Gilead/Spring Bank’s Phase II inarigivir/Vemlidy combo logical for HBV but inarigivir's modest data and unclear mechanism draws expert reservations

25 Jul 2018

Gilead Sciences (NASDAQ:GILD) and Spring Bank Pharmaceuticals’ (NASDAQ:SBPH) Phase II trial investigating inarigivir in combination with Gilead’s nucleoside analogue Vemlidy (tenofovir) for hepatitis B virus (HBV) infection has a promising rationale due to the combination’s synergistic antiviral approach. However, inarigivir’s monotherapy efficacy impact is still unclear, drawing uncertainties to its potential contribution in a combination setting, some noted.

If 20-30% of Phase II patients experience a single- or double-digit HBV surface antigen (HBsAg) log10 reduction, an element of the trial’s primary endpoint, it would be encouraging for future development, experts said. However, inarigivir’s monotherapy data has so far been modest and any potential dose effect is still unclear, some experts noted. Inarigivir’s mechanism still lacks clarity, with doubts lingering as to the strength of inarigivir’s antiviral impact, others said.

Whilst the trial’s primary endpoint lacks clinical value, the measure could still have value to indicate if the combination is worth investigating further, experts said. Although inarigivir and Vemlidy may have positive safety profiles independently, there is still the risk of unknown toxicities surfacing when used in combination, one expert noted.

Inarigivir/Vemlidy is in a 90-patient Phase II trial (NCT03434353), with an analyst report showing the 50mg inarigivir plus Vemlidy data expected in 2H. The trial includes three more arms: 100mg inarigivir in patients who are already receiving a nucleoside analogue, Vemlidy monotherapy and inarigivir 200mg with Vemlidy. Analysts have inarigivir pegged for USD 1.1bn in sales in 2030.

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