Selective depletion of HBV-infected hepatocytes by class A capsid assembly modulators require high levels of intrahepatic HBV core protein

Several classes of capsid assembly modulators (CAMs) are currently being developed for chronic hepatitis B (CHB) cure. Both class A (CAM-A) and class E (CAM-E) CAMs disrupt nucleocapsid assembly and reduce extracellular hepatitis B virus (HBV) DNA. However, only CAM-As have been shown to reduce the number of HBV-infected cells in the animal models. However, there has been limited efficacy to date of CAM-A molecules achieving this secondary mechanism of HBV-infected cell clearance in CHB clinical trials. To investigate this disconnect, we performed comparative experiments with tool compounds from each class to further explore these unique features and antiviral activity of CAM-A across HBV-infected primary human hepatocytes (PHH), as well as in two different HBV mouse models (immunodeficient mice repopulated with human hepatocytes and AAV-HBV). Mechanistic studies in HBV-infected PHH revealed that CAM-A, but not CAM-E, induced dose-dependent aggregation of HBV core protein (HBc) in the nucleus. Experiments with siRNA, resulted in identification of the ubiquitin-binding protein p62 as a factor negatively regulating the size of these aggregates. Furthermore, we found that only the CAM-A is able to induce HBc-positive cell death in vivo with the loss of HBV-infected cells positively correlated to the levels of intrahepatic HBc. Profiling of intrahepatic HBc levels across CHB patient liver biopsies demonstrated a significantly lower level of HBc per hepatocyte than either of the HBV mouse models. Taken together, these data demonstrate that CAMs of class A have a unique secondary mechanism that has potential to specifically affect viability of HBV-infected hepatocytes. At the same time, the clearance of infected hepatocytes may depend on the level of HBc expression thereby limiting the therapeutic potential for this class of molecules.