Presentation on theme: "Resistance Testing – Where Do I Start?"— Presentation transcript:
1 Resistance Testing – Where Do I Start? Iván Meléndez-Rivera, MDFellow, American Academy of Family PhysiciansAssistant Professor of Family MedicinePonce School of Medicine, Ponce PR, USABoard Member, American Academy of HIV MedicineFaculty, Florida/Caribbean AETCMedical Director, Centro Ararat, Inc Ponce PR, USA
2 Disclosures of Financial Relationships This speaker has significant financial relationships with the following commercial entities to disclose:Advisory Board or Panel: Gilead, MerckConsultant: Bristol-Myers SquibbGrants/Research Support: Abbott, Boehringer, GlaxoSmithKline, Napo, PfizerSpeakers Bureau: Abbott, Boehringer, Bristol-Myers Squibb, GlaxoSmithKline, Merck, Pfizer, TibotecThis speaker will not discuss any off-label use or investigational product during the program.This slide set has been peer-reviewed to ensure that there are no conflicts of interest represented in the presentation.
3 ObjectivesIntroduce major resistance mutations for each class of HIV therapyOrder currently available resistance testsPresent illustrative case(s) of diagnosing resistance pattern resulting in treatment plan adjustmentPresent objectives for the module.
4 Definition of Antiviral Drug’s Resistance Presence of viral mutations that reduce drug susceptibility compared with the susceptibility of wild-type viruses.Can directly or indirectly interfere with a drug's activity.Should be distinguished from other causes of drug failure such as:Non-adherenceInsufficient drug levelsDrug regimens with intrinsically weak antiviral activity.
5 Why does Resistance Develop? HIV can develop resistance quickly because:HIV reverse transcriptase makes errors in matching bases when converting HIV RNA to DNAHIV replicates at a rapid rate: 1 to 10 billion viral particles produced dailyIn an untreated infected host, every possible mutation occurs at least once every 24 hours, some of which may impart drug resistance.
6 If you have developed resistance to a drug, does that mean that you are resistant to ALL the drugs in the same class?TrueFalseFalse
7 When does resistance occur? Resistance occurs when the virus has an opportunity to replicate in the presence of sub-inhibitory concentrations of drugs.Treatment with <3 active drugsInappropriate selection of drugsPharmacokinetics or drug-drug interactions lead to inadequate drug exposuresNon-adherence to the treatment regimenInterruption of treatment (even for a few days)Adding one drug to a failing regimenProlonging a failing regimen
8 Selective Pressures of Therapy Drug-susceptible quasispeciesDrug-resistant quasispeciesTreatment beginsSelection of resistant quasispeciesViral loadIncomplete suppressionInadequate potencyInadequate drug levelsInadequate adherencePre-existing resistanceTime
9 What is viral resistance? A continuum of reduced susceptibility of HIV to the inhibitory effects of drugsMore SusceptibleMore ResistantThe terms "drug resistance" and "reduced drug susceptibility" have similar meanings, provided that each term is viewed as representing a continuum between susceptible and highly resistant.Because antiretroviral drugs differ in their potencies, reductions in susceptibility must be related to the activity of the drug against wild-type viruses.
10 Wild Virus vs Mutant virus Why is it important to measure drug resistance?Wild Virus vs Mutant virus
11 What is wild-type virus? HIV virus that has not been exposed to drug therapyThe predominant sequence of nucleotide bases in a heterogeneous mixture of virionsIt is the most fit form of HIV in the absence of drug
12 Identifying Mutations How do we identify a resistance mutation?M 184 M“184 is the codon position”M is the “wild-type” amino acid (AA)
13 Identifying Mutations How do we identify a resistance mutation?M 184 V“184 is the codon position”V is the mutant AAM is the “wild-type” amino acid
14 What is the Impact of HIV Mutations? To the virus, mutations can be:Decreasing the virus’ ability to survive and/or replicate (viral fitness) or may make the virus hypersusceptible to certain antiretrovirals (ARVs)No effect on virus functionChanging the structure of the virus to evade antiretroviral treatment. These mutations may or may not affect viral fitnessJohnson VA, et al. Topics in HIV Medicine. 2009;17:
15 Single-base Mutations May Confer Antiretroviral Resistance 3 nucleotides specify an amino acidHIV RNA wild typeSingle-base mutationHIV RNA mutantDrug resistantSPEAKING POINTS:Sets of 3 nucleotides in the HIV RNA, which code for a single amino acid of a protein are referred to as a codonSingle-base mutations to the codon may result in coding for a different amino acid, which may result in drug resistanceSuch resistance mutations occur in regions of the HIV RNA specific to the antiretroviral drug class (eg, PI, NNRTI, NRTI) and are named according to:A letter to the left that designates the amino acid in the wild type virusA number in the center that designates the location of the amino acid impacted by the mutationA letter to the right that designates the amino acid in the drug-resistant virus due to the mutationNote to Speaker:The components of this slide build in the following order:HIV RNA, wild typeSingle base mutationHIV RNA drug resistant mutantAA position, 123AA wild type, XAA mutation, Y123XYWild-type AA: XPosition AA: 123Mutant AA: YAA=amino acidHoffman C et al. HIV Medicine th ed. Paris, France: Flying Publisher
16 Resistance Profile and Potential for Cross Resistance Region of HIV RNA associated with antiretroviral drug class specific resistanceHIV RNA MutantDrug ADrug BDrug CSPEAKING POINTS:Single-point mutations associated with resistance to a given antiretroviral drug may also be associated with cross resistance to other antiretroviral drugsThis schematic shows how mutations that cause resistance to hypothetical antiretroviral drugs A and B can have cross resistance to drugs C and DDrugs A and B share no cross-resistance mutations and are therefore unlikely to have any impact on efficacy when used sequentially, following virologic failureDrug C can similarly be used sequentially after Drug A, but will be cross resistant to Drug B and likely demonstrate reduced efficacy if used sequentiallyDrug D is cross resistant to Drugs A and B and CNote to Speaker:The components of this slide build in the following order:Region of HIV RNA associated with ARV drug class specific resistanceDrug A associated resistance mutationsDrug B associated resistance mutationsDrug C associated resistance mutationsHighlight cross resistance of Drug C with Drug BDrug D associated resistance mutationsHighlight cross resistance of Drug D with Drugs A, B, CB cross resistanceDrug DA & B & C cross resistanceAdapted from: Paredes R, et al. Antiviral Res Jan;85(1):
17 How is resistance measured? By GenotypeAmino acid substitution on chainBy phenotype (IC50)IC50The minimum concentration of a drug needed to inhibit the growth of the virus by 50% in vitroIC50 is analogous to MIC90IC90 is not sufficiently reproducible for routine clinical useThe lower the IC50, the more potent the drug
20 Nucleoside Reverse Transcriptase Inhibitors (NRTI’s) Zidovudine (ZDV)Didanosine (ddI)Stavudine (d4T)Lamivudine (3TC)Abacavir (ABC)Tenofovir (TDF)Emtricitabine (FTC)Structure of a covalently trapped catalytic complex of HIV-1 RT published by Huang H et al, Science Accessed Sept 3, 2012
21 NRTI’s Resistance Mutations CLASSIFICATION OF MAJOR DRUG RESISTANCE MUTATIONS: NRTI-resistance mutations are classified into those that inhibit NRTI incorporation into the HIV-1 primer DNA strand ('Discriminatory' Mutations) and those that promote excision of chain-terminating NRTIs via ATP-mediated pyrophosphorolysis ('Excision' Mutations). Excision mutations are usually called TAMs (Thymidine Analog Mutations) because they are selected by AZT and d4T. Two mutation complexes are associated with high-levels of multi-NNRTI resistance: (i) A 2-amino acid insertion at codon 69, which nearly always occurs in combination with multiple TAMS; and (ii) Q151M which usually occurs with several otherwise uncommon accessory mutations: A62V, V75I, F77L, and F116Y.Red: Primary Mutations to confer resistance Gray: Secondary Mutations***: Increase susceptibilityAdapted from: Accessed Sept 3, 2012
22 NRTI’s Signature Mutations Medication with decrease susceptibilityM184VLamivudine (3TC) and Emtricitabine (FTC)K65RTenofovir (TDF)L74VAbacavir (ABC) and Didanosine (ddI)Y215FZidovudine (ZDV) and Stavudine (d4T)T69ins or Q151MAll except, Lamivudine (3TC) and Emtricitabine (FTC)
23 Not ALL mutations are bad M184V/I cause high-level resistance to 3TC and FTC and low-level resistance to ddI and ABC.M184V/I are not contraindications to continued treatment with 3TC or FTC because they increase susceptibility to AZT, TDF, and d4T and are associated with clinically significant decreased HIV-1 replication.
24 Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTI’s) Nevirapine (NVP)Efavirenz (EFV)Etravirine (ETR)Rilpivirine (RPV)The NNRTIs inhibit HIV-1 RT allosterically by binding to a hydrophobic pocket about 10 angstroms under the active site. The above figure shows the 5â€™ polymerase-coding region of HIV-1 RT encompassing the fingers, palm, and thumb subdomains of the p66 subunit bound to the NNRTI nevirapine (Kohlstaedt) PDB #. Positions associated with NNRTI resistance that make up the central NNRTI binding pocket are shown: L100, K101, K103, V106, V108, V179, Y181, Y188, G190, F227. Additional positions that make up the pocket include E138 which is contributed by the p51 subunit) not shown and M230, L234, P236, K238, and L318 which form part of an extended pocket. Additional accessory NNRTI-resistance abutting positions that form the NNRTI binding pocket include A98 and P225.Non-nucleoside RT inhibitor (NNRTI)-resistance mutationsAccessed Sept 3, 2012
25 NRTI’s Resistance Mutations MAJOR MUTATIONS: Mutations that are associated with high levels of phenotpyic resistance or clinical evidence for reduced virological response. Those in bold red are associated with the highest levels of phenotypic resistance or with the strongest clinical evidence for reduced virological response. Mutations in bold grey are intermediate to those in bold red vs. those in plain text. The mutations shown at positions 103, 106, 181, 188, and 190 are generally primary because they generally occur before the mutations L100I and K101EP (Bacheler 2000, Koval 2006, Reuman 2010). M230L is uncommon and may occur alone or with other mutations (Huang 2000, Vingerhoets 2005, RPV Prescribing Information) Position 138 is included because E138K is the most commonly occurring mutation to develop in patients receiving RPV (Rimsky 2011). V106M is more common than V106A in subtype C viruses. In contrast to V106A, V106M causes high-level EFV resistance (Brenner 2003, Grossman 2004, Cane 2004)Red: Highest Levels of resistance Gray: Intermediate level of resistanceAdapted from: Accessed Sept 3, 2012
26 NNRTI’s Signature Mutations Medication with decrease susceptibilityK103NEfavirenz (EFV) and Nevirapine (NVP)Y181I/VEtravirine (ETR) and Rilpivirine (RPV)Y188LRilpivirine (RPV)K101PALL NNRTI
28 PI’s Resistance Mutations MAJOR MUTATIONS: Mutations that are associated with high levels of phenotypic resistance or clinical evidence for reduced virological response. Those in bold red are associated with the highest levels of phenotypic resistance or with the strongest clinical evidence for reduced virological response. Underlined mutations are potential contraindications to the use of the indicated PIs when other alternatives are available. Positions 30, 32, 46, 47, 48, 50, 54, 82, and 84 are in or near (positions 46, 47, and 54) the substrate cleft. (Jacobsen 95; Partaledis 95; Condra 96; Carrillo 98; Patick 98; Schapiro 99; Atkinson 00; Gong 00; Scott 00; Maguire 02a; Parkin 03; Colonno 04; Doyon 05; Kagan 05; Vermeiren 07; De Meyer 08a; Marcelin 08; Sista 08; Van Marck 09; Llibre 10; Rhee 10; Schapiro 10). Positions 76, 88, and 90 interfere with PI susceptibility indirectly (Patick 98; Atkinson 00; Mahalingam 01; Malan 08; Rhee 10; Louis 11).Red: Highest Levels of resistance Gray: Intermediate level of resistanceAdapted from: Accessed Sept 3, 2012
31 INI Resistance Mutations MAJOR MUTATIONS: Mutations that cause high-levels of decreased susceptibility of strong clinical evidence for contributing to virological failure. Those in bold red are associated with the highest levels of phenotypic resistance or with the strongest clinical evidence for reduced virological response. Mutations in bold grey are intermediate to those in bold red vs. those in plain text. Although G140SA do not decrease INI susceptibility, they occur almost uniformly in combination with the highly potent Q148 INI-resistance mutations. The major mutations shown here have been selected in persons receiving RAL (Cooper 2008, Malet 2008, Sichtig 2009, Wittkp 2009, Canducci 2009, Baldanti 2010, Reuman 2010, Hatano 2010), or ELV (McColl HIVDRW 2007, Zolopa JID 2010) and characterized for in vitro susceptibility (Shimura 2007, Goethals 2008, Kobayashi 2008, Fransen 2009, Jones 2009, da Silva 2009, Reuman 2010, Goethals 2010, Kobayashi 2011). Mutations in bold red are associated with >5-10 fold decreased susceptibility. Although E138 and G140 mutations alone do not decrease INI susceptibility that greatly contributed to decreased susceptibility in combination with Q148 mutations.Red: Highest Levels of resistance Gray: Intermediate level of resistanceAdapted from: Accessed Sept 3, 2012
32 INI Signature Mutations Medication with decrease susceptibilityQ148H/K/RRaltegravir (RAL) and Elvitegravir(ELV)* In expanded access
35 CCR5 Antagonist Maraviroc (MVC) Moore J, et al. Proc Natl Acad Sci USA. 2003;100: ; Yost R, et al. Am J Health-Syst Pharm. 2009;66: Accessed Sept 3, 2012
36 CCR5 Antagonist Resistance is Associated with Amino Acid Changes in the V3 Loop of gp120* G/AVariable pattern of Maraviroc resistance-associated amino acid substitutionsNo signature mutations have been identifiedCurrently, there is no assay available to assess Maraviroc resistanceTipTipStemStemBaseBase*Substitutions outside the V3 loop of gp120 may also contribute to reduced susceptibility to MaravirocChangeMaraviroc-resistantInsertionDeletionAdapted from Data on file. ViiV Healthcare, RTP, NC.
37 CCR5-Resistant Virus Recognizes Drug-Bound Receptors Mutated gp120recognizes CCR5differentlyMVCres VirusMVCresgp120Binding site NOT disrupted by maravirocEntryMori J, et al. 16th IHIVDRW. Barbados, 2007.Abstract 10.
39 In which one of the following situations would HIV resistance testing NOT usually be recommended? Acute HIV infection, regardless of whether treatment is to be startedChronic HIV infection, at entry into careAfter discontinuation (>4 weeks) of ARVsSuboptimal suppression of viral load after starting antiretroviral therapy (ART)Answer: C
40 Trends of Phenotypic 1-, 2-, and 3-Class Resistance 606060PIPI and NRTINNRTIPI and NNRTINRTINRTI and NNRTI505050404040Resistant Samples (%)303030202020101010Speaker Notes:The study examined 68,587 resistant samples submitted for routine phenotypic and genotypic patient testing that showed phenotypic resistance to at least one drug within the ARV classes of PIs, NRTIs, and NNRTIs.Each bar represents the percentage of samples that exhibited reduced phenotypic susceptibility to either one, two, or three drug classes (NRTI, NNRTI, PI) compared to the sum total of all samples that exhibited reduced susceptibility to any drug class (NRTI, NNRTI, or PI).200320042005200620072008200920102003200420052006200720082009201020032004200520062007200820092010NNRTI=non-nucleoside reverse transcriptase inhibitor; NRTI=nucleoside reverse transcriptase inhibitor; PI=protease inhibitor.Adapted from Paquet A et al. 51st Interscience Conference on Antimicrobial Agents and Chemotherapy; September 17-20, 2011; Chicago, Illinois. Abstract H2-800.ARV=antiretroviral; NNRTI=non-nucleoside reverse transcriptase inhibitor; NRTI=nucleoside reverse transcriptase inhibitor; PI=protease inhibitor.Paquet A et al. 51st Interscience Conference on Antimicrobial Agents and Chemotherapy; September 17-20, 2011; Chicago, Illinois. Abstract H2-800.
41 Testing for Drug Resistance Before initiation of ART:Transmitted resistance in 6-16% of HIV-infected patientsIn absence of therapy, resistance mutations may decline over time and become undetectable by current assays, but may persist and cause treatment failure when ART is startedIdentification of resistance mutations may optimize treatment outcomesResistance testing (genotype) recommended for all at entry to careRecommended for all pregnant womenPatients with virologic failure:Perform while patient is taking ART, or ≤4 weeks after discontinuing therapyInterpret in combination with history of ARV exposure and ARV adherenceCoffey S. Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents: Initiation of Therapy [PowerPoint]. AIDS Education and Training Centers, National Resource Center; March Available at Accessed Sept 03, 2012.
42 Drug Resistance Testing: Recommendations RECOMMENDEDCOMMENTAcute HIV infection, regardless of whether treatment is to be startedTo determine if resistant virus was transmitted; guide treatment decisions.If treatment is deferred, consider repeat testing at time of ART initiation.Genotype preferred.Chronic HIV infection, at entry into careTransmitted drug-resistant virus is common in some areas; is more likely to be detected earlier in the course of HIV infection.If treatment is deferred, consider repeat testing at time of ART initiation. Genotype preferred to phenotype.Consider integrase genotypic resistance assay if integrase inhibitor resistance is a concern.Coffey S. Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents: Initiation of Therapy [PowerPoint]. AIDS Education and Training Centers, National Resource Center; March Available at Accessed Sept 03, 2012.
43 Drug Resistance Testing: Recommendations(2) RECOMMENDEDCOMMENTVirologic failure during ARTTo assist in selecting active drugs for a new regimen.Genotype preferred if patient on 1st or 2nd regimen; add phenotype if known or suspected complex drug resistance pattern.If virologic failure on integrase inhibitor or fusion inhibitor, consider specific genotypic testing for resistance to these to determine whether to continue them.(Coreceptor tropism assay if considering use of CCR5 antagonist; consider if virologic failure on CCR5 antagonist.)Suboptimal suppression of viral load after starting ARTCoffey S. Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents: Initiation of Therapy [PowerPoint]. AIDS Education and Training Centers, National Resource Center; March Available at Accessed Sept 03, 2012.
44 Drug Resistance Testing: Recommendations(3) RECOMMENDEDCOMMENTPregnancyRecommended before initiation of ART or prophylaxis.Recommended for all on ART with detectable HIV RNA levels.Genotype usually preferred; add phenotype if complex drug resistance mutation pattern.Coffey S. Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents: Initiation of Therapy [PowerPoint]. AIDS Education and Training Centers, National Resource Center; March Available at Accessed Sept 03, 2012.
45 Drug Resistance Testing: Recommendations(4) NOT USUALLY RECOMMENDEDCOMMENTAfter discontinuation (>4 weeks) of ARVsResistance mutations may become minor species in the absence of selective drug pressurePlasma HIV RNA <500 copies/mLResistance assays cannot consistently be performed if HIV RNA is lowCoffey S. Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents: Initiation of Therapy [PowerPoint]. AIDS Education and Training Centers, National Resource Center; March Available at Accessed Sept 03, 2012.
47 Genotypic and Phenotypic Resistance Tests Translation into linear string of amino acidsFolding into functional proteinHIV RNAPhenotypic assays test thisGenotypic assaystest this
48 Available Tests NRTI, NNRTI AND PI ENTRY INHIBITORS GENOTYPEVirtual PhenotypePHENOTYPEENTRY INHIBITORSINTEGRASE INHIBITORSCo-Receptor Tropism AssayRNADNA
49 General Limitations of Resistance Testing Lack of uniform quality controls across different laboratoriesHigh cost compared with other tests routinely done in HIV careCannot be reliably performed with HIV RNA < copies/mLMay not be able to detect minority populations of resistant virus if they account for < 20% of the sample—especially common after drug discontinuationResistant strains that are in viral reservoirs also not detectedResistance studies share certain limitations, including the lack of uniform quality controls across different laboratories, a high cost compared with other tests routinely done in HIV care, the fact that the tests cannot be reliably performed with an HIV RNA count less than copies/mL, and that they may not be able to detect minority populations which account for < 20% of the sample. In addition, resistance tests cannot detect HIV strains in unsampled viral reservoirs.
50 Reversion to Predominant Wild-Type Virus After Discontinuing ART It is clear, however, that patients who develop resistance while on ART, then discontinue ART, tend to experience a reversion of their virus to wild-type (though again, NNRTI resistance mutations may persist as these are generally not associated with a significant loss in viral fitness).Behrens C, Kindrick A, Harrington R. Antiretroviral Resistance Testing in the Management of HIV-Infected Patients [PowerPoint].Northwest AIDS Education and Training Center; July Available at Accessed SEP 3, 2012.Illustration by David Spach, MD
52 Advantages and Disadvantages of Genotype Testing Rapid turnaround (1-2 wks)Less expensive than phenotypingDetection of mutations may precede phenotypic resistanceWidely availableMore sensitive than phenotype for detecting mixtures of resistant and wild-type virusDisadvantagesIndirect measure of resistanceRelevance of some mutations unclearUnable to detect minority variants (< 20% to 25% of viral sample)Complex mutational patterns may be difficult to interpretEach type of resistance testing has advantages and disadvantages. Advantages of the genotype test include rapid turnaround time, lower cost, potential detection of mutations prior to phenotypic resistance, wide availability, and higher sensitivity than phenotype testing for detecting mixtures of resistant and wild‑type virus.One disadvantage of genotype testing is that it is an indirect measure of resistance. Another is the difficulty in determining the relevance of certain mutations without phenotypic correlates. And, as with all resistance tests, genotype testing is unable to detect minority variants comprising less than 20% to 25% of viral samples. The most significant disadvantage of genotype testing is the difficulty of interpretation when there are many mutations or highly complex patterns.
54 Genotype & Phenotype Data The Virtual PhenotypeGenotypeAccess DataHIVRTProteaseGenotype & Phenotype DataVirtual PhenotypeWild-type HIVThe virtual phenotype uses a combination of the genotypic and phenotypic techologies. Virologic, the company that offers this test, has a database containing over ten thousand samples of patient serum on which both genotypic and phenotypic assays were performed. When one submits a sample to Virologic for a virtual phenotype, a genotype is performed. From the database of paired genotype and phenotype results, patient samples having the same genotype as that obtained on the sample you submitted are drawn. The corresponding phenotypes for those samples are then analyzed, averaged, and reported to the ordering clinician as a ‘virtual phenotype’, i.e. the phenotype that might be expected if one actually performed a phenotypic assay on that sample. Potential advantages of this approach include the lower cost and quicker turn around time associated with the genotype, but the easy-to-interpret results of a phenotype. However, one should keep in mind that a phenotypic assay on the sample you submit is never actually performed, and that the clinical utility of this approach is not as clearly established as it is for the genotypic assay.Resistant HIVBehrens C, Kindrick A, Harrington R. Antiretroviral Resistance Testing in the Management of HIV-Infected Patients [PowerPoint].Northwest AIDS Education and Training Center; July Available at Accessed SEP 3, 2012.Illustration by David Spach, MD1
55 Advantages and Disadvantages of “Virtual” Phenotype Testing Similar advantages to genotype (turnaround time, cost, sensitivity)Defines resistance based on database of in vivo responses in treated patientsUses 2 clinical cutoffs (CCO) to define spectrum of resistanceCCO1: value below which response expected to be comparable to wild typeCCO2: value above which most virologic response would be lostIndicates which drugs have partial activityDisadvantagesIs an estimated phenotype based on the patient’s genotype, not an actual measured phenotypeReliability will depend on the accuracy of the genotypeAvailable only from 1 vendorMore expensive than genotype aloneMethodology of linking genotype to phenotypic database not intuitively obvious—uses a proprietary “virtual phenotype linear regressionCCO, clinical cutoff.“Virtual” phenotype testing has similar advantages to genotype testing in terms of turnaround time, cost, and sensitivity. Again, 2 different CCOs define the spectrum of resistance: CCO1 is the value below which response is expected to be comparable to wild‑type virus. CCO2 is the value above which most virologic activity would be lost. As a result, the virtual phenotype test can also identify drugs with partial activity.Disadvantages of virtual phenotyping include availability from a single vendor and its higher cost compared with genotype testing. Also, the methodology for linking genotype results to the phenotypic database uses a proprietary “virtual phenotype linear regression model engine,” the derivation of which is not always intuitively obvious to the user.
57 Drug Susceptibility Testing Involves culturing a fixed inoculum of HIV-1 in the presence of serial dilutions of an inhibitory drug.The concentrations of drug required to inhibit virus replication by 50% (IC50) or 90% (IC90)Drug susceptibility results depend on:inoculum size of virus testedcells used for virus replicationthe means of assessing virus replication.Drug susceptibility assays are not designed to determine the exact amount of drug required to inhibit virus replication in vivo but rather to identify differences in the drug concentration required to inhibit a fixed inoculum of a virus relative to the concentrations required to inhibit wild-type viruses.Accessed 06/OCT/12
58 Advantages and Disadvantages of Phenotype Testing Provides direct and quantitative measure of resistanceMethodology can be applied to any antiretroviral agent, including new drugs, for which genotypic correlates of resistance are unclearUses 2 clinical cutoffs (CCO) derived from clinical cohorts to define spectrum of resistanceCCO1: value below which reduced virologic response is likelyCCO2: value above which a virologic response is unlikelyIndicates which drugs have partial activityCan assess interactions among mutationsAccurate with non-B HIV subtypesDisadvantages:Susceptibility cutoffs not standardized between assaysClinical cutoffs not defined for some agentsMay be unable to detect minority variants for some mutations (< 20% to 25% of viral sample)Complex technology with longer turnaround (~ 3 wks)More expensive than genotypingPhenotype testing is significantly different from genotype testing. Its primary advantage is that it provides a direct and quantitative measure of resistance and, as such, the methodology can be applied to any antiretroviral agent, including new drugs, for which genotype correlates of resistance are unclear. Two clinical cutoffs (CCO) derived from clinical cohorts are used to define the spectrum of resistance. The lower cutoff, CCO1, is the fold change in susceptibility below which reduced virologic response is likely, whereas the higher cutoff, CCO2, is the fold change above which a virologic response is unlikely. In addition, phenotype resistance testing can assess interactions among mutations and has been shown to be accurate in non‑B clade HIV subtypes.Disadvantages of phenotype testing include variability between assays and that not all drugs have defined susceptibility cutoffs. As with genotype testing, phenotype testing may be unable to detect minority variants of some mutations. This is a complex technology with a turnaround time of approximately 3 weeks. It is also considerably more expensive than genotyping—approximately twice as much in the United States.
59 Integrase PhenotypePhenotypic integrase resistance assay is commercially availableAmplification threshold: HIV-1 RNA > 500 copies/mLBiological cutoff for raltegravir is fold change (FC) > 1.5Clinical cutoff not yet determinedReport does not detail genotypic mutationsHigh assay accuracy demonstrated by IC50 fold change values reported for site-directed mutantsFC, fold change; RAL, raltegravir.For more information, go online to:Fransen S, et al. ICAAC/IDSA Abstract Accessed SEP 3,
61 Typical HIV Co-Receptor Usage Patterns R5 VirusesUse only the CCR5 co-receptorMost prevalent in early diseasePredominate throughout infectionX4 VirusesUse only the CXCR4 co-receptorEmerge in later diseaseAssociated with accelerated CD4+ cell decline and disease progressionSlide: Typical HIV Co-Receptor Usage PatternsHIV-1 viruses can be characterized into four broad classifications based on their tropism status.1CCR5-tropic viruses or virus populations can use only the CCR5 chemokine co-receptor to infect CD4 cells. This is the most prevalent in early disease and predominates throughout HIV disease.1CXCR4-tropic viruses or virus populations can use only the CXCR4 chemokine co-receptor to infect CD4+ cells. These populations of virus usually emerge in later stages of disease and are associated with an accelerated CD4 cell decline and disease progression.1Dual (D)-tropic viruses or virus populations can use either the CCR5 or CXCR4 co-receptors to infect CD4+ cells.1Mixed (M)-tropic virus populations may contain various combinations of R5 virus, X4 virus, and/or dual-tropic viruses.1ReferenceTsibris AMN, Kuritzkes DR. Chemokine antagonists as therapeutics: focus on HIV-1. Annu Rev Med. 2007;58:Dual-Tropic VirusesUse either the CCR5 or theCXCR4 co-receptorMixed-TropicVirus PopulationTsibris AMN, Kuritzkes DR. Annu Rev Med. 2007;58:
62 No light generated No CXCR4 Use Light generated CCR5 Use Demonstration of R5 virusNo light generated No CXCR4 UseNot an X4 VirusVirusVirusLight generated CCR5 UseR5 VirusVirusExample of CCR5 virus entering R5 cell line and generating RLU (relative light units) in the Trofile assayCCR5CXCR4
64 Demonstration of dual virus Light is generated on both CCR5 and CXCR4 cell linesThis is a DUAL virusVirusVirusCCR5CXCR4Example of CCR5 virus entering R5 cell line and generating RLU (relative light units) in the Trofile assay
65 Demonstration of mixed virus population This population shows CCR5 AND CXCR4 co-receptor useThis is a mixed populationCCR5CXCR4Example of CCR5 virus entering R5 cell line and generating RLU (relative light units) in the Trofile assay
67 Virologic Failure With Resistance Virologic failure is defined as the inability of ARV regimen to achieve virologic suppression or occurrence of virologic rebound1A confirmed viral load >200 copies/mL can be considered virologic failure2Resistant VirusViral LoadTime on Antiviral TherapySpeaker Notes:Virologic failure is defined as the inability of ARV regimen to achieve virologic suppression or occurrence of virologic rebound1The DHHS Guidelines consider a confirmed viral load >200 copies/mL as a virologic failure2Virologic suppression to <50 copies/mL is a marker for the suppression of viral replication3Based on Clavel et al.3AIDSinfo. Glossary of HIV/AIDS-related terms. 7th ed Available at Accessed November 18, 2011DHHS Guidelines. Accessed November 18, 2011.Clavel F et al. N Engl J Med. 2004;350:ARV=antiretroviral; DHHS=Department of Health and Human Services.1. AIDSinfo. Glossary of HIV/AIDS-related terms. 7th ed Available at Accessed November 18, 20112. DHHS Guidelines. GL.pdf. Accessed November 18, 2011.3. Podsadecki TJ et al. J Infect Dis. 2007;196:
70 The follow factors leads to developing drug-resistance EXCEPT…? Poor drug absorptionPoor adherenceHigh drug levelsPre-existing resistanceInteractions with other drugs, supplements or recreational drugsAnswer: C
71 Case 1: 42 y/o AA female Dx in 2006 Current Medical Hx DiabetesHyperlipidemiaHypertensionBaseline Labs (1/06)VL: 230,000CD4: 320 cells/mm3Baseline GenotypeWild-TypePt request a once a day pill ARV and start 5/06 on EFV/TDF/ETC FDCViral Load quickly becomes undetectable and CD4+ counts raises over time
72 Case 1: 42 y/o AA femaleDateVLCD411/06<40040005/07<5048005/0860005/0968011/0930,000Patient experiences virologic failure on Nov 2009 while taking EVF/TDF/FTCPt. reports occasional poor adherence due to occasional sleep disturbances and concerns about lipid problems
73 Case 1: 42 y/o AA female What would be your next step? Enforce patient adherence and continue with same regimen.Perform Genotype test and keep patient on the same regiment until genotype results.Perform a tropism and Phenotype test and remove patient from medicines because there are toxic.Change patient regiment without any resistance test performed.
74 Case 1: 42 y/o AA female With this genotype result, is Efavirenz still available? Answer: BYesNo
75 Case 1: 42 y/o AA female Resistance testing result. January 2010 patient was place on EPZ/ATVLabs 04/10CD4: 700 cells/mm3VL: <50 copiesPt. continue with non-detectable (ND) viral load until 04/12CD4 800 cells/mm3VL: 15,000 copiesResistance testing result.NRTI’s: M184VNNTRI’s: K103NPI’s: I50L
76 Based on new resistance pattern (NRTI’s: M184V NNTRI’s: K103N; PI’s: I50L) which statement is true? All NNRT’s are available to useAtazanavir still available for use3Tc is a full active drugPatient loss susceptibility to rilpivirineKeeping patient on efavirenz will increase the amount of NNRTI mutations and reduce the susceptibility to all other NRTI’sAnswer: E
77 Case 2A 45 year-old man who is highly treatment-experienced with antiretroviral therapy has virologic failure on tenofovir/emtricitabine and lopinavir/ritonavir.His enhanced Trofile assay reveals a dual/mixed-tropic virus.His current genotype reveals reverse transcriptase mutations M41l, V90I, K103N, M184V, L210W, T215Y and protease inhibitors mutations V32I, I47V, I54A, V82L, I84V, and L90M.In addition, a 2006 genotype also reveled the envelope glycoprotein 41 mutation G36D.
78 Ritonavir-boosted darunavir Ritonavir-boosted tipranavir The next BEST antiretroviral regimen for this patient would include which of the following?EnfuvirtideMaravirocEtravirineRitonavir-boosted darunavirRitonavir-boosted tipranavirResponse: C
79 Bonus CaseA 21 years-old man who acquired HIV through vertical transmission presents for routine care.Recent genotypic analysis reveals a 69 insertion complex and K103N reverse transcriptase mutations and L10I, K20M, M46I, G48V, I50V, N88S and L90M protease mutations.
80 Which regimen would be the BEST for him? Raltegravir, etravirine, and atazanavir/ritonavirRaltegravir, etravirine, and darunavir/ritonavirRaltegravir, etravirine, and fosamprenavir/ritonavirRaltegravir, etravirine, and indinavir/ritonavirRaltegravir, etravirine, and maravirocResponse: B
81 Reference http://hivdb.stanford.edu/ Behrens C, Kindrick A, Harrington R. Antiretroviral Resistance Testing in the Management of HIV-Infected Patients [PowerPoint]. Northwest AIDS Education and Training Center; July Available at Accessed Sept 03, 2012.Coffey S. Guidelines for the Use of Antiretroviral Agents in Adults and Adolescents: Initiation of Therapy [PowerPoint]. AIDS Education and Training Centers, National Resource Center; March Available at Accessed Sept 03, 2012.Accessed Sept 03, 2012