Anti-Cancer Agents in Medicinal Chemistry (Formerly Current Medicinal Chemistry - Anti-Cancer Agents) - Volume 9, Issue 2, 2009

Marine organisms have attracted scientific community as a rich source of natural products with unusual structural features and remarkable biological activities. Marine macrolides are a prominent class of natural products characterized by a highly oxygenated polyene backbone containing a macrocyclic lactone as a conformational constraint. Many marine macrolides possess outstanding cell growth antiproliferative properties, making them valuable molecular probes for the investigation of biochemical pathways and promising lead compounds for the development of new antitumor chemotherapeutic agents. In the present review we intend to focus on marine macrolides with potent cytotoxic activity that could be exploited in cancer research and therapy, along with those macrolides currently in clinical trials and/or preclinical development.

Cancer is one of the leading causes of death in the world. American Cancer Society reported 12 million new cases of malignancy diagnosed worldwide in 2007, with 7.6 million people dying from the disease. Plant-derived molecules have played an important role in cancer chemotherapy. Many cytotoxic plant-derived molecules such as vinblastine, vincristine, navelbine, etoposide, teniposide, taxol, taxotere, topotecan and irinotecan have been approved as anticancer drugs. Flavonoids, a plant-derived molecule has shown to regulate proliferation and cell death pathways leading to cancer. Some Flavonoids have already entered in clinical trials, among them Quercetin is emerging as prospective anticancer drug candidates and its prodrug QC12 has entered in phase-I clinical studies. In this review authors have tried to cover in brief but comprehensive way, the chemistry related to synthesis and uses of “Quercetin & its derivatives” with special emphasis on the anticancer properties.

Gastrointestinal tumours constitute one of the worldwide leading causes of death. One important limitation in the battle against these types of cancer is their lack of sensitivity to currently available chemotherapy and the development of drug resistance during treatment. The mechanisms responsible for this refractivity include a reduction in drug uptake, enhanced drug export, intracellular inactivation of the effective agent, alteration of the molecular target, an increase in the activity of the target route to be inhibited or the appearance or stimulation of alternative routes, enhanced repair of drug-induced modification in the target molecules, and activation/inhibition of intracellular signalling pathways, which leads to a negative balance between apoptosis/survival of tumour cells. A better understanding of these mechanisms is needed in order to develop both accurate tests to predict the lack of response to chemotherapy and novel approaches aimed to overcome the drug resistance of gastrointestinal tumours. The complexity of this issue is further increased owing to the existence of marked differences among the types of primary malignant gastrointestinal tumours and the diversity of tissues from which metastatic cells can access the gut. Moreover, inter-individual variability plus the fact that sensitivity/refractivity may change during the evolution of the tumour further complicate the overall situation. The present article reviews anti-cancer agents used either alone or, more frequently, combined in regimens, as neoadjuvant or postsurgical adjuvant chemotherapy within the context of the available curative and palliative therapeutic options used to treat the most common types of cancer of the gastrointestinal tract and pancreas.

Metal-based antitumor drugs play a relevant role in antiblastic chemotherapy. Cisplatin is regarded as one of the most effective drugs, even if severe toxicities and drug resistance phenomena limit its clinical use. Therefore, in recent years there has been a rapid expansion in research and development of novel metal-based anticancer drugs to improve clinical effectiveness, to reduce general toxicity and to broaden the spectrum of activity. The variety of metal ion functions in biology has stimulated the development of new metallodrugs other than Pt drugs with the aim to obtain compounds acting via alternative mechanisms of action. Among non-Pt compounds, copper complexes are potentially attractive as anticancer agents. Actually, since many years a lot of researches have actively investigated copper compounds based on the assumption proposal that endogenous metals may be less toxic. It has been established that the properties of copper-coordinated compounds are largely determined by the nature of ligands and donor atoms bound to the metal ion. In this review, the most remarkable achievements in the design and development of copper(I, II) complexes as antitumor agents are discussed. Special emphasis has been focused on the identification of structure-activity relationships for the different classes of copper(I,II) complexes. This work was motivated by the observation that no comprehensive surveys of copper complexes as anticancer agents were available in the literature. Moreover, up to now, despite the enormous efforts in synthesizing different classes of copper complexes, very few data concerning the molecular basis of the mechanisms underlying their antitumor activity are available. This overview, collecting the most significant strategies adopted in the last ten years to design promising anticancer copper( I,II) compounds, would be a help to the researchers working in this field.

Protein tyrosine phosphorylation is one of the key mechanisms involved in signal transduction pathways. This modification is regulated by concerted action of protein tyrosine phosphatases and protein tyrosine kinases. Deregulation of either of these key regulators lead to abnormal cellular signaling, which is largely associated with human pathologies including cancer. Although the role of protein tyrosine kinases in cancer is well established, less is known about the involvement of protein tyrosine phosphatases in carcinogenesis and tumor progression. Moreover, several inhibitors targeting protein tyrosine kinases have demonstrated their value in cancer treatment, while interest in protein tyrosine phosphatases as a target for treatment has risen more recently. In this review we describe the progressive efforts and challenges concerning the development of drugs targeting phosphatases as promising novel cancer therapies. We focus on two key regulatory SH2 domain-containing phosphatases, SHP-1 and SHP-2 and one of their substrates, signal regulatory protein alpha. Since SHPs have been linked to many different malignancies, protein tyrosine phosphatases could offer a great spectrum of new, targeted drugs.

c-Met and RON are receptor tyrosine kinases (RTK) that are closely related, both from a homology as well as from a functional stand point. Both receptors can induce cell migration, invasion, proliferation and survival in response to their respective ligand. Moreover, both possess oncogenic activity in vitro, in animal models in vivo and are often deregulated in human cancers. c-Met attracted a lot of interest shortly after its discovery in the mid-1980s because of its unusual role in cell motility. Moreover, a causal role for c-Met activating mutations in human cancer propelled an intensive drug discovery effort throughout the research and pharmaceutical communities to find inhibitors of c-Met. While c-Met is now a well-accepted target for an anti-cancer drug, less is known about the role of RON in cancer. Interestingly, despite their many common attributes, c-Met and RON are activated by different mechanisms in cancer cells. Because of the homology between the two RTKs, some small molecule kinase inhibitors of c-Met have inhibitory activity on RON, opening the door to exploring the role of both receptors in human cancers. In this review we will discuss the relevance of both c-Met and RON deregulation in human cancers and the progress so far in identifying small molecule kinase inhibitors that can block the activity of these targets in vitro and lead to anti-tumor effects in animal models.

In the past, anti-cancer drugs were identified and developed without focusing on a particular macromolecular target. Currently, the fields of molecular biochemistry, molecular biology, genetics and pharmacology, among other disciplines, have grown considerably in their ability to identify biological targets. These disciplines are now searching for specific targets to treat cancer. These targets exist in different cellular compartments (membrane, cytoplasm, nucleus) as proteins, glycoproteins, nucleic acids, etc. Computational tools have recently been used to explore such targets and to corroborate previously obtained experimental data. These methods have also been used to design new drugs with the aim of decreasing illness and the economic resources needed to discover drug candidates. Some of these computational methods include quantum mechanics (ab initio and density functional theories) and molecular mechanics (docking, molecular dynamics, and protein folding). Docking and molecular dynamics are the most commonly used computational tools for elucidating cancer targets. Using these tools, one can identify the recognition processes between ligands and targets at the atomic level. In addition, one can identify the affinity and conformational changes of these molecular complexes. In conclusion, we propose that the use of such tools is necessary in order to identify new anti-cancer drugs.

Angiogenesis plays an important role in tumor metastasis and progression, and thus inhibiting angiogenesis is a promising strategy for treatment of cancer. However, tumor-associated angiogenesis is influenced by various angiogenic factors in the tumor microenvironment. Thymidine phosphorylase (TP, EC 2. 4. 2. 4), an enzyme involved in the reversible conversion of thymidine to thymine, is an important mediator of angiogenesis, tumorigenicity, metastasis and invasion. The angiogenic effect of TP requires the enzymatic activity of TP. TP activity is expressed at higher levels in a wide variety of solid tumors than in adjacent non-neoplastic tissue. The tumor microenvironment (hypoxia, acidosis) regulates the expression of TP, and TP expression in tumor tissue shows significant correlation with microvessel density and poor prognosis. 2-Deoxy-D-ribose (D-dRib), one of the degradation products of thymidine generated by TP activity, promotes angiogenesis and the chemotactic activity of endothelial cells and also confers resistance to hypoxia-induced apoptosis in some cancer cell lines. These findings suggest that D-dRib is a downstream mediator of TP function. 2-Deoxy-L-ribose, a stereoisomer of D-dRib, can inhibit D-dRib's anti-apoptotic effects and suppress metastasis and invasion of TP-expressing tumors in mice. Although the mechanism of action of D-dRib is still unknown, the physiological activities of D-dRib have recently been reported by several groups. We review the role of D-dRib in tumor progression and discuss inhibition of D-dRib as a promising approach for chemotherapy of various tumors.