Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.7.49 (reverse transcriptase)
31,746 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DuPont Merck and Gilead Sciences are finalizing a program to make their new, experimental anti-HIV drugs available free to people who are not benefiting from other treatments. Enrollment information is included. The program includes the drugs DMP-266 and adefovir dipivoxil, and is a model for how drug companies can work together effectively to make experimental treatments available through expanded access programs. Initially, DMP-266 enrollment will be limited to 2,000 people with CD4 counts below 50 who are failing their current regimen. Adefovir will be available to 1,000 patients with CD4 counts below 50 and viral loads above 30,000. DMP-266 is a non-nucleoside reverse transcriptase inhibitor that is only taken once a day and shows great promise when used in combination with indinavir. Adefovir belongs to the nucleotide analog reverse transcriptase inhibitor class, and shows a unique resistance profile. It is also taken only once a day.
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PMID:DMP-266 and adefovir dipivoxil: 2 new AIDS drugs available to patients without treatment options. 1136 9

Adefovir dipivoxil (Preveon), a nucleotide analog and a prodrug of PMEA, has been approved for a limited expanded access program for patients who have failed approved treatments. Earlier results from phase I/II trials reveal Preveon has modest anti-HIV activity. Preveon is active against virus that has developed resistance to AZT, 3TC, and other approved nucleoside analogs. To be eligible, patients must be at least 13 years old, failed at least two nucleoside analog reverse transcriptase inhibitors and one protease inhibitor, and within the last 2 months have had a CD4 count of 50 or less and a viral load of at least 30,000 by PCR or at least 15,000 by bDNA. The program will supply only Preveon and the L-carnitine. The AIDS community has expressed concerns about the drug's potential kidney toxicity with long-term use, a condition that becomes clinically evident usually after the first 4 months, possibly leading physicians into complacency in performing regular laboratory tests after that time. The study requires monthly urine testing, including serum creatinine, urine protein, and urine glucose. Another concern is the study's CD4 and viral load restrictions; AIDS advocates believe the restrictions do not allow physicians flexibility in their drug treatment decision-making.
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PMID:Adefovir dipivoxil (Preveon) expanded access begins. 1136 18

Sustiva (DMP 266 or efavirenz) has been available on an expanded access program since October 1. Sustiva is a non-nucleoside reverse transcriptase inhibitor, has fewer side effects than other drugs of its class, and is taken once a day at bedtime. Criteria for the program are T4 counts under 50 in patients whose current therapy is not working. Adefovir dipivoxil (bis-POM PMEA or Preveon) is a nucleotide analog that is also available through an expanded access program. Adefovir's properties make it less vulnerable to resistance. It is not as potent as other drugs of the same class; however, its effect seems to last longer. It is also effective against some herpesviruses and hepatitis B. Contact information is provided for both programs.
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PMID:Expanded access programs. 1136 31

A table charts the various nomenclature of drugs used to treat HIV and AIDS. The common name, generic name, and brand name are given for several categories including NARTIs (NRTIs, "Nukes", Nucleoside analogue reverse transcriptase inhibitors), NNRTIs (Non-nucleoside reverse transcriptase inhibitors), and PIs (Protease Inhibitors). Other drugs listed are Hydroxyurea (anti-cancer drug) and preveon (Adefovir (Nucleotide)).
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PMID:What's in a name? 1136 57

Attendees at the Second International Workshop on Salvage Therapy heard little to make them optimistic about the immediate future of salvage therapy. Treatment veterans with only a few virologic failures stand a slim chance of ongoing viral control. Current salvage treatment, even combination therapy, only pushes viral loads to below 500 copies in 20 to 40 percent of patients, and those patients who have had viral loads suppressed to below 20 copies/mL stand the best chance of having a sustained response to the treatment. Results of several studies are reviewed. Adefovir, which had been considered an option, has performed poorly in trials. One table shows the effects of nonnucleoside reverse transcriptase inhibitor/protease inhibitor (NNRTI/PI) salvage therapy in the NNRTI-naive patient. Another table presents figures to show that salvage success correlates significantly with lower viral loads prior to treatment. A third table shows the "megasalvage" track record, while a fourth presents a proposal for a rapid-assessment salvage study. The concept of using drug holidays as a means to force the immune system to begin fighting HIV on its own remains controversial.
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PMID:Salvage solitaire (or, HAART takes a holiday). 1136 32

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.
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PMID:Hepatitis B virus infection: resistance to antiviral agents. 1139 60

An antisense oligodeoxynucleotide against the human immunodeficiency virus type 1 (HIV-1) Rev response element, a ribozyme complementary to the HIV-1 5'-LTR, and the reverse transcriptase inhibitors 9-(2-phosphonylmethoxyethyl) adenine (PMEA) and (R)-9-(2-phosphonylmethoxypropyl)-adenine (PMPA) inhibited virus replication in monocyte-derived macrophages more effectively when delivered in pH-sensitive liposomes compared to the free drugs.
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PMID:Enhanced inhibition of HIV-1 replication in macrophages by antisense oligonucleotides, ribozymes and acyclic nucleoside phosphonate analogs delivered in pH-sensitive liposomes. 1156 68

To design combination strategies for chronic hepatitis B therapy, we evaluated in vitro the inhibitory activity of 4 nucleoside analogs, (-)FTC, L-FMAU, DXG, and DAPD, in comparison with lamivudine (3TC) and PMEA. In a cell-free assay for the expression of wild-type duck hepatitis B virus (DHBV) reverse transcriptase, DAPD-TP was found to be the most active on viral minus strand DNA synthesis, including the priming reaction, followed by 3TC-TP, (-)FTC-TP, and DXG-TP, whereas L-FMAU-TP was a weak inhibitor. In cell culture experiments, important differences in drug concentration allowing a 50% inhibition of viral replication or polymerase activity (IC50s) were observed depending on the cell type used, showing that antiviral effect of nucleoside analogs may depend on their intracellular metabolism. IC50s obtained for wild-type DHBV replication in primary duck hepatocytes were much lower than with DHBV transfected LMH cells. IC50s were also significantly lower in the 2.2.1.5 and HepG2 cells compared with HBV transfected HuH7 cells. Moreover, L-FMAU inhibited preferentially HBV plus strand DNA synthesis in these cell lines. The antiviral effect of these inhibitors was also evaluated against 3TC-resistant mutants of the DHBV and HBV polymerases. These mutants were found to be cross resistant to (-)FTC. By contrast, the double DHBV polymerase mutant was sensitive to DXG-TP and DAPD-TP. Moreover, both purine analogs remained active against DHBV and HBV 3TC-resistant mutants in transfected LMH and HepG2 cells, respectively. In conclusion, the unique mechanism of action of these new inhibitors warrants further evaluation in experimental models to determine their capacity to delay or prevent the selection of drug resistant mutants.
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PMID:Inhibitory activity of dioxolane purine analogs on wild-type and lamivudine-resistant mutants of hepadnaviruses. 1219 65

Because prevention of heterosexual HIV transmission is not always possible, it is important to develop effective strategies of postexposure prophylaxis (PEP). Since in vivo comparison of drug potency is difficult, we developed an in vitro model with cells resembling primary targets during sexual transmission: monocyte-derived dendritic cells (MO-DCs), Langerhans cells (MO-LCs), and resting autologous CD4(+) T cells. Nucleoside and nonnucleoside reverse transcriptase inhibitors (NRTIs and NNRTIs, respectively) were evaluated for their antiviral activity, when added immediately after infection or at a later time point. In parallel, their immune-suppressive effect was examined by measuring inhibition of mixed MO-DC/allogeneic CD4(+) T cell cultures. Most RTIs potently inhibited HIV replication, even if added 24 hr after infection (representing PEP). The sensitivity to antiretroviral drugs was similar in HIV-infected MO-DCs and MO-LCs, but decreased in cocultures with resting autologous CD4(+) T cells. The NNRTIs efavirenz and UC-781 as well as the NRTIs AZT, 3TC, and d4T showed a similar high potency in MO-DC plus autologous CD4(+) T cell cocultures as compared with CEM T cells, whereas their activity in phytohemagglutinin/interleukin 2 (PHA/IL-2)-activated CD4(+) T cells was lower. The dideoxynucleoside RTI abacavir as well as the phosphonates (R)-PMPA and PMEA were more active in infected MO-DCs as compared with either CEM T cells or PHA/IL-2 activated CD4(+) T cells. Infection in cocultures of MO-DCs and autologous CD4(+) T cells could be aborted in a proportion of the cultures, with high concentrations of PMEA and/or efavirenz, but not with AZT. Suppressive activity in mixed leukocyte cultures was observed only at very high concentrations of RTI. Our data suggest that cocultures of MO-DCs and autologous CD4(+) T cells can be used as a possible in vitro model to explore protocols for PEP after sexual HIV transmission.
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PMID:Activity of reverse transcriptase inhibitors in monocyte-derived dendritic cells: a possible in vitro model for postexposure prophylaxis of sexual HIV transmission. 1239 48

The pathogenesis of human immunodeficiency virus (HIV)-associated dementia has been linked to microglial responses after infection. We have recently confirmed expression of several ATP-dependent efflux transporters in microglia, namely, multidrug resistance protein 1 (MRP1) and P-glycoprotein (P-gp). In the present study, we investigated whether cultured rat microglia express two additional MRP family members, rMRP4 and rMRP5. Using reverse transcriptase-polymerase chain reaction, rMRP4 and rMRP5 mRNA was detected in primary cultures of microglia and in a rat microglia cell line, MLS-9. Western blot analysis further confirmed protein expression of the two MRP isoforms in MLS-9 cells. Bis(pivaloxymethyl)-9-(2-phosphonylmethoxyethyl)adenine [bis(POM)PMEA], a lipophilic ester prodrug of the well characterized MRP4 and 5 substrate 9-(2-phosphonylmethoxyethyl)adenine (PMEA), was chosen to examine transport characteristics in MLS-9. Using thin layer chromatography, we verified that more than 90% of radioactivity recovered in MLS-9 loaded with 1 microM [(3)H]bis(POM)PMEA for 1 h under ATP-depleting conditions was converted to PMEA. Efflux of PMEA by MLS-9 cell monolayers was ATP-dependent, glutathione-independent, and significantly inhibited by several MRP inhibitors (i.e., sulfinpyrazone, genistein, indomethacin, and probenecid) as well as the antiretroviral drug azidothymidine-monophosphate. Similar results were not observed in MRP1- or P-gp-overexpressing cell lines, suggesting that PMEA is not a substrate for either P-gp or MRP1. These studies provide further evidence that microglia express multiple subfamilies of ATP-binding cassette transporters (i.e., P-gp, MRP1, MRP4, and MRP5) that could restrict permeation of several different classes of antiretroviral drugs in a brain cellular target of HIV-1 infection.
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PMID:Multidrug resistance protein (MRP) 4- and MRP 5-mediated efflux of 9-(2-phosphonylmethoxyethyl)adenine by microglia. 1476 2


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