Managing Antiretroviral Therapy in Treatment-Experienced Patients: First Regimen Failure MATEC Catherine Creticos, M.D. Medical Director.

Managing Antiretroviral Therapy in Treatment-Experienced Patients: First Regimen Failure

MATECCatherine Creticos, M.D.

Medical Director

Objectives

Explain possible causes of drug failureDescribe tests used to assess viral resistance

Explain how to use resistance test results to select an effective new regimen

Discuss strategies for managing patients with limited treatment options

Case Study 1

A.D. is a 51 yo male HIV+ since 1989. He started Combivir in 1993, and his viral load remained undetectable until June 2006, with CD4 in the 400-600 range. Since June 2006, his viral load on 2 occasions has been 24,500 and 37,800 respectively. His most recent CD4 count was 378 cells.

First Antiretroviral Treatment Failure

Assessment What are possible causes of increased viral

load? Is intervention necessary at this point?

Why / Why not? What intervention(s)?

Reasons for First Antiretroviral Therapy Regimen Failure

Viral load , but patient not failing regimen recent infection (eg, HSV outbreak, bacterial

infection, acute hepatitis) recent vaccination

Poor adherence – regimen may still be salvagable

Poor absorption (unboosted PIs) Drug-drug interactions (eg, PPIs and

atazanavir) Incompletely suppressive regimen (eg, dual

nucleoside)

First Antiretroviral Failure: Interventions

Review adherence – last month, last few days Probe for recent events, problems (eg, recent

infection or other issues such as running out of medication or not taking medication on a trip)

Repeat viral load (can be done at same time as resistance assay)

Resistance assay – purpose is to identify specific drug resistance that has led to failure and to assist in the selection of the next regimen

Rationale for HIV Resistance Testing

Drug resistance at start of ART is predictor of virologic response

Several prospective studies support use of resistance testing to improve response to ART

Preliminary economic studies suggest resistance testing cost-effective after first HAART failure

Prevalence of resistance in acute/recent HIV infection 10%-26% in recent studies

Current Recommendations forUse of Resistance Testing (DHHS)

Recommended for selection of active drugs when changing therapy if viral suppression is suboptimal w/initial regimen

Recommended for pregnant women initiating therapy or with incomplete virologic suppression

May be useful in cases of acute infection or infection within the last 1-2 years

Not yet recommended at initiation of therapy in all treatment-naïve individuals until more information available on prevalence; however in areas of high prevalence, resistance testing may be useful

Both phenotyping and genotyping may be useful in patients with complex prior treatment history

Evolution of Drug Resistance

Causes of high genetic variability of HIV: DNA copy of RNA genome for replication Lack of proofreading by RT during replication Every possible point mutation occurs ~1,000-10,000 times a

day; double mutants common Genetic recombination between different viruses in the same

cell

Acquisition of resistance during tx depends on: Size and heterogeneity of viral population Extent of replication during drug therapy Ease of acquisition of particular mutation Effect of mutation on drug susceptibility and viral fitness

How drug resistance arises. Richman, DD. Scientific American , July 1998

How Drug Resistance Arises

Resistance Testing: Definitions

Mutation (molecular definition): change in nucleic acid sequence compared with consensus or wild-type virus

point mutation: AAA GAC AGT=>AAA AAC AGC insertion: AAA AAC AGT=> AAA AAC AGT AGT deletion: AAA AAC AGT=> AAA…AGT

Drug resistant mutation: change in amino acid sequence (vs. reference strain) that affects susceptibility to a drug

Major, primary: can solely affect susceptibility Minor, secondary, accessory: contributes to reduced susceptibility

Polymorphism: a naturally occurring change in amino acid sequence not shown to directly impact drug susceptibility

Mutational Nomenclature

Wild-type amino acid G48V Mutant amino acid

Codon Position

Mixtures are indicated by a slash K103K/N indicates mixture of wild-type and

mutant T215D/Y/F indicates mixture of 3 mutants

Resistance Assays: Phenotype and Genotype

Phenotype: Direct assay: measures ability of the virus to

grow in various concentrations of antiretroviral drugs.

Genotype: Indirect assay: detects drug resistance

mutations that are present in the relevant viral genes.

Both assays focus on the reverse transcriptase (RT) and protease (PR) genes of the virus

Phenotyping: Advantages

Provides resistance information on each drug regardless of the presence of multiple mutations

Interpretation may be more intuitive than for genotype assay

Very useful in patients with complex drug history and complicated mutation profile

Very useful for deciphering cross-resistance May be more useful than genotyping for

new drugs until appropriate mutations are established by clinical data

Phenotyping: Disadvantages

If drug resistant population is minor, the phenotypic effect may not be detected

Viral load needs to 1000 copies/ml Very expensive and time-consuming Consensus on drug-resistance cut-off values are not

yet fully determined - drugs to which a patient is actually still sensitive may be unnecessarily eliminated

initial cut-offs were based on assay variability on repeated testing of known sample

later cut-offs were based on natural variability of wild-type viruses from patients

current cut-offs are being developed based on outcome data from clinical trials

Antivirogramphenotype

PhenoSense HIV Report

Sequence-based Genotyping Assays

HIV circulating in patient’s plasma is isolated; RT and PR genes are copied, amplified & sequenced.

The test sequence is compared to a reference HIV strain and all changes (mutations) are noted.

Software compares changes found to a list of the mutations known to be associated with resistance.

A report documents any mutations and (optimally) the ARV drugs to which the virus is sensitive or resistant based on the presence or absence of particular mutations.

Available Genotypes

Company Product Name Turnaround Time

RNA Sensitivity

Mixture Sensitivity

Monogram Biosciences GeneSeq™ HIV 14 Days ≥ 500 copies 10%

LabCorp GenoSureGenoSure Plus 10-28 Days ≥ 1000 copies Not available

Quest Genotype (ABI kit)Vircotype 7-14 Days ≥ 600 copies 25%

ARUP ViroSeq (ABI kit) Variable ≥ 500 copies 10%Specialty Labs GenotypR Plus 7 Days ≥ 1000 copies Not available

Virco GenchecVirtual Phenotype 14 Days ≥ 1000 copies 10-20%

Bayer TRU-Gene (kit) 3-14 Days ≥ 1000 copies Not availableABI ViroSeq (kit) Variable ≥ 500 copies 20%

Genotyping: Advantages

Identification of all nucleotides, amino acid differences, deletions & insertions

Genotyping has the ability to detect resistant virus that constitutes only a small proportion (~ 20%) of the viral population.

This can provide “predictive” early warning of resistance before full resistance develops

Faster and less expensive than phenotype assay

Genotyping: Disadvantages

Reports may be difficult to interpret unless clinician is very experienced

Labs use different software to predict resistance - a consensus on which mutations are important is needed

There is a lot of variation in the quality of the “product” from different labs, especially in the ability to detect minority species in the population

Significance of many mutations still poorly understood Lack of understanding of the significance of

combinations of mutations Viral load needs to 1000 copies/ml

Phenotype/Genotype Discordance:

Interpretation Discordance interpretation is incorrect (especially new

drugs) data base is incomplete or lacking

Test Result Discordance PT sensitive but GT resistant mixtures transitional mutations antagonistic mutational interactions

Genotype-Phenotype Discordance

Observed differences between phenotype and genotype are not uncommon

Reasons for genotype-phenotype discordance use of inaccurate genotype interpretation

algorithms (not accounting for novel or unknown mutations, or for unrecognized effects of mutations)

Presence of mixtures of wild-type and resistant strains

Variability in phenotypic susceptibility with specific mutations

Virtual Phenotype

Determines genotype of test strainComputer algorithm matches genotype to strains that have been previously phenotyped

Presents expected phenotype based on the average phenotype of matching isolates

Virtual Phenotype: Pros and Cons

Pros Inexpensive, quick way

to generate phenotypic information

Clinical studies show good correlation between virtual and real PT and equal efficacy in predicting viral suppression

Cons number of matches

may be low “union” of limitations of

GT and PT techniques clinical studies do not

demonstrate benefit of virtual PT added to GT and expert advice

NRTIs

Major Mutations

NRTIs:Special Considerations

Require triphosphorylation, complicates in vitro assessment & PT testing discordance b/w in vitro and in vivo potency

NEMs (TAMs) selected primarily in patients treated with AZT or D4T; 10% of patients on DDI monotherapy; rarely during ABC monotherapy

Some NRTI mutations hypersensitize HIV to NNRTIs K65R confers intermediate resistance to DDI, ABC, TDF,

3TC. Recent study of ABC/3TC/TDF led to high failure rate Q151M is a 2-base pair change that causes intermediate

resistance to AZT, DDI, D4T, and ABC TDF efficacy reduced by 3 or more TAMs, especially in

presence of M41L or L210W

Mutational Interactions: M184V

M184V- causes high-level 3TC resistance and low-level resistance to ddI, ddC, ABC

M184V reverses T215Y-mediated AZT resistance

Resensitization clinically significant; slows AZT resistance in patients on AZT/3TC

M184V appears to reverse effect of NEMs on resistance to d4T, TDF

NNRTIs

Major Mutations

NNRTI Mutations:Special Consideration

Y181C/I causes high-level resistance to NVP and DLV, but low-level resistance to EFV. However, isolates only transiently respond to EFV

Y181C and L100I hypersensitize HIV to AZT G190A/S are resistant to NVP and EFV but

hypersensitive to DLV

PIs

Major Mutations

PIs:Special Considerations

Cross-resistance problematic; in one study of over 6,000 isolates, 59%-80% of isolates with a 10-fold decrease in susceptibility to one PI also had a 10-fold decrease to at least one other

For LPV/r, at least 4 of 11 mutations may be needed for significant resistance

NFV and ATV when used as first PI may select for mutations with little cross-resistance: NFV – D30N ATV – I50L

Stanford HIV Database

http://hivdb.stanford.eduCan insert mutations and receive an assessment of resistance and a discussion of significance of the mutations

Case Study 1:A.D.

Genotype shows:M184V, D67N, K70K/R, and K219K/Q

Reference lab predicted resistance to AZT, ABC, 3TC, FTC, d4T;

No resistance to DDI, TDF, all NNRTIs & PIs

Stanford database interpretationNucleoside RTI:

3TC: High-level resistance ABC: Low-level resistance AZT: Intermediate resistance D4T: Low-level resistance DDI: Potential low-level

resistance FTC: High-level resistance TDF: Susceptible

Non-Nucleoside RTI DLV: Susceptible EFV: Susceptible NVP: Susceptible

Stanford Database Comments on Significance of Mutations

D67N contributes some degree of resistance the NRTIs except 3TC and FTC. It usually occurs with mutations at positions 70 or 215. D67E/G occur in heavily treated patients and probably have a similar effect as D67N.

K70R causes low-level AZT and probably D4T resistance but appears to have little effect on the other NRTIs. K70E reduces TDF susceptibility. K70G/N are rare variants of unknown significance.

Stanford Database Comments on Significance of Mutations

M184V/I cause high-level resistance to 3TC and FTC, and low-level in vitro resistance to DDI and ABC. However, it has not been shown to limit the effectiveness of DDI and it has only been shown to limit the effectiveness of ABC when it occurs in combination with multiple TAMs. M184V partially reverses T215Y-mediated resistance to AZT, TDF, and D4T.

K219Q/E increase AZT and probably D4T resistance when present with K70R or T215Y/F but may not have any effect on the remaining NRTIs. K219N/R occur commonly in heavily NRTI-treated patients.

M184V partially reverses AZT, D4T, and TDF resistance caused by other TAMs.

Case Study 1:Treatment Selection and Response

Started Atripla (TDF/3TC/EFV) and Ziagen

What are other reasonable treatment choices?

6 weeks after initiating therapy, patient’s viral load is undetectable

Continued close f/u is warranted

Case Study 2

K.L. is a 36 yo male with diabetes and HIV. He has been treated with Combivir and Sustiva as well as glipizide. He presents with decreased vision bilaterally, R>>L eye. An ophtholmologic exam reveals acute retinal necrosis and w/u shows an RPR 1:512. He is treated for syphilitic retinitis with significant improvement in his vision. His viral load = 38,900 and CD4 = 285. He admits to poor adherence over past 2 months. A GT is performed and shows K103N & M184V mutations.

Clinical Decisions and Questions

What antiretroviral combinations would be appropriate to consider?

What type of follow-up should be done if therapy is changed?

What additional concerns need to be addressed?

Case Study 2Treatment Selection and Response

His regimen is changed to: ATV/RTV/TDF/3TC/ZDV.

After 3 months, the viral load is undetectable and CD4 is 354

Case Study 3

K.C. is a 41 y.o. female with a history of former IVDU and HCV/HIV co-infection. She was treated initially with Viracept and Combivir. She has a long history of non-compliance and her viral load was never undetectable. She was changed to Combivir and Kaletra, but her viral load remained high at 53,000. A GT is done and shows no resistance mutations. A discussion with the patient reveals very poor adherence due to GI side effects and difficulty remembering her pills.

Clinical Decisions and Questions

What is the meaning of the resistance assay and is it believable?

Is it appropriate to start a new antiretroviral regimen in this patient?

If so, what antiretroviral drugs would be appropriate?

What other concerns should be addressed?

What follow-up should be done?

Case Study 3:Treatment Selection and Response

She is changed to ATV/RTV/TDF/ETV and these are given daily with her methadone.

Patient’s viral load after 3 months (and subsequently for the next year) is undetectable