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PubMed2003

Cellular issues relating to the resistance of HIV to antiretroviral agents.

It has been proposed that the declining efficiency of antiretroviral agents in human immunodeficiency virus (HIV) infection may also depend on cellular factors at their site of action. Two in particular have been proposed: (i) the defective intracellular metabolism of NRTI in target cells and the altered uptake; and (ii) efflux of nucleoside reverse transcriptase inhibitors (NRTI) and protease inhibitors (PI) by cellular transporter molecules. Several studies have shown that: changes in the activities of various purine and pyrimidine biosynthetic enzymes may occur in lymphocytes of HIV-infected patients; HIV-infected patients on prolonged treatment with nucleoside analogues, e.g. zidovudine, show significantly decreased activity of thymidine kinase (TK) compared with untreated HIV-infected people; and NRTI and PI are substrates for the multidrug membrane transporters. With regard to the latter issue, it is known that the ATP-binding cassette transporter proteins such as the P-glycoprotein (MDR), and the newly discovered family of multidrug resistance-associated proteins (MRP1-6), promote the active extracellular efflux of a wide variety of therapeutics drugs and overexpression of some of them lowers intracellular concentration of PI. In the very near future such mechanisms, also called 'cellular drug resistance', might be taken into account, together with other immunological, virological and behavioural factors, to explain the 'drug failure' and/or the variability of response in HIV patients undergoing antiretroviral treatment.

Acquired Immunodeficiency Syndrome↗
PubMed1978

[Molecular biological aspects of oncogenesis caused by RNA tumor viruses (author's transl)].

This article concerns the molecular mechanisms by which RNA tumor viruses, commonly called as oncornaviruses, transfer their genetic information from the genomic RNA (70 s RNA) of the virions to the cellular DNA, leading to neoplastic transformations. The article describes biochemical and serological properties of reverse transcriptase, its role in the life cycle of RNA tumor viruses and broader implications to molecular biology. In this connection, the authors report their own findings on the role of reverse transcriptase in a preleukemic disease, myelofibrosis. This enzyme, discovered in their laboratory, is antigenically closely related to reverse transcriptase of certain primate RNA tumor viruses, and of human leukemic cells. The article also describes the role of reverse transcriptase inhibitors in viral oncogenesis. Of particular interest, is the partially thiolated polycytidylic acid (MPC) which has been developed by the authors, and is known to have a very high binding affinity to the viral reverse transcriptase. The implication of these basic data on the clinical effectivity of MPC in human leukemia, documented in a few cases, has been discussed.

Cell Transformation, Neoplastic↗
PubMed2003

Current concepts of metabolic abnormalities in HIV patients: focus on lipodystrophy.

HIV infection is associated with a number of metabolic abnormalities, including lipodystrophy, a difficult-to-define disorder whose characteristics include hyperlipidemia, insulin resistance, and fat redistribution. Current data suggest that lipodystrophy is caused by multiple factors. Dual-nucleoside reverse transcriptase inhibitor therapy combined with protease inhibitor therapy has been shown to increase the risk of metabolic abnormalities, but susceptibility independent of drug effects has also been shown. While many of the treatments for the broad range of signs and symptoms of lipodystrophy bring about improvements in patient status, none have been demonstrated to bring about a return to baseline levels.

Adipose Tissue↗
PubMed2003

Symptomatic hyperlactatemia in an HIV-positive patient: a case report and discussion.

Prolonged exposure to highly active antiretroviral therapy may be associated with adverse effects related to mitochondrial toxicity, such as hyperlactatemia. We describe a case of symptomatic hyperlactatemia in an HIV-positive patient to illustrate the subtle clinical symptoms and abnormal laboratory test results associated with this condition. We also review the pathophysiology, prevalence, spectrum and management of disturbances in lactate homeostasis induced by nucleoside reverse transcriptase inhibitors.

Adult↗
PubMed2000

Insights into the reasons for discontinuation of the first highly active antiretroviral therapy (HAART) regimen in a cohort of antiretroviral naïve patients. I.CO.N.A. Study Group. Italian Cohort of Antiretroviral-Naïve Patients.

OBJECTIVE: To evaluate the frequency of discontinuation of the first highly active antiretroviral regimen (HAART) and the factors predictive of discontinuing for toxicity and failure in a population-based cohort of HIV-positive individuals in Italy, naïve from antiretrovirals at enrolment. METHODS: The study population consisted of individuals who initiated HAART and had at least one follow-up visit. The primary end-points were discontinuation of any component of HAART for drug toxicity and discontinuation for failure. Survival analyses were performed to identify predictive factors for reaching the two end-points. RESULTS: Eight hundred and sixty-two individuals initiated HAART; in 727 of them (84.3%) this consisted of two nucleoside reverse transcriptase inhibitors (NRTI) and one protease inhibitor (PI). Over a median follow-up of 45 weeks, 312 patients (36.2%) discontinued therapy: 182 (21.1%) discontinued due to toxicity, 44 (5.1%) due to failure. The probability of discontinuing HAART at 1 year was 25.5% [95% confidence interval (CI), 21.9-28.9] due to toxicity and 7.6% (95% CI, 4.9-1 0.3) due to failure. Independent factors associated with discontinuation for toxicity were: gender [relative hazard (RH) = 0.51; 95% CI, 0.32-0.80 for men versus women], type of treatment (indinavir-containing regimens, RH = 1.94; 95% CI, 1.10-3.41 and ritonavir-containing regimens, RH = 3.83; 95% CI, 2.09-7.03 versus hard-gell saquinavir) and time spent on treatment (RH = 0.89; 95% CI, 0.80-0.98 for each additional month). Discontinuation due to failure was independently associated with the most recent HIV-RNA (RH = 3.20; 95% CI, 1.74-5.88 for log10 copies/ml higher), and with type of treatment (indinavir-containing regimens, RH = 0.21; 95% CI, 0.06-0.78 and ritonavir-containing regimens, RH = 0.23; 95% CI, 0.04-1.26 versus hard-gell saquinavir). CONCLUSIONS: If the current HAART regimen caused no toxicity, less than 10% of naïve patients discontinue their first HAART regimen because of failure after 1 year from starting therapy.

Adult↗
PubMedDate not supplied

Comparison of neuropsychiatric side effects in an observational cohort of efavirenz- and protease inhibitor-treated patients.

PURPOSE: To compare the extent of neuropsychiatric disturbances in two similar groups of HIV-infected patients treated for >4 weeks with either efavirenz (EFV) or protease inhibitors (PIs) as part of their antiretroviral therapy (ART). METHOD: A cross-sectional, questionnaire-based cohort of HIV patients who received two nucleoside reverse transcriptase inhibitors combined with either EFV (n = 75) or one or more PIs (n = 77) for at least 4 weeks and were tolerating therapy. The extent of neuropsychiatric disturbances was evaluated based on self-reported symptoms using the psychological evaluation test SCL-90-R. Treatment duration was broken down into quartiles of 30-198 days, >198-365 days, >365-637 days, and >637 days. RESULTS: In the first 6 months of therapy, significantly higher (worse) scores were seen in 39/75 (52%) of the patients receiving EFV. The EFV-treated group had significantly higher scores for somatization, anxiety, obsessive-compulsive behavior, the Global Severity Index, and the Positive Symptom Distress Index, with trends for higher scores in paranoid ideation and depression symptom subcategories. Over the following 6 to 12 months of therapy, the EFV group scored higher than the PI group in somatization, anxiety, obsessive-compulsive behavior, hostility, depression, the Global Severity Index, and the Positive Symptom Total, but the differences were not significant. After 12 months of therapy, the EFV group had significantly lower scores than the PI group for somatization, interpersonal sensitivity, Global Severity Index, and Positive Symptom Total. CONCLUSION: EFV-induced neuropsychiatric symptoms can last up to 200 days after treatment initiation. However, symptom severity appears to decline over time in EFV-treated patients versus patients treated with a PI-based ART.

Adult↗
PubMed2001

Economic analysis of initial HIV treatment. Efavirenz- versus indinavir-containing triple therapy.

OBJECTIVE: To compare the clinical and economic outcomes associated with triple therapy containing efavirenz or indinavir and 2 nucleoside reverse transcriptase inhibitors (NRTIs; zidovudine and lamivudine) in HIV-positive patients. DESIGN AND SETTING: An economic model based on viral load and CD4+ cell counts to predict long term outcomes such as progression to AIDS and AIDS-related death was developed and then analysed using data from a randomised clinical trial. Cost estimates from the healthcare system perspective were based on data from 6 state, all-payor databases, the AIDS Cost and Services Utilisation Study, and other literature. Analyses were carried out for time horizons between 5 and 15 years. PATIENTS AND INTERVENTIONS: HIV-positive patients with limited exposure to NRTIs. Initial regimens consisted of efavirenz or indinavir, each combined with 2 NRTIs. A maximum of 2 switches to other regimens was permitted. MAIN OUTCOME MEASURES AND RESULTS: The efavirenz-containing triple therapy regimen was predicted to prolong survival at a savings of up to 10,923 US dollars (1998 values) relative to initial therapy with the indinavir-containing regimen. Patients who receive efavirenz are expected to have 11% greater survival at 5 years and fewer treatment failures (28 vs 52%, at 2 years). Overall, the economic and health benefits predicted for the efavirenz-containing regimen were robust to reasonable variation in key parameters. CONCLUSIONS: The superior clinical trial outcomes for efavirenz-containing regimens should translate into substantial economic and health benefits.

Acquired Immunodeficiency Syndrome↗
PubMed2004

The impact of initial highly active antiretroviral therapy on future treatment sequences in HIV infection.

OBJECTIVES: To determine whether the initial use of non-nucleoside reverse transcriptase inhibitors (NNRTI) or protease inhibitors (PI) differentially influences subsequent HIV therapy. DESIGN: A cohort study using a prospective clinical database in a university-based HIV clinic. SUBJECTS: A total of 440 HIV-seropositive patients, naive or nucleoside experienced, initiating therapy with either an NNRTI or PI between January 1998 and July 2003 and followed to December 2003. MAIN OUTCOME MEASURES: Time until stopping the first regimen and until exposure to all antiretroviral classes (excluding tenofovir and enfuvirtide) according to the type of initial regimen. RESULTS: A total of 291 subjects initiated HAART with PI and 149 with NNRTI; median follow-up 3.1 and 2.3 years, respectively. Subjects starting NNRTI remained on their initial regimens longer (median time to change 2.1 versus 1.6 years; log rank P = 0.03). Overall, subjects initiating NNRTI-based regimens were less likely to alter their therapy. Previous nucleoside exposure was an important predictor of treatment modification. Subjects initiating NNRTI-based HAART were also less likely to experience virological failure than those initiating PI-based HAART. Individuals starting with NNRTI were exposed to fewer regimens (15 versus 25% received three or fewer regimens), and showed a trend towards lower rates of three-class exposure (7 versus 12%). CONCLUSION: There is a high rate of treatment modification among patients initiating HAART. The initial use of NNRTI-based HAART was associated with more durable treatment and lower rates of virological failure, which may translate into a reduced need for multiple salvage therapies.

Adolescent↗
PubMed1999

Advances in the medical management of patients with HIV-1 infection: an overview.

New guidelines for the management of patients with HIV-1 infection emphasize early aggressive treatment using multi-drug combination regimens. Accurate assessment of the effectiveness of these treatments and their potential (small as it now seems) to eradicate HIV-1 infection requires testing for viral levels in the blood, and in other compartments that may serve as long-term viral reservoirs, using the most sensitive assays. At present, most of our information regarding triple-drug combination therapies (usually two nucleosides and a protease inhibitor or a non-nucleoside reverse transcriptase inhibitor) has come from the assessment of viral levels in blood. Available results strongly support the virologic superiority of such treatments over monotherapy and two-drug combinations. There are important questions that remain to be answered regarding these highly effective therapies. Questions regarding the durability of these treatments in preventing the evolution of drug resistance can be addressed by using sensitive reverse transcription/polymerase chain reaction assays to assess treatment response. Others, such as how best to treat patients who have failed potent drug therapy, await results from new, large-scale, clinical trials. An important concern with respect to newer antiretroviral therapies is their complexity and thus the increased risk for non-compliance and resultant viral resistance. In addition, longer-term side-effects are increasingly recognized. Programs that enhance compliance with these treatments will increase the probability that they will provide durable suppression of viral replication and arrest the clinical progression of HIV disease.

Disease Management↗
PubMedDate not supplied

First-line nevirapine in combination with nucleoside analogues compared with nevirapine added to a salvage HAART.

BACKGROUND: Although non-nucleoside reverse transcriptase inhibitors are presently recommended as a part of an initial triple antiretroviral regimen, or as an adjunct to a rescue therapy in patients with poor response to highly active antiretroviral therapy (HAART), no controlled data are available comparing these two different strategies of administration of nevirapine. PATIENTS AND METHODS: Laboratorys data of 59 consecutive patients were prospectively followed up to compare the virologic and immunologic response to nevirapine in those starting a triple therapy combination (group A), versus subjects with prior HAART failure (group B). Laboratory data of 59 consecutive were prospectively followed up. RESULTS: In group A (33 cases), nevirapine was started with two nucleoside analogues in six subjects naïve to antiretrovirals, while in 27 cases it was added to a novel combination of nucleoside analogues. In group B (26 cases), highly experienced patients failing a protease inhibitor-containing HAART, were given nevirapine concurrently with nelfinavir in 19 cases, and with two protease inhibitors in seven patients. Compared with group B patients, subjects belonging to group A showed a more favorable 9-month virologic response (-2.2 Log10 after 9 months with two thirds of patients attaining viral suppression, versus -0.8 Log10 in group A, with only 34.6% of patients with undetectable viremia) (p < 0.001). A greater rise of mean absolute CD4+ lymphocyte count was also observed in group A as opposed to group B (p < 0.001). No significant difference was found comparing the laboratory response of antiretroviral-naïve versus -experienced patients, as well as of participants who changed one versus both nucleoside analogues at the time of nevirapine adjunct in group A, and between patients who switched to nelfinavir versus those treated with two protease inhibitors in group B. CONCLUSION: Nevirapine used as a component of an initial triple anti-HIV regimen seems to ensure a significantly more favorable virologic and immunologic outcome, compared with nevirapine adjunct to a salvage regimen carried out after HAART failure. Controlled data are needed, to better define the role of nevirapine in different therapeutic situations.

Adult↗
PubMed2001

Comparison of P-triglyceride levels among patients with human immunodeficiency virus on randomized treatment with ritonavir, indinavir or ritonavir/saquinavir.

This study compared the alterations in p-triglyceride (PT) in 111 protease inhibitor (PI)-naive patients on randomized treatment with either indinavir (800 mg 3 times daily), ritonavir (600 mg twice daily) or ritonavir/saquinavir (400 mg each twice daily) and 2 nucleoside reverse transcriptase inhibitors (NRTIs). PT (non-fasting) was measured at regular intervals until week 48. PT levels were evaluated in relation to PI regime, CD4 cell count and prior NRTI experience. The effect on PT levels of changing PI regime was analysed. For 24 patients fasting and non-fasting PT values were correlated. In the ritonavir-containing arms PT levels increased significantly (median PT at baseline: 1.80 mmol/l; week 36: 2.3 mmol/l; p < 0.001). In the indinavir arm no significant rise in PT levels was observed. Comparing the PI arms at week 48 showed significantly higher levels of PT in the ritonavir-containing arms than in the indinavir arm (p < 0.001). There was a high correlation between fasting and non-fasting PT values (p < 0.001, p = 0.88). A significant decline in PT values when changing PI treatment was observed (n = 13, p = 0.016). Ritonavir-containing regimens caused a rapid and sustained elevation of PT values, while indinavir did not significantly affect PT levels.

Anti-HIV Agents↗
PubMed2005

The 48-week efficacy of once-daily saquinavir/ritonavir in patients with undetectable viral load after 3 years of antiretroviral therapy.

OBJECTIVES: To evaluate the efficacy and safety of once-daily saquinavir-soft-gel-capsules/ritonavir (SQV-SGC/RTV) 1600 mg/100 mg plus dual nucleoside reverse transcriptase inhibitors (NRTIs) in HIV-infected patients with plasma viral load (pVL) <50 HIV-1 RNA copies/mL following 3 years of antiretroviral therapy. METHODS: A total of 69 patients with pVL <50 copies/mL after 162 weeks of antiretroviral treatment started SQV-SGC/RTV 1600 mg/100 mg once-daily while continuing dual NRTIs. Previous treatment consisted of 66 weeks of treatment with a half/full dose of zidovudine (ZDV)/zalcitabine (ddC), followed by 2 years of SQV-SGC twice a day (bid) plus ZDV/lamivudine (3TC) or didanosine (ddI)/stavudine (d4T). Efficacy (pVL), safety and immunological changes (CD4 cell counts) were evaluated after 48 weeks in this open-label, single-arm prospective study. RESULTS: SQV-SGC/RTV once-daily was well tolerated. No patient changed regimens or was lost to follow-up. After 48 weeks, 63 of 69 patients (91%) had pVL <50 copies/mL (five of the six remaining patients had pVL <400 copies/mL, and one patient had an unexplained rise to 39 500 copies/mL, which decreased to <50 copies/mL 12 weeks later). Median CD4 count increased from 534 cells/muL at the start of the SQV-SGC/RTV once-daily treatment to 664 cells/muL (P<0.001). Compared to the preceding 48 weeks on bid SQV-SGC, the CD4 cell count improved significantly on once-daily SQV-SGC/RTV (P<0.001). CONCLUSIONS: These data support the use of SQV-SGC/RTV 1600 mg/100 mg once-daily with two NRTIs as a convenient, safe and cost-saving regimen to maintain viral suppression and CD4 counts for 48 weeks in this preselected cohort on highly active antiretroviral therapy (HAART) with pVL <50 copies/mL. The CD4 count rise may be a result of continued immune reconstitution in patients with well-controlled infection.

Adult↗
PubMed2006

The design and synthesis of 9-phenylcyclohepta[d]pyrimidine-2,4-dione derivatives as potent non-nucleoside inhibitors of HIV reverse transcriptase.

Novel compounds, which can be considered as conformationally restricted analogues of MKC-442, have been synthesized and tested as inhibitors of the reverse transcriptase of human immunodeficiency virus type-1 (HIV-1). Reaction of urea with a beta-ketoester furnished 6,7,8,9-tetrahydro-9-phenyl-1H-cyclohepta[d]pyrimidine-2,4-(3H,5H)-dione (6a) and 6,7,8,9-tetrahydro-9-p-tolyl-1H-cyclohepta[d]pyrimidine-2,4-(3H,5H)-dione (6b) which were then alkylated at the N-1 position with chloromethyl ether, allyl bromide and benzyl bromide to afford the target compounds 7a-b, 8a-b, 9 and 10, respectively. The seven-membered, annelated compounds have a relatively rigid structures and can lock the orientation of the aromatic ring. Chemical modification at N-1 of the pyrinidine ring and the 9-phenyl ring was attempted, with the aim of improving the antiretroviral activity. In particular, replacement of the aliphatic group with the phenyl moiety at the terminus of N-1 side chain can enhance the activity. The most active compounds showed activity in the low micromolar range with IC50 values comparable to that of nevirapine. The biological activity results are in accordance with the docking results.

Anti-HIV Agents↗
PubMed2001

Hepatitis B virus infection: resistance to antiviral agents.

Chronic hepatitis B virus (HBV) infection imposes an enormous public health burden. In patients with chronic hepatitis and high levels of viral replication, inhibitors of the virus polymerase can reduce serum titre and favourably affect the inflammatory process in the liver. Lamivudine, a reverse transcriptase inhibitor, is the first nucleoside analogue to be licensed for treatment of chronic HBV infection. Treatment effects a rapid and profound decrease of serum virus titre, with attendant clinical benefit. Unfortunately drug-resistant species may emerge after 6 months of suppressive therapy. Lamivudine-resistant species have specific amino acid substitutions in the HBV-encoded polymerase. Emergence of these species is frequently associated with loss of clinical benefit. Published data suggest that lamivudine-resistant species exhibit cross-resistance to famciclovir, thereby limiting the potential use of famciclovir with lamivudine as combination therapy. Adefovir is under clinical evaluation for treatment of wild-type and lamivudine-resistant HBV. Preliminary data suggest that adefovir achieves potent inhibition of both species. Studies of drug resistance have followed hot-on-the-heels of the development of potent antiviral therapy for chronic HBV.

Antiviral Agents↗
PubMed2000

Lactic acidosis secondary to nucleoside analogue antiretroviral therapy.

A 53-year-old woman with newly diagnosed HIV infection was treated with the nucleoside analogue antiretroviral agents lamivudine and stavudine and the protease inhibitor indinavir. An illness characterized by severe lethargy, persistent nausea and vomiting, lactic acidosis, hyperglycemia, and microvesicular hepatic steatosis developed. Her symptoms improved gradually after withdrawal of the antiretroviral agents. The illness can be explained by mitochondrial dysfunction caused by inhibition of mitochondrial DNA (mtDNA) polymerase by the nucleoside analogues. The patient was successfully treated with nonnucleoside reverse transcriptase inhibitors, which lack affinity for mtDNA polymerase.

Acidosis, Lactic↗
PubMed2006

Influence of tenofovir, nevirapine and efavirenz on ritonavir-boosted atazanavir pharmacokinetics in HIV-infected patients.

OBJECTIVE: The influence of nevirapine, efavirenz and tenofovir co-administration on ritonavir-boosted atazanavir pharmacokinetics was investigated in HIV (human immunodeficiency virus)-infected patients. METHODS: A population pharmacokinetic analysis was performed in the context of therapeutic drug monitoring (87 patients, 121 samples). RESULTS: A significant increase of atazanavir clearance (Cl/F) was found when either tenofovir (group B), efavirenz (group C), or nevirapine (group D) were co administered with atazanavir/ritonavir in comparison with patients treated with atazanavir/ritonavir and nucleoside reverse transcriptase inhibitors (group A): 6.24+/-0.36 l h(-1) (group A) versus 7.42+/-0.25 l h(-1) (group B) versus 9.60+/-0.27 l h(-1) (group C) versus 17.53+/-0.57 l h(-1) (group D) (P<0.001). However, the decrease of the mean trough plasma concentration of atazanavir was significant only in group D: 1.02+/-0.86 mg/l (group A) versus 0.21+/-013 mg/l (group D) (P<0.001). CONCLUSION: The increase in atazanavir clearance when it is used in combination with nevirapine, efavirenz and/or tenofovir suggests that therapeutic drug monitoring of atazanavir should be performed in such circumstances.

Adenine↗
PubMed1994

Mutational analysis of residue 190 of human immunodeficiency virus type 1 reverse transcriptase.

S-2720 and other members of the quinoline/quinoxaline class of HIV-1-specific nonnucleoside reverse transcriptase inhibitors (NNRTIs) select for a glycine to glutamate substitution at residue 190 (Gly 190 Glu) of the reverse transcriptase (RT), when drug-resistant viruses are generated in cell culture. This mutation has not been described to appear upon selection for resistant viral variants using derivatives of any other class of NNRTIs. Notably, the RNA-dependent DNA polymerase activity of the Gly 190 Glu mutant enzyme is drastically diminished with respect to the wild-type RT. We describe here the effects of other amino acid substitutions at position 190 of the RT that were introduced by using site-directed mutagenesis. Polymerase activities and sensitivities to inhibition by a number of NNRTIs were determined for the different RT mutants. In general, an inverse correlation was found between the enzymatic activity and increasing length of the side chain, whereas the size of the residue and the level of resistance to NNRTIs appeared to be positively related. Double mutants, which contain the Gly 190 Glu mutation together with substitutions that confer resistance to other RT inhibitors, were all shown to possess severely diminished polymerase activity.

Antiviral Agents↗
PubMed2004

Novel mechanism of inhibition of HIV-1 reverse transcriptase by a new non-nucleoside analog, KM-1.

2-Naphthalenesulfonic acid (4-hydroxy-7-[[[[5-hydroxy-6-[(4 cinnamylphenyl)azo]-7-sulfo-2-naphthalenyl]amino]-carbonyl]amino]-3-[(4-cinnamylphenyl)]azo (KM-1)) is a novel non-nucleoside reverse transcriptase inhibitor (NNRTI) that was designed to bind at an unconventional site on human immunodeficiency virus type 1 reverse transcriptase (RT) (Skillman, A. G., Maurer, K. W., Roe, D. C., Stauber, M. J., Eargle, D., Ewing, T. J., Muscate, A., Davioud-Charvet, E., Medaglia, M. V., Fisher, R. J., Arnold, E., Gao, H. Q., Buckheit, R., Boyer, P. L., Hughes, S. H., Kuntz, I. D., and Kenyon, G. L. (2002) Bioorg. Chem. 30, 443-458). We have investigated the mechanism by which KM-1 inhibits wild-type human immunodeficiency virus type 1 RT by using pre-steady state kinetic methods to examine the effect of KM-1 on the parameters governing the single nucleotide incorporation catalyzed by RT. Analysis of the pre-steady-state burst phase of dATP incorporation showed that KM-1 decreased the amplitude of the reaction as previously shown for other NNRTIs, because of the slow equilibration of the inhibitor with RT. In the ternary enzyme-DNA-KM-1 complex (E-DNA-I), incorporation of the next nucleotide onto the primer is blocked. However, unlike conventional NNRTIs, the inhibitory effect was caused primarily by weakening the DNA binding affinity and displacing DNA from the enzyme. Wild-type RT binds a 25/45-mer DNA duplex with an apparent K(d) of 3 nm, which was increased to 400 nm upon saturation with KM-1. Likewise, the apparent K(d) for KM-1 binding to RT increased at higher DNA concentrations. We therefore conclude that KM-1 represents a new class of inhibitor distinct from nevirapine and related NNRTIs. KM-1 can bind to RT in both the absence and presence of DNA but weakens the affinity for DNA 140-fold so that it favors DNA dissociation. The data suggest that KM-1 distorts RT conformation and misaligns DNA at the active site.

Adenosine Triphosphate↗