The S68G polymorphism is a compensatory mutation associated with the drug resistance mutation K65R in CRF01_AE strains

Abstract

Background: The rate of S68G mutation in human immunodeficiency virus type 1 (HIV-1) reverse transcriptase has increased and is closely related to the K65R mutation among treatment-failure CRF01_AE-infected patients. We aim to explore the temporal association of S68G and K65R mutations among treatment-failure CRF01_AE-infected patients and disclose the role of the S68G mutation on nucleotide/nucleoside reverse transcriptase inhibitor (NRTI) susceptibility and viral replication with the K65R double mutation. Methods: Occurrence of S68G and K65R mutations was evaluated among HIV-1 of various subtypes in the global HIV Drug Resistance Database. The temporal association of S68G and K65R mutations was analyzed by next-generation sequencing (NGS). The impact of the S68G mutation on NRTI susceptibility and replication adaptability was analyzed with pseudovirus phenotypic resistance assays and growth competition assays, respectively. Results: The frequency of the S68G mutation increased significantly in all HIV subtypes and circulating recombinant forms in treatment-experienced patients (except for subtype F), as did the frequency of the K65R/S68G double mutation. NGS revealed that the S68G mutation occurred following K65R mutation among three out of four patients. No significant difference in fold-change for tenofovir, lamivudine or efavirenz was detected between K65R and K65R/S68G mutations in phenotypic resistance assays. The K65R/S68G double mutant outgrew the K65R mutant within 13 days of co-culture for any input ratio among all patients. Conclusions: S68G might be a natural polymorphism and compensatory mutation of K65R selected by NRTIs among the CRF01_AE strain of HIV-1, which does not affect NRTI susceptibility, but improves the replication adaptability on K65R mutants.