Current Medicinal Chemistry - Anti-Cancer Agents - Volume 5, Issue 6, 2005

The phosphatidylinositol 3-kinase (PI3K)/Akt (protein kinase B, PKB) signaling pathway plays a critical role in cell growth and survival. Dysregulation of this pathway has been found in a variety of cancer cells. Recently, constitutively active PI3K/Akt signaling has been firmly established as a major determinant for cell growth and survival in an array of cancers. Blocking the constitutively active PI3K/AKT signaling pathway provides a new strategy for targeted cancer therapy. Thus, inhibitors of this signaling pathway would be potential anticancer agents, particularly for cancer cells whose survival and growth are dominated by constitutively active PI3K/Akt signaling. This review describes the current understanding of small molecule drugs targeting this pathway both in vitro and in vivo. Inhibitors and functions of the upstream and downstream molecular targets of the PI3K/Akt pathway are discussed in the context of using the inhibitors to block this pathway for targeted cancer therapy. Special emphasis is placed on the following targets: receptor tyrosine kinases, PI3K, Akt, and the mammalian target of rapamycin. While the molecular therapeutic strategy holds great promise for the treatment of a variety of cancers, few small molecule inhibitors with potential high therapeutic indexes are available. Thus, new inhibitors with high selectivity, bioavailability, and potency are greatly needed. Novel approaches toward the development of PI3K/Akt pathway inhibitors as anticancer therapeutics are discussed in detail, with emphasis on chemical genetics-based and structure-based drug design.

The application of inorganic chemistry to medicine is a rapidly developing field, and novel therapeutic and diagnostic metals and metal complexes are now having an impact on medical practice. Advances in biocoordination chemistry are crucial for improving the design of compounds to reduce toxic side effects and understand their mechanisms of action. A lot of metal-based drugs are widely used in the treatment of cancer. The clinical success of cisplatin and other platinum complexes is limited by significant side effects acquired or intrinsic resistance. Therefore, much attention has focused on designing new coordination compounds with improved pharmacological properties and a broader range of antitumor activity. Strategies for developing new anticancer agents include the incorporation of carrier groups that can target tumor cells with high specificity. Also of interest is to develop complexes that bind to DNA in a fundamentally different manner than cisplatin, in an attempt to overcome the resistance pathways that have evolved to eliminate the drug. This review focuses on recent advances in developing lanthanide anticancer agents with an emphasis on lanthanide coordination complexes. These complexes may provide a broader spectrum of antitumor activity. They were compared with classical platinum anticancer drugs. Lanthanides are also of interest because of their therapeutic radioisotopes. The dominant pharmacological applications of lanthanides are as agents in radioimmunotherapy and photodynamic therapy.

Prostate cancer is the most common cancer amongst men in the USA and the second most common malignant cause of male death worldwide after lung cancer. The life time risk of having microscopic evidence of prostate cancer for a 50 year old man is 42%. Prostate cancer is thus becoming an increasingly significant global health problem in terms of mortality, morbidity, as well as economically. This review, discusses current medical therapeutic options for prostate cancer including traditional treatments using luteinising hormone releasing analogues (LHRH), anti-androgens and estrogen treatments, and the use of novel drugs directed against molecular targets considered important in oncogenesis and metastasis. Prostate cancer chemoprevention using 5a-reductase inhibitors and the role of gene therapy are also considered.

It was found that a class of sulfolipids known as sulfo-quinovosyl-acyl-glycerols (SQAGs) from ferns and algae are potent inhibitors of eukaryotic DNA polymerase α & β and effective anti-neoplastic agents. In developing a procedure for the chemical synthesis of sulfolipids, many derivatives and stereoisomers of SQAGs have been obtained including sulfo-quinovosyl-monoacyl-glycerols (SQMGs) and sulfo-quinovosyl-diacyl-glycerols (SQDGs). This review describes studies on the structure-function relationship between synthetic SQAGs and DNA polymerase α & β, and the relationship to cytotoxic activity. The major action was probably dependent on the fatty acid effect, which was reported previously, although each of the SQAGs was a much stronger inhibitor than just the fatty acid present in the SQAGs. The inhibitory effect could be influenced by the chain size of fatty acids in the SQAGs. The sulfonyl group in quinovose was also needed to inhibit the enzymes. Lineweaver-Burk plots of SQAGs indicated that DNA polymerase α was noncompetitively inhibited, but the SQAGs were effective as antagonists of both the template-primer DNA-binding and the nucleotide substrate-binding of DNA polymerase β. Based on these results, the molecular actions of SQAGs and drug design strategies for developing new anti-neoplastic agents were discussed.

Dietary chemoprevention has emerged as a cost effective approach to control most prevalent chronic diseases including cancer. In particular, tomato and tomato products are recognised to confer a wide range of health benefits. Epidemiological studies have provided evidence that high consumption of tomatoes effectively lowers the risk of reactive oxygen species (ROS)-mediated diseases such as cardiovascular disease and cancer by improving the antioxidant capacity. Tomatoes are rich sources of lycopene, an antioxidant carotenoid reported to be a more stable and potent singlet oxygen quenching agent compared to other carotenoids. In addition to its antioxidant properties, lycopene shows an array of biological effects including cardioprotective, anti-inflammatory, antimutagenic and anticarcinogenic activities. The anticancer activity of lycopene has been demonstrated both in in vitro and in vivo tumour models. The mechanisms underlying the inhibitory effects of lycopene on carcinogenesis could involve ROS scavenging, upregulation of detoxification systems, interference with cell proliferation, induction of gap-junctional communication, inhibition of cell cycle progression and modulation of signal transduction pathways. This review outlines the sources, structure, absorption, metabolism, bioavailability and pharmacological properties of lycopene with special reference to its antioxidant and anticarcinogenic effects.

The role of selenium in the prevention of cancer has been recently established by laboratory experiments, clinical trials, and epidemiological data. Most of the effects are related to the function of selenium in antioxidant enzyme systems. Animal data, epidemiological data, and intervention trials have shown a clear role for selenium derivatives in both prevention of specific cancers and antitumorigenic effects in postinitiation phases of cancer. Consequently, selenium supplementation has moved from the realm of correcting nutritional deficiencies to one of pharmacological intervention, especially in the clinical domain of cancer chemoprevention. Accordingly, there has been substantial interest directed toward the synthesis of selenium-containing derivatives in recent years that could be used as cancer chemopreventive agents. The current review aims to outline recent developments in the application of selenium derivatives as cancer preventive agents.