RAS inhibitors in hematologic cancers: biologic considerations and clinical applications

Pharmacological or genetic inhibition of hypoxia signaling attenuates oncogenic RAS-induced cancer phenotypes

Oncogenic Ras mutations are highly prevalent in hematopoietic malignancies. However, it is difficult to directly target oncogenic RAS proteins for therapeutic intervention. We have developed a Drosophila acute myeloid leukemia model induced by human KRAS^G12V, which exhibits a dramatic increase in myeloid-like leukemia cells. We performed both genetic and drug screens using this model. The genetic screen identified 24 candidate genes able to attenuate the oncogenic RAS-induced phenotype, including two key hypoxia pathway genes HIF1A and ARNT (HIF1B). The drug screen revealed that echinomycin, an inhibitor of HIF1A, can effectively attenuate the leukemia phenotype caused by KRAS^G12V. Furthermore, we showed that echinomycin treatment can effectively suppress oncogenic RAS-driven leukemia cell proliferation, using both human leukemia cell lines and a mouse xenograft model. These data suggest that inhibiting the hypoxia pathway could be an effective treatment approach and that echinomycin is a promising targeted drug to attenuate oncogenic RAS-induced cancer phenotypes.

This article has an associated First Person interview with the first author of the paper.

Summary: Hypoxia pathway inhibition, either genetically or pharmacologically, rescues RAS-induced oncogenesis in a Drosophila acute myeloid leukemia model, mouse xenograft model and human leukemia cells.

A systems biology approach for the study of cumulative oncogenes with applications to the MAPK signal transduction pathway

The Extracellular signal Regulated Kinase (ERK) pathway is one of the most well-studied signaling pathways in cell cycle regulation. Disruption in the normal functioning of this pathway is linked to many forms of cancer. In a previous study [D.K. Pant, A. Ghosh, Automated oncogene detection in complex protein networks, with applications to the MAPK signal transduction pathway, Biophys. Chem. 113 (2005) 275-288.], we developed a novel approach to predict single point mutations that are likely to cause cellular transformation in signaling transduction networks. We have extended this method to study disparate pair mutation in enzyme/protein interactions and in expression levels in signal transduction pathway and have applied it to the MAPK signaling pathway to study how synergistic or cooperative mutation within signaling networks acts in unison to cause malignant transformation. The method provides a quantitative ranking of the modifier pair of ERK activation. It is seen that the highest ranking single point mutations comprise the highest ranking pair mutations. We validate some of our results with experimental literature on multiple mutations. A second order sensitivity analysis scheme is additionally used to determine the effect of correlations among mutations at different sites in the pathways.

Lupeol, a fruit and vegetable based triterpene, induces apoptotic death of human pancreatic adenocarcinoma cells via inhibition of Ras signaling pathway

Pancreatic cancer is an exceptionally aggressive disease, the treatment of which has largely been unsuccessful due to higher resistance offered by pancreatic cancer cells to conventional approaches such as surgery, radiation and/or chemotherapy. The aberration of Ras oncoprotein has been linked to the induction of multiple signaling pathways and to the resistance offered by pancreatic cancer cells to apoptosis. Therefore, there is a need for development of new and effective chemotherapeutic agents which can target multiple pathways to induce responsiveness of pancreatic cancer cells to death signals. In this study, human pancreatic adenocarcinoma cells AsPC-1 were used to investigate the effect of Lupeol on cell growth and its effects on the modulation of multiple Ras-induced signaling pathways. Lupeol caused a dose-dependent inhibition of cell growth as assessed by MTT assay and induction of apoptosis as assessed by flow cytometry, fluorescence microscopy and western blotting. Lupeol treatment to cells was found to significantly reduce the expression of Ras oncoprotein and modulate the protein expression of various signaling molecules involved in PKCalpha/ODC, PI3K/Akt and MAPKs pathways along with a significant reduction in the activation of NFkappaB signaling pathway. Our data suggest that Lupeol can adopt a multi-prong strategy to target multiple signaling pathways leading to induction of apoptosis and inhibition of growth of pancreatic cancer cells. Lupeol could be a potential agent against pancreatic cancer, however, further in-depth in vivo studies are warranted.

Inhibition of PI3-kinase sensitises HL60 human leukaemia cells to both chemotherapeutic drug- and Fas-induced apoptosis by a JNK independent pathway

Increasing resistance to chemotherapeutic regimes remains a serious problem in the treatment of acute myeloid leukaemia. We have shown that phosphatidylinositol (PI) 3-kinase inhibition significantly sensitises the AML derived cell line, HL60 to chemotherapeutic drug- and Fas-induced apoptosis. PI3-kinase inhibition significantly potentiates cytotoxic drug-induced c-jun N-terminal kinase (JNK) activation, reported to be a requirement for apoptosis. However, JNK inhibition does not enhance cell viability following treatment with drug and inhibitor. Furthermore, PI3-kinase inhibition significantly increases sensitivity to apoptosis mediated by an exogenous receptor agonist, again by a JNK independent mechanism. These results suggest that PI3-kinase inhibitors could be of significant therapeutic importance, lowering the threshold for apoptosis induced by both chemotherapy and cell-mediated immune response.

Molecular signals in anti-apoptotic survival pathways

Drug resistance, to date, has primarily been attributed to increased drug export or detoxification mechanisms. Despite correlations between drug export and drug resistance, it is increasingly apparent that such mechanisms cannot fully account for chemoresistance in neoplasia. It is now widely accepted that chemotherapeutic drugs kill tumour cells by inducing apoptosis, a genetically regulated cell death programme. Evidence is emerging that the exploitation of survival pathways, which may have contributed to disease development in the first instance, may also be important in the development of the chemoresistance. This review discusses the components of and associations between multiple signalling cascades and their possible contribution to the development of neoplasia and the chemoresistant phenotype.

Insights into the biologic and molecular abnormalities in adult acute lymphocytic leukemia

The last 3 decades have seen much progress in the treatment and outcome of patients with ALL. Unfortunately, the success that has been achieved in children with ALL has not yet been translated into adult patients. Insight into the biologic and molecular abnormalities in ALL may, however, provide the necessary clues that allow a clearer understanding of the crucial differences in the behavior of ALL in different groups of patients. As the molecular basis of the disease is deciphered, new targets are discovered that may prove useful for therapeutic interventions in the future.