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A series of new somatostatin analogs were synthesized in order to study the relative importance of specific substitutions in relation to selectivity between their endocrine and antitumor effects. Substitutions were carried out in all positions, except for Lys in position 5. Peptides were tested for their ability to inhibit in vitro and in vivo GH release, proliferation of the MCF 7 breast carcinoma cell line and tyrosine kinase activity in the HT 29 human colon carcinoma cell line. Selective biological activity was achieved in GH release and antitumor activity by the different amino acid substitutions. One of the analogs, with a five-residue ring (D-Phe-Cys-Tyr-D-Trp-Lys-Cys-Thr-NH2, TT-232), was unique. It had no GH release inhibitory activity, but did have strong tyrosine kinase inhibitory and antiproliferative effects.

A novel gonadotropin hormone releasing hormone analog, (D-Phe6,Gln8,des-Gly10)GnRH ethylamide, has been developed in our laboratory which stimulates not only ovulation but also follicular maturation in various kinds of fish and mammals. A large-scale liquid phase synthesis has been worked out for this analog. The synthetic product was characterized for structure and purity by various physicochemical methods. Though its structure was derived from the native chicken type I sequence, this peptide was one of the most effective analogs among those reported so far in the literature for artificial propagation of fish. The peptide was effective both during and out of spawning season. It was also potent in treating various sexual disorders such as anestrous, inactive ovaries and follicular cysts in cows.