Structural insights into small-molecule KRAS inhibitors for targeting KRAS mutant cancers.

The Kirsten rat sarcoma viral (KRAS) oncogene is the most frequently mutated isoform of RAS, associated with 85 % of RAS-driven cancers. KRAS functions as a signaling hub, participating in various cellular signaling pathways and regulating a wide range of important activities, including cell proliferation, differentiation, growth, metabolism, and migration. Despite being the most frequently altered oncogenic protein in solid tumors, over the past four decades, KRAS has historically been considered "undruggable" owing to a lack of pharmacologically targetable pockets within the mutant isoforms. However, improvements in drug design and development have culminated in the development of selective inhibitors for KRAS mutants. Recent developments have led to the successful targeting of the KRASG12C mutant through covalent inhibitors that exploit the unique cysteine residue introduced by the mutation at 12th position. These inhibitors bind covalently to C12, locking KRAS in its inactive GDP-bound state and preventing downstream signaling. Some of these inhibitors have shown encouraging results in KRASG12C mutant cancer patients but suffer from drug resistance, toxicity, and low therapeutic efficacy. Recently, there have been great advancements in the discovery of drugs that directly target the switch I (S-I), switch-II (S-II) and S-I/II interface sites of KRAS mutant proteins. These include KRASG12C inhibitors like AMG510 (Sotorasib) and MRTX849 (Adagrasib), which have got FDA approval for non-small cell lung cancer harboring the KRASG12C mutation. There is no approved drug for cancers harboring other KRAS mutations, although efforts have expanded to target other KRAS mutations and the Switch I/II interface, aiming to disrupt KRAS-driven oncogenic signaling. Structure-activity relationship (SAR) studies have been instrumental in optimizing the binding affinity, selectivity, and pharmacokinetic properties of these inhibitors, leading to the development of promising therapeutic agents like Sotorasib and Adagrasib. This review provides an overview of the KRAS pathway, KRAS binding sites, strategies for direct and indirect inhibition using small molecules, and SAR based on the co-crystal structures of inhibitors with KRAS mutants which is expected to offer new hope for patients with KRAS-driven cancers through the development of new KRAS-targeted drugs.

High Pressure Promotes Binding of the Allosteric Inhibitor Zn2+-Cyclen in Crystals of Activated H-Ras.

In this work, we experimentally investigate the potency of high pressure to drive a protein toward an excited state where an inhibitor targeted for this state can bind. Ras proteins are small GTPases cycling between active GTP-bound and inactive GDP-bound states. Various states of GTP-bound Ras in active conformation coexist in solution, amongst them, state 2 which binds to effectors, and state 1, weakly populated at ambient conditions, which has a low affinity for effectors. Zn2+-cyclen is an allosteric inhibitor of Ras protein, designed to bind specifically to the state 1. In H-Ras(wt).Mg2+.GppNHp crystals soaked with Zn2+-cyclen, no binding could be observed, as expected in the state 2 conformation which is the dominant state at ambient pressure. Interestingly, Zn2+-cyclen binding is observed at 500 MPa pressure, close to the nucleotide, in Ras protein that is driven by pressure to a state 1 conformer. The unknown binding mode of Zn2+-cyclen to H-Ras can thus be fully characterized in atomic details. As a more general conjunction from our study, high pressure x-ray crystallography turns out to be a powerful method to induce transitions allowing drug binding in proteins that are in low-populated conformations at ambient conditions, enabling the design of specific inhibitors.

Targeted genetic and small molecule disruption of N-Ras CaaX cleavage alters its localization and oncogenic potential.

Ras GTPases and other CaaX proteins undergo multiple post-translational modifications at their carboxyl-terminus. These events initiate with prenylation of a cysteine and are followed by endoproteolytic removal of the 'aaX' tripeptide and carboxylmethylation. Some CaaX proteins are only subject to prenylation, however, due to the presence of an uncleavable sequence. In this study, uncleavable sequences were used to stage Ras isoforms in a farnesylated and uncleaved state to address the impact of CaaX proteolysis on protein localization and function. This targeted strategy is more specific than those that chemically inhibit the Rce1 CaaX protease or delete the RCE1 gene because global abrogation of CaaX proteolysis impacts the entire CaaX protein proteome and effects cannot be attributed to any specific CaaX protein of the many concurrently affected. With this targeted strategy, clear mislocalization and reduced activity of farnesylated and uncleaved Ras isoforms was observed. In addition, new peptidomimetics based on cleavable Ras CaaX sequences and the uncleavable CAHQ sequence were synthesized and tested as Rce1 inhibitors using in vitro and cell-based assays. Consistently, these non-hydrolyzable peptidomimetic Rce1 inhibitors recapitulate Ras mislocalization effects when modeled on cleavable but not uncleavable CaaX sequences. These findings indicate that a prenylated and uncleavable CaaX sequence, which can be easily applied to a wide range of mammalian CaaX proteins, can be used to probe the specific impact of CaaX proteolysis on CaaX protein properties under conditions of an otherwise normally processed CaaX protein proteome.

GTP-Bound N-Ras Conformational States and Substates Are Modulated by Membrane and Point Mutation.

Oncogenic Ras proteins are known to present multiple conformational states, as reported by the great variety of crystallographic structures. The GTP-bound states are grouped into two main states: the "inactive" state 1 and the "active" state 2. Recent reports on H-Ras have shown that state 2 exhibits two substates, directly related to the orientation of Tyr32: toward the GTP-bound pocket and outwards. In this paper, we show that N-Ras exhibits another substate of state 2, related to a third orientation of Tyr32, toward Ala18 and parallel to the GTP-bound pocket. We also show that this substate is highly sampled in the G12V mutation of N-Ras and barely present in its wild-type form, and that the G12V mutation prohibits the sampling of the GTPase-activating protein (GAP) binding substate, rendering this mutation oncogenic. Furthermore, using molecular dynamics simulations, we explore the importance of the membrane on N-Ras' conformational state dynamics and its strong influence on Ras protein stability. Moreover, the membrane has a significant influence on the conformational (sub)states sampling of Ras. This, in turn, is of crucial importance in the activation/deactivation cycle of Ras, due to the binding of guanine nucleotide exchange factor proteins (GEFs)/GTPase-activating proteins (GAPs).

Biophysical and Biochemical Characterization of Structurally Diverse Small Molecule Hits for KRAS Inhibition.

We describe six compounds as early hits for the development of direct inhibitors of KRAS, an important anticancer drug target. We show that these compounds bind to KRAS with affinities in the low micromolar range and exert different effects on its interactions with binding partners. Some of the compounds exhibit selective binding to the activated form of KRAS and inhibit signal transduction through both the MAPK or the phosphatidylinositide 3-kinase PI3K-protein kinase B (AKT) pathway in cells expressing mutant KRAS. Most inhibit intrinsic and/or SOS-mediated KRAS activation while others inhibit RAS-effector interaction. We propose these compounds as starting points for the development of non-covalent allosteric KRAS inhibitors.

Rasal1 regulates calcium dependent neuronal maturation by modifying microtubule dynamics.

BACKGROUND: Rasal1 is a Ras GTPase-activating protein which contains C2 domains necessary for dynamic membrane association following intracellular calcium elevation. Membrane-bound Rasal1 inactivates Ras signaling through its RasGAP activity, and through such mechanisms has been implicated in regulating various cellular functions in the context of tumors. Although highly expressed in the brain, the contribution of Rasal1 to neuronal development and function has yet to be explored. RESULTS: We examined the contributions of Rasal1 to neuronal development in primary culture of hippocampal neurons through modulation of Rasal1 expression using molecular tools. Fixed and live cell imaging demonstrate diffuse expression of Rasal1 throughout the cell soma, dendrites and axon which localizes to the neuronal plasma membrane in response to intracellular calcium fluctuation. Pull-down and co-immunoprecipitation demonstrate direct interaction of Rasal1 with PKC, tubulin, and CaMKII. Consequently, Rasal1 is found to stabilize microtubules, through post-translational modification of tubulin, and accordingly inhibit dendritic outgrowth and branching. Through imaging, molecular, and electrophysiological techniques Rasal1 is shown to promote NMDA-mediated synaptic activity and CaMKII phosphorylation. CONCLUSIONS: Rasal1 functions in two separate roles in neuronal development; calcium regulated neurite outgrowth and the promotion of NMDA receptor-mediated postsynaptic events which may be mediated both by interaction with direct binding partners or calcium-dependent regulation of down-stream pathways. Importantly, the outlined molecular mechanisms of Rasal1 may contribute notably to normal neuronal development and synapse formation.

CAMSAP2 enhances lung cancer cell metastasis by mediating RASAL2 degradation.

AIMS: Cancer metastasis significantly contributes to mortality in lung cancer patients. Calmodulin-regulated spectrin-associated protein family member 2 (CAMSAP2) plays a significant role in cancer cell migration; however, its role in lung cancer metastasis and the underlying mechanism remain largely unknown. The present study aimed to investigate the impact of CAMSAP2 on lung cancer. MAIN METHODS: The clinical relevance of CAMSAP2 in lung cancer patients was assessed using public database. RNA interference experiments were conducted to investigate role of CAMSAP2 in cell migration through transwell and wound healing assays. Molecular mechanisms were explored by identifying the possible interacting partners and pathways using the BioGRID and KEGG pathway analyses. The impact of CAMSAP2 on Ras protein activator-like 2 (RASAL2)-mediated lung cancer metastasis was investigated through biochemical assays. Additionally, in vivo experimentation using a murine tail vein metastasis model was performed to comprehend CAMSAP2's influence on metastasis. KEY FINDINGS: A high expression level of CAMSAP2 was associated with poor overall survival in lung cancer patients and it positively correlated with cell migration in non-small cell lung cancer (NSCLC) cell lines. Knockdown of CAMSAP2 inhibited lung cancer cell motility in vitro and metastasis in vivo. Proteomic and biochemical analyses revealed the interaction between CAMSAP2 and RASAL2, which facilitates the degradation of RASAL2 through the ubiquitin-proteasome system. These degradation processes resulted in the activation of the extracellular signal-regulated kinase (ERK) signaling pathway, thereby promoting lung cancer metastasis. Collectively, the results of this study suggest that CAMSAP2 is a crucial regulator of cancer cell migration and metastasis and a promising therapeutic target for lung cancer.

2-Bromopalmitate inhibits malignant behaviors of HPSCC cells by hindering the membrane location of Ras protein.

Palmitoylation, which is mediated by protein acyltransferase (PAT) and performs important biological functions, is the only reversible lipid modification in organism. To study the effect of protein palmitoylation on hypopharyngeal squamous cell carcinoma (HPSCC), the expression levels of 23 PATs in tumor tissues of 8 HPSCC patients were determined, and high mRNA and protein levels of DHHC9 and DHHC15 were found. Subsequently, we investigated the effect of 2-bromopalmitate (2BP), a small-molecular inhibitor of protein palmitoylation, on the behavior of Fadu cells in vitro (50 µM) and in nude mouse xenograft models (50 µmol/kg), and found that 2BP suppressed the proliferation, invasion, and migration of Fadu cells without increasing cell apoptosis. Mechanistically, the effect of 2BP on the transduction of BMP, Wnt, Shh, and FGF signaling pathways was tested with qRT-PCR, and its drug target was explored with western blotting and acyl-biotinyl exchange assay. Our results showed that 2BP inhibited the transduction of the FGF/ERK signaling pathway. The palmitoylation level of Ras protein decreased after 2BP treatment, and its distribution in the cell membrane structure was reduced significantly. The findings of this work reveal that protein palmitoylation mediated by DHHC9 and DHHC15 may play important roles in the occurrence and development of HPSCC. 2BP is able to inhibit the malignant biological behaviors of HPSCC cells, possibly via hindering the palmitoylation and membrane location of Ras protein, which might, in turn, offer a low-toxicity anti-cancer drug for targeting the treatment of HPSCC.

Mechanistic Insights of Polyphenolic Compounds from Rosemary Bound to Their Protein Targets Obtained by Molecular Dynamics Simulations and Free-Energy Calculations.

Rosemary represents an important medicinal plant that has been attributed with various health-promoting properties, especially antioxidative, anti-inflammatory, and anticarcinogenic activities. Carnosic acid, carnosol, and rosmanol, as well as the phenolic acid ester rosmarinic acid, are the main compounds responsible for these actions. In our earlier research, we carried out an inverse molecular docking at the proteome scale to determine possible protein targets of the mentioned compounds. Here, we subjected the previously identified ligand-protein complexes with HIV-1 protease, K-RAS, and factor X to molecular dynamics simulations coupled with free-energy calculations. We observed that carnosic acid and rosmanol act as viable binders of the HIV-1 protease. In addition, carnosol represents a potential binder of the oncogene protein K-RAS. On the other hand, rosmarinic acid was characterized as a weak binder of factor X. We also emphasized the importance of water-mediated hydrogen-bond networks in stabilizing the binding conformation of the studied polyphenols, as well as in mechanistically explaining their promiscuous nature.

Mapping the KRAS proteoform landscape in colorectal cancer identifies truncated KRAS4B that decreases MAPK signaling.

The KRAS gene is one of the most frequently mutated oncogenes in human cancer and gives rise to two isoforms, KRAS4A and KRAS4B. KRAS post-translational modifications (PTMs) have the potential to influence downstream signaling. However, the relationship between KRAS PTMs and oncogenic mutations remains unclear, and the extent of isoform-specific modification is unknown. Here, we present the first top-down proteomics study evaluating both KRAS4A and KRAS4B, resulting in 39 completely characterized proteoforms across colorectal cancer cell lines and primary tumor samples. We determined which KRAS PTMs are present, along with their relative abundance, and that proteoforms of KRAS4A versus KRAS4B are differentially modified. Moreover, we identified a subset of KRAS4B proteoforms lacking the C185 residue and associated C-terminal PTMs. By confocal microscopy, we confirmed that this truncated GFP-KRAS4BC185∗ proteoform is unable to associate with the plasma membrane, resulting in a decrease in mitogen-activated protein kinase signaling pathway activation. Collectively, our study provides a reference set of functionally distinct KRAS proteoforms and the colorectal cancer contexts in which they are present.

A novel antiproliferative PKCα-Ras-ERK signaling axis in intestinal epithelial cells.

We have previously shown that the serine/threonine kinase PKCα triggers MAPK/ERK kinase (MEK)-dependent G1→S cell cycle arrest in intestinal epithelial cells, characterized by downregulation of cyclin D1 and inhibitor of DNA-binding protein 1 (Id1) and upregulation of the cyclin-dependent kinase inhibitor p21Cip1. Here, we use pharmacological inhibitors, genetic approaches, siRNA-mediated knockdown, and immunoprecipitation to further characterize antiproliferative ERK signaling in intestinal cells. We show that PKCα signaling intersects the Ras-Raf-MEK-ERK kinase cascade at the level of Ras small GTPases and that antiproliferative effects of PKCα require active Ras, Raf, MEK, and ERK, core ERK pathway components that are also essential for pro-proliferative ERK signaling induced by epidermal growth factor (EGF). However, PKCα-induced antiproliferative signaling differs from EGF signaling in that it is independent of the Ras guanine nucleotide exchange factors (Ras-GEFs), SOS1/2, and involves prolonged rather than transient ERK activation. PKCα forms complexes with A-Raf, B-Raf, and C-Raf that dissociate upon pathway activation, and all three Raf isoforms can mediate PKCα-induced antiproliferative effects. At least two PKCα-ERK pathways that collaborate to promote growth arrest were identified: one pathway requiring the Ras-GEF, RasGRP3, and H-Ras, leads to p21Cip1 upregulation, while additional pathway(s) mediate PKCα-induced cyclin D1 and Id1 downregulation. PKCα also induces ERK-dependent SOS1 phosphorylation, indicating possible negative crosstalk between antiproliferative and growth-promoting ERK signaling. Importantly, the spatiotemporal activation of PKCα and ERK in the intestinal epithelium in vivo supports the physiological relevance of these pathways and highlights the importance of antiproliferative ERK signaling to tissue homeostasis in the intestine.

Megaviruses contain various genes encoding for eukaryotic vesicle trafficking factors.

Many intracellular pathogens, such as bacteria and large viruses, enter eukaryotic cells via phagocytosis, then replicate and proliferate inside the host. To avoid degradation in the phagosomes, they have developed strategies to modify vesicle trafficking. Although several strategies of bacteria have been characterized, it is not clear whether viruses also interfere with the vesicle trafficking of the host. Recently, we came across SNARE proteins encoded in the genomes of several bacteria of the order Legionellales. These pathogenic bacteria may use SNAREs to interfere with vesicle trafficking, since SNARE proteins are the core machinery for vesicle fusion during transport. They assemble into membrane-bridging SNARE complexes that bring membranes together. We now have also discovered SNARE proteins in the genomes of diverse giant viruses. Our biochemical experiments showed that these proteins are able to form SNARE complexes. We also found other key trafficking factors that work together with SNAREs such as NSF, SM, and Rab proteins encoded in the genomes of giant viruses, suggesting that viruses can make use of a large genetic repertoire of trafficking factors. Most giant viruses possess different collections, suggesting that these factors entered the viral genome multiple times. In the future, the molecular role of these factors during viral infection need to be studied.

Loss of PTEN-Induced Kinase 1 Regulates Oncogenic Ras-Driven Tumor Growth By Inhibiting Mitochondrial Fission.

Mitochondrial metabolism and dynamics (fission and fusion) critically regulate cell survival and proliferation, and abnormalities in these pathways are implicated in both neurodegenerative disorders and cancer. Mitochondrial fission is necessary for the growth of mutant Ras-dependent tumors. Here, we investigated whether loss of PTEN-induced kinase 1 (PINK1) - a mitochondrial kinase linked to recessive familial Parkinsonism - affects the growth of oncogenic Ras-induced tumor growth in vitro and in vivo. We show that RasG12D-transformed embryonic fibroblasts (MEFs) from PINK1-deficient mice display reduced growth in soft agar and in nude mice, as well as increased necrosis and decreased cell cycle progression, compared to RasG12D-transformed MEFs derived from wildtype mice. PINK1 re-expression (overexpression) at least partially rescues these phenotypes. Neither PINK1 deletion nor PINK1 overexpression altered Ras expression levels. Intriguingly, PINK1-deficient Ras-transformed MEFs exhibited elongated mitochondria and altered DRP1 phosphorylation, a key event in regulating mitochondrial fission. Inhibition of DRP1 diminished PINK1-regulated mitochondria morphological changes and tumor growth suggesting that PINK1 deficiency primarily inhibits Ras-driven tumor growth through disturbances in mitochondrial fission and associated cell necrosis and cell cycle defects. Moreover, we substantiate the requirement of PINK1 for optimal growth of Ras-transformed cells by showing that human HCT116 colon carcinoma cells (carrying an endogenous RasG13D mutation) with CRISPR/Cas9-introduced PINK1 gene deletions also show reduced mitochondrial fission and decreased growth. Our results support the importance of mitochondrial function and dynamics in regulating the growth of Ras-dependent tumor cells and provide insight into possible mechanisms underlying the lower incidence of cancers in Parkinson's disease and other neurodegenerative disorders.

The utility of the Ion Torrent PGM next generation sequencing for analysis of the most commonly mutated genes among patients with colorectal cancer in India.

Background: The requirement for the mutation analysis for Kirsten rat sarcoma viral oncogene (KRAS) in colorectal cancer (CRC) is rapidly increasing as it is a predictive biomarker and also, its absence signifies response to anti-epidermal growth factor receptor (anti-EGFR) antibody treatment. The aim of our study was to investigate the pathological diagnosis and distribution of KRAS mutations in colorectal cancer with the use of next generation sequencing platform (Ion Torrent). Methods: A total of 56 CRC samples were tested to identify the genetic mutations, especially KRAS using the primers which included ~2800 COSMIC mutations of 50 oncogenes. Ion Torrent personal genome machine (semiconductor-based sequencing) was used for the sequencing and analysis. Along with KRAS, other 49 genes were also studied for COSMIC mutations. Results: KRAS mutation 25 (44.6%) had the highest frequency, followed by TP53 10 (17.9%) and PIK3CA mutation 4 (7.1%). Of all the KRAS mutations identified, mutations in codon 12 were most frequent followed by mutations in codon 13 and 61. The most frequent substitution was glycine to aspartate mutation in codon 12 (p.Gly12Asp) followed by glycine to valine (p.Gly12Val). Combinations of mutations were also studied. Our study revealed that seven cases (12.5%) had both KRAS and TP53 mutations (highest of all the combinations). Conclusion: The analysis of KRAS mutation frequency and its mutational subtype analysis in human CRCs by using semiconductor-based platform in routine clinical practices have been performed in Indian population. The findings were similar to earlier published reports from the Western literature.

Development of a versatile HPLC-based method to evaluate the activation status of small GTPases.

Small GTPases cycle between an inactive GDP-bound and an active GTP-bound state to control various cellular events, such as cell proliferation, cytoskeleton organization, and membrane trafficking. Clarifying the guanine nucleotide-bound states of small GTPases is vital for understanding the regulation of small GTPase functions and the subsequent cellular responses. Although several methods have been developed to analyze small GTPase activities, our knowledge of the activities for many small GTPases is limited, partly because of the lack of versatile methods to estimate small GTPase activity without unique probes and specialized equipment. In the present study, we developed a versatile and straightforward HPLC-based assay to analyze the activation status of small GTPases by directly quantifying the amounts of guanine nucleotides bound to them. This assay was validated by analyzing the RAS-subfamily GTPases, including HRAS, which showed that the ratios of GTP-bound forms were comparable with those obtained in previous studies. Furthermore, we applied this assay to the investigation of psychiatric disorder-associated mutations of RHEB (RHEB/P37L and RHEB/S68P), revealing that both mutations cause an increase in the ratio of the GTP-bound form in cells. Mechanistically, loss of sensitivity to TSC2 (a GTPase-activating protein for RHEB) for RHEB/P37L, as well as both decreased sensitivity to TSC2 and accelerated guanine-nucleotide exchange for RHEB/S68P, is involved in the increase of their GTP-bound forms, respectively. In summary, the HPLC-based assay developed in this study provides a valuable tool for analyzing small GTPases for which the activities and regulatory mechanisms are less well understood.

Engineering a cell-penetrating hyperstable antibody scFv(Ras) - An extraordinary approach to cancer therapeutics.

In the modern pharmaceutical industry, monoclonal antibodies are often used as therapeutic agents. However, they are restricted to cell surface antigens due to their inability to penetrate the outer cell membrane and maintain normal function in the reducing environment. Additionally, it can lead to cytotoxicity since it attacks cancerous cells by mimicking the human immune system. As an alternative, this study modifies the hyperstable single-chain fragment variable(scFv) antibody to eliminate cancer using its linear shape. The scFv(F8) antibody model was modified to recognize human Ras protein by altering residues in the antigen-binding site. Furthermore, a cell-penetrating peptide (CPP) was attached to the scFv(Ras) antibody model to allow entrance to the cell, creating CPP-scFv(Ras). Sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE), western blotting, and the binding assay were performed to prove its effectiveness. As a result, CPP-scFv(Ras) was successfully engineered and bound to the antigen, HRas(G12V).

The KRAS-regulated kinome identifies WEE1 and ERK coinhibition as a potential therapeutic strategy in KRAS-mutant pancreatic cancer.

Oncogenic KRAS drives cancer growth by activating diverse signaling networks, not all of which have been fully delineated. We set out to establish a system-wide profile of the KRAS-regulated kinase signaling network (kinome) in KRAS-mutant pancreatic ductal adenocarcinoma (PDAC). We knocked down KRAS expression in a panel of six cell lines and then applied multiplexed inhibitor bead/MS to monitor changes in kinase activity and/or expression. We hypothesized that depletion of KRAS would result in downregulation of kinases required for KRAS-mediated transformation and in upregulation of other kinases that could potentially compensate for the deleterious consequences of the loss of KRAS. We identified 15 upregulated and 13 downregulated kinases in common across the panel of cell lines. In agreement with our hypothesis, all 15 of the upregulated kinases have established roles as cancer drivers (e.g., SRC, TGF-ß1, ILK), and pharmacological inhibition of one of these upregulated kinases, DDR1, suppressed PDAC growth. Interestingly, 11 of the 13 downregulated kinases have established driver roles in cell cycle progression, particularly in mitosis (e.g., WEE1, Aurora A, PLK1). Consistent with a crucial role for the downregulated kinases in promoting KRAS-driven proliferation, we found that pharmacological inhibition of WEE1 also suppressed PDAC growth. The unexpected paradoxical activation of ERK upon WEE1 inhibition led us to inhibit both WEE1 and ERK concurrently, which caused further potent growth suppression and enhanced apoptotic death compared with WEE1 inhibition alone. We conclude that system-wide delineation of the KRAS-regulated kinome can identify potential therapeutic targets for KRAS-mutant pancreatic cancer.

Low Expression of Rasal2 Promotes Non-small Cell Lung Cancer Metastasis through Ras/ERK Pathway.

The RAS protein activator like 2 (Rasal2) has been reported to be a tumor suppressor in variety of cancers; while an oncogenic protein in ovarian cancer and triple negative breast cancer (TNBC). However, the exact role of Rasal2 in non-small cell lung cancer (NSCLC) is lacking. This study aimed to investigate the role of Rasal2 in NSCLC and the underlying mechanisms. Rasal2 expression level was measured in NSCLC tissue and cells by using quantitative (q)-PCR and immunoblotting analysis. The clinical implication of Rasal2 in NSCLC patients was also analyzed. The function role of Rasal2 in NSCLC cells were measured by small interfering RNA (si-RNA), immunostaining, transwell assay and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Low Rasal2 expression level was observed in human NSCLC tissue and cell lines and significantly related to tumor thickness, ulceration and TNM staging in NSCLC patients. Rasal2 knockdown significantly increased NSCLC cell invasion and migration. Mechanistically, we showed that Rasal2 knockdown significantly increased the phosphorylation level of extracellular signal-regulated kinase (ERK)/Raf1/mitogen-activated protein extracellular kinase (MEK) thus activated Ras/ERK signal pathway. Thus, our data showed that Rasal2 is downregulated in NSCLC cells and act as an epithelial-mesenchymal transition (EMT) and metastasis suppressor through the Ras/ERK pathway. Rasal2 may be a prognostic biomarker for NSCLC in the future.

New possible silver lining for pancreatic cancer therapy: Hydrogen sulfide and its donors.

As one of the most lethal diseases, pancreatic cancer shows a dismal overall prognosis and high resistance to most treatment modalities. Furthermore, pancreatic cancer escapes early detection during the curable period because early symptoms rarely emerge and specific markers for this disease have not been found. Although combinations of new drugs, multimodal therapies, and adjuvants prolong survival, most patients still relapse after surgery and eventually die. Consequently, the search for more effective treatments for pancreatic cancer is highly relevant and justified. As a newly re-discovered mediator of gasotransmission, hydrogen sulfide (H2S) undertakes essential functions, encompassing various signaling complexes that occupy key processes in human biology. Accumulating evidence indicates that H2S exhibits bimodal modulation of cancer development. Thus, endogenous or low levels of exogenous H2S are thought to promote cancer, whereas high doses of exogenous H2S suppress tumor proliferation. Similarly, inhibition of endogenous H2S production also suppresses tumor proliferation. Accordingly, H2S biosynthesis inhibitors and H2S supplementation (H2S donors) are two distinct strategies for the treatment of cancer. Unfortunately, modulation of endogenous H2S on pancreatic cancer has not been studied so far. However, H2S donors and their derivatives have been extensively studied as potential therapeutic agents for pancreatic cancer therapy by inhibiting cell proliferation, inducing apoptosis, arresting cell cycle, and suppressing invasion and migration through exploiting multiple signaling pathways. As far as we know, there is no review of the effects of H2S donors on pancreatic cancer. Based on these concerns, the therapeutic effects of some H2S donors and NO-H2S dual donors on pancreatic cancer were summarized in this paper. Exogenous H2S donors may be promising compounds for pancreatic cancer treatment.

Sequence-Selective Covalent CaaX-Box Receptors Prevent Farnesylation of Oncogenic Ras Proteins and Impact MAPK/PI3†K Signaling.

Oncogenic Ras proteins are implicated in the most common life-threatening cancers. Despite intense research over the past two decades, the progress towards small-molecule inhibitors has been limited. One reason for this failure is that Ras proteins interact with their effectors only via protein-protein interactions, which are notoriously difficult to address with small organic molecules. Herein we describe an alternative strategy, which prevents farnesylation and subsequent membrane insertion, a prerequisite for the activation of Ras proteins. Our approach is based on sequence-selective supramolecular receptors which bind to the C-terminal farnesyl transferase recognition unit of Ras and Rheb proteins and covalently modify the essential cysteine in the so-called CaaX-box.