Development of hexadecyloxypropyl tenofovir (CMX157) for treatment of infection caused by wild-type and nucleoside/nucleotide-resistant HIV.

CMX157 is a lipid (1-0-hexadecyloxypropyl) conjugate of the acyclic nucleotide analog tenofovir (TFV) with activity against both wild-type and antiretroviral drug-resistant HIV strains, including multidrug nucleoside/nucleotide analog-resistant viruses. CMX157 was consistently >300-fold more active than tenofovir against multiple viruses in several different cell systems. CMX157 was active against all major subtypes of HIV-1 and HIV-2 in fresh human peripheral blood mononuclear cells (PBMCs) and against all HIV-1 strains evaluated in monocyte-derived macrophages, with 50% effective concentrations (EC(50)s) ranging between 0.20 and 7.2 nM. The lower CMX157 EC(50)s can be attributed to better cellular uptake of CMX157, resulting in higher intracellular levels of the active antiviral anabolite, TFV-diphosphate (TFV-PP), inside target cells. CMX157 produced >30-fold higher levels of TFV-PP in human PBMCs exposed to physiologically relevant concentrations of the compounds than did TFV. Unlike conventional prodrugs, including TFV disoproxil fumarate (Viread), CMX157 remains intact in plasma, facilitating uptake by target cells and decreasing relative systemic exposure to TFV. There was no detectable antagonism with CMX157 in combination with any marketed antiretroviral drug, and it possessed an excellent in vitro cytotoxicity profile. CMX157 is a promising clinical candidate to treat wild-type and antiretroviral drug-resistant HIV, including strains that fail to respond to all currently available nucleoside/nucleotide reverse transcriptase inhibitors.

Biochemical and mechanistic basis for the activity of nucleoside analogue inhibitors of HIV reverse transcriptase.

HIV encodes an RNA directed DNA polymerase (reverse transcriptase, RT) that is an essential enzyme in the viral replication cycle. This enzyme catalyzes the synthesis of double stranded proviral DNA from single stranded genomic RNA via a bireactant-biproduct mechanism. The functional enzyme purified from virus particles is a complex consisting of two polypeptides of molecular weight 66,000 and 51,000. Two of the four classes of currently approved anti-HIV drugs, the nucleoside reverse transcriptase inhibitors (NRTIs) and the non-nucleoside reverse transcriptase inhibitors (NNRTIs), act by inhibiting this enzyme. In this review each step of DNA synthesis catalyzed by the RT is described and the mechanism of inhibition of catalysis and termination of DNA synthesis by NRTIs is detailed. The individual steps in the catalytic cycle and the effects that the NRTIs have on them have been examined using transient kinetic analysis. The impact of stereoisomerism and resistance mutations on the rate of NRTI triphosphate incorporation (k(pol)), binding in the catalytic complex (K(d)) and the overall efficiency of incorporation (k(pol)/K(d)) are summarized for lamivudine, coviracil and zalcitabine. The results provide insight into the molecular forces and structural features that make these molecules effective inhibitors.

New synthesis of L-FMAU from L-arabinose.

A new synthesis of 2'-deoxy-2'-fluoro-5-methyl-beta-L-arabinofuranosyl uracil (13, L-FMAU) was achieved in 10 steps from L-arabinose.

Synthesis of (-)-DAPD.

A new synthesis of (-)-DAPD, suitable for large scale development, is described.

Evaluation of hexadecyloxypropyl-9-R-[2-(Phosphonomethoxy)propyl]- adenine, CMX157, as a potential treatment for human immunodeficiency virus type 1 and hepatitis B virus infections.

9-R-[2-(Phosphonomethoxy)propyl]-adenine (tenofovir) is an acyclic nucleoside phosphonate with antiviral activity against human immunodeficiency virus type 1 (HIV-1) and hepatitis B virus (HBV). Tenofovir is not orally bioavailable but becomes orally active against HIV-1 infection as the disoproxil ester (tenofovir disoproxil fumarate [Viread]). We have developed an alternative strategy for promoting the oral availability of nucleoside phosphonate analogs which involves esterification with a lipid to form a lysolecithin mimic. This mimic can utilize natural lysolecithin uptake pathways in the gut, resulting in high oral availability. Since the mimic is not subject to cleavage in the plasma by nonspecific esterases, it remains intact in the circulation and facilitates uptake by target cells. Significant drops in apparent antiviral 50% effective concentrations (EC(50)s) of up to 3 logs have been observed in comparison with non-lipid-conjugated parent compounds in target cells. We have applied this technology to tenofovir with the goal of increasing oral availability, decreasing the apparent EC(50), and decreasing the potential for nephrotoxicity by reducing the exposure of the kidney to the free dianionic tenofovir. Here we report that, in vitro, the hexadecyloxypropyl ester of tenofovir, CMX157, is 267-fold more active than tenofovir against HIV-1 and 4.5-fold more active against HBV. CMX157 is orally available and has no apparent toxicity when given orally to rats for 7 days at doses of 10, 30, or 100 mg/kg/day. Consequently, CMX157 represents a second-generation tenofovir analog which may have an improved clinical profile.