Efficacy of dideoxynucleosides against human foamy virus and relationship to its reverse transcriptase amino acid sequence and structure.

Human foamy virus (HFV), a retrovirus of simian origin which occasionally infects humans, is the basis of retroviral vectors in development for gene therapy. Clinical considerations of how to treat patients developing an uncontrolled infection by either HFV or HFV-based vectors need to be raised. We determined the susceptibility of the HFV to dideoxynucleosides and found that only zidovudine was equally efficient against the replication of human immunodeficiency virus type 1 (HIV-1) and HFV. By contrast, zalcitabine (ddC), lamivudine (3TC), stavudine (d4T), and didanosine (ddI) were 3-, 3-, 30-, and 46-fold less efficient against HFV than against HIV-1, respectively. Some amino acid residues known to be involved in HIV-1 resistance to ddC, 3TC, d4T, and ddI were found at homologous positions of HFV reverse transcriptase (RT). These critical amino acids are located at the same positions in the three-dimensional structure of HIV-1 and HFV RT, suggesting that both enzymes share common patterns of inhibition.

Prevalence and conditions of selection of E44D/A and V118I human immunodeficiency virus type 1 reverse transcriptase mutations in clinical practice.

Recently, it has been shown that a new mutational pattern (the E44D/A and/or V118I mutation) confers moderate phenotypic lamivudine resistance in the absence of the M184V mutation. The E44D/A and/or the V118I mutation does not exist in drug-naive patients, and the prevalence increases with the number of treatment regimens and lamivudine experience. The mutations can preexist in nucleoside-experienced but lamivudine-naive patients. They are always associated with zidovudine resistance-associated mutations, even in the absence of M184V. These mutations are more stable than the M184V substitution during antiretroviral treatment interruptions.

Early virological failure in naive human immunodeficiency virus patients receiving saquinavir (soft gel capsule)-stavudine-zalcitabine (MIKADO trial) is not associated with mutations conferring viral resistance.

The MIKADO trial was designed to evaluate the efficacy of stavudine-zalcitabine-saquinavir (soft gel capsule) [d4T-ddC-SQV(SGC)] in 36 naive patients (-3.3 log(10) units at week 24 [W24]). Among the 29 patients remaining on d4T-ddC-SQV(SGC) until W24, 10 harbored a virological failure (viral load of >200 copies/ml at W24) (group 1). To determine the reasons for therapeutic failure, genotypic and phenotypic resistance test results and SQV concentrations in plasma were analyzed and compared to those in successfully treated patients (viral load of <200 copies/ml at W24) (group 2). Reverse transcriptase and protease genotypic analyses in group 1 revealed the acquisition of only one SQV-associated mutation (L90M) in only two patients. There was no significant increase in the 50 or 90% inhibitory concentration of SQV in patients with or without the L90M mutation. However, the fact that two patients developed an L90M mutation only 4 weeks after relapse points to the need for genotypic resistance testing in the context of an initial failure of the antiretroviral regimen. At W24, the median SQV concentration in group 1 (71 ng/ml) was significantly lower than in group 2 (475 ng/ml), and the plasma SQV concentration was correlated with the viral load at W24 (r = -0.5; P<0.05) and with the drop in viral load between day 0 and W24 (r = -0.5; P<0.01). These results and the fact that the plasma SQV concentrations in the two groups prior to relapse (W12) were not significantly different strongly suggest that the early failure of this combination is not due to viral resistance but to a lack of compliance, pharmacological variability, and drug interactions or a combination of these factors.

[Polymorphism of protease genes in patients infected with HIV-1 and response to therapy including a protease inhibitor]. / Etude du polymorphisme du gène de la protéase de patients infectés par le VIH-1 et réponse à un traitement comprenant un inhibiteur de la protéase.

Protease inhibitors (PIs) are recently introduced drugs that have improved the survival of HIV-infected patients when given in combination with two reverse transcriptase inhibitors. The HIV-1 protease gene is naturally highly polymorphic. Selection pressure due to IP use can result in major or minor resistance-associated mutations (RAMs). This study investigated whether presence before IP therapy of minor RAMs on the protease gene predicts the virological response. Of the 58 PI-naive patients included in the study, 12 had received two nucleoside reverse transcriptor inhibitors, 14 had received indinavir, 16 ritonavir, and 28 saquinavir-SGC. Viral load was measured on D0 (prior to PI initiation) and at M3 and M6 (Roche Monitor 1.5 with 200 and 20 copies/ml as the thresholds). The protease gene was fully sequenced on D0 using the ABI 377 automatic sequencer after RNA amplification by nested RT-PCR. None of the viral strains exhibited major mutations, but 57 of 58 (98%) had at least one minor mutation (median number of substitutions, 4), 60% had 1 to 4 substitutions, and 40% had 5 to 9 substitutions. Substitutions seen with a prevalence > 20% were located at codons 15, 35, 37, 41, 63, and 77. Numbers of substitutions at M3 and M6 were not correlated with viral load or the nature of the PI used, and neither were they significantly different between patients with more or fewer than 20 copies/ml. These data suggest that the protease genotype at PI initiation does not predict the efficacy of a regimen including a PI and is of no assistance in deciding whether or not to include a PI in a triple combination regimen.

[Conditions of "thymidine analog mutations" (TAMs) in naive patients treated with different combinations of d4T]. / Conditions de sélection des "thymidines analogues mutations" (TAMs) chez des patients naïfs traités par différentes combinaisons incluant la d4t.

Recently, d4T/ddI combination has been associated with the selection of thymidine analogue mutations (TAMs) in 50% of patients with a detectable viral load after 6 to 12 months of this bi-therapy (ALBI, STADI and BMS A1460 tests). We evaluated the rate of selection of the TAMs in naive patients with a viral load of > 200 copies/mL after: 6 months to 1 year of d4T/3TC bi-therapy (group 1); 1 year or more of a treatment including d4T/3TC (group 2); and more than 6 months of tri-therapy including d4T/ddI (group 3). The reverse transcriptase gene has ben studied in 33 patients in group 1, 17 patients in group 2 and ten patients in group 3. For the latter patients, the tri-therapies were as follows: d4T/ddI/PI (n = 5), d4T/ddI/NNRTI (n = 4), d4T/ddI/NRTI (n = 1). For the group 1 patients, at baseline, two patients already had TAMs. At M6, all the patients acquired the 3TC-associated mutations, M184V. Only one patient selected a MDR mutation profile (F116Y, Q151M). At M12, 26 of 33 plasmas were analysed. Only one patient selected one TAM (T215Y). For the group 2 patients, only three patients selected TAMs after more than 30 months of treatment. For the group 3 patients, at baseline, only one patient already harbored TAMs. None of the other patients had selected TAMs. In patients who received d4T/ddI/3TC, only the M184V, the 3TC-associated mutation, was selected. In conclusion, stavudine in association with 3TC selected a low rate of TAMs; in patients receiving a treatment including d4T/3TC, time of exposure to stavudine seemed to be an important parameter for the selection of TAMs; and in contrast to results obtained on d4T/ddI, tri-therapies including d4T/ddI did not select any TAMs, whatever the combination (NRTI, NNRTI, PI).