Transcriptional targeting to anterior pituitary lactotrophic cells using recombinant adenovirus vectors in vitro and in vivo in normal and estrogen/sulpiride-induced hyperplasic anterior pituitaries

The use of pituitary cell type-specific promoters is a powerful molecular t ool to achieve pituitary cell type-specific transcriptional targeting of tr ansgenes encoded by viral vectors. It has recently been proposed that trans criptional targeting of therapeutic genes could be harnessed as a gene ther apy strategy for the treatment of pituitary disease. We describe the succes sful use of the human PRL promoter (hPrl) encoded within recombinant adenov irus vectors to target transgene expression of Herpes Simplex Virus Type 1- Thymidine Kinase (HSV1-TK) or beta-galactosidase to lactotrophic cells in v itro and in, vivo. Functionally, the restriction of expression of HSV1-TK t o lactotrophic tumor cells, using the hPrl promoter, resulted in the cell t ype-specific induction of apoptosis in the lactotrophic GH3 tumor cell line , in the presence of ganciclovir (GCV). In the corticotrophic AtT20 cell li ne, we detected neither HSV1-TK expression, nor apoptosis in the presence o f GCV. The hPrl promoter encoded within a recombinant adenoviral vector als o restricted transgene expression to lactotrophic cells in primary anterior pituitary (AP) cultures, and importantly, within the anterior pituitary gl and in vivo. When the HSV1-TK driven by hPrl promoter was used in an in viv o model of estrogen/sulpiride lactotroph induced hyperplasia within the AP in situ, the treatment was not effective in either reducing the weight of t he gland, the number of lactotrophic cells within the transduced area in vi vo, or the circulating PRL levels. This is in contrast to the human cytomeg alovirus promoter (hCMV) driving expression of HSV1-TK in the same experime ntal paradigm, which was effective in reducing pituitary weight and circula ting PRL levels. Our results have important implications in the design of g ene therapy strategies for pituitary tumors. We demonstrate that both the c hoice of the in vivo animal model, i.e. adenoma in the AP gland in situ, an d the particular gene therapy strategy chosen, i.e. use of strong ubiquitou s promoters us. weaker but cell type-specific promoters, determine the expe rimental therapeutic outcome.