Phenolphthalein as a prototype drug for a group of structurally related calcium channel blockers in human platelets.
J Cardiovasc Pharmacol 2009;
53:231-40. [PMID:
19247192 DOI:
10.1097/fjc.0b013e31819b5494]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Thrombin increases intracellular free Ca ([Ca]i) in human platelets by 2 mechanisms: internal mobilization and the influx of Ca via store-operated Ca entry (SOCE). 2-Aminoethoxydiphenyl borate (2-APB) is an inhibitor of SOCE. In search for nonboron analogues of 2-APB, we identified a well-known compound, phenolphthalein, structurally related to 2-APB. Many phenolphthalein analogues inhibited the ability of thrombin and thapsigargin (a specific activator of SOCE) to increase [Ca]i. Phenolphthalein has an IC50 approximately 10 microM to inhibit thrombin-induced [Ca]i elevation, its active analogues have a similar potency. Several phenolphthalein analogues also inhibited thrombin-induced intracellular Ca mobilization, which indicates action on inositol 1,4,5-trisphosphate receptors. We identified structural features among active and inactive phenolphthalein analogues that are responsible for the activity. Opening of the 5-membered lactone ring of phenolphthalein resulted in a total loss of activity. If the diphenyl rings possessed primary amine, dimethyl amine, or a cyano group, there was no activity. Modifications to the diphenyl groups that were tolerated include phosphate, sulfate, iodine, bromine, methyl, nitrite, and methoxy. Inhibition of thrombin-induced [Ca]i increase by phenolphthalein was not mediated by an increase in cyclic adenosine monophosphate because the inhibitor of cyclic adenosine monophosphate-dependent protein kinase A, 4-cyano-3-methylisoquinoline, did not affect the inhibitory action of phenolphthalein. The inhibitory effect of phenolphthalein was not mediated by an increase in NO/cyclic guanosine monophosphate (cGMP) because the inhibitors of NO-sensitive soluble guanylyl cyclase, methylene blue, and ODQ did not affect the inhibition. Phytohemagglutinin and thapsigargin-induced SOCE in Jurkat cells was also inhibited by phenolphthalein and 2-APB to the same extent as seen in platelets. Therefore, phenolphthalein and its derivatives structurally similar to 2-APB inhibit SOCE in platelets and other cells.
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