Monotherapy with either dolutegravir or raltegravir fails to durably suppress HIV viraemia in humanized mice.

Objectives: To compare the effectiveness of HIV integrase inhibitor monotherapy between raltegravir and dolutegravir as an approach to simplify therapy.
Methods: We evaluated and compared the efficacy of 20 week monotherapy with dolutegravir or raltegravir in humanized mice (HSC-NSG) infected with HIVBaL. Plasma HIV RNA was measured by quantitative RT-PCR (limit of detection of 150 copies/45 μL of plasma) and drug levels by LC-MS/MS. Escape viruses were genotyped and analysed for replication capacity and drug susceptibility in tissue culture.
Results: Drug-untreated control mice maintained constant viraemia throughout the study. Virus isolates from these mice were susceptible to both raltegravir (EC50 of <8 nM) and dolutegravir (EC50 of <1 nM). Mice treated with raltegravir or dolutegravir had plasma drug levels comparable to those in humans. Monotherapy with raltegravir initially suppressed HIV viraemia, but failed to maintain suppression in 4/4 mice. Viruses from raltegravir failing mice developed mutations G140G/S and Q148H/K, and were resistant to both raltegravir (EC50 values of >100 nM) and dolutegravir (EC50 values ranging from 8.8 to 13.3 nM). Monotherapy with dolutegravir suppressed viraemia in 5/5 of mice, but viraemia rebounded in one animal. The virus from this mouse had mutations E138K, G140S, Q148H, N155H and S230R, was highly resistant to both raltegravir (EC50 of >1000 nM) and dolutegravir (EC50 of 550 nM), and replicated to levels similar to those of control viruses in PBMCs. Conclusions: Monotherapy with either raltegravir or dolutegravir does not consistently maintain HIV suppression, suggesting that dual therapy may be required in simplification strategies.