Gilead, Spring Bank's hep B combo shows 'incremental benefit,' but all eyes on higher doses: analysts

test tubes
Inarigivir is designed to block hepatitis B viral replication by activating inside liver cells’ retinoic acid-inducible gene 1. (Pixabay)

Spring Bank Pharmaceuticals’ hepatitis B drug, given in tandem with Gilead’s Vemlidy, tamped down on chronic disease in more than one-fifth of patients in a phase 2 study—a result that Jefferies analysts called an “incremental positive benefit” over either drug alone. The data, from the lowest dose of the treatment, inarigivir, set the stage for potentially better performances from higher doses. 

The company reported data on Thursday from 30 patients who had received the inarigivir-Vemlidy combination and 12 patients who took Vemlidy alone. After 12 weeks of treatment, 7 of the 30 patients taking the combo—about 23%—met the primary endpoint of HBsAg levels from baseline, compared to 3 out of 12—or 25% of—Vemlidy patients and 7%, or 1 of 14, patients in a separate study who received inarigivir alone. HBsAg is the surface antigen of the hepatitis B virus and shows if a person is infected. 

Spring Bank also reported data from patients who did not have an ALT flare, or a surge of liver enzymes that indicates an immune response to the virus, ahead of the trial. Among these patients, 18% of 28 patients responded to the combination, versus 10%—1 of 10—of patients who responded to Vemlidy. After 12 weeks of treatment, patients in both arms will receive Vemlidy for 36 weeks. 

“We are very encouraged that these preliminary results suggest the addition of a low dose of inarigivir to a NUC therapy in chronic HBV patients could enhance the size of the HBsAg responder population as compared to the experience with the 50mg monotherapy dose in our completed Phase 2 ACHIEVE dose escalation trial,” said Spring Bank CEO Martin Driscoll.  

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Inarigivir is designed to block hepatitis B viral replication by activating inside liver cells’ retinoic acid-inducible gene 1 (RIG-I). Vemlidy is a nucleoside analog, or NUC, that also inhibits viral replication.

The company—and the Jefferies analysts—expect the higher doses to do even better. Spring Bank expects to report data on the 200mg and 400mg doses of inarigivir next year. 

“We look forward to the data from the higher dose cohorts of this trial and our ongoing CATALYST Phase 2b studies evaluating longer durations of treatment with inarigivir monotherapy and co-administered with a NUC that could further expand the chronic HBV responder population with the goal to significantly elevate functional cure rates for HBV patients.” 

“SBPH has zeroed-in on 400mg inargivir activity/safety profile as most favorable, and this dose is being tested in ph.II CATALYST 1&2 -- goal is to generate rich dataset next 2 to 3 quarters to inform a HBV pivotal start potentially by YE20,” the analysts wrote. 

Because recruiting for the phase 2b study has been on a roll, Spring Bank could present 24-week data as early as the European Association for the Study of the Liver (EASL) meeting next year, they wrote. As for the phase 1 study, which is testing inarigivir alone and in combination with Vemlidy in treatment-naive patients, the company expects to announce interim 12-week data at EASL.