Clinical management of HIV drug resistance

Abstract

Combination antiretroviral therapy for HIV-1 infection has resulted in profound reductions in viremia and is associated with marked improvements in morbidity and mortality. Therapy is not curative, however, and prolonged therapy is complicated by drug toxicity and the emergence of drug resistance. Management of clinical drug resistance requires in depth evaluation, and includes extensive history, physical examination and laboratory studies. Appropriate use of resistance testing provides valuable information useful in constructing regimens for treatment-experienced individuals with viremia during therapy. This review outlines the emergence of drug resistance in vivo, and describes clinical evaluation and therapeutic options of the individual with rebound viremia during therapy.

Keywords: HIV; clinical management; drug resistance testing.

Figure 1.

HIV Phenotyping of HIV protease (PRO), RT, integrase (IN) in Cell Based Assays. (A) Schematic of sample processing from phlebotomy to construction of chimeric recombinant plasmids composed of patient derived sequences in standard laboratory based HIV standard clones. Single round assays use HIV derivatives encoding a reporter gene instead of HIV env. Upon transfection into producer cells expressing a helper virus envelope, virions are produced which can undergo a single round of replication. Multiple round assays introduce patient-derived material into standard laboratory HIV, and recombinant plasmids transfected into producer cells. (B) Virions produced by transfection are standardized and used to infect susceptible cells. In single round assays, pseudo typed viruses undergo reverse transcription and integration, but are unable to propagate. Production of reporter gene product (e.g., luciferase, green fluorescent protein) denotes successful round of replication. In multiple round infections, virus is inoculated and production measured by standardized measures, typically production of p24 antigen in media. (C) To determine phenotypic response to antivirals, virus is inoculated in the presence of increasing concentrations of single antiretrovirals. Dose response curves are constructed and measure of drug inhibition; the amount of drug necessary to inhibit 50% of virus replication (IC₅₀) is calculated. Adapted from [68].

Figure 1.

HIV Phenotyping of HIV protease (PRO), RT, integrase (IN) in Cell Based Assays. (A) Schematic of sample processing from phlebotomy to construction of chimeric recombinant plasmids composed of patient derived sequences in standard laboratory based HIV standard clones. Single round assays use HIV derivatives encoding a reporter gene instead of HIV env. Upon transfection into producer cells expressing a helper virus envelope, virions are produced which can undergo a single round of replication. Multiple round assays introduce patient-derived material into standard laboratory HIV, and recombinant plasmids transfected into producer cells. (B) Virions produced by transfection are standardized and used to infect susceptible cells. In single round assays, pseudo typed viruses undergo reverse transcription and integration, but are unable to propagate. Production of reporter gene product (e.g., luciferase, green fluorescent protein) denotes successful round of replication. In multiple round infections, virus is inoculated and production measured by standardized measures, typically production of p24 antigen in media. (C) To determine phenotypic response to antivirals, virus is inoculated in the presence of increasing concentrations of single antiretrovirals. Dose response curves are constructed and measure of drug inhibition; the amount of drug necessary to inhibit 50% of virus replication (IC₅₀) is calculated. Adapted from [68].

Figure 2.

Mutations conferring resistance to nucleotide reverse transcriptase inhibitors (NRTIs) are depicted; multidrug resistance profile (Q151 complex) is indicated and thymidine associated mutations (TAMS) are noted.

Figure 3.

(A) Crystal structure of HIV reverse transcriptase p66/p561 dimer is depicted with locations of four common NNRTI resistance mutations in a hydrophobic pocket within the palm domain noted in yellow. Mutations change the binding characteristics of NNRTI, explaining cross resistance of nevirapine, delavirdine, and efavirenz. Structural data are from [99] and are displayed using RASMOL [100,101]. (B) Mutations conferring resistance to individual NNRTIs. Despite some cross resistance, etravirine has antiviral activity even in the presence of a number of mutations conferring resistance to nevirapine and efavirenz.

Figure 4.

(A) Crystal structure of HIV protease depicting active site residues (yellow) and a series of residues conferring resistance near the active site or at flap domains (circled). Structural data are from [114] and are displayed using RASMOL [100,101]. (B) Chart depicting resistance to HIV-1 protease.

Figure 4.

(A) Crystal structure of HIV protease depicting active site residues (yellow) and a series of residues conferring resistance near the active site or at flap domains (circled). Structural data are from [114] and are displayed using RASMOL [100,101]. (B) Chart depicting resistance to HIV-1 protease.

Figure 5.

Crystal structure of human foamy virus integrase (similar to HIV integrase) complexed with DNA substrate, noting the positions of resistance mutations 143, 148, and 155 relative to the binding site for raltegravir and elvitegravir, and proximity to DNA. Structure is from Cherapenov and coworkers [128] and rendered in RASMOL [100,101].