Mechanisms of HIV Antiretroviral Failure

1. Mechanisms of HIV Antiretroviral Failure Basic science aspects on how resistance develops Dr. Bhavna Chohan, PhD 22, May 2014 NASCOP Breakfast CME 1

2. Life Cycle of HIV 1. Free Virus 7.. Maturation 2. Attachment 6. Assembly 3. Entry 5. Integration 4. Reverse Transcription During this life cycle a lot of genetic mutations occur

3. Fidelity of Retroviral Replication After acquisition of HIV undergoes replication Reverse transcriptase highly error prone enzyme - causes many genetic mutations • These mutations are completely random and by chance. • Rapid turnover of virus = high mutation rate - 1010virus particles per day in HIV-1 infected individual • During chronic infection - viral quasispecies detected • 3

4. HIV-1 diversifies in sequence in the infected person as a result of immune and other factors Bottleneck at Transmission Chronic infection Early Infection ~1% diversification per year in the envelope sequence, typically ~5-8% during course of infecion High viral diversity identified in chronic infection

5. HIV Mutations May Affect: Ability of HIV-1 to generate new virus variants allows virus to evade immune systems and foster development of ARV drug resistance ARV Resistance - consequence of viral replication in the presence of ARV drugs - resistance may require single mutations or multiple mutations to confer phenotypic resistance 5

6. How Drug Resistance Arises Population Dynamics DR strains of HIV within an individual on therapy How drug resistance arises. Richman, DD. Scientific American , July 1998 Drug resistance can be: - Acquired – occurs within infected individual through drug selection process - Transmitted (from person to person) 6

7. Factors Leading to Resistance (1) One or more of these factors can lead to ARV resistance in a given patient: • VIRUS related • VIRUS & DRUG related • DRUG related • PATIENT related (adherence problem) 7

8. Factors Leading to Resistance (2)  High replication rate  High mutation rate – error prone RT enzyme  Drug resistance with primary HIV infection • Inadequate potency • Inadequate durability • Drug-drug interactions • Poor tolerability • Inconvenience Virus Drug Patient  Adherence <100%  Toxicity or inconvenience All factors lead to persistent viral replication in presence of drug pressure and hence leads to drug resistance 8

9. Virus related Factors • High replication rate of HIV. – Turnover of 10 billion virions daily. • Frequent errors made during replication (RT enzyme). • High mutation rate. – 20 billion mutations daily. • Latent reservoirs of HIV. – Enable drug resistant HIV to hide for 20-30 yrs 9

10. Latent Reservoirs and Resistance • ARV resistance, once it develops, is probably life- long, since resistant HIV can hide in latent cellular reservoirs, which can be activated many years later. • Once a patient is resistant to an ARV drug, that drug will probably be ineffective in the future. HIV does not “forgive” treatment errors or the nonadherence 10

11. Viral Mutations and Antiretroviral Genetic Barriers Efficacy of ARV treatment regimen depends on: -Activity of regimen’s individual ARV drugs -# of HIV mutations required for development of resistance to each drug (genetic barrier) 11

12. Mutations • Molecular definition: change in nucleic acid sequence compared to a reference sequence • Biological definition: change in nucleic acid sequence that results in a change in structure or function of the nucleic acid or a resulting protein Codon AAA GAC AGT AAA GAC AGT Silent Mutation AAA GAC AGT AAC GAC AGC Lys (K) Asn (N) Asp (D) Ser (S) Asp (D) Ser (S) 12

13. Mutational Nomenclature M184V Wild-type (wt) amino acid M = Methionine (consensus or reference) Mutant amino acid V=Valine Codon position RT: 1-540 amino acids M184M/V (mix of wt and mutant) M184V/I (mix of 2 mutants)

14. Mutations and Resistance • For certain ARVs, only one mutation is needed to stop the drug from working; example: K103N a NNRTI mutation: AAA AAG AAC AAT Asn (N) Asn (N) Lys (K) Lys (K) LOW GENETIC BARRIER • For other ARVs, multiple, step-wise mutations must occur before the drug loses affect; example: I47A Protease inhibitor mutation (2 base mutation change): ATT ATC ATA GCT GCC GCA Ile (I) Ile (I) Ile (I) Ala (A) HIGH GENETIC BARRIER Ala (A) Ala (A) 14

15. Genetic barrier & Potency of some ARVs (HIV-1 Antiretroviral Resistance. Scientific Principals and Clinical Implications. Drugs 2012) Genetic Barrier to 6 classes of ARVS NRTIs, NNRTIs, PIs, Integrase Inhibitor, CCR-5 inhibitor, Fusion inhibitor 15

16. Adherence-resistance relationship http://home.mindspring.com/~rd_spitzer/livhiv2.htm

17. Adherence-resistance relationship (in order of likelihood of acquired resistance) • NVP, EFV: highest risk at low adherence • 3TC/FTC: highest risk at moderate-to-high adherence • TDF, AZT, d4T: highest risk at moderate adherence • Boosted Protease Inhibitors (bPIs): highest risk at moderate-to-high adherence Adapted from Gardner et al, AIDS 2009

18. DRMs: relationship to ARVs ARV Significant DRMs NRTIs 3TC/FTC M184 I/V Zidovudine (AZT) TAM 1 TAM 2 Non-TAM M41L/L210W/T215Y D67N/K70R/T215F/T219E/Q Q151M K65R Q151M Tenofovir NNRTIs Nevirapine Efavirenz K103N/Y181C/G190A K103N/Y181C/G190A Wainberg et al, NEJM August 2011

19. Reverse Transcriptase Mutations Selected by NRTIs –TAMs TAMs are selected mutations, commonly seen in patients treated with thymidine analogue NRTIs (AZT or d4T) • TAMs can confer cross-resistance to other NRTIs. • Viruses with multiple TAMs, more likely to develop additional TAMs when treated with other NRTIs. • • TAMs occurs in higher proportion of patients receiving AZT- regimen then patients receiving TDF- or ABC- containing ART 19

20. Major Mutations Selected by PIs ARV Major Mutations Specific mutations Kaletra (LPV/r) I47A, L76V, V82ATSF Atzanavir/r I50L, I84V, N88S High genetic barrier & large number of mutations required for resistance (Reduced responses V32I, I50V, I54M, L76V, and V82F) Darunavir/r 20