Identification of a small molecule with synthetic lethality for K-ras and protein kinase C iota

RAS degraders: The new frontier for RAS-driven cancers

The function and significance of RAS proteins in cancer have been widely studied for decades. In 2013, the National Cancer Institute established the RAS Initiative to explore innovative approaches for attacking the proteins encoded by mutant forms of RAS genes and to create effective therapies for RAS-driven cancers. This initiative spurred researchers to develop novel approaches and to discover small molecules targeting this protein that was at one time termed "undruggable." More recently, advanced efforts in RAS degraders including PROTACs, linker-based degraders, and direct proteolysis degraders have been explored as novel strategies to target RAS for cancer treatment. These RAS degraders present new opportunities for RAS therapies and may prove fruitful in understanding basic cell biology. Novel delivery strategies will further enhance the efficacy of these therapeutics. In this review, we summarize recent efforts to develop RAS degraders, including PROTACs and E3 adaptor and ligase fusions as cancer therapies. This review also details the direct RAS protease degrader, RAS/RAP1-specific endopeptidase that directly and specifically cleaves RAS.

Differential Inhibition of Anaplerotic Pyruvate Carboxylation and Glutaminolysis-Fueled Anabolism Underlies Distinct Toxicity of Selenium Agents in Human Lung Cancer

Past chemopreventive human trials on dietary selenium supplements produced controversial outcomes. They largely employed selenomethionine (SeM)-based diets. SeM was less toxic than selenite or methylseleninic acid (MSeA) to lung cancer cells. We thus investigated the toxic action of these Se agents in two non-small cell lung cancer (NSCLC) cell lines and ex vivo organotypic cultures (OTC) of NSCLC patient lung tissues. Stable isotope-resolved metabolomics (SIRM) using 13C6-glucose and 13C5,15N2-glutamine tracers with gene knockdowns were employed to examine metabolic dysregulations associated with cell type- and treatment-dependent phenotypic changes. Inhibition of key anaplerotic processes, pyruvate carboxylation (PyC) and glutaminolysis were elicited by exposure to MSeA and selenite but not by SeM. They were accompanied by distinct anabolic dysregulation and reflected cell type-dependent changes in proliferation/death/cell cycle arrest. NSCLC OTC showed similar responses of PyC and/or glutaminolysis to the three agents, which correlated with tissue damages. Altogether, we found differential perturbations in anaplerosis-fueled anabolic pathways to underlie the distinct anti-cancer actions of the three Se agents, which could also explain the failure of SeM-based chemoprevention trials.

Small-Molecule RAS Inhibitors as Anticancer Agents: Discovery, Development, and Mechanistic Studies

Mutations of RAS oncogenes are responsible for about 30% of all human cancer types, including pancreatic, lung, and colorectal cancers. While KRAS1 is a pseudogene, mutation of KRAS2 (commonly known as KRAS oncogene) is directly or indirectly associated with human cancers. Among the RAS family, KRAS is the most abundant oncogene related to uncontrolled cellular proliferation to generate solid tumors in many types of cancer such as pancreatic carcinoma (over 80%), colon carcinoma (40-50%), lung carcinoma (30-50%), and other types of cancer. Once described as 'undruggable', RAS proteins have become 'druggable', at least to a certain extent, due to the continuous efforts made during the past four decades. In this account, we discuss the chemistry and biology (wherever available) of the small-molecule inhibitors (synthetic, semi-synthetic, and natural) of KRAS proteins that were published in the past decades. Commercial drugs, as well as investigational molecules from preliminary stages to clinical trials, are categorized and discussed in this study. In summary, this study presents an in-depth discussion of RAS proteins, classifies the RAS superfamily, and describes the molecular mechanism of small-molecule RAS inhibitors.

Impact of deleterious missense PRKCI variants on structural and functional dynamics of protein

Protein kinase C iota (PKC_ɩ) is a novel protein containing 596 amino acids and is also a member of atypical kinase family. The role of PKC_ɩ has been explored in neurodegenerative diseases, neuroblastoma, ovarian and pancreatic cancers. Single nucleotide polymorphisms (SNPs) have not been studied in PKC_ɩ till date. The purpose of the current study is to scrutinize the deleterious missense variants in PKC_ɩ and determine the effect of these variants on stability and dynamics of the protein. The structure of protein PKC_ɩ was predicted for the first time and post translational modifications were determined. Genetic variants of PKC_ɩ were retrieved from ENSEMBL and only missense variants were further analyzed because of its linkage with diseases. The pathogenicity of missense variants, effect on structure and function of protein, association with cancer and conservancy of the protein residues were determined through computational approaches. It is observed that C1 and the pseudo substrate region has the highest number of pathogenic SNPs. Variations in the kinase domain of the protein are predicted to alter overall phosphorylation of the protein. Molecular dynamic simulations predicted noteworthy change in structural and functional dynamics of the protein because of these variants. The study revealed that nine deleterious variants can possibly contribute to malfunctioning of the protein and can be associated with diseases. This can be useful in diagnostics and developing therapeutics for diseases related to these polymorphisms.

Automated synthesis of 18F radiolabelled indole containing Oncrasin-like molecules; a comparison of iodonium salts and boronic ester chemistry

Background

Oncrasin-1 is a small molecule which was identified from a screen of KRAS mutant cancer cells and has shown specificity for KRAS mutant cell killing. We aimed to develop a radiolabelled form of Oncrasin-1 to enable in-vivo imaging of mutant KRAS expression in malignant tumours. This work outlines the synthesis of 3 fluorinated derivatives and development of iodonium salt and boronic ester precursors for radiolabelling with the ¹⁸F isotope.

Results

In our hands, synthesis of iodonium salts were not easily accessible due to the 3-carbaldehyde indole structure being preferentially oxidized by conditions required for iodonium salt formation, rather than benzyl iodide. Synthesis and radiolabelling of boronic acid pinacol ester precursors were successful, with the products being obtained in yields of 10.76% ± 0.96% (n = 5), 14.7% ±8.58% (n = 3) and 14.92% ±3.9% (n = 3) for ¹⁸F KAM001, ¹⁸F KAM002 and ¹⁸F KAM003 respectively, with radiochemical purity of greater than 99%.

Conclusions

The successful synthesis of these tracers has been undertaken utilizing boronic ester radio-fluorination methods and will allow for investigation of Oncrasin based molecules as potential diagnostics for cancers expressing mutant KRAS protein.

Supplementary Information

Supplementary information accompanies this paper at 10.1186/s41181-020-00104-x.

Design, synthesis, and evaluation of novel N'-substituted-1-(4-chlorobenzyl)-1H-indol-3-carbohydrazides as antitumor agents

In continuity of our search for novel anticancer agents acting as procaspase activators, we have designed and synthesised two series of (E)-N′-benzylidene-carbohydrazides (4a–m) and (Z)-N'-(2-oxoindolin-3-ylidene)carbohydrazides (5a–g) incorporating 1-(4-chlorobenzyl)-1H-indole core. Bioevaluation showed that the compounds, especially compounds in series 4a–m, exhibited potent cytotoxicity against three human cancer cell lines (SW620, colon cancer; PC-3, prostate cancer; NCI-H23, lung cancer). Within series 4a–m, compounds with 2-OH substituent (4g–i) exhibited very strong cytotoxicity in three human cancer cell lines assayed with IC₅₀ values in the range of 0.56–0.83 µM. In particular, two compounds 4d and 4f bearing 4-Cl and 4-NO₂ substituents, respectively, were the most potent in term of cytotoxicity with IC₅₀ values of 0.011–0.001 µM. In caspase activation assay, compounds 4b and 4f were found to activate caspase activity by 314.3 and 270.7% relative to PAC-1. This investigation has demonstrated the potential of these simple acetohydrazides, especially compounds 4b, 4d, and 4f, as anticancer agents.

Addiction to protein kinase Cɩ due to PRKCI gene amplification can be exploited for an aptamer-based targeted therapy in ovarian cancer

PRKCI, the gene for protein kinase Cι (PKCι), is frequently amplified in ovarian cancer and recent studies have shown that PKCι participates in ovary tumorigenesis. However, it is unknown whether PKCι is differentially involved in the growth/survival between PRKCI-amplified and non-amplified ovarian cancer cells. In this study, we analyzed ovarian cancer patient dataset and revealed that PRKCI is the only PKC family member significantly amplified in ovarian cancer and PRKCI amplification is associated with higher PKCι expression. Using a panel of ovarian cancer cell lines, we found that abundance of PKCι is generally associated with PRKCI amplification. Interestingly, silencing PKCι led to apoptosis in PRKCI-amplified ovarian cancer cells but not in those without PRKCI amplification, thus indicating an oncogenic addiction to PKCɩ in PRKCI-amplified cells. Since small-molecule inhibitors characterized to selectively block atypical PKCs did not offer selectivity nor sensitivity in PRKCI-amplified ovarian cancer cells and were even cytotoxic to non-cancerous ovary surface or fallopian tube epithelial cells, we designed an EpCAM aptamer-PKCι siRNA chimera (EpCAM-siPKCι aptamer). EpCAM-siPKCι aptamer not only effectively induced apoptosis of PRKCI-amplified ovarian cancer cells but also greatly deterred intraperitoneal tumor development in xenograft mouse model. This study has demonstrated a precision medicine-based strategy to target a subset of ovarian cancer that contains PRKCI amplification and shown that the EpCAM aptamer-delivered PKCι siRNA may be used to suppress such tumors.

Regulation of the Ras-Related Signaling Pathway by Small Molecules Containing an Indole Core Scaffold: A Potential Antitumor Therapy

The Ras-Related signaling pathway plays an important role in cell development and differentiation. A growing body of evidence collected in recent years has shown that the aberrant activation of Ras is associated with tumor-related processes. Several studies have indicated that indole and its derivatives can target regulatory factors and interfere with or even block the aberrant Ras-Related pathway to treat or improve malignant tumors. In this review, we summarize the roles of indole and its derivatives in the isoprenylcysteine carboxyl methyltransferase-participant Ras membrane localization signaling pathway and Ras-GTP/Raf/MAPK signaling pathway through their regulatory mechanisms. Moreover, we briefly discuss the current treatment strategies that target these pathways. Our review will help guide the further study of the application of Ras-Related signaling pathway inhibitors.

Thermal Proteome Profiling Identifies Oxidative-Dependent Inhibition of the Transcription of Major Oncogenes as a New Therapeutic Mechanism for Select Anticancer Compounds

Identification of the molecular mechanism of action (MoA) of bioactive compounds is a crucial step for drug development but remains a challenging task despite recent advances in technology. In this study, we applied multidimensional proteomics, sensitivity correlation analysis, and transcriptomics to identify a common MoA for the anticancer compounds RITA, aminoflavone (AF), and oncrasin-1 (Onc-1). Global thermal proteome profiling revealed that the three compounds target mRNA processing and transcription, thereby attacking a cancer vulnerability, transcriptional addiction. This led to the preferential loss of expression of oncogenes involved in PDGF, EGFR, VEGF, insulin/IGF/MAPKK, FGF, Hedgehog, TGFβ, and PI3K signaling pathways. Increased reactive oxygen species level in cancer cells was a prerequisite for targeting the mRNA transcription machinery, thus conferring cancer selectivity to these compounds. Furthermore, DNA repair factors involved in homologous recombination were among the most prominently repressed proteins. In cancer patient samples, RITA, AF, and Onc-1 sensitized to poly(ADP-ribose) polymerase inhibitors both in vitro and ex vivo These findings might pave a way for new synthetic lethal combination therapies.Significance: These findings highlight agents that target transcriptional addiction in cancer cells and suggest combination treatments that target RNA processing and DNA repair pathways simultaneously as effective cancer therapies.

Synthetic Lethality in Lung Cancer-From the Perspective of Cancer Genomics

Cancer is a genetic disease, and this concept is now widely exploited by both scientists and clinicians to develop new genotype-selective anticancer therapeutics. Although the quest of cancer genomics is in its dawn, recognition of the widespread applicability of genetic interactions with biological processes of tumorigenesis is propelling research throughout academic fields. Lung cancer is the most common cause of cancer death worldwide, with an estimated 1.6 million deaths each year. Despite the development of targeted therapies that inhibit oncogenic mutations of lung cancer cases, continued research into new therapeutic approaches is required for untreatable lung cancer patients, and the development of therapeutic modalities has proven elusive. The "synthetic lethal" approach holds the promise of delivering a therapeutic regimen that preferentially targets malignant cells while sparing normal cells. We highlight the potential challenges in synthetic lethal anticancer therapeutics that target untreatable genetic alterations in lung cancer. We also discuss both challenges and opportunities regarding the application of new synthetic lethal interactions in lung cancer.

Inhibition of Thioredoxin/Thioredoxin Reductase Induces Synthetic Lethality in Lung Cancers with Compromised Glutathione Homeostasis

Glutathione (GSH)/GSH reductase (GSR) and thioredoxin/thioredoxin reductase (TXNRD) are two major compensating thiol-dependent antioxidant pathways that maintain protein dithiol/disulfide balance. We hypothesized that functional deficiency in one of these systems would render cells dependent on compensation by the other system for survival, providing a mechanism-based synthetic lethality approach for treatment of cancers. The human GSR gene is located on chromosome 8p12, a region frequently lost in human cancers. GSR deletion was detected in about 6% of lung adenocarcinomas in The Cancer Genome Atlas database. To test whether loss of GSR sensitizes cancer cells to TXNRD inhibition, we knocked out or knocked down the GSR gene in human lung cancer cells and evaluated their response to the TXNRD inhibitor auranofin. GSR deficiency sensitized lung cancer cells to this agent. Analysis of a panel of 129 non-small cell lung cancer (NSCLC) cell lines revealed that auranofin sensitivity correlated with the expression levels of the GSR, glutamate-cysteine ligase catalytic subunit (GCLC), and NAD(P)H quinone dehydrogenase 1 (NQO1) genes. In NSCLC patient-derived xenografts with reduced expression of GSR and/or GCLC, growth was significantly suppressed by treatment with auranofin. Together, these results provide a proof of concept that cancers with compromised expression of enzymes required for GSH homeostasis or with chromosome 8p deletions that include the GSR gene may be targeted by a synthetic lethality strategy with inhibitors of TXNRD. SIGNIFICANCE: These findings demonstrate that lung cancers with compromised expression of enzymes required for glutathione homeostasis, including reduced GSR gene expression, may be targeted by thioredoxin/thioredoxin reductase inhibitors.

A novel three-dimensional high-throughput screening approach identifies inducers of a mutant KRAS selective lethal phenotype

The RAS proteins are the most frequently mutated oncogenes in cancer, with highest frequency found in pancreatic, lung, and colon tumors. Moreover, the activity of RAS is required for the proliferation and/or survival of these tumor cells and thus represents a high-value target for therapeutic development. Direct targeting of RAS has proven challenging for multiple reasons stemming from the biology of the protein, the complexity of downstream effector pathways and upstream regulatory networks. Thus, significant efforts have been directed at identifying downstream targets on which RAS is dependent. These efforts have proven challenging, in part due to confounding factors such as reliance on two-dimensional adherent monolayer cell cultures that inadequately recapitulate the physiologic context to which cells are exposed in vivo.  To overcome these issues, we implemented a High Throughput Screening (HTS) approach using a spheroid-based 3-dimensional culture format, thought to more closely reflect conditions experienced by cells in vivo. Using isogenic cell pairs, differing in the status of KRAS, we identified Proscillaridin A as a selective inhibitor of cells harboring the oncogenic KRas^G12V allele. Significantly, the identification of Proscillaridin A was facilitated by the 3D screening platform and would not have been discovered employing standard 2D culturing methods.

Anti-leukemia activity of NSC-743380 in SULT1A1-expressing acute myeloid leukemia cells is associated with inhibitions of cFLIP expression and PI3K/AKT/mTOR activities

Our recent study showed that acute myeloid leukemia (AML) cells expressing SULT1A1 are highly sensitive to NSC-743380, a small molecule that inhibits STAT3 activity and induces SULT1A1-dependent apoptosis of various cancer cell lines. In this study, we characterized the molecular mechanisms of NSC-743380-mediated anti-leukemia activity in AML cell lines and antileukemia activity of NSC-743380 in patient-derived primary leukemia cells from AML patients. Our results showed that treatment with NSC-743380 triggered robust apoptosis in SULT1A1-positive AML cells. Treatment with NSC-743380 did not increase intracellular reactive oxygen species or change of STAT3 activity in AML cells, but did dramatically and rapidly decrease cFLIP expression. Proteomic analysis with reverse phase protein microarray revealed that treatment of U937 and THP-1 AML cells with NSC-743380 led to drastic and time-dependent suppression of phosphorylation of several key nodes in the PI3K/AKT/mTOR pathway, including AKT and mTOR. Moreover, primary AML cells expressed SULT1A1 were highly sensitive to treatment with NSC-743380, which was not affected by co-culture with bone marrow mesenchymal stem cells. Thus, our results provide proof-of-concept evidence that AML cells expressing SULT1A1 can be targeted by small molecules that induce apoptosis through inhibiting the expression or activities of multiple targets.

Simultaneous determination and validation of oncrasin-266 and its metabolites by HPLC-MS/MS: Application to a pharmacokinetic study

Oncrasins are a class of RNA polymerase II inhibitors. Oncrasin-72 is an indole-3 carbinol analog that has shown to inhibit growth and induce the cell death of various human cancer cell lines. Oncrasin-266, a prodrug of oncrasin-72, has been shown to have improved pharmacokinetic properties and safety than Oncrasin-72. With respect to the potential therapeutic advantages of this class of compounds, there is a need for further preclinical assessment for future clinical trials. The development of and validation of an analytical method is essential for the quantification of oncrasins in biological fluids for pharmacokinetic studies. This study focuses on the HPLC-MS/MS method development and validation of oncrasin-266, oncrasin-72 and its aldehyde metabolite in rat plasma. Blank rat plasma, coupled with 1-(3-chlorobenzyl)-1H-indole, as internal standard, was used for generating standard curves ranging from 1 to 250ng/mL for oncrasin-266 and oncrasin-72; and 0.5-125ng/mL for the aldehyde metabolite. The chromatographic separation was achieved by a Zorbax 300SB-C18 HPLC column at 50°C with a flow rate of 1.1mL/min under gradient elution. Mass detection was performed under positive ionization electrospray. Intra- and inter-day accuracy and precision of the assay were less than 10%. We report a simple, specific and reproducible HPLC-MS/MS method for the quantification of oncrasins in rat plasma. This study was successfully used for the quantification of oncrasins in rat plasma for pharmacokinetic studies in three dose groups of 10, 25, and 50mg/kg via intravenous administration.

Synthetic lethality in lung cancer and translation to clinical therapies

Lung cancer is a heterogeneous disease consisting of multiple histological subtypes each driven by unique genetic alterations. Despite the development of targeted therapies that inhibit the oncogenic mutations driving a subset of lung cancer cases, there is a paucity of effective treatments for the majority of lung cancer patients and new strategies are urgently needed. In recent years, the concept of synthetic lethality has been established as an effective approach for discovering novel cancer-specific targets as well as a method to improve the efficacy of existing drugs which provide partial but insufficient benefits for patients. In this review, we discuss the concept of synthetic lethality, the various types of synthetic lethal interactions in the context of oncology and the approaches used to identify these interactions, including recent advances that have transformed the ability to discover novel synthetic lethal combinations on a global scale. Lastly, we describe the specific synthetic lethal interactions identified in lung cancer to date and explore the pharmacological challenges and considerations in translating these discoveries to the clinic.

Aphanin, a triterpenoid from Amoora rohituka inhibits K-Ras mutant activity and STAT3 in pancreatic carcinoma cells

Mutations of the K-Ras gene occur in over 90 % of pancreatic carcinomas, and to date, no targeted therapies exist for this genetically defined subset of cancers. STAT3 plays a critical role in KRAS-driven pancreatic tumorigenesis, suggesting its potential as a therapeutic target in this cancer. Therefore, finding novel and potential drugs to inhibit oncogenic K-Ras is a major challenge in cancer therapy. In an attempt to develop novel anti-KRAS mutant chemotherapeutics, we isolated three novel triterpenoids from Amoora rohituka stem and their chemical structures were characterized by extensive 1H-NMR, 13C-NMR, Mass, IR spectroscopic studies and chemical transformations. Aphanin (3 alpha-angeloyloxyolean-12-en-28-oic acid) is one of the isolated novel triterpenoid compounds. We found aphanin exhibited antiproliferative effects, caused G0-G1 cell cycle arrest, inhibits K-Ras G12D mutant activity by decreased STAT3, p-STAT3, Akt, p-Akt, cyclin D1 and c-Myc expressions, and induced apoptosis in pancreatic cancer HPAF-II (ΔKRAS G12D ) cells. The apoptosis proceeded through depletion of GSH with a concomitant increase in the reactive oxygen species production. The results of our study have important implications for the development of aphanin as potential novel agent for the treatment of K-Ras mutant pancreatic cancer, and STAT3-cMyc-cyclinD1 axis may serve as an important predictive biomarker for the therapeutic efficacy.

Defeat mutant KRAS with synthetic lethality

Ras proteins are considered as the founding members of a large superfamily of small GTPases that control fundamental cellular functions. Mutationally activated RAS genes were discovered in human cancer cells more than 3 decades ago, but intensive efforts on Ras structure, biochemistry, function and signaling continue even now. Because mutant Ras proteins are inherently difficult to inhibit and have yet been therapeutically conquered, it was designated as “the Everest of oncogenes” in the cancer genome landscape, further promoting a “renaissance” in RAS research. Different paths to directly or indirectly targeting mutant Ras signaling are currently under investigation in the hope of finding an efficacious regimen. Inhibitors directly binding to KRAS^G12C to block its downstream signaling have been revealed, supporting the notion of Ras' druggability. An alternative indirect approach by targeting synthetic lethal interactors of mutant RAS is underway. We recently employed a synthetic lethal drug screen plus a combinatorial strategy using a panel of clinical agents and discovered that KRAS-mutant cancers were fragile to the combined inhibition of polo-like kinase 1 (Plk1) and RhoA/Rho kinase (ROCK). The combined regimen of BI-2536 (a Plk1 inhibitor) and fasudil (a ROCK inhibitor) promoted a significant inhibition of patient-derived lung cancer xenografts and prolonged the survival of LSL-KRAS^G12D mice. In this commentary, we will summarize the state-of-the art for the direction of synthetic lethality, and also speculate on the future development of this approach.

Cancer of the Pancreas: Molecular Pathways and Current Advancement in Treatment

Pancreatic cancer is one of the most lethal cancers among all malignances, with a median overall survival of <1 year and a 5-year survival of ~5%. The dismal survival rate and prognosis are likely due to lack of early diagnosis, fulminant disease course, high metastasis rate, and disappointing treatment outcome. Pancreatic cancers harbor a variety of genetic alternations that render it difficult to treat even with targeted therapy. Recent studies revealed that pancreatic cancers are highly enriched with a cancer stem cell (CSC) population, which is resistant to chemotherapeutic drugs, and therefore escapes chemotherapy and promotes tumor recurrence. Cancer cell epithelial to mesenchymal transition (EMT) is highly associated with metastasis, generation of CSCs, and treatment resistance in pancreatic cancer. Reviewed here are the molecular biology of pancreatic cancer, the major signaling pathways regulating pancreatic cancer EMT and CSCs, and the advancement in current clinical and experimental treatments for pancreatic cancer.

Synthetic Lethality of a Novel Small Molecule Against Mutant KRAS-Expressing Cancer Cells Involves AKT-Dependent ROS Production

AIMS

We recently reported the death-inducing activity of a small-molecule compound, C1, which triggered reactive oxygen species (ROS)-dependent autophagy-associated apoptosis in a variety of human cancer cell lines. In this study, we examine the ability of the compound to specifically target cancer cells harboring mutant KRAS with minimal activity against wild-type (WT) RAS-expressing cells.

RESULTS

HCT116 cells expressing mutated KRAS are susceptible, while the WT-expressing HT29 cells are resistant. Interestingly, C1 triggers activation of mutant RAS, which results in the downstream phosphorylation and activation of AKT/PKB. Gene knockdown of KRAS or AKT or their pharmacological inhibition resulted in the abrogation of C1-induced ROS production and rescued tumor colony-forming ability. We also made use of HCT116 mutant KRAS knockout (KO) cells, which express only a single WT KRAS allele. Exposure of KO cells to C1 failed to increase mitochondrial ROS and cell death, unlike the parental cells harboring mutant KRAS. Similarly, mutant KRAS-transformed prostate epithelial cells (RWPE-1-RAS) were more sensitive to the ROS-producing and death-inducing effects of C1 than the vector only expressing RWPE-1 cells. An in vivo model of xenograft tumors generated with HCT116 KRAS(WT/MUT) or KRAS(WT/-) cells showed the efficacy of C1 treatment and its ability to affect the relative mitotic index in tumors harboring KRAS mutant.

INNOVATION AND CONCLUSION

These data indicate a synthetic lethal effect against cells carrying mutant KRAS, which could have therapeutic implications given the paucity of KRAS-specific chemotherapeutic strategies. Antioxid. Redox Signal. 24, 781-794.

Pharmacological modulation of oncogenic Ras by natural products and their derivatives: Renewed hope in the discovery of novel anti-Ras drugs

Oncogenic rat sarcoma (Ras) is linked to the most fatal cancers such as those of the pancreas, colon, and lung. Decades of research to discover an efficacious drug that can block oncogenic Ras signaling have yielded disappointing results; thus, Ras was considered "undruggable" until recently. Inhibitors that directly target Ras by binding to previously undiscovered pockets have been recently identified. Some of these molecules are either isolated from natural products or derived from natural compounds. In this review, we described the potential of these compounds and other inhibitors of Ras signaling in drugging Ras. We highlighted the modes of action of these compounds in suppressing signaling pathways activated by oncogenic Ras, such as mitogen-activated protein kinase (MAPK) signaling and the phosphoinositide-3-kinase (PI3K) pathways. The anti-Ras strategy of these compounds can be categorized into four main types: inhibition of Ras-effector interaction, interference of Ras membrane association, prevention of Ras-guanosine triphosphate (GTP) formation, and downregulation of Ras proteins. Another promising strategy that must be validated experimentally is enhancement of the intrinsic Ras-guanosine triphosphatase (GTPase) activity by small chemical entities. Among the inhibitors of Ras signaling that were reported thus far, salirasib and TLN-4601 have been tested for their clinical efficacy. Although both compounds passed phase I trials, they failed in their respective phase II trials. Therefore, new compounds of natural origin with relevant clinical activity against Ras-driven malignancies are urgently needed. Apart from salirasib and TLN-4601, some other compounds with a proven inhibitory effect on Ras signaling include derivatives of salirasib, sulindac, polyamine, andrographolide, lipstatin, levoglucosenone, rasfonin, and quercetin.

Protein Kinase Cι Drives a NOTCH3-dependent Stem-like Phenotype in Mutant KRAS Lung Adenocarcinoma

We report that the protein kinase Cι (PKCι) oncogene controls expression of NOTCH3, a key driver of stemness, in KRAS-mediated lung adenocarcinoma (LADC). PKCι activates NOTCH3 expression by phosphorylating the ELF3 transcription factor and driving ELF3 occupancy on the NOTCH3 promoter. PKCι-ELF3-NOTCH3 signaling controls the tumor-initiating cell phenotype by regulating asymmetric cell division, a process necessary for tumor initiation and maintenance. Primary LADC tumors exhibit PKCι-ELF3-NOTCH3 signaling, and combined pharmacologic blockade of PKCι and NOTCH synergistically inhibits tumorigenic behavior in vitro and LADC growth in vivo demonstrating the therapeutic potential of PKCι-ELF3-NOTCH3 signal inhibition to more effectively treat KRAS LADC.

Expression of sulfotransferase SULT1A1 in cancer cells predicts susceptibility to the novel anticancer agent NSC-743380

The small molecule anticancer agent NSC-743380 modulates functions of multiple cancer-related pathways and is highly active in a subset of cancer cell lines in the NCI-60 cell line panel. It also has promising in vivo anticancer activity. However, the mechanisms underlying NSC-743380's selective anticancer activity remain uncharacterized. To determine biomarkers that may be used to identify responders to this novel anticancer agent, we performed correlation analysis on NSC-743380's anticancer activity and the gene expression levels in NCI-60 cell lines and characterized the functions of the top associated genes in NSC-743380–mediated anticancer activity. We found sulfotransferase SULT1A1 is causally associated with NSC-743380's anticancer activity. SULT1A1 was expressed in NSC-743380–sensitive cell lines but was undetectable in resistant cancer cells. Ectopic expression of SULT1A1 in NSC743380 resistant cancer cells dramatically sensitized the resistant cells to NSC-743380. Knockdown of the SULT1A1 in the NSC-743380 sensitive cancer cell line rendered it resistance to NSC-743380. The SULT1A1 protein levels in cell lysates from 18 leukemia cell lines reliably predicted the susceptibility of the cell lines to NSC-743380. Thus, expression of SULT1A1 in cancer cells is required for NSC-743380's anticancer activity and can be used as a biomarker for identification of NSC-743380 responders.

RAS signaling and anti-RAS therapy: lessons learned from genetically engineered mouse models, human cancer cells, and patient-related studies

Activating mutations of oncogenic RAS genes are frequently detected in human cancers. The studies in genetically engineered mouse models (GEMMs) reveal that Kras-activating mutations predispose mice to early onset tumors in the lung, pancreas, and gastrointestinal tract. Nevertheless, most of these tumors do not have metastatic phenotypes. Metastasis occurs when tumors acquire additional genetic changes in other cancer driver genes. Studies on clinical specimens also demonstrated that KRAS mutations are present in premalignant tissues and that most of KRAS mutant human cancers have co-mutations in other cancer driver genes, including TP53, STK11, CDKN2A, and KMT2C in lung cancer; APC, TP53, and PIK3CA in colon cancer; and TP53, CDKN2A, SMAD4, and MED12 in pancreatic cancer. Extensive efforts have been devoted to develop therapeutic agents that target enzymes involved in RAS posttranslational modifications, that inhibit downstream effectors of RAS signaling pathways, and that kill RAS mutant cancer cells through synthetic lethality. Recent clinical studies have revealed that sorafenib, a pan-RAF and VEGFR inhibitor, has impressive benefits for KRAS mutant lung cancer patients. Combination therapy of MEK inhibitors with either docetaxel, AKT inhibitors, or PI3K inhibitors also led to improved clinical responses in some KRAS mutant cancer patients. This review discusses knowledge gained from GEMMs, human cancer cells, and patient-related studies on RAS-mediated tumorigenesis and anti-RAS therapy. Emerging evidence demonstrates that RAS mutant cancers are heterogeneous because of the presence of different mutant alleles and/or co-mutations in other cancer driver genes. Effective subclassifications of RAS mutant cancers may be necessary to improve patients' outcomes through personalized precision medicine.

Predictive biomarkers in precision medicine and drug development against lung cancer

The molecular characterization of various cancers has shown that cancers with the same origins, histopathologic diagnoses, and clinical stages can be highly heterogeneous in their genetic and epigenetic alterations that cause tumorigenesis. A number of cancer driver genes with functional abnormalities that trigger malignant transformation and that are required for the survival of cancer cells have been identified. Therapeutic agents targeting some of these cancer drivers have been successfully developed, resulting in substantial improvements in clinical symptom amelioration and outcomes in a subset of cancer patients. However, because such therapeutic drugs often benefit only a limited number of patients, the successes of clinical development and applications rely on the ability to identify those patients who are sensitive to the targeted therapies. Thus, biomarkers that can predict treatment responses are critical for the success of precision therapy for cancer patients and of anticancer drug development. This review discusses the molecular heterogeneity of lung cancer pathogenesis; predictive biomarkers for precision medicine in lung cancer therapy with drugs targeting epidermal growth factor receptor (EGFR), anaplastic lymphoma kinase (ALK), c-ros oncogene 1 receptor tyrosine kinase (ROS1), and immune checkpoints; biomarkers associated with resistance to these therapeutics; and approaches to identify predictive biomarkers in anticancer drug development. The identification of predictive biomarkers during anticancer drug development is expected to greatly facilitate such development because it will increase the chance of success or reduce the attrition rate. Additionally, such identification will accelerate the drug approval process by providing effective patient stratification strategies in clinical trials to reduce the sample size required to demonstrate clinical benefits.

Anti-lung cancer potential of pure esteric-glycoside condurangogenin A against nonsmall-cell lung cancer cells in vitro via p21/p53 mediated cell cycle modulation and DNA damage-induced apoptosis

BACKGROUND

Marsdenia condurango (condurango) is a tropical woody vine native to South America. Our earlier study was limited to evaluation of anti-cancer potentials of crude condurango extract and its glycoside-rich components in vitro on lung cancer.

OBJECTIVE

This study aims at evaluating the effect of the single isolated active ingredient condurangogenin A (ConA; C32H42O7) on A549, H522 and H460-nonsmall-cell lung cancer cells.

MATERIALS AND METHODS

ConA was isolated by column chromatography and analyzed by mass spectroscopy, Fourier transform infrared spectroscopy and proton-nuclear magnetic resonance. diphenyltetrazolium bromide assays were conducted on three cell-types using 6%-alcohol as control. Critical studies on cellular morphology, cell-cycle regulation, reactive oxygen species, mitochondrial membrane potential, and DNA-damage were made, and expressions of related signaling markers studied.

RESULTS

As IC50 doses of ConA proved to be too high and toxic to both A549 and H522 cells, all experimental studies were carried out on H460 cells with the IC50 dose (32 μg/ml - 24 h). Cellular morphology revealed typical apoptotic features after ConA treatment. At early treatment hours (2 h-12 h), maximum cells were arrested at G0/G1 phase that could be correlated with reduced level of cyclin D1-CDK with p21 up-regulation. At 18 h - 24 h, sub G0/G1 cell population was increased gradually, as revealed from cytochrome-c release and caspase-3 activation, further confirming the apoptosis-inducing ability of ConA at later phases. Gradual increase of TUNEL-positive cells with significant modulation of mitochondria-dependent apoptotic markers at longer time-points would establish apoptosis-induction property of ConA, indicating its potential as a strong candidate for anti-cancer drug formulation.

CONCLUSION

Further studies are warranted against other types of cancer cells and animal models before its possible human use.

Prodrug oncrasin-266 improves the stability, pharmacokinetics, and safety of NSC-743380

Through synthetic lethality screening of isogenic cell lines with and without the oncogenic KRAS gene and through lead compound optimization, we recently developed a novel anticancer agent designated NSC-743380 (oncrasin-72) that has promising in vitro and in vivo anticancer activity in a subset of cancer cell lines, including KRAS-mutant cancer cells. However, NSC-743380 tends to form dimers, which dramatically reduces its anticancer activity. To improve the physicochemical properties of NSC-743380, we synthesized a prodrug of NSC-743380, designated oncrasin-266, by modifying NSC-743380 with cyclohexylacetic acid and evaluated its in vitro and in vivo properties. Oncrasin-266 spontaneously hydrolyzed in phosphate-buffered saline in a time-dependent manner and was more stable than NSC-743380 in powder or stock solutions. In vivo administration of oncrasin-266 in mice led to the release of NSC-743380 which improved the pharmacokinetics of NSC-743380. Tissue distribution analysis revealed that oncrasin-266 was deposited in liver, whereas released NSC-743380 was detected in liver, lung, kidney, and subcutaneous tumor. Oncrasin-266 was better tolerated in mice at a higher dose level treatment (150-300 mg/kg, ip) than the parent agent was, suggesting that the prodrug reduced the acute toxicity of the parent agent. Our results demonstrated that the prodrug strategy could improve the stability, pharmacokinetic properties, and safety of NSC-743380.

Strategies to overcome resistance to epidermal growth factor receptor monoclonal antibody therapy in metastatic colorectal cancer

Administration of monoclonal antibodies (mAbs) against epidermal growth factor receptor (EGFR) such as cetuximab and panitumumab in combination with conventional chemotherapy substantially prolongs survival of patients with metastatic colorectal cancer (mCRC). However, the efficacy of these mAbs is limited due to genetic variation among patients, in particular K-ras mutations. The discovery of K-ras mutation as a predictor of non-responsiveness to EGFR mAb therapy has caused a major change in the treatment of mCRC. Drugs that inhibit transformation caused by oncogenic alterations of Ras and its downstream components such as BRAF, MEK and AKT seem to be promising cancer therapeutics as single agents or when given with EGFR inhibitors. Although multiple therapeutic strategies to overcome EGFR mAb-resistance are under investigation, our understanding of their mode of action is limited. Rational drug development based on stringent preclinical data, biomarker validation, and proper selection of patients is of paramount importance in the treatment of mCRC. In this review, we will discuss diverse approaches to overcome the problem of resistance to existing anti-EGFR therapies and potential future directions for cancer therapies related to the mutational status of genes associated with EGFR-Ras-ERK and PI3K signalings.

Development of synthetic lethality anticancer therapeutics

The concept of synthetic lethality (the creation of a lethal phenotype from the combined effects of mutations in two or more genes) has recently been exploited in various efforts to develop new genotype-selective anticancer therapeutics. These efforts include screening for novel anticancer agents, identifying novel therapeutic targets, characterizing mechanisms of resistance to targeted therapy, and improving efficacies through the rational design of combination therapy. This review discusses recent developments in synthetic lethality anticancer therapeutics, including poly ADP-ribose polymerase inhibitors for BRCA1- and BRCA2-mutant cancers, checkpoint inhibitors for p53 mutant cancers, and small molecule agents targeting RAS gene mutant cancers. Because cancers are caused by mutations in multiple genes and abnormalities in multiple signaling pathways, synthetic lethality for a specific tumor suppressor gene or oncogene is likely cell context-dependent. Delineation of the mechanisms underlying synthetic lethality and identification of treatment response biomarkers will be critical for the success of synthetic lethality anticancer therapy.

Protein Kinase C (PKC) Isozymes and Cancer

Protein kinase C (PKC) is a family of phospholipid-dependent serine/threonine kinases, which can be further classified into three PKC isozymes subfamilies: conventional or classic, novel or nonclassic, and atypical. PKC isozymes are known to be involved in cell proliferation, survival, invasion, migration, apoptosis, angiogenesis, and drug resistance. Because of their key roles in cell signaling, PKC isozymes also have the potential to be promising therapeutic targets for several diseases, such as cardiovascular diseases, immune and inflammatory diseases, neurological diseases, metabolic disorders, and multiple types of cancer. This review primarily focuses on the activation, mechanism, and function of PKC isozymes during cancer development and progression.

Novel synthetic oleanane triterpenoid AMR-MeOAc inhibits K-Ras through ERK, Akt and survivin in pancreatic cancer cells

K-Ras activating mutations are a major problem that drives aggressive tumor growth and metastasis in pancreatic cancer. Currently, there are no effective targeted therapies for this genetically defined subset of cancers harboring oncogenic K-Ras mutations that confer drug resistance, aggressive tumor growth, metastasis and poor clinical outcome. We identified a novel synthetic oleanane triterpenoid compound designated AMR-MeOAc that effectively kills K-Ras mutant pancreatic cancer HPAF-II cells. The cytotoxic effects correlated with apoptosis induction, as was evidenced by increase of apoptosis cells upon the treatment of AMR-MeOAc in HPAF-II cells. Our studies revealed that AMR-MeOAc treatment inhibits cancer associated survival gene survivin. Moreover, AMR-MeOAc also led to down regulation of Akt, ERK1/2 and survivin protein levels. Our results indicate that AMR-MeOAc or its active analogs could be a novel class of anticancer agents against K-Ras driven human pancreatic cancer.

Genetic Interactions of STAT3 and Anticancer Drug Development

Signal transducer and activator of transcription 3 (STAT3) plays critical roles in tumorigenesis and malignant evolution and has been intensively studied as a therapeutic target for cancer. A number of STAT3 inhibitors have been evaluated for their antitumor activity in vitro and in vivo in experimental tumor models and several approved therapeutic agents have been reported to function as STAT3 inhibitors. Nevertheless, most STAT3 inhibitors have yet to be translated to clinical evaluation for cancer treatment, presumably because of pharmacokinetic, efficacy, and safety issues. In fact, a major cause of failure of anticancer drug development is lack of efficacy. Genetic interactions among various cancer-related pathways often provide redundant input from parallel and/or cooperative pathways that drives and maintains survival environments for cancer cells, leading to low efficacy of single-target agents. Exploiting genetic interactions of STAT3 with other cancer-related pathways may provide molecular insight into mechanisms of cancer resistance to pathway-targeted therapies and strategies for development of more effective anticancer agents and treatment regimens. This review focuses on functional regulation of STAT3 activity; possible interactions of the STAT3, RAS, epidermal growth factor receptor, and reduction-oxidation pathways; and molecular mechanisms that modulate therapeutic efficacies of STAT3 inhibitors.

Regulation of polarized morphogenesis by protein kinase C iota in oncogenic epithelial spheroids

Protein kinase C iota (PKCι), a serine/threonine kinase required for cell polarity, proliferation and migration, is commonly up- or downregulated in cancer. PKCι is a human oncogene but whether this is related to its role in cell polarity and what repertoire of oncogenes acts in concert with PKCι is not known. We developed a panel of candidate oncogene expressing Madin-Darby canine kidney (MDCK) cells and demonstrated that H-Ras, ErbB2 and phosphatidylinositol 3-kinase transformation led to non-polar spheroid morphogenesis (dysplasia), whereas MDCK spheroids expressing c-Raf or v-Src were largely polarized. We show that small interfering RNA (siRNA)-targeting PKCι decreased the size of all spheroids tested and partially reversed the aberrant polarity phenotype in H-Ras and ErbB2 spheroids only. This indicates distinct requirements for PKCι and moreover that different thresholds of PKCι activity are required for these phenotypes. By manipulating PKCι function using mutant constructs, siRNA depletion or chemical inhibition, we have demonstrated that PKCι is required for polarization of parental MDCK epithelial cysts in a 3D matrix and that there is a threshold of PKCι activity above and below which, disorganized epithelial morphogenesis results. Furthermore, treatment with a novel PKCι inhibitor, CRT0066854, was able to restore polarized morphogenesis in the dysplastic H-Ras spheroids. These results show that tightly regulated PKCι is required for normal-polarized morphogenesis in mammalian cells and that H-Ras and ErbB2 cooperate with PKCι for loss of polarization and dysplasia. The identification of a PKCι inhibitor that can restore polarized morphogenesis has implications for the treatment of Ras and ErbB2 driven malignancies.

A cancer-associated mutation in atypical protein kinase Cι occurs in a substrate-specific recruitment motif

Atypical protein kinase Cι (PKCι) has roles in cell growth, cellular polarity, and migration, and its abundance is frequently increased in cancer. We identified a protein interaction surface containing a dibasic motif (RIPR) that bound a distinct subset of PKCι substrates including lethal giant larvae 2 (LLGL2) and myosin X, but not other substrates such as Par3. Further characterization demonstrated that Arg471 in this motif was important for binding to LLGL2, whereas Arg474 was critical for interaction with myosin X, indicating that multiple complexes could be formed through this motif. A somatic mutation of the dibasic motif (R471C) was the most frequent mutation of PKCι in human cancer, and the intact dibasic motif was required for normal polarized epithelial morphogenesis in three-dimensional cysts. Thus, the R471C substitution is a change-of-function mutation acting at this substrate-specific recruitment site to selectively disrupt the polarizing activity of PKCι.

Targeted regulation of PI3K/Akt/mTOR/NF-κB signaling by indole compounds and their derivatives: mechanistic details and biological implications for cancer therapy

Indole compounds, found in cruciferous vegetables, are potent anti-cancer agents. Studies with indole-3-carbinol (I3C) and its dimeric product, 3,3'-diindolylmethane (DIM) suggest that these compounds have the ability to deregulate multiple cellular signaling pathways, including PI3K/Akt/mTOR signaling pathway. These natural compounds are also effective modulators of downstream transcription factor NF-κB signaling which might help explain their ability to inhibit invasion and angiogenesis, and the reversal of epithelial-to-mesenchymal transition (EMT) phenotype and drug resistance. Signaling through PI3K/Akt/mTOR and NF-κB pathway is increasingly being realized to play important role in EMT through the regulation of novel miRNAs which further validates the importance of this signaling network and its regulations by indole compounds. Here we will review the available literature on the modulation of PI3K/Akt/mTOR/NF-κB signaling by both parental I3C and DIM, as well as their analogs/derivatives, in an attempt to catalog their anticancer activity.

Targeting mutant KRAS for anticancer therapeutics: a review of novel small molecule modulators

The RAS proteins play a role in cell differentiation, proliferation, and survival. Aberrant RAS signaling has been found to play a role in 30% of all cancers. KRAS, a key member of the RAS protein family, is an attractive cancer target, as frequent point mutations in the KRAS gene render the protein constitutively active. A number of attempts have been made to target aberrant KRAS signaling by identifying small molecule compounds that (1) are synthetic lethal to mutant KRAS, (2) block KRAS/GEF interactions, (3) inhibit downstream KRAS effectors, or (4) inhibit the post-translational processing of RAS proteins. In addition, inhibition of novel targets outside the main KRAS signaling pathway, specifically the cell cycle related kinase PLK1, has been shown have an effect in cells that harbor mutant KRAS. Herein we review the use of various high-throughput screening assays utilized to identify new small-molecule compounds capable of targeting mutant KRAS-driven cancers.

Identification of cetrimonium bromide and irinotecan as compounds with synthetic lethality against NDRG1 deficient prostate cancer cells

The N-myc downstream regulated gene 1 (NDRG1) has been identified as a metastasis-suppressor gene in prostate cancer (PCa). Compounds targeting PCa cells deficient in NDRG1 could potentially decrease invasion/metastasis of PCa. A cell based screening strategy was employed to identify small molecules that selectively target NDRG1 deficient PCa cells. DU-145 PCa cells rendered deficient in NDRG1 expression by a lentiviral shRNA-mediated knockdown strategy were used in the primary screen. Compounds filtered from the primary screen were further validated through proliferation and clonogenic survival assays in parental and NDRG1 knockdown PCa cells. Screening of 3360 compounds revealed irinotecan and cetrimonium bromide (CTAB) as compounds that exhibited synthetic lethality against NDRG1 deficient PCa cells. A three-dimensional (3-D) invasion assay was utilized to test the ability of CTAB to inhibit invasion of DU-145 cells. CTAB was found to remarkably decrease invasion of DU-145 cells in collagen matrix. Our results suggest that CTAB and irinotecan could be further explored for their potential clinical benefit in patients with NDRG1 deficient PCa.

Approaches to Ras signaling modulation and treatment of Ras-dependent disorders: a patent review (2007--present)

INTRODUCTION

Ras proteins are small GTPases molecular switches that cycle through two alternative conformational states, a GDP-bound inactive state and a GTP-bound active state. In the active state, Ras proteins interact with and modulate the activity of several downstream effectors regulating key cellular processes including proliferation, differentiation, survival, senescence, migration and metabolism. Activating mutations of RAS genes and of genes encoding Ras signaling members have a great incidence in proliferative disorders, such as cancer, immune and inflammatory diseases and developmental syndromes. Therefore, Ras and Ras signaling represent important clinical targets for the design and development of pharmaceutically active agents, including anticancer agents.

AREAS COVERED

The authors summarize methods available to down-regulate the Ras pathway and review recent patents covering Ras signaling modulators, as well as methods designed to kill specifically cancer cells bearing activated RAS oncogene.

EXPERT OPINION

Targeted therapy approach based on direct targeting of molecules specifically altered in Ras-dependent diseases is pursued with molecules that down-regulate expression or inhibit the biological function of mutant Ras or Ras signaling members. The low success rate in a clinical setting of molecules targeting activated members of the Ras pathway may require development of novel approaches, including combined and synthetic lethal therapies.

Ferroptosis: an iron-dependent form of nonapoptotic cell death

Nonapoptotic forms of cell death may facilitate the selective elimination of some tumor cells or be activated in specific pathological states. The oncogenic RAS-selective lethal small molecule erastin triggers a unique iron-dependent form of nonapoptotic cell death that we term ferroptosis. Ferroptosis is dependent upon intracellular iron, but not other metals, and is morphologically, biochemically, and genetically distinct from apoptosis, necrosis, and autophagy. We identify the small molecule ferrostatin-1 as a potent inhibitor of ferroptosis in cancer cells and glutamate-induced cell death in organotypic rat brain slices, suggesting similarities between these two processes. Indeed, erastin, like glutamate, inhibits cystine uptake by the cystine/glutamate antiporter (system x(c)(-)), creating a void in the antioxidant defenses of the cell and ultimately leading to iron-dependent, oxidative death. Thus, activation of ferroptosis results in the nonapoptotic destruction of certain cancer cells, whereas inhibition of this process may protect organisms from neurodegeneration.

Killing of Kras-mutant colon cancer cells via Rac-independent actin remodeling by the βGBP cytokine, a physiological PI3K inhibitor therapeutically effective in vivo

Activating mutations in Kras are the most frequent mutations in human cancer. They define a subset of patients who do not respond to current therapies and for whom prognosis is poor. Oncogenic Kras has been shown to deregulate numerous signaling pathways of which the most intensively studied are the Ras/extracellular signal-regulated kinase cascade and the phosphoinositide 3-kinase (PI3K)/Akt cascade. However, to date, there are no effective targeted therapies in the clinic against Kras-mutant cancers. Here, we report that the β-galactoside-binding protein (βGBP) cytokine, a physiologic inhibitor of class I PI3Ks, is a potent activator of apoptosis in Kras-mutant colorectal cancer cells, even when coharboring mutant-activated PIK3CA. Our study unveils an elective route to intrinsic and extrinsic apoptosis, which involves the cytoskeleton. Early events are inhibition of PI3K activity and Rac-independent actin rearrangement assignable to phosphoinositide changes at the plasma membrane. Cyclin E deregulation, arrest of DNA synthesis, and checkpoint kinase 2 activation underscore events critical to the activation of an intrinsic apoptotic program. Clustering of CD95/Fas death receptors underscore events critical to the activation of extrinsic apoptosis. In nude mice, we present the first evidence that xenograft tumor development is strongly inhibited by Hu-r-βGBP. Taken together, our results open a new therapeutic opportunity to a subset of patients refractive to current treatments. This first demonstration of therapeutic efficacy against Kras-mutant colon cancer suggests that Hu-r-βGBP may also be therapeutically effective against other cancers harboring activating Ras mutations as well as PIK3CA mutations.

Novel tubulin polymerization inhibitors overcome multidrug resistance and reduce melanoma lung metastasis

PURPOSE

To evaluate abilities of 2-aryl-4-benzoyl-imidazoles (ABI) to overcome multidrug resistance (MDR), define their cellular target, and assess in vivo antimelanoma efficacy.

METHODS

MDR cell lines that overexpressed P-glycoprotein, MDR-associated proteins, and breast cancer resistance protein were used to evaluate ABI ability to overcome MDR. Cell cycle analysis, molecular modeling, and microtubule imaging were used to define ABI cellular target. SHO mice bearing A375 human melanoma xenograft were used to evaluate ABI in vivo antitumor activity. B16-F10/C57BL mouse melanoma lung metastasis model was used to test ABI efficacy to inhibit tumor lung metastasis.

RESULTS

ABIs showed similar potency to MDR cells compared to matching parent cells. ABIs were identified to target tubulin on the colchicine binding site. After 31 days of treatment, ABI-288 dosed at 25 mg/kg inhibited melanoma tumor growth by 69%; dacarbazine at 60 mg/kg inhibited growth by 52%. ABI-274 dosed at 25 mg/kg showed better lung metastasis inhibition than dacarbazine at 60 mg/kg.

CONCLUSIONS

This new class of antimitotic compounds can overcome several clinically important drug resistant mechanisms in vitro and are effective in inhibiting melanoma lung metastasis in vivo, supporting their further development.

Antitumor activity of a novel STAT3 inhibitor and redox modulator in non-small cell lung cancer cells

NSC-743380 is a novel STAT3 inhibitor that suppresses the growth of several NCI-60 cancer cell lines derived from different tissues and induces regression of xenograft tumors in vivo at various doses. To evaluate the antitumor activity of NSC-743380 in lung cancer cells, we analyzed the susceptibility of 50 NSCLC cell lines to this compound using cell viability assay. About 32% (16 of 50) of these cell lines were highly susceptible to this compound, with a 50% inhibitory concentration (IC₅₀) of < 1 μM. In mechanistic studies, the increased numbers of apoptotic cells as well as increased PARP cleavage showed that cytotoxic effects correlate with apoptosis induction. Treatment with NSC-743380 inhibited transcription factor STAT3 activation and induced ROS production in sensitive human lung cancer cell lines but not in resistant cells. Blocking ROS generation with the antioxidant NDGA dramatically abolished NSC-743380-induced growth suppression and apoptosis, but had minimal effect on NSC-743380-induced STAT3 inhibition, suggesting that STAT3 inhibition is not caused by ROS production. Interestingly, knockdown of STAT3 with use of shSTAT3 induced ROS generation and suppressed tumor cell growth. Moreover, scavenging ROS induced by STAT3 inhibition also diminished antitumor activity of STAT3 inhibition. In vivo administration of NSC-743380 suppressed tumor growth and p-STAT3 in lung tumors. Our results indicate that NSC-743380 is a potent anticancer agent for lung cancer and that its apoptotic effects in lung cancer cells are mediated by induction of ROS through STAT3 inhibition.

Genetic interactions in translational research on cancer

Genetic interactions are functional crosstalk among different genetic loci that lead to phenotypic changes, such as health or viability alterations. A disease or lethal phenotype that results from the combined effects of gene mutations at different loci is termed a synthetic sickness or synthetic lethality, respectively. Studies of genetic interaction have provided insight on the relationships among biochemical processes or pathways. Cancer results from genetic interactions and is a major focus of current studies in genetic interactions. Various basic and translational cancer studies have explored the concept of genetic interactions, including studies of the mechanistic characterization of genes, drug discovery, biomarker identification and the rational design of combination therapies. This review discusses the implications of genetic interactions in the development of personalized cancer therapies, the identification of treatment-responsive genes, the delineation of mechanisms of chemoresistance and the rational design of combined therapeutic strategies to overcome drug resistance.

Antitumor activity of a novel oncrasin analogue is mediated by JNK activation and STAT3 inhibition

Background

To optimize the antitumor activity of oncrasin-1, a small molecule identified through synthetic lethality screening on isogenic K-Ras mutant tumor cells, we developed several analogues and determined their antitumor activities. Here we investigated in vitro and in vivo antitumor activity of NSC-743380 (1-[(3-chlorophenyl) methyl]-1H-indole-3-methanol, oncrasin-72), one of most potent analogues of oncrasin-1.

Methodology and Principal Findings

In vitro antitumor activity was determined in NCI-60 cancer cell line panel using cell viability assay. In vivo antitumor activity was determined in parallel with NSC-741909 (oncrasin-60) in xenograft tumors established in nude mice from A498, a human renal cancer cell line. Changes in gene expression levels and signaling pathway activities upon treatment with NSC-743380 were analyzed in breast and renal cancer cells by Western blot analysis. Apoptosis was demonstrated by Western blot analysis and flow cytometric analysis. NSC-743380 is highly active against a subset of cancer cell lines derived from human lung, colon, ovary, kidney, and breast cancers. The 50% growth-inhibitory concentration (GI₅₀) for eight of the most sensitive cell lines was ≤10 nM. In vivo study showed that NSC-743380 has a better safety profile and greater antitumor activity than NSC-741909. Treatment with NSC-743380 caused complete regression of A498 xenograft tumors in nude mice at the tested doses ranging from 67 mg/kg to 150 mg/kg. Mechanistic characterization revealed that NSC-743380 suppressed the phosphorylation of C-terminal domain of RNA polymerase II, induced JNK activation, inhibited JAK2/STAT3 phosphorylation and suppressed cyclin D1 expression in sensitive human cancer cells. Blocking JNK activation or overexpression of constitutively active STAT3 partially blocked NSC-743380-induced antitumor activity.

Conclusions

NSC-743380 induces antitumor activity through modulation of functions in multiple cancer related pathways and could be a potential anticancer agent for some solid tumors.

Molecular biology of lung cancer: clinical implications

Lung cancer is a heterogeneous disease clinically, biologically, histologically, and molecularly. Understanding the molecular causes of this heterogeneity, which might reflect changes occurring in different classes of epithelial cells or different molecular changes occurring in the same target lung epithelial cells, is the focus of current research. Identifying the genes and pathways involved, determining how they relate to the biological behavior of lung cancer, and their utility as diagnostic and therapeutic targets are important basic and translational research issues. This article reviews current information on the key molecular steps in lung cancer pathogenesis, their timing, and clinical implications.