A52
Effects of GnRH receptor activation on proliferation of transformed cells in vitro and in vivo
Kevin Morgan1, Alan Stewart1, Nicola Miller1, Peter Mullen2, Simon Langdon2, Robert Millar1
1MRC Human Reproductive Sciences Unit, Edinburgh, UK, 2Edinburgh Breakthrough Research Unit, Edinburgh, UK
Background
Activation of gonadotropin releasing hormone (GnRH) receptor using GnRH analog drugs can elicit cell growth inhibition. Here, receptor signaling induces apoptosis only when plasma membrane GnRH receptor levels exceed a threshold level.
Method
Several rat B35 neuroblastoma cell lines stably expressing rat GnRH receptor cDNA were generated using plasmid DNA transfection, G418 selection and in vitro cloning, and their responses to GnRH analog were compared.
Results
Relative levels of cell surface GnRH receptor varied from 1.0 to 1.2 or 2.7 in B35-2, B35-20 and B35-2b respectively. These levels equated to 50%, 60% and 135% that of pituitary gonadotrope levels (alphaT3 cells).
In vitrocell growth was inhibited by 13%, 24% and 87% respectively in B35 clones following treatment with D-Trp6-GnRH-I (Triptorelin) for 4 days.
Receptor signaling intensity correlated with growth retardation of cell-derived tumour xenografts propagated subcutaneously in female athymic mice treated daily with Triptorelin.
B35-2 and B35-2b tumour growth was retarded by 32% and 48% respectively relative to vehicle treated animals following 12 days treatment with Triptorelin. Vehicle treated tumour volumes increased 3.8 fold and 4.2 fold respectively over 12 days whilst Triptorelin-treated tumours increased in volume by 2.6 fold and 2.2 fold.
Growth of xenografts expressing lower levels of GnRH receptor was unaffected by treatment with Triptorelin.
Conclusion
Strategies aimed at increasing levels of GnRH receptor or the intensity of receptor signaling may be required in order to maximize the potential of GnRH analogs for the treatment of tumours expressing low levels of GnRH receptor.
