Current medicinal chemistry. Anti-cancer agents最新文献

In addition to all-trans-retinoic acid and its 9 and 13-cis isomers, four synthetic retinoids are currently available to treat diseases of hyperproliferation, such as acne, psoriasis, and actinic keratosis, or cancers such as acute promelocytic leukemia, cutaneous T-cell lymphoma, and squamous or basal cell carcinoma. The retinoids extert their antiproliferative effects by interacting with their retinoic acid and retinoid X receptors that act as ligand-inducible transcription factors. These homologous receptors function either directly on retinoid response elements or indirectly by modifying the responses of other transcription factors. Their major domains for binding DNA and their ligands have been characterized by either nuclear magnetic resonance spectroscopy or X-ray crystallography. The identification and design of synthetic retinoids are overviewed, as are their selective interactions with specific retinoid receptor subtypes and their clinical effects against cancer. Emphasis is placed on the retinoid X receptors and their ligands.

Surgery is the only method of cure in lung cancer. Seldom its application with radical intent is possible. Despite the efforts aimed at integrating all the therapeutic strategies, the overall outcome of the management of this disease remains disappointing. For this reason, in the last three decades, thousands of preclinical and clinical attempts have been realised in order to investigate any possible way to cure this disease and significant steps forward have been made on the basis of the increasing "molecular knowledge" in the so called "post-genomic era". Particularly the impressive step forward in the biological characterization of cancer as a result of genetic/epigenetic multistep process has brought in a multitude of variables with staggering classification potentialities. "Benchside" and "bedside" scientists have assembled in functional teams to move the common efforts "translationally" to bridge basic and clinical research for a mutual synergistic enhancement. This paper represents the effort of a lung cancer focused translational research team made up of molecular biologists, medical oncologists and thoracic surgeons to achieve a comprehensive, but simple, review of the current status of the shift from cytotoxic to molecularly targeted therapy in lung cancer treatment potentially useful in the planning of translational research trials.

Acronycine, a natural alkaloid originally extracted from the bark of the Australian ash scrub Acronychia baueri, has shown a significant antitumor activity in animal models. Acronycine has been tested against human cancers in the early 1980s, but the clinical trials showed modest therapeutic effects and its development was rapidly discontinued. In order to optimize the antineoplastic effect, different benzoacronycine derivatives were synthesized. Among those, the di-acetate compound S23906-1 was recently identified as a promising anticancer drug candidate and a novel alkylating agent specifically reacting with the exocylic 2-NH2 group of guanines in DNA. The study of DNA bonding capacity of acronycine derivatives leads to the identification of the structural requirements for DNA alkylation. In nearly all cases, the potent alkylating agents, such as S23906-1, were found to be much more cytotoxic than the unreactive analogs such as acronycine itself or diol derivatives. Alkylation of DNA by the monoacetate derivative S28687-1, which is a highly reactive hydrolysis metabolite of S23906-1, occurs with a marked preference for the N2 position of guanine. Other bionucleophiles can react with S23906-1. The benzacronycine derivatives, which efficiently alkylate DNA, also covalently bind to the tripeptide glutathione (GSH) but not to the oxidized product glutathione disulfide. Here we review the reactivity of S23906-1 and some derivatives toward DNA and GSH. The structure-activity relationships in the benzacronycine series validate the reaction mechanism implicating DNA as the main molecular target. S23906-1 stands as the most promising lead of a medicinal chemistry program aimed at discovering novel antitumor drugs based on the acronycine skeleton.

In spite of the impressive progress in diagnosis, surgery and therapy that occurred since the Sixties, the overall cancer mortality is still high and the medical need is largely unmet. A number of innovative strategies, aimed to target malignant abnormalities of tumor cells are in development and begin to give important results. In alternative, angiogenesis inhibition has been addressed with the aim to limit the tumor ability to grow and metastasize. However, it will likely take some years to fully define the therapeutic role of different innovative drugs. Therefore, cytotoxic drugs will continue to represent a chief part of the therapy in the forthcoming years, possibly in combination with innovative agents addressing molecular targets. Most important traditional chemotherapeutic drugs or investigational anticancer agents were derived from natural sources also through synthetic structural modifications. In the Nineties, taxanes and camptothecins represented important success stories of this approach, while among DNA interacting agents anthracyclines continued to represent a structural platform for discovering new drugs and DNA minor groove binders represented a new field of investigation. Combinatorial chemistry combined with high-throughput screening programs are an important source of totally synthetic new agents, however, it should not be disregarded the fact that nature already performed combinatorial chemistry and leads selection through the ages. New natural or semisynthetic agents acting as tubulin stabilizers or DNA interactive agents of various mechanisms of action are presently investigated and will probably continue to give important contribution to cancer therapy in the near future. In this review, the medicinal chemistry and the development status of these anticancer cytotoxic agents are focused and discussed.

The natural plant product ellipticine was isolated in 1959 from the Australian evergreen tree of the Apocynaceae family. This compound was found to be an extremely promising anticancer drug. The planar polycyclic structure was found to interact with DNA through intercalation, exhibiting a high DNA binding affinity (10(6) M(-1)). The presence of protonatable ring nitrogens distinguished ellipticine from other simple intercalators. Both monocationic and uncharged species were found to be present under physiological conditions. The positive charge stabilized the binding of ellipticine to nucleic acids, while the more lipophilic uncharged compound was shown to readily penetrate membrane barriers. The structural nature of these compounds offers a plausible basis for the implication of multiple modes of action, including DNA binding, interactions with membrane barriers, oxidative bioactivation and modification of enzyme function; most notably that of topoisomerase II and telomerase. Pharmacologically, a number of toxic side effects have been shown to be problematic, but the amenability of ellipticine towards systematic structural modification has permitted the extensive application of rational drug design. A number of successful ellipticine analogs have been designed and synthesized with improved toxicities and anticancer activities. More recently the synthetic focus has broadened to include the design of hybrid compounds, as well as drug delivery conjugates. Considerable research efforts have been directed towards gaining a greater understanding of the mechanism of action of these drugs that will aid further in the optimization of drug design.

Lung cancer is the leading cause of death worldwide. Current treatment modalities, including chemotherapy, radiotherapy and surgery, provide only limited improvement in the natural course of this disease. Therefore, the development of new therapeutic strategies is highly awaited. This review focuses on recent achievements on a novel class of anticancer drugs targeting the EGFR (Epidermal Growth Factor Receptor). The EGFR family is a group of four structurally similar growth factor receptors with tyrosine-kinase activity (EGFR, HER2/neu, ErbB-3, ErbB-4), which dimerize upon binding with a number of ligands, including EGF (Epidermal Growth Factor) and TGF (Transforming Growth Factor), allowing downstream transduction of mitogenic signals. Overexpression of EGFR and HER2 is frequently found in non-small-cell lung cancer (NSCLC), which accounts for over 80% of all malignant lung tumors, and has been associated with a worse clinical outcome. New agents developed to inhibit EGFR function include monoclonal antibodies and small-molecule receptor tyrosine-kinase inhibitors. In this review, results of most recent clinical with EGFR inhibitors including monoclonal antibodies, such as Trastuzumab (Herceptin), IMC-C225 (Cetuximab) and others (ABX-EGF, EMD 72000), and tyrosine-kinase inhibitors, such as ZD1839 (Gefitinib, Iressa), OSI-774 (Erlotinib, Tarceva) and others (CI-1033, GW2016), are summarized. In particular, final results of phase II (IDEAL 1 and 2) and III (INTACT 1 and 2) studies of ZD1839 are reported. In IDEAL trials (ZD1839 single agent in patients pre-treated with chemotherapy) there was clear evidence of tumor regression, symptoms improvement and overall clinical benefit, whereas in the two INTACT trials (ZD1839 in combination with standard platinum-based chemotherapy in chemo-naive patients) ZD1839 did not improve either survival or other clinical endpoints. Possible explanations for these contradictory results and future perspectives are discussed.

Protein tyrosine kinases play a fundamental role in signal transduction pathways regulating a number of cellular functions such as cell growth, differentiation and cell death. Tyrosine kinases are, therefore attractive targets for the design of new therapeutic agents, not only against cancer, but also against many other diseases. Numerous tyrosine kinase inhibitors have been discovered by screening of plant extracts based on ethnopharmacological and chemotaxonomical knowledge. Specific screening approaches have led to the isolation of structurally distinct classes of inhibitors, including phenylpropanes, chalcones, flavonoids, coumarins, styrenes, quinones and terpenes. These natural inhibitors have served as valuable leads for further design and synthesis of more active analogues. Many of these inhibitors have also been used in probing the molecular and cellular mechanisms involved in the protein tyrosine kinase mediated signal transduction. In this review, plant-derived protein tyrosine kinase inhibitors and their synthetic analogues were systematically evaluated based on their plant origin, structure-activity relationship and anticancer efficacy.

The knowledge that Ras was readily prenylated by protein FTase and that the inhibition of this reaction has the ability to revert the transformed phenotype, provided the rationale for the development of FTIs as anticancer drugs. Studies have shown that farnesylation of Ras is the first, obligatory first step in a series of post-translational modifications leading to membrane association, which, in turn, determines the switch from an inactive to an active Ras-GTP bound form. Based on the theorical assumption that preventing Ras farnesylation might result in the inhibition of Ras functions, a range of FTIs have been synthesized. Their biology is fascinating since after substantial investigation and their use in several phase II studies and at least two phase III trials, the exact mechanism of action remains unclear. FTIs can block the farnesylation of several additional proteins, such as RhoB, prelamins A and B, centromere proteins (CENP-E, CENP-F), etc. While the FTIs clearly do not or only partly target Ras, these agents appear to have clinical activity in leukemia and in some solid tumors regardless of their Ras mutational status. Although inhibition of FTase by these compounds has been well documented also in normal tissues, their toxic effects seem to be manageable. However, preliminary results of early Phase II-III studies suggest that the activity of FTIs, as a single-agent, is modest and generally lower than that obtained by standard cytotoxic drugs. Ongoing clinical studies are assessing the role of FTIs for early stage disease or in combination with cytotoxic agents or with other molecular targeted therapies for advanced stage tumors. Further insights in the molecular mechanism of action of FTIs might help in better define their optimal use in combination with standard therapies in the treatment of cancer patients.

Thymidine phosphorylase (TP) is markedly upregulated in many solid tumors such as colorectal, breast and kidney cancers. Because TP is identical to platelet-derived endothelial cell growth factor, this enzyme is believed to have angiogenic properties, although the precise mechanisms through which it promotes neoangiogenesis are still not fully elucidated. TP is involved as well in the tumoral activation of widely prescribed pyrimidine-derived antimetabolites such as 5-FU, 5'-dFUR and newly marketed capecitabine, and, in this respect, has been presented as a determinant to fluoropyrimidine efficacy in various in vitro and in vivo models. This dual and apparently contradictory role that TP plays yields inconsistent results in the study of relationships between this enzyme expression and clinical outcome in patients treated with fluoropyrimidine analogs. Some studies have shown that high tumoral TP expression was associated indeed with poor clinical response and tumor aggressiveness. Conversely, other reports demonstrated that tumoral TP could be considered as a good response factor in patients exposed to fluoropyrimidine drugs. TP exhibits then its more favorable profile, probably in converting 5-FU to active metabolites responsible for its efficacy as antitumor agent. As a result, TP-targeting as a rationale for anticancer therapy remains unclear. TP inhibitors are being synthesized as an attempt to fight neoangiogenesis, whereas promising new strategies such as taxotere/capecitabine or radiotherapy/fluoropyrimidines associations aim at nothing but boosting TP activity to optimize drug activation in tumors. Such a discrepancy illustrates the complexity of understanding and predicting the exact role of TP in the clinical outcome of patients exposed to fluoropyrimidines, a group of major drugs extensively used in oncology.