DIFFERENTIAL-EFFECTS OF TAMOXIFEN-LIKE COMPOUNDS ON OSTEOCLASTIC BONEDEGRADATION, H-ATPASE ACTIVITY, CALMODULIN-DEPENDENT CYCLIC-NUCLEOTIDE PHOSPHODIESTERASE ACTIVITY, AND CALMODULIN-BINDING()

We studied effects of calmodulin antagonists on osteoclastic activity and calmodulin-dependent HCl transport. The results were compared to e ffects on the calmodulin-dependent phosphodiesterase and antagonist-ca lmodulin binding affinity. Avian osteoclast degradation of labeled bon e was inhibited similar to 40% by trifluoperazine or tamoxifen with ha lf-maximal effects at 1-3 mu M. Four benzopyrans structurally resembli ng tamoxifen were compared: d-centchroman inhibited resorption 30%, wi th half-maximal effect at similar to 100 nM, cischroman and CDRI 85/28 7 gave 15-20% inhibition, and l-centchroman was ineffective. No benzop yran inhibited cell attachment or protein synthesis below 10 mu M. How ever, ATP-dependent membrane vesicle acridine transport showed that H-ATPase activity was abolished by all compounds with 50% effects at 0. 25-1 mu M. All compounds also inhibited cai modulin-dependent cyclic n ucleotide phosphodiesterase at micromolar calcium. Relative potency va ried with assay type, but d- and l-centchroman, surprisingly, inhibite d both H+-ATPase and phosphodiesterase activity at similar concentrati ons. However, d- and l-centchroman effects in either assay diverged at nanomolar calcium. Of benzopyrans tested, only the d-centchroman effe cts were calcium-dependent. interaction of compounds with calmodulin a l similar concentrations were confirmed by displacement of labeled cal modulin from immobilized trifluoperazine. Thus, the compounds tested a ll interact with calmodulin directly to varying degrees, and the obser ved osteoclast inhibition is consistent with calmodulin mediated effec ts. However, calmodulin antagonist activity varies between specific re actions, and free calcium regulates specificity of some interactions. Effects on whole cells probably also reflect other properties, includi ng transport into cells. (C) 1997 Wiley-Liss, Inc.