Induction of G1 cycle arrest in T lymphocytes results in increased extracellular levels of beta-chemokines: a strategy to inhibit R5 HIV-1

Usnic Acid and Usnea barbata (L.) F.H. Wigg. Dry Extracts Promote Apoptosis and DNA Damage in Human Blood Cells through Enhancing ROS Levels

Nowadays, numerous biomedical studies performed on natural compounds and plant extracts aim to obtain highly selective pharmacological activities without unwanted toxic effects. In the big world of medicinal plants, Usnea barbata (L) F.H. Wigg (U. barbata) and usnic acid (UA) are well-known for their therapeutical properties. One of the most studied properties is their cytotoxicity on various tumor cells. This work aims to evaluate their cytotoxic potential on normal blood cells. Three dry U. barbata extracts in various solvents: ethyl acetate (UBEA), acetone (UBA), and ethanol (UBE) were prepared. From UBEA we isolated usnic acid with high purity by semipreparative chromatography. Then, UA, UBA, and UBE dissolved in 1% dimethyl sulfoxide (DMSO) and diluted in four concentrations were tested for their toxicity on human blood cells. The blood samples were collected from a healthy non-smoker donor; the obtained blood cell cultures were treated with the tested samples. After 24 h, the cytotoxic effect was analyzed through the mechanisms that can cause cell death: early and late apoptosis, caspase 3/7 activity, nuclear apoptosis, autophagy, reactive oxygen species (ROS) level and DNA damage. Generally, the cytotoxic effect was directly proportional to the increase of concentrations, usnic acid inducing the most significant response. At high concentrations, usnic acid and U. barbata extracts induced apoptosis and DNA damage in human blood cells, increasing ROS levels. Our study reveals the importance of prior natural products toxicity evaluation on normal cells to anticipate their limits and benefits as potential anticancer drugs.

CDKN2A Deletion in Melanoma Excludes T Cell Infiltration by Repressing Chemokine Expression in a Cell Cycle-Dependent Manner

T-cell-mediated immune response is the prerequisite for T-cell-based immunotherapy. However, the limitation of T-cell infiltration in solid tumors restricted the therapeutic effect of T-cell-based immunotherapy. The present study screened the molecular and genetic features of The Cancer Genome Atlas (TCGA)-skin cutaneous melanoma (SKCM) cohort, revealing that T-cell infiltration negatively correlated with genome copy number alteration. The analysis of the TCGA-SKCM cohort indicated that the copy number of CDKN2A was significantly decreased in patients with low T-cell infiltration. The results were validated in the other two melanoma cohorts (DFCI, Science 2015, and TGEN, Genome Res 2017). Besides, the immunohistochemistry analysis of CDKN2A and CD8 expression in 5 melanoma in situ and 15 invasive melanoma patients also showed that CD8 expression was decreased in the patients with low CDKN2A expression and there was a positive correlation between CDKN2A and CD8 expression in these patients. Interestingly, the CDKN2A deletion group and the group with low expression of T-cell markers shared similar gene and pathway alteration as compared with the normal CDKN2A group and the group with high expression of T-cell markers, especially the chemokine pathway. Further mechanistic study indicated that CDKN2A enhanced T cell recruitment and chemokine expression possibly through modulating MAPK and NF-κB signaling pathways in a cell cycle–dependent manner. Finally, we also found that CDKN2A deletion negatively correlated with the expression of T-cell markers in many other cancer types. In conclusion, CDKN2A deletion could inhibit T cell infiltration by inhibiting chemokine expression in a cell cycle dependent manner.

Phosphodiesterase 1: A Unique Drug Target for Degenerative Diseases and Cognitive Dysfunction

The focus of this chapter is on the cyclic nucleotide phosphodiesterase 1 (PDE1) family. PDE1 is one member of the 11 PDE families (PDE 1-11). It is the only phosphodiesterase family that is calcium/calmodulin activated. As a result, whereas other families of PDEs 2-11 play a dominant role controlling basal levels of cyclic nucleotides, PDE1 is involved when intra-cellular calcium levels are elevated and, thus, has an "on demand" or activity-dependent involvement in the control of cyclic nucleotides in excitatory cells including neurons, cardiomyocytes and smooth muscle. As a Class 1 phosphodiesterase, PDE1 hydrolyzes the 3' bond of 3'-5'-cyclic nucleotides, cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Here, we review evidence for this family of enzymes as drug targets for development of therapies aimed to address disorders of the central nervous system (CNS) and of degenerative diseases. The chapter includes sections on the potential for cognitive enhancement in mental disorders, as well as a review of PDE1 enzyme structure, enzymology, tissue distribution, genomics, inhibitors, pharmacology, clinical trials, and therapeutic indications. Information is taken from public databases. A number of excellent reviews of the phosphodiesterase family have been written as well as reviews of the PDE1 family. References cited here are not comprehensive, rather pointing to major reviews and key publications.

Mechanisms and Factors That Drive Extensive Human Immunodeficiency Virus Type-1 Hypervariability: An Overview

The extensive hypervariability of human immunodeficiency virus type-1 (HIV-1) populations represents a major barrier against the success of currently available antiretroviral therapy. Moreover, it is still the most important obstacle that faces the development of an effective preventive vaccine against this infectious virus. Indeed, several factors can drive such hypervariability within and between HIV-1 patients. These factors include: first, the very low fidelity nature of HIV-1 reverse transcriptase; second, the extremely high HIV-1 replication rate; and third, the high genomic recombination rate that the virus has. All these factors together with the APOBEC3 proteins family and the immune and antiviral drugs pressures drive the extensive hypervariability of HIV-1 populations. Studying these factors and the mechanisms that drive such hypervariability will provide valuable insights that may guide the development of effective therapeutic and preventive strategies against HIV-1 infection in the near future. To this end, in this review, we summarized recent advances in this area of HIV-1 research.

VS411 reduced immune activation and HIV-1 RNA levels in 28 days: randomized proof-of-concept study for antiviral-hyperactivation limiting therapeutics

Background

A new class of antiretrovirals, AntiViral-HyperActivation Limiting Therapeutics (AV-HALTs), has been proposed as a disease-modifying therapy to both reduce Human Immunodeficiency Virus Type 1 (HIV-1) RNA levels and the excessive immune activation now recognized as the major driver of not only the continual loss of CD4⁺ T cells and progression to Acquired Immunodeficiency Syndrome (AIDS), but also of the emergence of both AIDS-defining and non-AIDS events that negatively impact upon morbidity and mortality despite successful (ie, fully suppressive) therapy. VS411, the first-in-class AV-HALT, combined low-dose, slow-release didanosine with low-dose hydroxycarbamide to accomplish both objectives with a favorable toxicity profile during short-term administration. Five dose combinations were administered as VS411 to test the AV-HALT Proof-of-Concept in HIV-1-infected subjects.

Methods

Multinational, double-blind, 28-day Phase 2a dose-ranging Proof-of-Concept study of antiviral activity, immunological parameters, safety, and genotypic resistance in 58 evaluable antiretroviral-naïve HIV-1-infected adults. Randomization and allocation to study arms were carried out by a central computer system. Results were analyzed by ANOVA, Kruskal-Wallis, ANCOVA, and two-tailed paired t tests.

Results

VS411 was well-tolerated, produced significant reductions of HIV-1 RNA levels, increased CD4⁺ T cell counts, and led to significant, rapid, unprecedented reductions of immune activation markers after 28 days despite incomplete viral suppression and without inhibiting HIV-1-specific immune responses. The didanosine 200 mg/HC 900 mg once-daily formulation demonstrated the greatest antiviral efficacy (HIV-1 RNA: −1.47 log₁₀ copies/mL; CD4⁺ T cell count: +135 cells/mm³) and fewest adverse events.

Conclusions

VS411 successfully established the Proof-of-Concept that AV-HALTs can combine antiviral efficacy with rapid, potentially beneficial reductions in the excessive immune system activation associated with HIV-1 disease. Rapid reductions in markers of immune system hyperactivation and cellular proliferation were obtained despite the fact that VS411 did not attain maximal suppression of HIV RNA, suggesting this effect was due to the HALT component.

Trial Registration

ITEudraCT 2007-002460-98

Treating HIV/AIDS by reducing immune system activation: the paradox of immune deficiency and immune hyperactivation

PURPOSE OF REVIEW

To collect published evidence in support of a novel immune therapeutic approach to reduce the excess of immune activation that ultimately turns into immune deficiency in HIV/AIDS.

RECENT FINDINGS

A large body of evidence has been collected in support of the pathogenetic interpretation that prolonged immune overactivation induced by HIV during the course of chronic infection exhausts the immune system and leads to AIDS. Some groups are exploring the possibility of therapeutic interventions to limit the immune system overload. Cytostatic drugs appear promising candidates to achieve the goal, as they restrain cell proliferation without blocking it. At the same time, they do not affect cellular response to antigenic stimulation, and at appropriate dosages are not immune suppressive.

SUMMARY

Presently available antiretrovirals only partially reduce immune system activation during chronic HIV infection. Further clinical research is warranted to test cytostatic drugs to avert immune overactivation and prevent progression to AIDS.

G protein coupled receptors as allosteric proteins and the role of allosteric modulators

Seven transmembrane receptors (7TMRs) are proteins that convey signals through changes in conformation. These conformations are stabilized by external molecules (i.e. agonists, antagonists, modulators) and act upon other bodies (termed 'guests') which can be other molecules in the extracellular space, or proteins along the plane of the membrane (receptor oligomerization) or signaling proteins in the cytosol (i.e. G protein, β-arrestin). These elements comprise allosteric systems and a great deal of 7TMR pharmacology can be considered in terms of allosteric behavior. Allosteric ligands acting on 7TMRs possess four unique behaviors that can be valuable therapeutically; (1) the ability to alter the interaction of very large proteins, (2) probe dependence, (3) saturable effect, and (4) induction of separate changes in affinity and efficacy of other ligands. Two of these behaviors (namely probe dependence for CCR5-based HIV-1 entry inhibitors and functional selectivity for biased agonism) will be highlighted with examples.

Strategies to improve efficacy and safety of a novel class of antiviral hyper-activation-limiting therapeutic agents: the VS411 model in [corrected] HIV/AIDS

BACKGROUND AND PURPOSE

Antiviral hyper-activation-limiting therapeutic agents (AV-HALTs) are a novel experimental drug class designed to both decrease viral replication and down-regulate excessive immune system activation for the treatment of chronic infections, including human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome. VS411, a first-in-class AV-HALT, is a single-dosage form combining didanosine (ddI, 400 mg), an antiviral (AV), and hydroxyurea (HU, 600 mg), a cytostatic agent, designed to provide a slow release of ddI to reduce its maximal plasma concentration (C(max)) to potentially reduce toxicity while maintaining total daily exposure (AUC) and the AV activity.

EXPERIMENTAL APPROACH

This was a pilot phase I, open-label, randomized, single-dose, four-way crossover trial to investigate the fasted and non-fasted residual variance of AUC, C(max) and the oral bioavailability of ddI and HU, co-formulated as VS411, and administered as two different fixed-dose combination formulations compared to commercially available ddI (Videx EC) and HU (Hydrea) when given simultaneously.

KEY RESULTS

Formulation VS411-2 had a favourable safety profile, displayed a clear trend for lower ddI C(max) (P= 0.0603) compared to Videx EC, and the 90% confidence intervals around the least square means ratio of C(max) did not include 100%. ddI AUC(∞) was not significantly decreased compared to Videx EC. HU pharmacokinetic parameters were essentially identical to Hydrea, although there was a decrease in HU exposure under fed versus fasted conditions.

CONCLUSIONS AND IMPLICATIONS

A phase IIa trial utilizing VS411-2 formulation has been fielded to identify the optimal doses of HU plus ddI as an AV-HALT for the treatment of HIV disease.

Hydroxycarbamide stimulates the production of proinflammatory cytokines by endothelial cells: relevance to sickle cell disease

BACKGROUND AND OBJECTIVE

The clinical hallmarks of sickle cell disease (SCD) are vaso-occlusive crises (VOC) triggered by red blood cells (RBC) stiffening and abnormal adhesion to vascular endothelial cells (VEC) in the context of chronic inflammation, cell activation, and vascular tone abnormalities. Hydroxycarbamide (HC) is the only drug with a proven efficacy in decreasing VOC frequency. HC decreases RBC stiffening, modulates adhesion protein expression by RBC and VEC, and reduces endothelin-1 production by VEC. Our objective was to test whether HC could also affect inflammation through its action on VEC.

METHODS

We used microarrays to study the effect of HC on the transcriptome of transformed human bone marrow endothelial cell, a cell line derived from bone marrow microcirculation (the predilection site of VOC), in basal and proinflammatory conditions. Microarray results were confirmed by real-time quantitative PCR and protein analysis on transformed human bone marrow endothelial cell (TrHBMEC) and on two other VEC types in the primary culture: human pulmonary microcirculation endothelial cell (HPMEC) and human umbilical vein endothelial cell (HUVEC a classical model for the macrocirculation).

RESULTS

HC had a significant effect on the expression of genes of the 'inflammation pathway'. Strikingly, it stimulates the expression of proinflammatory genes such as IL1A, IL1B, IL6, IL8, CCL2, CCL5, CCL20, and CCL8 in all the tested VEC types.

CONCLUSION

Our study confirms that VECs are significant targets of HC in the context of SCD and identifies its earlier unsuspected action on another major component of SCD pathophysiology, that is, the 'inflammation pathway'.

Seven transmembrane receptors as shapeshifting proteins: the impact of allosteric modulation and functional selectivity on new drug discovery

It is useful to consider seven transmembrane receptors (7TMRs) as disordered proteins able to allosterically respond to a number of binding partners. Considering 7TMRs as allosteric systems, affinity and efficacy can be thought of in terms of energy flow between a modulator, conduit (the receptor protein), and a number of guests. These guests can be other molecules, receptors, membrane-bound proteins, or signaling proteins in the cytosol. These vectorial flows of energy can yield standard canonical guest allostery (allosteric modification of drug effect), effects along the plane of the cell membrane (receptor oligomerization), or effects directed into the cytosol (differential signaling as functional selectivity). This review discusses these apparently diverse pharmacological effects in terms of molecular dynamics and protein ensemble theory, which tends to unify 7TMR behavior toward cells. Special consideration will be given to functional selectivity (biased agonism and biased antagonism) in terms of mechanism of action and potential therapeutic application. The explosion of technology that has enabled observation of diverse 7TMR behavior has also shown how drugs can have multiple (pluridimensional) efficacies and how this can cause paradoxical drug classification and nomenclatures.

First report on a series of HIV patients undergoing rapamycin monotherapy after liver transplantation

INTRODUCTION

Some experimental trials have demonstrated that rapamycin (RAPA) is able to inhibit HIV-1 progression in three different ways: (1) reducing CCR5-gene transcription, (2) blocking interleukin-2 intracellular secondary messenger (mammalian target of rapamycin), and (3) up-regulating the beta-chemokine macrophage inflammatory protein (MIP; MIP-1alpha and MIP-1beta). We present the preliminary results of a prospective nonrandomized trial concerning the first HIV patient series receiving RAPA monotherapy after liver transplantation (LT).

METHODS

Since June 2003, 14 HIV patients have received cadaveric donor LT due to end-stage liver disease (ESLD) associated or not associated with hepatocellular carcinoma, scored by the model for ESLD system. Patients were assessed using the following criteria for HIV characterization: CD4 T-cell count more than 100/mL and HIV-RNA levels less than 50 copies/mL. Primary immunosuppression was based on calcineurin inhibitors (CI), whereas switch to RAPA monotherapy occurred in cases of CI complications or Kaposi's sarcoma.

RESULTS

Mean overall post-LT follow-up was 14.8 months (range: 0.5-52.6). Six of 14 patients were administered RAPA monotherapy. Mean preswitch period from CI to RAPA was 67 days (range: 10-225 days). Mean postswitch follow-up was 11.9 months (range: 2-31 months). All patients were affected by ESLD, which was associated with hepatocellular carcinoma in seven patients. ESLD occurred due to hepatitis C virus (HCV)-related hepatopathy for nine patients, hepatitis B virus-related hepatopathy for one patient, and hepatitis B virus-HCV hepatopathy for four patients. Significantly better control of HIV and HCV replication was found among patients taking RAPA monotherapy (P=0.0001 and 0.03, respectively).

CONCLUSIONS

After in vitro and in vivo experimental evidence of RAPA antiviral proprieties, to our knowledge, this is the first clinical report of several significant benefits in long-term immunosuppression maintenance and HIV-1 control among HIV positive patients who underwent LT.

[CCR5 antagonists and HIV-1 infection: Bases and consequences of this therapeutic approach]

La molécule CCR5 est un récepteur de chimiokines qui joue un rôle important en pathologie infectieuse : corécepteur des souches du VIH-1 à tropisme R5, il est également impliqué dans la défense immunitaire contre certains agents transmissibles. Les antagonistes de CCR5 constituent une nouvelle approche thérapeutique antirétrovirale. Trois inhibiteurs du CCR5 ont atteint les phases IIb et III de développement clinique : aplaviroc (GlaxoSmithKine), vicriviroc (Schering-Plough) et maraviroc (Pfizer). Le développement de l’aplaviroc a été interrompu pour toxicité hépatique. Les essais ACTG 5211 et Motivate ont démontré une amélioration de la réponse antirétrovirale par l’addition respectivement de vicriviroc (actuellement en phase III) et de maraviroc (ayant déjà obtenu l’Autorisation de Mise sur le Marché) à un traitement optimisé chez des patients en échec thérapeutique. Le rôle de cette nouvelle cible thérapeutique dans les stratégies de traitement initial, de substitution ou de sauvetage reste à préciser, de même que leur intérêt chez des patients ayant une réponse immunovirologique dissociée, en immunodépresssion sévère ou infectés par des souches à tropisme non-R5. Plusieurs points sont également à éclaircir comme la tolérance à long terme, le risque d’induire une commutation R5-X4, en particulier dans les tissus, le risque d’interférer avec les réponses immunitaires, ainsi que l’impact d’une discordance de tropisme entre le plasma et les autres compartiments de l’organisme.

HIV-1 viral protein R (Vpr) and its interactions with host cell

Human immunodeficiency virus type 1 (HIV-1) is engaged in dynamic and antagonistic interactions with host cells. Once infected by HIV-1, host cells initiate various antiviral strategies, such as innate antiviral defense mechanisms, to counteract viral invasion. In contrast, the virus has different strategies to suppress these host responses to infection. The final balance between these interactions determines the outcome of the viral infection and disease progression. Recent findings suggest that HIV-1 viral protein R (Vpr) interacts with some of the host innate antiviral factors, such as heat shock proteins, and plays an active role as a viral pathogenic factor. Cellular heat stress response factors counteract Vpr activities and inhibit HIV replication. However, Vpr overcomes these heat-stress-like responses by preventing heat shock factor-1 (HSF-1)-mediated activation of heat shock proteins. In this review, we will focus on the virus-host interactions involving Vpr. In addition to heat stress response proteins, we will discuss interactions of Vpr with other proteins, such as EF2 and Skp1/GSK3, their involvements in cellular responses to Vpr, as well as strategies to develop novel antiviral therapies aimed at enhancing anti-Vpr responses of the host cell.

The relative activity of "function sparing" HIV-1 entry inhibitors on viral entry and CCR5 internalization: is allosteric functional selectivity a valuable therapeutic property?

Six allosteric HIV-1 entry inhibitor modulators of the chemokine (C-C motif) receptor 5 (CCR5) receptor are compared for their potency as inhibitors of HIV-1 entry [infection of human osteosarcoma (HOS) cells and peripheral blood mononuclear cells (PBMC)] and antagonists of chemokine (C-C motif) ligand 3-like 1 [CCL3L1]-mediated internalization of CCR5. This latter activity has been identified as a beneficial action of CCL3L1 in prolonging survival after HIV-1 infection ( Science 307: 1434-1440, 2005 ). The allosteric nature of these modulators was further confirmed with the finding of a 58-fold (HOS cells) and 282-fold (PBMC) difference in relative potency for blockade of CCL3L1-mediated internalization versus HIV-1 entry. For the CCR5 modulators, statistically significant differences in this ratio were found for maraviroc, vicriviroc, aplaviroc, Sch-C, TAK652, and TAK779. For instance, although TAK652 is 13-fold more potent as an HIV-1 inhibitor (over blockade of CCL3L1-mediated CCR5 internalization), this ratio of potency is reversed for Sch-C (22-fold more potent for CCR5-mediated internalization over HIV-1 entry). Quantitative analyses of the insurmountable antagonism of CCR5 internalization by these ligands suggest that all of them reduce the efficacy of CCL3L1 for CCR5 internalization. The relatively small magnitude of dextral displacement accompanying the depression of maximal responses for aplaviroc, maraviroc and vicriviroc suggests that these modulators have minimal effects on CCL3L1 affinity, although possible receptor reserve effects obscure complete interpretation of this effect. These data are discussed in terms of the possible benefits of sparing natural CCR5 chemokine function in HIV-1 entry inhibition treatment for AIDS involving allosteric inhibitors.

Vesicular stomatitis virus oncolysis of T lymphocytes requires cell cycle entry and translation initiation

Vesicular stomatitis virus (VSV) is a candidate oncolytic virus that replicates and induces cell death in cancer cells while sparing normal cells. Although defects in the interferon antiviral response facilitate VSV oncolysis, other host factors, including translational and growth regulatory mechanisms, also appear to influence oncolytic virus activity. We previously demonstrated that VSV infection induces apoptosis in proliferating CD4(+) T lymphocytes from adult T-cell leukemia samples but not in resting T lymphocytes or primary chronic lymphocytic leukemia cells that remain arrested in G(0). Activation of primary CD4(+) T lymphocytes with anti-CD3/CD28 is sufficient to induce VSV replication and cell death in a manner dependent on activation of the MEK1/2, c-Jun NH(2)-terminal kinase, or phosphatidylinositol 3-kinase pathway but not p38. VSV replication is specifically impaired by the cell cycle inhibitor olomoucine or rapamycin, which induces early G(1) arrest, but not by aphidicolin or Taxol, which blocks at the G(1)1S or G(2)1M phase, respectively; this result suggests a requirement for cell cycle entry for efficient VSV replication. The relationship between increased protein translation following G(0)/G(1) transition and VSV permissiveness is highlighted by the absence of mTOR and/or eIF4E phosphorylation whenever VSV replication is impaired. Furthermore, VSV protein production in activated T cells is diminished by small interfering RNA-mediated eIF4E knockdown. These results demonstrate that VSV replication in primary T lymphocytes relies on cell cycle transition from the G(0) phase to the G(1) phase, which is characterized by a sharp increase in ribogenesis and protein synthesis.

Rapamycin reduces CCR5 mRNA levels in macaques: potential applications in HIV-1 prevention and treatment

G1 cytostatic drugs reduce CCR5 co-receptor expression and enhance the antiviral activity of a CCR5 antagonist in vitro. The administration of rapamycin, a G1 cytostatic agent, to three cynomolgous macaques led to decreased CCR5 messenger RNA expression in peripheral blood mononuclear cells and cervicovaginal tissue. These results support further clinical evaluation of G1 cytostatic agents such as rapamycin targeting the downregulation of CCR5 expression as a strategy for both the prevention and treatment of HIV infection.

Optimal suppression of HIV replication by low-dose hydroxyurea through the combination of antiviral and cytostatic ('virostatic') mechanisms

BACKGROUND

The hydroxyurea-didanosine combination has been shown to limit immune activation (a major pathogenic component of HIV/AIDS) and suppress viral load by both antiviral and cytostatic ('virostatic') activities. Virostatics action represent a novel approach to attack HIV/AIDS from multiple directions; however, the use of these drugs is limited by the lack of understanding of their dose-dependent mechanism of action and by fear of pancreatic toxicity, even though a large review of ACTG studies has shown that hydroxyurea does not increase the incidence of pancreatitis.

METHODS

In vitro cytostatic and cytotoxic activity, inhibition of viral replication and immune activation by pharmacologically attainable plasma concentrations of hydroxyurea (10-100 micromol/l) and didanosine (1-5 micromol/l) were analyzed by cell proliferation, viability, apoptosis and infection assays using peripheral blood mononuclear cells. In vivo, 600, 900 and 1200 mg daily doses of hydroxyurea in combination with standard doses of didanosine and stavudine were studied in 115 randomized chronically infected patients.

RESULTS

A cytostatic low (10 micromol/l) concentration of hydroxyurea inhibited cell proliferation and HIV replication in vitro. A gradual switch from cytostatic to cytotoxic effects was observed by increasing hydroxyurea concentration to 50-100 micromol/l, predicting that lower doses of hydroxyurea would be less toxic and more potent in vivo. The clinical results confirmed that 600 mg hydroxyurea was better tolerated, had fewer side effects and was more potent in suppressing HIV replication than the higher doses.

CONCLUSIONS

A bimodal, dose-dependent, cytostatic-cytotoxic switch is an immune-based mechanism explaining the apparent paradox that lowering the dose of hydroxyurea to 600 mg daily induces maximal antiviral suppression in HIV-infected patients.

Hydroxyurea exerts a cytostatic but not immunosuppressive effect on T lymphocytes

OBJECTIVE

To demonstrate that, despite a dose-dependent cytostatic effect, hydroxyurea (HU) does not have immunosuppressive effects.

METHODS

The effects of HU on T lymphocyte proliferation parameters, activation phenotype and cytokine production were examined in vitro after exposure to clinically relevant concentrations of HU (10, 50, and 100 micromol/l). The effects of HU in vivo on CD4 T cell counts, viral load, activation phenotype and virus-specific response were examined in 17 Rhesus macaques infected with SIV(mac251) and randomized into three groups: untreated controls; treated with (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) and didanosine (ddI) only; and treated with PMPA, didanosine, and HU.

RESULTS

The in vitro inhibition of T lymphocyte proliferation confirmed the cytostatic effect of HU, with a linear dose-dependent effect; however, no relevant differences were found in the expression of activation markers between treated and untreated controls. Both T helper type 1 and type 2 cytokine production were enhanced by HU. Consistent with the in vitro results, a blunted increase of peripheral CD4 T cells was observed in vivo in the HU group, without relevant effects on the expression of activation markers, and SIV-specific T cell responses were not affected by HU.

CONCLUSIONS

Hyper-proliferation of T-lymphocytes is a major factor contributing to HIV pathogenesis. HU exerts a cytostatic effect on T lymphocytes, without altering their activation and apparently without having an immunosuppressive effect. The increase in cytokine production at the single cell level might compensate for the decrease in the percentage of activated CD4 T lymphocytes, without overall impairment of HIV-specific immune responses.

Regulation of cell cycle proteins by chemokine receptors: A novel pathway in human immunodeficiency virus neuropathogenesis?

In order to test the hypothesis that alteration of cell cycle proteins are involved in the neuronal damage caused by human immunodeficiency virus (HIV), the authors have been studying the effect of chemokines on the CDK/Rb/E2F-1 pathway--which is involved in neuronal apoptosis and differentiation. First, they have asked whether CXCR4, the specific receptor for the chemokine SDF-1 and X4-using gp120s, can regulate Rb and E2F-1 activity in cultures of differentiated rat neurons. Although CCR3 and CCR5 are known to mediate infection of microglia by HIV-1, recent evidence indicate that CXCR4 also play important roles in HIV-induced neuronal injury, and dual-tropic isolates that use CXCR4 to infect macrophages have recently been reported. The authors have focused on two specific brain areas in which CXCR4 is physiologically relevant, i.e., the cerebellum and the hippocampus. So far, the data indicate that changes in the nuclear and cytosolic levels of Rb, which result in the functional loss of this protein, are associated with apoptosis in these neurons, and that SDF-1alpha and gp120IIIB affect this pathway. A summary of the findings are presented.

Rapamycin causes down-regulation of CCR5 and accumulation of anti-HIV beta-chemokines: an approach to suppress R5 strains of HIV-1

Propagation of R5 strains of HIV-1 on CD4 lymphocytes and macrophages requires expression of the CCR5 coreceptor on the cell surface. Individuals lacking CCR5 (CCR5 Delta 32 homozygous genotype) are phenotypically normal and resistant to infection with HIV-1. CCR5 expression on lymphocytes depends on signaling through the IL-2 receptor. By FACS analysis we demonstrate that rapamycin (RAPA), a drug that disrupts IL-2 receptor signaling, reduces CCR5 surface expression on T cells at concentrations as low as 1 nM. In addition, lower concentrations of RAPA (0.01 nM) were sufficient to reduce CCR5 surface expression on maturing monocytes. PCR analysis on peripheral blood mononuclear cells (PBMCs) showed that RAPA interfered with CCR5 expression at the transcriptional level. Reduced expression of CCR5 on PBMCs cultured in the presence of RAPA was associated with increased extracellular levels of macrophage inflammatory protein (MIP)-1 alpha and MIP-1 beta. In infectivity assays, RAPA suppressed the replication of R5 strains of HIV-1 both in PBMC and macrophage cultures. In total PBMC cultures, RAPA-mediated inhibition of CCR5-using strains of HIV-1 occurred at 0.01 nM, a concentration of drug that is approximately 103 times lower than therapeutic through levels of drug in renal transplant recipients. In addition, RAPA enhanced the antiviral activity of the CCR5 antagonist TAK-779. These results suggest that low concentrations of RAPA may have a role in both the treatment and prevention of HIV-1 infection.