1. Inhibition of cyclin-dependent kinases by purine analogues: crystal structure of human cdk2 complexed with roscovitine
W F De Azevedo, S Leclerc, L Meijer, L Havlicek, M Strnad, S H Kim Eur J Biochem. 1997 Jan 15;243(1-2):518-26. doi: 10.1111/j.1432-1033.1997.0518a.x.
Cyclin-dependent kinases (cdk) control the cell division cycle (cdc). These kinases and their regulators are frequently deregulated in human tumours. A potent inhibitor of cdks, roscovitine [2-(1-ethyl-2-hydroxyethylamino)-6-benzylamino-9-isopropylpurin e], was identified by screening a series of C2,N6,N9-substituted adenines on purified cdc2/cyclin B. Roscovitine displays high efficiency and high selectivity (Meijer, L., Borgne, A., Mulner, O., Chong, J. P. J., Blow, J. J., Inagaki, N., Inagaki, M., Delcros, J.-G. & Moulinoux, J.-P. (1997) Eur. J. Biochem. 243, 527-536). It behaves as a competitive inhibitor for ATP binding to cdc2. We determined the crystal structure of a complex between cdk2 and roscovitine at 0.24-nm (2.4 A) resolution and refined to an Rfactor of 0.18. The purine portion of the inhibitor binds to the adenine binding pocket of cdk2. The position of the benzyl ring group of the inhibitor enables the inhibitor to make contacts with the enzyme not observed in the ATP-complex structure. Analysis of the position of this benzyl ring explains the specificity of roscovitine in inhibiting cdk2. The structure also reveals that the (R)-stereoisomer of roscovitine is bound to cdk2. The (R)-isomer is about twice as potent in inhibiting cdc2/cyclin B than the (S)-isomer. Results from structure/activity studies and from analysis of the cdk2/roscovitine complex crystal structure should allow the design of even more potent cdk inhibitors.
2. Involvement of delta-opioid receptors in the effects induced by endogenous enkephalins on learned helplessness model
P Tejedor-Real, J A Micó, C Smadja, R Maldonado, B P Roques, J Gilbert-Rahola Eur J Pharmacol. 1998 Jul 31;354(1):1-7. doi: 10.1016/s0014-2999(98)00423-3.
Pharmacological, neurochemical and behavioural findings support a possible role of endogenous opioids in clinical depression. There is evidence from animal studies that delta-opioid receptors are involved in several behavioural responses to opioids, including motivational activities. In the present study, the mixed enkephalin catabolism inhibitor, RB 101 (N(R,S)-2-benzyl-3[(S)-(2-amino-4-methylthiobutyldithio]-1-oxoprop yl)-L-phenylalanine benzyl ester) (1.25, 2.5 and 5 mg/kg), induced a dose-dependent antidepressant-like effect in a learned helplessness model. Thus, RB 101 reversed escape deficits in rats previously subjected to inescapable shocks, suggesting the involvement of endogenous enkephalins in depression. Similar effects were observed after administration of the selective delta-opioid receptor agonist, BUBU (Tyr-D.Ser-(O-tert-butyl)-Gly-Phe-Leu-Thr(O-Tet-butyl-OH) (1 and 2 mg/kg). Moreover, RB 101 effects were antagonized by administration of naltrindole (NTI) (0.1 mg/kg), which points to a preferential involvement of delta-opioid receptors in this enkephalin-controlled behaviour. As RB 101 has been reported to be almost devoid of opiate-related side-effects, it could represent a promising alternative in the treatment of depressive patients who are unresponsive to, or intolerant of, classical antidepressants.
3. Role of endogenous cholecystokinin in the facilitation of mu-mediated antinociception by delta-opioid agonists
F Noble, C Smadja, B P Roques J Pharmacol Exp Ther. 1994 Dec;271(3):1127-34.
Published results suggest that delta-opioid agonists can modulate the mu-mediated analgesia. In this work, the antinociceptive effects produced by the mu agonist [D-Ala2,NMe-Phe4,Gly-ol5]enkephalin or the mixed inhibitor of enkephalin-degrading enzymes RB 101 (N- [(R,S)-2-benzyl-3[(S)(2-amino-4-methyl- thio)butyldithio]-1-oxopropyl]-L-phenylalanine benzyl ester) were studied after administration of the systemically active and selective delta agonist Tyr-D-Ser(O-tert-butyl)-Gly-Phe-Leu- Thr(O-tert-butyl). In the hot-plate test in mice, Tyr-D-Ser(O-tert-butyl)-Gly- Phe-Leu-Thr(O-tert-butyl) (i.v.) potentiated the antinociceptive responses elicited by [D-Ala2,NMe-Phe4,Gly-ol5]enkephalin (i.v.) or RB 101 (i.v.). These facilitatory effects were reversed not only by prior administration of the delta-selective antagonist naltrindole (0.5 mg/kg s.c.), but also unexpectedly by the selective cholecystokinin CCK-A antagonist MK-329 (20 micrograms/kg i.p.). In addition, the CCK analog [Boc- Tyr(SO3H)-Nle-Gly-Trp-Nle-Asp-Phe-NH2] (a mixed CCK-A/CCK-B agonist) increased the jump latency and this effect was blocked by MK-329 (20 micrograms/kg i.p.) and by naloxone, but not by the selective CCK-B antagonist L-365,260 (5 mg/kg i.p.). In contrast, the selective CCK-B agonist BC 264 (62 micrograms/kg i.v.) produced a hyperalgesic effect that was antagonized by L-365,260 (5 mg/kg i.p.). Taken together, these findings suggest that the potentiating effects of delta agonists on mu-mediated analgesia are due to an increase in the release of endogenous CCK interacting with CCK-A and CCK-B receptors and resulting in positive and negative regulation of the endogenous opioid system.(ABSTRACT TRUNCATED AT 250 WORDS)
