Genotypic and phenotypic characterization of human immunodeficiency virus type 1 variants isolated from AIDS patients after prolonged adefovir dipivoxil therapy

Abstract

Adefovir dipivoxil [bis(pivaloyloxymethyl)-ester prodrug], an orally bioavailable prodrug of adefovir [9-(2-phosphonylmethoxyethyl)adenine], is currently in phase III clinical trials for the treatment of human immunodeficiency virus (HIV). In vitro experiments demonstrated that either a K65R or a K70E mutation in HIV reverse transcriptase (RT) was selected in the presence of adefovir, conferring a 16- or 9-fold decrease in susceptibility to adefovir, respectively. Previous data demonstrated that patients receiving adefovir dipivoxil monotherapy (125 mg daily) for 12 weeks experienced a median decrease in HIV RNA levels of 0.5 log10 copies/ml and that resistance to adefovir dipivoxil did not arise during that period. In the present investigation, a further study was undertaken to investigate whether RT mutations developed among viruses from patients who completed the 12-week study and who opted to enroll in a maintenance phase of prolonged (6- to 12-month) adefovir dipivoxil therapy (120 mg daily). Concomitant treatment with antiretroviral agents was permitted during the maintenance phase. The median decreases in HIV RNA levels for patients who completed 6 or 12 months of maintenance-phase dosing were 0.6 and 1.14 log10 copies/ml, respectively. The reductions in the HIV RNA levels were similar among patients who received adefovir dipivoxil with or without concomitant treatment with antiretroviral agents. Viruses from 8 of 29 patients dosed for up to 12 months developed RT mutations that were not present at baseline; these mutations may have been related to adefovir dipivoxil therapy. Viruses from two of the eight patients developed the K70E mutation while the patients were on therapy, but none of the viruses from patients developed the K65R RT substitution. Despite the development of RT mutations, sustained reductions (6 to 12 months) in viral load (> or = 0.7 log10 copies/ml decrease from baseline) were observed in all eight patients.

FIG. 1

Median log change in plasma HIV RNA load (log₁₀ copies per milliliter) for all patients after 3, 6, and 12 months of maintenance-phase therapy. Standard error bars are shown.

FIG. 2

Viral loads and prior anti-HIV therapies for patients who received adefovir dipivoxil monotherapy for the entire maintenance phase and whose viruses developed a sequence change from baseline that may have been associated with adefovir dipivoxil therapy. Prior and current therapies are boxed above the viral load responses. The viral load (HIV RNA copies per milliliter) is indicated on the y axis (limit of quantification, 400 copies/ml; Roche Amplicor assay). Time (in weeks) is indicated on the x axis. Each point on the graph represents the number of HIV RNA copies per milliliter in plasma measured at the identified time of treatment. Nucleotides 1 to 900 (amino acids 1 to 300) of the HIV RT gene were sequenced at all of the time points indicated. The only RT amino acids that are shown in Fig. 2 are those that were wild type at baseline and that became mutated during therapy or those that are nucleoside-associated resistance mutations present at entry into the maintenance phase. Other sequence variations between that of the RT of virus from patients and the consensus HXB2D sequence are not listed. WT, wild-type sequence; italics, a sequence change from baseline. (A) Patient A. (B) Patient B. (C) Patient C. (D) Patient D. Additional patient data are presented in Tables 1 and 2.

FIG. 3

Median change in HIV RNA loads (log₁₀ copies per milliliter) after 6 months of adefovir dipivoxil therapy among different groups of patients on the basis of prior AZT experience and presence of AZT resistance mutations at initiation of maintenance-phase adefovir dipivoxil dosing. Other antiretroviral agents were concomitantly used by 50% of the patients. The four patient groups include all patients (n = 28), patients who were AZT naive (n = 7), patients who were AZT experienced but whose viruses had no AZT-associated resistance mutations (n = 7), and patients who were AZT experienced and whose viruses had one or more AZT-associated resistance mutations (n = 14), as indicated by the bars from top to bottom, respectively. Standard error bars are indicated.