Je. Rivier et al., Constrained corticotropin releasing factor antagonists (astressin analogues) with long duration of action in the rat, J MED CHEM, 42(16), 1999, pp. 3175-3182
In an earlier report we identified specific modifications and substitutions
of corticotropin releasing factor (CRF) that led to the discovery of antag
onists with extended duration of action as compared to that of astressin {c
yclo(30-33)[DPhe(12),Nle(21),Glu(30),Lys(33),Nle(38)]hCRF((12-41))}. These
additional modifications included elongation of the peptide chain by three
residues at the N-terminus, its acetylation, and the [C alpha MeLeu(27)] su
bstitution to yield cyclo(30-33)[DPhe(12), Nle(21),C alpha MeLeu(27),Glu(30
),Lys(33),Nle(38)]Ac-hCRF((9-41)), which was found to be longer acting than
astressin (Rivier, J.; et al. J. Med. Chem. 1998, 41, 5012-5019). To furth
er increase the efficiency (potency, duration of action, and bioavailabilit
y) of this family of antagonists, we introduced two or more C alpha Me-leuc
ine residues at positions shown in earlier studies to be favorable (Hernand
ez, J,-F.; et al. J. Med. Chem. 1993, 36, 2860-2867). Whereas the introduct
ion of C alpha Me-leucine residues at positions 27 and either 18 (11), 37 (
17), or 40 (19) resulted in dramatic increases in duration of inhibitory ac
tion in the adrenalectomized (adx) rat after intravenous injection, the sam
e substitution at positions 27 and either 15 (7, 8), 17 (9), 19 (12, 13), o
r 41 (20) led to short acting analogues. Other substitutions by C alpha MeL
eu at positions 27 and either 10 (4), 13 (5), 14 (6), 21 (14), 24 (15), 36
(16), or 38 (18) yielded analogues with duration of action intermediate bet
ween those mentioned above. Cyclo(30-33)[DPhe(12), Nle(21),C alpha MeLeu(27
),Glu(30),Lys(33),Nle(38),C alpha MeLeu(40)]Ac-hCRF((9-41)) (astressin B, 1
9) was one of the most efficacious analogues of this series (> 4 h inhibiti
on of ACTH secretion at 25 mu g/adx rat). It was found to be even longer ac
ting via subcutaneous administration in either an aqueous (>24 h inhibition
of ACTH secretion at 100 mu g/adx rat) or lipid milieu (DMSO/peanut oil, >
24 h inhibition of ACTH secretion at 30 mu g/adx rat) than after intravenou
s administration (<12 h inhibition of ACTH secretion at 100 mu g/adx rat).
We concluded that C alpha-methylation at some positions may favor a bioacti
ve conformation while also preventing degradation and/or elimination, resul
ting in significant extension of duration of action.