Ectopic FVIII expression and misfolding in hepatocytes as a potential cause of human hepatocellular carcinoma

Clotting Factor VIII (FVIII) is the protein deficient in hemophilia A (HA), an X chromosome-linked bleeding disorder affecting 24.6 per 100,000 males at birth. Scientists and clinical physicians have been striving hard to find a cure for this disease. Presently, HA therapy involves prophylactic infusion of plasma-derived or recombinant-derived FVIII. Recent clinical studies have reported success using recent adeno-associated-virus (AAV) vector mediated delivery of a FVIII gene. FVIII is a 330 kDa glycoprotein comprised of three domains (A1-A2-B-A3-C1-C2). The B domain is dispensable and B domain-deleted (BDD) FVIII is used in the clinic as an effective protein replacement therapy for HA. Previously, we observed that hydrodynamic tail vein injection of the BDD-FVIII vector resulted in FVIII aggregation and endoplasmic reticulum (ER) stress in murine livers. Additionally, mice that were exposed to transient ER stress and then fed a high fat diet (HFD) for 9 months developed hepatocellular carcinoma (HCC). Therefore, we deduced that ectopic transient expression of FVIII in hepatocytes of mice with subsequent HFD feeding may also develop HCC. Here, we tested hepatocyte expression of two BDD-FVIII variants in vivo. BDD-FVIII aggregates in the ER and induces hepatocyte apoptosis, and N6-FVIII is more efficiently folded and secreted from the ER and causes less hepatocyte apoptosis. We performed tail vein injections of vectors directing expression of BDD-FVIII or N6-BDD to hepatocytes of 6-week old mice. One week after injection, mice were fed 60% HFD for 65 weeks. We found that 50% of mice that received N6-BDD developed liver tumors; in contrast, 90% of mice given BDD-FVIII developed liver tumors. Of the mice injected with BDD-FVIII, 30% developed carcinomas and 60% developed adenomas. Similar masses were not observed in mice that received empty vector. These findings raise concerns about the safety of long-term ectopic expression of FVIII in hepatocytes during FVIII gene therapy.