Reverse transcriptase virus

The viruses responsible for AIDS are human immunodeficiency virus 1 and 2 (HIV 1 and HIV 2) Both are retroviruses, meaning that their genetic material is RNA rather than DNA HI Vs require a host cell to reproduce and the hosts m humans are the T4 lymphocytes which are the cells primarily responsible for inducing the immune system to respond when provoked The HIV penetrates the cell wall of a T4 lymphocyte and deposits both its RNA and an enzyme called reverse transcriptase inside There the reverse transcriptase catalyzes the formation of a DNA strand that is complementary to the viral RNA The transcribed DNA then serves as the template from which the host lymphocyte produces copies of the virus which then leave the host to infect other T4 cells In the course of HIV reproduction the ability of the T4 lymphocyte to reproduce Itself IS compromised As the number of T4 cells decrease so does the body s ability to combat infections... 

Reverse transcriptase inhibitors are also used against certain viruses which although they are not retroviruses do require re verse transcriptase to repro duce The virus that causes heptatitis B is an example... 

Reverse transcriptase (from avian or murine RNA tumour viruses) [9068-38-6] [EC 2.7.7.49]. Purified by solubilising the virus with non-ionic detergent. Lysed virions were adsorbed on DEAE-cellulose or DEAE-Sephadex columns and the enzyme eluted with a salt gradient, then chromatographed on a phosphocellulose column and enzyme activity eluted in a salt gradient. Purified from other viral proteins by affinity chromatography on a pyran-Sepharose column. [Verna Biochim Biophys Acta 473 1 7977 Smith Methods Enzymol 65 560 1980 see commercial catalogues for other transcriptases.]... 

Other nucleosides such as 2, 3 -dideoxyinosine (ddl) also block the action of reverse transcriptase and are often combined with AZT in drug cocktails. Using a mixture of drugs makes it more difficult for a virus to develop resistance than using a single drug. 

The most recent advance in treating HIV infections has been to simultaneously attack the virus on a second front using a protease inhibitor. Recall from Section 27.10 that proteases are enzymes that catalyze the hydrolysis of proteins at specific points. When HIV uses a cell s DNA to synthesize its own proteins, the initial product is a long polypeptide that contains several different proteins joined together. To be useful, the individual proteins must be separated from the aggregate by protease-catalyzed hydrolysis of peptide bonds. Protease inhibitors prevent this hydrolysis and, in combination with reverse transcriptase inhibitors, slow the reproduction of HIV. Dramatic reductions in the viral load in HIV-infected patients have been achieved with this approach. 

In the realm of natural product synthesis, Kepler and Rehder utilized the K-R reaction to synthesize ( )-calanolide A (56), a potent non-nucleosidal human irmnunodeficiency virus (HIV-1) specific reverse transcriptase inhibitor. Propiophenone 57 was allowed to react with acetic anhydride in the presence of sodium acetate to afford benzopyranone 58 in 56% yield subsequent deacetylation of 58 gave 59. Flavone 59 was then transformed to ( ) calanolide A (56) over several steps. 

Mansky LM, Temin HM (1995) Lower in vivo mutation rate of human immunodeficiency virus type 1 than that predicted from the fidelity of purified reverse transcriptase, J Virol 69 5087-5094... 

Hurwitz SJ, Schinazi RF (2002) Development of a pharmacodynamic model for HIV treatment with nucleoside reverse transcriptase and protease inhibitors. Antiviral Res 56 115-127 Hurwitz SJ, Tennant BC, Korba BE, Gerin JL, Schinazi RF (1998) Pharmacodynamics of (—)-beta-2, 3 -dideoxy-3 -thiacytidine in chronically virus-infected woodchucks compared to its pharmacodynamics in humans, Antimicrob Agents Chemother 42 2804-2809 Hurwitz SJ, Otto MJ, Schinazi RF (2005) Comparative pharmacokinetics of Racivir, (+/-)-beta-2, 3 -dideoxy-5-fluoro-3 -thiacytidine in rats, rabbits, dogs, monkeys and HIV-infected humans, Antivir Chem Chemother 16 117-127... 

The first lead compounds for non-nucleoside reverse transcriptase (RT) inhibitors (NNRTl) were discovered about 15 years ago (Pauwels et al. 1990 Merluzzi et al. 1990 Goldman et al. 1991 De Clercq 1993 Riibsamen-Waigmann et al. 1997). Since then they have become an important ingredient of the dmg combination schemes that are currently used in the treatment of human immunodeficiency virus type 1 (HlV-1) infections. Starting from the HEPT and TIBO derivatives, numerous classes of compounds have been described as NNRTIs. Four compounds (nevirapine, delavirdine, efavirenz and etravirine) have so far been approved for clinical use and several others are the subject of clinical trials (Balzarini 2004 Stellbrink 2007). 

De Clercq E (1993) HlV-l-spedfic RT inhibitors highly selective inhibitors of human immunodeficiency virus type 1 that are specifically targeted at the viral reverse transcriptase. Med Res Rev 13 229-258... 

Gibson W (1996) Structure and assembly of the virion. Intervirology 39 389 00 Goldman ME, Nunberg JH, O Brien JA, Quintero JC, Schleif WA, Freund KF, Gaul SL, Saari WS, Wai IS, Hoffman JM et al. (1991) Pyridinone derivatives specific human immunodeficiency virus type 1 reverse transcriptase inhibitors with antiviral activity. Proc Natl Acad Sci USA... 

Burke DH, Scales L, Andrews K, Gold L (1996) Bent pseudoknots and novel RNA inhibitors of type 1 human immunodeficiency virus (HlV-1) reverse transcriptase. J Mol Biol 264 650-666 Burrer R, Neuman BW, Ting JP, Stein DA, Moulton HM, Iversen PL, Kuhn P, Buchmeier MJ (2007) Antiviral effects of antisense morphoUno oligomers in murine coronavirus infection models, J Virol 81 5637-5648... 

The hepatitis B virus (HBV) genome is one of the smallest viral genomes (approximately 3,200 base pairs) and encodes only one viral enzyme, namely the HBV reverse transcriptase (RT). Like the HIV RT, the HBV RT is an error-prone enzyme lacking proofreading activity. In combination with a high virus production, this results in an HBV quasispecies. 

Hertogs K, de Bethune MP, Miller V, Ivens T, Schel P, Van Cauwenberge A, Van Den Eynde C, Van Gerwen V, Azijn H, Van Houtte M, Peelers F, Staszewski S, Conant M, Bloor S, Kemp S, Larder B, Pauwels R (1998) A rapid method for simultaneous detection of phenotypic resistance to inhibitors of protease and reverse transcriptase in recombinant human immunodeficiency virus type 1 isolates from patients treated with antiretroviral drugs. Antimicrob Agents Chemother 42 269-276... 

Kleim JP, ROsner M, Winkler I, Paessens A, Kirsch R, Hsiou Y, Arnolds E, Riess G (1996) Selective pressure of a quinoxaline nonnucleoside inhibitor of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) on HIV-1 replication results in the emergence of nucleoside RT-inhibitor-specific (RT Leu-74 -> Val or He and Val-75 - > Leu or He) HIV-1 mutants, Proc Natl Acad Sci USA 93 34-38... 

Najera I, Richman DD, Olivares I, Rojas JM, Peinado MA, Perucho M, Najera R, Lopez GaHndez C (1994) Natural occurrence of drug resistance mutations in the reverse transcriptase of human immunodeficiency virus type 1 isolates. AIDS Res Hum Retroviruses 10 1479-1488 Nijhuis M, Boucher CAB, Schipper R Leitner T, Schuurman R, Albert J (1998) Stochastic processes strongly influence HIV-1 evolution during suboptimal protease inhibitor therapy. Proc Natl Acad Sci USA 95 14441-14446... 

Warner N, Locamini S, Kuiper M, Bartholomeusz A, Ayres A, Yuen L, Shaw T (2007) The L80I substitution in the reverse transcriptase domain of the hepatitis B virus polymerase is associated with lamivudine resistance and enhanced viral replication in vitro, Antimicrob Agents Chemother 51 2285-2292... 

Autoradiography The detection of radioactive molecules (eg, DNA, RNA, protein) by visualization of their effects on photographic film. Bacteriophage A virus that infects a bacterium. Blunt-ended DNA Two strands of a DNA duplex having ends that are flush with each other. cDNA A single-stranded DNA molecule that is complementary to an mRNA molecule and is synthesized from it by the action of reverse transcriptase. 

Schweinsburg BC, Taylor MJ, Alhassoon OM, Gonzalez R, Brown GG, Ellis RJ, Letendre S, Videen JS, McCutchan JA, Patterson TL, Grant I (2005) Brain mitochondrial injury in human immunodeficiency virus-seropositive (HIV-I-) individuals taking nucleoside reverse transcriptase inhibitors. J Neurovirol ll(4) 356-364... 

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