Reversible axonal neuropathy from the treatment of AIDS and related disorders with 2',3'-dideoxycytidine (ddC)

A total of 20 patients with acquired immune deficiency syndrome (AIDS) or AIDS-related complex (ARC) received the anti-retroviral drug 2',3',dideoxycytidine in a phase I study at doses ranging from 0.03 mg/kg every 8 hours to 0.25 mg/kg every 8 hours. Of the 11 patients who participated in the study for more than 5 weeks, 9 developed symptoms and signs of a mainly sensory painful neuropathy that was confirmed by electromyography to be mixed sensory and motor neuropathy of axonal type. The neuropathy which developed on dideoxycytidine occurred between 9 and 12 weeks of treatment. One patient, who had the drug stopped at 3 weeks owing to thrombocytopenia, developed a similar clinical picture of a sensory peripheral neuropathy after 2 weeks off dideoxycytidine. However, he did not have electromyographic evidence of a neuropathy, and he subsequently returned to normal clinically while taking a lower dose of dideoxycytidine in an alternating regimen. Five patients were withdrawn from the study because of the neuropathy. The pattern of this neuropathy was different from that of the slowly progressive painful neuropathy of AIDS, in that there was (1) a sudden onset of intense burning discomfort in both feet sparing the hands at about the tenth week (mean 10.4 weeks) of treatment, (2) there was motor involvement in some patients without progression, and (3) onset of the neuropathy was temporally related to the administration of dideoxycytidine and began to resolve 3-5 weeks after its discontinuation. We believe that dideoxycytidine can be an axonal toxin, especially when given in high dose continuous regimens.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo activity against HIV and favorable toxicity profile of 2',3'-dideoxyinosine

The purine analog 2',3'-dideoxyinosine (ddI), which has anti-retroviral activity in vitro was administered for up to 42 weeks to 26 patients with acquired immunodeficiency syndrome (AIDS) or severe AIDS-related complex (ARC). Ten of these individuals were AZT-intolerant. Eight dose regimens were studied. The drug was orally bioavailable and penetrated into the cerebrospinal fluid (CSF). Comparatively little evidence of an effect against human immunodeficiency virus (HIV) was seen at the lowest four doses. However, patients in the four highest dose groups (ddI at 1.6 milligrams per kilogram intravenously and then greater than or equal to 3.2 milligrams per kilogram orally at least every 12 hours or higher) had increases in their circulating CD4+ T cells (P less than 0.0005), increased CD4/CD8 T cell ratios (P less than 0.01), and, where evaluable, more than an 80% decrease in serum HIV p24 antigen (P less than 0.05). The patients also had evidence of improved immunologic function, had reduced viremic symptomatology, and gained a mean of 1.6 kilogram with these comparatively infrequent dosing schedules (every 8 or 12 hours). The most notable adverse effects directly attributable to ddI administration at the doses used in this study included increases in serum uric acid (due to hypoxanthine release) and mild headaches and insomnia. These results suggest that serious short-term toxicity at therapeutic doses is not an inherent feature in the profile of agents with clinical anti-HIV activity. Further controlled studies to define the safety and efficacy of this agent may be worth considering.

Regulation of viral expression of human immunodeficiency virus in vitro by an antisense phosphorothioate oligodeoxynucleotide against rev (art/trs) in chronically infected cells

In this report, we demonstrate the sequence-specific suppression of viral expression in T cells chronically infected with human immunodeficiency virus 1 (HIV-1), using antisense phosphorothioate oligodeoxynucleotides. As a target for antisense intervention, we used the HIV-1 gene rev, which is essential for viral replication and regulates the expression of virion proteins, in part, by affecting the splicing of the viral mRNA. A phosphorothioate oligomer complementary to the initiation sequence of HIV-1 rev had a significant and selective inhibitory effect on the production of several viral proteins in chronically HIV-1-infected T cells and drastically reduced the unspliced (genomic) viral mRNA transcripts, with relative sparing of smaller (spliced) transcripts. By contrast, the antisense sequence with unmodified normal phosphodiester linkages as well as phosphorothioate oligomers containing sense, random, homopolymeric sequences, or antisense sequence with N3-methylthymidine residues did not have an inhibitory effect on viral expression. Thus, sequence specificity and nuclease resistance were critical for the anti-viral-gene regulatory effect of the antisense molecules. The altered HIV-1 mRNA profile induced by the antisense phosphorothioate oligomer suggests that the mechanism for the inhibition of viral expression is due to an interference with the regulatory gene, rev, by translation arrest.

Reversal of brain metabolic abnormalities following treatment of AIDS dementia complex with 3'-azido-2',3'-dideoxythymidine (AZT, zidovudine): a PET-FDG study

Brain glucose metabolism was evaluated in four patients with acquired immunodeficiency syndrome (AIDS) dementia complex using [18F]fluorodeoxyglucose (FDG) and positron emission tomography (PET) scans at the beginning of therapy with 3'-azido-2',3'-dideoxythymidine (AZT, zidovudine), and later in the course of therapy. In two patients, baseline, large focal cortical abnormalities of glucose utilization were reversed during the course of therapy. In the other two patients, the initial PET study did not reveal pronounced focal alterations, while the post-treatment scans showed markedly increased cortical glucose metabolism. The improved cortical glucose utilization was accompanied in all patients by immunologic and neurologic improvement. PET-FDG studies can detect cortical metabolic abnormalities associated with AIDS dementia complex, and may be used to monitor the metabolic improvement in response to AZT treatment.

1-(3-cyano-2,3-dideoxy-beta-D-erythro-pentofuranosyl)thymine (cyanothymidine): synthesis and antiviral evaluation against human immunodeficiency virus

1-(3-Cyano-2,3-dideoxy-beta-D-erythro-pentofuranosyl)thymine (cyanothymidine) (3a) has been prepared by an unambiguous route starting from D-xylose. The relative and absolute stereochemistry of 3a and its anomeric isomer 9 have been confirmed by NOE experiments and by X-ray diffraction analysis. In antiviral tests vs HIV 3a was shown to be inactive, a surprising result in view of a preliminary disclosure claiming potent anti-HIV activity. The activity previously assigned to 3a is believed to be due to contamination of that sample with the known antiviral nucleoside analogue 5b.

Replication of human immunodeficiency virus in monocytes. Granulocyte/macrophage colony-stimulating factor (GM-CSF) potentiates viral production yet enhances the antiviral effect mediated by 3'-azido-2'3'-dideoxythymidine (AZT) and other dideoxynucleoside congeners of thymidine

We have investigated the influence of granulocyte-macrophage CSF (GM-CSF) on the replication of HIV-1 in cells of monocyte/macrophage (M/M) lineage, and its effect on the anti-HIV activity of several 2'3'-dideoxynucleoside congeners of thymidine in these cells in vitro. We found that replication of both HTLV-IIIBa-L (a monocytotropic strain of HIV-1) and HTLV-IIIB (a lymphocytotropic strain) is markedly enhanced in M/M, but not in lymphocytes exposed to GM-CSF in culture. Moreover, GM-CSF reduced the dose of HIV required to obtain productive infection in M/M. Even in the face of this increased infection, GM-CSF also enhanced the net anti-HIV activity of 3'-azido-2'3'-dideoxythymidine (AZT) and several related congeners: 2'3'-dideoxythymidine (ddT), 2'3'-dideoxy-2'3'-didehydrothymidine (D4T), and 3'-azido-2'3'-dideoxyuridine (AZddU). Inhibition of viral replication in GM-CSF-exposed M/M was achieved with concentrations of AZT and related drugs, which were 10-100 times lower than those inhibitory for HIV-1 in monocytes in the absence of GM-CSF. Other dideoxynucleosides not related to AZT showed unchanged or decreased anti-HIV activity in GM-CSF-exposed M/M. To investigate the possible biochemical basis for these effects, we evaluated the metabolism of several drugs in M/M exposed to GM-CSF. We observed in these cells markedly increased levels of both parent and mono-, di-, and triphosphate anabolites of AZT and D4T compared with M/M not exposed to GM-CSF. By contrast, only limited increases of endogenous competing 2'-deoxynucleoside-5'-triphosphate pools were observed after GM-CSF exposure. Thus, the ratio of AZT-5'-triphosphate/2'-deoxythymidine-5'-triphosphate and 2'3'-dideoxy-2'3'-didehydrothymidine-5'-triphosphate/2'-deoxythymi dine- 5'-triphosphate is several-fold higher in GM-CSF-exposed M/M, and this may account for the enhanced activity of such drugs in these cells. Taken together, these findings suggest that GM-CSF increases HIV-1 replication in M/M, while at the same time enhancing the anti-HIV activity of AZT and related congeners in these cells. These results may have implications in exploring new therapeutic strategies in patients with severe HIV infection.

The pharmacokinetics of zidovudine administered by continuous infusion in children

STUDY OBJECTIVE

To define the pharmacokinetics of zidovudine (azidothymidine) in children with human immunodeficiency virus infection.

DESIGN

Plasma, urine, and cerebrospinal fluid were obtained following a single 80 mg/m2 body surface dose infused over 1 hour (n = 9), and during a continuous infusion of 0.5 (n = 3), 0.9 (n = 8), 1.4 (n = 7), or 1.8 (n = 3) mg/kg body weight per hour.

SETTING

Outpatient clinic and inpatient ward of the Pediatric Branch of the National Cancer Institute.

PATIENTS

Twenty-one children (seventeen boys) ranging in age from 14 months to 12 years with symptomatic human immunodeficiency virus infection who were being treated on a phase I-II study of continuous intravenous infusion zidovudine.

MEASUREMENTS AND MAIN RESULTS

Zidovudine disappearance following bolus administration was rapid and biexponential with half-lives of 9.6 and 92 minutes, and a total clearance of 705 +/- 330 mL/min.m2. Zidovudine remained above 1 mumol/L, the optimal virostatic concentration in vitro, for only 1.5 hours. In contrast, with continuous infusion steady-state plasma zidovudine concentrations (Css) were maintained above 1 mumol/L continuously, even at the lowest infusion rate. At steady state the ratio of cerebrospinal fluid zidovudine concentration to plasma was 24% +/- 9%. Patients who developed severe neutropenia (absolute neutrophil count less than 0.5 X 10(9)/L) on the continuous infusion regimen had significantly higher plasma Css. Six of eight had a Css greater than 3.0 mumol/L.

CONCLUSIONS

Pharmacokinetic parameters show that continuous infusion is better than an intermittent schedule in maintaining minimal virostatic concentrations of the drug with a lower daily dose.

Stepwise mechanism of HIV reverse transcriptase: primer function of phosphorothioate oligodeoxynucleotide

Primer recognition by purified HIV reverse transcriptase has been investigated. Earlier we found that the reaction pathway for DNA synthesis is ordered, with template-primer and free enzyme combining to form the first complex in the reaction sequence (Majumdar et al., 1988). We now find that d(C)28 is a linear competitive inhibitor of DNA synthesis against poly[r(A)].oligo[d(T)] as template.primer, indicating that d(C)28 and the template.primer combine with the same form of the enzyme in the reaction scheme, i.e., the free enzyme. The phosphorothioate oligodeoxynucleotide Sd(C)28 also is a linear competitive inhibitor against template.primer. However, the Ki for inhibition (approximately 2.8 nM) is approximately 200-fold lower than the Ki for inhibition by d(C)28. Since the inhibition is linear competitive, the dissociation constant is equal to the Ki for inhibition. Filter binding assays confirmed high-affinity binding between Sd(C)28 and the enzyme and yielded a KD similar to the Ki for inhibition. Substrate kinetic studies of DNA synthesis using Sd(C)28 as primer, and poly[r(I)] as template, revealed that the Km for Sd(C)28 is 24 nM. The Km for this primer is, therefore, 8-fold higher than the KD for enzyme-primer binding (2.8 nM). These results enable calculation of real time rate values for the enzyme-primer association (kon = 5.7 x 10(8) M-1 s-1) and dissociation (koff = 1.6 s-1).

T-cell response towards HIV in infected individuals with and without zidovudine therapy, and in HIV-exposed sexual partners

HIV-specific T-cell response in HIV-infected individuals at different stages of the disease and during zidovudine therapy was studied using HIV and HIV-envelope derived native and recombinant proteins as antigens. Neither antibody-negative at-risk individuals nor HIV-infected individuals responded to HIV or its envelope-derived proteins, even though they responded to a recall antigen, purified protein derivative of tuberculin (PPD). However, five out of 14 antibody- and antigen-negative sexual partners of known HIV-positive men did respond to HIV, native gp 120 and recombinant envelope and core proteins. Some AIDS-related complex (ARC) and AIDS patients treated with zidovudine also showed a low T-cell response which diminished along with clinical deterioration. A synthetic peptide representing one of the major T-cell epitopes in HIV envelope, frequently recognized by immunized and infected primates, gave only marginal stimulation in man. Our findings suggest that HIV infection in man results in a T-helper cell anergy directed against viral proteins. The response observed in the antibody- and antigen-negative sexual partners and in some of the zidovudine-treated patients implies that at least some epitopes on HIV envelope are immunogenic in man.

Synthesis of phosphorothioate analogues of oligodeoxyribonucleotides and their antiviral activity against human immunodeficiency virus (HIV)

Nuclease-resistant phosphorothioate analogues of oligodeoxynucleotides (oligos) were synthesized by sulfurization of either internucleoside phosphite linkages, in a repetitive manner during chain extension, or internucleoside hydrogen phosphonate linkages, in a single step following chain assembly. These analogues were tested as antiviral agents against human immunodeficiency virus (HIV). In a cytopathic effect inhibition assay using HIV-uninfected susceptible T cells (tetanus toxoid-specific normal T cells) co-cultured with irradiated chronically HIV-infected cells, phosphorothioate oligomers inhibited the cytopathic effect and replication of several isolates of HIV-1 and HIV-2. Thus phosphorothioate analogues of oligos could inhibit cell-to-cell transmission of the virus as well as the infection by cell-free virus particles and also could inhibit a variety of isolates of human retroviruses.

Metabolic pathways for the activation of the antiretroviral agent 2',3'-dideoxyadenosine in human lymphoid cells

The pathways of 2',3'-dideoxyadenosine (ddAdo) metabolism, a selective inhibitor of the replication of human immunodeficiency virus, were investigated with use of the human T-lymphoid cell line CCRF-CEM which is deficient in either deoxycytidine kinase or adenosine kinase activity, or both. At an extracellular concentration of 10 microM, which blocks the cytopathic effect of human immunodeficiency virus in vitro, ddAdo was found to be metabolized to its mono-, di-, and triphosphates and to dideoxyinosine monophosphate (ddIMP). The metabolism of ddAdo in the kinase-deficient mutants was found to be unchanged by comparison with that in parental cells; however, the inhibition of ddAdo deamination to 2',3'-dideoxyinosine (ddIno) by the adenosine deaminase inhibitor, 2'-deoxycoformycin, reduced ddAdo nucleotide formation in deoxycytidine kinase-deficient, adenosine kinase-deficient, and doubly kinase-deficient mutants by 42, 54, and 80%, respectively. Incubation of the CCRF-CEM cells with 20 microM L-alanosine, an amino acid antagonist that inhibits purine biosynthesis at the level of adenylosuccinate/lyase synthetase, resulted in 80% inhibition in the accumulation of ddAdo nucleotides in both wild-type and kinase-deficient mutants and also increased ddIMP accumulation 2- to 3-fold. These findings indicate that ddAdo activation in human T-lymphoblasts can occur by three metabolic pathways: directly, by phosphorylation to ddAMP by the action of either deoxycytidine kinase or adenosine kinase and, indirectly, through deamination to ddIno with consequent phosphorylation of ddIno to ddIMP, and reamination to ddAMP in a reaction catalyzed by adenylosuccinate synthetase/lyase. However, in the absence of 2'-deoxycoformycin, the activation of ddAdo to ddATP in T-lymphoid cells is primarily a function of the indirect route.

Studies on the mechanism of human immunodeficiency virus reverse transcriptase. Steady-state kinetics, processivity, and polynucleotide inhibition

A study of steady-state kinetics of polymerization by purified human immunodeficiency virus DNA polymerase (reverse transcriptase) has been conducted. DNA synthesis was examined using a system of poly(rA) as template, oligo(dT) as primer, and dTTP as nucleotide substrate. The substrate initial velocity patterns point to an ordered mechanism with template-primer adding first. Product inhibition kinetics with either pyrophosphate or phosphonoformate are consistent with this mechanism. The human immunodeficiency virus reverse transcriptase acts processively in this replication system, but exhibits some probability of terminating after each dTMP addition to the nascent chain. The probability of terminating was approximately 20-fold higher after the first dTMP addition than after subsequent additions. With this information on the mode of polymerization, appropriate kinetic models and steady-state rate equations are discussed. In further studies, we found that a heterologous polynucleotide, poly(rC), is a potent inhibitor of the enzyme. The pattern of this inhibition is uncompetitive against template-primer, suggesting that interaction with free enzyme is not the mechanism of the inhibition.

Factors determining the activity of 2',3'-dideoxynucleosides in suppressing human immunodeficiency virus in vitro

Mitsuya and Broder [Proc. Natl. Acad. Sci. USA 83:1911-1915 (1986)] demonstrated that every purine (adenosine, guanosine, and inosine) and pyrimidine (cytidine and thymidine) nucleoside containing the 2',3'-dideoxyribose configuration, when evaluated against human immunodeficiency virus (HIV) in vitro, significantly suppressed both the infectivity and the cytopathic effect of the virus, with 2',3'-dideoxycytidine (ddCyd) being the most potent of the series (total antiviral protection at 0.5-1.0 microM). We have compared three factors likely to be of significance in determining the pharmacological activity of these compounds, i.e., (i) their abilities to influence pool sizes of physiological deoxynucleoside-5'-triphosphates, (ii) their capacity to generate the corresponding 2',3'-dideoxynucleoside-5'-triphosphates, and (iii) the effectiveness of these nucleoside-5'-triphosphates as inhibitors of HIV reverse transcriptase. In MOLT-4 cells (a human T cell line), ddCyd was the compound most efficiently converted to its 5'-triphosphate, whereas 2',3'-dideoxyguanosine and 2',3'-dideoxythymidine were the compounds least efficiently converted, generating levels of their corresponding 5'-triphosphates less than 0.1% of that seen with ddCyd when these nucleosides were compared on an equimolar basis (5 microM). The 3'-azido analogue of 2',3'-dideoxythymidine fell intermediate between these two extremes. As inhibitors of HIV reverse transcriptase, however, all the 5'-triphosphates, with the exception of 2',3'-dideoxyinosine-5'-triphosphate, fell within a narrow range of activity (Ki, 0.10-0.26 microM), affinities some 40-60 fold greater than those of the corresponding physiological 2'-deoxynucleoside-5'-triphosphates. Significant alterations in pool sizes of physiological 2'-deoxynucleoside-5'-triphosphates were not observed at pharmacologically effective drug levels. The relative ability of 2',3'-dideoxynucleosides to generate 5'-triphosphates intracellularly thus correlates much more closely than do the other two factors examined, in capacity to block HIV replication. These studies support the conclusion that, for purposes of design of new compounds of this general class, factors influencing efficiency of nucleotide formation and degradation (e.g., membrane transport mechanisms, affinities for nucleoside kinases and for nucleotide kinases and phosphatases) may be of equal or even greater importance than differences in the relative abilities of the resultant 2',3'-dideoxynucleoside-5'-triphosphates to inhibit the viral reverse transcriptase.

Pharmacokinetics of 2',3'-dideoxycytidine in patients with AIDS and related disorders

The clinical pharmacokinetics of 2',3'-dideoxycytidine (DDC) were determined after oral and intravenous administration in ten patients with AIDS or AIDS-related complex. A high performance liquid chromatography (HPLC) analysis procedure using cation exchange extraction columns was used to measure DDC levels as low as 0.1 microM (21 ng/mL) in plasma and urine. The kinetics of DDC were linear over the dose range of 0.03 to 0.5 mg/kg. Total body clearance was 227 mL/min/m2 and did not change after 6 to 14 days of dosing. The volume of distribution at steady state was 0.54 L/kg. Plasma half-life was 1.2 hours, and bioavailability was 88%. Most (75%) of the parent drug was found unchanged in the urine. As a result, renal function could play a role in dose adjustment of DDC. Comparison is made between the kinetics of DDC and 3'-azido-2',3'-dideoxythymidine (AZT). Similarities are noted in half-life and bioavailability. However, differences are observed for total body clearance, cerebrospinal fluid penetration, volume of distribution, metabolism, and recovery in urine.

Adenallene and cytallene: acyclic-nucleoside analogues that inhibit replication and cytopathic effect of human immunodeficiency virus in vitro

Although several antiretroviral compounds are already known, almost no acyclic nucleoside derivatives lacking an oxacyclopentane have been reported to exert significant inhibition against human immunodeficiency virus type 1 (HIV-1) in vitro. We found two unsaturated acyclic nucleoside derivatives, adenallene [9-(4'-hydroxy-1',2'-butadienyl)adenine] and cytallene [1-(4'-hydroxy-1',2'-butadienyl)cytosine], that protect various CD4+ T-cell lines from the infectivity and cytopathic effect of HIV-1. These compounds inhibit the expression of HIV-1 gag-encoded protein and suppress viral DNA synthesis at concentrations that do not affect functions of normal T cells in vitro. They also inhibit the in vitro infectivity of another human retrovirus, HIV-2. Further in vitro analyses of the anti-HIV-1 activity revealed that the presence of two cumulated double bonds between the 1' and 2' carbons and between the 2' and 3' carbons confers antiretroviral activity in certain pyrimidine or purine derivatives containing a four-carbon chain. We have also found that the 4'-hydroxyl group is critical for the in vitro anti-HIV activity of adenallene. Our observations may provide structure-activity relationships for acyclic nucleoside analogues and may be of value in developing a new class of experimental drugs for the therapy of HIV-related diseases.

1-(2,3-Anhydro-beta-D-lyxofuranosyl)cytosine derivatives as potential inhibitors of the human immunodeficiency virus

We report here that 1-(2,3-anhydro-beta-D-lyxofuranosyl)cytosine has activity against the human immunodeficiency virus in vitro. A number of 2',3'-anhydro-beta-D-lyxofuranosyl nucleoside derivatives were prepared, but none had the activity of the title compound. New efficient procedures were developed for the synthesis of 3'-deoxy-3'-alkyl- and 3'-deoxy-beta-D-arabinosylpyrimidine derivatives.