Hepatoselective Dihydrozuinolizone (HS-DHQ) Molecules for Treatment and Prevention of Hepatitis A Virus (HAV) Infection

ABSTRACT This is a Phase II proposal to develop Harlingene’s hepatoselective dihydroquinolizinones (HS-DHQs) for treatment and prevention of hepatitis A virus (HAV) infection. This will be the first antiviral therapy to treat HAV infection, which, despite vaccines to prevent disease, causes thousands of hospitalizations and many deaths each year in the U.S. DHQs, exemplified by the Roche compound, RG7834, have antiviral activity against hepatitis B virus (HBV) and have been under development for HBV by small and major pharmaceutical companies. We are pioneering the development of DHQs for treatment and prevention of hepatitis A. We have shown DHQs have potent activity against HAV in cell culture and in mice. DHQs inhibit the nucleotidyltransferases TENT4A/B, which play a role in cellular mRNA “quality control” and are essential host factors for both HAV and HBV. However, their mechanism of action against HAV and HBV are distinct. By inhibiting host TENT4A/B, DHQs directly suppress HAV RNA synthesis, whereas they destabilize and promote degradation of HBV mRNAs. This offers a unique strategy for antiviral therapy of hepatitis A with a very low risk for resistance. While dose-limiting adverse effects have hindered the most advanced DHQ compounds, GS8873 (Gilead) and AB161 (Arbutus), these compounds do not exhibit the same liabilities, suggesting that the observed adverse effects are not inherent to the class. To mitigate these extra-hepatic toxicities, we developed DHQs that are specifically concentrated in hepatocytes, the cell type infected by HAV, thereby reducing plasma and peripheral tissue exposure. These first- in-class hepatoselective HS-DHQs leverage transporters enriched on hepatocytes to achieve liver-selective distribution. Our lead HS-DHQ, HS83128, has picomolar activity against HAV in cell culture and shows selective liver distribution in mice, with tissue-to-liver ratios ranging from 0.25 to 0.02 across plasma, heart, kidney, spinal cord, sciatic nerve, bone marrow, brain, and testis. This selective distribution suggests a lower risk of off-target effects in these tissues. Oral administration of HS83128 (12.8 mg/kg) is highly effective in suppressing HAV replication and reversing liver injury in mice and is an effective prophylactic when given prior to infection. In this STTR Phase II application, our primary objective is to advance the premier lead, HS83128, to non-GLP safety assessment in preparation for a GLP IND-enabling study. This will be achieved through comprehensive in vitro and in vivo safety testing, as well as extensive efficacy evaluations to determine the optimal dosing regimen. The second goal is to develop backup compounds with diverse structures that maintain liver selectivity and demonstrate efficacy in the HAV-infected mouse model. This will be accomplished by integrating the unique fatty acid arms—identified in the Phase I study as transporter recognition motifs—with other DHQ cores known to exhibit activity. Successful execution of the proposed studies will pave the way for advancing these unprecedented, liver-targeted antivirals to Phase I clinical trials for the treatment and prevention of HAV infection.