Frontiers in Clinical Drug Research: HIV

The treatment of human immunodeficiency virus (HIV) infection has been a great success story of our time; from the widespread panic in the early 1980’s when the virus was identified as the cause of AIDS, to the availability of a whole plethora of drugs to treat and effectively control HIV infection, developed after millions of dollars of research funding investments. However, this treatment is not entirely problem-free. From the early days of antiretroviral (ARV) monotherapy, to the mid 1990’s when triple therapy (highly active antiretroviral treatment, HAART) was discovered to be not only more effective but less toxic, there has been ongoing work to change the face of HIV treatment. This work can be broadly split into three categories, being:

1. developing drugs to target different stages of the life cycle.

2. developing novel drugs and refining the use of current drugs to reduce toxicities and side effects.

3. reducing the pill burden and the impact of daily therapy.

In part I, the life cycle of HIV and the targets of current therapy will be presented in terms of their individual actions and side effects. This section is completed by an exploration of wider issues surrounding anti-HIV therapy including distribution, cost and regular access. Part II will examine three key aspects of new drugs in development. This examination will be of new ARV agents in development, including some agents very recently licensed. The first aspect will be drugs in the pipeline which are directed against existing drug targets; potential differences between these drugs compared to current agents will be outlined. The second aspect is the most exciting, focusing on the development of novel drugs for novel targets in the HIV life cycle. The final aspect of part II will be to examine the role of these new drugs in adding to an already complex treatment arena - are these drugs for patients who have failed other therapies, or do their new actions and side effect profiles make them more useful for first line treatment? Will their expense or mode of delivery make them simply inaccessible to people living with HIV?

Part III will contain the conclusions pertaining to the preceding section, and will examine potential for the development of even newer drugs in terms of targets, efficacy, toxicities and acceptability. The two facets that will be explored are the potential for the correction of deficits in current treatment and potential new drugs.

Viral suppression is necessary to control the evolution of drug resistance, reduce the chronic immune activation, which is associated with morbidity and mortality in HIV-infected patients, reducing viral transmission, including transmission of drug resistance. In general, the proportion of viremic patients who achieved suppression increases with the number of pharmacokinetically active antiretroviral therapy regimen in. Guidelines to antiretroviral treatment today recommend the use of at least three antiretroviral agents (ART) selected from different drug classes, which may include inhibitors of reverse transcriptase nucleoside (NRTI), reverse transcriptase inhibitors Non-nucleoside inhibitors (NNRTIs) inhibitors protease (PI's), entry inhibitors and integrase inhibitors. There is regarding when to start therapy, what drugs should be used, how to manage the risk of toxicity and how to improve adherence to treatment. The impact of co-morbidities conditions in the selection of drugs and the risk of emergence of resistant viruses must also be considered as deciding factors. Thus, this review covers the last advances in ART, specifically focusing integrase inhibitors and entry inhibitors.

Translation of the full-length messenger RNA of human immunodeficiency virus of type 1 (HIV-1) uses a programmed -1 ribosomal frameshift to generate the polyprotein Gag-Pol, the precursor of the viral enzymes. This recoding event occurs at a slippery sequence followed by an irregular hairpin, the frameshift stimulatory signal, which controls the efficiency of frameshifting. In this chapter, we review the characteristics of the mechanism accounting for HIV-1 frameshifting and we examine the different approaches investigated to develop novel anti-HIV-1 drugs interfering with the frameshift, including the high-throughput screening of libraries of chemical compounds with a bicistronic reporter whose second cistron is expressed via HIV-1 frameshift, the use of antisense oligonucleotides binding to the frameshift stimulatory signal, and the selection and modification of chemical compounds that bind to the frameshift stimulatory signal. This latter approach is the most promising and we present results based on the modification of a compound selected by screening of a resin-bound dynamic combinatorial library. This lead compound specifically bound to HIV-1 frameshift stimulatory signal, increased HIV-1 frameshift efficiency and decreased HIV-1 infectivity.

Single nucleotide polymorphisms (SNPs) are gaining increasing attention in modern diagnostics and research, serving as markers on genetic predispositions, clinically evident disorders and diverse drug responses. Genome of human immunodeficiency virus (HIV-1) contains multiple SNPs due to mistakes of reverse transcriptase converting RNA genome of HIV-1 into cDNA. Some of these SNPs cause resistance to drugs applied for the treatment of HIV/AIDS. Generally, current assays for SNP diagnostics, including HIV-1, can be divided into two broad categories: 1) sophisticated, high-throughput laboratory machines, and 2) easy-to-use, portable devices. Present sophisticated SNP diagnostics of HIV-1 primarily use enzymatic reactions in different formats including sequencing, polymerase-chain reaction (PCR) and microarrays. In doing this, the enzymes help to address the required sensitivity and specificity of the detection. On the other hand, an ideal portable method for the detection of SNP would work by allowing a simple mixing of a cDNA or RNA target with a probe and obtaining a single right away without applying an enzyme or state-ofthe- art equipment. Remarkable progress has been achieved in recent years within both categories of methods. To date, most enzymatic and enzyme-free diagnostic strategies apply fluorescently labeled oligonucleotides - rationally designed probes or primers containing a dye(s) of choice in the desired position(s) of a nucleotide chain. In this chapter, current SNP sensing approaches in HIV-1 cDNA and RNA are described with a main focus on recently developed fluorescent oligonucleotide probes. The chapter includes up-to-date review of sophisticated and portable biosensors for HIV diagnostics, and several exciting emerging technologies are highlighted.

Much attention has been paid to branched-sugar nucleosides due to their biological activities. During our ongoing research project utilizing unsaturated-sugar nucleosides, epoxy-sugar derivatives were found to be useful precursor for the stereoselective synthesis of these nucleoside derivatives on the basis of their ring opening with organoaluminum or organosilicon reagents. In this chapter, we describe novel synthetic methods for 1’ and 4’-branched-sugar nucleosides. During this research, a novel anti-HIV agent, 4’-ethynylstavudine (4’-Ed4T) has emerged.

4’-Ed4T possessed more potent anti-HIV activity than the parent compound stavudine (d4T). Other characteristic biological properties of 4’-Ed4T are as follows: 1) much less toxic to various cells and also to mitochondorial DNA synthesis than d4T, 2) better substrate for human thymidine kinase than d4T, 3) resistant not only to chemical glycosidic bond cleavage but also to catabolism by thymidine phosphorylase, 4) the activity improves in the presence of a major mutation, K103N, associated with resistance to non-nucleoside reverse transcriptase inhibitors (NNRTIs). The detailed antiviral activities, pharmacology and clinical developments (Phase I and Phase IIa) of 4’-Ed4T are described.

In recent years, HIV integrase has emerged as an important target for the development of new HIV inhibitors. Following the synthesis of viral DNA by reverse transcriptase, integrase performs two functions; 3’-processing and strand transfer/ integration. The catalysis of both functions by the enzyme relies on the presence of magnesium ions (Mg2+) in the active site. All three of the current FDA approved integrase inhibitors operate as strand transfer inhibitors and have chelation of the Mg2+ ion as an integral part of their respective pharmacophores. Interesting new developments in the field involve the targeting of one or more of the range of cellular cofactors involved in the integration process and inhibitors with a novel mode of action known as allosteric inhibitors.

The introduction of highly active antiretroviral therapy (HAART) in 1990s radically changed the course and management of HIV infection. Although there have been substantial reductions in morbidity and mortality of HIV- virus Infected patients, the antiretroviral medications have been associated with various toxicities, including those affecting the kidney. The prevalence of acute and chronic kidney disease has been increasing among HIV-infected patients in the United States and kidney disease has emerged as a key predictor of mortality [1-3]. The toxicities associated with the long term use of this treatment have now become a major issue and researchers have focused on understanding the cellular mechanisms underlying these drug-induced adverse effects [4]. Nephrotoxicity from antiretroviral drugs may manifest as tubular necrosis, kidney stones, acute and chronic kidney diseases. The objective of this article is to review the potential adverse effects of HAART on the kidney, with emphasis on specific antiretroviral agents that have been associated with direct kidney injury and associated metabolic disorders. Kidney injury caused by HAART is typically reversible with early detection and discontinuation of the offending agent. Nephrologists should be aware of the potential toxicity of these agents to avoid delays in diagnosis and treatment [5].