EXPRESSION OF TRANSGENES IN NORMAL AND NEOPLASTIC ANTERIOR-PITUITARY-CELLS USING RECOMBINANT ADENOVIRUSES - LONG-TERM EXPRESSION, CELL-CYCLE DEPENDENCY, AND EFFECTS OIL HORMONE-SECRETION

Adenovirus vectors have recently been used to transfer genes into a va riety of cell types, including neurons, glial cells, Schwann cells, an d epithelial cells. To evaluate the efficiency of gene transfer into p ituitary cells using viral vectors, we used replication-deficient reco mbinant adenovirus vectors (RAds) encoding beta-galactosidase driven b y various viral promoters. We tested the ability of RAds to infect and express beta-galactosidase within the different identified cell popul ations of the anterior pituitary anterior pituitary gland and also in tumor cells of anterior pituitary origin, i.e. GH(3) and AtT20 cells. Our results demonstrate that transgenes encoded by RAds are expressed within all cell types of the adenohypophysis in vitro and also within AtT20 and GH(3) endocrine tumor cells. Our long term expression studie s indicate that long term expression with low cytotoxicity can be achi eved, but that the longevity of transgene expression from RAds depends on the proliferative status of the target cells. Slowly dividing cell s (endocrine population) express transgenes for longer than actively d ividing cells (tumor cells and nonendocrine anterior pituitary cells). The ability of anterior pituitary cells to secrete ACTH or LH through the regulated secretory pathway decreased after infection with RAds a t high multiplicity of infection (greater than or equal to 20 plaque-f orming units/target cell), whereas cell viability was not affected. We also demonstrate that a higher percentage of cells expressed the tran sgene beta-galactosidase when we infected actively dividing GH(3) cell s compared with the infection of growth-arrested GH(3) cells. This cou ld reflect differential virus entry or differential activity of the in dividual promoters during different stages of the cell cycle. This wor k demonstrates that high efficiency gene transfer into all pituitary c ell types can be achieved with RAds, and that this system can be explo ited to characterize and experimentally manipulate pituitary-specific gene expression. The higher efficiency of infection and transgene expr ession in actively dividing cells compared to that in their growth-arr ested counterparts could also be exploited for the treatment of pituit ary adenomas that do not respond to classical treatment strategies, us ing suicide or cytotoxic gene therapy.