We have been investigating the efficacy of an intratumoral interferon (IFN)-alpha gene transfer against solid cancers, and found that when the gene is transduced into the subcutaneous rumors, IFN-alpha concentration is markedly increased in the injected tumor but not in the serum. To explain this effective confinement of IFN-alpha to target tissues, we hypothesized that the extracellular matrix in the tumors interacts with IFN-alpha. In this study, a solid-phase-binding assay and immunoprecipitation demonstrated that the IFN-alpha binds directly to matrix proteins. Immunohistochemical staining showed a co-localization of IFN-alpha with pericellular fibronectin. In addition, matrix-bound IFN-alpha protein transduced intracellular signaling and potentiated its cytotoxic activity, suggesting that the retention of IFN-alpha protein on extracellular matrix is likely to play a role in its in vivo biological activity. The data Suggest a therapeutic advantage of the intratumoral IFN-alpha gene transfer over the conventional parenteral therapy both in the safety and efficacy. (C) 2008 Elsevier Inc. All rights reserved.