New developments in the chemotherapy of lentivirus (human immunodeficiency virus) infections: sensitivity/resistance of HIV-1 to non-nucleoside HIV-1-specific inhibitors

Intrahypothalamic injection of the HIV-1 envelope glycoprotein induces fever via interaction with the chemokine system

Wasting syndrome is a common complication of HIV infection and is marked by progressive weight loss and weakness, often associated with fever. The mechanisms involved in the pathogenesis of these syndromes are not well defined, and neither are the brain areas involved. The present study tests a new hypothesis: that the preoptic anterior hypothalamus (POAH), the main brain area for thermoregulation and fever, has a role in the pathogenesis of fever induced by glycoprotein 120 (gp120), the surface envelope protein used by the HIV to gain access into immune cells, and that the CXC chemokine receptors (CXCR4) that serve as a coreceptor for HIV entry mediate the effect. A sterilized stainless steel C313G cannula guide was implanted into the POAH, and a biotelemetry system was used to monitor the body temperature (Tb) changes. The administration of gp120 into the POAH induced fever in a dose-dependent manner. To demonstrate possible links between the gp120 and CXCR4 in generating the fever, we pretreated the rats with 1,1'-[1,4-phenylenebis(methylene)]bis[1,4,8,11-tetraazacyclotetradecane] octohydrobromide dihydrate (AMD 3100), an antagonist of stromal cell-derived growth factor (SDF)-1alpha/CXCL12, acting at its receptor, CXCR4, 30 min before administration of gp120. AMD 3100 significantly reduced the gp120-induced fever. The present studies show that the presence of HIV-1 envelope glycoprotein gp120 in the POAH provokes fever via interaction CXCR4 pathway.

Understanding HIV resistance, fitness, replication capacity and compensation: targeting viral fitness as a therapeutic strategy

The increasingly prevalent emergence of drug-resistant virus strains in patients being treated with highly active antiretroviral regimens and the increasing rates of transmission of drug-resistant virus strains have focused attention on the critical need for additional antiretroviral agents with novel mechanisms of action and enhanced potency. Furthermore, novel means of employing highly active antiretroviral therapy are needed to reduce or eliminate the virological treatment failures that currently occur. Over the past several years, evidence has mounted supporting the fact that the emergence of resistant strains is associated with reductions in viral fitness, yielding decreases in plasma virus load in treated patients harbouring resistant populations of the virus. Additional mutations that serve to modify fitness (compensatory mutations) and mutations that impact the viral replication capacity also emerge under the selective pressure of drug treatment, and have both negative and positive effects on virus growth. Fitness is generally accepted to refer to the ability of HIV to replicate in a defined environment and thus is used to describe the viral replication potential in the absence of the drug. Although viral fitness and replication capacity are related in some ways, it is important to recognise that viral fitness is not the same as viral replication capacity. This review will assess the recent literature on antiviral drug resistance, viral fitness and viral replication capacity, and discuss means by which the adaptability of HIV to respond rapidly to antiviral treatment through mutation may be used against it. This would be done by treating patients with an aim to lock the deleterious mutations into the resistant virus genome, resulting in a positive therapeutic outcome despite the presence of resistance to the selecting agents. The review will specifically discuss the literature on nucleoside and non-nucleoside reverse transcriptase inhibitors, protease inhibitors, integrase inhibitors, fusion inhibitors, as well as other biological factors involved in viral fitness.

Effects of drug resistance mutations L100I and V106A on the binding of pyrrolobenzoxazepinone nonnucleoside inhibitors to the human immunodeficiency virus type 1 reverse transcriptase catalytic complex

We have previously described a novel class of nonnucleoside reverse transcriptase (RT) inhibitors, the pyrrolobenzoxazepinone (PBO) and the pyridopyrrolooxazepinone (PPO) derivatives, which were effective inhibitors of human immunodeficiency virus type 1 (HIV-1) RT, either wild type or carrying known drug resistance mutations (G. Campiani et al., J. Med. Chem. 42:4462-4470, 1999). The lead compound of the PPO class, (R)-(-)-PPO464, was shown to selectively target the ternary complex formed by the viral RT with its substrates nucleic acid and nucleotide (G. Maga et al., J. Biol. Chem. 276:44653-44662, 2001). In order to better understand the structural basis for this selectivity, we exploited some PBO analogs characterized by various substituents at C-3 and by different inhibition potencies and drug resistance profiles, and we studied their interaction with HIV-1 RT wild type or carrying the drug resistance mutations L100I and V106A. Our kinetic and thermodynamic analyses showed that the formation of the complex between the enzyme and the nucleotide increased the inhibition potency of the compound PBO354 and shifted the free energy (energy of activation, DeltaG(#)) for inhibitor binding toward more negative values. The V106A mutation conferred resistance to PBO 354 by increasing its dissociation rate from the enzyme, whereas the L100I mutation mainly decreased the association rate. This latter mutation also caused a severe reduction in the catalytic efficiency of the RT. These results provide a correlation between the efficiency of nucleotide utilization by RT and its resistance to PBO inhibition.

The stereoselective targeting of a specific enzyme-substrate complex is the molecular mechanism for the synergic inhibition of HIV-1 reverse transcriptase by (R)-(-)-PPO464: a novel generation of nonnucleoside inhibitors

The human immunodeficiency virus type 1 (HIV-1) nonnucleoside reverse transcriptase (RT) inhibitor pyrrolopyridooxazepinone (PPO) derivative, (+/-)-PPO294, was shown to be active toward wild type and mutated HIV-1 RT and to act synergistically in combination with 3'-azido-3'-deoxythymidine (Campiani, G., Morelli, E., Fabbrini, M., Nacci, V., Greco, G., Novellino, E., Ramunno, A., Maga, G., Spadari, S., Caliendo, G., Bergamini, A., Faggioli, E., Uccella, I., Bolacchi, F., Marini, S., (1999) J. Med. Chem. 42, 4462-4470). The (+/-)-PPO294 racemate was resolved into its pure enantiomers, and the absolute configuration was determined by x-ray analysis. Only one enantiomer, (R)-(-)-PPO464, displayed antiviral activity against both the wild type and the K103N mutant HIV-1 RT and was found to interact exclusively with the reaction intermediate formed by RT complexed with both the DNA and the nucleotide substrates. Being the first compound of its class to display this behavior, (R)-(-)-PPO464 is the representative of a novel generation of nonnucleoside inhibitors. (R)-(-)-PPO464 showed significant synergism when tested in combination with other RT inhibitors and efficiently inhibited viral replication when tested against the laboratory strain HIV-1 IIIB or against either wild type or multidrug-resistant clinical isolates. Pharmacokinetic studies in mice and rats showed a more favorable profile for (R)-(-)-PPO464 than for the corresponding racemate. (R)-(-)-PPO464 was also found to easily cross the blood-brain barrier. The coadministration of the HIV-1 protease inhibitor ritonavir increased the bioavailability of (R)-(-)-PPO464, having little effect on its plasma and brain elimination rates.

Poliovirus RNA-dependent RNA polymerase (3D(pol)). Assembly of stable, elongation-competent complexes by using a symmetrical primer-template substrate (sym/sub)

Detailed studies of the kinetics and mechanism of nucleotide incorporation catalyzed by the RNA-dependent RNA polymerase from poliovirus, 3D(pol), have been limited by the inability to assemble elongation complexes that permit activity to be monitored by extension of end-labeled primers. We have solved this problem by employing a short, symmetrical, heteropolymeric RNA primer-template that we refer to as "sym/sub." Formation of 3D(pol)-sym/sub complexes is slow owing to a slow rate of association (0.1 microM(-1) s(-1)) of 3D(pol) and sym/sub and a slow isomerization (0. 076 s(-1)) of the 3D(pol)-sym/sub complex that is a prerequisite for catalytic competence of this complex. Complex assembly is stoichiometric under conditions in which competing reactions, such as enzyme inactivation, are eliminated. Inactivation of 3D(pol) occurs at a maximal rate of 0.051 s(-1) at 22 degrees C in reaction buffer lacking nucleotide. At this temperature, ATP protects 3D(pol) against inactivation with a K(0.5) of 37 microM. Once formed, 3D(pol)-sym/sub elongation complexes are stable (t((1)/(2)) = 2 h at 22 degrees C) and appear to contain only a single polymerase monomer. In the presence of Mg(2+), AMP, 2'-dAMP, and 3'-dAMP are incorporated into sym/sub by 3D(pol) at rates of 72, 0.6, and 1 s(-1), respectively. After incorporation of AMP, 3D(pol)-sym/sub product complexes have a half-life of 8 h at 22 degrees C. The stability of 3D(pol)-sym/sub complexes is temperature-dependent. At 30 degrees C, there is a 2-8-fold decrease in complex stability. Complex dissociation is the rate-limiting step for primer utilization. 3D(pol) dissociates from the end of template at a rate 10-fold faster than from internal positions. The sym/sub system will facilitate mechanistic analysis of 3D(pol) and permit a direct kinetic and thermodynamic comparison of the RNA-dependent RNA polymerase to the other classes of nucleic acid polymerases.

What clinicians need to know about antiviral drugs and viral resistance

The development of safe and effective antiviral therapies for the management of a variety of viral infections has expanded tremendously in recent years. Treatment is now possible for serious and potentially life-threatening infections with herpesviruses, respiratory viruses such as influenza A and respiratory syncytial virus, and the human immunodeficiency virus. The increased availability and use of antiviral drugs, however, has led to the emergence of drug-resistant viruses, especially in immunocompromised hosts. With this review, the major antiviral agents are presented with a description of the mechanisms of action, the evolution of drug resistance, and the need for in vitro antiviral susceptibility testing.

Chemotherapy of human immunodeficiency virus (HIV) infection: anti-HIV agents targeted at early stages in the virus replicative cycle

Several compounds have been identified that inhibit an early stage in the replicative cycle of the human immunodeficiency virus (HIV): i) virus adsorption: polysulfates, polysulfonates, polycarboxylates, polyphosphates, and polyoxometalates; or ii) virus-cell fusion: plant lectins, negatively charged albumins and betulinic acid derivatives; iii) virus fusion/uncoating: bicyclam derivatives; iv) reverse transcription: dideoxynucleoside analogues, acyclic nucleoside phosphonates and non-nucleoside reverse transcriptase inhibitors. In principle, HIV may develop resistance to any of these specific anti-HIV agents. However, virus breakthrough can be completely prevented if these agents, alone or in combination, are added to the HIV-infected cells from the beginning at sufficiently high ('knock-out') concentrations.