Current Medicinal Chemistry - Volume 16, Issue 17, 2009

Although chemotherapy is considered the mainstay of cancer therapy, unfortunate side effects of chemotherapy create a continuous demand for developing other novel and specific targets for cancer therapy. Re-expression of epigenetically silenced tumor suppressor genes is a rational strategy for the treatment of human neoplasms. Epigenetic modifiers like DNA methyltransferase (DNMT) inhibitors and histone deacteylase (HDAC) inhibitors induce the re-expression of epigenetically silenced genes in vitro and in vivo. Moreover, they demonstrate safety and efficacy against neoplastic diseases in clinical trials. DNMT inhibitors like 5-azacytidine and 5-aza-2'-deoxycytidine are currently FDA approved for the treatment of myelodysplastic syndrome. Nonetheless, the mechanism of action behind their clinical efficacy remains unclear. Ongoing clinical trials are attempting to identify tumor suppressor genes that upon re-expression can induce remission and cure in patients. On the other hand, the pleiotropic biological effects of DNMT inhibitors and recent reports demonstrating lack of association between clinical response and methylation reversal of candidate tumor suppressor genes, suggest a complex mechanism behind their clinical efficacy that may involve a cytotoxic effect.

Benzamide derivatives are known as antipsychotic and antiemetic drugs. Owing to its neurotropic characteristic this class of compounds was found useful for imaging melanoma and melanoma metastases. [123I]BZA (N-(2- diethylaminoethyl)-4-[123I]iodobenzamide) was the first example which was clinically applied as an imaging agent demonstrating high tumor uptake. This finding initiated research efforts to further improve the affinity and pharmacological properties of this agent. In order to optimize the use of these molecules with respect to costs and wide spread distribution, 99mTc labeled benzamides have been developed. Indeed, several 99mTc complexes were found suitable for melanoma imaging; however, they were less eligible than radioiodinated benzamides. Besides their use as radiotracers benzamides have been evaluated for magnetic resonance imaging. Molecular imaging with paramagnetic metal contrast agents for magnetic resonance tomography (MRT) is hampered by the inferior sensitivity of MRT. Biochemical trapping was thought to overcome this problem using the polyamine transporter of melanoma cells. One of the neutral, DTPA based Gd complexes comprising 2-(diethylamino)ethylamine and bis-(2-aminoethyl)amine in the side chain led to intracellular uptake values well above the MRI detection limit. An overview about benzamides used for molecular imaging and as transporters for cytostatic agents as well as inhibitors for histone deacetylases concludes this review, demonstrating that benzamide derivatives represent a versatile class of compounds leading to novel imaging and therapeutic agents.

Protein tyrosine phosphatases (PTPs) play a critical role in physiological signaling pathways by controlling the level of tyrosine phosphorylation. The past decade has seen a vast increase in both academic and industrial interest in PTPs and their relevance as potential therapeutic targets, with several PTP inhibitors recently entering clinical trials. Despite these developments, there are numerous examples of failed PTP drug discovery programs, such that PTPs have attained a reputation as ‘undruggable’ targets. This review attempts to illustrate the many obstacles that must be overcome to successfully develop a PTP drug, ranging from validation of PTPs as therapeutic targets to the difficulties of assessing the true inhibitory nature of apparently well-behaved compounds, along with the need to balance the physiocochemical properties required for active site binding with the characteristics needed for in vivo activity. A number of examples of structure-based design are presented, along with cautionary tales of PTP inhibitor programs that have failed due to unexpected shortcomings.

During more than five decades, pyridinium oximes have been developed as therapeutic agents used in the medical treatment of poisoning with organophosphorus compounds. Their mechanism of action is reactivation of acetylcholinesterase (AChE) inhibited by organophosphorus agents. Organophosphorus compounds (OPC) are used as pesticides and developed as warfare nerve agents such as tabun, soman, sarin, VX and others. Exposure to even small amounts of an OPC can be fatal and death is usually caused by respiratory failure resulting from paralysis of the diaphragm and intercostal muscles, depression of the brain respiratory center, bronchospasm, and excessive bronchial secretions. The mechanism of OPC poisoning involves phosphorylation of the serine hydroxyl group at the active site of AChE leading to the inactivation of this essential enzyme, which has an important role in neurotransmission. AChE inhibition results in the accumulation of acetylcholine at cholinergic receptor sites, producing continuous stimulation of cholinergic fibers throughout the central and peripheral nervous systems. Presently, a combination of an antimuscarinic agent, e.g. atropine, AChE reactivator such as one of the standard pyridinium oximes (pralidoxime, trimedoxime, obidoxime, HI-6) and diazepam has been used for the treatment of organophosphate poisoning in humans. Despite enormous efforts devoted to synthesis and development of new pyridinium oximes as potential antidotes against poisoning with OPC, only four compounds have found their application in human medicine so far. However, they differ in their activity in poisoning with warfare nerve agents and pesticides and there is still no universal broad-spectrum oxime capable of protecting against all known OPC. In this article, we review data on structure-activity relationship of pyridinium oximes and discuss their pharmacological and toxicological significance.

The anticonvulsant and neuroprotective properties of agonist and antagonist of metabotropic glutamate receptors (mGluRs ) have been known for 15 years or so. However, it is not yet clear whether these agents, and allied compounds, can be considered as candidate drugs for eventual use in the clinic to control the development of epilepsy, (i.e. as anti- epileptogenics), or for the control of seizures themselves (i.e. as anticonvulsants). In fact, few studies have been designed to test for these properties by, for instance, administering these agents during the chronic stages of experimental epilepsy to determine whether a tendency to generate spontaneously recurrent seizures, which often appear by epileptogenesis, could be prevented or stopped. Even in the acute stages, there are substantial differences in experimental design between the published studies. Thus, there are large variations in such factors as timing, and the route of administration of candidate drugs, the age, or species and strain of experimental animal used, and the experimental epilepsy model employed. Such variations often make it difficult to accurately assess the anticonvulsant, neuroprotective and antiepileptogenic properties of each candidate drug across a wide range of studies. This paper, will review neuroanatomical, neurochemical, neuropharmacological studies of mGluRs in animal models and in patients with temporal lobe epilepsy, and summarize anticonvulsive and neuroprotective effects of their agonists and antagonists in different seizure and epilepsy models in order to give direction for the development of new generation antiepileptogenic and anticonvulsive drugs.

Carbazole derivatives are well known for their various pharmacological activities, including anti-HIV, anticancer, antibacterial and antifungal activities. This review will focus on carbazoles that possess antifungal activity against Candida albicans, the major human fungal pathogen. In our search for new fungicidal compounds, we identified a series of substituted carbazoles, termed N-alkylated 3,6-dihalogenocarbazoles, that exhibit fungicidal activity against C. albicans and the emerging pathogen Candida glabrata. The most potent fungicidal compounds of this series were characterized by minimal fungicidal concentration (MFC) between 8.5 and 25 μM. To analyse the structural determinants for fungicidal activity of these carbazole derivatives, we selected 10 such derivatives and performed further analyses. Interestingly, some of these N-alkaylated 3,6-dihalogenocarbazoles were active against Candida biofilms grown in microtiterplates. In this review, we will further discuss the putative therapeutic potential of the antifungal carbazole compounds as antimycotics.