Anti-tumour activity of ICI 118630, a new potent luteinizing hormone-releasing hormone agonist

Experiments were undertaken with DMBA-induced mammary tumours of the rat to determine the anti-tumour properties of a new and potent luteinizing hormone releasing hormone (LH-RH) agonist, [D-Ser(But) 6Azgly10]-LH-RH (ICI 118630). Tumours were classified according to their oestrogen-receptor (ER) content. Twice daily i.m. injections of either 5 micrograms or 0.5 micrograms ICI 118630 in saline were as effective as ovariectomy or tamoxifen therapy in causing the regression of ER+ DMBA-induced mammary tumours. ER- mammary tumours showed a more equivocal overall response to ICI 118630, some tumours progressing, others regressing. About one-third of the ER+ tumours disappeared in the 20-day treatment period. Those tumours which did regrow after the cessation of treatment proved to be hormone-dependent. In addition to the inhibitory effects of the LH-RH agonist on pre-existing tumours, ICI 118630 also reduced the total number of new tumours formed during and after treatment.