Azepane-1-carbonyl-Leu-D-Trp(For)-D-Trp-OH

During treatment of prostate cancer patients with luteinizing hormone-releasing hormone agonist, a transient LH and sex steroid release, which precedes the secretion blockade, may result in a flare-up of the disease, whereas the antagonists induce an immediate suppression. The administration of the modern, superactive LHRH antagonist SB-75 before or together with the agonist D-Trp-6-LHRH should prevent the "flare-up" phenomena. In order to demonstrate that the LHRH antagonist can prevent the initial stimulation of gonadotropins in response to LHRH agonists, groups of 5-7 male rats were injected s.c. with the antagonist SB-75 in doses in 100, 500, and 1,000 micrograms/rat 1 hour prior to or 1, 2, and 3 days before administration of D-Trp-6-LHRH agonist (50 micrograms/rat). Supraphysiological doses of the agonist were used in order to obtain prolonged stimulation of LH release, which was necessary to study the duration and the extent of LH release inhibition. Blood samples were taken before and 2, 6, 24, 48, and 72 hours after D-Trp-6-LHRH stimulation for measurement of LH levels. The administration of SB-75 in doses of 500 and 1,000 micrograms/rat 3 days prior to administration of the agonist significantly lowered LH response (P less than 0.01), as compared to animals injected with D-Trp-6-LHRH alone. The D-Trp-6-LHRH-stimulated LH secretion was markedly more suppressed by all 3 doses of the antagonist in rats pretreated with SB-75 2 days prior to the stimulation with the agonist. An even greater reduction in LH response could be observed in rats injected with SB-75 1 day prior to the agonist, the magnitude of LH response being decreased by 75% with 500 micrograms/rat SB-75 and by 90% with 1 mg/rat SB-75. The LH response was virtually abolished when the antagonist, SB-75 was given in doses of 500 or 1,000 micrograms/rat 1 hour prior to the D-Trp-6-LHRH injection. Under these conditions, the agonist-induced LH and testosterone secretion was completely suppressed during the whole period of the experiment. The antagonist to agonist dose ratio of 2 to 1 produced a 90% decrease in the LH response to D-Trp-6-LHRH at 2 hours and 75% at 5 hours after agonist administration. The effects of LHRH decapeptide itself (500 micrograms/rat) on LH secretion could be totally suppressed by an injection of 50 micrograms/rat of SB-75 1 hour beforehand.(ABSTRACT TRUNCATED AT 400 WORDS)

In the preceding paper, using ECEPP, including the effects of water, and the chain build-up procedure, we computed the low energy structures for GnRH and found that there were no distinct low energy structures or structures with high statistical weights. To attempt to deduce possible structures of GnRH that may bind to the GnRH receptor, we computed the low energy structures for GnRH peptides that have L- and D-amino acids substituting for Gly 6. The L-amino acid-substituted peptides (L-Ala and L-Val) have very low or no affinity for the receptor and on activity (release of FSH and LH) while the D-Ala-, D-Leu-, D-Trp- and D-Phe-substituted peptides have significantly higher relative affinities and activities than those for native GnRH; the D-Val-substituted peptide has about one-third of the affinity and activity as native GnRH. Unlike native GnRH, our computations suggest that both sets of peptides form well-defined structures in water: the L-amino acid-substituted peptides are predominantly α-helical while the D-amino acid-substituted peptides adopted E*A A A E D*(C*) A E C A(C*) and minor variants of these structures. By eliminating structures that lay in common to the D-Ala and L-Val peptides and further eliminating structures that differed between the D-Ala and D-Leu peptides, we reduced the number of possible distinct binding conformations to 254. Searching for structures among these 254 conformations that had relative statistical weights that paralleled their relative affinities, we found two candidate structures: D*E A A E C*A E C A and D*G A A E D*A E C G*, both of which have conformations for residues 3-9 that are similar to the computed most probable structures for the D-amino acid-substituted GnRH peptides in water.

Many clinical approaches for the treatment of hormone-sensitive tumors are being developed based on analogs of LH-RH and somatostatin. Inhibition of the pituitary-gonadal axis forms the basis for oncological applications of LH-RH agonists like [D-Trp6]-LH-RH and new LH-RH antagonists free of edematogenic effects such as [Ac-D-Nal(2)1-D-Phe(4Cl)2-D-Pal(3)3,D-Cit6,D-Ala10]-LH -RH (SB-75). Agonists and antagonists of LH-RH have been used in patients with prostate cancer and might be also beneficial for the treatment of breast cancer and ovarian, endometrial and pancreatic carcinomas. Some of the effects of LH-RH analogs can be due to direct action since LH-RH receptors have been found in these cancers. The use of sustained delivery systems based on microcapsules of PLG, makes the treatment more efficacious. Octapeptide analogs of somatostatin such as D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Trp-NH2 (RC-160) and related analogs were designed specifically for antitumor activity. These somatostatin analogs, by virtue of having a wide spectrum of activities appear to inhibit various tumors through multiple mechanisms. Direct antiproliferative actions of somatostatin analogs appear to be mediated by specific receptors located on tumor cells. High affinity binding sites for RC-160 and related analogs have been found in human pancreatic, prostate, breast and ovarian cancers and brain tumors such as meningiomas. In vivo administration of analog RC-160 inhibits the growth of Dunning R-3327 prostate cancers in rats, MXT mammary tumors in mice and BOP-induced ductal pancreatic cancers in hamsters. Combination of microcapsules of RC-160 with [D-Trp6]-LH-RH results in synergistic potentiation of the inhibition of these cancers. Somatostatin analog RC-160 and LH-RH antagonist SB-75 are the object of further experimental studies and clinical trials aimed at the exploration of their inhibitory effects on the processes of malignant growth.