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

Abstract

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 <i>in vitro</i>. Our objective was to assess the <i>in vitro</i> and <i>in vivo</i> effects of tsK/β-gal, a temperature-sensitive HSV-1-derived vector harbouring the <i>E. coli</i> β-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 <i>in vitro</i> in normal and hyperplastic (lactotrophic) dispersed AP cells exposed for 24 h to tsK/β-gal as well as <i>in vivo</i> in ectopic AP grafts. In some oestrogen-induced prolactinoma-carrying rats, vector suspension was stereotaxically injected into the glands to assess transgene expression <i>in vivo</i>. Methods: GH and PRL release was measured by specific RIAs. <i>In vivo</i> transgene expression was assessed by immunohistochemistry for β-galactosidase and enzymohistochemistry (5-bromo-4-chloro-3-indolyl-β-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/β-gal showed widespread expression of the β-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.