Inhibition of the growth of some hormone dependent tumors by D-Trp6-LH-RH.

We have investigated the effects of chronic administration of D-Trp6-LH-RH on the growth of various hormone dependent tumors in rats and mice. Treatment of male Copenhagen F-1 rats bearing the Dunning R-3327H prostate adenocarcinoma with 25 micrograms of D-Trp6-LH-RH bid for 21 days significantly reduced tumor weight and volume as compared to controls. Serum LH, prolactin and testosterone levels in Copenhagen F-1 rats bearing Dunning tumors were significantly decreased after treatment with D-Trp6-LH-RH. Administration of D-Trp6-LH-RH in doses of 25 micrograms/day for 21 days to mice bearing the MXT mammary carcinoma significantly decreased tumor weight and volume. In rats bearing the MT/W9A mammary adenocarcinoma, D-Trp6-LH-RH, at a dose of 25 micrograms bid for 28 days significantly decreased tumor weight and volume. Administration of D-Trp6-LH-RH in a dose of 25 micrograms/day, 3-18 days after inoculation with the tumor, inhibited the growth of the prolactin (PRL) and ACTH-secreting pituitary tumor 7315a in female Buffalo rats. In three experiments D-Trp6-LH-RH (30-60 micrograms/day) decreased tumor weight and/or volume of the Swarm chondrosarcoma. Regression of these hormone-dependent tumors in rats and mice in response to chronic administration of D-Trp6-LH-RH suggests that this compound can be used for treatment of prostate cancer and breast cancer, and also considered for the development of a new endocrine therapy for chondrosarcomas, osteosarcomas, pituitary tumors and other hormone-dependent neoplasias. The demonstration of the successful use of LH-RH agonists for the palliative management of stage C and D prostate cancer has already shown that this treatment could be employed instead of surgical orchiectomy or estrogen therapy. Preliminary clinical trials suggest that agonists of LH-RH might also be of help in the treatment of breast cancer in premenopausal women.