Concurrent inhibition of oncogenic and wild-type RAS-GTP for cancer therapy.

RAS oncogenes (collectively NRAS, HRAS and especially KRAS) are among the most frequently mutated genes in cancer, with common driver mutations occurring at codons 12, 13 and 611. Small molecule inhibitors of the KRAS(G12C) oncoprotein have demonstrated clinical efficacy in patients with multiple cancer types and have led to regulatory approvals for the treatment of non-small cell lung cancer2,3. Nevertheless, KRASG12C mutations account for only around 15% of KRAS-mutated cancers4,5, and there are no approved KRAS inhibitors for the majority of patients with tumours containing other common KRAS mutations. Here we describe RMC-7977, a reversible, tri-complex RAS inhibitor with broad-spectrum activity for the active state of both mutant and wild-type KRAS, NRAS and HRAS variants (a RAS(ON) multi-selective inhibitor). Preclinically, RMC-7977 demonstrated potent activity against RAS-addicted tumours carrying various RAS genotypes, particularly against cancer models with KRAS codon 12 mutations (KRASG12X). Treatment with RMC-7977 led to tumour regression and was well tolerated in diverse RAS-addicted preclinical cancer models. Additionally, RMC-7977 inhibited the growth of KRASG12C cancer models that are resistant to KRAS(G12C) inhibitors owing to restoration of RAS pathway signalling. Thus, RAS(ON) multi-selective inhibitors can target multiple oncogenic and wild-type RAS isoforms and have the potential to treat a wide range of RAS-addicted cancers with high unmet clinical need. A related RAS(ON) multi-selective inhibitor, RMC-6236, is currently under clinical evaluation in patients with KRAS-mutant solid tumours (ClinicalTrials.gov identifier: NCT05379985).

Fixing a hole where the Ras gets in.

A clinically efficacious Ras inhibitor has eluded drug-discovery efforts for decades. In a paper in Nature, Zimmermann and et al. show that blocking a hole in PDEδ that normally engages the lipid tail of Ras disrupts downstream signaling, pointing to a potentially promising route to develop Ras inhibitors for cancer treatment.

Tumours with class 3 BRAF mutants are sensitive to the inhibition of activated RAS.

Approximately 200 BRAF mutant alleles have been identified in human tumours. Activating BRAF mutants cause feedback inhibition of GTP-bound RAS, are RAS-independent and signal either as active monomers (class 1) or constitutively active dimers (class 2). Here we characterize a third class of BRAF mutants-those that have impaired kinase activity or are kinase-dead. These mutants are sensitive to ERK-mediated feedback and their activation of signalling is RAS-dependent. The mutants bind more tightly than wild-type BRAF to RAS-GTP, and their binding to and activation of wild-type CRAF is enhanced, leading to increased ERK signalling. The model suggests that dysregulation of signalling by these mutants in tumours requires coexistent mechanisms for maintaining RAS activation despite ERK-dependent feedback. Consistent with this hypothesis, melanomas with these class 3 BRAF mutations also harbour RAS mutations or NF1 deletions. By contrast, in lung and colorectal cancers with class 3 BRAF mutants, RAS is typically activated by receptor tyrosine kinase signalling. These tumours are sensitive to the inhibition of RAS activation by inhibitors of receptor tyrosine kinases. We have thus defined three distinct functional classes of BRAF mutants in human tumours. The mutants activate ERK signalling by different mechanisms that dictate their sensitivity to therapeutic inhibitors of the pathway.

Structure-based development of new RAS-effector inhibitors from a combination of active and inactive RAS-binding compounds.

The RAS gene family is frequently mutated in human cancers, and the quest for compounds that bind to mutant RAS remains a major goal, as it also does for inhibitors of protein-protein interactions. We have refined crystallization conditions for KRAS169Q61H-yielding crystals suitable for soaking with compounds and exploited this to assess new RAS-binding compounds selected by screening a protein-protein interaction-focused compound library using surface plasmon resonance. Two compounds, referred to as PPIN-1 and PPIN-2, with related structures from 30 initial RAS binders showed binding to a pocket where compounds had been previously developed, including RAS effector protein-protein interaction inhibitors selected using an intracellular antibody fragment (called Abd compounds). Unlike the Abd series of RAS binders, PPIN-1 and PPIN-2 compounds were not competed by the inhibitory anti-RAS intracellular antibody fragment and did not show any RAS-effector inhibition properties. By fusing the common, anchoring part from the two new compounds with the inhibitory substituents of the Abd series, we have created a set of compounds that inhibit RAS-effector interactions with increased potency. These fused compounds add to the growing catalog of RAS protein-protein inhibitors and show that building a chemical series by crossing over two chemical series is a strategy to create RAS-binding small molecules.

Mule/Huwe1/Arf-BP1 suppresses Ras-driven tumorigenesis by preventing c-Myc/Miz1-mediated down-regulation of p21 and p15.

Tumorigenesis results from dysregulation of oncogenes and tumor suppressors that influence cellular proliferation, differentiation, apoptosis, and/or senescence. Many gene products involved in these processes are substrates of the E3 ubiquitin ligase Mule/Huwe1/Arf-BP1 (Mule), but whether Mule acts as an oncogene or tumor suppressor in vivo remains controversial. We generated K14Cre;Mule(flox/flox(y)) (Mule kKO) mice and subjected them to DMBA/PMA-induced skin carcinogenesis, which depends on oncogenic Ras signaling. Mule deficiency resulted in increased penetrance, number, and severity of skin tumors, which could be reversed by concomitant genetic knockout of c-Myc but not by knockout of p53 or p19Arf. Notably, in the absence of Mule, c-Myc/Miz1 transcriptional complexes accumulated, and levels of p21CDKN1A (p21) and p15INK4B (p15) were down-regulated. In vitro, Mule-deficient primary keratinocytes exhibited increased proliferation that could be reversed by Miz1 knockdown. Transfer of Mule-deficient transformed cells to nude mice resulted in enhanced tumor growth that again could be abrogated by Miz1 knockdown. Our data demonstrate in vivo that Mule suppresses Ras-mediated tumorigenesis by preventing an accumulation of c-Myc/Miz1 complexes that mediates p21 and p15 down-regulation.

K-Ras(G12C) inhibitors allosterically control GTP affinity and effector interactions.

Somatic mutations in the small GTPase K-Ras are the most common activating lesions found in human cancer, and are generally associated with poor response to standard therapies. Efforts to target this oncogene directly have faced difficulties owing to its picomolar affinity for GTP/GDP and the absence of known allosteric regulatory sites. Oncogenic mutations result in functional activation of Ras family proteins by impairing GTP hydrolysis. With diminished regulation by GTPase activity, the nucleotide state of Ras becomes more dependent on relative nucleotide affinity and concentration. This gives GTP an advantage over GDP and increases the proportion of active GTP-bound Ras. Here we report the development of small molecules that irreversibly bind to a common oncogenic mutant, K-Ras(G12C). These compounds rely on the mutant cysteine for binding and therefore do not affect the wild-type protein. Crystallographic studies reveal the formation of a new pocket that is not apparent in previous structures of Ras, beneath the effector binding switch-II region. Binding of these inhibitors to K-Ras(G12C) disrupts both switch-I and switch-II, subverting the native nucleotide preference to favour GDP over GTP and impairing binding to Raf. Our data provide structure-based validation of a new allosteric regulatory site on Ras that is targetable in a mutant-specific manner.

Small molecule inhibition of the KRAS-PDEδ interaction impairs oncogenic KRAS signalling.

The KRAS oncogene product is considered a major target in anticancer drug discovery. However, direct interference with KRAS signalling has not yet led to clinically useful drugs. Correct localization and signalling by farnesylated KRAS is regulated by the prenyl-binding protein PDEδ, which sustains the spatial organization of KRAS by facilitating its diffusion in the cytoplasm. Here we report that interfering with binding of mammalian PDEδ to KRAS by means of small molecules provides a novel opportunity to suppress oncogenic RAS signalling by altering its localization to endomembranes. Biochemical screening and subsequent structure-based hit optimization yielded inhibitors of the KRAS-PDEδ interaction that selectively bind to the prenyl-binding pocket of PDEδ with nanomolar affinity, inhibit oncogenic RAS signalling and suppress in vitro and in vivo proliferation of human pancreatic ductal adenocarcinoma cells that are dependent on oncogenic KRAS. Our findings may inspire novel drug discovery efforts aimed at the development of drugs targeting oncogenic RAS.

5-Arylidene(chromenyl-methylene)-thiazolidinediones: Potential New Agents against Mutant Oncoproteins K-Ras, N-Ras and B-Raf in Colorectal Cancer and Melanoma.

Background and objectives: Cancer represents the miscommunication between and within the body cells. The mutations of the oncogenes encoding the MAPK pathways play an important role in the development of tumoral diseases. The mutations of KRAS and BRAF oncogenes are involved in colorectal cancer and melanoma, while the NRAS mutations are associated with melanoma. Thiazolidine-2,4-dione is a versatile scaffold in medicinal chemistry and a useful tool in the development of new antitumoral compounds. The aim of our study was to predict the pharmacokinetic/pharmacodynamic properties, the drug-likeness and lead-likeness of two series of synthetic 5-arylidene(chromenyl-methylene)-thiazolidinediones, the molecular docking on the oncoproteins K-Ras, N-Ras and B-Raf, and to investigate the cytotoxicity of the compounds, in order to select the best structural profile for potential anticancer agents. Materials and Methods: In our paper we studied the cytotoxicity of two series of thiazolidine-2,4-dione derivatives, their ADME-Tox properties and the molecular docking on a mutant protein of K-Ras, two isoforms of N-Ras and an isoform of B-Raf with 16 mutations. Results: The heterocyclic compounds strongly interact with K-Ras and N-Ras right after their posttranslational processing and/or compete with GDP for the nucleotide-binding site of the two GTPases. They are less active against the GDP-bound states of the two targets. All derivatives have a similar binding pattern in the active site of B-Raf. Conclusions: The data obtained encourage the further investigation of the 5-arylidene(chromenyl-methylene)-thiazolidinediones as potential new agents against the oncoproteins K-Ras, N-Ras and B-Raf.

A novel antitubulin agent, DPQZ, induces cell apoptosis in human oral cancer cells through Ras/Raf inhibition and MAP kinases activation.

6-(N,N-Dimethylamino)-2-(naphthalene-1-yl)-4-quinazolinone (DPQZ)-induced apoptosis was accompanied by the characteristics of DNA fragmentation and phosphatidylserine externalization in human oral cancer HSC-3 cells. The IC50 (half maximal inhibitory concentration) value of DPQZ is about 0.25 µM at 24 h. The interference in the dynamics of tubulin and cell division of DPQZ, like vinblastine (0.01 µM), has been proven in this study. Treatment of HSC-3 cells with DPQZ resulted in many of mitotic cells with multipolar spindles. Up-regulation of MAP kinases, such as ERK, JNK, and p38, mediated by DPQZ appears to be involved in DPQZ-induced apoptosis in HSC-3 cells. It is worthy of note that the expression of Ras and c-Raf that lie upstream of ERK were inhibited by DPQZ. In addition, the DPQZ-induced cell death was attenuated by JNK inhibitor SP600125 (3 or 10 µM), not by the ERK or p38 inhibitors. JNK inhibitor abolished the DPQZ-induced increase in the phosphorylation of Bcl-2 and the protein levels of proform caspase-3, caspase-8, and caspase-9, indicating that JNK is an upstream activator of Bcl-2 and caspase family members and plays a key role in DPQZ-induced HSC-3 cell apoptosis. We also attempted to develop an anticancer drug that is designed to kill rapidly dividing cancer cells while causing less damage to normal cells. The DPQZ-induced cytotoxicity against human gingival fibroblasts was less than that against HSC-3 cells. Our work provides a new strategy and mechanism for developing anticancer drug and may contribute to clinical anticancer drug discovery and application.

Epithelial-mesenchymal transition suppresses ERas to activate autophagy in retinal pigment epithelial cells in proliferative vitreoretinopathy.

OBJECTIVE: Proliferative vitreoretinopathy (PVR) is a complex ocular disease that leads to detached retinas and irreversible vision loss. The epithelial-mesenchymal transition (EMT) of retinal pigment epithelial (RPE) cells plays a critical role in PVR occurrence. However, the core targets driven by the EMT process that lead to the pathogenesis of PVR remain unclear. In our study, the relationship between embryonic stem cell-expressed Ras (ERas) and EMT in RPE cells was investigated. PATIENTS AND METHODS: The subretinal and epiretinal membrane specimens of human PVR were examined for ERas and hallmarks of autophagy and EMT using Western blotting and immunofluorescence. EMT was induced by transforming growth factor (TGF)-ß1 or epidermal growth factor (EGF) in ARPE-19 cells. Autophagy was inhibited by U0126 or bafilomycin A1 in ARPE-19 cells. RESULTS: ERas was decreased and the classical autophagy biomarker microtubule associated protein 1 light chain 3 alpha (LC3) was upregulated in the subretinal and epiretinal membranes of PVR patients in vivo. Moreover, ERas was downregulated and autophagy was activated in RPE ARPE-19 cells in response to transforming growth factor (TGF)-ß1 and epidermal growth factor (EGF) induction. Finally, overexpression of ERas in RPE cells inhibited autophagy via impaired formation of autophagosomes and lysosomes. CONCLUSIONS: Our study revealed the role of ERas in the pathogenesis of PVR through EMT and provided a novel therapeutic target for PVR prevention and treatment.

Specific repression of mutant K-RAS by 10-23 DNAzyme: sensitizing cancer cell to anti-cancer therapies.

Point mutations of the Ras family are frequently found in human cancers at a prevalence rate of 30%. The most common mutation K-Ras(G12V), required for tumor proliferation, survival, and metastasis due to its constitutively active GTPase activity, has provided an ideal target for cancer therapy. 10-23 DNAzyme, an oligodeoxyribonucleotide-based ribonuclease consisting of a 15-nucleotide catalytical domain flanked by two target-specific complementary arms, has been shown to effectively cleave the target mRNA at purine-pyrimidine dinucleotide. Taking advantage of this specific property, 10-23 DNAzyme was designed to cleave mRNA of K-Ras(G12V)(GGU-->GUU) at the GU dinucleotide while left the wild-type (WT) K-Ras mRNA intact. The K-Ras(G12V)-specific 10-23 DNAzyme was able to reduce K-Ras(G12V) at both mRNA and protein levels in SW480 cell carrying homozygous K-Ras(G12V). No effect was observed on the WT K-Ras in HEK cells. Although K-Ras(G12V)-specific DNAzymes alone did not inhibit proliferation of SW480 or HEK cells, pre-treatment of this DNAzyme sensitized the K-Ras(G12V) mutant cells to anti-cancer agents such as doxorubicin and radiation. These results offer a potential of using allele-specific 10-23 DNAzyme in combination with other cancer therapies to achieve better effectiveness on cancer treatment.

Ras and TGF[beta] cooperatively regulate epithelial cell plasticity and metastasis: dissection of Ras signaling pathways.

Multistep carcinogenesis involves more than six discrete events also important in normal development and cell behavior. Of these, local invasion and metastasis cause most cancer deaths but are the least well understood molecularly. We employed a combined in vitro/in vivo carcinogenesis model, that is, polarized Ha-Ras-transformed mammary epithelial cells (EpRas), to dissect the role of Ras downstream signaling pathways in epithelial cell plasticity, tumorigenesis, and metastasis. Ha-Ras cooperates with transforming growth factor beta (TGFbeta) to cause epithelial mesenchymal transition (EMT) characterized by spindle-like cell morphology, loss of epithelial markers, and induction of mesenchymal markers. EMT requires continuous TGFbeta receptor (TGFbeta-R) and oncogenic Ras signaling and is stabilized by autocrine TGFbeta production. In contrast, fibroblast growth factors, hepatocyte growth factor/scatter factor, or TGFbeta alone induce scattering, a spindle-like cell phenotype fully reversible after factor withdrawal, which does not involve sustained marker changes. Using specific inhibitors and effector-specific Ras mutants, we show that a hyperactive Raf/mitogen-activated protein kinase (MAPK) is required for EMT, whereas activation of phosphatidylinositol 3-kinase (PI3K) causes scattering and protects from TGFbeta-induced apoptosis. Hyperactivation of the PI3K pathway or the Raf/MAPK pathway are sufficient for tumorigenesis, whereas EMT in vivo and metastasis required a hyperactive Raf/MAPK pathway. Thus, EMT seems to be a close in vitro correlate of metastasis, both requiring synergism between TGFbeta-R and Raf/MAPK signaling.

The Application of the RNA Interference Technologies for KRAS: Current Status, Future Perspective and Associated Challenges.

KRAS is a member of the murine sarcoma virus oncogene-RAS gene family. It plays an important role in the prevention, diagnosis and treatment of tumors during tumor cell growth and angiogenesis. KRAS is the most commonly mutated oncogene in human cancers, such as pancreatic cancers, colon cancers, and lung cancers. Detection of KRAS gene mutation is an important indicator for tracking the status of oncogenes, highlighting the developmental prognosis of various cancers, and the efficacy of radiotherapy and chemotherapy. However, the efficacy of different patients in clinical treatment is not the same. Since RNA interference (RNAi) technologies can specifically eliminate the expression of specific genes, these technologies have been widely used in the field of gene therapy for exploring gene function, infectious diseases and malignant tumors. RNAi refers to the phenomenon of highly specific degradation of homologous mRNA induced by double-stranded RNA (dsRNA), which is highly conserved during evolution. There are three classical RNAi technologies, including siRNA, shRNA and CRISPR-Cas9 system, and a novel synthetic lethal interaction that selectively targets KRAS mutant cancers. Therefore, the implementation of individualized targeted drug therapy has become the best choice for doctors and patients. Thus, this review focuses on the current status, future perspective and associated challenges in silencing of KRAS with RNAi technology.

Overview of Current Immunotherapies Targeting Mutated KRAS Cancers.

The occurrence of somatic substitution mutations of the KRAS proto-oncogene is highly prevalent in certain cancer types, which often leads to constant activation of proliferative pathways and subsequent neoplastic transformation. It is often seen as a gateway mutation in carcinogenesis and has been commonly deemed as a predictive biomarker for poor prognosis and relapse when conventional chemotherapeutics are employed. Additionally, its mutational status also renders EGFR targeted therapies ineffective owing to its downstream location. Efforts to discover new approaches targeting this menacing culprit have been ongoing for years without much success, and with incidences of KRAS positive cancer patients being on the rise, researchers are now turning towards immunotherapies as the way forward. In this scoping review, recent immunotherapeutic developments and advances in both preclinical and clinical studies targeting K-ras directly or indirectly via its downstream signal transduction machinery will be discussed. Additionally, some of the challenges and limitations of various K-ras targeting immunotherapeutic approaches such as vaccines, adoptive T cell therapies, and checkpoint inhibitors against KRAS positive cancers will be deliberated.

KRAS: A Promising Therapeutic Target for Cancer Treatment.

Kirsten rat sarcoma 2 viral oncogene homolog (KRAS) is the most commonly mutated oncogene in human cancer. The developments of many cancers depend on sustained expression and signaling of KRAS, which makes KRAS a high-priority therapeutic target. Scientists have not successfully developed drugs that target KRAS, although efforts have been made last three decades. In this review, we highlight the emerging experimental strategies of impairing KRAS membrane localization and the direct targeting of KRAS. We also conclude the combinatorial therapies and RNA interference technology for the treatment of KRAS mutant cancers. Moreover, the virtual screening approach to discover novel KRAS inhibitors and synthetic lethality interactors of KRAS are discussed in detail.

Targeting Mutant KRAS for Anticancer Therapy.

Over the past decades, designing therapeutic strategies to target KRAS-mutant cancers, which is one of the most frequent mutant oncogenes among all cancer types, have proven unsuccessful regardless of many concerted attempts. There are key challenges for KRAS-mutant anticancer therapy, as the complex cellular processes involved in KRAS signaling has present. Herein, we highlight the emerging therapeutic approaches for inhibiting KRAS signaling and blocking KRAS functions, in hope to serve as a more effective guideline for future development of therapeutics.

Binimetinib, a novel MEK1/2 inhibitor, exerts anti-leukemic effects under inactive status of PI3Kinase/Akt pathway.

A MEK1/2 inhibitor, binimetinib is promising as a therapeutic agent for malignant melanoma with N-RAS mutation. We examined in vitro effects of binimetinib on 10 human myeloid/lymphoid leukemia cell lines, and found that three of five cell lines with N-RAS mutation and one of five without N-RAS mutation were responsive to treatment with binimetinib. Binimetinib inhibited cell growth mainly by inducing G1 arrest and this action mechanism was assisted by gene set enrichment analysis. To identify signaling pathways associated with binimetinib response, we examined the status of MAP kinase/ERK and PI3Kinase/Akt pathways. The basal levels of phosphorylated ERK and Akt varied between the cell lines, and the amounts of phosphorylated ERK and Akt appeared to be reciprocal of each other. Interestingly, most of the binimetinib-resistant cell lines revealed strong Akt phosphorylation compared with binimetinib-sensitive ones. The effect of binimetinib may not be predicted by the presence/absence of N-RAS mutation, but rather by Akt phosphorylation status. Moreover, combination of binimetinib with a PI3K/Akt inhibitor showed additive growth-suppressive effects. These results suggest that binimetinib shows potential anti-leukemic effects and the basal level of phosphorylated Akt might serve as a biomarker predictive of therapeutic effect.