Long-acting delivery systems for peptides: inhibition of rat prostate tumors by controlled release of [D-Trp6]luteinizing hormone-releasing hormone from injectable microcapsules.

Intramuscular injection of [6-D-tryptophan]-luteinizing hormone-releasing hormone [( D-Trp6]LH-RH) in microcapsules of poly(DL-lactide-co-glycolide), designed to release a controlled dose of the peptide over a 30-day period, decreased the weights of androgen-dependent Dunning prostate tumors in rats and suppressed serum testosterone levels more effectively than daily subcutaneous administration of equivalent or double doses of unencapsulated [D-Trp6]LH-RH. The microcapsules or daily injections of [D-Trp6]LH-RH also significantly decreased tumor volumes. Microcapsules of [D-Trp6]LH-RH or related analogs that can be injected once a month should make the treatment of patients with prostate carcinoma and other neoplasms or disorders more convenient and efficacious.