rolonged and Inducible Transgene Expression in the Liver sing Gutless Adenovirus: A Potential Therapy for Liver Cancer IN WANG,* RUBÉN HERNÁNDEZ-ALCOCEBA,* VIJAY SHANKAR,‡ MAIDER ZABALA,*

H c ackground & Aims: Gene therapy of liver diseases ould benefit from systems allowing prolonged, regulale, and tissue-specific transgene expression. We atempted to produce a vector fulfilling these requireents. Methods: We generated gutless adenoviral ectors containing a mifepristone (RU486)-inducible sysem for controlled and liver-specific expression of huan interleukin-12 (hIL-12) (GL-Ad/RUhIL-12) and ouse IL-12 (mIL-12) (GL-Ad/RUmIL-12). The properties f these vectors were tested both in vitro and in vivo. esults: Infection of cells with GL-Ad/RUhIL-12 resulted n high level of hIL-12 expression in the presence of U486 only in hepatocytic cells. In animals injected with L-Ad/RUhIL-12, the administration of RU486 induced a ransient rise of serum hIL-12 that peaked at 10 hours nd completely disappeared by 72 hours. The peak alue of hIL-12 was dependent on the doses of the ector and the inducer. High and sustained serum levels f hIL-12 could be attained by continuing administration f RU486 every 12 or 24 hours. Repetitive induction of IL-12 could be obtained over, at least, a period of 48 eeks after a single injection of GL-Ad/RUhIL-12. Alhough the vector was detected in many tissues after ystemic injection, transcription of the transgene was nly found in the liver. Treatment of liver metastases ith 5 108 infectious units of GL-Ad/RUmIL-12 plus U846 resulted in complete tumor regression in all nimals. Conclusion: Gutless adenoviral vectors allow iver-specific and regulable transgene expression for proonged periods of time. These vectors are promising ools for gene therapy of liver cancer and could also be seful for other forms of hepatic disease.