Selective expression of nonsecreted interferon by an adenoviral vector confers antiproliferative and antiviral properties and causes reduction of tumor growth in nude mice

Replication-deficient adenoviruses expressing human interferon-alpha 2b (Hu IFN-alpha 2b) or the hybrid IFN-alpha2 alpha1 or those with the secretory s ignal deleted, whose express is driven by the alpha -fetoprotein (AFP) prom oter, were constructed and characterized. Synthesis of IFN protein and secr etion or intracellular retention were tested by Western blotting and immuno assay, Expression of IFN by the recombinant adenoviruses was restricted to cells that constitutively express AFP, In these cells, expression of both s ecreted and nonsecreted recombinant IFN resulted in inhibition of cell prol iferation, resistance to viral infection, induction of major histocompatibi lity complex (MHC) class I expression, increased apoptosis, and activation of an IFN-stimulated response element (ISRE)-containing promoter, Also, the induction of protein kinase R (PKR), increased phosphorylation of Stat1, a nd accumulation of hypophosphorylated pRb were observed for both the secret ed and nonsecreted IFN, suggesting that the nonsecreted IFN may act through a similar pathway, Hep3B cells, an AFP-positive line derived from a patien t with hepatocellular carcinoma (HCC), were injected subcutaneously (s.c.) into athymic nude mice to generate established tumors. Intratumoral injecti on of recombinant adenoviruses expressing secreted as well as the nonsecret ed IFN caused suppression of tumor growth. As the AFP promoter is activated in many HCC cells but is silent in normal cells, these constructs may be u seful in restricting IFN effects to the tumor cells while reducing toxicity to the neighboring tissues.