considerable interest and effort in targeting Ras signaling for the development of novel approaches for cancer treatment. In particular, current evaluation is focused on clinical evaluation of small molecule kinase inhibitors of the Raf-MEK-ERK pathway. However, these efforts have been complicated by the fact that Ras can also utilize multiple Raf-independent effector pathways to promote oncogenesis. Furthermore, the Raf-MEK-ERK cascade is not a simple linear signaling pathway, but instead, represents the core of a complex signaling network that is regulated by an ever-expanding roster of functionally diverse signaling molecules. In particular, several scaffold proteins dictate the input signals that activate this kinase cascade and serve to diversify the spatial and temporal nature of the signaling output. Our recent preliminary observations determined that (a) the subfamily-D regulators of G protein signaling (RGS) proteins (RGS12 and RGS14) are putative effectors of Ras and that (b) RGS12 may function as a scaffold protein that regulates the Raf-MEK-ERK cascade. In light of the important role of the ERK MARK pathway in neoplastic cell biology, we hypothesize that RGS12 and RGS14 will be found to be important effectors of Ras-mediated oncogenesis and that RGS12 will be a critical regulator of Raf-MEK-ERK signaling and function. Four specific aims are proposed to critically evaluate the role of subfamily D RGS proteins in aberrant Ras and Raf signaling and oncogenesis to: (1) determine the roles of RGS12 and RGS14 as effectors of Ras-mediated oncogenes, (2) determine if RGS12 is critical for mutant B-Raf-mediated oncogenesis, (3) determine if RGS12 is an endosome-specific effector of Ras function, and (4) determine the structures of RGS12 (and/or RGS14) with Ras-MAPK binding partners.

DESCRIPTION (provided by applicant): DLC-1 expression is lost in lung and other cancers and ectopic re-expression of DLC-1 impairs the transformed and tumorigenic growth of DLC-1-deficient tumor cell lines. Thus, DLC-1 exhibits properties of a tumor suppressor. DLC-1 encodes a GTPase activating protein (GAP) and negative regulator of Ras homologous (Rho) small GTPases. Constitutive activation of Rho GTPases causes growth transformation and promotes tumor cell invasion, metastasis and angiogenesis. Therefore, we hypothesize that the loss of DLC-1 function may result in persistent Rho GTPase activation and promotion of NSCLC oncogenesis. However, in addition to a RhoGAP catalytic domain, DLC-1 also contains START lipid-binding and SAM protein-protein interaction domains. Our recent results determined that DLC-1 suppresses NSCLC growth by both RhoGAP- dependent and -independent mechanisms. In addition to RhoA, we also determined that the RhoGAP domain regulates the biologically distinct RhoB and RhoC isoforms, as well as Cdc42, providing the basis for our studies to establish the full repertoire of Rho GTPases inactivated by DLC-1 (Aim 1). We also identified the SAM domain as an autoinhibitory domain that regulates DLC-1 RhoGAP activity. How this domain may regulate DLC-1 activity, and whether MEK-ERK-RSK protein kinase and PI3K-AKT lipid kinase signaling pathway-mediated phosphorylation of DLC-1 may regulate DLC-1 activity will be determined (Aim 3). DLC-1 is associated with focal adhesions (FAs) and this association is critical for DLC-1 tumor suppression but surprisingly, not for Rho GTPase inactivation in vivo. It has been determined recently that DLC-1 association with FAs is mediated by binding to tensin proteins. We also determined that the SAM and START domains may also regulate DLC-1 subcellular localization distinct from association with focal adhesions. We found that ectopic expression of DLC-1 inactivated RhoA at the leading edge of migrating cells and inhibited tumor cell invasion in vitro. These observations provide the rationale for our studies to determine the importance of spatially-restricted DLC-1-mediated Rho GTPase inactivation for inhibition of tumor growth (Aim 3). These studies will determine if SAM, START and FA-targeted DLC-1 preferentially inactivates Rho GTPases in specific subcellular compartments important for tumor suppression. Finally, to complement our ectopic re- expression studies that show DLC-1 inhibition of tumor growth, we propose interfering RNA and dominant negative DLC-1 studies to determine the biological consequences of DLC-1 loss of expression, and to evaluate a lung tumor tissue microarray to determine if loss of DLC-1 protein expression is associated with specific genetic properties and clinical outcomes of NSCLCs (Aim 4). PUBLIC HEALTH RELEVANCE: Lung cancer remains the most common fatal cancer in men (31%) and women (28%) in the US, and NSCLC accounts for 80% of all lung cancer cases and is the leading cause of cancer mortality (http://www.cancer.org/). The most recent statistics found that lung cancer death rates were increasing at a much slower rate than in the past. Unfortunately, this modest improvement is attributed primarily to decreased smoking, rather than improved therapy. Despite recent advances in molecularly targeted therapies, treatment outcomes for advanced lung cancer remain disappointing. The recent fast-track approval of EGFR inhibitors (gefitinib and erlotinib) for advanced NSCLC that have failed conventional chemotherapy have proven effective against only ~10% of NSCLCs and their impact has been modest, increasing survival by two months (erlotinib). Furthermore, the failure of gefitinib to show a survival benefit has prompted the FDA to reverse its approval for the treatment new lung cancer patients. Thus, while a subset of patients with EGFR mutations is responsive the general consensus is that EGFR inhibitors have been a disappointment for NSCLC treatment. Therefore, new target-based treatment strategies are clearly needed in NSCLC therapy. One possible class of targets is the Ras homologous Rho small GTPases. There is considerable and growing evidence for aberrant Rho GTPase function in oncogenesis, in particular in breast, pancreatic, and head and neck carcinomas, and melanomas. However, to date, there has been surprisingly limited study of the role of aberrant Rho GTPases in NSCLC growth. We propose studies to address one key mechanism by which Rho GTPase function may be deregulated in a majority of NSCLCs, the loss of the DLC-1 tumor suppressor. Our recent evidence supports our hypothesis that loss of DLC-1 causes hyperactivation of Rho GTPases in NSCLC. Hence, we believe that our elucidation of the mechanism by which DLC-1 loss may deregulate Rho GTPases and promote NSCLC growth may define novel directions for targeted therapies for lung cancer treatment.

There is now substantial evidence that aberrant activation of members of the Rho family of Ras-related small GTPases contributes significantly to the uncontrolled proliferation and invasive properties of malignant tumor cells. Like Ras, Rho GTPases function as regulated switches that control diverse signaling pathways regulating cell proliferation and survival, actin organization, and gene expression. Therefore, like activation of Ras, persistent activation of Rho GTPases can contribute significantly to the aberrant growth and metastatic properties of human malignancies. However, whereas direct mutational activation of Ras proteins is found in 30% of human cancers, this has not been found to date for Rho GTPases. Instead, Rho GTPases are aberrantly activated in human cancers by a diversity of indirect mechanisms. For example, Racl is activated in breast and colon cancers by alternative splicing and expression of the variant Raclb protein that is constitutively activated, whereas increased expression of RhoC is implicated in breast cancer progression and invasion. A third mechanism involves aberrant activation of Rho guanine nucleotide exchange factors (RhoGEFs;also called Dbl family oncoproteins). In particular, both Ras and G protein-coupled receptors utilize RhoGEFs to mediate growth transformation and tumor cell invasion. Rho GTPases in turn utilize the ROCK serine/threonine kinase to promote oncogenesis. Similarly, recent studies have implicated GEFs for another family of Ras-related proteins (RalGEFs), the Ral small GTPases, as important mediators of Ras transformation of human cells. A key downstream effector of Ral GTPases is RalBPl, which is a Rho GAP and a negative regulator of Rho GTPases. Thus, Rho GTPases and their regulators and effectors represent important targets for anti-cancer drug development. The Rho and Ral GTPases are modified posttranslationally by geranylgeranyltransferase I (GGTasel), and this modification is required for their transforming functions. We propose four specific aims to further evaluate the role of Rho and Ral GEFs and their GTPase targets in cancer development, and the feasibility of pharmacologic inhibition of their functions by using inhibitors of Rho GTPase function (inhibitors of GGTase I, RhoGEFs and ROCK), for cancer treatment.

DESCRIPTION (provided by applicant): Pancreatic cancer (PDAC) is a lethal disease with 5-year survival of 4% and current therapeutic options are few and ineffective. Therefore, there remains a dire need for novel targeted therapies for this cancer. Recent studies have implicated the importance of signaling pathways that activate the Rac small GTPase in PDAC tumorigenic growth and invasion. We therefore hypothesize that inhibitors of Rac signaling will be an effective strategy for PDAC treatment. However, while well validated as key disease drivers, Rac and other small GTPases (e.g. Ras) are not currently considered to be attractive or druggable targets for cancer treatment. While recent synthetic lethality genetic screens have been established to identify key components of Ras oncogenesis, no such mammalian cell assay has been identified for Rac. Therefore, novel approaches are needed. We have established, validated and performed a novel C. elegans-based positive-selection functional screen for (a) identifying genes whose functions are critical for Rac activity and (b) high-throughput chemical library screening to identify small molecule inhibitors of Rac lethality. In our model, constitutive activation of the Rac ortholog in C. elegans, CED-10, causes 100% lethality, thus providing positive selection for our genetic and pharmacologic screens. This model combines genetic amenability, low cost and culture conditions compatible with genome wide genetic and high-throughput chemical screening in a whole animal context. Our application of this C. elegans model, when coupled with mammalian cell culture and mouse models for validation and further analyses, may identify novel approaches for blocking Rac in PDAC. If successful, our proof-of-concept studies will show that C. elegans-based models can be effective for drug discovery and will stimulate renewed interest both in targeting small GTPases and in development of other organism-based functional screens for drug discovery. We propose three aims to accomplish this goal: (1) identify the genes whose disruption specifically suppressed activated CED-10/Rac, (2) identify small molecule inhibitors that suppress CED-10/Rac lethality, and (3) apply cell- and mouse-based validation of genetically defined Rac signaling components and small molecule inhibitors. Relevance: Effective therapeutic options for pancreatic cancer, a lethal disease with 5-year survival of 4%, are few and ineffective. Traditional drug discovery approaches have not been effective in addressing this problem. We propose our application of an innovative new model system for drug discovery focused on a validated new therapeutic target for this deadly disease PUBLIC HEALTH RELEVANCE: Effective chemotherapeutic options for pancreatic cancer, a lethal disease with 5-year survival of 4%, are few and ineffective. Traditional drug discovery approaches have not been effective in addressing this problem. We propose the study of a novel target, the Rac small GTPase, and the application of a C. elegans nematode model for genome-wide genetic and high-throughput chemical screens to identify novel Rac-specific targets and therapies for pancreatic cancer.

DESCRIPTION (provided by applicant): Inhibitors of Ras effector signaling are considered the most viable direction for successful development of effective anti-Ras therapies for the treatment of pancreatic ductal adenocarcinoma (PDAC), with most efforts focused on the Raf-MEK-ERK mitogen-activated protein kinase (MAPK) cascade. Eighteen Raf or MEK inhibitors are currently under Phase I-III clinical evaluation. However, signaling reprogramming mechanisms that restore ERK activation downstream of the inhibitor block, or that activate parallel activities to reduce ERK dependency, have severely limited their anti-tumor activities. SCH772984 is a recently developed novel, highly selective ATP-competitive and allosteric ERK1 and ERK2 inhibitor that is currently under Phase Ib clinical evaluation for RAS or BRAF mutant cancers. We propose studies to define signaling mechanisms that overcome ERK inhibition and drive ERK isoform differences, with the long-term goal to advance the clinical development of SCH772984 and other ERK inhibitors. First, our preliminary studies found SCH772984 more effective than MEK inhibition for blocking PDAC cell line anchorage-dependent and -independent growth. However, a subset of PDAC lines showed de novo (primary) resistance to SCH772984. We have also found that high-dose SCH772984 treatment of sensitive PDAC lines resulted in the outgrowth of subpopulations with acquired (secondary) resistance. We will apply druggable genome siRNA screens to identify genes that control de novo versus acquired PDAC resistance to SCH772984. We hypothesize that these studies will identify combination inhibitor approaches that synergistically enhance the anti-tumor activity of ERK inhibitors. Second, surprisingly, despite their high sequence and biochemical identity, we determined that ERK1 and ERK2 display distinct, non-overlapping essential functions in PDAC growth. A genome-wide phosphoproteomics approach will be applied to identify ERK isoform-specific substrates essential for PDAC growth. In addition to delineating novel signaling mechanisms driven by ERK activation, these studies may identify directions for isoform-selective anti-ERK therapeutic strategies. Our application of innovative strategies to study ERK-dependent PDAC growth are high risk; but with the critical importance of ERK in PDAC growth, our findings have high-gain potential for a breakthrough in PDAC therapy.

DESCRIPTION (provided by applicant): Recent exome sequencing of pancreatic ductal adenocarcinoma (PDAC) determined that aside from the near 100% mutational activation of KRAS, no other oncoproteins are mutationally activated beyond single digit percentages. This has renewed interest in efforts to make undruggable K-Ras druggable. The most promising direction involves inhibitors of K-Ras effector signaling, prompting current clinical evaluation of the Raf-MEK- ERK cascade and the phosphatidylinositol 3-kinase (PI3K)-AKT-mTOR signaling network. However, to date, when applied as monotherapy, or with limited combination approaches, these inhibitors have shown little to no clinical efficacy for RAS mutant cancers. Two key issues contribute to this failure. First, kinome reprogramming mechanisms drive resistance mechanisms that reactivate the pathway downstream of the inhibitor block point. Second, it is clear that cancer cell dependency on mutant K-Ras cannot be attributed to the Raf and PI3K effectors alone, prompting efforts to validate noncanonical effectors for anti-K-Ras drug discovery. We propose that therapeutic targeting of the lesser studied Rac small GTPase effector pathway and its key effector, the Group I PAK serine/threonine kinases will address both issues. To accomplish this, we propose the application of three innovative tools to interrogate the role and mechanism by which the Rac-PAK effector network contributes to K-Ras-driven cancer growth. Specifically, our studies will focus on two immerging themes in signal transduction targeted therapies: (i) dynamic signal reprogramming mechanisms that drive de novo or acquired resistance to limit the therapeutic activity of signaling inhibitors and (ii) the cancer driver function of a signaling protein is strongly dependent on subcellular location. We have assembled a team of researchers with diverse and complementary expertise to (1) define the mechanisms of PAK1 activation by aberrant K-Ras- Rac1 signaling and the driver functions of plasma membrane-associated, cytoplasmic and nuclear PAK1, (2) identify the spatio-temporal phosphorylation events essential for aberrant PAK1 activation and PAK1- dependent cancer growth, (3) profile kinome reprogramming to identify the compensatory protein kinases that overcome PAK1 inhibition to promote cancer cell resistance, and (4) determine if Group I PAK suppression enhances PDAC sensitivity to inhibitors of the Raf or PI3K effector pathways.

? DESCRIPTION (provided by applicant): The goal of research supported by this FOA is to identify targets whose inhibition would induce synthetic lethality in cancers dependent on the expression of mutant KRas alleles, with a focus on one or more of the four most frequently observed alleles...in one or more of the predominant mutant KRas-dependent cancers e.g., pancreas..., and utilizing advanced screens that go beyond the current screens in 2D tissue culture. To accomplish this goal, we have assembled a well-integrated team of five investigators at three institutions. Our team will apply three complementary and highly innovative advanced screens to identify and validate targets whose inhibition would induce synthetic lethality in KRAS-mutant pancreatic ductal adenocarcinoma (PDAC). Each of our screens differs substantially from those in previously published RNAi-based synthetic lethal screens. We will focus not only on K-Ras G12D and G12V but also on G12R, the third most frequent KRAS mutation in PDAC and one whose properties we believe differ from those of other G12 mutants. We propose three specific aims: (1) a robust chemical library screen to convert pharmacologic inhibitors of K-Ras effector signaling from cytostatic to cytotoxic activities; (2) a focused genetic screen to identify cancer signaling pathway components whose activation overcomes addiction to mutant K-Ras; and (3) an unbiased, genome-wide gain-of-function insertional mutagenesis screen to identify genes whose overexpression overcomes addiction to mutant KRAS. Aim 1 will use a powerful chemical library screen (Drug Sensitivity and Resistance Testing, DSRT) of compounds selected specifically to allow rapid clinical transition of positive results. Aims 2 and 3 will employ complementary innovative gain-of-function genetic screens. Aim 2 will take a signaling-centric approach (Cancer Toolkit) shown in preliminary data to be able to identify both known and unknown mechanisms of inhibitor resistance, whereas Aim 3 will apply a genome-wide unbiased approach (CDt/MS) that is mass spectrometry-based and uniquely reads out at the protein level, thereby enabling a cheaper, faster and more informative process than conventional functional genomic screens. Aims 1 and 2 share a signaling focus, whereas Aims 2 and 3 share a conceptual theme. We will utilize low passage KRAS-mutant pancreatic cancer patient-derived xenograft (PDX)-derived cell lines throughout our studies. While the initial Aim 1 screens will be done in conventional high throughput 2D assays, validation of the hits will be done in 3D culture models including pancreatic organoids. Aim 2 and 3 screens will be done in both 2D and 3D culture as well as in vivo in tumor-bearing mice, and hits will be validated in 2D and 3D culture. The top hits from Aims 1-3 will then be further validated in PDX orthotopic pancreatic cancer models. We will apply pathway and network analysis, and expect to find significant overlap of important hits among the three screening approaches. Information from each of these strategies will be integrated across all platforms to identify the best synthetic lethal targets for pharmacologic inhibition and induction of cytotoxicity in KRAS-mutant pancreatic cancer cells.

ABSTRACT Despite more than three decades of intensive effort, currently no effective anti-RAS therapies have reached clinical application. The history of anti-RAS drug discovery has been marked by missteps and mistakes, due in large part to our incomplete understanding of the full complexities of RAS. There remain many perplexing issues that until recently have been ignored by the field. We argue that if these issues remain unresolved, this will compromise the success of anti-RAS drug discovery. In Project 1, we challenge the perception that ?all RAS mutations are created equal?. Our studies focus on pancreatic ductal adenocarcinoma (PDAC), arguably the human cancer most addicted to mutant KRAS, to pursue three key issues. First, there is the still-prevalent assumption that the highly related RAS proteins (HRAS, KRAS 4A/4B and NRAS) are largely functionally equivalent proteins. Therefore, it is perplexing why there is exclusive mutation of KRAS in PDAC. Does this simply reflect the inability of carcinogenic assault to cause mutational activation of HRAS and NRAS in PDAC? Or alternatively and more provocatively ? despite their significant functional similarities, do mutant HRAS and NRAS not have the capability to drive tumor initiation and progression in the pancreas? Second, a survey of all cancers finds that there are 134 distinct cancer-associated missense mutations found in KRAS, with 99% at one of three mutational hotspots (G12, G13 and Q61) ? do they all cause equivalent perturbations in protein function and have equivalent capabilities to drive cancer development? In PDAC, there is a near-exclusive occurrence of G12 mutations, with G13 and Q61 mutations rare ? does this simply reflect DNA mutation frequencies or do G12 mutations cause distinct perturbations that favor their presence in PDAC? Finally, while there are six possible single base change missense mutations at each hotspot, the frequencies are not uniform, and can exhibit striking cancer-type differences. Do the different amino acid substitutions at each hotspot cause distinct perturbations in protein function that then translate to different capabilities to drive cancer development? We propose three aims that will provide further clarity for these three issues. We will determine if: (1) KRAS G12R is distinct among G12 mutations and exhibits mutation-specific regulation and effector dependencies and driver functions in PDAC; (2) there is a biological basis for why KRAS G13 mutations are rare in PDAC; and (3) KRAS Q61 mutants are biochemically and biologically distinct from KRAS G12 and G13 mutants and have distinct consequences for KRAS protein function in PDAC. We propose that ?all RAS mutations are NOT created equal? and that mutation-specific biochemical and/or signaling properties can be exploited for mutation-selective therapeutic strategies. Project 1 studies are tightly interrelated and highly synergistic with Projects 2-4, in both scientific themes and experimental strategies.  

?DESCRIPTION (provided by applicant): The RAS oncogenes (HRAS, KRAS and NRAS) comprise the most frequently mutated oncogene family in cancer. Despite more than three decades of intensive effort, presently no effective RAS-targeted therapies have reached the clinic. Contributing to this failure have been missteps and mistakes made in drug development, resulting from the field underestimating the complexities of RAS. While recent cancer genome sequencing studies have provided a more comprehensive genetic portrait of specific cancers, they have also verified that RAS mutations are the major drivers of cancers that comprise three of the four major causes of cancer deaths in the US (lung, colorectal and pancreatic cancer). A RAS Renaissance has now begun, with renewed intense interest and effort to identify and develop new pharmacologic strategies to target aberrant RAS function for cancer treatment. Our rationale for this Program Project is based on our belief that key issues regarding RAS function remain to be resolved and that their resolution will be vital to facilitate more knowledgeable and effective approaches for anti-RAS drug discovery. Our overall premise is that RAS mutations are not created equal. Our overarching hypotheses are that there are significant differences among RAS isoforms and RAS mutations, and that these have distinct oncogenic consequences in different cancers. Four Projects comprise our P01, each led by a long-standing RAS researcher who brings complementary and distinct experimental expertise to a Program designed for strong inter-project collaborations that leverage our strengths and minimize our weaknesses. Collectively, we will produce a cohesive and comprehensive study that could not be achieved by individual laboratories working on their own. Our structural, biochemical and biological efforts will identify RAS isoform- and mutation-specific perturbations to RAS function. In the long term, these distinct perturbations may represent targetable vulnerabilities that will reveal new approaches to develop mutation-specific anti-RAS therapies for cancer treatment. Project 1 focuses on cellular studies of KRAS mutations in pancreatic cancer, closely coordinated with the structural and biochemical studies of KRAS in Project 2. Project 2 studies of NRAS are complemented by Project 3 studies of mutant NRAS and wild type RAS alleles in melanoma. Project 4 will use genetically engineered mouse models of lung cancer to address the basis for the preferential mutation of KRAS in cancer. Core A will provide financial oversight, administrative coordination of information exchange, and biostatistics support across this inter-institutional Program Project. Core B will provide innovative proteomics technologies for unbiased profiling of RAS mutation-selective effector signaling. Our Program findings will help to reshape anti-RAS drug discovery with the goal of developing therapies targeting specific subsets of RAS mutations. Relevance to Public Health: RAS mutations are very common in three of the top four causes of US cancer deaths. Development of effective anti-RAS treatment strategies will significantly reduce the loss of productivity and human lives to cancer.

DESCRIPTION Core A is comprised of two components that provide two important support services for the Program Project. The first service is the Administration Sub-Core (A1) that will provide administrative and financial oversight, communication, coordination among the four Projects and Core B. This will include providing secretarial support to the PI, Project Leaders and Core Directors. The Administrative component also coordinates overall program oversight by the Internal and External Advisory Boards. It will provide a centralized structure for the coordination of the research meetings, travel arrangements, and annual retreats. It will also provide overall support for the preparation of the annual research progress reports and facilitate communication with the Internal and External Advisory Boards. The second service is the Biostatistics Sub-Core (A2). This component provides direct biostatistics support and Program Data and Resource Management for the four Projects and Core B.  

PROJECT SUMMARY This proposal seeks support for 14 postdoctoral fellows for a two year training curriculum within an established and highly successful program (Interdisciplinary Training in Cancer Model Systems ? ITCMS) that instills interdisciplinary approaches to address basic and translational approaches in cancer research. The 51 ITCMS mentors are chosen from 325 core faculty of the UNC Lineberger Cancer Center (LCCC). Faculty are housed within academic departments in the UNC School of Medicine, the College of Arts and Sciences, and the School of Pharmacy and are members of the five basic/translational LCCC programs: Cancer Cell Biology, Immunology, Molecular Therapeutics, Virology and Cancer Genetics as well as the Clinical Research Program. This pool of mentors allows fellows to engage in interdisciplinary studies from basic science to bioinformatics to translational studies, utilizing state of the art cancer models. The ITCMS program is administered by its Director and Associate Director, with advice from the Training Committee, and both External and Internal Advisory Boards. Preceptor and trainee input on the training program is accomplished through an annual, anonymous survey. Training is enhanced by access to the Center's core facilities, supported by the Center's NCI Core Grant (rated ?exceptional?). LCCC commitment to ITCMS is significant and includes support for an additional two postdoctoral slots. Fellows jointly apply to the ITCMS and one or more mentor laboratories and undergo a rigorous selection process. Upon appointment, each fellow develops a training plan approved by the mentor, the mentoring committee, and the Director. Each fellow participates in the following: (i) monthly in-house postdoctoral seminars given by the fellows, (ii) the annual Lineberger Postdoctoral-Faculty Research Day, organized by a Faculty Advisor and the Postdoctoral Fellows Committee, (iii) panel discussions on careers including advice for successful faculty applications and interviews, (iv) sessions on ethics in research (vi) a monthly research club, (vi) clinical exposure (physician shadowing and tumor board participation), (vii) interactions with patient advocates, and (viii) a grant writing and grant review program. Based on the individualized training plan, fellows participate in relevant training workshops (such as proteomics, microscopy, mouse histopathology, genomics, etc.). Progress is monitored annually by the Director and Associate Director, along with the Training Oversight Committee, before renewal for Year 2 support. Since its inception, the program has been committed to recruiting and successful training of minorities. The success of previous fellows, with the great majority continuing in a cancer or science-related field, underscores the importance placed on postdoctoral training in the ITCMS.

PROJECT SUMMARY/ABSTRACT My Outstanding Investigator Award (OIA) research plan will build on themes developed during my more than three decades of RAS research, pursuing directions generally ignored by the RAS field and by the NCI RAS Initiative, to make ?undruggable? RAS druggable. I was a member of the research team that made the initial identification of activated RAS oncogenes in human cancers. Since that discovery, my research has centered on understanding the basic biochemistry, signaling and biology of RAS proteins, with the long-term goal of utilizing that information for the development of anti-RAS cancer therapies. My research focuses on pancreatic ductal adenocarcinoma (PDAC), a cancer where effective targeted therapies remain to be found. With a 95% KRAS mutation frequency and with substantial experimental evidence that ?correcting? the KRAS defect will significantly impair PDAC growth, PDAC is arguably the most RAS-addicted cancer. The OIA supports research that ?take[s] greater risks, [is] more adventurous?. Based on our unpublished findings from studies initiated 3-4 years ago and just now coming into fruition, I have identified four new high risk / high reward research directions. First, despite the well-established interdependency between the RAS and MYC oncogenes in driving cancer growth, targeting MYC as an anti-KRAS strategy is not widely considered. Our MYC degradation screen identified novel protein kinases that regulate MYC protein stability; we will exploit these to cause MYC loss. Second, we have found that the ERK protein kinases are largely responsible for KRAS-dependent metabolic perturbations (autophagy, glycolysis, macropinocytosis, mitochondrial function). We suggest that targeting ERK, rather than the metabolic enzymes considered by the field, will be a more effective therapeutic strategy to target cancer metabolism. We will pursue an issue still largely neglected, the determination of the key ERK substrates that are critical for ERK-dependent KRAS-mutant PDAC growth. Third, as with other targeted therapies, anti-KRAS therapies will be limited by mechanisms of acquired resistance. While much of the field is focused on YAP1, it is also clear that YAP1-independent mechanisms will also play significant role in how cancers escape KRAS-dependency. We will apply experimental approaches not previously utilized to define these YAP1?independent mechanisms. These findings will be critical for development of anti-KRAS therapies that can achieve long-lasting clinical efficacy. Finally, our surprising finding that one KRAS mutant (G12R) cannot utilize a key RAS effector, PI3K, and drives metabolic activities distinct from the most prevalent KRAS mutations, provides our rationale to pursue outlier mutations in PDAC, to identify mutation-specific vulnerabilities as the basis for development of mutation-selective therapies. In summary, since adherence to long-held dogma has at times stifled progress, less mainstream directions must be taken if we are to finally achieve the breakthroughs needed for development of effective anti-RAS therapies.

PROJECT SUMMARY This project focuses upon Diffuse Gastric Cancer (DGC), a frequently lethal cancer, marked by its characteristic growth patterns with lack of cellular cohesion, highly invasive spread and marked propensity for metastasis. This proposal builds upon new progress in the study of DGC, bringing together a collaborative team of investigators with provocative new findings regarding the role of RHOA in the pathogenesis of this disease and several newly developed mouse model systems. These data and resources bring new opportunities to substantively advance the study of these deadly and understudied cancers. A first set of data underlying this application followed our recent identification of a novel stem cell population in gastric glands marked by Mist1 expression (Yokoyama et al, Cancer Cell 2015). These cells were demonstrated to give rise to DGC following engineered loss of tumor suppressor Cdh1. However, development of DGC required the secretion of Wnt5a by cells in the stem cell niche, with Wnt5a acting by activating GTPase RhoA in the Cdh1- null gastric cells. In parallel, we made a set of novel genomic discoveries, finding that ~20- 30% of DGCs harbor genomic aberrations impacting RHOA, either highly recurrent missense mutations of RHOA or a recurrent fusion gene including ARHGAP26, a RHOA regulator (TCGA, Nature, 2014). In this context, delineating the functions of RhoA in DGC pathogenesis, spanning both the role of Wild-type RHOA following Cdh1 loss and the oncogenic functions of RHOA mutations, emerge as critical paths towards the identification of therapeutic targets and understanding of basic pathophysiology of DGC formation. In our first Aim, we evaluate activation of wild-type RHOA in normal gastric corpus stem cells, and in early progression of Cdh1- deficient diffuse gastric cancer. We propose to test our hypothesis that RHOA is a mediator of Wnt5a effects upon corpus stem cells, especially following Cdh1 loss. These results will have immediate relevance to the definition of mechanisms of DGC initiation, clearly informing efforts to prevent and treat these deadly cancers. Our second aim evaluates RHOA somatic mutations in the initiation and progression of diffuse gastric cancer. In this aim we further characterize the biochemical and phenotypic effects of highly recurrent missense mutations of the RHOA GTPase identified in DGC. We will also functionally validate which RHOA effectors are essential for oncogenic activity of these mutants in both in vitro and in vivo systems, including our novel DGC mouse model driven by Cdh1 loss and RhoA mutation. Through these studies we hope to determine mechanisms of RHOA mediated transformation and identify specific pathways that are critical to the pathogenesis of DGC, findings with immediate potential relevance to the development of new therapeutic targets.

The RAS oncogenes (HRAS, KRAS and NRAS) comprise the most frequently mutated oncogene family in cancer. Despite more than three decades of intensive effort, presently no effective RAS-targeted therapies have reached the clinic. Contributing to this failure have been missteps and mistakes made in drug development, resulting from the field underestimating the complexities of RAS. While recent cancer genome sequencing studies have provided a more comprehensive genetic portrait of specific cancers, they have also verified that RAS mutations are the major drivers of cancers that comprise three of the four major causes of cancer deaths in the US (lung, colorectal and pancreatic cancer). A ?RAS Renaissance? has now begun, with renewed intense interest and effort to identify and develop new pharmacologic strategies to target aberrant RAS function for cancer treatment. Our rationale for this Program Project is based on our belief that key issues regarding RAS function remain to be resolved and that their resolution will be vital to facilitate more knowledgeable and effective approaches for anti-RAS drug discovery. Our overall premise is that RAS mutations are not created equal. Our overarching hypotheses are that there are significant differences among RAS isoforms and RAS mutations, and that these have distinct oncogenic consequences in different cancers. Four Projects comprise our P01, each led by a long-standing RAS researcher who brings complementary and distinct experimental expertise to a Program designed for strong inter-project collaborations that leverage our strengths and minimize our weaknesses. Collectively, we will produce a cohesive and comprehensive study that could not be achieved by individual laboratories working on their own. Our structural, biochemical and biological efforts will identify RAS isoform- and mutation-specific perturbations to RAS function. In the long term, these distinct perturbations may represent targetable vulnerabilities that will reveal new approaches to develop mutation-specific anti-RAS therapies for cancer treatment. Project 1 focuses on cellular studies of KRAS mutations in pancreatic cancer, closely coordinated with the structural and biochemical studies of KRAS in Project 2. Project 2 studies of NRAS are complemented by Project 3 studies of mutant NRAS and wild type RAS alleles in melanoma. Project 4 will use genetically engineered mouse models of lung cancer to address the basis for the preferential mutation of KRAS in cancer. Core A will provide financial oversight, administrative coordination of information exchange, and biostatistics support across this inter-institutional Program Project. Core B will provide innovative proteomics technologies for unbiased profiling of RAS mutation-selective effector signaling. Our Program findings will help to reshape anti-RAS drug discovery with the goal of developing therapies targeting specific subsets of RAS mutations. Relevance to Public Health: RAS mutations are very common in three of the top four causes of US cancer deaths. Development of effective anti-RAS treatment strategies will significantly reduce the loss of productivity and human lives to cancer.