Using the adenovirus vector AdCF126(CRE8).Luc to deliver an expression cassette containing multiple cyclic adenosine monophosphate (cAMP) response elements driving the luciferase reporter gene, this study is directed toward evaluating the possibility of controlling genes transferred to the liver using pharmacological agents that raise hepatocyte cAMP levels. Infection of primary rat hepatocytes with AdCF126(CRE8).Luc yielded a low level of luciferase activity that was enhanced 16-fold by the addition of forskolin. Direct intrahepatic administration of the Ad vector in C57B1/6 mice resulted in low-level luciferase activity that was increased 76-fold by the administration of theophylline and 8-bromo-cAMP to increase cAMP levels. In contrast, animals receiving intrahepatic administration of a control vector containing a constitutively active Rous sarcoma virus (RSV) viral promoter driving the luciferase gene had no response to elevated cAMP. Strikingly, delivery of the vector to the liver by the intravenous route permitted a 258- fold enhancement of liver luciferase activity following administration of the same cAMP-elevating agents. In comparison, a control Ad vector with the RSV promoter was not activated by the elevation in cAMP. The maximum luciferase levels achieved by the combination of AdCF126(CRE8).Luc and pharmacological cAMP elevation was 45-fold greater than that with the RSV promoter. These results show the feasibility of using a chimeric promoter to permit pharmacological induction of high-level expression from an expression cassette transferred to the liver with an adenovirus vector, an approach that may be useful in a variety of liver-related gene-transfer strategies.
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