Paper # 556|
Comparison of Raltegravir Susceptible and Resistant Viruses Define the Contribution of Secondary Mutations to Reductions in Raltegravir Susceptibility
Signe Fransen*, A Frantzell, S Gupta, C Petropoulos, and W Huang
Monogram Biosci, Inc, South San Francisco, CA, US
Background: Previous studies have described primary (N155H,
Q148R(H)(K),Y143R(C)) and secondary (V72I, L74I, T97A, V151I, V201I, S230N) raltegravir
(RAL) resistance mutations. Several secondary mutations exist as common polymorphisms,
and in isolation, do not alter RAL susceptibility. In this study we compared
the frequency of V72I, L74I(V)(M), T97A, V151I, G163E(R) and S230N(R) in RAL
susceptible and RAL resistant viruses, and the effects of combinations of these
mutations on RAL susceptibility.
Methods: Phenotypic (PhenoSense® Integrase) and
genotypic (Geneseq® Integrase) analyses were performed on 593 RAL susceptible
and 175 RAL resistant patient viruses as well as a panel of isogenic viruses
engineered to contain one or more secondary mutations. RAL resistance was
defined as a change in IC50 > 1.5-fold.
Results: A higher frequency of integrase
substitutions L74I(V)(M), T97A, V151I, G163E(R) was observed in RAL resistant
viruses compared to RAL susceptible viruses, but not for substitutions at V72I,
V201I or S230N(R). Irrespective of overall frequency, certain substitutions were
enriched in RAL resistant viruses: S230R was only detected in RAL resistant
virus, and L74M and G163R were more common in resistant viruses (6, 9 and 12 percent)
versus sensitive viruses (0, 0.5 and 0.3 percent), respectively. Based on
studies using a panel of site directed mutant viruses, substitutions V72I,
L74M, T97A, V151I, G163R and S230R alone generally did not reduce susceptibility
to RAL. However some combinations of these substitutions resulted in reductions
in RAL susceptibility. This observation was consistent with a patient virus
that exhibited a 9-fold reduction in RAL susceptibility and contained V72I,
T97A and G163R in the absence of a primary mutation. An additional four patient
viruses that exhibited reduced RAL susceptibility (range of IC50 fold
change = 2 to 80) also lacked primary RAL resistance mutations, but all
contained at least one secondary mutation.
Conclusions: As previous groups have shown, viruses
containing individual IN polymorphisms remain susceptible to RAL, however
certain substitutions increase in frequency under RAL selective pressure.
Combinations of these secondary mutations can result in reduced susceptibility
to RAL, however the selection of these combinations of secondary substitutions in
the absence of primary RAL resistance mutations appears infrequent.