In vitro and in vivo herpetic vector-mediated gene transfer in the pituitary gland: impact on hormone secretion

Objective: Herpes simplex virus type 1 (HSV-1)-derived vectors are known to be effective tools to deliver transgenes into normal and neoplastic anteri or pituitary (AP) cells in vitro. Our objective was to assess the in vitro and in vivo effects of tsK/beta -gal, a temperature-sensitive HSV-1-derived vector harbouring the E. coli beta -galactosidase gene, on AP hormone secr etion as well as on transgene expression in rat AP tumours (hyperplastic pr olactinomas). Design: The impact of vector infection on prolactin (PRL) and GH release wa s determined in vitro in normal and hyperplastic (lactotrophic) dispersed A P cells exposed for 24 h to tsK/beta -gal as well as in vivo in ectopic AP grafts. In some oestrogen-induced prolactinoma-carrying rats, vector suspen sion was stereotaxically injected into the glands to assess transgene expre ssion in vivo. Methods: GH and PRL release was measured by specific RIAs. In vivo transgen e expression was assessed by immunohistochemistry for beta -galactosidase a nd enzymohistochemistry (5-bromo-4-chloro-3-indolyl-beta -D-galactopyranosi de). Ectopic pituitary grafts and stereotaxic surgery were performed follow ing standard procedures. Results: At a multiplicity of infection of 0.5, the vector induced a 30 and 22% fall in PRL and GH release respectively in normal AP cells, whereas th e corresponding hormone release inhibition for hyperplastic AP cells was 41 and 33% for PRL and GH respectively. In ectopic pituitary grafts, the effe ct of vector infection on hormone secretion was assessed by measuring serum PRL levels in the host rats every 5 days for 4 weeks post-grafting. In the pituitary-grafted rats that received the viral vector, serum PRL failed to increase to the levels achieved in control-grafted animals. Finally, pitui tary tumours stereotaxically injected with tsK/beta -gal showed widespread expression of the beta -galactosidase transgene around the injection areas. Conclusions: The results reported here have implications for basic studies using gene transfer to pituitary gland as well as potential gene therapy ap proaches to pituitary diseases.