In Vitro Antiretroviral Activity and In Vitro Toxicity Profile of SPD754, a New Deoxycytidine Nucleoside Reverse Transcriptase Inhibitor for Treatment of Human Immunodeficiency Virus Infection

Abstract

Nucleoside reverse transcriptase inhibitors (NRTIs) are the backbone of highly active antiretroviral therapy (HAART) recommended for the treatment of human immunodeficiency virus (HIV) infection (7,20), and the use of NRTI-containing combination therapy has significantly decreased the morbidity and mortality associated with HIV disease in treated patients (18,19). NRTIs share a common mechanism of action. All undergo intracellular activation to the NRTI triphosphate (NRTI-TP) form, after which they compete with endogenous deoxynucleotide triphosphates for binding to the viral reverse transcriptase (RT) enzyme, and incorporation of the monophosphate (MP) into the nascent DNA. Since NRTIs lack a substituent capable of supporting further DNA elongation, the incorporation of the NRTI-MP results in the termination of chain elongation and inhibition of reverse transcription.Many patients whose viral replication is effectively controlled by combination antiretroviral therapy ultimately experience virologic failure because of the development of antiretroviral resistance (for reviews, see references 23 and 24). A 6-year survey of viral genotypes in France found that almost 80% of clinical HIV samples collected until 2002 had mutations conferring resistance to NRTIs (29). Primary infection with resistant strains is also being increasingly recognized as a clinical problem in some countries (10,14,26,31). NRTI resistance results from mutational changes within the RT gene. The resulting resistance mechanisms fall into two main categories (for reviews, see references 4 and 8). One group of RT mutations acts to increase the rate of RT-catalyzed phosphorolysis, i.e., the RT-catalyzed excision of the incorporated NRTI-MP from the chain-terminated DNA. These mutations include M41L, D67N, K70R, L210W, T215Y, and K219Q and are sometimes referred to collectively as thymidine analogue mutations (TAMs). The accumulation of these mutations confers high-level resistance to zidovudine and affects viral sensitivity to other NRTIs, including stavudine, tenofovir, and abacavir (4). The other mechanism by which mutations in RT can cause resistance to NRTIs is by altering the discrimination between deoxynucleoside triphosphate substrates and NRTI-TP inhibitors by the substrate binding site of RT. Examples of such mutations include the M184V mutation, which is found frequently in patients experiencing virologic failure during treatment with lamivudine-containing HAART (6,15). This mutation causes high-level resistance to lamivudine and (in combination with other mutations) reduces sensitivity to didanosine, zalcitabine, and abacavir (32). Other mutations

Kinetics of Inhibition of HIV Type 1 Reverse Transcriptase-Bearing NRTI-associated Mutations by Apricitabine Triphosphate

“…By contrast, the presence of TAMs should favour apricitabine -MP unblocking; however, the extent of this effect was significantly less than that observed with zidovudineterminated primers (28% for apricitabine-MP vs 95% for zidovudine-MP by TAMs RT) (Girouard et al, 2003). Also, clinical isolates and site-directed mutants harbouring TAMs were shown to display low-level decreased susceptibility to apricitabine in the presence or absence of the M184V mutation (Gu et al, 2006), suggesting that the effect of TAMs on apricitabine-mediated viral inhibition by apricitabine is not significant. Interestingly, both K65R and TAMs have been shown to exhibit bi-directional phenotypic and genotypic antagonism, which may explain the negative association of these mutations in genotype databases and the infrequent emergence of K65R in patients receiving zidovudine (Boucher et al, 2006;Parikh et al, 2006a;Parikh et al, 2006b).…”

“…Previously published observations of the effects of M184V, K65R and TAM mutations on susceptibility to apricitabine compared with WT viruses (Gu et al, 2006) prompted us to investigate the underlying molecular mechanisms associated with changes in susceptibility to apricitabine-TP by WT and NRTI-resistant RTs in cellfree assays.…”

“…In vitro, apricitabine shows good antiviral activity against HIV-1 harbouring the M184V mutation and thymidine analogue mutations (TAMs) (Gu et al, 2006). In addition, apricitabine has been shown to be equally effective against subtype B and non-subtype-B HIV-1 clinical isolates and to display low myelotoxicity against human bone marrow progenitor cells and low-level mitochondrial toxicity in vitro (Gu et al 2006). Recently, treatment-naive patients who received 10 days of apricitabine as monotherapy showed good virological response and a low propensity to develop apricitabine drug resistance (Cahn et al, 2006).…”

Antiviral and Cellular Metabolism Interactions between Dexelvucitabine and Lamivudine

“…Previous in vitro studies with 3TC or FTC with apricitabine (ATC or AVX754), a 2Ј-deoxycytidine analog formerly known as BCH-10618, (Ϫ)-dOTC, or SPD754, demonstrated a significant reduction in the active nucleoside triphosphate (NTP) levels of ATC-triphosphate (ATC-TP) in primary human peripheral blood mononuclear (PBM) cells (12). Interestingly, the intracellular levels of 3TC-TP in humans were unaffected by coadministration of ATC, but the levels of ATC-TP were reduced by approximately sixfold in the presence of 3TC (4,5).…”

In Vitro Interactions between Apricitabine and Other Deoxycytidine Analogues

“…1) and is a potent inhibitor of HIV replication in vitro, with concentrations producing 50% inhibition (EC 50 ) against HIV-1 ranging from 1.0 to 10.0 M in T-cell lines and from 0.1 to 3.0 M in peripheral blood mononuclear cellc (PBMC). In addition to potent antiviral activity, ATC shows a low potential for mitochondrial and cytotoxicity in vitro (11).…”