Construction of gene therapy vectors targeting adrenocortical cells: Enhancement of activity and specificity with agents modulating the cyclic adenosine 3 ',5 '-monophosphate pathway

In preliminary studies we demonstrated that the CYP11B1 (11 beta-hydroxylas e) promoter could direct specific expression of a suicide gene in adrenocor tical cancer cells, providing a potentially specific therapeutic option for adrenocortical cancer. In this present study we describe our attempts to e nhance the activity of the CYP11B1 promoter while maintaining its specifici ty for adrenal cells. Using a putative enhancer element from the cholestero l side-chain cleavage (P450scc) gene, the activity of the CYP11B1 promoter in and its specificity for adrenocortical cells were enhanced. Treatment wi th 8-bromo-cAMP or forskolin resulted in further enhancement. In stably tra nsfected Y-1 cells, in which the herpes simplex virus thymidine kinase (HSV -TK) gene was driven by the CYP11B1 promoter with the P450scc enhancer elem ent, HSV-TK expression and ganciclovir sensitivity were augmented by treatm ent with 8-bromo-cAMP, forskolin, and ACTH. In summary, we report the const ruction of a suicide HSV-TK vector with preferential toxicity to adrenocort ical cells. We propose that a similar strategy using differentiating agents may be useful in the gene therapy of tumors with unique differentiated pro perties, including those arising from other endocrine organs.