Three-drug synergistic inhibition of HIV-1 replication in vitro by zidovudine, recombinant soluble CD4, and recombinant interferon-alpha A

Drug Combination of AZT and ddl: Synergism of Action and Prevention of Appearance of AZT-Resistance

Both 3′-azido-3′-deoxythymidine (AZT) and 2′,3′-dideoxynosine (ddl) strongly inhibit the replication of human immunodeficiency virus type 1 (HIV-1). Here, it is shown that combination of AZT and ddl at concentrations that are readily achievable in vivo synergistically inhibit HIV-1 replication in C8166 cells and peripheral blood mononuclear cells. The synergism is significant even when the effect of AZT and ddl alone was negligible.

Our findings show that AZT-resistance is less likely to occur when a combination of AZT and ddl is used. Particularly, generation of AZT-resistant strains by in vitro selection is prevented, or delayed, by the combination of AZT plus ddl.

Taken together these observations provide a rationale for combination of AZT and ddl in the therapy of AIDS patients.

Synergistic Inhibition of Human Immunodeficiency Virus Type 1 in vitro by 6-0-butanoylcastanospermine (MDL 28574) in Combination with Inhibitors of the Virus-Encoded Reverse Transcriptase and Proteinase

The anti-human immunodeficiency virus type 1 (HIV-1) activity of the α-glucosidase 1 inhibitor 6-0-butanoylcastanospermine (MDL 28574) was assessed in combination with the 2′,3′-dideoxynucleoside analogues zidovudine (AZT), didanosine (ddl) and zalcitabine (ddC). MDL 28574 was also evaluated in combination with the non-nucleoside reverse transcriptase (RT) inhibitor nevirapine and the HIV proteinase inhibitor saquinavir (Ro-31-8959). Drug interactions were examined by the isobologram technique and by calculating combination indices (C.l.s). In all cases synergistic inhibition of HIV-1 replication was observed. In three-drug combinations, a marked synergistic antiviral effect was also observed, with C.I. values in the range 0.35-0.44 for MDL 28574 in combination with AZT and nevirapine, and in the range 0.34-0.67 for MDL 28574 in combination with AZT and saquinavir. Moreover, the combination of MDL 28574 with other drugs did not produce detrimental effects on cell division. MDL 28574 is currently in clinical trials and may have an important role in combination chemotherapy for HIV infections.

Synergistic Inhibition of Human Immunodeficiency Virus Type 1 in vitro by Interferon Alpha and Coumermycin A1

Interferon alpha, either leukocyte derived or the recombinant form, and the DNA gyrase inhibitor coumermycin A1 both inhibited human immunodeficiency virus type 1 (HIV) replication in vitro. We have found that combinations of these two agents synergistically inhibited HIV replication in human peripheral blood leucocytes (PBL). Significant inhibition was detected when both virion-associated reverse transcriptase activity and p24 levels were used as markers of replication. Mathematical analysis of data using the procedure of Chou and Chou (1987) produced combination indices of less than 1.0 for most effect levels at several combination ratios. Synergy was also evident when the classical isobologram technique was used for data analysis. Synergistic drug interactions were observed at concentrations not associated with cytotoxicity or anti-proliferative effects, and were seen at concentrations achievable in vivo.

Env-glycoprotein heterogeneity as a source of apparent synergy and enhanced cooperativity in inhibition of HIV-1 infection by neutralizing antibodies and entry inhibitors

We measured the inhibition of infectivity of HIV-1 isolates and derivative clones by combinations of neutralizing antibodies (NAbs) and other entry inhibitors in a single-cycle-replication assay. Synergy was analyzed both by the current linear and a new non-linear method. The new method reduced spurious indications of synergy and antagonism. Synergy between NAbs was overall weaker than between other entry inhibitors, and no stronger where one ligand is known to enhance the binding of another. However, synergy was stronger for a genetically heterogeneous HIV-1 R5 isolate than for its derivative clones. Enhanced cooperativity in inhibition by combinations, compared with individual inhibitors, correlated with increased synergy at higher levels of inhibition, while being less variable. Again, cooperativity enhancement was stronger for isolates than clones. We hypothesize that genetic, post-translational or conformational heterogeneity of the Env protein and of other targets for inhibitors can yield apparent synergy and increased cooperativity between inhibitors.

3-drug synergistic interactions of small molecular inhibitors of hepatitis C virus replication

Small molecular inhibitors of hepatitis C virus (HCV) replication provide remarkable potency, but the rapid selection of resistance mutations will require that these agents be used in combination for clinical treatment. Using a model HCV replicon system, we have extended prior in vitro studies of double combinations of candidate small molecular inhibitors to studies evaluating the simultaneous use of 3 agents. This was done in an effort to anticipate conditions that might ultimately be required clinically. We formally demonstrate synergistic antiviral activity with 3-drug combinations in this model, further supporting the concept of clinical investigations of combination therapy for HCV infection.

Theoretical basis, experimental design, and computerized simulation of synergism and antagonism in drug combination studies

The median-effect equation derived from the mass-action law principle at equilibrium-steady state via mathematical induction and deduction for different reaction sequences and mechanisms and different types of inhibition has been shown to be the unified theory for the Michaelis-Menten equation, Hill equation, Henderson-Hasselbalch equation, and Scatchard equation. It is shown that dose and effect are interchangeable via defined parameters. This general equation for the single drug effect has been extended to the multiple drug effect equation for n drugs. These equations provide the theoretical basis for the combination index (CI)-isobologram equation that allows quantitative determination of drug interactions, where CI < 1, = 1, and > 1 indicate synergism, additive effect, and antagonism, respectively. Based on these algorithms, computer software has been developed to allow automated simulation of synergism and antagonism at all dose or effect levels. It displays the dose-effect curve, median-effect plot, combination index plot, isobologram, dose-reduction index plot, and polygonogram for in vitro or in vivo studies. This theoretical development, experimental design, and computerized data analysis have facilitated dose-effect analysis for single drug evaluation or carcinogen and radiation risk assessment, as well as for drug or other entity combinations in a vast field of disciplines of biomedical sciences. In this review, selected examples of applications are given, and step-by-step examples of experimental designs and real data analysis are also illustrated. The merging of the mass-action law principle with mathematical induction-deduction has been proven to be a unique and effective scientific method for general theory development. The median-effect principle and its mass-action law based computer software are gaining increased applications in biomedical sciences, from how to effectively evaluate a single compound or entity to how to beneficially use multiple drugs or modalities in combination therapies.

TAK-220, a novel small-molecule CCR5 antagonist, has favorable anti-human immunodeficiency virus interactions with other antiretrovirals in vitro

TAK-220 is a CCR5 antagonist, part of the new class of anti-human immunodeficiency virus type 1 (anti-HIV-1) entry inhibitors. We evaluated the anti-HIV-1 interactions between TAK-220 and various antiretrovirals in vitro. Synergy was observed with all drugs at the 90 and 95% inhibitory concentrations. The favorable drug interactions observed suggest that further clinical evaluation is warranted.

The appealing story of HIV entry inhibitors : from discovery of biological mechanisms to drug development

Current therapeutic intervention in HIV infection relies upon 20 different drugs. Despite the impressive efficacy shown by these drugs, we are confronted with an unexpected frequency of adverse effects, such as mitochondrial toxicity and lipodystrophy, and resistance, not only to individual drugs but to entire drug classes.Thus, there is now a great need for new antiretroviral drugs with reduced toxicity, increased activity against drug-resistant viruses and a greater capacity to reach tissue sanctuaries of the virus. Two different HIV molecules have been selected as targets of drug inhibition so far: reverse transcriptase and protease. Drugs that target the interactions between the HIV envelope and the cellular receptor complex are a 'new entry' into the scenario of HIV therapy and have recently raised great interest because of their activity against multidrug-resistant viruses. There are several compounds that are at different developmental stages in the pipeline to counter HIV entry, among them: (i) the attachment inhibitor dextrin-2-sulfate; (ii) the inhibitors of the glycoprotein (gp) 120/CD4 interaction PRO 542, TNX 355 and BMS 488043; (iii) the co-receptor inhibitors subdivided in those targeting CCR5 (SCH 417690 [SCH D], UK 427857 GW 873140, PRO 140, TAK 220, AMD 887) and those targeting CXCR4 (AMD 070, KRH 2731); and (iv) the fusion inhibitors enfuvirtide (T-20) and tifuvirtide (T-1249). The story of the first of these drugs, enfuvirtide, which has successfully completed phase III clinical trials, has been approved by the US FDA and by the European Medicines Agency, and is now commercially available worldwide, is an example of how the knowledge of basic molecular mechanisms can rapidly translate into the development of clinically effective molecules.

Unusual codon 69 insertions: influence on human immunodeficiency virus type 1 reverse transcriptase drug susceptibility

INTRODUCTION

Multiple amino acid changes in the reverse transcriptase (RT) enzyme of the human immunodeficiency virus 1 (HIV-1) confer simultaneous resistance to most nucleoside RT inhibitors (NRTI). It may take place through different pathways: one of these is the codon 69 insertion, which can involve several 2-amino acid patterns.

MATERIALS AND METHODS

We are reporting the case of three patients treated with various antiretroviral compounds. For these subjects we have conducted both a genotypical and a phenotypical analysis in order to understand what kind of influence these insertions may have on HIV-1 RT drug susceptibility. Plasma samples from these patients have been extracted and the RT region has been amplified, cloned and sequenced; meanwhile their PBMCs have been separated, cultivated and then tested for drug susceptibility.

RESULTS

Data obtained from the cloning assay showed that the patients had different mutational patterns but constant multiple resistance to NRTI. In particular, they harbored mutations related to Zidovudine (ZDV), 3TC and various NRTIs. Moreover, all three samples had a T69S substitution followed by three different dual amino acid insertions: SG, TG and VG. Several phenotypic experiments revealed that the viruses were resistant to 3TC as well as to ZDV and ABC. Different results were obtained using d4T and ddI.

DISCUSSION

In our three patients, all mutation inserts impaired the use of NRTI, particularly ZDV and 3TC. Patient 001 presented a pattern that should not cause a high phenotypic resistance to 3TC per se, and so we can argue that the concomitant presence of the insertion T69S (SG) makes this isolate moderately resistant to this drug. We observed a similar phenomenon in subject 003. d4T was less involved in the resistance generation caused by the RT insertion (in one out of three cases). Moreover, we identified a new 2aa insertion (TG) that has, to the best of our knowledge, never been reported before. A careful survey of novel RT genotypic insertion is thus warranted.

The combination of interferon alpha-2b and n-butyl deoxynojirimycin has a greater than additive antiviral effect upon production of infectious bovine viral diarrhea virus (BVDV) in vitro: implications for hepatitis C virus (HCV) therapy

Interferon alpha-2b (IFN) alone or in combination with Ribavirin is approved in the United States for the treatment of chronic hepatitis C virus (HCV) infection. We have previously reported that the glucosidase inhibitor, n-butyl deoxynojirimycin (nB-DNJ) inhibits the production of infectious bovine diarrhea virus (BVDV) (Proc. Natl. Acad. Sci. 96 (1999) 11878). Since BVDV has been used as a model for HCV and grows productively in tissue culture, and IFN and glucosidase inhibitors are thought to act at different steps in the virus life cycle, it was of interest to determine the antiviral impact of combining nB-DNJ with IFN. Using plaque reduction and single-step growth analyses of the cytopathic BVDV strain NADL, data are presented that shows human IFN inhibited BVDV production in a dose dependent manner, with 3 IU/ml inhibiting 50% of the yield of virus (IC50) when added within 1 h post infection. Under the same conditions, the glucosidase inhibitors nB-DNJ and castanospermine (CST) also prevented BVDV production in a dose dependent manner with IC50s of 226 microM and 47 microM, respectively. In combination with 138 microM nB-DNJ the apparent IC50 for IFN was 0.056 IU/ml. This 54-fold increase in IFN potency suggests that nB-DNJ can synergize with IFN. Two additional independent analyses were performed to measure combination effects which demonstrated that the combined antiviral effect of nB-DNJ and IFN were greater than would be expected for a simple additivity. These data are consistent with an interpretation that glucosidase inhibitors and IFN have a synergistic antiviral effect in tissue culture. The relevance of these finding to treatment of HCV infection is discussed.

Mechanism of inhibitory effect of NCC164 on replication of human immunodeficiency virus

The effect of a novel anti-HIV (human immunodeficiency virus) compound, designated NCC164, has been studied with HIV infected cultures. The agent exhibited concentration-dependent inhibition of HIV replication in primary infected cultures of H9 cell line and PBMCs. Substantial inhibition of viral replication was observed at concentration of NCC164 that showed little cytotoxicity. The ratio of IC50 values for the MTT (3-4,5 dimethylthiazol-2,5 diphenyl tetrazolium bromide) to RT (reverse transcriptase) assays means the selectivity index was more than 100. In attempting to define the inhibitory mechanism of NCC164, we investigated its effect on each step of HIV replication. This agent was highly effective against HIV replication regardless of the addition period during early stages of infection (adsorption to integration) but did not inhibit reverse transcriptase activity directly. The agent efficiently blocked virus maturation without side effect and the number of progeny produced by NCC164-treated cells was markedly reduced.

Induction and Maintenance Treatment Regimens for HIV-1 Infection in Vitro

Can aggressive anti-human immunodeficiency virus (HIV) induction regimens be simplified after sufficient virus suppression is achieved? In vitro studies were conducted to evaluate the hypothesis that aggressive induction regimens could be followed by less aggressive maintenance regimens. A clinical HIV-1 isolate and lymphoblastoid cell line (H9) were employed. Virus multiplicities were varied, as were drug inhibitory concentrations (IC90, IC99) and induction periods (1, 2 and 3 weeks) of a three-drug regimen (zidovudine plus lamivudine and indinavir), following which maintenance regimens (no drug, zidovudine alone, indinavir alone, zidovudine plus lamivudine) were employed. After 1 week inductions at IC99 concentrations, viral rebound occurred on none or one-drug maintenance regimens but not on a two-drug regimen. After 2 week inductions, viral rebound occurred with no-drug maintenance, but not with one- and two-drug regimens. After 3 week inductions, viral rebound did not occur in zero-, one-, or two-drug maintenance regimens, although HIV-1 DNA persisted in cultured cells. These studies suggest that although some induction–maintenance regimens will fail, after a sufficient period of HIV-1 suppression with a three-drug antiretroviral regimen, maintenance on fewer drugs may be feasible.

Interferon-alpha: evolving therapy for AIDS-associated Kaposi's sarcoma

This article reviews developments over nearly 15 years in the application of interferon-alpha (IFN-alpha) to the treatment of Kaposi's sarcoma (KS) in patients with acquired immunodeficiency syndrome (AIDS). The initial success of IFN treatment for selected patients with AIDS-associated KS occurred before identification of the human immunodeficiency virus (HIV) and in the absence of any coherent view of KS pathogenesis. A more comprehensive understanding of the biology of both AIDS and KS, together with increased knowledge of the biologic effects of IFN and therapeutic advances in the treatment of HIV infection, have made IFN therapy for KS both more rational and more successful. There is every reason to believe that the current results with IFN for KS can be improved on by capitalizing on recent improvements in HIV therapy and the availability of specific inhibitors of angiogenic cytokines. I sincerely thank the Milstein family and my colleagues in the International Society for Interferon and Cytokine Research (ISICR) for recognizing this work, which is the product of many collaborations between clinical and basic scientists in my own institution and elsewhere.

Activities of the human immunodeficiency virus type 1 (HIV-1) protease inhibitor nelfinavir mesylate in combination with reverse transcriptase and protease inhibitors against acute HIV-1 infection in vitro

Nelfinavir mesylate (formerly AG1343) is a potent and selective, nonpeptidic inhibitor of human immunodeficiency virus type 1 (HIV-1) protease that was discovered by protein structure-based design methodologies. We evaluated the antiviral and cytotoxic effects of two-drug combinations of nelfinavir with the clinically approved antiretroviral therapeutics zidovudine (ZDV), lamivudine (3TC), dideoxycytidine (ddC; zalcitabine), stavudine (d4T), didanosine (ddI), indinavir, saquinavir, and ritonavir and a three-drug combination of nelfinavir with ZDV and 3TC against an acute HIV-1 strain RF infection of CEM-SS cells in vitro. Quantitative assessment of drug interaction was evaluated by a universal response surface approach (W. R. Greco, G. Bravo, and J. C. Parsons, Pharm. Rev. 47:331-385, 1995) and by the method of M. N. Prichard and C. Shipman (Antiviral Res. 14:181-206, 1990). Both analytical methods yielded similar results and showed that the two-drug combinations of nelfinavir with the reverse transcriptase inhibitors ZDV, 3TC, ddI, d4T, and ddC and the three-drug combination with ZDV and 3TC resulted in additive to statistically significant synergistic interactions. In a similar manner, the combination of nelfinavir with the three protease inhibitors resulted in additive (ritonavir and saquinavir) to slightly antagonistic (indinavir) interactions. In all combinations, minimal cellular cytotoxicity was observed with any drug alone and in combination. These results suggest that administration of combinations of the appropriate doses of nelfinavir with other currently approved antiretroviral therapeutic agents in vivo may result in enhanced antiviral activity with no associated increase in cellular cytotoxicity.

Stabilities of free and complexed human immunodeficiency virus p24 antigens during short- and long-term storage

By the standard p24 assay there was a 25 to 27% decrease in free p24 antigen in serum after storage at 4 degrees C over 14 days but no loss at -70 degrees C. There was no loss at either temperature by the immune complex dissociation (ICD) procedure. Furthermore, there was no significant loss of detectable p24 in serum by either the ICD or the standard p24 assay after 700 days of storage at -70 degrees C.

Evaluation of reverse transcriptase and protease inhibitors in two-drug combinations against human immunodeficiency virus replication

Current treatments for human immunodeficiency virus (HIV) include both reverse transcriptase and protease inhibitors. Results from in vitro and clinical studies suggest that combination therapy can be more effective than single drugs in reducing viral burden. To evaluate compounds for combination therapy, stavudine (d4T), didanosine (ddI), or BMS-186,318, an HIV protease inhibitor, were combined with other clinically relevant compounds and tested in a T-cell line (CEM-SS) that was infected with HIV-RF or in peripheral blood mononuclear cells infected with a clinical HIV isolate. The combined drug effects were analyzed by the methods described by Chou and Talalay (Adv. Enzyme Regul. 22:27-55, 1984) as well as by Prichard et al. (Antimicrob. Agents Chemother. 37:540-545, 1993). The results showed that combining two nucleoside analogs (d4T-ddI, d4T-zidovudine [AZT], and d4T-zalcitabine [ddC]), two HIV protease inhibitors (BMS-186,318-saquinavir, BMS-186,318-SC-52151, and BMS-186,318-MK-639) or a reverse transcriptase and a protease inhibitor (BMS-186,318-d4T, BMS-186,318-ddI, BMS-186,318-AZT, d4T-saquinavir, d4T-MK-639, and ddI-MK-639) yielded additive to synergistic antiviral effects. In general, analysis of data by either method gave consistent results. In addition, combined antiviral treatments involving nucleoside analogs gave slightly different outcomes in the two cell types, presumably because of a difference in phosphorylation patterns. Importantly, no strong antagonism was observed with the drug combinations studied. These data should provide useful information for the design of clinical trials of combined chemotherapy.

Drug combinations and effect parameters of zidovudine, stavudine, and nevirapine in standardized drug-sensitive and resistant HIV type 1 strains

Reference strains of HIV-1 from the NIH AIDS Research and Reference Reagent Program, including wild-type IIIB, G762-3, and AZT resistant with RT 215T-->Y (G910-11/AZT); 67D-->N, 70K-->R, 215T-->F, 219K-->Q (G691-2/AZT); as well as nevirapine (NEV) resistant with 181Y-->C (N119/NEV); and 103K-->N, 181Y-->C (A17/NEV), were subjected to quantitative parametric efficacy analysis using AZT, stavudine (D4T), and nevirapine (NEV) singly or in combinations in MT4 or MT2 cells. The median-effect principle and combination index (CI) method of Chou-Talalay (see Ref. 26) have been used, which take into account both the potency (Dm value or EC50) and the shape of the dose-effect curve (m value). Under standardized assay conditions, G910-11 and G691-2 strains showed 600- and 7800-fold resistance to AZT, and N119 and A17 strains showed 3600- and 1000-fold resistance to NEV at the EC50 level, respectively. AZT-resistant strains exhibited slight cross-resistance to D4T. Computerized analysis indicates that IIIB gave sigmoidal dose-effect curves (m = 2.8, 3.4, and 3.1 for AZT, D4T, and NEV, respectively) whereas drug-resistant strains showed negative sigmoidicity toward the corresponding AZT or NEV, with m = 0.27-0.73. Therefore, the degrees of drug resistance are drastically different at classic EC50 and at therapeutically more relevant EC95 levels (ranging from severalfold to several log orders). Combinations of AZT+NEV and AZT+NEV+D4T showed synergism against IIIB, G762-3 (wild type) and A17/NEV, G910-11/AZT strains. D4T+NEV and AZT+D4T showed nearly additive or moderate antagonism. Synergism or additive effect leads to a favorable dose-reduction index (DRI). The present study on RT inhibitors provides quantitative assessment of the combinations of AZT, NEV, and D4T against HIV infections involving drug-sensitive and drug-resistant HIVs.

Consensus symposium on combined antiviral therapy; overview of interferon and IL-2 combinations for the treatment of HIV infection

Among the immunomodulatory cytokines that have been evaluated for the treatment of HIV disease, alpha-interferon and interleukin-2 (IL-2) have been the most extensively studied. Monotherapy with alpha-interferon is effective therapy for HIV-associated Kaposi's sarcoma (KS) in patients with CD4 counts > 150 cells/mm3. However, the doses necessary to achieve a significant anti-tumor effect are often poorly tolerated. Combination therapy with alpha-interferon and zidovudine is associated with dose-limiting toxicities and an anti-tumor effect similar to that of higher dose alpha-interferon monotherapy. The combination of alpha-interferon and zidovudine can synergistically inhibit HIV replication in vitro; however, in vivo results suggest the anti-HIV effect of this combination is no greater than that seen with zidovudine monotherapy. Whether combination of interferon-alpha and other antiviral drugs will be useful in the treatment of HIV infection remains to be seen. Recent studies employing intermittent courses of IL-2 combined with continuous antiretroviral therapy indicate that sustained rises in CD4 counts can be achieved. The ability of IL-2 therapy to result in a sustained rise in CD4 counts is critically dependent on the pre-treatment CD4 count. The immunologic and clinical significance of these IL-2-induced increases in CD4 counts is unknown. Larger, controlled trials are currently underway to evaluate the role of intermittent IL-2 therapy in HIV infection.

Efficacy of combination antiretroviral therapy

Combination therapy with two nucleosides has been shown to improve clinical outcome compared with zidovudine monotherapy. There is every expectation that more potent antiretroviral combination regimens will increase the clinical benefits. However, this remains to be proven definitely. The increasing number of choices of antiretroviral therapies create new challenges for those studying and those using these therapies.

Efficacy and safety of alpha-interferon treatment for chronic hepatitis C in HIV-infected patients. HIV-Hepatitis Spanish Study Group

The efficacy and safety of recombinant alpha-interferon (IFN) therapy for chronic hepatitis C (CHC) was assessed in 57 HIV-infected individuals with CD4+ T cells above 200/mm3 and compared to the response obtained in 21 HIV-negative patients with CHC. IFN 5 megaU was given three times a week subcutaneously for 3 months. In responding patients, IFN 3 megaU three times a week was additionally administered for 9 months. After 8 months follow-up in HIV-infected patients, 38% (22/57) achieved normal (complete response, CR) alanine aminotransferase (ALT) values. Partial response (PR) was seen in 21% (12/57), and 40% (23/57) did not respond. Patients with CD4+ cells above 500/mm3 achieved CR in 58% (14/24) of cases compared to 24% (8/33) among those having a lower CD4+ count (P < 0.01). Females attained CR in 60% (9/15) of cases, and men in only 30.9% (13/42) (P < 0.01). No serious side effects or opportunistic infections were observed during the study period. However, three (5.2%) patients showed a dramatic fall in total CD4+ T cell count after beginning IFN therapy. Among 21 HIV-negative patients, after 8 months follow-up, CR was achieved in 10 (47%), PR in four (19%), and seven (33%) did not respond. We concluded that IFN therapy seems to be well tolerated and useful in HIV-infected patients suffering CHC. The rate of CR was not significantly different compared to that observed in HIV-negative patients (38% vs. 47%), relative risk (RR) = 0.67 (0.19-2.37).(ABSTRACT TRUNCATED AT 250 WORDS)

Antiviral therapy for human immunodeficiency virus infections

Depending on the stage of their intervention with the viral replicative cycle, human immunodeficiency virus inhibitors could be divided into the following groups: (i) adsorption inhibitors (i.e., CD4 constructs, polysulfates, polysulfonates, polycarboxylates, and polyoxometalates), (ii) fusion inhibitors (i.e., plant lectins, succinylated or aconitylated albumins, and betulinic acid derivatives), (iii) uncoating inhibitors (i.e., bicyclams), (iv) reverse transcription inhibitors acting either competitively with the substrate binding site (i.e., dideoxynucleoside analogs and acyclic nucleoside phosphonates) or allosterically with a nonsubstrate binding site (i.e., non-nucleoside reverse transcriptase inhibitors), (v) integration inhibitors, (vi) DNA replication inhibitors, (vii) transcription inhibitors (i.e., antisense oligodeoxynucleotides and Tat antagonists), (viii) translation inhibitors (i.e., antisense oligodeoxynucleotides and ribozymes), (ix) maturation inhibitors (i.e., protease inhibitors, myristoylation inhibitors, and glycosylation inhibitors), and finally, (x) budding (assembly/release) inhibitors. Current knowledge, including the therapeutic potential, of these various inhibitors is discussed. In view of their potential clinical the utility, the problem of virus-drug resistance and possible strategies to circumvent this problem are also addressed.

HIV-1 infection despite immediate combination antiviral therapy after infusion of contaminated white cells

We present a sixth human case in which primary human immunodeficiency virus (HIV-1) infection occurred, despite antiretroviral prophylaxis, after accidental inoculation of infected blood. In the prior five instances, variables such as large virus dose, late administration of antivirals, viral resistance to zidovudine, and pre-existent immunosuppression, may have played a role in the treatment failure. In this case, high-dosage oral zidovudine was given within minutes of the accident and replaced 2 1/2 days later with interferon alpha and dideoxyinosine (ddl). Despite aggressive treatment, HIV-1 infection was demonstrated in blood, spleen, and brain tissue at autopsy 16 days later. Of the tissues studied, detection of HIV-1 was most prominent in the spleen. Double-label immunocytochemistry confirmed the morphologic impression that while some of the infected spleen cells were CD3-positive T cells, the majority were macrophages. Thus, current single or dual (zidovudine, ddl-interferon) therapies for accidental HIV-1 inoculation may not be effective in preventing early infection. Further trials in animals appear warranted to evaluate protection by other strategies, such as passive immunity or combinations of agents that penetrate the brain and attack HIV-1 viral replication at differing sites.

Combination therapy: more effective control of HIV type 1?

The rationale for combining anti-HIV-1 agents is to provide more complete viral suppression, to limit the emergence of drug resistance during chronic viral replication, and to provide more effective antiretroviral treatment even when mixtures of drug-resistant and drug-sensitive strains are present. In vitro experiments reveal increased suppression with multiple-drug therapy, but viral breakthrough occurs after prolonged time in culture even during triple-drug therapy. Clinical results available to date indicate that drugs should be given simultaneously for optimal benefit. There appears to be a rationale for early initiation of combination therapy before the onset of increased viral burden and the emergence of syncytium-inducing viral variants. The results of ACTG protocol 155 revealed benefit of zidovudine and zalcitabine over monotherapy with either agent in patients with CD4+ cell counts > or = 150 cells/mm3. However, further clinical studies will be necessary before firm recommendations can be made about the indications for combination antiretroviral therapy in HIV-1-infected individuals at different stages of disease. Ultimately, we need better drugs, in combination, which significantly impact on HIV-1 burden to achieve more complete viral suppression and to reduce selection of drug-resistant viral variants.

Inhibition of human immunodeficiency virus infection by agents that interfere with thiol-disulfide interchange upon virus-receptor interaction

The cell surface of mammalian cells is capable of reductively cleaving disulfide bonds of exogenous membrane-bound macromolecules (for instance, the interchain disulfide of diphtheria toxin), and inhibiting this process with membrane-impermeant sulfhydryl reagents prevents diphtheria toxin cytotoxicity. More recently it was found that the same membrane function can be inhibited by bacitracin, an inhibitor of protein disulfide-isomerase (PDI), and by monoclonal antibodies against PDI, suggesting that PDI catalyzes a thiol-disulfide interchange between its thiols and the disulfides of membrane-bound macromolecules. We provide evidence that the same reductive process plays a role in the penetration of membrane-bound human immunodeficiency virus (HIV) and show that HIV infection of human lymphoid cells is markedly inhibited by the membrane-impermeant sulfhydryl blocker 5,5'-dithiobis(2-nitrobenzoic acid), by bacitracin, and by anti-PDI antibodies. The results imply that HIV and its target cell engage in a thiol-disulfide interchange mediated by PDI and that the reduction of critical disulfides in viral envelope glycoproteins may be the initial event that triggers conformational changes required for HIV entry and cell infection. These findings suggest additional approaches to impede cell infection by HIV.

Alternating versus continuous drug regimens in combination chemotherapy of human immunodeficiency virus type 1 infection in vitro

We compared the in vitro efficacies of two-, three-, and four-drug combinations given continuously or in alternating regimens against a clinical isolate of human immunodeficiency virus type 1. In H9 cells and peripheral blood mononuclear cells, at the drug concentrations used in this study, there was greater suppression of human immunodeficiency virus type 1 infection as the number of drugs in the regimen was increased from one to four simultaneously administered agents. Although alternating drug regimens were effective, they were not better than continuous administration of either single drugs or combinations of agents and were less effective than giving all drugs of an alternating regimen simultaneously.

Generation of multiple drug resistance by sequential in vitro passage of the human immunodeficiency virus type 1

We have sequentially passaged both laboratory and clinical isolates of the human immunodeficiency virus type 1 (HIV-1) in MT-4 cells in the presence of increasing concentrations of different drugs to derive viral variants that are multiply resistant to various combinations of ddC, ddI, d4T and AZT. The EC50 values obtained for the viruses thus generated varied between 50-100 times above those of parental wild-type strains in the case of AZT, 20-30 times for d4T, but only 10-15 times for ddI and ddC. Cultivation of AZT-resistant viruses in the presence of increasing concentrations of ddI yielded viruses that were resistant to the latter compound, with no apparent decrease in susceptibility to AZT. Sometimes, viruses selected for resistance against ddI were cross-resistant as well against ddC, although most viruses selected for resistance to ddC were not cross-resistant to ddI. Combinations of two or three of these compounds inhibited replication of HIV variants that displayed resistance to the same drugs when tested individually. No emergence of drug resistance was demonstrable when combinations of drugs were employed simultaneously in these selection protocols or when single drugs were used in concert with interferon-2 alpha or high dilutions of virus-neutralizing antisera. Cloning and sequencing of some viruses resistant to each of AZT, ddI, and ddC revealed the simultaneous presence of mutations at sites 41, 74, 184 and 215 within the HIV pol gene open reading frame.

Bisheteroarylpiperazine reverse transcriptase inhibitor in combination with 3'-azido-3'-deoxythymidine or 2',3'-dideoxycytidine synergistically inhibits human immunodeficiency virus type 1 replication in vitro

Bisheteroarylpiperazine compounds are nonnucleoside reverse transcriptase inhibitors of human immunodeficiency virus type 1 (HIV-1). To provide a rationale for combination therapy with a second-generation bisheteroarylpiperazine, we investigated the effect of U-90152 in combination with 3'-azido-3'-deoxythymidine (AZT) or 2',3'-dideoxycytidine (ddC). HIV-1-infected cells were cultured in the presence of test compounds, and drug effects on p24 core antigen production were measured by an enzyme-linked immunosorbent assay. In a CD4+ T-cell line (H9) infected with HIV-1IIIB, the 50% effective concentrations for U-90152, AZT, and ddC were 6.0, 80.4, and 31.8 nM, respectively. In human peripheral blood mononuclear cells infected with the molecularly cloned clinical isolate HIV-1JRCSF, the 50% effective concentrations for U-90152, AZT, and ddC were 5.3, 5.9, and 25.0 nM, respectively. Over a range of drug concentrations (U-90152 and AZT at 0.3, 1, 3, 10, and 30 nM; ddC at 3, 10, 30, and 100 nM), U-90152 in combination with AZT or ddC synergistically inhibited the replication of a laboratory-adapted strain and a clinical isolate of HIV-1.

Combinative interactions of a human immunodeficiency virus (HIV) Tat antagonist with HIV reverse transcriptase inhibitors and an HIV protease inhibitor

Combinations of the human immunodeficiency virus (HIV) Tat protein antagonist Ro 24-7429 with either the HIV protease inhibitor Ro 31-8959 or the HIV reverse transcriptase inhibitors AZT (3'-azido-3'-deoxythymidine), ddC (2',3'-dideoxycytidine), ddI (2',3'-dideoxyinosine), and nevirapine were synergistic or additive in reducing HIV type 1 p24 antigen production in CEM cells or inhibiting HIV type 1-induced syncytium formation in HT4-6C cells.

Zidovudine. An update of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy

Zidovudine remains the mainstay in the treatment of patients infected with human immunodeficiency virus (HIV). The drug delays disease progression to acquired immunodeficiency syndrome (AIDS) and to AIDS-related complex (ARC), reduces opportunistic infections, and increases survival in patients with advanced HIV infection. There is evidence to suggest that zidovudine also delays disease progression in patients with mild symptomatic disease. Although one study has shown zidovudine to have no significant beneficial effects on survival or disease progression in patients with asymptomatic HIV infection, several other studies have shown zidovudine to delay disease progression in this patient group. Results from related ongoing studies are awaited with interest. Zidovudine reduces the incidence of AIDS dementia complex (ADC) and appears to prolong survival in these patients, and improves other neurological complications of HIV infection. The drug also appears to enhance the efficacy of interferon-alpha in patients with Kaposi's sarcoma. Although zidovudine is widely used as postexposure prophylaxis following accidental exposure to HIV, its efficacy in preventing seroconversion is unclear. Whether zidovudine prevents vertical transmission also remains to be determined. The overall efficacy of zidovudine in the treatment of children with HIV infection appears similar to that in adults despite more rapid disease progression in younger patients. Zidovudine-resistant isolates can emerge as early as after 2 months' therapy, and primary infection with zidovudine-resistant strains has been documented. Both zidovudine resistance and the syncytium-inducing HIV phenotype appear to be associated with poor clinical outcome. However, zidovudine resistance may revert on drug withdrawal or switching to an alternative therapy. Zidovudine-associated haematotoxicity may be dose-limiting. Nonhaematological adverse events associated with zidovudine therapy are generally mild and usually resolve spontaneously. Dosages of approximately 500 to 600 mg/day appear to be at least as effective as dosages of 1200 to 1500 mg/day and are better tolerated in patients with less advanced disease. However, optimal dosage are unclear. Despite beneficial effects, zidovudine monotherapy is not curative. There is evidence to suggest that the concomitant administration of zidovudine with didanosine or zalcitabine is effective in patients with HIV disease progression despite receiving zidovudine monotherapy, and there is some evidence that concomitant zidovudine plus didanosine therapy is more effective than alternating monotherapy. However, results from studies of combination therapy in asymptomatic patients, and from comparative combination therapy studies are awaited. Cotherapy with agents that augment haematopoiesis allows the continuation of therapeutic zidovudine dosages.(ABSTRACT TRUNCATED AT 400 WORDS)

Experimental study of transplacental passage of alpha interferon by two assay techniques

Two methods of assaying alpha interferon (IFN-alpha) were compared during an experiment aimed at determining whether IFN-alpha crosses the human placenta. Human placentas, collected after delivery following a normal pregnancy to term, were catheterized on both sides: fetal and maternal. The IFN-alpha was introduced in known amounts in the maternal circulation and was assayed in the efferent fetal fluid. The following two detection methods were used: radioimmunoassay by competition with [125I]IFN-alpha and assay with a biological system in which IFN-alpha protected Madin-Darby bovine kidney cells from destruction by vesicular stomatitis virus. The results obtained by the two methods were in perfect agreement for the efferent fetal fluid samples. They showed the absence of placental transfer of IFN-alpha. The biological method was found to be more sensitive than radioimmunoassay for low IFN-alpha titers (< 10 IU/ml) but was less reproducible, probably owing to the use of twofold dilutions. The specificities of the two methods were similar and their practicalities were equivalent; the biological method, however, was less costly. The study illustrates the complementarity of the two methods, which were based on different principles. The agreement obtained between the two methods provides a clear confirmation of the experimental results.

Evaluation of the combination effect of different antiviral compounds against HIV in vitro

3'-azido-3'deoxythymidine (AZT), a clinically used anti-HIV compound, was evaluated for antiviral effect on HIV infection in combination with other antiviral compounds in vitro. Interactions were evaluated by the median-effect principle and the isobologram technique. Synergistic effect was obtained by combining many evaluated antiviral agents with AZT. We observed a difference in the degree of synergism depending on the evaluated compound; the results indicate that compounds with the same target in the viral replicative cycle (ddI: 2',3'-dideoxyinosine, didanosine; d4T: 2',3'-dideoxy-2',3'-didehydrothymidine stavodine; TIBO: tetrahydro-imidazole-benzodiazepin) had a synergistic effect at all concentrations, agents that disturb the infectivity of virus (CAS: Castanospermine; AME: Amphotericin B Methyl Ester) exerted a strong synergistic effect at low concentrations, and finally compounds interfering with the adhesion/penetration process of virus (ConA: Concanavalin A; DS: dextran sulfate) were most potent with AZT when used in rather high concentrations. At this moment in the HIV epidemic, these observations suggest that combinations of antiviral compounds should be evaluated in clinical trials, with the major emphasis on nucleoside analogues and compounds influencing the infectivity of the virus.

Three-drug synergistic inhibition of HIV-1 replication in vitro by 3'-fluoro-3'-deoxythymidine, recombinant soluble CD4, and recombinant interferon-alpha

3'-Fluoro-3'deoxythymidine (FLT), recombinant soluble CD4 (CD4), and recombinant interferon-alpha (IFN alpha) were evaluated in two- and three-drug regimens against HIV-1 replication in vitro. Peripheral blood mononuclear cells were studied using p24 antigen production as the virologic endpoints. FLT showed 2.5-fold higher efficacy and a similar selectivity index to zidovudine. Drug interactions were evaluated by the median effect principle and the isobologram technique. FLT, CD4, and interferon alpha at noncytotoxic concentrations inhibited HIV-1 synergistically in two- and three-drug combinations with a combination index smaller than one and dose reduction index greater than one. The three-drug regimen provided greater virus suppression than the two-drug regimen. These results suggest that FLT is an alternative agent to AZT for the treatment of HIV infection either as a single agent or in combination with CD4 and/or interferon-alpha.

A randomized, double-blind, phase I/II trial of tumor necrosis factor and interferon-gamma for treatment of AIDS-related complex (Protocol 025 from the AIDS Clinical Trials Group)

To determine safety and efficacy of tumor necrosis factor (TNF) and interferon-gamma (IFN gamma) in the treatment of patients with acquired immunodeficiency syndrome (AIDS)-related complex, a randomized, double-blind study was conducted. Twenty-five patients with AIDS-related complex and CD4 lymphocytes less than or equal to 500 x 10(6)/L attended an AIDS Clinical Trials Unit of a tertiary referral center. Patients were administered tumor necrosis factor (TNF) (10 micrograms/m2) or IFN gamma (10 micrograms/m2), or both intramuscularly three times weekly for 16 weeks. Side effects from all three preparations included fever, constitutional symptoms, and local reactions. No significant hematologic, hepatic, renal, or coagulation abnormalities were observed. CD4 lymphocyte counts, beta 2-microglobulin, p24 antigen levels, and anti-p24 antibody did not change significantly during therapy. Similarly, no significant change was noted in rates of HIV isolation from peripheral blood mononuclear cells or plasma. TNF and IFN gamma were tolerable after premedication with acetaminophen; however, no significant change in markers of human immunodeficiency virus infection was demonstrated. These cytokines alone do not appear to be of benefit, nor do they appear to hasten the progression of HIV infection.

Characterization and anti-HIV properties of CD 4-coated red blood cells

Entry of HIV into its target cells requires its binding to the CD 4 molecule, the HIV receptor. Blocking this initial step of HIV life cycle is a potential target for the design of anti-HIV drugs. Soluble recombinant CD 4 efficiently blocks HIV infection in vitro and is the least toxic anti-HIV drug in humans. However, this molecule has a short half-life in vivo, and poorly neutralizes fresh isolates of HIV-1. Modifications of soluble CD 4 have been constructed, aimed at increasing its half life and other anti-viral properties. We have previously described an efficient method to cross-link soluble CD 4 to human red blood cells. We show here that these cells are uniformly coated as observed by immunofluorescence staining. Each of 8 different anti-CD 4 monoclonal antibodies stained these cells indicating that the epitopes recognized by these antibodies are correctly exposed at the cell membrane. These CD 4-expressing RBC inhibit specifically and in a dose dependent manner the HIV binding to, and infection of, CD 4+ target cells. On a CD 4 molar basis, this inhibition is approximately 15 times more efficient with CD 4-coated red blood cells than with soluble CD 4.

Antiviral agents

In recent years, the antiviral armamentarium has expanded considerably. Currently available agents are virustatic, inhibiting specific steps in the process of viral replication. No agent is active against nonreplicating or latent viruses. Acyclovir is useful in the treatment of genital herpes, herpes simplex encephalitis, mucocutaneous herpetic infection, varicella infection in the immunosuppressed host, and herpes zoster infection in the normal and the immunosuppressed host. It can also be used for prevention of herpesvirus infection in immunocompromised patients. Ganciclovir is indicated for the treatment of cytomegalovirus retinitis in patients with acquired immunodeficiency syndrome (AIDS) and is effective in the management of organ-specific cytomegalovirus infection in other immunocompromised patients. Chronic hepatitis C and condyloma acuminatum due to human papillomavirus respond to therapy with interferon alfa-2b. Patients with human immunodeficiency virus infection and CD4 lymphocyte counts of less than 500 cells/mm3 should be treated with zidovudine. Amantadine is useful in a therapeutic and prophylactic role in the management of influenza A virus infection. With the expanded use of and indications for antiviral therapy, clinically significant resistance to these agents has been encountered with increasing frequency.

HIV-1 infection. Diagnosis and management

This article discusses the epidemiology, diagnostic methods, prevention of complications, and medical management of HIV-1 infection. Many different therapeutic strategies for HIV-1 infection are being evaluated, but until the immune suppression is eradicated, presumably through more effective antiviral therapy, complications of AIDS and HIV-1 infection will continue to be encountered.

Phase 1 study of recombinant human CD4-immunoglobulin G therapy of patients with AIDS and AIDS-related complex

The safety and pharmacokinetics of recombinant CD4-immunoglobulin G (rCD4-IgG) were evaluated in a phase 1 study with dose escalation. A total of 16 patients, 6 with AIDS and 10 with AIDS-related complex, were evaluated at two university-affiliated hospital clinics. rCD4-IgG was administered once weekly for 12 weeks to four patients each at doses of 0.03, 0.1, 0.3, and 1.0 mg/kg of body weight. Dosing was intravenous for two patients in the 1.0-mg/kg dose group and intramuscular for the remaining patients. Dosing was intravenous for two patients in the 1.0-mg/kg dose group and intramuscular for the remaining patients. Pharmacokinetic, toxicity, and immunologic variables were monitored with all patients. Administration of rCD4-IgG was well tolerated, with no important clinical or immunologic toxicities noted. No subjects required dose reduction or discontinuation of therapy due to toxicity. No consistent changes were seen in human immunodeficiency virus antigen levels in serum or CD4 lymphocyte populations. The volume of distribution was small, and compared with that of rCD4, the half-life of the hybrid molecule was markedly prolonged following intramuscular or intravenous administration. The rate and extent of absorption following intramuscular dosing were variable. Intramuscular administration of rCD4-IgG appears to be inferior to intravenous dosing from a pharmacokinetic standpoint, with lower peak concentrations and variable absorption. After intravenous administration, peak concentrations of rCD4-IgG in serum (20 to 24 micrograms/ml) that have shown antiviral activity in vitro against more sensitive clinical isolates of human immunodeficiency virus were achieved. The peak concentrations in serum after intramuscular administration were below these levels. Treatment with rCD4-IgG was well tolerated at the doses administered to patients in this study but did not result in significant changes in CD4 lymphocyte counts or p24 antigen levels in serum.

Analysis of synergism/antagonism between HIV-1 antibody-positive human sera and soluble CD4 in blocking HIV-1 binding and infectivity

We tested human immunodeficiency virus type 1 (HIV-1) antibody-positive human sera and sCD4, alone and in combination, for synergistic, additive, or antagonistic effects on blocking of HIV binding and infectivity. Data were analyzed by an application of the median effect principle derived from the law of mass action. This allows the assessment of synergism/antagonism at any desired level of effect. Using three assays (whole virus binding to CD4 cells, neutralization of HIV infectivity, and binding of purified gp120 to solid-phase sCD4), we generally observed additive effects or slight synergism between antibody and sCD4 in inhibiting gp120-CD4 interaction. We used a fourth assay to measure the irreversible inactivation of HIV infectivity by sCD4, a property that can also be mediated by antibody but with considerably less potency than sCD4. The reduction in HIV infectivity mediated by mixtures of sCD4 and antibody was always equal to or greater than the arithmetic sum of the reductions by either agent alone. The relevant antiviral effects of sCD4 and anti-HIV sera may include reversible blockage of receptor binding, irreversible inactivation of HIV infectivity, and in the case of antibody, additional reactions that are independent of receptor binding. Although predictions concerning the in vivo situation are speculative, we find no evidence in vitro for antagonism between sCD4 and antibody with respect to the net effect of the two in blocking HIV binding and infectivity.