Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Anti-Cancer Agents) - Volume 12, Issue 4, 2012

Cancer-related morbidity is one of the leading causes of deaths in the world. Due to the social and health impact of cancer, research on cellular and molecular pathways leading to oncogenesis and carcinogenesis is one of the most active areas of biomedical investigation. Moreover, the uncovering of pathways that foster cancer growth and cell death resistance may also result in the development of more efficient therapeutic options for the treatment of cancer. In this special issue of Anti Cancer Agents in Medicinal Chemistry, a group of expert leaders summarize emerging evidence on the exciting role of cholesterol and sphingolipids (SLs) in the regulation of cancer cell biology and therapy. In addition to playing a key structural role in biological membranes, recent data have uncovered a critical function for cholesterol and SLs in the modulation of essential pathways involved in cancer cell biology. Particularly, ceramide and cholesterol regulate cell death pathways and hence play a crucial role in determining the susceptibility of cancer cells to current therapy, thus providing a rationale for novel therapeutic combinations. In this regard, Ballereau et al., examine the role of ceramide functionalization at the C1-OH position as a promising approach for cancer therapy (1). Although ceramide is well recognized as a proapoptotic lipid moiety, ceramide metabolism in cancer cells is altered giving rise to other metabolites involved in tumor progression and drug resistance. The authors review data indicating the key role of enzymes that modify ceramide at the C1-OH position generating other biologically important SLs in cancer, such as sphingomyelin, ceramide-1-phosphate or glucosylceramide. Thus, modulating these enzymes may open novel opportunities for improving current chemotherapy. In the review by Mullen and Obeid, the authors provide an extensive overview of the role of ceramide and apoptosis (2). In particular, the authors explore enigmatic connections between sphingolipid metabolism and programmed cell death, particularly focussing on the role of de novo sphingolipid synthesis and sphingosine salvage in producing proapoptotic ceramide, involving mitochondrial membrane permeabilization. Due to the critical role of mitochondria in the regulation of cell death pathways this connection may be of relevance in regulating cancer cells susceptibility to apoptosis and chemotherapy......

Sphingolipids are membrane lipids that play important roles in the regulation of cell functions and homeostasis. Alterations in their metabolism have been associated with several pathologies. For this reason, therapeutic strategies based on the design of small molecules to restore sphingolipid levels to their physiological condition have rapidly emerged. In addition, some of these new chemical entities, even if they fail to succeed along the pipeline, can become valuable pharmacological tools for the study of sphingolipid function. Implications of altered sphingolipid metabolism in cancer progression have allowed the identification of new targets for the development of potential anticancer agents. Based on these premises, this review is focused on the most recent achievements in the field, with special attention to the development of small molecules, mainly enzyme inhibitors, able to disrupt some of the key sphingolipid metabolic pathways implicated in cancer progression. On the other hand, metabolic dysregulation can also be modulated by the use of sphingolipid analogs, which can alter the sphingolipid balance driving cells to death or survival and thus becoming useful candidates for subsequent drug development.

The use of statins has scaled up to become one of the most prescribed medicines in the world and have been very useful in the manegement of cardiovascular diseases and related mortality. The disclosure of their chemical structure similar to that of hydroxy methyl glutaryl-CoA (HMG-CoA) revealed their ability to compete with and inhibit the rate-limiting enzyme HMG-CoA reductase that catalyzes the synthesis of mevalonate, which then serves as the precursor for isoprenoids and cholesterol in the mevalonate pathway. While most of the effects of statins are associated with the lowering of cellular cholesterol levels, it is clear that they also blunt the non-sterol branch of the mevalonate pathway, decreasing formation of isoprenoids and altering protein-prenylation, a critical event in the posttranslational modulation of proteins involved in the regulation of cell cycle progression, proliferation and signaling pathways. Randomized controlled trials for the prevention of cardiovascular diseases indicated that statins elicited provocative and unexpected benefits for reducing a number of different types of cancers, including colorectal carcinoma, melanoma, prostate and hepatocellular carcinoma, although in other cancer types the preclinical expectations of statins were dissapointing. In this review, we will describe the evidence and mechanisms underlying the potential beneficial use of statins and the role of protein prenylation in cancer prevention. Of relevance, the combination of statins with other anti cancer drugs may be a significant asset in malignancies resistant to current therapy.

Sphingolipids, which are complex lipidic components of the cell membranes, lie in a key position to modulate the pathways of trans-membrane signaling and allow the cell to adapt to environmental stresses. In malignancies, reduced production of some sphingolipid species able to induce apoptosis such as ceramide and conversely, increased levels of some other metabolites involved in tumor progression and drug resistance of cancer cells, are often described. In this context, the discovery of new chemical entities able to specifically modify ceramide metabolism should offer novel pharmacological tools in cancer therapy. The review dedicates particular attention to the enzymes that modify ceramide at the C1-OH position generating other biologically important sphingolipids in cancer, such as sphingomyelin, ceramide-1-phosphate or glucosylceramide. Findings reported in the literature leading to the development of new chemical entities specifically designed to achieve the above goals have been collected and are discussed. The effects of enzyme inhibitors of sphingomyelin synthase, ceramide kinase and glucosylceramide synthase on cancer cell proliferation, sensitivity to chemotherapeutics, induction of apoptosis or growth of xenografts are presented.

Apoptosis is a form of programmed cell death required for the development and for the proper functioning of multicellular organisms. It is defined by a combination of morphological and biochemical modifications that result from the activation of a family of proteases called caspases. Several pathways can lead to caspase activation and they often involve the release of apoptogenic factors normally sequestered in the mitochondrial intermembrane space. Complete release of mitochondrial pro-apoptotic factors ultimately results in cell death, whether in a caspase-dependent or independent manner. A tight control of mitochondrial permeability is therefore essential. Mutations of regulators of the process, such as proteins of the Bcl-2 family, have indeed been reported in many cancers. In addition, the contributions of lipids, both as regulators of protein activities and as components of the pore itself, are starting to be unravelled. Early on, the role of the mitochondria-specific phospholipid cardiolipin as a targeting signal for pro-apoptotic proteins of the Bcl-2 family was discovered. This role was then expanded since it was shown that cardiolipin also supports conformational changes undergone by proteins of the Bcl-2 family, serves as a docking station for additional pro-apoptotic factors, and is essential for the permeabilisation of synthetic liposomes by activated Bax and Bak. More recently, cholesterol, whose level is increased in most cancer cells, was shown to contribute to their resistance to cytotoxic stresses. Reducing cholesterol levels might therefore represent an interesting novel target to sensitize cancer cells to chemotherapeutic agents.

Programmed cell death, or apoptosis, is a complex process whereby eukaryotic cells react to physiologic or pathophysiologic stimuli by undergoing genetically programmed suicide. Programmed cell death involves many well-characterized signaling pathways including permeabilization of the mitochondrial outer membrane and activation of caspases. Other pathways, such as pro-apoptotic lipid signaling, are less understood despite many years of study. The sphingolipid ceramide has received considerable attention as a key regulator of programmed cell death, yet the mechanisms of its up-regulation and ability to control cell fate remain ill-defined. In this review, we will examine the connections between sphingolipid metabolism and programmed cell death with a focus on the role of de novo sphingolipid synthesis and sphingosine salvage in producing pro-apoptotic ceramide. We will also highlight the evidence supporting an increasingly complex role for ceramide in regulating apoptosis and provide a framework in which to ask new questions about the functions of this enigmatic lipid.

Sphingolipids (SLs) and cholesterol are critical structural components of membrane bilayers. Although recent evidence has revealed an emerging role of both lipids in signaling pathways, their contribution to cancer development and treatment has been largely overlooked. Sphingolipids comprise a family of bioactive lipids with divergent roles in numerous cellular processes. In particular, ceramide is the prototype of SLs and identified as a cell death effector whose levels increase in response to apoptotic stimuli such as ionizing radiation or chemotherapy. In the liver, ceramide/cholesterol accumulation contributes to a wide range of pathologies, including the transition from steatosis to steatohepatitis, which can further progress to cirrhosis and hepatocellular carcinoma (HCC). Moreover, different studies have shown that either pharmacologic ceramide accumulation or systemic intravenous administration of liposomal ceramide is an effective approach against HCC. In addition, mitochondrial cholesterol trafficking has emerged as a novel factor regulating cell death pathways and HCC tumor growth and chemoresistance. Due to the poor efficacy of current HCC treatments, understanding the role of ceramide/cholesterol in HCC may open up novel avenues for therapy. Here we describe recent evidence indicating that ceramide-generating agents and/or pharmacological targeting of sphingolipid/cholesterol metabolism, alone or in combination with other chemotherapeutic compounds, may be a promising strategy in HCC management.

Subcellular organelles such as mitochondria, endoplasmic reticulum and the Golgi complex are involved in the progression of cell death program. Recent evidence unveils that Fas ligand-mediated apoptosis induces scrambling of mitochondrial and secretory organelles via a global alteration of membrane traffic that is modulated by apical caspases. On the basis of the biochemical nature of lipid rafts, composed by sphingolipids, including gangliosides and sphingomyelin, cholesterol and signaling proteins, it has been suggested that they are part of this traffic and can participate in cell remodelling leading to cell death program execution. Although detected in various cell types, the role of lipid rafts in apoptosis has been mostly studied in T cells, where the physiological apoptotic program occurs through CD95/Fas. In this review, the possible contribution of lipid rafts to the cascade of events leading to T cell apoptosis after CD95/Fas ligation is summarized. We focused on the paradigmatic component of rafts GD3, which can proceed from the cell plasma membrane (and/or from trans Golgi network) to the mitochondria via a microtubule-dependent mechanism. This transport may be regulated by CLIPR-59, a new CLIP-170-related protein, involved in the regulation of microtubule dynamics. Particular attention has been given to mitochondrial raft-like microdomains, which may represent preferential sites where key reactions take place. Indeed, GD3, by interacting with mitochondrial raft-like microdomains, may trigger specific events involved in the apoptogenic program, including mitochondria hyperpolarization and depolarization, fission-associated changes, megapore formation and release of apoptogenic factors. These findings introduce an additional task for identifying new molecular target(s) of anti-cancer agents.

Non small cell lung cancer is known to resist apoptotic stimuli of various antitumor agents and become progressively incurable. The present study was undertaken to evaluate the in vitro antineoplastic effect of polyphenols extracted from both green tea (GTPs) and ginger (GPs) on non-small cell lung cancer cells (NSCLC-NCI-H460). Methods: The direct antitumor effect of GTPs and GPs on H460 cells was assessed by investigating the proliferation rate, metabolic activity assay (MTT method) and the apoptotic effect (determined by an annexin V apoptosis assay). Also, the inhibition concentrations (IC50) of both extracts and the levels of P 53 and Bcl-2 proteins were determined. Results: GTPs and GPs have inhibited the proliferation of H460 cells in a dose-dependent manner. At the end of treatment period (96 h) the cell population has decreased to 16% and 26% when treated with 80μg GTPs or GPs, respectively, compared to the untreated cells. The IC50 values of both extracts were 32.9 and 55.5 g/ml, respectively. GTPs was more effective in reduction of cell metabolic activity (measured by MTT assay), where cell count decreased to 22% compared to 64% in cells treated with similar concentration (80μg) of GPs. Lower concentration (20μg) of cisplatin induced 15% reduction in cell metabolic activity. Moreover, 80μg of GTPs and GPs extracts induced apoptosis by 71% and 39% of the living cells, respectively. The apoptotic effect of both extracts, especially GTPs, seems to be mediated by both P 53 and Bcl-2. Conclusion: The study reports the antiproliferative and apoptosis-mediated cytotoxic effects of green tea and ginger polyphenolic extracts on human H460 cell line, indicating their promising chemopreventive effect against lung cancer.

Progress in identifying and understanding the molecular and cellular causes of cancer has led to the discovery of anomalies that characterize cancer cells and that represent targets for the development of cancer therapeutics. One such target is the epidermal growth factor receptor (EGFR), a transmembrane protein that is frequently dysregulated in cancer cells and associated with the development, progression and aggressiveness of a number of malignancies. Inhibition of EGFR signaling has thus been identified as an attractive strategy in control of tumor proliferation, and over a decade of intense activity in the field has culminated in the discoveries and subsequent approvals of gefitinib and erlotinib for the treatment of non-small cell lung cancer. However, the drug's resistance to gefitinib and erlotinib has been clinically observed. Therefore, intensive efforts have been made in the discovery of novel potent and selective EGFR inhibitors. This review will focus on the developments of small molecule EGFR inhibitors based on the quinazoline core scaffolds in recent 5 years. Diverse EGFR inhibitors are classified as 4-anilinoquinazolines and 4-nonanilininoquinazolines, their biological data are described, and the structure-activity relationships (SARs) are discussed.

The tumor microenvironment is characterized by a poor circulation which results in the selection of neoplastic cells that can grow or survive under hypoxic conditions. The relationship between hypoxia and histone deacetylase (HDAC) inhibitors has been previously established. In this work we evaluated the effects of novel HDAC inhibitors (the natural peptide FR235222 and three tetrapeptide analogs) in the human breast cancer cell line MDAMB231, cultured under hypoxia (2% O2 ≈ 14 mmHg) or normoxia (20% O2 ≈ 140 mmHg). First, we found that the novel HDAC inhibitors reduced cell proliferation in MDAMB231 cells at an extent which was similar or even higher than that exerted by the classic HDAC inhibitors trichostatin-A and suberoylanilide hydroxamic acid. More interestingly, the antiproliferative effects of the novel HDAC inhibitors were, in general, significantly higher in hypoxic cells than in normoxic controls. Hypoxic MDAMB231 cells expressed high levels of the hypoxia-inducible factor (HIF)-1α and HIF-1α-related genes, such as vascular endothelial growth factor, Bcl-2/E1B 19 kDa interacting protein-3, glucose transporter-1, carbonic anhydrase IX, as determined by Western blot analysis and qRT-PCR. Finally, we found that HIF-1α and HIF-1α-related genes were significantly downregulated by FR235222 and analogs. In conclusion, the identification of novel effects exerted by the HDAC inhibitors, characterized by a strong efficacy in inhibiting the expression of HIF-1α and its related genes, may have important implications in the pharmacological control of several tumors, including breast cancer, characterized by the presence of hypoxia, angiogenesis and metabolic derangements.