Identification of Genotypic Changes in Human Immunodeficiency Virus Protease That Correlate with Reduced Susceptibility to the Protease Inhibitor Lopinavir among Viral Isolates from Protease Inhibitor-Experienced Patients

Abstract

The association of genotypic changes in human immunodeficiency virus (HIV) protease with reduced in vitro susceptibility to the new protease inhibitor lopinavir (previously ABT-378) was explored using a panel of viral isolates from subjects failing therapy with other protease inhibitors. Two statistical tests showed that specific mutations at 11 amino acid positions in protease (L10F/I/R/V, K20M/R, L24I, M46I/L, F53L, I54L/T/V, L63P, A71I/L/T/V, V82A/F/T, I84V, and L90M) were associated with reduced susceptibility. Mutations at positions 82, 54, 10, 63, 71, and 84 were most closely associated with relatively modest (4-and 10-fold) changes in phenotype, while the K20M/R and F53L mutations, in conjunction with multiple other mutations, were associated with >20-and >40-fold-reduced susceptibility, respectively. The median 50% inhibitory concentrations (IC 50 ) of lopinavir against isolates with 0 to 3, 4 or 5, 6 or 7, and 8 to 10 of the above 11 mutations were 0.8-, 2.7-, 13.5-, and 44.0-fold higher, respectively, than the IC 50 against wild-type HIV. On average, the IC 50 of lopinavir increased by 1.74-fold per mutation in isolates containing three or more mutations. Each of the 16 viruses that displayed a >20-fold change in susceptibility contained mutations at residues 10, 54, 63, and 82 and/or 84, along with a median of three mutations at residues 20, 24, 46, 53, 71, and 90. The number of protease mutations from the 11 identified in these analyses (the lopinavir mutation score) may be useful for the interpretation of HIV genotypic resistance testing with respect to lopinavir-ritonavir (Kaletra) regimens and may provide insight into the genetic barrier to resistance to lopinavir-ritonavir in both antiretroviral therapy-naive and protease inhibitor-experienced patients.

Human immunodeficiency virus type 1: drug resistance in treated and untreated Brazilian children

“…The V82A occurs predominantly in HIV-1 isolates from patients receiving treatment with IDV or RTV (Condra et al 1996, Molla et al 1996. By themselves, mutations at position 82 confer reduced susceptibility in vitro to IDV, RTV, and LPV but not to NFV, SQV, or APV (Kempf et al 2001). However, when present with other PI mutations, V82A contributes to clinical resistance to each of the PIs.…”

“…et al 2000a) and has not been shown to confer crossresistance to other PIs, except possibly LPV (Kempf et al 2001). Both children were receiving NFV or RTV and presented possible resistance to LPV.…”

“…Additional mutations in the enzyme flap and in other parts of the molecule are usually required for resistance to emerge in vivo. This requirement for multiple mutations to overcome the activity of PI has been referred to as a "genetic barrier" to drug resistance (Kempf et al 2001). The L63P protease mutation is common in viruses that have never exposed to PIs (Kozal et al 1996) and may be more prevalent in viruses from patients in whom a protease inhibitorcontaining regimen has failed.…”

Mutation Patterns and Structural Correlates in Human Immunodeficiency Virus Type 1 Protease following Different Protease Inhibitor Treatments

“…Although 16 antiretroviral drugs have been approved for the treatment of HIV-1, cross-resistance within each of the three antiretroviral drug classes-nucleoside reverse transcriptase (RT) inhibitors, nonnucleoside RT inhibitors, and protease inhibitors-often leads to the development of multidrug resistance. HIV-1-specific protease inhibitors pose a high genetic barrier to drug resistance because multiple protease mutations are usually required for the development of resistance to these inhibitors (4,13,19). Nonetheless, resistance to multiple protease inhibitors occurs commonly, attesting to the conformational flexibility of the HIV-1 protease enzyme (5,10,13,26).…”

Isolation and Molecular Characterization of a Nelfinavir (NFV)-Resistant Human Immunodeficiency Virus Type 1 That Exhibits NFV-Dependent Enhancement of Replication

“…When suppression of HIV-1 replication by PI-containing therapy is incomplete, variants with reduced sensitivity to the PI can emerge by accumulating nonsynonymous mutations in the PR gene (4,14,17,20), causing a serious reduction in the clinical efficacy of HAART (1,5,10). PI resistance-associated mutations often affect the substrate specificity of PR (8) and can impair enzyme function, resulting in reduction of the replicative capacity of the variants (2,7,(16)(17)(18)28).…”