P2T purinoceptor antagonists. A QSAR study of some 2-substituted ATP analogues.

FPL67085MX represents the first in a class of novel, highly potent and selective P2T purinoceptor antagonists which are inhibitors of adenosine diphosphate (ADP)-induced platelet aggregation in-vitro. In an early series of compounds we studied the effect of variation of the adenine 2-substituent on potency and derived quantitative structure-activity relationships (QSARs) between the properties of the molecules and their biological activity. This work has recently been revisited using comparative molecular-field analysis (CoMFA) and the comparison of the predictions from the two methods is discussed along with their relative merits in terms of compound design. The model suggests that the receptor for these molecules has a narrow lipophilic cleft, which is occupied by the adenine 2-substituent.

FPL 66096: a novel, highly potent and selective antagonist at human platelet P2T-purinoceptors.

1. ADP-dependent platelet aggregation is mediated by the P2T-purinoceptor and is specifically inhibited by ATP, which is a competitive P2T-purinoceptor antagonist. However, ATP functions as an agonist at other P2-purinoceptor subtypes in other tissues and is, therefore, non-selective. This paper describes the effects of the novel ATP analogue, FPL 66096 (2-propylthio-D-beta,gamma-difluoromethylene ATP), on ADP-induced and ADP-independent aggregation of human washed platelets and in standard preparations containing P2X- (rabbit ear artery) and P2Y-purinoceptors (guinea-pig aorta). 2. In suspensions of human washed platelets, FPL 66096 (1-100 nM) produced concentration-dependent rightward displacement of concentration-effect (E/[A]) curves obtained for ADP-induced platelet aggregation. Logistic fitting of E/[A] data indicated that the effect of FPL 66096 was consistent with simple competition with a pKB value of 8.66. FPL 66096 (10-1000 nM) had no effect on aggregation produced by the thromboxane A2-mimetic, U46619 (0.1-10 microM) when the response to this agent was rendered ADP-independent by inclusion of the non-selective P2-purinoceptor antagonist, suramin (100 microM). 3. The anti-aggregatory potency of FPL 66096 was not influenced by increasing the incubation time from 2 to 15 min nor by inclusion of the P1-purinoceptor antagonist 8-sulphophenyltheophylline at a concentration (300 microM) that produced a 68 fold rightward displacement of the anti-aggregatory E/[A] curve for the P1-purinoceptor agonist, 5'-N-ethylcarboxamidoadenosine (0.1-1000 microM). 4. FLP 66096 behaved as a weak (pA" 3.68) but full P2x-purinoceptor agonist in preparations of the rabbit isolated ear artery and as a weak, competitive antagonist (apparent pKB 4.71) at P2Y purinoceptors in the guinea-pig isolated aorta, indicating a selectivity of at least 9000 fold for the P2t-subtype. In the latter preparation, non-specific relaxations were produced by concentrations of FPL 66096 >10M gM.5. These results indicate that FPL 66096 is a P2-purinoceptor antagonist of unprecedented potency and selectivity and that its effects are consistent with simple competition at the P2-purinoceptor. Therefore,FPL 66096 represents a novel pharmacological tool in the classification of P2-purinoceptors and in the elucidation of the mechanisms involved in activation of platelets by ADP.