Resistance to HCV direct-acting antivirals: What should we know? Heidar Sharafi, MSc, PhDc Middle East Liver Diseases (MELD) Center E mail: h.sharafi@meldcenter.com

Approved HCV Direct-acting Antiviral (DAA) Agents Core E1 E2 P7 NS2 NS3 4A NS4B NS5A NS5B 5’UTR 3’UTR Protease Inhibitors Simeprevir (SMV) Paritaprevir (PTV) Grazoprevir (GZR) NS5A Inhibitors Ledipasvir (LDV) Daclatasvir (DCV) Ombitasvir (OMV) Elbasvir (EBR) Velpatasvir (VEL) NS5B NUC Inhibitors Sofosbuvir (SOF) NS5B non-NUC Inhibitors Dasabuvir (DSV) Bertino G. World Journal of Hepatology. 2016;8(2):92-106.

Mechanism of Action Mechanism of action: Resistance: Binding and blocking the active site of the protein (NS3, NS5A & NS5B) Resistance: Mutations close to active site reduce affinity to drug

HCV displays a high genetic diversity Production of 1012 virions daily ~1 error per 10,000 bases for RNA polymerase Within one patient HCV exists as a population of genetically distinct but closely related variants (quasispecies) RAVs: Resistance-associated Variants

The Theory for Resistance to new DAAs 2-12 weeks after termination of treatment Quasispecies with dominant wild-type virus and single resistant variants After few days, wild-type virus is eliminated At the end of treatment v Treatment with DAAs Baseline Wild type Medium resistance/more fit High resistance/unfit Resistance with increased fitness

Barriers to Genetic Resistance by DAAs Approved (GT1) Protease Inhibitors NS5A Inhibitors NS5B NUC Inhibitors NS5B non-NUC Inhibitors DAAs in class Simeprevir Paritaprevir Grazoprevir Ledipasvir Daclatasvir Ombitasvir Elbasvir Sofosbuvir Dasabuvir Barrier to resistance Low (1a < 1b) High (1a = 1b) Very Low (1a < 1b) RAVs to one DAA are generally cross-resistant to other DAAs within a class, although this is not always the case Bertino G. World Journal of Hepatology. 2016;8(2):92-106.

NS5A Resistance Overview Baseline polymorphisms associated with resistance are relatively prevalent (15-30%) Currently available NS5A inhibitors suffer from broad cross-resistance at key positions Q30R, L31M/V, Y93H/N 75% of patients harbor RAVs after treatment failure with SOF/LDV NS5A variants persist for prolonged periods Selected NS5A RAVs impact re-treatment responses

Broad Cross-resistance with NS5A inhibitors Fold-change in resistance GT1a GT1b M28T Q30R L31M/V Y93H/N L31V LDV 20x >100x >100x/ >1,000x >1,000x/ >10,000x >100x/-- OMV >1000x <3x <10x 20x/50x DCV EBR >10x VEL <3x/-- http://iasusa.org/sites/default/files/uploads/2016hivsny_naggie.pdf

Baseline NS5A RAVs in DAA-naïve Patients Genotype 1a Genotype 1b Baseline RAVs in GT1a (M28, Q30, L31 & Y93) have the largest clinical impact. Y93H in GT1b; most common but little impact Y93H in GT1b ~100-fold change while in GT1a ~10,000-fold shift The subtype background has much to do with whether the RAV has a clinical impact. Dietz J. PloS one. 2015;10(8):e0134395.

Treatment-Naïve: Baseline NS5A Resistance and SOF/LDV ~4% delta in SVR if RAV Analysis of baseline samples (n=1904) in phase 2/3 SOF/LDV studies 93% SVR12 92% SVR12 97% SVR12 NS5A RAVs 95% SVR12 16% 16% 84% 84% No RAVs 96% SVR12 98% SVR12 Sarrazin C. AASLD. 2014;Abstract#1926.

Baseline NS5A Resistance and SOF/LDV SVR12, % Sarrazin C. AASLD. 2014;Abstract#1926.

Baseline NS5A Resistance and SOF/LDV SVR12, % Sarrazin C. AASLD. 2014;Abstract#1926.

Impact of Baseline NS5A RAVs in Patients with Cirrhosis Treated with SOF/LDV Impact of subtype and fold-change SVR12, % SVR12, % SVR12 combined: 98% no RAVs vs 89% RAVs [@15% level] Sarrazin C. EASL. 2015;Abstract#P0773.

Impact of Baseline NS5A RAVs in Patients with Cirrhosis Treated with SOF/LDV Impact of duration and RBV SVR12, % Sarrazin C. EASL. 2015;Abstract#P0773.

Consideration for NS5A Resistance Testing in DAA-Naïve Patients – G1a Only SOF/LDV Apparent role in treatment-naïve patients 8 weeks Rx Cirrhosis Could baseline testing be used to “optimize” therapy in TE patients, particularly those with cirrhosis? 24 weeks + RBV for all TE cirrhosis with baseline NS5A RAVs? Overtreatment of many patients?

High Durability of Treatment Emergent NS5A RAVs Patients with NS5A RAVs, % Dvory-Sobol H. EASL. 2015;Abstract#77.

NS5A RAVs are Associated with Retreatment Failure-SOF/LDV for 24 Weeks (n=41) SVR12, % SVR12, % Lawitz E. EASL. 2015;Abstract#O005.

SUMMARY Additional data are needed, particularly in the setting of DAA failure, to define the role of resistance testing in deciding best therapy. In case of HCV genotype 1 infection, the following are parameters associated with resistance: Subtype 1a Duration of treatment Cirrhosis Adding RBV Fold change caused by the RAV In the future, resistance testing may play a role in deciding how long to treat as well as what to use