Current Molecular Pharmacology - Volume 1, Issue 2, 2008

Overexpression of ATP-binding cassette (ABC) drug transporters that actively efflux a variety of amphipathic compounds can cause multidrug resistance (MDR) in cancer cells, which is a major obstacle in the success of cancer chemotherapy. The development of synthetic small molecule compounds or the identification of natural products that block ABC transporter-mediated efflux has been the conventional approach used to combat MDR. The strategy of using chemosensitizers, however, has not been successful in clinical cancer chemotherapy. Therefore, alternative approaches to identify or to synthesize compounds that can induce selective toxicity in cancer cells overexpressing one or more ABC transporters have been undertaken. This review summarizes the recent advances in identifying strategies to restore sensitivity to chemotherapeutics in multidrug resistant cancer cells.

Neurons communicate through the exocytotic release of transmitters from presynaptic axon terminals and the ensuing activation of postsynaptic receptors. Instantaneous responses of postsynaptic cells to released neurotransmitters are mediated by ligand-gated ion channels, whereas G protein-coupled receptors mediate rather delayed effects. Moreover, the actions of ionotropic receptors are transient (milliseconds to seconds) and those of G protein-coupled receptors are more long lasting (seconds to minutes). Accordingly, neuronal signalling via ligand-gated ion channels is termed neurotransmission, whereas signalling via G protein-coupled receptors is termed neuromodulation. Exocytotic transmitter release is modulated by a variety of mechanisms such as previous activity at the synapse and the presence of extracellular neurotransmitters. Like the postsynaptic responses, presynaptic modulation is not only mediated by slowly acting G protein- coupled receptors, but also by fast acting ligand-gated ion channels. Accordingly, members of all known families of ligand-gated ion channels (cys-loop receptors, such as GABAA, glycine, nicotinic acetylcholine, and 5-HT3 receptors, ionotropic glutamate receptors, P2X receptors, and vanilloid receptors) are known to control transmitter release. All these ligand-gated ion channels display heterogeneous structures and functions. Therefore, activation of such presynaptic receptors can control transmitter release in different ways and through a multitude of mechanisms. This review provides a summary of the functions of the different presynaptic ligand-gated ion channels and presents prototypic examples for the physiological and pharmacological relevance of these presynaptic receptors.

The universal prevalence of hepatitis C virus (HCV) infection, which causes chronic hepatitis, cirrhosis, liver failure, and hepatocellular carcinoma, has become a significant health problem worldwide. Interferon-based therapies, the current standard, IFN-based therapies have limited efficacy and undesirable adverse effects. In addition, neither vaccination against HCV nor specific antiviral reagents for HCV are yet available. Thus, a major medical need still exists for novel and more efficacious anti-HCV reagents showing broad-spectrum clinical efficacy with enhanced tolerability. With the progress in our current understanding of the function and regulation of HCV gene products, the three-dimensional structures of virally encoded enzymes and the recent establishment of the HCV-replicon system, several pharmacological targets are being studied for HCV therapy, including cellular receptors mediating HCV entry, factors facilitating HCV replication and assembly, and intracellular pathways. Recently developed mouse models will be very helpful in evaluating the in vivo efficacy of novel antiviral reagents. Currently many novel antiviral drugs are under evaluation in clinical trials. This review will comprehensively discuss the current treatment options and various novel antiviral reagents available. Ongoing clinical studies of promising lead drugs are also reviewed.

Aromatic diamidines and related compounds are DNA minor groove binders that have been screened against a variety of pathogenic microorganisms such as bacteria, fungi and protozoa and show promising results. Parasitic infections are widespread in developing countries and are major contributors to human mortality and morbidity, causing considerable economic hardship. Trypanosomes are unicellular protozoan organisms that cause serious public health problems in developing countries: African trypanosomiasis (sleeping sickness) in Africa, and Chagas' disease, in Latin America. Sleeping sickness, caused by sub-species of Trypanosome brucei (T. brucei gambiense and T. brucei rhodesiense), is a fatal disease if left untreated, with about 60 million people currently at risk. Trypanosoma cruzi is the etiological agent of Chagas' disease, an important parasitic illness that affects nearly 17 million individuals in endemic areas. The fact that the available clinical drugs are expensive, toxic, require long treatment periods, frequently exhibit reduced activity towards certain parasite strains and evolutive stages, and are beginning to show development of resistance, demonstrates the urgent need for the development of new drugs for both pathologies. For some time much attention has been focused on the effect of diamidines (and related compounds) on African trypanosomes. However more recent studies have pointed to their potential activity against T.cruzi. In this review the current therapeutic state of the art of aromatic diamidines and related compounds used against T.brucei and T.cruzi is reviewed with a focus on their potential use as antiparasitic drugs for the treatment of both these important neglected diseases.

DNA is modified by many mutagens, including reactive oxygen species (ROS). When ROS react with DNA, various kinds of modified base and/or sugar moieties are produced. One of the most important oxidative DNA lesions is 7,8-dihydro-8-oxoguanine (8-oxo-G). Contrary to normal deoxyguanosine, 8-oxo-G favors a syn conformation, enabling it to form a Hoogsteen base pair with adenine which resembles a normal Watson-Crick base pair in shape and geometry. As a consequence, most human DNA polymerases (pols) studied so far show significant error-prone bypass of 8-oxo-G. The 1,2-dihydro-2-oxoadenine (2-OH-A) is another common DNA lesion produced by ROS. 2-OH-A possesses significant mutagenic potential in living cells. When challenged with a 2-OH-A lesion on the template, DNA pols often misinsert G and C nucleotides, with various efficiencies depending upon the sequence context. We have recently shown that human DNA pol λ is extremely efficient in performing error-free bypass of both 8-oxo-G and 2-OH-A lesions, and that its efficiency is positively modulated by the auxiliary factors proliferating cell nuclear antigen and replication protein A. In this review we will summarize the most recent advancements in the field of oxidative DNA damage tolerance with special emphasis on the pro- and anti-mutagenic roles of DNA pols and auxiliary proteins.

Infection with the hepatitis C virus (HCV) is a major health problem worldwide due to the associated risk of developing liver cirrhosis and its sequelae. Approximately 200 million persons are chronically infected worldwide. Furthermore, about one third of HIV-infected individuals in Europe and the US are co-infected with HCV. Currently pegylated interferon-?? in combination with ribavirin represents the backbone of HCV-specific therapy. However, with interferon-based combination therapy sustained virologic response (SVR) is achieved in only about 50% of HCV-infected patients in clinical studies and may be even lower in clinical practice. HCV genotype and viral load are major determinants of treatment response in HCV infection. However, emerging data suggest host genetic factors also influence response to treatment. These data might hold the keys to better understand and predict outcome of HCV-specific therapy and might help to develop novel anti-HCV strategies. Here, we review the role of genetic aspects including the role of cytokines, chemokines/ chemokine receptors, and MHC alleles with respect to HCV therapy that have been elucidated so far and offer suggestions for how to use these observations as platforms for future research to further understand differential response to antiviral therapy in HCV-infected patients.