title: Phenolphthalein as a prototype drug for a group of structurally related calcium channel blockers in human platelets.
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.
authors.affiliation: Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, VA 23501-1980, USA.
authors.forename: Yuliya
authors.initials: Y
authors.lastname: Dobrydneva
authors.forename: Emily
authors.initials: E
authors.lastname: Wilson
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Abelt
authors.forename: Peter F
authors.initials: PF
authors.lastname: Blackmore
mesh_terms: D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D001896:Boron Compounds / Q000737:chemistry / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology*; D015220:Calcium Channels / Q000378:metabolism*; D006801:Humans; D017136:Ion Transport; D019169:Jurkat Cells; D020113:Phenolphthalein / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D013917:Thrombin / Q000494:pharmacology
chemical_list: D001896:Boron Compounds; D002121:Calcium Channel Blockers; D015220:Calcium Channels; D020113:Phenolphthalein; C109986:2-aminoethoxydiphenyl borate; D013917:Thrombin; D002118:Calcium