Synthesis and anti-HIV activity of isonucleosides

A series of isomeric 2',3'-dideoxynucleosides which contains a modified carbohydrate moiety has been prepared. This class of compounds was designed to mimic the activity of known anti-HIV dideoxynucleosides, while imparting enhanced chemical and enzymatic stability. Isonucleosides containing the standard heterocyclic bases (A, C, G, T) were synthesized via nucleophilic addition of the base to an isomeric sugar unit. Modified derivatives were generated by manipulation of the intact isonucleoside. Two of the compound prepared, iso-ddA (1) and iso-ddG (6), exhibit significant and selective anti-HIV activity, as well as beneficial hydrolytic stability.

The immunology of HIV infection: implications for therapy

It is known that antiretroviral drugs can induce immunologic improvement in patients with acquired immunodeficiency syndrome (AIDS) and other manifestations of HIV infection. However, the improvements so attained are often partial and transient. This may result from a number of factors, including incomplete inhibition of human immunodeficiency virus (HIV) replication by available agents, the development of viral drug resistance, the effect of cytokines, or thymic damage. An understanding of this problem may be important in further development of AIDS therapies. It will also be important to learn how to best assess the response to various therapies. In this regard, the CD4 count is evolving as a mortality risk indicator in AIDS and as such may find utility in assessing new therapeutic approaches. We have observed that in a cohort of gay men receiving antiretroviral therapy in a research environment, nearly all deaths occurred in individuals with fewer than 50 CD4 cells/mm3. However, the relationship between the CD4 count and the hazard of dying may be influenced by a number of factors (e.g., active intravenous drug use, extreme poverty, etc.), and further studies are needed to define the relationship between CD4 and clinical endpoints under a variety of conditions.

Correlations between the in vitro and in vivo activity of anti-HIV agents: implications for future drug development

Some 10 years after the first recognition of acquired immunodeficiency syndrome (AIDS) as a new syndrome, we have identified a number of molecular targets to interrupt the replicative cycle of human immunodeficiency virus (HIV), the causative agent. A number of dideoxynucleosides have been identified as having anti-HIV activity in vitro, and several of these have been found to have clinical activity in patients. In contrast, while a number of agents have been found to block viral binding to the target cell in vitro, these agents have generally not shown clear-cut evidence of clinical activity. Agents which act at a variety of steps in the HIV replicative cycle are now under development, and it is likely that we will have an increased armamentarium to fight this disease in the near future.

Oligodeoxyribonucleotide phosphorothioate fluxes and localization in hematopoietic cells

An antisense oligonucleotide phosphorothioate, previously shown to inhibit HIV-1 viral expression in chronically infected H9 cells, was fluorescently labeled to study oligonucleotide fluxes and localization within living cells. Observations based on flow cytometry and fluorescence microscopy show the following: within around 0.5-2 h, an apparent steady-state distribution of the oligonucleotide is achieved in which the intracellular oligonucleotide concentration is less than that present in the external medium; following oligonucleotide uptake and resuspension of the cells in oligonucleotide-free medium, an oligonucleotide efflux, with a time constant similar to that for uptake, is observed (although a significant fraction of the phosphorothioate remains within the cell); cellular uptake as a function of the external oligonucleotide concentration is nonlinear, being more efficient at lower concentrations (less than 2 microM); and a predominant oligonucleotide localization within the cell nucleus and perinuclear organelles is observed.

In vitro inhibition of hepatitis B virus replication by 2',3'-dideoxyguanosine, 2',3'-dideoxyinosine, and 3'-azido-2',3'-dideoxythymidine in 2.2.15 (PR) cells

Hep G2-derived hepatoblastoma cells (2.2.15), which actively produce hepatitis B virus (HBV), were cultured in the presence of 2',3'-dideoxyguanosine (ddG), 2',3'-dideoxyinosine, or 3'-azido-2',3'-dideoxythymidine (AZT). ddG was the most potent agent. It diminished viral replication by up to 95%, as assessed by the amount of episomal HBV DNA, without impairing cellular growth. AZT was the least effective against HBV. Northern blot analysis revealed no apparent difference in the pregenomic viral RNA profile, suggesting that these dideoxynucleosides suppress reverse transcription in the replicative cycle of HBV. The effect of varying the time of drug exposure showed that these agents can suppress HBV replication even when added late in culture. HBV replication in another 2.2.15 cell population of the same lineage was affected by ddG differently, which may enable the investigation of phenotypic or genetic alterations during culture. The present data suggest that some 2',3'-dideoxynucleosides can exert a potent antiviral activity against HBV in vitro, at least under certain circumstances, although the data do not prove that any of these agents have utility in patients with hepatitis.

Pharmacokinetics of 2',3'-dideoxyinosine in patients with severe human immunodeficiency infection. II. The effects of different oral formulations and the presence of other medications

2',3'-Dideoxyinosine (ddI) has shown activity against human immunodeficiency virus in phase I clinical trials. The drug is rapidly degraded by acid, however, thus raising questions as to the efficiency and reproducibility of its absorption after oral administration. This investigation studies the bioavailability of several oral dosage forms of ddI. When ddI was given to fasting patients as an oral solution with antacid, the bioavailability was 41% +/- 7% (mean +/- SEM). However, when given as buffered tablets, the bioavailability was considerably less (25% +/- 5%). The bioavailability increased slightly when the tablets were given with supplemental antacid (36% +/- 6%). Two enteric-coated preparations had reasonable bioavailability (36% +/- 5% and 26% +/- 5%), but the peak plasma level was much lower and occurred at a much later time than with the oral solution. When ddI was given as a premeasured powder containing sucrose and buffer to be reconstituted by the patient (the "sachet" preparation), the bioavailability was 29% +/- 6%. This was similar to that of the oral solution for this particular group of patients (30% +/- 7%). However, the bioavailability of the sachet was only 17% +/- 4% when administered with food. When the sachet was given to patients receiving ranitidine, no consistent change in bioavailability was noted. Also, no change in ddI pharmacokinetics was noted in patients receiving ganciclovir.

CD4 count and the risk for death in patients infected with HIV receiving antiretroviral therapy

OBJECTIVE

To investigate the relation between CD4 count and the immediate hazard of dying in patients receiving zidovudine (azidothymidine [AZT])-based antiretroviral therapy.

SETTING

A research hospital that recruits patients from the entire United States.

DESIGN

Retrospective analysis of a cohort of patients with the acquired immunodeficiency syndrome (AIDS) or AIDS-related complex participating in long-term zidovudine-based antiretroviral protocols.

PATIENTS

Fifty-five patients with human immunodeficiency virus (HIV) infection and either AIDS or severe AIDS-related complex who were followed for as many as 4 years while they received antiretroviral therapy.

MEASUREMENTS

CD4 counts were measured.

MAIN RESULTS

Ten patients are known to be alive and 1 was lost to follow-up. Of the 44 patients who are known to have died, the CD4 range was known within 6 months of death in 41. All but 1 of these 41 assessable deaths occurred in patients whose CD4 counts were known to have fallen below 50 CD4 cells/mm3 (P less than 10(-10)). The hazard of dying in the cohort ranged from 0 deaths/patient-month (95% CI, 0 to 0.008 deaths/patient-month) in patients with 200 or more CD4 cells/mm3 to 0.07 deaths/patient-month (CI, 0.050 to 0.094 deaths/patient-month) in patients with fewer than 50 CD4 cells/mm3. For the patients who died and whose cases were assessable, the mean of the last three CD4 counts obtained before death was 7.7 CD4 cells/mm3 (CI, 0.9 to 63.3 cells/mm3). The median survival of patients once their CD4 counts fell below 50 CD4 cells/mm3 was 12.1 months (CI, 7.2 to 19.4 months).

CONCLUSIONS

In a carefully followed cohort treated with zidovudine-based antiretroviral therapy, nearly all deaths occurred in patients with fewer than 50 CD4 cells/mm3. These findings may have implications in the monitoring of patients with AIDS and in the use of CD4 count as a clinical trials end point for the antiretroviral therapy of HIV infection.

Targeted therapy of human immunodeficiency virus-related disease

Since the discovery of human immunodeficiency virus (HIV) as a pathogenic retrovirus linked to acquired immunodeficiency syndrome (AIDS), a number of potentially useful strategies for antiretroviral therapy of AIDS and its related diseases have emerged. One such strategy involves use of the broad family of 2',3'-dideoxynucleosides, to which 3'-azido-2',3'-dideoxythymidine (AZT) belongs. AZT has been shown to reduce the replication of HIV in vivo and to confer significant clinical benefits in patients in both early and advanced stages of infection. Other members of the family, 2',3'-dideoxycytidine (ddC), 2',3'-dideoxyinosine (ddI), and 2',3'-didehydro-2',3'-dideoxythymidine (d4T), have also been reported to be active against HIV in short-term clinical trials. The armamentarium of antiretroviral agents is rapidly growing. Various nonnucleoside agents have recently been identified to be active against HIV in vitro. HIV-1 protease inhibitors are notable as possible new therapies for HIV-1-related diseases. However, we have faced several new challenges in the antiretroviral therapy in AIDS. These include long-term drug-related toxicities; emergence of drug-resistant HIV variants; and development of various cancers, particularly as effective therapies prolong survival. Progress in understanding structure-activity relations and clinical effectiveness will continue with dideoxynucleoside analogs. However, it seems certain that a variety of nonnucleoside analogs affecting multiple steps in viral replication will become available before long, and combination therapies using multiple antiretroviral drugs will be available. Such therapies will exert major effects against the moribidity and mortality caused by HIV.

Progress and challenges in the global effort against cancer

The new decade has given birth to a large number of new concepts in our approach to cancer. The progress in molecular technology that occurred in the 1980's is being transferred in the 1990's to the bedside. The practical clinical application of basic science innovations is aimed at prevention and curative treatment of cancer in all of its forms, and is becoming a central theme of cancer therapeutics. The progress to date reflects a climate that fosters a unity of basic and clinical investigations, for example, where an understanding of tumor genetics or molecular immunoregulation can translate into an innovative clinical approach such as gene transfer therapy. The challenges that we face in this new decade arise in part from progress in certain areas, such as the discovery of natural products that have important antitumor activity but a limited source, or the increasing incidence in AIDS-related lymphomas that has come about from antiretroviral therapy-induced prolongation of survival for AIDS patients. There are critical challenges from a lack of progress in other areas, as well. The challenge of developing curative therapies is surpassed by the need to prevent those cancers before they arise. The challenge of prevention, as exemplified by the link between lung cancer and smoking, is of paramount importance. The ultimate challenge placed before the global oncology community is to ensure that the fruits of modern technology are available to all who need them.

Inhibitors of IMP dehydrogenase stimulate the phosphorylation of the anti-human immunodeficiency virus nucleosides 2',3'-dideoxyadenosine and 2',3'-dideoxyinosine

2',3'-Dideoxyadenosine (ddAdo) and its deamination product 2',3'-dideoxyinosine (ddIno) (didanosine) inhibit the replication and infectivity of the human immunodeficiency virus (HIV) in a number of in vitro assay systems. Early clinical studies (phase I) have indicated a role for ddIno in the treatment of patients with severe HIV infection. In the present in vitro study, the formation in human T cells (MOLT-4, ATH8, and CCRF-CEM) of the pharmacologically active metabolite of ddIno and ddAdo, 2',3'-dideoxyadenosine-5'-triphosphate (ddATP), was found to be stimulated 2-4-fold by appropriate concentrations of inosinate dehydrogenase (IMPD) inhibitors such as ribavirin, tiazofurin, and mycophenolic acid. Concomitant with this increase in ddATP formation from ddIno was an increase in anti-HIV activity of this agent when it was combined with ribavirin in the ATH8 cell assay system and with tiazofurin in the MOLT-4 assay system. No change was noted in the intracellular concentration of the corresponding physiological deoxynucleoside-5'-triphosphate, dATP; positive correlation was observed, however, between the increase in ddATP formation from ddIno and the increase in intracellular IMP occurring as a consequence of IMPD inhibition. The results support the hypothesis that the stimulation of ddATP formation seen when ddIno is combined with ribavirin or other IMPD inhibitors is a consequence of an increased concentration of IMP, the major phosphate donor for the initial phosphorylation step in the anabolism of ddIno to ddATP, i.e., ddIno----ddIMP.

Projections of the incidence of non-Hodgkin's lymphoma related to acquired immunodeficiency syndrome

Advances in antiretroviral therapy and treatment or prophylaxis against opportunistic infection have resulted in prolongation of the survival of patients with acquired immunodeficiency syndrome (AIDS). Previous research has demonstrated an association between AIDS and risk of non-Hodgkin's lymphoma (NHL). In addition to the approximately 3% of individuals found to have NHL at the time of AIDS onset, others continue to develop NHL following AIDS diagnosis. Data from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute demonstrated a sharply increasing incidence of NHL among men in the age range 20-49 years since 1983 in the United States. Based on new data on the risk of NHL following AIDS diagnosis, on estimates of improved survival following AIDS diagnosis, and on projections of future AIDS incidence, we considered four sets of assumptions and estimated the number of AIDS-related NHL cases in 1992 to be between 2900 and 9800. Three of these projections were higher than the estimate of 4700 cases obtained by linear extrapolation of SEER incidence trends. These projections of AIDS-related NHL incidence suggest that between 8% and 27% of all NHL cases that occur in the United States in 1992 will arise as a consequence of infection with the human immunodeficiency virus (HIV), imposing a substantial health care burden. More research into the pathogenesis of lymphoma and new approaches to antiretroviral and antilymphoma therapy will be necessary to prevent and treat this formidable complication of infection with HIV.

The human costs of cancer and the response of the National Cancer Program

The three foundations of the National Cancer Program are basic research, clinical trials (in prevention and treatment), and cancer centers. These foundations have supported a great deal of progress against cancer over the past 20 years. Nevertheless, a number of challenges remain, and continued progress will depend on the speed with which research advances can be translated into practical realities. Poverty is a risk factor for cancer incidence and mortality. Thus, a lack of access to the technologies generated by the National Cancer Program can be a force for bringing about differential burdens of cancer in underserved populations.

The occurrence of opportunistic non-Hodgkin's lymphomas in the setting of infection with the human immunodeficiency virus

The incidence of non-Hodgkin's lymphoma (NHL) has increased by over 50% in the United States since 1973. There is epidemiologic evidence that some of this increase is the result of AIDS-related lymphoma and that this component is increasing. Prolonged survival in the setting of a variety of immunodeficiency states is associated with an increased incidence of NHL. The development of antiretroviral therapy and improved therapy for the complications of AIDS has resulted in prolonged survival of patients with AIDS. As these patients survive longer with profound immunodeficiency, they have an increased cumulative risk of developing NHL. This may result in even more AIDS-related NHL in the future than predicted from current epidemiological studies. An increased understanding of the pathogenesis of AIDS-related NHL may lead to means of preventing their occurrence. Also, therapies that may prevent immunodeficiency from developing in HIV-infected patients may reduce the likelihood of NHL developing. Current efforts at treating these lymphomas are aimed at preventing the myelosuppression and immunosuppression associated with current regimens, lymphoma relapses within the central nervous system, and the opportunistic infections associated with treatment of these tumors. Ultimately, the best means of preventing the development of these lymphomas is by preventing infection with HIV.

Lipophilic halogenated congeners of 2',3'-dideoxypurine nucleosides active against human immunodeficiency virus in vitro

Four 2-amino-6-halo- and four 6-halo-2',3'-dideoxypurine ribofuranosides (ddPs) were synthesized and tested for in vitro activity to suppress the infectivity, cytopathic effect, Gag protein expression, and DNA synthesis of human immunodeficiency virus (HIV). The comparative order of in vitro anti-HIV activity of the eight 6-halo-ddPs was as follows: 2-amino-6-fluoro, 2-amino-6-chloro, 6-fluoro greater than 2-amino-6-bromo greater than 2-amino-6-iodo, 6-chloro greater than 6-bromo greater than 6-iodo. 2-Amino-6-fluoro-, 2-amino-6-chloro-, and 6-fluoro-ddPs showed a potent activity against HIV comparable to that of 2',3'-dideoxyinosine (ddI) or 2',3'-dideoxyguanosine (ddG) and completely blocked the infectivity of HIV without affecting the growth of target cells. The lipophilicity order was as follows: 2-amino-6-iodo greater than 2-amino-6-bromo greater than 2-amino-6-chloro greater than 2-amino-6-fluoro much greater than ddG greater than ddI. All eight 6-halo-ddPs were substrates for adenosine deaminase (ADA; adenosine aminohydrolase, EC 3.5.4.4). The relative rates of hydrolysis by ADA were as follows: ddA, 2-amino-6-fluoro much greater than 2-amino-6-chloro, 2-amino-6-bromo greater than 2-amino-6-iodo. Taken together, these compounds may represent an additional class of lipophilic prodrugs for ddI and ddG and may also provide a strategy for endowing therapeutic purine nucleosides with desirable lipophilicity.

Initial clinical experience with dideoxynucleosides as single agents and in combination therapy

Several dideoxynucleosides, including 3'-azido-2',3'-dideoxythymidine (zidovudine, azidothymidine, AZT), 2',3'-dideoxycytidine (ddC), and 2',3'-dideoxyinosine (ddI), have been shown to be potent inhibitors of human immunodeficiency virus (HIV) replication in human T cells and macrophages. These compounds undergo anabolic phosphorylation within target cells to a 3'-triphosphate moiety; as triphosphates, they act at the level of HIV DNA polymerase (reverse transcriptase). AZT has been shown to reduce the morbidity and mortality of patients with severe HIV infection and to at least temporarily ameliorate certain cases of HIV-induced dementia. In phase 1 studies, ddC and ddI have been shown to induce immunologic and virologic improvements in patients with AIDS or related disorders; phase 2 studies of ddC and ddI are underway. The use of these drugs can be associated with toxicity. AZT can cause bone marrow toxicity or myositis with prolonged use, ddC can cause peripheral neuropathy at high doses, and ddI can cause sporadic pancreatitis and peripheral neuropathy at high doses. For each compound, however, a therapeutic window exists in which an anti-HIV effect can be attained without short-term toxicity in most patients. Dose-intensity appears to be an important determinant of the toxicity of dideoxynucleosides. Studies are underway to explore how the therapeutic profiles of these compounds may be enhanced by attention to scheduling or through the use of combination therapy.

Quantitative analysis of HIV-1 proviral DNA in peripheral blood mononuclear cells from patients with AIDS or ARC: decrease of proviral DNA content following treatment with 2',3'-dideoxyinosine (ddI)

A rapid and simple method for determining the proviral DNA content in peripheral blood mononuclear cells (PBM) from patients with human immunodeficiency virus type 1 (HIV-1) infection was established by using the polymerase chain reaction (PCR) technique. We found that the majority of HIV proviral DNA copies detectable in unfractionated PBM resided in T cells, while B cells/monocytes contained lesser amounts of HIV DNA (93.9 +/- 3.5% for T cells vs. 6.1 +/- 3.5% for B cells/monocytes: p less than 0.05). When we compared the amount of HIV proviral DNA in PBM from 13 patients with AIDS or AIDS-related complex (ARC) before and during antiretroviral therapy with 2',3'-dideoxyinosine (ddI) which was given as an escalating dose in a Phase I clinical study, a significant decrease was observed in 9 of 12 evaluable patients receiving the drug for 8 to 14 weeks (p less than 0.02). The decrease appeared more pronounced in patients receiving relatively high doses of the drug. These data suggest that the quantitation of HIV viral DNA in PBM by PCR is feasible and may theoretically contribute to an overall monitoring of patients receiving experimental therapy. However, larger studies will be required to determine the sensitivity and specificity of this assay and further longitudinal studies will be essential.

NIH conference. Antiretroviral therapy in AIDS

OBJECTIVE

To review recent developments of antiretroviral therapy for the acquired immunodeficiency syndrome (AIDS) and related disorders.

DATA SOURCES, STUDY SELECTION, AND DATA EXTRACTION

An edited and updated summary of a Clinical Staff Conference held 26 October 1988 at the National Institutes of Health. The speakers discussed their own work as well as related work from other groups.

DATA SYNTHESIS

The discovery that human immunodeficiency virus (HIV) causes AIDS has permitted the development of rational antiviral therapy for this disease. Various steps in the replicative cycle of HIV can be targeted for intervention. More basic research into the life cycle of HIV is therefore likely to yield new therapeutic approaches. In 1985, nucleoside analogues called dideoxynucleosides were discovered to be potent inhibitors of HIV replication in vitro. Dideoxynucleosides selectively inhibit HIV reverse transcriptase after they are phosphorylated intracellularly to 5'-triphosphates. One dideoxynucleoside, 3'-azido-2',3'-dideoxythymidine (AZT or zidovudine) has been found to prolong the life of patients with AIDS. This drug can partially reverse HIV dementia and decrease short-term progression to AIDS; it has been approved for treating HIV-infected patients with fewer than 500 CD4+ cells/mm3. AZT is only a first step in developing new therapy for AIDS. Its use is associated with toxicities, particularly bone marrow suppression. Several groups have reported the development of AZT-resistant strains of HIV. Other dideoxynucleosides whose toxicity profiles differ from that of AZT have also shown activity against HIV in early clinical studies. Large-scale, randomized trials of these drugs are now under way. Studies have shown that the binding of HIV to CD4 may be blocked by genetically engineered forms of CD4 and that HIV protease may be inhibited by substrate analogues. Protease inhibitors are an excellent area for further study in patients. Antisense oligonucleotide therapy may target the regulatory genes of HIV and is also being considered.

CONCLUSION

With these advances, AIDS is gradually changing from an imminently fatal disease to one that can be managed with the judicious use of drugs and biologics. Progress against AIDS will continue, provided that researchers adhere to the principles of controlled trials.

Molecular targets for AIDS therapy

The development of antiretroviral therapy against acquired immunodeficiency syndrome (AIDS) has been an intense research effort since the discovery of the causative agent, human immunodeficiency virus (HIV). A large array of drugs and biologic substances can inhibit HIV replication in vitro. Nucleoside analogs--particularly those belonging to the dideoxynucleoside family--can inhibit reverse transcriptase after anabolic phosphorylation. 3'-Azido-2',3'-dideoxythymidine (AZT) was the first such drug tested in individuals with AIDS, and considerable knowledge of structure-activity relations has emerged for this class of drugs. However, virtually every step in the replication of HIV could serve as a target for a new therapeutic intervention. In the future, non-nucleoside-type drugs will likely become more important in the experimental therapy of AIDS, and antiretroviral therapy will exert major effects against the morbidity and mortality caused by HIV.