Inhibition of ras oncogene: a novel approach to antineoplastic therapy

Highlights from the 1st Latin American meeting on metronomic chemotherapy and drug repositioning in oncology, 27-28 May, 2016, Rosario, Argentina

Following previous metronomic meetings in Marseille (2011), Milano (2014), and Mumbai (2016), the first Latin American metronomic meeting was held in the School of Medical Sciences, National University of Rosario, Rosario, Argentina on 27 and 28 of May, 2016. For the first time, clinicians and researchers with experience in the field of metronomics, coming from different countries in Latin America, had the opportunity of presenting and discussing their work. The talks were organised in three main sessions related to experience in the pre-clinical, and clinical (paediatric and adult) areas. The different presentations demonstrated that the fields of metronomic chemotherapy and repurposing drugs in oncology, known as metronomics, constitute a branch of cancer therapy in permanent evolution, which have strong groups working in Latin

America, both in the preclinical and the clinical settings including large, adequately designed randomised studies. It was shown that metronomics offers treatments, which, whether they are combined or not with the standard therapeutic approaches, are not only effective but also minimally toxic, with the consequent improvement of the patient’s quality of life, and inexpensive, a feature very important in low resource clinical settings. The potential use of metronomic chemotherapy was proposed as a cost/effective treatment in low-/middle-income countries, for adjuvant therapy in selected tumours. The fundamental role of the governmental agencies and non-governmental alliances, as the Metronomic Global Health Initiative, in supporting this research with public interest was underlined.

The involvement of Kras gene 3'-UTR polymorphisms in risk of cancer and influence on patient response to anti-EGFR therapy in metastatic colorectal cancer: a meta-analysis

BACKGROUND

Genetic variation of the Kras oncogene is a candidate factor for increasing susceptibility to carcinoma and modulating response of metastatic colorectal cancer (mCRC) patients treated with anti-epidermal growth factor receptor monoclonal antibody (anti-EGFR). However, results from an increasing number of studies concerning the association of Kras gene rs712 and rs61764370 polymorphisms with risk of cancer and treatment of mCRC using anti-EGFR remain equivocal.

METHODS

Risk associations were evaluated in 1,661 cases and 2,139 controls from six studies concerning rs712 and 14,796 cases and 14,985 controls from 29 studies concerning rs61764370. Response association was also examined in a subset of four studies pertaining to rs61764370 and anti-EGFR treatment in mCRC.

RESULTS

Results of a meta-analysis showed that allele T (P-value of heterogeneity test [P H] =0.08, odds ratio [OR] =1.33, 95% confidence interval [CI]: 1.08-1.64) and genotype GT/TT (P H=0.14, OR =1.30, 95% CI: 1.10-1.55) in rs712 were strongly associated with cancer in Chinese subjects. No evidence of association was observed between rs712 and risk of cancer in the overall population or between rs61764370 and ovarian, breast, colorectal, or non-small-cell lung cancer risk in the Caucasian population. No significant association was found between rs61764370 and patient response to anti-EGFR therapy in mCRC.

CONCLUSION

The findings not only provide further evidence that allele T of rs712 increases genetic predisposition to cancer in Chinese population, but also no significant association between rs61764370 and cancer risk in Caucasian population, and suggest that genotype GT/TT of rs61764370 may not be a biomarker for predicting clinical outcome of anti-EGFR therapy in mCRC.

Inhibition of mesothelin as a novel strategy for targeting cancer cells

Mesothelin, a differentiation antigen present in a series of malignancies such as mesothelioma, ovarian, lung and pancreatic cancer, has been studied as a marker for diagnosis and a target for immunotherapy. We, however, were interested in evaluating the effects of direct targeting of Mesothelin on the viability of cancer cells as the first step towards developing a novel therapeutic strategy. We report here that gene specific silencing for Mesothelin by distinct methods (siRNA and microRNA) decreased viability of cancer cells from different origins such as mesothelioma (H2373), ovarian cancer (Skov3 and Ovcar-5) and pancreatic cancer (Miapaca2 and Panc-1). Additionally, the invasiveness of cancer cells was also significantly decreased upon such treatment. We then investigated pro-oncogenic signaling characteristics of cells upon mesothelin-silencing which revealed a significant decrease in phospho-ERK1 and PI3K/AKT activity. The molecular mechanism of reduced invasiveness was connected to the reduced expression of β-Catenin, an important marker of EMT (epithelial-mesenchymal transition). Ero1, a protein involved in clearing unfolded proteins and a member of the ER-Stress (endoplasmic reticulum-stress) pathway was also markedly reduced. Furthermore, Mesothelin silencing caused a significant increase in fraction of cancer cells in S-phase. In next step, treatment of ovarian cancer cells (OVca429) with a lentivirus expressing anti-mesothelin microRNA resulted in significant loss of viability, invasiveness, and morphological alterations. Therefore, we propose the inhibition of Mesothelin as a potential novel strategy for targeting human malignancies.

Raf kinase as a target for anticancer therapeutics

The Ras-Raf-MEK-ERK (ERK) pathway is a logical therapeutic target because it represents a common downstream pathway for several key growth factor tyrosine kinase receptors which are often mutated or overexpressed in human cancers. Although considered mainly growth-promoting, in certain contexts, this pathway also seems to be apoptosis-suppressing. Several novel agents targeting this pathway have now been developed and are in clinical trials. One of the most interesting new agents is BAY 43-9006. Although initially developed as a Raf kinase inhibitor, it can also target several other important tyrosine kinases including VEGFR-2, Flt-3, and c-Kit, which contributes to its antiproliferative and antiangiogenic properties. To date, encouraging results have been seen with BAY 43-9006, particularly in renal cell cancers which are highly vascular tumors. This review will provide an overview of the ERK signaling pathway in normal and neoplastic tissue, with a specific focus on novel therapies targeting the ERK pathway at the level of Raf kinase.

Diacylglycerol kinase iota regulates Ras guanyl-releasing protein 3 and inhibits Rap1 signaling

To study the physiological function of diacylglycerol (DAG) kinase iota (DGKiota), which converts DAG to phosphatidic acid, we deleted this gene in mice. In contrast to previous studies showing that DGK isoforms decrease Ras activity, signaling downstream of Ras in embryonic fibroblasts was significantly reduced in cells lacking DGKiota. DGKs regulate Ras signaling by attenuating the function of the DAG-dependent Ras guanyl nucleotide-releasing proteins (RasGRPs). We tested whether DGKiota inhibited the four known RasGRPs and found that it inhibited only RasGRP3. In addition to activating Ras, RasGRP3 also activates Rap1, which in some cases can antagonize the function of Ras. We demonstrate that DGKiota bound to RasGRP3 and inhibited its activation of Rap1 by metabolizing DAG. This inhibition consequently affected Ras signaling. We tested the physiological consequence of deleting DGKiota by crossing wild-type or DGKiota-deficient mice with mice carrying a v-Ha-Ras transgene, and then we assessed tumor formation. We observed significantly fewer tumors in DGKiota-deficient mice. Because Rap1 can antagonize the function of Ras, our data are consistent with a model in which DGKiota regulates RasGRP3 with a predominant effect on Rap1 activity. Additionally, we found that DGKzeta, which is structurally similar to DGKiota, inhibited RasGRPs 1, 3, and 4 and predominantly affected Ras signaling. Thus, type IV DGKs regulate RasGRPs, but the downstream effects differ depending on the DGK.

Hsp25 and Hsp70 in rodent tumors treated with doxorubicin and lovastatin

Heat shock protein 27 (Hsp27) and Hsp70 have been involved in resistance to anticancer drugs in human breast cancer cells growing in vitro and in vivo. In this study, we examined the expression of Hsp25 (the rodent homologue to human Hsp27) and Hsp70 in 3 different rodent tumors (a mouse breast carcinoma, a rat sarcoma, and a rat lymphoma maintained by subcutaneous passages) treated in vivo with doxorubicin (DOX) and lovastatin (LOV). All tumors showed massive cell death under control untreated conditions, and this massive death increased after cytotoxic drug administration. In this study, we show that this death was due to classic apoptosis. The tumors also showed isolated apoptotic cells between viable tumor cells, and this occurred more significantly in the lymphoma. The tumor type that was more resistant to cell death was the sarcoma, and this was found in sarcomas growing both under control conditions and after cytotoxic drug administration. Moreover, sarcomas showed the highest expression levels of Hsp25 in the viable tumor cells growing under untreated conditions, and these levels increased after DOX and LOV administration. After drug treatment, only sarcoma tumor cells showed a significant increase in Hsp70. In other words, sarcomas were the tumors with lower cell death, displayed a competent Hsp70 and Hsp25 response with nuclear translocation, and had the highest levels of Hsp25. In sarcomas, Hsp25 and Hsp70 were found in viable tumor cells located around the blood vessels, and these areas showed the most resistant tumor cell phenotype after chemotherapy. In addition, Hsp25 expression was found in endothelial cells as unique feature revealed only in lymphomas. In conclusion, our study shows that each tumor type has unique features regarding the expression of Hsp25 and Hsp70 and that these proteins seem to be implicated in drug resistance mainly in sarcomas, making these model systems important to perform more mechanistic studies on the role of Hsps in resistance to certain cytotoxic drugs.

Alterations in metastatic properties of hepatocellular carcinoma cell following H-ras oncogene transfection

AIM: To demonstrate the relationship between H-ras oncogene and hepatocellular carcinoma (HCC) metastasis.

METHODS: Activated H-ras oncogene was transfected into SMMC 7721, a cell line derived from human HCC, by calcium phosphate transfection method. Some metastasis-related parameters were detected in vitro, including adhesion assay, migration assay, expression of collagenase IV (cIVase) and epidermal growth factor receptor (EGFR).

RESULTS: The abilities of H-ras-transfected cell clones in adhesion to laminin (LN) or fibronectin (FN), migration, cIVase secretion increased markedly, and the expression of EGFR elevated moderately. More importantly, these alterations were consistent positively with the expression of p21, the protein product of H-ras oncogene.

CONCLUSION: H-ras oncogene could induce the metastatic phenotype of HCC cell in vitro to raise its metastatic potential.

Diagnosis and management of neurofibromatosis type 1

Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder whose major feature is the occurrence of multiple neurofibromas, which are benign tumors of the nerve sheath. It affects an estimated one in 3000 to 4000 individuals. In addition to neurofibromas, there are many other clinical manifestations, including malignant tumors such as gliomas or malignant peripheral nerve sheath tumors, and nontumor effects such as skeletal dysplasia and learning disability. Diagnosis is established on the basis of clinical criteria. Molecular genetic testing is feasible, but the large size of the gene and wide range of pathogenic mutations have so far impeded the development of a clinical diagnostic test. Insights into pathogenesis have followed from identification of the NF1 gene and the development of animal models. The major function of the gene product appears to be regulation of the ras protein. Tumors are believed to arise by the loss of function of the NF1 protein, suggesting that NF1 behaves as a tumor suppressor gene. Heterozygous effects on some cell types are also likely, however. The role of ras in the pathogenesis of tumors in NF1 has suggested an approach to treatment using ras inhibitors, some of which are likely to begin in clinical trials in NF1 patients in the near future.