Current Pharmaceutical Design - Volume 11, Issue 29, 2005

The field of developing topical microbicides as preventive agents against HIV is rapidly emerging. This issue of anti-HIV drug design focuses on introducing novel approaches in designing anti-HIV microbicides. The selection of this topic was made with the intention to complement the first two issues of anti-HIV Drug Design (Current Pharmaceutical Sciences, 2002, Volume 8, number 8) and (Current Pharmaceutical Sciences, 2003, Volume 9, number 22). Additionally several strategies in designing non-nucleoside reverse transcriptase inhibitors (NNRTIs) that can have applications as microbicides are discussed in the last review article. Microbicides are anti-infective prophylactic agents formulated for topical self-administration prior to intercourse to protect against sexually transmitted pathogens such as HIV-1. The article by Mary K. Howett and Jeffrey P. Kuhl summarizes the concept and ideal design of microbicides, principles of microbicide mechanisms, and major types of microbicides such as nonoxynol 9, antibodies and monoclonal antibodies, peptides, high molecular weight charged polymers, entry and fusion inhibitors, and alkyl sulfates. The review by Pomerantz and his colleagues summarizes some of the important products such as BufferGel, Acidform, nonoxynol 9, sodium lauryl sulfate, sodium dodecyl sulfate, C31G, sulfate esters of polysaccacharides, Carrageenan, PRO- 2000, cellulose acetate phthalate, dendrimers, proteins, and NNRTIs, currently in developments stages as HIV microbicides. Amphiphiles are surfactant agents that have been investigated as microbicides due to their broad-spectrum of activity and fastacting effect, but they disrupt cell membranes such as epithelial cells and normal vagina flora. The review by Richard D. Gandour discusses amphiphilic acylcarnitine analogues such as Z-14 and Z-15 that may have applications as non-irritating topical microbicides. Alkylureas have been introduced as protein denaturing agents that irreversibly disrupt free and intracellular HIV-1 with a wide margin of safety. These compounds are also spermicidal above their virucidal concentration without mucosal toxicity. The review by Arye Rubinstein discusses the anti-HIV 1 properties of alkylureas, their effect on peripheral blood mononuclear cells and epithelial cell viability, mechanism of action, and their toxicological studies Indolyl aryl sulfones (IASs) have been introduced as potent non-nucleoside reverse transcriptase inhibitors against wt HIV-1 and resistant mutants. In a comprehensive review, Dr. Silvestri and his colleague discuss the latest developments in designing novel IASs. I would like to thank all of the authors for their valuable contributions to this issue. Without their dedication, the publication of this issue would not have been possible. References [1] Howett, M. K., Kuhl, J. P. Microbicides for Prevention of Transmission of Sexually Transmitted Diseases. Curr Pharm Design 2005; 11(29): 3731-3746. [2] Scholand, S. J., DeSimone, J. A., Pomerantz, R. J. Anti-HIV-1 Microbicides - 'Chemical Condoms' Designed to Limit the Scourge of the HIV-1 Pandemic. Curr Pharm Design 2005; 11(29): 3747-3756. [3] Gandour, R. A. Toward a Design of Affordable, Topical Microbicide: Acylcarnitine Analogues. Curr Pharm Design 2005; 11(29): 3757-3767. [4] Rubinstein, A. Preclinical Studies of Alkylureas as Anti-HIV Contraceptive and Non-Contraceptive Vaginal Microbicides. Curr Pharm Design 2005; 11(29): 3769-3778. [5] Silvestri, R., Artico, M. Indolyl Aryl Sulfones (IASs): Development of Highly Potent NNRTIs Active Against wt-HIV-1 and Clinically Relevant Drug Resistant Mutants. Curr Pharm Design 2005; 11(29): 3779-3806.

In the last 50 years, changes in cultural and scientific realities and customs have resulted in a worldwide epidemic of sexually transmitted diseases (STD). This is a multi-factorial problem resulting in part from: 1) an increased permissiveness in sexual attitudes in the Western world that results in earlier onset of intercourse and increased numbers of partners and types of sex acts; 2) a global transportation network that facilitates contacts and interactions between urban and rural areas as well as between countries resulting in migration and spread of infections; 3) an emergence of new and mutated forms of pathogens with increased capabilities to cause infections and for which there are no available vaccines or therapies; and, 4) at risk populations in developing countries who are susceptible to these pathogens while having societal infrastructures that lack basic health education and proper access to healthcare. Overwhelming examples of increasing and emerging STD pathogens exist in the early twenty-first century. These include human immunodeficiency virus type 1 (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS), with over 42 million current cases of infection, 20 million deaths to date, and an estimated 500,000 deaths per year; human papillomavirus (HPV) infections, the causative agents of genital warts and cervical cancer, with approximately 1 in 4 women harboring virus DNA in genital epithelium, 1-3 percent of women showing symptoms of infection and 250,000 deaths per year in women worldwide from cervical cancer; and numerous others. Topical microbicides have been proposed as agents to break the chain of transmission in these infections by providing chemical, biological, and/or physical barriers to infection by blocking and/or inactivating pathogens at the mucosal surface where infection can occur. For many sexually transmitted infections, vaccines do not exist, and therapeutic agents are only partially effective, expensive, and difficult to distribute. In addition, female partners in many relationships do not control pregnancy or STD risk and may benefit from discrete methods, other than condoms, that would provide protection. Thus, microbicides should be valuable additions to preventing these diseases if they can be shown effective. Currently, 62 microbicides are in development with 6 entering Phase III clinical trials, 11 entering Phase I clinical trials, and 44 in pre-clinical development. In this review, we will describe many of the principles of microbicide mechanisms and give examples of major types of microbicides and their actions. Space precludes a complete description of all of the agents and their mechanisms of action. We will also put forth the argument for alkyl sulfate microbicides, including sodium dodecyl sulfate (SDS), agents that are in active development in our laboratories.

The HIV pandemic continues to spread throughout the world, particularly affecting populations in developing countries. Women now comprise half of those infected. Efforts to limit this scourge need to be maximally implemented. A multi-faceted approach, including the research and advance of microbicides - or 'chemical condoms' - offers promise. Microbicides are self-administered, prophylactic products designed to protect against sexually transmitted pathogens, including HIV-1. Important features include safety, efficacy and user acceptability. This review summarizes some of the important products in the development pipeline.

Most heterosexual women want to reduce the risk of acquiring a sexually transmitted infection; many also want to control their fertility. Several chemical agents have been proposed to dramatically slow the spread of HIV infections. Ideally, vaginal microbicides, with or without contraceptive properties, should be safe, effective, and affordable for women everywhere. Amphiphiles, which are surfactants that can act as detergents, have a long history as microbicides against many pathogens. Amphiphiles have several desirable traits; e.g., they are inexpensive, fast-acting, and capable of a broad spectrum of activity. An "ideal" amphiphilic microbicide will rapidly and selectively inactivate pathogens and sperm without irritating tissue. In this review, we discuss a homologous series of amphiphilic acylcarnitine analogues as microbicides. Two homologues, Z-14 and Z-15, possess excellent spermicidal, anti-HIV, anti-chlamydial, anti-gonorrhea, and anti-Haemophilus activities; both have outstanding anti-Candida activity. A 4% Z-15 gel that is comprised of 3% carboxymethylcellulose in water gives a dramatically low score in a rabbit-vaginal-irritation study. The mechanisms of action of these compounds are not fully understood as yet, but we present several possibilities. Moreover, the results of our limited structure-activity study with a homologous series have stimulated additional questions and ideas for designing the next generation of microbicidal amphiphiles. The above studies support the idea that Z-14 and Z-15 can potentially serve as safe (non-irritating), effective topical microbicides.

The HIV-1 epidemic continues to spread at a rate of over 15, 000 new cases daily. HIV-1 transmission through heterosexual contact became the dominant risk for women globally. About half of the over 40 million HIV-1 infected individuals worldwide are now women. The lack of empowerment of women is the fundamental cause for the rampant spread of HIV-1 in women. Topical microbicides applied intravaginally offer an option for female-initiated HIV-1 prevention. There is an urgent need to develop microbicides with and without contraceptive qualities to also address sociocultural settings where the woman's status is linked to fertility. A safe and efficacious anti-HIV-1 vaginal formulation is not yet available though a large number of candidates are in preclinical or clinical studies. Presently marketed topical microbicides are by and large toxic and damage the vaginal mucosa with frequent use. The microbicidal system of alkylureas evaluated here lends itself to contraceptive and non-contraceptive anti- HIV-1 formulations. Alkylureas are agents that irreversibly disrupt free and intracellular HIV-1, have a wide margin of safety and are spermicidal above their virucidal concentration without any mucosal toxicity. Butylurea, the lead compound is also effective against other sexually transmitted diseases (STDs) while sparing the normal vaginal flora. Alkylureas with longer alkyl chains still have to be explored and may have a greater selective microbicidality.

Indolyl aryl sulfones (IASs) are a potent class of NNRTIs developed from L-737,126, a lead agent discovered by Merck AG. IAS derivatives are endowed with inhibitory activities against wt HIV-1 in the low nanomolar concentration range. Introduction of two methyl groups at positions 3 and 5 of the phenyl ring of the aryl sulfonyl moiety furnished IAS derivatives such as 5-chloro- or 5-bromo-3-[(3,5-dimethylphenyl)sulfonyl]indole-2-carboxyamide, which showed very potent and selective anti-HIV-1 activity against some mutants carrying NNRTI resistant mutations at positions 103 and 181 of the reverse transcriptase. IAS derivatives bearing 2-hydroxyethylcarboxyamide or 2- hydroxyethylcarboxyhydrazide groups at position 2 of the indole nucleus were more active than L-737,126 against the K103N-Y181C double mutant. A great improvement of antiviral activity against wt HIV-1 and resistant mutants was obtained by coupling 1-3 simple amino acids, such as glycine and alanine, in sequence, with the 3-[(3,5- dimethylphenyl)sulfonyl]-1H-indole-2-carbonyl moiety. The transformation of the chain terminus into amide or hydrazide, produced short peptides with high selectivity and potent activity against wt HIV-1, and the viral mutants Y181C, K103N-Y181C and EFVR. IAS having two halogen atoms at the indole showed potent inhibitory activity against the Y181C and the EFVR resistant mutant strains. In particular, the introduction of a fluorine atom at position 4 of the indole ring notably contributed to improve the antiviral activities against both wt and the related resistant mutants. 5- Nitro-IASs were highly active against wt HIV-1 and exhibited low cytotoxicity. Experimental data highlighted the class IAS derivatives as promising candidates for clinical trials.

In the central nervous system (CNS), abnormal deposition of insoluble protein aggregates or inclusion bodies within nerve cells is commonly observed in association with several neurodegenerative diseases. The ubiquitinated protein aggregates are believed to result from malfunction or overload of the ubiquitin-proteasome pathway or from structural changes in the protein substrates which prevent their recognition and degradation by the ubiquitin-proteasome pathway. Impaired proteolysis might also contribute to the synaptic dysfunction seen early in neurodegenerative diseases because the ubiquitin-proteasome pathway is known to play a role in normal functioning of synapses. Because specificity of the ubiquitin proteasome mediated proteolysis is determined by specific ubiquitin ligases (E3s), identification of specific E3s and their allosteric modulators are likely to provide effective therapeutic targets for the treatment of several CNS disorders. Another unexplored area for the discovery of drug targets is the proteasome. Although many inhibitors of the proteasome are available, no effective drugs exist that can stimulate the proteasome. Since abnormal protein aggregation is a common feature of different neurodegenerative diseases, enhancement of proteasome activity might be an efficient way to remove the aggregates that accumulate in the brain. In this review, we discuss how the components of the ubiquitinproteasome pathway could be potential targets for therapy of CNS diseases and disorders.

Current interest in studies on tissue distribution stems from the limited capacity to predict tissue concentrations and the pharmacological response from plasma drug levels, and from the limitations - both methodological and deontological- involved in doing so, especially in humans. In this review we carry out a comparative analysis of the methods used for studying tissue distribution, placing special focus on recently developed noninvasive methods for the research of tissue distribution in humans, such as positron emission tomography and nuclear magnetic resonance spectroscopy. We describe the strategies of tissue distribution pharmacokinetic analysis that have evolved from analysis based on compartment and physiological models to analyses based on spatial and fractal models and, mainly, pharmacokinetic-pharmacodynamic models. Model-independent analysis based on the use of mean transit times or deconvolution strategies has become a good alternative for the pharmacokinetic analysis of tissue distribution. The need to increase the selectivity of many drugs justifies the desire to gain further insight into the design of new analogues prodrugs and carrier systems that will guarantee the specific delivery of a given drug to a particular organ or tissue, optimising the response. In silico models for drug distribution have become a helpful tool in drug discovery and development. The therapeutic implications of drug tissue distribution are also analysed, special reference being made to antiretroviral therapy and antitumoural gene therapy, among others.

The novel carbocyclic nucleoside, abacavir, is metabolized in cells to carbovir triphosphate which is a potent inhibitor of HIV reverse transcriptase (Ki 0.021 μM with calf thymus DNA template primer). Abacavir exhibits potent in vitro antiviral activity against wild-type HIV-1 (IC50 4.0 μM, MT-4 cells) but this activity is lower than the activity of AZT (IC50 0.040 μM, MT-4 cells). However, there is no significant difference between the levels of activity of abacavir (IC50 0.26 μM) and AZT (IC50 0.23 μM) against clinical isolates of HIV-1. The in vitro toxicity data (CC50) of abacavir were: 160 μM (CEM cells); 140 μM (CD4+ CEM cells) and 110 μM (normal bone progenitor cells, BFU-E). Abacavir has been approved in the United States for the treatment of pediatric and adult HIV infection and current recommendations consist of combination therapy in children with HIV infection. Resistance to abacavir develops relatively slowly, with most of the mutations conferring minimal resistance. The M184V mutation appears to be the cornerstone of higher level resistance in regimens containing abacavir, imparting a 2-4 fold reduction in the susceptibility of HIV to abacavir.