The antiproliferative properties of tamoxifen and phenothiazines may be mediated by a unique histamine receptor (?H3) distinct from the calmodulin-binding site.
N,N-diethyl-2-[(4-phenylmethyl)-phenoxy]-ethanamine HCl (DPPE), a novel histamine antagonist (?H3), which selectively binds with high affinity to the antiestrogen-binding site (AEBS/?H3), inhibits the activity of calmodulin-dependent myosin light chain kinase (MLCK) only at concentrations greater than 1 mM, as opposed to tamoxifen (TAM), which has an IC50 = 4 microM in the same assay. This suggests that the antiestrogen-binding site is distinct from the site on calmodulin which binds TAM and phenothiazines. However, at an in vitro concentration of 1 X 10(-6) M, the antiproliferative effects of DPPE and several phenothiazines, which also compete for binding to AEBS/?H3, are about equal; this suggests that affinity for AEBS/?H3 rather than that for the calmodulin-binding site may correlate with clinically relevant antigrowth effects of these compounds.
D000818:Animals; D001665:Binding Sites; D002147:Calmodulin / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects*; D008862:Microsomes, Liver / Q000378:metabolism; D010647:Phenyl Ethers / Q000494:pharmacology*; D051381:Rats; D011968:Receptors, Histamine / Q000494:pharmacology*; D013629:Tamoxifen / Q000494:pharmacology*
D002147:Calmodulin; D010647:Phenyl Ethers; D011968:Receptors, Histamine; D013629:Tamoxifen; C043062:tesmilifene