Nonsteroidal selective glucocorticoid modulators: the effect of C-5 alkyl substitution on the transcriptional activation/repression profile of 2,5-dihydro-10-methoxy-2,2,4-trimethyl-1H-[1]benzopyrano[3,4-f]quinolines.

The preparation and characterization of a series of selective glucocorticoid receptor modulators are described. The preliminary structure-activity relationship of nonaromatic C-5 substitution on the tetracyclic quinoline core showed a preference for small lipophilic side chains. Proper substitution at this position maintained the transcriptional repression of proinflammatory transcription factors while diminishing the transcriptional activation activity of the ligand/glucocorticoid receptor complex. The optimal compounds described in this study were the allyl analogue 18 and cyclopentyl analogue 32. These candidates showed slightly less potent, highly efficacious E-selectin repression with significantly reduced levels of glucocorticoid response element activation in reporter gene assays vs prednisolone. Allyl analogue 18 was evaluated in vivo. An oral dose of 18 showed an ED(50) = 1.7 mg/kg as compared to 1.2 mg/kg for prednisolone in the Sephadex-induced pulmonary eosinophilia model and an ED(50) = 15 mg/kg vs 4 mg/kg for prednisolone in the carrageenan-induced paw edema model.

Persistent activation of the dopamine D1 receptor contributes to prolonged receptor desensitization: studies with A-77636.

A-77636 is a dopamine (DA) D1 receptor-selective agonist that was previously shown to elicit beneficial responses in animal models of Parkinson's disease (PD) (Kebabian et al.: Eur. J. Pharmacol. 229: 203, 1992). However, A-77636 is of limited potential for PD therapy because it induces rapid tolerance in vivo. To understand the basis of rapid onset of tolerance to the compound, we conducted studies to compare the in vitro properties of A-77636 and A-81686; the latter is a structurally related D1 agonist that did not induce significant tolerance in vivo under similar experimental conditions. With SK-N-MC, a neuroblastoma cell line, as an in vitro model for the D1 receptor, significant differences in D1 receptor function were noted after pretreatment with the two compounds. Specifically, 1-hr pretreatment with A-77636 resulted in significant residual cAMP production, even after the drug solution was removed and the cells were washed. The residual cAMP activity was selectively inhibited by SCH 23390, a selective D1 antagonist. The residual cAMP activity declined with pretreatment time, and after 4-hr pretreatment, little residual cAMP production was observed. Cotreatment of SK-N-MC cells with SCH 23390 and A-77636 did not prevent residual cAMP production by A-77636. In contrast, A-81686 did not elicit residual cAMP production is SK-N-MC cells. Although A-77636 treated cells were devoid of agonist response 4 hr after drug removal, A-81686-treated cells exhibited significant cAMP response after drug removal. Preincubation of rat striatal membranes with A-77636 resulted in a large decrease in D1 receptor binding, despite repeated washings, whereas A-81686 pretreatment caused only a small reduction in D1 receptor binding. On the basis of the present data, we conclude that A-77636 dissociates slowly from the D1 receptor. The continued activation of the D1 receptor by A-77636 leads to inability of the receptor to recover its responsivity, which may explain its long duration of action and its ability to induce rapid behavioral tolerance in vivo.

Novel Asp32-replacement tetrapeptide analogues as potent and selective CCK-A agonists.

A series of novel CCK tetrapeptide analogues of the general formula Boc-Trp-Lys(Tac)-N(R)-(CH2)nCON(R')Phe-NH2 (Tac = o-tolylaminocarbonyl), where R,R' = H or Me and n = 1-5, have been synthesized and tested. These analogues, which lack an acidic residue at the penultimate position, demonstrated surprisingly high CCK-A receptor affinity and selectivity. The effect of N-methylation pattern on CCK-A receptor affinity showed consistent trends for analogues in which n = 1, 2, or 3, with the di-N-methylated analogues having the highest affinity in each case. However, none of these analogues had full agonist activity, as measured by percent maximal PI hydrolysis. Two conformationally constrained analogues also demonstrated high CCK-A receptor affinity and selectivity, as well as nearly maximal agonist activity. In addition, one of these conformationally-constrained analogues demonstrated anorectic activity in rats.

Tetrapeptide CCK agonists: structure-activity studies on modifications at the N-terminus.

We had reported earlier on a novel series of potent and selective tetrapeptide cholecystokinin-A (CCK-A) agonists of the general structure Boc-Trp-Lys[epsilon-Y]-Asp-N(R)PheNH2 [Y = amides, ureas; R = H, Me] that were potent anorectic agents in rats. In an effort to optimize the potency, selectivity, stability, and efficacy of our lead candidate A-71623 [R = Me, Y = o-tolylaminocarbonyl; Tac] toward development of a clinical candidate, we have explored a series of analogues in which the N-terminal Boc functionality was systematically replaced with various amides, ureas, carbamates, and sulfonamides of differing size, hydrophobicity, and stereoelectronic properties. In general, these analogues maintained good potency and selectivity for the CCK-A receptor (guinea pig pancreas), as well as potent anorectic activity in rats. Those analogues exhibiting equal or superior activity compared to A-71623 but differing physicochemical properties may represent superior drug candidates.