Current Cancer Drug Targets - Volume 13, Issue 4, 2013

Current evidence suggests a significant role of aberrant splicing in the development and maintenance of malignancy. This multistep, tightly regulated epigenetic process leads to the production of abnormal proteins with abnormal functions contributing to underlying mechanisms of malignant transformation. Splicing patterns in malignant cells can be altered not only by the mutations detected on the aberrantly spliced gene, but also by the mutations detected on the genes encoding splicing factors. For example, aberrant pre-mRNA splicing, leading to intracellular or extracellular HA synthesis by HASs, contributes to the initiation and progression of various types of cancer. The influence of intracellular HA appears to be particularly significant and is promoted by aberrant splicing. In this review we report a model describing oncogenic potential of aberrant splicing, with a focus on HAS1 and intracellular HA. We also suggest that the influence of splicing mutations on malignant disease is likely multifactorial. For the triple axis of HA, HAS1 and RHAMM, mutations in HAS1 provide an indicator that these aberrations contribute to the events that lead to malignancy through increased risk and predisposition. Here, we also summarize the impact of splicing abnormalities on cancer and the possible oncogenic impact of aberrantly spliced HAS1. In conclusion, we emphasize that specific gene splice variants and the splicing process itself offer potential targets for novel drug treatment strategies.

As of 21st century, cancer is arguably the most complex and challenging disease known to mankind and an inevitable public health concern of this millennium. Nanotechnology, suitably amalgamated with cancer research, has ushered an era of highly personalized and safer medicines which can improve cancer diagnosis and therapy. A wide variety of nanomedicines are currently under investigation, including polymeric/non-polymeric nanoparticles, dendrimers, quantum dots, carbon nanotubes, lipid- and micelle-based nanoparticles. The bases of these nanomedicines in reducing toxicity associated with cancer therapy are their ability to carry a large payload and multivalent-ligand targeting. This imparts specificity for targeting the tissues as well as bypass resistance mechanisms. The major hurdles on these future medicines are potential toxicity of nanoparticles, which imposes the need of extensive regulatory evaluation before nanomedicines could be utilized as cancer therapeutics. This review highlights nanopharmaceuticals that have been investigated in oncology for various applications (diagnosis, therapeutic delivery and theranostics). It also discusses the effects of nano-sized materials on tissues/organ functions, the possibility of overcoming multi-drug resistance by using nanomedicines and their current clinical status.

DNA methylation is an epigenetic modification involved in gene expression regulation. In cancer, the DNA methylation pattern becomes aberrant, causing an array of tumor suppressor genes to undergo promoter hypermethylation and become transcriptionally silent. Reexpression of methylation silenced tumor suppressor genes by inhibiting the DNA methyltransferases (DNMT1, DNMT3A, and DNMT3B) has emerged as an effective strategy against cancer. The expression of DNA methyltransferase 1 (DNMT1) being high in S-phase of cell cycle makes it a specific target for methylation inhibition in rapidly dividing cells as in cancer. This review discusses nucleoside analogues (azacytidine, decitabine, zebularine, SGI-110, CP-4200), non-nucleoside ihibitors both synthetic (hydralazine, RG108, procaine, procainamide, IM25, disulfiram) and natural compounds (curcumin, genistein, EGCG, resveratrol, equol, parthenolide) which act through different mechanisms to inhibit DNMTs. The issues of bioavailability, toxicity, side effects, hypomethylation resistance and combinatorial therapies have also been highlighted.

Pancreatic cancer has a poor prognosis, with only 10% survival one year following diagnosis. Despite significant advances in conventional therapies (chemotherapy and radiotherapy), little improvement in patient survival has occurred in the last decade. Therefore, there is a critical need for novel and effective therapeutic approaches for this cancer. This article reviews current concepts in the pathogenesis and treatment of pancreatic cancer, the latter including tumor resection approaches and the current standard of care. We further describe recent advances in new and combination therapies, which result only in modest increases in survival, and discuss challenges in drug delivery and limiting toxicity.

The purpose of this study was to determine the effects of the histone deacetylase inhibitor, MS-275, on the Fas signaling pathway and susceptibility of osteosarcoma (OS) to Fas ligand (FasL)-induced cell death. OS metastasizes almost exclusively to the lungs. We have shown that Fas expression in OS cells is inversely correlated with their metastatic potential. Fas+ cells are rapidly eliminated when they enter the lungs via interaction with FasL, which is constitutively expressed in the lungs. Fas- OS cells escape this FasL-induced apoptosis and survive in the lung microenvironment. Moreover, upregulation of Fas in established OS lung metastases results in tumor regression. Therefore, agents that upregulate Fas expression or activate the Fas signaling pathway may have therapeutic potential. Treatment of Fas- metastatic OS cell lines with 2 μM MS-275 sensitized cells to FasL-induced cell death in vitro. We found that MS-275 did not alter the expression of Fas on the cell surface; rather it resulted in the downregulation of the anti-apoptotic protein, c-FLIP (cellular FLICE-inhibitory protein), by inhibiting c-FLIP mRNA. Downregulation of c- FLIP correlated with caspase activation and apoptosis induction. Treatment of nu/nu-mice with established OS lung metastases with oral MS-275 resulted in tumor regression, increased apoptosis and a significant inhibition of c-FLIP expression in tumors. Histopathological examination of mice showed no evidence of significant toxicity. Overall, these results suggest that the mechanism by which MS-275 sensitizes OS cells and lung metastases to FasL-induced cell death may be by a direct reduction in the expression of c-FLIP.

Progression of solid tumors depends on vascularization and angiogenesis in a malignant tissue. Among a whole range of proangiogenic factors, a vascular endothelial growth factor A (VEGF-A) plays a key role. Blockade of VEGF may lead to regression of vascular network and inhibition of a tumor growth. In the present time, bevacizumab has been introduced into wide clinical practice in therapy of breast cancer, colorectal cancer and recurrent high-grade gliomas (HGGs). Coadministration of antiangiogenic therapy with irinotecan may increase probability of the response to the treatment and prolong progression-free survival rate (PFS). Moreover, bevacizumab is well tolerated and significantly improves patient’s quality of life. However, in the case of brain tumors, the efficiency of such an approach is controversial. The antiangiogenic therapy can slightly delay tumor growth and does not lead to complete recovery. In addition, it contributes to enhanced tumor cell invasion into the normal brain. The mechanisms of resistance include activation of alternative proangiogenic signaling pathways, of an invasive population of tumor cells, metabolic change toward glycolysis and recruitment of myeloid bone marrow-derived cells to tumors. Obviously, that anti-VEGF therapy as monotherapy was not effective against HGGs. To enhance the antitumor treatment efficacy, it is necessary to develop a multi-target strategy to inhibit critical processes in malignancy progression such as angiogenesis, invasion, autophagy, metastatic spread, recruitment of bone marrow-derived endothelial cells and tumor stem-like cells. In addition, anti-VEGF antibodies have shown a promising result as a tumor-targeting vector for delivery therapeutic and diagnostic drugs in brain tumors.

Until 2010 docetaxel was the only agent with a proven survival benefit in the treatment of castration-resistant prostate cancer (CRPC). Recent evidence suggests that CRPC is caused by augmented androgen/androgen receptor (AR) signaling involving AR hypersensitivity, promiscuous activation of the AR, de novo production of androgens and activation of the AR by cytokines and growth factors; these findings have led to the development of novel agents targeting AR signaling. Several novel drugs targeting the AR axis, including the cytochrome P17 inhibitor abiraterone acetate and anti-androgen enzalutamide (MDV3100), have shown promising results in prolonging survival in clinical trials in a postchemotherapy setting. Because of these encouraging findings, these drugs have also been evaluated in a pre-chemotherapy setting. In addition, several novel drugs targeting non-AR signaling, including the novel taxoid compound cabazitaxel, antisense oligonucleotide OGX-011 (custirsen), sipuleucel-T immunotherapy and Alpharadin-based radiotherapy, have also been demonstrated to improve overall survival in CRPC. However, there is no consensus with regard to the sequence in which these novel drugs and taxanes should be used in the treatment of CRPC. In this review, we summarize recently developed and developing novel agents for use against CRPC. We also discuss the sequence of use of these agents and taxanes, mainly from the standpoint of factors related to drug resistance.

Pancreas cancer is the fourth leading cause of cancer death due to the limited treatment success rate. The wide number of signalling pathway aberrations contributing to tumorigenesis, progression and drug resistance, is the main reason for unsuccessful treatments in pancreatic cancer. An additional and still under-investigated intracellular cancer target is the peroxisome proliferator activated receptor gamma (PPAR-γ). Several studies have shown the in vitro antitumor activity of PPAR-γ agonists in cancer cells but, if used in monotherapy, they were poorly effective in cancer treatment. The present review will focus on the potential therapeutic role of PPAR-γ agonists in combination with other drugs (type I interferons, gemcitabine and COX-2 inhibitors), highlighting molecular interactions and signalling pathways involved in pancreatic cancer cells. Understanding of the underlying molecular mechanisms and survival pathways activated in cancer cells should promote the development of more successful strategies based on the specific targeting of molecular pathways involved in the resistance to anti-cancer agents.

Identification of novel chemotherapeutic agents from traditional medicines and elucidation of the molecular basis of their anticancer effects are critical and urgently needed for modern pharmacotherapy. We previously found that analogs of the compounds present in Valeriana jatamansi, a traditional medicine used to treat mental disorders, possess notable antitumor properties; however, the underlying molecular mechanisms have not been fully demonstrated. In this study, we evaluated the anticancer effects of IVHD-valtrate, one of the most active Valeriana jatamansi derivatives, against human ovarian cancer cells in vitro and in vivo. IVHD-valtrate inhibited the growth and proliferation of the A2780 and OVCAR-3 ovarian cancer cell lines in a concentration-dependent manner, while relatively low cytotoxicity to immortalized non-tumorigenic human ovarian surface epithelial cells (IOSE-144) was observed. Treatment with IVHDvaltrate arrested the ovarian cancer cells in the G2/M phase and induced apoptosis, and significantly suppressed the growth of A2780 and OVCAR3 xenograft tumors in a dose-dependent manner. The detailed in vitro and in vivo study on the molecular mechanisms of this compound demonstrated that IVHD-valtrate exposure modulated the expression of numerous molecules involved in cell cycle progression and apoptosis regardless of p53 status, leading to increase the level of p53, Rb, p21, p27 and decrease Mdm2, E2F1, Cyclin B1, Cdc25C and Cdc2. It also down-regulated Bcl-2/Bax and Bcl-2/Bad ratio and enhanced the cleavage of PARP and Caspases. Our preclinical results indicated IVHD-valtrate is a potential therapeutic agent for ovarian cancer, providing a basis for development of the compound as a novel chemotherapeutic agent.