LAGOCICLOVIR is a nucleoside reverse transcriptase inhibitor with activity against human immunodeficiency virus and hepatitis B virus.

Alovudine (3’ -deoxy-3’ fluorothymidine) is a nucleoside reverse transcriptase inhibitor (NRTI) initially tested in the early 1990s, before the era of combination therapy and before the availability of plasma viral load measurement. Initial toxicity studies showed that the primary target organ of toxicity was the bone marrow. A lack of clear advantages in activity over zidovudine, the only drug approved in the early 1990s, and the potential for bone marrow toxicity caused alovudine development to be stopped [6]. However, later in vitro studies found alovudine to be very effective at suppressing several NRTI-resistant HIV-1 mutants, including isolates with multiple thymidine-associated mutations (TAMs) or multi-NRTI-resistance mutations. Alovudine at a dose of 7.5 mg/day added to a failing antiretroviral combined regimen in patients with isolates resistant to other NRTIs yielded a median viral load decline after a 4-week period in patients not receiving concomitant stavudine. In July 2003, Medivir out-licensed it's HIV antiviral MIV-310 to Boehringer Ingelheim. Under the terms of the agreement, Boehringer Ingelheim will make upfront and milestone payments to Medivir totaling up to 122 million euro in the event that all development and performance milestones are met. In March 2005, Boehringer Ingelheim recently completed a clinical trial of MIV-310 (alovudine) in HIV/AIDS. The efficacy exhibited by MIV-310 at the doses tested showed antiviral activity but did not achieve the target level of efficacy which had previously been defined. Boehringer Ingelheim, therefore, decided to stop the development of this investigational drug.

Lersivirine (UK-453,061) is a novel second-generation non-nucleoside reverse transcriptase inhibitor (NNRTI). It binds reverse transcriptase in a distinct way leading to a unique resistance profile. Lersivirine is a second-line NNRTI, which was investigated in a Phase IIb clinical trial. Lersivirine has shown encouraging virologic efficacy in a Phase IIa monotherapy study in NNRTI-naive patients. In a Phase IIb clinical trial in ART naive patients, clinical efficacy of lersivirine was compared with efavirenz, each administered together with tenofovir disoproxil fumarate/emtricitabine. After 48 weeks, lersivirine exhibited a slightly lower virologic response but similar immunologic efficacy. However, the trial was not powered for formal hypothesis testing of noninferiority of lersivirine. The development of lersivirine was recently stopped because the developing company determined that the compound would not provide an improvement over existing NNRTIs.

Palinavir (formerly BILA2011BS) is a potent inhibitor of the human immunodeficiency virus type 1 (HIV-1) and type 2 (HIV-2) proteases and was studied for the treatment of HIV infections. However, information about the current development of this drug is not available.

Droxinavir is hydroxyethylurea human immunodeficiency virus type 1 (HIV-1) protease inhibitor. Position 88 of HIV-1 protease gene plays a key role in the interaction between droxinavir and the protease molecule. A mutation in this position, located outside the active site, confers resistance to the hydroxyethylurea inhibitor droxinavir. The V82A and N88S substitutions conferred droxinavir resistance on HIV-1 recombinant variants. Positions 82 and 88 are reported to be variable in natural populations isolated from patients who have not been treated with protease inhibitors. Droxinavir had been in preclinical phase for the treatment of HIV-1 infection. However, this study was discontinued.

Elvucitabine (ACH-126443 or beta-L-Fd4C) is a reverse transcriptase inhibitor exerting antiviral properties. Elvucitabine, an L-cytosine nucleoside analog, is intracellularly phosphorylated to its active 5′-triphosphate metabolite, which has an intracellular half-life of at least 20 hours. Elvucitabine triphosphate inhibits the activity of HIV reverse transcriptase by competing with natural substrates and by causing DNA chain termination after incorporation into viral DNA. Elvucitabine has also demonstrated in vitro and in vivo activity against HBV. Achillion, under license from Vion is developing elvucitabine for the potential treatment of HIV and hepatitis B virus (HBV) infection.

Dideoxyadenosine (2′,3′-dideoxyadenosine) is a prodrug form of didanosine (2',3'-dideoxyinosine), a nucleoside reverse transcriptase inhibitor analog of adenosine. 2',3'-Dideoxyadenosine and 2',3'-dideoxyinosine were shown to be equally effective in the inhibition of HIV proliferation in human T cells. Dideoxyadenosine competitively inhibits adenylyl cyclase, thereby reducing levels of cyclic adenosine monophosphate (cAMP). By inhibiting cAMP-mediated gene activation in tumor cells, this agent may retard tumor cell proliferation. 2',3'-dideoxyadenosine inhibits retroviral DNA synthesis and mRNA expression in T cells exposed to the virus that causes acquired immunodeficiency syndrome, and affords such cells long-term protection in vitro under conditions of substantial viral excess. 2',3'-dideoxyadenosine appears to completely block reverse transcription from viral RNA to viral DNA. 2',3'-dideoxyadenosine was also shown not only to possess antibacterial activity in vitro against a variety of Enterobacteriaceae, but also to be effective in vivo, dideoxyadenosine was active in experimental mouse infections by the oral route against 5 Salmonella strains, 2 of 3 Arizona strains, 5 of 7 Citrobacter strains, 3 of 8 Klebsiella strains, 3 of 5 Escherichia strains, 1 of 3 Shigella strains, and 3 of 15 Serratia strains at concentrations generally well below the toxic level.

Bevirimat (3-O-(3',3'-dimethylsuccinyl) betulinic acid or MPC-4326 or PA-457) potently inhibits replication of both WT and drug-resistant HIV-1 isolates and demonstrate that the compound acts by disrupting a late step in Gag processing involving conversion of the capsid precursor (p25) to mature capsid protein (p24). Bevirimat inhibits replication of both wild-type and drug-resistant HIV-1 isolates in vitro, achieving similar 50% inhibitory concentration values with both categories. Serial drug passage studies have identified six single amino acid substitutions that independently confer bevirimat resistance. These resistance mutations occur at or near the CA-SP1 cleavage site, which is not a known target for resistance to other antiretroviral drugs. Bevirimat has been in phase 2 trial for the treatment of HIV infections. Bevirimat has demonstrated a consistent pharmacokinetic profile in healthy volunteers and HIV-infected patients. The demonstration of an antiviral effect following a single oral dose of bevirimat validates maturation inhibition as a potential target for antiretroviral therapeutics in humans.

LASINAVIR, a hydroxyethylene derivative, is highly specific human immunodeficiency virus (HIV) protease inhibitor with an IC50 of 1 nM. Its clinical development was discontinued.

Dexelvucitabine is a cytidine analogue, which has been shown to be active in both naive and HIV-experienced individuals and has in vitro activity against a variety of NRTI-resistant strains. Dexelvucitabine belongs to a class of HIV drugs called nucleoside reverse transcriptaseinhibitors (NRTIs). In the Phase IIb study most side effects were generally mild and included headache, fatigue, and gastrointestinal disorders. However, some participants developed severe hyperlipasemia and pancreatitis. Drug development is discontinued due to 40% incidence of grade 4 hyperlipasemia including one case of pancreatitis.