Symmetric covalent linkage of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) results in novel derivatives with increased inhibitory activities against calcium/calmodulin complex

A useful calmodulin (CaM) antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), was invented by Hidaka et al. in 1978. Here, we have designed new CaM antagonists on the basis of the three-dimensional structure of Ca²⁺/CaM complexed with W-7. Eleven new compounds all share a similar architecture, in which two W-7 molecules are linked between their aminohexyl termini by a linker with different functionalities. A wide range of inhibitory activities against Ca²⁺/CaM-dependent protein kinase I (CaM kinase I) has been observed with these self-crosslinked W-7 analogs, (W-7)₂. In vitro competitive CaM kinase I assays using CaM kinase I and nuclear magnetic resonance studies indicated that one (W-7)₂ molecule binds to one CaM molecule as expected, with the two chloronaphthalene rings of (W-7)₂ being anchored separately to the N- and C-terminal hydrophobic pockets of Ca²⁺/CaM. The most potent compound, N,N'-bis[6-(5-chloro-1-naphthalenesulfonyl)-amino-1-hexyl]-p-xylene-diamine ((W-7)₂- 10), inhibits CaM kinase I activity at an IC₅₀ value of 0.23 μM; about 75 times more effectively than W-7. The length and basicity of the linker sequence in (W-7)₂ significantly contribute to inhibitory activity. The present study opens an avenue for developing powerful CaM antagonists that could be used at low doses in vivo.