Direct-acting antiviral agents against hepatitis C virus (HCV) have recently been developed and are ultimately hoped to replace interferon-based therapy.
However, direct-acting antiviral agents monotherapy results in rapid emergence of resistant strains and direct-acting antiviral agents must be used in combinations that present a high genetic barrier to resistance, although viral kinetics of multidrug-resistant strains remain poorly characterized.
Dr Kazuaki Chayama and colleagues from Japan studied the emergence and fitness of resistance using combinations of telaprevir and NS5A or NS5B inhibitors with genotype 1b clones.
HCV-infected chimeric mice were treated with direct-acting antiviral agents, and resistance was monitored using direct and ultra-deep sequencing.
|NS3-V36A telaprevir resistance mutation resulted in poor response to telaprevir monotherapy|
|American Journal of Gastroenterology|
Combination therapy with telaprevir and BMS-788329 (NS5A inhibitor) reduced serum HCV RNA to undetectable levels.
The team noted that presence of an NS3-V36A telaprevir resistance mutation resulted in poor response to telaprevir monotherapy but showed significant HCV reduction when telaprevir was combined with BMS-788329.
However, a BMS-788329-resistant strain emerged at low frequency.
The team noted that infection with a BMS-788329-resistant NS5A-L31V mutation rapidly resulted in gain of an additional NS5A-Y93A mutation that conferred telaprevir resistance during combination therapy.
The research team found that infection with dual NS5AL31V/NS5AY93H mutations resulted in poor response to combination therapy and development of telaprevir resistance.
Although HCV RNA became undetectable soon after the beginning of combination therapy with BMS-788329 and BMS-821095 (NS5B inhibitor), rebound with emergence of resistance against all 3 drugs occurred.
Triple resistance also occurred following infection with the NS3V36A/NS5AL31V/NS5AY93H triple mutation.
Dr Chayama's team concludes, "Resistant strains easily develop from cloned virus strains."
"Sequential use of direct-acting antiviral agents should be avoided to prevent emergence of multidrug-resistant strains."