Sanctuary growth of human immunodeficiency virus in the presence of 3'-azido-3'-deoxythymidine

Abstract

Human immunodeficiency virus (HIV) resistance to the nonnucleoside reverse transcriptase inhibitors emerges very rapidly under selection in culture and in patients. In contrast, zidovudine (3-azido-3-deoxythymidine [AZT])-resistant HIV generally emerges in patients only after more-prolonged therapy. Although HIV can be cultured from many patients shortly after the initiation of AZT treatment, characterization of the virus that is cultured generally indicates that it is sensitive to AZT. To initiate an evaluation of the mechanisms contributing to early HIV breakthrough in the presence of AZT and other nucleoside analogs, we have utilized replication-defective HIV encoding reporter genes. These recombinant HIV allow a quantitative analysis of a single cycle of infection. Results with these defective HIV indicate that early infection in the presence of AZT often results from the infection of a cell which is refractory to the antiretroviral effects of AZT. Characterization of a cell line derived from one such cell has demonstrated decreased accumulation of AZT triphosphate, increased phosphorylation of thymidine to thymidine triphosphate, and increased levels of thymidine kinase activity. In addition, AZT inhibition of replication-competent HIV infection is also significantly impaired in this cell line. Attempts to detect and characterize the mechanisms responsible for early viral infection after initiation of AZT therapy may result in the development of new strategies for prolonged suppression of viral infection prior to the emergence of drug-resistant virus.

Use of recombinant viruses to assess the pattern of early human immunodeficiency virus breakthrough infection in the presence of stavudine

“…in the presence of 50 µM d4T ( Table 1). The similar levels of infection with these two recombinant viruses is in contrast to infections performed in the presence of the NNRTI TIBO (Strair et al, 1993 ;Medina et al, 1995Medina et al, , 1998. In those prior studies with the NNRTI, there was a 20-fold increased rate of infection with the rescued HIV-gpt virus ( Fig.…”

“…The presence of these variants was subsequently confirmed by genetic analysis of unselected HIV (Najera et al, 1995), and kinetic analysis of the emergence of resistance in treated patients (Havlir et al, 1996 ;Havlir & Richman, 1994). The absence of a disparity of infection rates with the two virus populations in the presence of either AZT (Medina et al, 1995) or d4T (Table 1) suggests that a component of early infection in the presence of these drugs may be a consequence of infection with virus that is not genetically resistant to the drug. The virus produced by COS cell transfection of plasmids ( Fig.…”

“…Medina & R. K. Strair, unpublished). Therefore, recombinant virus produced by rescue with unselected replication-competent virus will be heterogeneous and may reflect the drug sensitivity profile of the virus used for rescue (Strair et al, 1993 ;Medina et al, 1995). In a prior experiment, the heterogeneity introduced by the replication-competent virus used for rescue resulted in a calculation of the prevalence of HIV genetically resistant to an NNRTI in an unselected population that was very similar to the prevalence subsequently calculated from in vivo studies of HIV dynamics after the initiation of an NNRTI (Havlir et al, 1996 ;Strair et al, 1993).…”

“…In prior studies, a quantitative in vitro model system has been used to analyse a single cycle of recombinant HIV infection in the presence of antiviral drugs (Strair et al, 1993 ;Medina et al, 1995Medina et al, , 1998). This model system has demonstrated a pattern of virus infection that shares some important characteristics with the pattern of infection seen in the initial clinical studies analysing virus dynamics : (i) early breakthrough infection in the presence of an NNRTI that is dependent on genetic drug resistance ; and (ii) early breakthrough infection in the presence of AZT that is, at least partially, independent of the presence of genetic resistance (Strair et al, 1993 ;Medina et al, 1995). Furthermore, this recombinant virus system has allowed an estimate of the prevalence of unselected NNRTI-resistant variants in a population of unselected replication-competent HIV-1 that has subsequently been approximated by mathematical modelling of HIV-1 kinetics after the initiation of an NNRTI (Havlir et al, 1996 ;Strair et al, 1993).…”

Reactivation of thymidine kinase-defective herpes simplex virus is enhanced by nucleoside

“…Either or both of these factors may be important in viral pathogenesis. In support of this suggestion, it is noted that decreased cellular TK levels may account for the ineffectiveness of zidovudine in some situations (29).…”