K65R, TAMs and tenofovir

Area of Science:

• Virology
• Pharmacology
• Infectious Diseases

Background:

• Management of HIV disease necessitates addressing drug resistance, particularly within nucleoside reverse transcriptase inhibitors (NRTIs).
• Thymidine analogue mutations (TAMs) are well-established causes of broad cross-resistance to NRTIs, impacting therapies like zidovudine and stavudine.
• Certain TAM patterns can limit the efficacy of tenofovir disoproxil fumarate (TDF).

Purpose of the Study:

• To investigate the resistance and cross-resistance patterns of the K65R mutation within the NRTI class.
• To evaluate the impact of the K65R mutation on the efficacy of various NRTI therapies, including tenofovir.
• To assess the clinical manageability of the K65R mutation in the context of sequential HIV treatment regimens.

Main Methods:

• In vitro phenotypic analysis of the K65R mutation's resistance profile against individual NRTIs.
• Enzymatic level assessment of viral replication capacity associated with the K65R mutation.
• Cross-sectional genotypic analysis to differentiate K65R and TAM resistance patterns.

Main Results:

• The K65R mutation confers low-level resistance to tenofovir and other NRTIs, with no cross-resistance to zidovudine.
• Phenotypic data suggest partial to full activity of multiple NRTIs, including tenofovir, against K65R-mutant HIV.
• K65R, similar to M184V, is associated with reduced viral replication capacity.
• Genotypic analyses indicate K65R and TAMs represent distinct NRTI resistance pathways.

Conclusions:

• The K65R mutation exhibits manageable resistance characteristics, distinct from TAMs.
• Clinical data show successful second-line regimens can be established in treatment-naive patients who develop K65R.
• The K65R mutation is a manageable factor in sequencing HIV treatment regimens.