Current Drug Targets - Infectious Disorders - Volume 2, Issue 3, 2002

In the era of highly active antiretroviral therapy (HAART) the central nervous system (CNS) becomes increasingly important as a sanctuary site for the human immunodeficiency virus (HIV-1). HIV-1-associated brain disease is subdivided into the minor cognitive / motor disorder, the minor cognitive / motor complex and the AIDS dementia complex, all of which are predictive for patients deaths. CNS effective therapy therefore influences the prognosis of each individual patient. Thus, there is urgent need both for prophylactic and therapeutic strategies preventing or treating HIV-1-associated CNS disease. HAART consisting of two nucleoside analogues (NAs), one or two protease inhibitors (PIs) and / or one non-nucleoside inhibitor of the reverse transcriptase (NNRTI) has a neuroprophylactic value with regard to the manifestation of HIV-1 associated CNS disease. With regard to therapeutic effects, the NAs zidovudine and stavudine penetrate into the cerebrospinal fluid and positively influence HIV-1-associated brain disease. Adding a second NA has no additional therapeutic effect. NNRTIs (nevirapine and efavirenz) are also CNS effective. However, there is a subgroup of non-responders, who obviously need other forms of therapeutic interventions. The very few existing studies point out that patients with high plasma viral loads and neurological abnormalities should be treated with a combination of two NAs and one NNRTI. The value of PIs for CNS protection remains to be evaluated.

Improved hygienic conditions in Western societies have reduced early microbial exposure, which has been proposed as a reason for the continuously rising prevalence of atopy and subsequent atopic diseases: atopic eczema, allergic rhinitis and asthma (The Hygiene Hypothesis of Allergy). This hypothesis is supported by immunological data showing that the immune response to microbial antigens, both pathogenic and non-pathogenic ones, is accompanied by preferential expression of cytokines that counterbalance the T-helper 2-polarized cytokine production of neonates, the continuity of which might lead to enhanced IgE production, atopy, and atopic disease. Experimental, epidemiological and clinical studies, conducted over the last decade, indicate that nonpathogenic microbes in the gut might be a major factor essential for the maturation of the human immune system to a nonatopic mode. A recent randomised, placebo-controlled trial demonstrated that perinatal administration of probiotics, cultures of potentially beneficial bacteria of the healthy gut microflora, halved the later development of atopic eczema during the first two years of life.Some putative mechanisms of action of gut commensals in host-microbe interactions have been described. Two structural components of bacteria, the lipopolysaccharide portion of Gram-negative bacteria and specified CpG motif in bacterial DNA, activate immunomodulatory genes via Toll-like receptors present e.g. on intestinal epithelial cells thus controlling physiological cytokine milieu in the gut. Probiotics have also been shown to reverse increased intestinal permeability and to reduce antigen load in the gut by degrading and modifying macromolecules. The actual preventive role of natural and genetically constructed supplementary microbes in the development of immunological diseases, like allergy, remains to be elucidated.

The chlamydiae are obligate intracellular gram-negative bacteria that are exquisitely adapted for exploitation of their hosts and contribute to a wide range of acute and chronic human diseases. Acute infections treated with non-cidal antibiotics can lead to the development of persistent, non-replicating bacteria with the corollary that these persistent (yet viable) chlamydiae can resist eradication by further antimicrobial treatment and cause chronic disease. These findings highlight an urgent need for therapeutics that are effective against persistent infections and call for creative approaches to identify potential drug targets. The C. pneumoniae and C. trachomatis genome projects have greatly expanded our knowledge of chlamydial pathogenesis and have provided an enormous potential for the identification and characterization of unknown genes and potential virulence factors in these bacteria. As intracellular pathogens, chlamydiae rely on host cells for all aspects of their survival, from the initial attachment with host cell membranes, to cellular invasion, acquisition of host cell metabolites and intracellular replication. As such, the molecules participating in interactions with the host could be attractive targets for therapeutic intervention. This review describes recent advances in chlamydial genomics, proteomics and cell biology that have cast light on host-pathogen relations that are essential for chlamydial survival. Using this knowledge, we discuss how strategically interfering with essential interactions between chlamydiae and the host cell could be exploited to develop an innovative, and potentially more relevant arsenal of therapeutic compounds.

HIV integrase (IN) is a viral-encoded protein that catalyzes the breaking and joining reactions that mediate integration of viral DNA into the host genome. Therefore, IN offers a unique target for the development of novel anti-HIV and anti-AIDS therapeutics. To take advantage of this potential, drug discovery efforts via structurebased design approaches have been undertaken. Presented is a review of computer-aided drug design efforts targeting HIV IN. Included is an overview of the lifecycle of HIV, with emphasis on the mechanism of action of IN, biological assays for measuring IN activity and identifying IN inhibitors, and the appropriate cell-based assays required for determining the antiviral activity of IN inhibitors. This is followed by a review of the available three-dimensional structures of HIV IN. Structure-based drug design efforts are then critiqued, including both ligand-based (e.g. pharmacophore) and target-based (e.g. docking) methods. Results from recent computational chemistry studies of IN are also discussed.

Pathogenic bacteria must be able to sense and respond rapidly to signals emanating from the host environment and use the signals to modulate the expression of genes required for the infection process. Two-component signal transduction systems, and their more complex variants known as phosphorelays, are woven within the fabric of bacterial cellular regulatory processes and are used to regulate the expression of genes involved in the virulence and antibiotic resistance responses of a large number of pathogens of major public health concern.The emergence of strains of pathogenic bacteria that are resistant to multiple antibiotics has driven the search for new targets and / or modes of action for anti-microbial agents. The presence of essential two-component systems in bacteria and the central role that these regulatory systems play in virulence and antibiotic resistance has meant that two-component systems and phosphorelays have been recognized as targets for antimicrobial intervention. This review will discuss the role of these signal transduction pathways in virulence responses and antibiotic sensitivity of pathogenic microorganisms and their potential use as targets for antimicrobial therapy. In addition, the current status on the development of inhibitors specific for two-component systems will be discussed.

Recent advances in microbiology implicate the cytoskeleton in the life cycle of some pathogens, such as intracellular bacteria, Rickettsia and viruses. The cellular cytoskeleton provides the basis for intracellular movements such as those that transport the pathogen to and from the cell surface to the nuclear region, or those that produce cortical protrusions that project the pathogen outwards from the cell surface towards an adjacent cell.Transport in both directions within the neuron is required for pathogens such as the herpesviruses to travel to and from the nucleus and perinuclear region where replication takes place. This trafficking is likely to depend on cellular motors moving on a combination of microtubule and actin filament tracks. Recently, Bearer et al. reconstituted retrograde transport of herpes simplex virus (HSV) in the giant axon of the squid. These studies identified the tegument proteins as the viral proteins most likely to recruit retrograde motors for the transport of HSV to the neuronal nucleus. Similar microtubule-based intracellular movements are part of the biological behavior of vaccinia, a poxvirus, and of adenovirus.Pathogen-induced surface projections and motility within the cortical cytoplasm also play a role in the life cycle of intracellular pathogens. Such motility is driven by pathogen-mediated actin polymerization. Virulence depends on this actin-based motility, since virulence is reduced in Listeria ActA mutants that lack the ability to recruit Arp2 / 3 and polymerize actin and in vaccinia virus mutants that cannot stimulate actin polymerization.Inhibition of intracellular movements provides a potential strategy to limit pathogenicity. The host cell motors and tracks, as well as the pathogen factors that interact with them, are potential targets for novel antimicrobial therapy.

With the discovery that CCR5 is the critical protein required for infection by M-tropic HIV, has come huge research efforts, both in academia and industry, to try to exploit this finding. Thus, research advances in the fields of virology, structural protein chemistry, and receptor pharmacology have combined to add a new understanding to the process of HIV fusion and possible mechanisms to prevent HIV entry. This review will approach this field from a receptor pharmacology viewpoint and outline some concepts of receptor allosterism and protein-protein interaction which may be relevant to CCR5 blockade. Many of these ideas may be explored in a practical sense with the advent of new small molecule CCR5 inhibitors currently entering the clinic.