Astressin analogues (corticotropin-releasing factor antagonists) with extended duration of action in the rat

In earlier reports we identified specific point substitutions (DPhe(12),Nle (21,38)), cyclization strategies [in particular, introduction of lactam rin gs such as that of cyclo(Glu(30),Lys(33))], and deletions (residues 1-7) in the CRF molecule that led to agonists. We also noted that further deletion s (residues 8-14) produced antagonists such as astressin {cyclo(30-33)[DPhe (12),Nle(21,38),Glu(30), Lys(33)]hCRF((12-41))} (1). We hypothesized that t he lactam ring promoted conformational stability to yield analogues with in creased potency both in vitro and in vivo as compared to that of their line ar counterparts. Additionally, we reported that cyclo(30-33)[DPhe(12),Nle(2 1,38), Glu(30),DHis(32),Lys(33)]hcRF((12-41)) (3) and dicyclo(26-36,30-33)[ Ac-Asp(9),DPhe(12),Nle(21,38),Cys(26), Glu(30),Lys(33),Cys(36)]hCRF((9-41)) were ca. twice and 1/100 as potent as astressin, respectively, suggesting a putative turn that encompasses residues 30-33 (previous paper: Koerber et al. J. Med. Chem. 1998, 41). To increase the potency of 1 and/or 3 in vivo , we extended their chain length by one (5-8), two (9, 10), and three (11, 12) residues at the N-terminus and acetylated (6, 8, 10, 12). Of the compou nds tested for duration of action (1, 3-6, 8), we found 6 and 8 to be sligh tly longer-acting than astressin or [DHis32]astressin, while their potencie s in vitro were not significantly different from that of 3. Additionally, w e introduced C alpha Me-leucine residues in Lieu of leucine at positions 14 , 15, 19, 27, and 37 in [DHis(32)]astressin. The analogue [C alpha Me-Leu(2 7),DHis(32)]astressin (16) was more potent (although not statistically in a ll cases) than the other four analogues in vitro. While acetylation of the N-terminus of 16 (i.e., 18) or of [C alpha Me-Leu(27)]astressin (i.e., 19) did not have a significant effect on in vitro potency, elongation of the N- terminus by one or three residues in addition to acetylation resulted in cy clo(30-33)[DPhe(12),Nle(21),C alpha Me-Leu(27),Glu(30),DHis(32),Lys(33),Nle (38)]Ac-hCRF((11-41)) (21), cyclo(30-33)[DPhe(12),Nle(21),C alpha Me-Leu(27 ),Glu(30),Lys(33),Nle(38)]Ac-HCRF(9-41) (22), and cyclo(30-33)[DPhe(12),Nle (21),C alpha Me-Leu(27),Glu(30),DHis(32),Lys(33),Nle(38)]Ac-hCRF((9-41)) (2 3) that were longer-acting than 6 and 8 (ca. 2 h inhibition of ACTH secreti on at 25 mu g/adrenalectomized rat). Analogues 22 and 23 were also more pot ent than astressin at reversing intracisternal CRF- and abdominal surgery-i nduced delay of gastric emptying in conscious rats.