Current Cancer Drug Targets - Volume 14, Issue 4, 2014

Various natural agents, including grape seed extract (GSE), have shown considerable chemopreventive and anti-cancer efficacy against different cancers in pre-clinical studies; however, their specific protein targets are largely unknown and thus, their clinical usefulness is marred by limited scientific evidences about their direct cellular targets. Accordingly, herein, employing, for the first time, the recently developed drug affinity responsive target stability (DARTS) technique, we aimed to profile the potential protein targets of GSE in human colorectal cancer (CRC) cells. Unlike other methods, which can cause chemical alteration of the drug components to allow for detection, this approach relies on the fact that a drug bound protein may become less susceptible to proteolysis and hence the enriched proteins can be detected by Mass Spectroscopy methods. Our results, utilizing the DARTS technique followed by examination of the spectral output by LC/MS and the MASCOT data, revealed that GSE targets endoplasmic reticulum (ER) stress response proteins resulting in overall down regulation of proteins involved in translation and that GSE also causes oxidative protein modifications, specifically on methionine amino acids residues on its protein targets. Corroborating these findings, mechanistic studies revealed that GSE indeed caused ER stress and strongly inhibited PI3k-Akt–mTOR pathway for its biological effects in CRC cells. Furthermore, bioenergetics studies indicated that GSE also interferes with glycolysis and mitochondrial metabolism in CRC cells. Together, the present study identifying GSE molecular targets in CRC cells, combined with its efficacy in vast pre-clinical CRC models, further supports its usefulness for CRC prevention and treatment.

Haem oxygenase-1 (HO-1) catalyses the rate-limiting step in haem degradation. All three metabolites resulting from haem degradation (carbon monoxide (CO), biliverdin and free iron) have anti-inflammatory and anti-apoptotic properties. HO-1 is a stress-inducible enzyme found extensively expressed in a vast variety of both human and murine cancers, where it serves as an essential survival molecule by modulating expression of molecules regulating apoptosis and stimulating angiogenesis. In addition, HO-1 contributes in a critical manner to inhibition or termination of inflammation. Consequently, several anticancer strategies aim at targeting HO-1. The inhibition of HO-1 may cause tumour cells to become more sensitive to chemotherapy and radiation therapy. The water-soluble forms of the HO-1 inhibitor Zinc protoporphyrin (ZnPP) have seemed promising in different in-vivo models, in which it has induced growth arrest in tumour cells with few, if any, side effects. Studies have suggested that HO-1 may also function to disrupt the tumour metastasising process, since the expression of the metalloprotease MMP9 is inversely correlated with HO-1 expression. Additionally, HO-1 has anti-inflammatory functions which play a very important role in the negative regulation of the immune system. Immunological targeting of HO-1 might represent an interesting approach, as epitopes derived from HO- 1 have been found exclusively on tumour tissue. Natural HO-1-specific T-cell responses have been identified in cancer patients. Hence, recently HO-1-specific, CD8+ regulatory T cells were described in cancer patients, which in concert with HO-1 expression might be responsible for a highly immunosuppressive tumour microenvironment. Here, we summarise current knowledge of the role of HO-1 in cancer, report the different results of the targeting of HO-1 in preclinical and clinical settings, and discuss future opportunities.

Approximately 85% of pancreatic cancer patients suffer from glucose intolerance or even diabetes because high glucose levels can contribute to oxidative stress which promotes tumor development. As one of the reactive oxygen species (ROS)-regulating factors, thioredoxin-interacting protein (TXNIP), is involved in the maintenance of thioredoxin (TRX)-mediated redox regulation. In this study, we demonstrated that high glucose levels increased the expression of TXNIP in time- and concentration-dependent manners and modulated the activity of TRX and ROS production in pancreatic cancer cells, BxPC-3 and Panc-1. We also found that glucose activated both p38 MAPK and ERK pathways and inhibitors of these pathways impaired the TXNIP/TRX/ROS axis. Knockdown of TXNIP restored TRX activity and decreased ROS production under high glucose conditions. Moreover, we observed that the integrated optical density (IOD) of TXNIP staining as well as the protein and mRNA expression levels of TXNIP were higher in the tumor tissues of pancreatic cancer patients with diabetes. Taken together, these results indicate that hyperglycemia-induced TXNIP expression is involved in diabetes-mediated oxidative stress in pancreatic cancer via p38 MAPK and ERK pathways.

In recent years, our knowledge regarding the metabolism of melanoma has greatly advanced and consequently new therapeutic strategies are being developed. This review is focused on metabolic pathways contributing to melanoma proliferation, the influence of BRAF inhibitors on those metabolic pathways and finally a presentation of potential therapeutic strategies aimed at blocking metabolic signaling pathways and therefore melanoma development.

The αvβ3 integrin is highly expressed in prostate cancer (PCa), in which it is a key player in tumour invasion, angiogenesis and metastasis formation. Therefore, αvβ3 integrin is considered a very promising target for molecular imaging of PCa. This study tested the potential of the novel αvβ3 integrin affine agent [68Ga]NOTA-RGD in comparison with the established [18F]fluoroethylcholine (FEC) and [18F]fluorodeoxyglucose (FDG) for assessing PCa using positron emission tomography (PET). [68Ga]NOTA-RGD showed a lower uptake in PC-3 and DU-145 cells compared with FEC and FDG. μPET imaging studies showed a good delineation of the PCa xenografts in mice. The means tumor-to-muscleand tumor-to-bone-ratio amounted 5.1 ± 1.4 and 5.2 ± 1.2 for [68Ga]NOTA-RGD compared with 2.6 ± 0.9 and 2.9 ± 1.6 for FDG, and 2.4 ± 0.7 and 0.8 ± 0.2 for FEC, respectively. The uptake of [68Ga]NOTA-RGD into tumor was fully inhibited by c(RGDfV), known to bind specifically to αvβ3 integrin, confirming the specificity of the tumor uptake in vivo. These results suggest that [68Ga]NOTA-RGD is a promising candidate for PET imaging of αvβ3 integrin expression in PCa and warrant further in vivo validations to ascertain its potential as an imaging agent for clinical use. The simple and fast preparation of [68Ga]NOTA-RGD may greatly facilitate its translation to a clinical setting.

The natural compound curcumin has been investigated as an anticancer agent in many cellular systems, in animal models and in the clinic. The overriding negative characteristics of curcumin are its low solubility, weak potency and poor bioavailability. We have examined the efficacy and mechanism of action of a synthetic curcumin analog, UBS109, in head and neck squamous cell carcinoma. By nephelometry, this analog exhibits considerably greater solubility than curcumin. Pharmacokinetic studies of a single oral dose of UBS109 in mice revealed that peak plasma concentrations were reached at 0.5 hours post-dose (Tmax) with average plasma concentrations (Cmax) of 131 and 248 ng/mL for oral doses of 50 and 150 mg/kg, respectively. The terminal elimination half-lives (T½) for these doses averaged 3.7 and 4.5 hours, respectively. In both in vitro and in vivo studies, we found that UBS109 decreased the levels of phosphorylated IKKβ and phosphorylated p65 and, unexpectedly, increased the levels of phosphorylated IκBα by Western blot analysis. These observations may suggest that UBS109 suppresses tumor growth through, in part, inhibition of NF-κB p65 phosphorylation by PKAc and not through IκBα. Finally, we demonstrate that UBS109 is efficacious in retarding the growth of Tu212 (head and neck) squamous cell carcinoma (SCC) xenograft tumors in mice and may be useful for treating head and neck SCC tumors.

Study of the process of cancer initiation, growth and progression in altered gravity is of utmost importance considering the health status of researchers visiting in space and future scope of space tourism. Microgravity affects various cells in the body differently; however, the mechanisms of such effects are not understood completely. Therefore, it is imperative to explore various physiological and biochemical processes, particularly those which can influence the process of carcinogenesis. If the changes in physiological or biochemical processes do not revert back to normalcy even after returning from the space to earth, it may lead to various aberrations and morphological changes during the life span. Such changes could lead to pathological conditions including cancer. For example, microgravity is observed to suppress the activity of immune cells, which itself increases the risk of cancer development. It is little known how the microgravity affects cellular and molecular events that determine physiological and biological responses. There is also a possibility of changes in epigenetic signatures during microgravity exposure which remains unexplored. Herein, we have reviewed the effect of microgravity on relevant molecular and biological processes, and how it could influence the course of cancer development. In this regard, we have also highlighted the areas of research that require more attention to bridge the gap of understanding for such biological processes.

Pancreatic cancer is one of the highly aggressive malignant diseases worldwide. To achieve better treatment outcome of pancreatic cancer, in the current study we explore the underlying molecular mechanism of drug resistance in pancreatic cancer cells. We found that resistance to gemcitabine is associated with epithelial-mesenchymal transition (EMT) phenotype in a panel of pancreatic cancer cell lines. Notably, gemcitabine-resistant pancreatic cancer cells acquire EMT phenotype. Moreover, gemcitabine-resistant cells have increased migration and invasion activities. Furthermore, we observed the high expression of HIF-1α in gemcitabine-resistant cells. More importantly, inhibition of HIF-1α in gemcitabine-resistant cells caused partial reversal of EMT phenotype, suggesting that HIF-1α was critically involved in gemcitabine-resistant-mediated EMT. Therefore, targeting HIF-1α could be an effective strategy for the treatment of pancreatic cancer.