ARV failure and resistance for the paediatrician

Douglas Watson, M.D.University of Maryland

11 December 2013

REVERSE TRANSCRIPTASE INHIBITORS (NRTIs & NNRTIs)

PROTEASE INHIBITORS

Attachment Inhibitors

Integrase inhibitors

Fusion Inhibitors

HIV DRUG TARGETS

Antiretrovirals in the U.S.- 2013Nucleoside analogues (NRTIs)Zidovudine (ZDV, AZT, Retrovir)Lamivudine (3TC, Epivir)Tenofovir (TDF, Viread)Emtricitabine (FTC, Emtriva)Abacavir (ABC, Ziagen)Stavudine** (D4T, Zerit)Didanosine** (DDI, Videx)

Non-nucleoside reverse transcriptase inhibitors (NNRTIs)Efavirenz (EFV, Sustiva)Nevirapine (NVP, Viramune) Etravirine (ETV, Intelence)Delavirdine** (DLV, Rescriptor)Rilpivirine (Edurant)

Protease inhibitorsLopinavir/ritonavir (LPV/r, Kaletra)Atazanavir (ATV, Reyataz)Fosamprenavir (fAMP, Lexiva)Darunavir (DRV, Prezista)Tipranavir* (TPV, Aptivus)Saquinavir* (SQV, Invirase)Nelfinavir* (NFV, Viracept)Indinavir** (IDV, Crixivan)

Integrase inhibitorsRaltegravir (RAL, Isentress)ElvitegravirDolutegravir (Tivacay)

Attachment inhibitor Maraviroc (Selzentry)

Fusion inhibitorEnfuvirtide* (T-20, Fuzeon) P450 inhibitor (for “boosting” PIs)

Ritonavir (RTV or r, Norvir)Cobicistat*Uncommonly used. **No useful role

WHO 2013 recommendations for 1st-line ART in children < 3 y of age

• “ABC should be considered the preferred NRTI whenever possible.”

• LPV//r should not be given to infants < 14 d of age or in premature infants until after 14 d after their due date

WHO 2013: Start with LPV/r and switching to NNRTI?

NOTE: •The quoted study enrolled only children with history of SD NVP exposure•The quoted study used < 50 copies/ml as primary endpoint and < 1,000 c/ml as secondary endpoint- NOT < 400 c/ml as stated above. •The switch-to-NVP group had fewer cases of VL > 50 but more cases of VL > 1,000 and more resistance than group that stayed on LPV/r

WHO 2013 recommendations for 1st line ART in children > 3 y of age

Adherence failurePotency failure

Virologic failure

Immunologic failure

Clinical failure

Treatment failure: progressive steps, different definitions

Genotypic failure (resistance)

Expected fall in viral loadTime Log fold

drop in viral load

Fold-drop in viral load

Viral load (example)

Viral load (example)

0 -- -- 600,000 100,000

1 month 2 100+ < 6,000 < 1,000

3 months 3 1,000 600 100

6 months 4 10,000 60 <50

If viral load at these follow up times is 3-fold or more than these examples, full suppression not likely

10

100

1000

10000

100000

1000000

-20 0 20 40 60 80 100 120 140 160 180Days

HIV viral load response to D4T/3TC/NFV/NVPTherapy started at day 0 (6 weeks old)

Vir

al lo

ad

CD

4 C

ou

nt

Start ZDV/3TC/NVP

Nonadherence

NVP resistance

3TC resistance

Gradual ZDV resistance

Clinical deterioration

1 year 2 years

Course of treatment failure

ABC

NNRTI (NVP or EFV)Blocks reverse transcriptase

by binding at active site

NRTI (such as ABC(P3) is added onto cDNA chain, blocking further

reverse transcription

cDNA

Mechanism of reverse transcriptase inhibitors

NRTI = Nucleoside reverse transcriptase inhibitorNNRTI = Non-nucleoside reverse transcriptase inhibitor

HIV reverse

transcriptase

The K103N mutation: how it can take over

Nevirapine

Resistant 103N HIV

Sensitive K103 HIV wild type (wt)

NVP blocks sensitive HIV, not resistant HIV

In presence of NVP, only the resistant virus grows. Soon almost all virus is resistant!

wt always present

Drug resistance mutations in Thai patients failing D4T/3TC/NVP for an average of 4-5 months by viral load monitoring. Sungkanuparph S. CID 2007; 44:447–52

Stavudine(D4T)

Zidovudine(AZT)

Abacavir(ABC)

Tenofovir(TDF)

Didanosine(DDI)

Lamivudine(3TC) or Emtricitabine (FTC)

Thymidine analogue mutations(TAMS)ResistanceAZTD4TTDF

TAMS +184VResistance3TC, FTC > D4T, DDI, AZT, ABC > TDF

K65RResistanceTDF, ABC, DDID4T3TC, FTC

HypersensitivityAZT

L74V+ M184VResistanceABCDDI3TC FTC

HypersensitivityAZTTDF

M184VResistance3TCFTC

HypersensitivityTDF > AZT > D4T

Q151MResistanceAZT, D4T,DDI, ABC >TDF, 3TC, FTC

Nucleoside reverse transcriptase inhibitor resistance and cross-resistance

Summary: NRTI resistance patterns & options

Regimen Common pattern Other patterns

Geno Resistance Options* Geno Resistance Options*

D4T/3TC M184V,

TAMS

3TC >

D4T, ZDV, ABC, DDI >TDF

TDF/3TC (+/-ZDV)>

(ZDV/3TC/ABC)

(how good depends on # of TAMS)

K65R, M184V

or

M184V, Q151M

3TC, TDF, ABC, DDI, d4T

3TC, ZDV, D4T, DDI, ABC, (TDF)

ZDV/3TC

(TDF/3TC)

ZDV/3TC “ “ “

TDF/3TC K65R,

(M184V)

3TC, TDF, ABC, DDI, d4T

ZDV/3TC

ABC/3TC M184V, L74V

3TC, ABC, DDI

ZDV/3TC M184V, K65R

3TC, TDF, ABC, DDI, d4T

ZDV/3TC

DDI/3TC M184V, L74V

3TC, ABC, DDI

ZDV/3TC

*Options: Underline = excellent, () = weak, others fair

NNRTI resistance• 1st generation (nevirapine, efavirenz, delavirdine)

– High potency but low genetic barrier to resistance– Most commonly K103N- resistance to all 1st generation– NVP also selects for Y181C (especially in newborns) which has

mild effect on EFV but associated with increased failures– Other mutation patterns also seen

• 2nd generation (Etravirine)– NO EFFECT of K103N– Resistance increases with other NNRTI mutations- 3 or more

yield

Protease inhibitor resistance• Some PIs select for drug-specific mutations (e.g. NFV,

ATV)• Some PIs can be boosted or unboosted (ATV, fAPV)-

low-level resistance may be clinically significant if not boosted

• Boosted PIs more durable• Resistance to LPV requires 5-10 mutations• Virologic failure while receiving LPV/r usually due to

nonadherence• Prolonged virologic failure while on LPV/r eventually

will lead to LPV resistance

Drug resistance testing

• Commercial methods start with RT PCR of bulk virus in plasma

• Not sensitive to minor strains- e.g. genotyping (sequencing) cannot detect strain representing < 10-25% of circulating virus

• When to get resistance testing (resource-rich)– Baseline: resistant strains (especially NNRTI resistance)

circulating in population

– Whenever resistance suspected (e.g. failing and patient appears adherent)

– Selective pressure- patient taking medication

HIV drug resistance genotype• RT PCR bulk plasma virus to produce cDNA• Sequence pol gene• Derive predicted amino acid sequence• Identify mutations known to confer resistance (e.g.

Stanford database, IAS-USA, etc.)• Virtual phenotype™ genotype interpretation

– Identified set of significant mutations is matched with massive database of genotype-phenotype correlations

– Reported as predicted fold resistance (used to also give number of matches)

– Fold-resistance interpreted according to in vitro or clinical measure of activity

IAS-USA, Topics in HIV Medicine, March 2013

Interpretation of resistance testing

• Complete treatment and viral load history are essential

• What is current regimen and is patient taking it?

• Many resistance mutations cause decreased viral fitness: if there is not selective pressure, wild-type virus rapidly outgrows mutant, but archive of mutant remains

WHO 2013

Johnny B. Goode

• Newly infected adolescent

• CD4 = 320, VL = 58,000

• Prescribed TDF/FTC/ATV/r

• VL 1 month later = 5,200

• VL at 2 months = 4,000

• Genotype is wild-type

• How do you interpret this situation?

• How to proceed?