Antimicrobial properties of the medicinal plant Cardiospermum halicacabum L: new evidence and future perspectives

The emergence and rapid spread of multidrug-resistance in human pathogenic microorganisms urgently require the development of novel therapeutic strategies for the treatment of infectious diseases. From this perspective, the antimicrobial properties of the natural plant-derived products may represent an important alternative therapeutic option to synthetic drugs. Among medicinal plants, the Cardiospermum halicacabum L. (C. halicacabum), belonging to Sapindaceae family, could be a very promising candidate for its antimicrobial activity against a wide range of microorganisms, including both Gram-positive and Gram-negative bacteria, as well as fungal pathogens. Although the antimicrobial properties of C. halicacabum have been intensively studied, the mechanism/s by which it exerts the inhibitory activity towards the pathogenic microbes have not yet been completely understood. This review focuses on the main antimicrobial activities displayed in vitro by the plant extract, with particular attention on our recent advances. We demonstrated that C. halicacabum is able to exert in vitro a dose-dependent fungistatic effect against Trychophyton rubrum (T. rubrum) through molecular interaction with the fungal heat shock protein (Hsp)-90 chaperone. These findings are supported by a growing body of research indicating the crucial role played by the Hsp90 in the virulence of the pathogenic microorganisms, including fungal pathogens. The possible future use of C. halicacabum for treating a wide range of infectious diseases is also discussed.

Effect of maraviroc on non-R5 tropic HIV-1: refined analysis of subjects from the phase IIb study A4001029

We characterized maraviroc susceptibility of dual/mixed tropic viruses from subjects enrolled onto phase IIb study A4001029. Maraviroc baseline plasma samples from 13 multidrug-experienced subjects were sequenced and the HIV-1-env gene cloned into pNL4.3Δenv to obtain recombinant viruses. The V3 region was sequenced by the Sanger method and ultradeep sequencing. By analysing subjects having a weighted optimized background therapy susceptibility (wOBT) score of <1, 3/7 subjects were characterized by good in vivo and in vitro response to maraviroc therapy. Molecular docking simulations allowed us to rationalize the maraviroc susceptibility of dual/mixed tropic viruses. A subset of subjects with dual/mixed tropic viruses responded to maraviroc. Further investigations are warranted of CCR5 antagonists in subjects carrying dual/mixed tropic virus that explore the feasible use of maraviroc in subjects that is potentially larger than those infected with a pure R5 virus.

Natural polymorphisms of HIV-1 subtype-C integrase coding region in a large group of ARV-naïve infected individuals

PURPOSE

Integrase (IN) is an enzyme produced by human immunodeficiency virus (HIV)-1 that enables its genetic material to be integrated into the DNA of the infected cell. Still now, few data are available with detailed analysis of the natural IN polymorphisms of HIV-1 subtype-C in datasets retrieved from antiretroviral-naïve patients; this study focuses on these polymorphisms.

METHODS

The analysis included 335 HIV-1 subtype-C IN sequences (one per patient). Multi-alignment of IN sequences was performed, and for the definition of a polymorphism, only amino acid changes with prevalence ≥3 % among treatment-naïve patients were considered.

RESULTS

Seventy IN amino acid positions were fully conserved. Differently, forty-six IN amino acid polymorphic positions were observed, 12 within the N-terminal domain and 13 within the C-terminal domain. In the DDE-catalytic motif, only one mutation per site (D64G/D116G/E152K) was found, while a low variability (<1 %) was observed for IN positions interacting with LEDGF/p75. A major drug resistance mutation for raltegravir (RAL) and elvitegravir (EVG), Q148H, was retrieved from one patient and another RAL primary resistance mutation, Y143H, was also retrieved from another patient.

CONCLUSIONS

The results from the IN sequences analyzed underlined that some unexpected baseline substitutions affecting the susceptibility to RAL/EVG could be detected in drug-naïve individuals, and, therefore, it should be genotyped before the consideration of HIV-1 IN inhibitors (INIs). The impact of these mutations on the baseline drug susceptibility of HIV-1 subtype-C to INIs may need to be addressed prior to the introduction of these drugs in some Asiatic and African countries.

NeuroAIDS: virological aspects of HIV infection

NeuroAIDS is one of the main complications of chronic HIV-infection. The Central Nervous System is an immunologic sanctuary for HIV and allows the persistence of the virus despite an efficient antiretroviral therapy. HIV-1 could promote the neurodegeneration through the induction of inflammation by the release of neurotoxins from infected cells. In addition, several viral proteins can directly contribute to the neuronal damages, activate cell-signaling involved in the control of cellular survival and apoptosis, favoring functional alterations in the target cells. Macrophages play a key role in the pathogenesis of NeuroAIDS, they are the main reservoirs of the infection in brain, promoting the inflammatory escalation, astrogliosis and degeneration process. This review aims to highlight the virological aspects associated with NeuroAIDS including pathogenesis, and treatment of HIV-1 in the CNS sanctuaries.

Inhibition of human immunodeficiency virus (HIV-1) infection in human peripheral blood leucocytes-SCID reconstituted mice by rapamycin

The capacity of the immunomodulatory drug rapamycin (RAPA) to inhibit replication of the CCR5 strain of human immunodeficiency virus (HIV) in vitro prompted us to test its effects in a murine preclinical model of HIV infection. RAPA (0.6 or 6 mg/kg body weight) or its vehicle were administered daily, per os, to SCID mice reconstituted with human peripheral blood leucocytes (hu-PBL) starting 2 days before the intraperitoneal challenge with the R5 tropic SF162 strain of HIV-1 (1000 50% tissue culture infective dose/ml). Relative to hu-PBL-SCID mice that received no treatment, HIV-infected hu-PBL-SCID mice treated with the vehicle control for 3 weeks exhibited a severe depletion of CD4(+) cells (90%), an increase in CD8(+) cells and an inversion of the CD4(+)/CD8(+) cell ratio. In contrast, treatment of HIV-infected mice with RAPA prevented a decrease in CD4(+) cells and the increase of CD8(+) cells, thereby preserving the original CD4(+):CD8(+) cell ratio. Viral infection also resulted in the detection of HIV-DNA within peritoneal cells and spleen, and lymph node tissues of the vehicle-treated mice within 3 weeks of the viral challenge. In contrast, treatment with RAPA decreased cellular provirus integration and reduced HIV-RNA levels in the blood. Furthermore, in co-cultivation assays, spleens from RAPA-treated mice exhibited a reduced capacity for infecting allogeneic T cells which was dose-dependent. These data show that RAPA possesses powerful anti-viral activity against R5 strains of HIV in vivo and support the use of additional studies to evaluate the potential application of this drug in the management of HIV patients.

Carbohydrate-binding agents (CBAs) inhibit HIV-1 infection in human primary monocyte-derived macrophages (MDMs) and efficiently prevent MDM-directed viral capture and subsequent transmission to CD4+ T lymphocytes

Carbohydrate-binding agents (CBAs) have been proposed as innovative anti-HIV compounds selectively targeting the glycans of the HIV-1 envelope glycoprotein gp120 and preventing DC-SIGN-directed HIV capture by dendritic cells (DCs) and transmission to CD4(+) T-lymphocytes. We now show that CBAs efficiently prevent R5 HIV-1 infection of human primary monocyte-derived macrophage (MDM) cell cultures in the nanomolar range. Both R5 and X4 HIV-1 strains were efficiently captured by the macrophage mannose-binding receptor (MMR) present on MDM. HIV-1 capture by MMR-expressing MDM was inhibited by soluble mannose-binding lectin and MMR antibody. Short pre-exposure of these HIV-1 strains to CBAs is able to prevent virus capture by MDM and subsequent syncytia formation in cocultures of the CBA-exposed HIV-1-captured MDM and uninfected CD4(+) T-lymphocytes. The potential of CBAs to impair MDM in their capacity to capture and to transmit HIV to T-lymphocytes might be an important property to be taken into consideration in the eventual choice to select microbicide candidate drugs for clinical investigation.

Antiviral profile of HIV inhibitors in macrophages: implications for therapy

Macrophages (M/M) are identified as the second cellular target of HIV and a crucial virus reservoir. M/M are persistently infected cells and not susceptible to the HIV cytophatic effects typical of infected CD4+ T-lymphocytes. HIV replication in M/M is a crucial pathogenetic event during the whole course of the disease. Moreover, the dynamics of HIV-1 replication and cumulative virus production is quite different in M/M and CD4+ T-lymphocytes in the presence or in the absence of antiviral drugs. Thus, for their unique cellular characteristics, the activity of anti-HIV compounds could be different in M/M than in CD4+ T-lymphocytes. Indeed, nucleoside analogues inhibitors of HIV-reverse transcriptase (NRTIs) show potent antiviral activity in macrophages, although the limited penetration of these compounds in sequestered body compartments and the scarce phosphorylation ability of macrophages, suggest that a phosphate group linked to NRTIs may confer a greater anti-HIV activity in such cells. The antiviral activity of non-nucleoside reverse transcriptase inhibitors (NNRTIs) in macrophages is similar to that found in CD4-lymphocytes. Interestingly, protease inhibitors (PIs), acting at post-integrational stages of virus replication, are the only drugs able to interfere with virus production and release from macrophages with established and persistent HIV infection. For these reasons, a careful analysis of the distribution of antiviral drugs, and the assessment of their activity in cells of macrophage lineage, represent key factors in the development of therapeutic strategies aimed to the treatment of the HIV-infected patients.

HIV/HCV co-infection: the magnitude of the problem

Hepatitis C virus (HCV) and human immunodeficiency virus (HIV) share routes of transmission, therefore their coinfection is relatively common. Nevertheless, the clinical relevance of this event has been minimal until few years ago when, due to the increased survival of HIV-infected individuals (favoured by highly active antiretroviral therapy) morbility and mortality caused by pathologies not strictly related to HIV (such as HCV infection) raised sharply. Despite differences in their general characteristics (including lifecycle, target cells, and type of persistence in the infected host) a remarkable level of interaction exists between HCV and HIV; this makes the progression of both liver disease and immunological damage easier and more rapid. A therapeutic approach to HIV/HCV coinfection thus requires the utilization of drugs and strategies effective against both viruses, yet, timing, drug types, and effective combinations still remain poorly defined. New and innovative studies specifically focused on HIV/HCV coinfection are thus warranted to increase the knowledge about their interaction, and define therapeutic strategies aimed to the best management of the infection by both viruses during coinfection.

Antiretrovirus activity of a novel class of acyclic pyrimidine nucleoside phosphonates

A novel class of acyclic nucleoside phosphonates has been discovered in which the base consists of a pyrimidine preferably containing an amino group at C-2 and C-4 and a 2-(phosphonomethoxy)ethoxy (PMEO) or a 2-(phosphonomethoxy)propoxy (PMPO) group at C-6. The 6-PMEO 2,4-diaminopyrimidine (compound 1) and 6-PMPO 2,4-diaminopyrimidine (compound 11) derivatives showed potent activity against human immunodeficiency virus (HIV) in the laboratory (i.e., CEM and MT-4 cells) and in primary (i.e., peripheral blood lymphocyte and monocyte/macrophage) cell cultures and pronounced activity against Moloney murine sarcoma virus in newborn NMRI mice. Their in vitro and in vivo antiretroviral activity was comparable to that of reference compounds 9-[(2-phosphonomethoxy)ethyl]adenine (adefovir) and (R)-9-[(2-phosphonomethoxy)-propyl]adenine (tenofovir), and the enantiospecificity of (R)- and (S)-PMPO pyrimidine derivatives as regards their antiretroviral activity was identical to that of the classical (R)- and (S)-9-(2-phosphonomethoxy)propyl purine derivatives. The prototype PMEO and PMPO pyrimidine analogues were relatively nontoxic in cell culture and did not markedly interfere with host cell macromolecular (i.e., DNA, RNA, or protein) synthesis. Compounds 1 and 11 should be considered attractive novel pyrimidine nucleotide phosphonate analogues to be further pursued for their potential as antiretroviral agents in the clinical setting.

Productive infection of primary macrophages with human herpesvirus 7

Here we demonstrate replication of human herpesvirus 7 (HHV-7), a T-lymphotropic virus, in macrophages. Productive replication was lost after 2 weeks, but HHV-7 DNA was detected up to 1 month after infection. Thus, macrophages become infected by HHV-7 and might play an important role as a viral reservoir, as has been demonstrated for human immunodeficiency virus type 1.

Macrophages: a crucial reservoir for human immunodeficiency virus in the body

The replication of Human Immunodeficiency Virus (HIV) in cells of macrophage lineage represents a key pathogenetic event of the neurological damages typically found during the course of this disease. Macrophages are persistently infected cells and thus not susceptible to the cytophatic effect typical of infected activated CD4-lymphocytes. The resistance of macrophages to HIV infection is at least in part mediated by the autocrine production of the nerve growth factor (NGF), a neurokine able to sustain the survival of some cells of bone marrow origin, including monocyte-derived macrophages. This anti-apoptotic effect of NGF in HIV-infected macrophages can be even more relevant at the central nervous system level, where many cells are able to physiologically produce NGF, thus further increasing the survival of macrophages infected by HIV, and enhancing the damages that these cells may induce upon bystander neurons. The proapoptotic effect of soluble factors released by HIV-infected macrophages may heavily affect the survival and functions also of astrocytes, that in turn become unable to sustain neuronal homeostasis. Taken together, this information supports the importance of therapeutic attempts aimed at attacking virus replication in infected macrophages and/or to selectively eliminate these chronically infected and persistently virus-producing cells.

The LD78beta isoform of MIP-1alpha is the most potent CC-chemokine in inhibiting CCR5-dependent human immunodeficiency virus type 1 replication in human macrophages

The CC-chemokines RANTES, macrophage inflammatory protein 1alpha (MIP-1alpha), and MIP-1beta are natural ligands for the CC-chemokine receptor CCR5. MIP-1alpha, also known as LD78alpha, has an isoform, LD78beta, which was identified as the product of a nonallelic gene. The two isoforms differ in only 3 amino acids. LD78beta was recently reported to be a much more potent CCR5 agonist than LD78alpha and RANTES in inducing intracellular Ca2+ signaling and chemotaxis. CCR5 is expressed by human monocytes/macrophages (M/M) and represents an important coreceptor for macrophage-tropic, CCR5-using (R5) human immunodeficiency virus type 1 (HIV-1) strains to infect the cells. We compared the antiviral activities of LD78beta and the other CC-chemokines in M/M. LD78beta at 100 ng/ml almost completely blocked HIV-1 replication, while at the same concentration LD78alpha had only weak antiviral activity. Moreover, when HIV-1 infection in M/M was monitored by a flow cytometric analysis using p24 antigen intracellular staining, LD78beta proved to be the most antivirally active of the chemokines. RANTES, once described as the most potent chemokine in inhibiting R5 HIV-1 infection, was found to be considerably less active than LD78beta. LD78beta strongly downregulated CCR5 expression in M/M, thereby explaining its potent antiviral activity.

Cyclosaligenyl-2',3'-didehydro-2',3'-dideoxythymidine monophosphate: efficient intracellular delivery of d4TMP

Cyclosaligenyl-2',3'-didehydro-2', 3'-dideoxythymidine-5'-monophosphate (cycloSal-d4TMP) is a potent and selective inhibitor of human immunodeficiency virus replication in cell culture and differs from other nucleotide prodrug approaches in that it is designed to selectively deliver the nucleotide 5'-monophosphate by a controlled, chemically induced hydrolysis. Its antiviral efficacy in cell culture is at least as good as, if not superior to, that of d4T. CycloSal-d4TMP was found to lead to the efficient intracellular release of d4TMP in a variety of cell lines, including both wild-type CEM and thymidine kinase-deficient CEM/TK(-) cells. Under similar experimental conditions, exposure of CEM/TK(-) cells to d4T failed to result in significant d4TTP levels. The intracellular conversion of cycloSal-d4TMP proved to be both time and dose dependent. The half-life of d4TTP generated intracellularly from d4T- or cycloSal-d4TMP-treated CEM cells was approximately 3.5 h, and the intracellular ratios of d4TTP/d4TMP in cells exposed to cycloSal-d4TMP gradually increased from 1 to 3.4 upon prolonged incubation. Radiolabeled cycloSal-d4TMP could be separated as its two R(p) and S(p) diastereomers on high-performance liquid chromatography. The R(p) diastereomer of cycloSal-d4TMP was 3- to 7-fold more efficient in releasing d4TMP and generating d4TTP than the S(p) cycloSal-d4TMP diastereomer. This correlated well with the 5-fold more pronounced antiviral activity of the R(p) diastereomer versus the S(p) diastereomer. d4TMP is a poor substrate for the cytosolic 5'(3')-deoxyribonucleotidase (V(max)/K(m) for d4TMP: 0.08 of V(max)/K(m) for dTMP) and is only slowly hydrolyzed to d4T. This contributes to the efficient conversion of the prodrug of d4TTP.

Primary macrophages infected by human immunodeficiency virus trigger CD95-mediated apoptosis of uninfected astrocytes

Infection of macrophages (M/M) by human immunodeficiency virus (HIV) is a main pathogenetic event leading to neuronal dysfunction and death in patients with AIDS dementia complex. Alteration of viability of neurons and astrocytes occurs in vivo even without their infection, thus it is conceivable that HIV-infected M/M may affect viability of such cells even without direct infection. To assess this hypothesis, we studied the effects of HIV-infected M/M on an astrocytic cell-line lacking CD4-receptor expression. Exposure to supernatants of HIV-infected M/M triggers complete disruption and apoptotic death of astrocytic cells. This effect is not related to HIV transmission from infected M/M, because HIV-DNA and p24 production in astrocytic cells remained negative. Apoptotic death of astrocytes is mainly mediated by Fas ligand released in supernatants of HIV-infected M/M (as demonstrated by complete reversal of such phenomenon by adding neutralizing antibodies against CD95 receptor). Treatment of astrocytic cells with recombinant (biologically active) Tat induces < 10% apoptosis, and gp120 was totally ineffective. Treatment of HIV-infected M/M with AZT completely reverses the proapoptotic effect of their supernatants on astrocytes, thus demonstrating that productive virus replication within M/M is required for the induction of astrocytic cell death. Taken together, data suggest that homeostasis of astrocytes may be affected by HIV-infected M/M in the absence of productive infection of target cells. This phenomenon may help to explain the cellular damage found in HIV-infected patients also in areas of the brain not strictly adjacent to HIV-infected M/M.

Presence of 2',5'-Bis-O-(tert-butyldimethylsilyl)-3'-spiro-5"-(4"-amino-1",2"-oxath iole-2",2"-dioxide) (TSAO)-resistant virus strains in TSAO-inexperienced HIV patients

HIV-1 samples from six patients undergoing diverse anti-HIV therapies possessed the E138A mutation in their reverse transcriptase (RT) genome. Patients were receiving the following therapies: TIBO monotherapy (one patient); zidovudine plus didanosine combination therapy (one); zidovudine monotherapy (one); sequential therapy with zidovudine, then stavudine and finally zalcitabine plus didanosine (one); and two were drug naive. E138K, not E138A, is a known TSAO-specific resistance mutation, emerging under selective pressure in vitro. Our phenotypic data on the patient isolates, confirmed by data on an E138A mutant acquired through in vitro mutagenesis, indicated that an alanine substitution for glutamate at codon 138 of the HIV-1 RT renders the virus TSAO resistant, confirming the importance of this amino acid residue in the activity of TSAO derivatives. In addition, we have demonstrated through phenotypic analysis of the E138A and A98S mutants (after in vitro mutagenesis) that the mutation A98S, found in one of these patients, could be partially responsible for the phenotypic reversal of TSAO resistance. This reversal could be explained by the restoration of a hydrogen bond between 98S and the main-chain residue L349, which compensates for the loss of the E138-G99 main-chain hydrogen bond. As TSAO derivatives have not been used in the clinical setting, the presence of the E138A mutation at a frequency of 6.7% in our study of 90 TSAO-inexperienced HIV-seropositive individuals implies that 138A of the RT must be a natural variant and that the mutant virus is replication competent. Our observations suggest that the E138A mutation may likely arise in patients under the selective pressure of TSAO or related compounds that show a decreased antiviral potency toward the E138A variant.

Viral dynamics and mutations in the pol gene during primary HIV-1 infection

The understanding of viral dynamics and appearance of mutations during primary infection could be useful for the design of an efficient therapy. For this reason a cohort of samples from naive primary patients was examined. The results pointed out that only a few secondary mutations in protease gene (having no effect on resistance) were found, while a single mutation conferring resistance to non-nucleosides inhibitors of reverse transcriptase was found both in plasma and cerebrospinal fluid of a patient. As both the protease secondary mutations and the single non nucleoside reverse transcriptase mutation map far from the catalytical sites of the enzymes, neither one is able to impair viral fitness. Overall data suggest that treated donors carrying resistant strains may be in part unable to transfer them to the recipient, and/or virus in the recipient tends to revert to wild type. These results should be taken into account in the planning of early HAART treatment of HIV infection.

Activities of masked 2',3'-dideoxynucleoside monophosphate derivatives against human immunodeficiency virus in resting macrophages

The anti-human immunodeficiency virus (HIV) activity of aryloxyphosphoramidate protides of a number of anti-HIV nucleoside analogues was assessed in resting primary monocyte-macrophages (M/M). While 2',3'-dideoxythymidine (d4T), 2',3'-dideoxyadenosine (ddA), and 2',3'-dideoxy-2',3'-didehydroadenosine (d4A) protides showed an anti-HIV activity that was 25- to 625-fold greater than the parent nucleotides d4T, ddA, and d4A, respectively, other aryloxyphosphoramidate protides showed similar or even lower anti-HIV activities than their parent compounds. This variable anti-HIV effect is most likely related to the different dynamics of intracellular nucleoside monophosphate release from the protides. Our results indicate the potential advantage of therapeutic use of this approach for some nucleotide analogues to affect HIV replication in M/M, one of the major reservoirs of HIV in vivo.

Intracellular metabolism of CycloSaligenyl 3'-azido-2', 3'-dideoxythymidine monophosphate, a prodrug of 3'-azido-2', 3'-dideoxythymidine (zidovudine)

The administration of CycloSaligenyl 3'-azido-2',3'-dideoxythymidine monophosphate (CycloSal-AZTMP) to CEM cells resulted in a concentration- and time-dependent conversion to the 5'-monophosphate (AZTMP), 5'-diphosphate (AZTDP), and 5'-triphosphate (AZTTP) derivatives. High ratios of AZTMP/AZTTP were found in the CEM cell cultures treated with CycloSal-AZTMP. The intracellular T(1/2) of AZTTP in CEM cell cultures treated with either AZT and CycloSal-AZTMP was approximately 3 h. A variety of human T- and B-lymphocyte cell lines efficiently converted the prodrug to the AZT metabolites, whereas peripheral blood lymphocytes and primary monocyte/macrophages showed at least 10-fold lower metabolic conversion of the prodrug. CycloSal-AZTMP failed to generate marked levels of AZT metabolites in thymidine kinase-deficient CEM/TK(-) cells, an observation that is in agreement with the substantial loss of antiviral activity of CycloSal-AZTMP in CEM/TK(-) cells. The inability of CycloSal-AZTMP to generate AZTMP in CEM/TK(-) cells is presumably due to a relatively high hydrolysis rate of AZTMP to the parent nucleoside AZT, combined with the inability of CEM/TK(-) cells to phosphorylate AZT to AZTMP through the cytosolic salvage enzyme thymidine kinase.

Nerve growth factor is an autocrine factor essential for the survival of macrophages infected with HIV

Nerve growth factor (NGF) is a neurotrophin with the ability to exert specific effects on cells of the immune system. Human monocytes/macrophages (M/M) infected in vitro with HIV type 1 (HIV-1) are able to produce substantial levels of NGF that are associated with enhanced expression of the high-affinity NGF receptor (p140 trkA) on the M/M surface. Treatment of HIV-infected human M/M with anti-NGF Ab blocking the biological activity of NGF leads to a marked decrease of the expression of p140 trkA high-affinity receptor, a concomitant increased expression of p75(NTR) low-affinity receptor for NGF, and the occurrence of apoptotic death of M/M. Taken together, these findings suggest a role for NGF as an autocrine survival factor that rescues human M/M from the cytopathic effect caused by HIV infection.

Clinical implications of HIV dynamics and drug resistance in macrophages

Macrophages are widely recognized as the second major target of HIV in the body. The cellular characteristics of such resting cells markedly affect the dynamics of virus lifecycle, that is slower but far more prolonged that in lymphocytes. In addition, the limited concentrations of endogenous nucleotide pools in macrophages downregulate the enzymatic activity of reverse transcriptase. As a consequence, both the anti-HIV activity and the development of resistance to antiviral drugs in macrophages are substantially different than those found in activated lymphocytes. These peculiar characteristics of virus replication and efficacy of antiviral drugs in macrophages have a natural in vivo counterpart in extralymphoid tissues, where macrophages account for the majority of cells infected by HIV. Furthermore, the replication of HIV in macrophages of testis and central nervous system is far less affected by antiviral drugs than in lymph nodes, because of the presence of natural barriers that markedly diminish the concentration of such drugs. For all these reasons, HIV infection of macrophages should be taken into account in therapeutic strategies aimed to achieve an optimal therapeutic effect in all tissue compartments where the virus hides and replicates.

Relative potency of protease inhibitors in monocytes/macrophages acutely and chronically infected with human immunodeficiency virus

The activity of three human immunodeficiency virus (HIV) protease inhibitors was investigated in human primary monocytes/macrophages (M/M) chronically infected by HIV-1. Saquinavir, KNI-272, and ritonavir inhibited the replication of HIV-1 in vitro, with EC50s of approximately 0.5-3.3 microM. However, only partial inhibition was achievable, even at the highest concentrations tested. Also, the activity of these drugs in chronically infected M/M was approximately 7- to 26-fold lower than in acutely infected M/M and approximately 2- to 10-fold lower than in chronically infected H9 lymphocytes. When protease inhibitors were removed from cultures of chronically infected M/M, production of virus rapidly returned to the levels found in untreated M/M. Therefore, relatively high concentrations of protease inhibitors are required to suppress HIV-1 production in chronically infected macrophages, and such cells may be a vulnerable point for the escape of virus in patients taking these drugs.

[Correlation between HIV-inhibiting drug activity in human macrophages and clinical outcome]

PURPOSE

To assess the comparative efficacy of drugs inhibitors of human immunodeficiency virus (HIV) in human macrophages and lymphocytes, and to correlate the results with the clinical outcome.

MATERIALS AND METHODS

Human primary macrophages and lymphocytes were infected with HIV in the presence of the following HIV inhibitors, all currently in clinical use: zidovudine, stavudine, zalcitabine, didanosine, lamivudine, PMEA, PMPA (all inhibitors of HIV reverse transcriptase), saquinavir and U-75875 (inhibitors of HIV protease).

RESULTS

All reverse transcriptase inhibitors tested showed a markedly higher antiviral activity in macrophages than in lymphocytes. Also protease inhibitors have a substantial anti-HIV activity in macrophages, yet their efficacy is markedly diminished if the drugs are added to macrophage culture after HIV, that is when the virus has established a chronical infection. Under these experimental conditions, however, only protease inhibitors among all HIV-inhibitors in clinical use are able to decrease virus replication in chronically-infected macrophages.

CONCLUSIONS

The results have strong clinical implications, due to the important role of macrophages in the pathogenesis of HIV infection. Macrophages are the major source of HIV at extralymphoid tissue levels, particularly in the central nervous system, where the blood-brain barrier strongly limits the penetration of antiviral drugs. For these reasons, only drugs, like stavudine and zidovudine, provided with good anti-HIV activity in macrophages, and reasonable barrier penetration have substantial chances to be effective in the central nervous system, and thus affect virus replication in a sanctuary where HIV hides and replicates out of the control of the immune system.

S-adenosylhomocysteine hydrolase inhibitors interfere with the replication of human immunodeficiency virus type 1 through inhibition of the LTR transactivation

Various analogues of adenosine have been described as inhibitors of S-adenosylhomocysteine (AdoHcy) hydrolase, and some of these AdoHcy hydrolase inhibitors (e.g., 3-deazaadenosine, 3-deazaaristeromycin, and 3-deazaneplanocin A) have also been reported to inhibit the replication of human immunodeficiency virus type 1 (HIV-1). When evaluated against HIV-1 replication in MT-4 cells, macrophages, or phytohemagglutinin-stimulated peripheral blood lymphocytes infected acutely or chronically with HIV-1IIIB or HIVBaL strains, a wide range of adenosine analogues did not inhibit HIV-1IIIB replication for 50% at subtoxic concentrations. However, they inhibited HIV-1 replication in HeLa CD4+ LTR-LacZ cells at concentrations well below cytotoxicity threshold. A close correlation was found among the inhibitory effect of the compounds on AdoHcy hydrolase activity, their inhibition of HIV-1 replication in Hela CD4+ LTR-LacZ cells, and their inhibition of the HIV-1 Tat-dependent and -independent transactivation of the long terminal repeat, whereas no inhibitory effect was seen on HIV-1 reverse transcription or a Tat-independent cytomegalovirus promoter. Our results suggest that AdoHcy hydrolase and the associated S-adenosylmethionine-dependent methylation mechanism play a role in the process of long terminal repeat transactivation and, hence, HIV replication.

Inhibition of replication of HIV in primary monocyte/macrophages by different antiviral drugs and comparative efficacy in lymphocytes

Several anti-HIV drugs acting on different steps of virus replication were tested in our experimental model of primary monocyte/macrophages; the results were compared with the activity found in lymphocytes. Nucleoside analogues (AZT, ddI, ddC, d4T, PMEA, 3TC etc.) show greater activity in macrophages (M/M) than in lymphocytes. In particular, the EC50 of AZT, ddC, and ddI in M/M is 2- to 100-fold lower than that found in lymphocytes. This greater efficacy of nucleoside analogues in M/M depends on the enhancement of their chain-terminating activity by the low levels of endogenous deoxynucleoside-triphosphates (dNTP) usually found in resting cells such as M/M. Non-nucleoside reverse transcriptase inhibitors (NNRTI) do not act as chain terminators (thus their antiviral effect is not related to the intracellular concentrations of dNTP); as a consequence the activity of TSAO, HEPT, TIBO, and other NNRTI tested in M/M is similar to that found in lymphocytes. Regarding inhibitors of binding and fusion of HIV, we found that their anti-HIV activity is markedly decreased (or even nullified) when M/M are treated with cytokine activators of M/M function and enhancers of HIV replication. More relevant from a clinical standpoint, protease inhibitors are able to inhibit HIV replication in chronically infected macrophages (i.e., cells carrying the proviral genome already integrated in the host genome). All other inhibitors of late stage of virus life cycle tested (antisense-rev, anti-tat, interferon-alpha and -gamma, phosphorothioate analogues, GLQ-223, etc.) were totally inactive in chronically infected macrophages. The different effects of various classes of HIV inhibitors in lymphocytes and macrophages suggests that AIDS therapy should consider all aspects of the pathogenesis of HIV infection and must be restricted to drugs, or combinations of drugs, active against both lymphocytes and M/M in all body compartments where the virus hides and replicates.

Intracellular GSH content and HIV replication in human macrophages

In vitro HIV-1 infection induced a significant decrease in intracellular reduced glutathione (GSH) in human macrophages. Such a decrease was observed at the time of infection corresponding to maximum release of virus from infected cells and was not related to cell cytotoxicity. GSH los was not related to its oxidation or leakage through the cell membrane. Inhibition of intracellular GSH synthesis by buthionine sulfoximine (BSO) did not further decrease GSH levels with respect to the decrease caused by HIV alone. However, treatment of macrophages with BSO significantly increased the HIV yield in the supernatant. Exogenous GSH strongly suppressed the production of p24 gag protein as well as the virus infectivity. Previous observations with other RNA and DNA viruses consistently showed that GSH antiviral effect occurred at late stages of virus replication and was related to the selective decrease of specific glycoproteins, such as gp120, which are particularly rich in disulfide bonds.

Conversion of 2',3'-dideoxyadenosine (ddA) and 2',3'-didehydro-2',3'-dideoxyadenosine (d4A) to their corresponding aryloxyphosphoramidate derivatives markedly potentiates their activity against human immunodeficiency virus and hepatitis B virus

2',3'-Dideoxyadenosine (ddA), 2',3'-didehydro-2',3'-dideoxyadenosine (d4A) and their lipophilic 5'-monophosphate triester (aryloxyphosphoramidate) prodrugs were evaluated for their anti-retrovirus and anti-hepatitis B virus activity in various cell culture models. The aryloxyphosphoramidate derivatives of ddA (Cf 1093) and d4A (Cf 1001) showed markedly superior (100-1000-fold) efficacies than the parent drugs against human immunodeficiency virus type 1 (HIV-1), HIV-2, simian immunodeficiency virus (SIV), Moloney murine sarcoma virus (MSV) and human hepatitis B virus (HBV) replication regardless of the cell type in which the virus replication was studied (i.e., human T-lymphocyte CEM, MT-4, Molt/4 and C8166 cells, peripheral blood lymphocytes (PBL), monocyte/macrophages (M/M), murine embryo fibroblasts and human hepatocyte cells). Also the selectivity index (ratio of cytotoxic concentration/antivirally effective concentration) of both aryloxyphosphoramidate prodrugs was markedly increased. In particular the d4A prodrug Cf 1001 showed a selectivity index of 300-3000 as compared with 2-3 for the parental d4A in established laboratory cell lines. Also Cf 1001 had a selectivity index of 400-650 in HIV-1-infected PBL and M/M, respectively. Both Cf 1001 and Cf 1093 were equally efficient as 3TC (lamivudine) in inhibiting HBV replication in hepatocytes, and rank among the most potent HIV and HBV inhibitors reported so far in cell culture.

Red blood cells mediated delivery of 9-(2-phosphonylmethoxyethyl)adenine to primary macrophages: efficiency metabolism and activity against human immunodeficiency virus or herpes simplex virus

Red blood cells (RBC) may act as selective carriers of drugs to macrophages, an important reservoir of viruses such as human immunodeficiency virus (HIV) and herpes simplex virus type 1 (HSV-1). We therefore assessed the incorporation of 9-(2-phosphonylmethoxyethyl)adenine (PMEA), a potent inhibitor of HIV and HSV-1) into RBC, its delivery to macrophages and its activity against HIV or HSV-1. Loading of PMEA in artificially aged opsonized RBC affords significant levels of intracellular PMEA. RBC metabolize PMEA to its active congener PMEA-diphosphate, although with low efficiency. Exposure of macrophages to RBC-encapsulated PMEA inhibits the replication of both HIV and HSV-1 (about 90% inhibition at the highest RBC:macrophages ratios) even if RBC were removed before virus challenge. By contrast, the antiviral activity of free PMEA removed before virus challenge was irrelevant at concentrations up to 150-fold higher than the 50% effective concentration (EC50). Finally, the antiviral effect of RBC-encapsulated PMEA correlates with PMEA levels in macrophages about 500-fold higher than those achieved by free PMEA (at concentrations 10-fold higher than the EC50). The efficacy of RBC-mediated delivery to macrophages of PMEA (and perhaps of compounds with shorter intracellular half-lives) warrants further studies in infectious diseases involving phagocytizing cells as main targets of the pathogen.

HIV infection in macrophage: role of long-lived cells and related therapeutical strategies

Therapeutical strategies aimed to the maximal inhibition (if not the eradication) of infection by human immunodeficiency virus should take into account the issue of the viral reservoir in the body. Recent data clearly show that latently infected lymphocytes represent a minimal part of the viral reservoir, while the majority of these cells are macrophages (variably differentiated) scattered in the tissues and lymph nodes. Immunologically-sequestred areas, such as the central nervous system, are particularly relevant in view of the different concentrations of antiviral drugs achieved in the organs. Thus, a careful analysis of the distribution of antiviral drugs, and the assessment of their activity in cells of macrophage lineage, represent key factors in the development of therapeutical strategies aimed to the "cure" of infectious patients.

Dynamics and modulation of human immunodeficiency virus type 1 transcripts in vitro and in vivo

The dynamics of human immunodeficiency virus type 1 (HIV-1) transcription was analyzed in vitro and in vivo by using a specific molecular approach which allows accurate quantitation of the different classes of viral mRNAs. Unspliced (US) and multiply spliced (MS) HIV-1 transcripts were assayed by competitive reverse transcription (cRT)-PCR, using a single competitor RNA bearing in tandem internally deleted sequences of both template species. Acute HIV-1 infection of primary peripheral blood mononuclear cells (PBMCs), monocytes/macrophages cells, and the A3.01 T-lymphocyte-derived cell line was studied; both classes of HIV-1 mRNAs increased exponentially (r2 > 0.98) at days 1 to 3 and 1 to 4 postinfection in HIV(IIIB)-infected A3.01 cells and PBMCs, respectively, whereas monocytes/macrophages infected with monocytotropic HIV(BaL) exhibited a linear (r2 = 0.81 to 0.94) accumulation of US and MS transcripts. Following induction of chronically infected ACH-2 cells, MS transcripts increased 2 h postinduction and peaked at 5 h (doubling time, 58 min), while at 24 h, US mRNAs increased 3,053-fold compared with basal time (doubling time, 137 min). To address the biopathological significance of HIV-1 expression pattern during infection progression, pilot cross-sectional and longitudinal analyses were carried out with samples from untreated and treated HIV-1-infected patients. In almost all untreated (recently infected, long-term nonprogressor, and progressor) patients, MS transcript levels followed the general trend of systemic HIV-1 activity. In patients under treatment with powerful antiretroviral compounds, viral MS transcripts rapidly fell to undetectable levels, indicating that in vivo, levels of MS mRNAs in PBMCs are closely associated with the number of newly infected cells and suggesting a new role for the quantitative analysis of HIV-1 transcription in infected patients.

Glutathione inhibits HIV replication by acting at late stages of the virus life cycle

We investigated the effect of glutathione on the replication of human immunodeficiency virus (HIV) in chronically infected macrophages, a known reservoir of the virus in the body. We found that exogenous GSH strongly suppresses the production of p24gag protein as well as the virus infectivity. This is related to a dramatic decrease in both budding and release of virus particles from chronically infected cells (either macrophages or lymphocytes), together with a selective decrease in the expression of gp120, the major envelope glycoprotein, rich in intrachain disulfide bonds and thus potentially sensitive to the effect of a reducing agent such as GSH. Overall data suggest that GSH can interfere with late stages of virus replication. This would be in agreement with data obtained in cells exposed to herpesvirus type 1 (a DNA virus) or to Sendai (an RNA virus), showing that the suppression of virus replication by GSH is related to the selective inhibition of envelope glycoproteins. These results suggest a potential role of GSH in combination with other antivirals in the treatment of virus-related diseases.

Highly favorable antiviral activity and resistance profile of the novel thiocarboxanilide pentenyloxy ether derivatives UC-781 and UC-82 as inhibitors of human immunodeficiency virus type 1 replication

The novel human immunodeficiency virus type 1-specific thiocarboxanilide derivatives that contain either a substituted furanyl (UC-781) or thienyl (UC-82) ring linked to the thiocarboxy group and a pentenyloxyether chain linked to the 4-chlorophenyl ring in meta position show highly favorable antiviral properties. Compounds UC-781 and UC-82 discovered by scientists at Uniroyal Chemical Ltd. proved to be > or = 5-10-fold more inhibitory to wild-type human immunodeficiency virus type 1 strains (EC50 approximately 0.002 microgram/ml) than the thiocarboxanilide oxime ether UC-10 and other non-nucleoside reverse transcriptase inhibitors such as nevirapine, bis(heteroaryl)piperazine, and tetrahydroimidazo[4,5,l-jk][1,4]-benzodiazepin-2(1H)-one. In addition, the compounds were able to knock out virus replication in cell culture at concentrations that were 20-50-fold lower than those of nevirapine or bis(heteroaryl)piperazine. They were also highly efficient (EC50 < or = 0.02 microgram/ml) in suppressing the replication of mutant virus strains that contained mutations in their reverse transcriptase that conferred resistance to other non-nucleoside reverse transcriptase inhibitors (i.e., Tyr181 to Cys, Lys103 to Asn, Val106 to Ala, and Leu100 to Ile). The compounds selected for virus mutants that were only marginally resistant to the thiocarboxanilides ( < 10-20-fold). The antiviral activity of the compounds was only slightly affected by the presence of high concentrations of human serum, and the compounds were shown to be highly stable in the presence of human serum for at least 24 hr at room temperature.

Potent inhibition of human immunodeficiency virus and herpes simplex virus type 1 by 9-(2-phosphonylmethoxyethyl)adenine in primary macrophages is determined by drug metabolism, nucleotide pools, and cytokines

The efficacy of 9-(2-phosphonylmethoxyethyl)adenine (PMEA) against the replication of human immunodeficiency virus (HIV) and herpes simplex virus type 1 (HSV-1) and its cellular metabolism were investigated in human primary macrophages from seronegative donors. PMEA potently inhibited the replication of both HIV and HSV-1 in macrophages, with similar EC50 values (0.025 and 0.032 microM, respectively), whereas the EC50 values of PMEA in lymphocytic C8166 cells and fibroblastoid Vero cells were 150-200-fold higher (3.5 and 7.9 microM, respectively). Granulocyte/macrophage colony-stimulating factor and macrophage colony-stimulating factor, two cytokine enhancers of the replication of HIV (and HSV-1), decreased the activity of PMEA against both viruses, yet EC50 values were still lower than in lymphocytes and fibroblasts. Thus, the selectivity index of PMEA in macrophages was > 2 orders of magnitude higher than that in lymphocytes and fibroblasts and still > 1 log higher under conditions of enhancement of virus replication in macrophages. The intracellular levels of 2'-deoxyadenosine-5'-triphosphate, the natural competitor of PMEA-diphosphate at the level of viral DNA polymerase (either RNA or DNA dependent), were 5-12-fold lower in macrophages than in other cells. Furthermore, intracellular concentrations of PMEA-diphosphate (the active metabolite of PMEA) were unusually much higher in macrophages (with or without cytokines) than in lymphocytes and fibroblasts. Consequently, the ratio of PMEA-diphosphate to 2'-deoxyadenosine-5'-triphosphate in monocytes/macrophages was approximately 2 orders of magnitude higher in macrophages than in the other cells and correlated closely with the pronounced antiviral potency of PMEA. The dual potent activity of PMEA against HIV and HSV-1 stresses the importance of clinical trials to assess the role of this drug in the therapy of HIV-related disease.

Mechanism of anti-HIV action of masked alaninyl d4T-MP derivatives

So324 is a 2',3'-dideoxy-2',3'-didehydrothymidine-5'-monophosphate (d4T-MP) prodrug containing at the phosphate moiety a phenyl group and the methylester of alanine linked to the phosphate through a phosphoramidate linkage. So324 has anti-HIV activity in human CEM, MT4, and monocyte/macrophage cells that is superior to that of d4T. In contrast to d4T, So324 is also able to inhibit HIV replication in thymidine kinase-deficient CEM cells. After uptake of So324 by intact human lymphocytes, d4T-MP is released and subsequently converted intracellularly to d4T-TP. In addition, accumulation of substantial amounts of a novel d4T derivative has been found. This d4T metabolite has been characterized as alaninyl d4T-MP. The latter metabolite accumulates at approximately 13- to 200-fold higher levels than d4T-TP depending the experimental conditions. Alaninyl d4T-MP should be considered as an intra- and/or extracellular depot form of d4T and/or d4T-MP. These findings may explain the superior anti-retroviral activity of So324 over d4T in cell culture.

Activity of the (R)-enantiomers of 9-(2-phosphonylmethoxypropyl)-adenine and 9-(2-phosphonylmethoxypropyl)-2,6-diaminopurine against human immunodeficiency virus in different human cell systems

The (S)- and (R)-enantiomers of 9-(2-phosphonylmethoxypropyl) derivatives of adenine (PMPA) and 2,6-diaminopurine (PMPDAP) were evaluated for their inhibitory effect on HIV replication in several human cell systems, including natural peripheral blood lymphocytes (PBL) and freshly isolated monocyte/macrophages (M/M). The (R)-enantiomers of PMPDAP and PMPA were approximately 10-to-100-fold more effective against HIV than their (S)-enantiomeric counterparts. The antiviral efficacy of (R)-PMPA was comparable to that of the prototype acyclic nucleoside phosphonate 9-(2-phosphonylmethoxyethyl)adenine (PMEA). The most potent and selective HIV inhibitor was (R)-PMPDAP. Its 50% effective concentration ranged from 0.01 microM for HIV-1/Ba-L in M/M to 1-2.8 microM for HIV-1/IIIB and HIV-1/HE in C8166, CEM, Molt/4, MT-4 and PBL cells. Both (R)-PMPA and (R)-PMPDAP were not toxic to the host cells at 300 microM.

1,2,3-Triazole-[2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D- ribofuranosyl]-3'-spiro-5"-(4"-amino-1",2"-oxathiole 2",2"-dioxide) (TSAO) analogues: synthesis and anti-HIV-1 activity

Several 4- or 5-monosubsituted and 4,5-disubstituted 1,2,3-triazole analogues of the anti-HIV-1 lead compound [1-[2',5'-bis-O-(tert-butyldimethylsilyl)-beta-D- ribofuranosyl]thymine]-3'-spiro-5"-(4"-amino-1",2"-oxathiole 2",2"-dioxide) (TSAO-T) have been prepared and evaluated as inhibitors of HIV-1-induced cytopathicity. These analogues have been prepared by 1,3-diplar cycloaddition of [2,5-bis-O-(tert-butyldimethylsilyl)-beta-D-ribofuranosyl]- 3-spiro-5'-(4'-amino- and 4'-(N-acetylamino)-1',2'-oxathiole 2',2'-dioxide) (TSAO) azides to various substituted acetylenes. Several 4- and 5-substituted 1,2,3-triazole-TSAO analogues proved superior to the unsubstituted derivative by 1-2 orders of magnitude. In particular the 5-substituted amido-, (methylamido)-, and (dimethylamido)-1,2,3-triazole derivatives of TSAO were endowed with potent anti-HIV-1 activity (50% effective concentration: 0.056-0.52 microM). They show a similar resistance spectrum as previously noted for TSAO-T and related derivatives.

In vitro activity of inhibitors of late stages of the replication of HIV in chronically infected macrophages

Because of the importance of macrophages in the pathogenesis of the disease caused by HIV, we investigated the efficacy of various anti-HIV drugs in human primary macrophages acutely or chronically infected by this virus. The results obtained for acutely infected macrophages show that dideoxynucleosides (AZT, ddI, and ddC), interferon-alpha and -gamma, mismatched double-stranded RNA, Tat inhibitor, phosphorothioate antisense, and inhibitors of HIV protease, all significantly inhibit virus replication at concentrations far below those toxic for the cells. However, in macrophages in which proviral DNA is already integrated (chronically infected macrophages), only the three inhibitors of HIV protease induced significant virus inhibition at concentrations 100 or more times higher than those effective in acutely infected macrophages. Treatment of macrophages with macrophage colony-stimulating factor does not affect the anti-HIV efficacy of protease inhibitors. These results suggest that therapeutic strategies with activity for macrophages, including inhibitors of HIV protease, are worth pursuing in patients with HIV infection.

Inhibition of the protease of human immunodeficiency virus blocks replication and infectivity of the virus in chronically infected macrophages

Because of the importance of monocytes/macrophages (M/M) as an in vivo reservoir of human immunodeficiency virus (HIV), a study was done to investigate whether viral replication in chronically infected macrophages (HIV M/M) could be inhibited by various drugs, including U-75875, an inhibitor of HIV protease. HIV replication in M/M and in chronically infected T cells was dramatically decreased by U-75875, while other drugs, including zidovudine, interferon-alpha, and an antisense oligodeoxynucleotide against the rev gene, were effective antiviral agents only in de novo-infected cells. Virus titer in HIV M/M was reduced approximately 10(5)-fold by nontoxic concentrations of U-75875, while no effect on HIV DNA or virus antigen expression on cell membrane was achieved in M/M infected either chronically or de novo. Thus, U-75875 essentially worked against late stages of viral replication. These data support the use of protease inhibitors, alone or in combination, in the therapy of HIV-infected patients.