Current Cancer Drug Targets - Volume 12, Issue 8, 2012

Radiotherapy (RT) allows for tumor control through the cytotoxic action of ionizing radiation (IR). Although modern technologies permit precise IR delivery to the tumor mass while minimizing exposure of surrounding healthy tissues, the efficacy of RT remains limited by the intrinsic or acquired radioresistance of many tumors. There is thus an ongoing search for agents that augment the sensitivity of tumor cells to IR cytotoxicity, with recent interest in targeting components of signaling pathways involved in tumor growth and radioresistance. Here, we review the evidence suggesting that disabling one of these components, the mechanistic target of rapamycin (mTOR) kinase, may enhance RT efficacy. This molecule constitutes the catalytic subunit of the mTORC1 and mTORC2 protein complexes, which regulate cell growth and other processes implicated in tumorigenesis. Much work has focused on mTORC1 because it is selectively blocked by the microbial product rapamycin and its analogs (collectively designated rapamycins) that are approved for cancer treatment, and is frequently hyperactivated in malignant cells. In several, but not all human cancer cell lines, rapamycins increased IR cytotoxicity in vitro, apparently through multiple mechanisms, including the promotion of autophagic cell death. Rapamycins also potentiated fractionated RT in tumor xenograft models, in part by suppressing tumor angiogenesis. Synthetic kinase inhibitors that simultaneously target PI3K and both mTOR complexes also enhanced RT in vitro and in vivo, but with greater efficiency than rapamycins. These encouraging data have led to early clinical trials of rapamycins and catalytic mTOR inhibitors combined with RT in various cancers.

Polysialic acid (polySia) is a carbohydrate polymer critical for neuronal cell migration and axon pathfinding in embryonic development. Besides brain regions requiring persistent neuronal plasticity, polySia is essentially absent from the adult body. However, polySia is aberrantly re-expressed on many tumours, where it decorates the surface of NCAM (neuronal cell adhesion molecule) and modulates cell adhesion, migration and invasion. PolySia-NCAM expression is strongly associated with poor clinical prognosis and correlates with aggressive and invasive disease in many cancers, including lung cancer, neuroblastoma and gliomas. The synthesis of polySia is mediated by two polysialyltransferases (polySTs), ST8SiaIV (PST) and particularly ST8SiaII (STX) in cancer cells. The demonstration that polyST knock-down negates events associated with tumour cell dissemination indicates that PST and STX are validated targets. Selective inhibition of polySTs therefore presents a therapeutic opportunity to inhibit tumour invasion and metastasis.

The phosphatidylinositol 3'-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) signaling pathway contributes to prostate cancer progression and transition to androgen-independent disease. Furthermore, recent microarray analysis demonstrates that this pathway is often deregulated during prostate cancer progression. Thus, targeting of PI3K/AKT/mTOR may present a promising therapy for castration-refractory prostate cancer (CRPC). In recent years, several interesting strategies have been developed that interfere with distinct components of the PI3K/AKT/mTOR cascade. This article discusses many of the mechanisms involved, specifically in the context of prostate cancer. In addition, we present an overview of preliminary data on the activity of mTOR inhibitors and on the key steps to evaluate which of these compounds are most suitable for the treatment of prostate cancer. Particular emphasis is also placed on the development of novel perspectives to improve the poor prognosis of patients with CRPC.

Esophageal cancer (EC) is the most common esophageal malignancy and has a dismal prognosis. Developing novel strategies to reverse the resistance to chemotherapeutics in EC is currently of intense interest. The wide-type p53 induced gene 1 (WIG-1) is a p53-regulated transcription factor. The effect of WIG-1 on the regulation of cisplatin (DDP) sensitivity was evaluated in DDP-resistant EC cells both in vitro and in vivo. The DDP-resistant sub-line EC109/DDP was successfully selected following eight months of culture. Overexpression of WIG-1 in EC109/DDP cells significantly lowered the IC50 of DDP to 1.11 ± 0.54 μg/ml when compared to Control cells (4.57 ± 0.98 μg/ml, P < 0.05). In addition, WIG-1 exerted a negative effect on cell proliferation and on the cloning efficiency of EC109/DDP cells. A significant increase in the apoptosis index and in TUNEL-positive nuclei was observed when the expression of WIG-1 was upregulated. Furthermore, WIG-1-overexpressing DDP-resistant EC cells exhibited suppressed xenograft tumor growth and a lower green fluorescent protein (GFP) fluorescence intensity following DDP injection. WIG-1 also reduced the expression of ERCC1 and increased the expression of Bax in DDP-resistant EC cells, while the expression of Bcl-2, P-gp and GST-π was not significantly altered after up- or down-regulation of WIG-1. In summary, these results show that WIG-1 may reverse the DDP resistance of EC cells by reducing ERCC1 expression and increasing Bax expression. This study will provide a framework for understanding the mechanism of DDP resistance by WIG-1 and will aid in the therapeutic use of DDP in ESCC.

Membrane transporters govern the movement of drugs and their metabolites across biological membranes, thereby determining their pharmacokinetics, efficacy and adverse drug reactions. Platinum-based anticancer drugs are a mainstay of chemotherapy for many human malignancies. However, their clinical utility is limited by tumor resistance and normal tissue toxicities, which are determined at least in part by the level of tissue accumulation of platinum. Recently, several members of the ATP-binding cassette (ABC), solute carrier (SLC) and ATPase membrane protein superfamilies have been found to contribute to the net accumulation of platinum drugs in malignant and normal tissues. Herein, a review has been carried out to critically evaluate current preclinical and clinical evidence implicating membrane transporters as determinants of the pharmacology of cisplatin, oxaliplatin, carboplatin and related investigational compounds. The evidence includes studies of recombinant cell systems with genetically modified expression of individual membrane transporters, platinum-resistant or -sensitive human cancer cells and in vivo xenografted tumors, animal models of platinum-induced nephro-, oto- or neurotoxicity, and clinical studies of associations between the membrane transporter tumor expression and patient outcomes from platinum-based chemotherapy. Understanding the role of membrane transporters as determinants of the pharmacology of platinum drugs will be a basis for targeting these drug transporters in individualized and optimized platinum-based cancer therapy, and new drug development.

The current therapy for ovarian cancer has advanced from alkylating agents, to a combination of carboplatinum and paclitaxel offering increased survival. Although most patients respond to this first-line therapy, initially, the majority of these patients relapse within 2 years. The mechanisms responsible for acquired drug resistance in ovarian cancer have been elucidated only in part. They include i) enhanced drug export, ii) activation/inhibition of intracellular signalling pathways, iii) molecular alterations in tubulin isotype composition. A better understanding of these mechanisms is needed, in order to develop new approaches, aimed at overcoming resistance to anticancer agents, and to reveal the complexity of causes, which contribute to drug resistance. In this review we offer an updated overview of proteomic studies on the molecular mechanisms of paclitaxel resistance. These proteomic studies also identify potential targets for modulating drug resistance, that could be predictive of response to chemotherapy in ovarian carcinomas.

The main aim of nanomedicine is to revolutionize the health care system and find effective approaches to fighting fatal diseases. Therapeutic beams, which are employed in radiation therapy, do not discriminate between normal and cancerous cells and must rely on targeting the radiation beams to specific cells. Interestingly, the application of nanoscale particles in radiation therapy has aimed to improve outcomes in radiation therapy by increasing toxicity in tumors and reducing it in normal tissues. This review focuses on approaches to nanotechnology-based cancer radiation therapy methods such as radionuclide therapy, photodynamic therapy, and neutron capture therapy. Moreover, we have investigated nanotechnology-based thermotherapy methods, including hyperthermia and thermoablation, as non-ionizing modalities of treatment using thermal radiation. The results strongly demonstrate that nanotechnology-based cancer radiation therapy and thermotherapy methods hold substantial potential to improve the efficacy of anticancer radiation and thermotherapy modalities.

Adult high grade gliomas (HGG) are the most frequent and fatal primary central nervous system (CNS) tumors. Despite recent advances in the knowledge of the pathology and the molecular features of this neoplasm, its prognosis remains poor. In the last years temozolomide (TMZ) has dramatically changed the life expectancy of these patients: the association of this drug with radiotherapy (RT), followed by TMZ alone, is the current standard of care. However, malignant gliomas often remain resistant to chemotherapy (CHT). Therefore, preclinical and clinical research efforts have been directed on identifying and understanding the different mechanisms of chemo-resistance operating in this subset of tumors,in order to develop effective strategies to overcome resistance. Moreover, the evidence of alterations in signal transduction pathways underlying tumor progression, has increased the number of trials investigating molecular target agents, such as anti-epidermal growth factor receptor (EGFR) and anti- vascular endothelial growth factor (VEGF) signaling. The purpose of this review is to point out the current standard of treatment and to explore new available target therapies in HGG.

Leucine-rich repeat (LRR) genes encode transmembrane proteins that are essential for normal brain development and are often dysregulated in central nervous system tumors. Leucine-rich repeat C4 (LRRC4) is a member of the LRR protein superfamily and specifically expressed in brain tissue. Importantly it acts as a tumor suppressor in the pathogenesis of malignant gliomas. However, the molecular mechanisms by which LRRC4 regulates glioma tumorigenesis are largely unknown. In this report, we found that miR-185 is markedly upregulated by LRRC4. We also found that miR-185 was downregulated in glioma, and overexpression of miR-185 inhibited glioma cell invasion. Low expressions of LRRC4 and miR-185 were associated with a poor outcome in glioma patients. Further investigation revealed that LRRC4 mediated its tumor suppressor function by regulating miR-185 targets CDC42 and RhoA. LRRC4 overexpression inhibited glioma cell invasion through miR-185-mediated CDC42 and RhoA direct regulation and VEGFA indirect regulation. Together, our findings suggest that the altered expression of the tumor suppressor LRRC4 may be an important event that leads to the dysregulation of miR-185 in human gliomas. LRRC4 and miR-185 may also be good prognostic markers and therapeutic targets in glioma.