Background. Virological failure of first-line antiretroviral therapy based on lopinavir boosted with ritonavir (lopinavir/r) has rarely been associated with resistance in protease. We identified a new genotypic resistance pathway in 3 patients who experienced failure of first-line lopinavir/r treatment. Methods. Viral protease and the C-term part of Gag were sequenced. The observed mutations were introduced in a reference strain to investigate impact on protease inhibitor susceptibility and replication capacity. Results. A detailed longitudinal analysis demonstrated the selection of the M46I+L76V protease mutations in all 3 patients. The L76V conferred a solitary 3.5-fold increase in one-half the maximal inhibitory concentration to lopinavir but severely hampered viral replication. Addition of M46I, which did not confer any lopinavir resistance on its own, had a dual effect. It partly compensated for the loss in replication capacity and increased the one-half maximal inhibitory concentration to above the lower clinical cutoff (11-fold). Analysis of a large clinical database (>180,000 human immunodeficiency virus [HIV] sequences) demonstrated a significant association (Spearman p, 0.93) between the increased presence of L76V in clinical samples (0.5% in 2000 to 3.4% in 2006) and lopinavir prescription over time. Conclusions. The HIV protease substitution L76V, in combination with M46I, confers clinically relevant levels of lopinavir resistance and represents a novel resistance pathway to first-line lopinavir/r therapy.

DNA sequence, Gag protein, Human immunodeficiency virus, Human immunodeficiency virus 1, Human immunodeficiency virus 1 infection, Human immunodeficiency virus infection, IC 50, RNA sequence, site directed mutagenesis, abacavir, amino acid sequence, amino acid substitution, amprenavir, animal cell, anti human immunodeficiency virus agent, antiviral resistance, article, association, atazanavir, carboxy terminal sequence, case report, controlled study, darunavir, drug blood level, drug effect, drug mechanism, drug sensitivity, drug substitution, drug treatment failure, drug withdrawal, efavirenz, genetics, genotype, human, human cell, indinavir, isoleucine, lamivudine, leucine, longitudinal study, lopinavir, lopinavir plus ritonavir, methionine, missense mutation, molecular genetics, nelfinavir, nonhuman, nucleotide sequence, p16 protease, phylogeny, plasmid DNA, polymerase chain reaction, polyneuropathy, prescription, primary medical care, priority journal, protein blood level, proteinase, pyrimidinone derivative, reference database, reversed phase high performance liquid chromatography, ritonavir, saquinavir, sequence homology, stavudine, tenofovir, tipranavir, treatment failure, valine, virus RNA, virus culture, virus mutation, virus protein, virus replication, virus strain, zidovudine,
The Journal of Infectious Diseases
Erasmus MC: University Medical Center Rotterdam

Nijhuis, M, Wensing, A.M.J, Bierman, W.F.W, de Jong, D, Kagan, R, Fun, A, … Boucher, C.A.B. (2009). Failure of treatment with first-line lopinavir boosted with ritonavir can be explained by novel resistance pathways with protease mutation 76V. The Journal of Infectious Diseases, 200(5), 698–709. doi:10.1086/605329