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 anterior 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 secretion as well as on transgene expression in rat AP tumours (hyperplastic prolactinomas). Design: The impact of vector infection on prolactin (PRL) and GH release was determined in vitro in normal and hyperplastic (lactotrophic) dispersed AP 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 suspension was stereotaxically injected into the glands to assess transgene expression in vivo. Methods: GH and PRL release was measured by specific RIAs. In vivo transgene expression was assessed by immunohistochemistry for beta -galactosidase and enzymohistochemistry (5-bromo-4-chloro-3-indolyl-beta -D-galactopyranoside). Ectopic pituitary grafts and stereotaxic surgery were performed following 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 the corresponding hormone release inhibition for hyperplastic AP cells was 41 and 33% for PRL and GH respectively. In ectopic pituitary grafts, the effect 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, pituitary 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 approaches to pituitary diseases.