The objective of this study was to elucidate patterns evolved under treatment regimens containing NNRTI. To this end, we have comparatively analysed the genetic variation in the RT gene of subtype B and subtype C HIV-1 from drug-naive and drug-experienced patients. We compared the frequency at which individual drug resistance mutations were selected in subtype B and C patients who failed therapy. We further compared our results to a large public-access database.
Patients in our study were not randomized into specific treatment arms. The patients had different ethnic backgrounds, and this may have affected both adherence and pharmacokinetics. Such issues were not studied here. However, patients were treated by the same physicians in the same clinics. The drugs received, follow-up time, baseline viral load and CD4 cell counts were similar (Table 1). Although all the mutations associated with resistance to NNRTI in subtype B-infected patients were found also in subtype C-infected patients, different patterns and frequencies of specific mutations were found in each subtype. Significant differences in frequency of individual mutations were found only for A98G/S, V106M and Y188C. However, the frequency differences for all of the other mutations combined reached significance, with more NNRTI resistance-associated mutations in subtype C patients. This applies to each of the three groups, drug-naive, NNRTI-naive and NNRTI-treated patients. The relatively high frequency of NNRTI resistance-associated mutations in subtype C-infected patients is conspicuous when compared with other RT mutations, the NAM and M184V. As previously reported, the frequency of NAM was higher in B infected patients and that of M184V was equal in subtype B- and subtype C-infected patients. In contrast, NNRTI resistance-associated mutations appear to accumulate rapidly in subtype C patients and to manifest a unique pattern. Even in subtype C patients who were treated with NRTI, and not with NNRTI, there was an increased frequency of mutations associated with resistance to NNRTI. The implied cross-reactivity between NRTI and NNRTI should be further investigated.
V106M and K103N can coexist: of 13 patients who developed V106M, five (38.5%) also had K103N. The prevalence of K103N following EFV treatment was significantly lower in EFV-treated subtype C patients than in subtype B patients treated with this drug. It seems that in some cases V106M arose in subtype C-infected patients at the expense of K103N. Our findings confirm Brenner's in vitro evidence that EFV selects preferentially for V106M in subtype C-infected patients.
Although not conclusive, these data suggest that baseline polymorphism in the subtype C RT influences the rate at which certain mutations develop in patients failing therapy and the mutation pattern. This may be the case also for other non-B subtypes. In spite of the higher mutation frequency in NNRTI-associated RT positions in subtype C-infected patients, we cannot conclude at this stage that the efficacy of NNRTI in the treatment of subtype C patients is lower in these patients than in subtype B patients (differences in viral load or CD4 cell count were insignificant). Prospective clinical trials and phenotypic assays are needed to address this issue.
We thank M. Ofir, of VGI, Israel, for excellent technical assistance. M. Amit and Y. Shaked helped in database development. The Stanford HIV database is under the direction of R. Shafer.
Sponsorship: This work was supported by Bristol-Myers Squibb, Israel.
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Additional contributing coauthors
Dan Engelhard, Shlomo Maayan, Hadassah University Hospital, Jerusalem; Zvi Bentwich, Dina Torten, Kaplan Hospital, Hebrew University Hadassah Medical School, Rehovot; Ella Mendelson, Fernando Mileguir, Daniela Ram, Hagit Rudich, National HIV Reference Center, Central Virology Lab, Public Health Laboratories, Ministry of Health; Eduardo Shahar, Einat Kedem, Sholomo Pollack, Rambam Medical Center, Haifa; Bat Sheva Gotessman, Giora Gotessman, Meir Medical Center, Kfar-Saba, Israel.