Development of myosin light chain kinase-inhibitors for anti-secretory and anti-ulcer drugs.

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This work was conducted to search a potential application of myosin light chain kinase inhibitors for anti-ulcer drugs with new mechanism of action. In the present study, we obtained data showing that parietal cell contains a new type of myosin kinase and its new substrate, and they suggested a unique regulation was conducted in the cell. As a candidate substrate for the kinase, we identified a new protein of 100 kDa. This protein was purified, partially sequenced, and suggested to be a rabbit homologue of Mena, a cytoskeletal protein. Mena has been reported to be involved in the actin polymerization as well as interacting with SH3-domain via its proline-rich domain. As the regulation of Mena by phosphorylation has not been studied yet, this work is the first time to postulate this protein as a new drug target. In order to find out a lead compound that inhibit the enzyme, we screened a group of compounds supplied by Kyowa Hakko Kogyo Co. Ltd., as well as the known various types of inhibitors, using isolated rabbit gastric glands and partially purified enzyme. This enzyme did not depend on calcium-calmodulin, showing clear difference from conventional myosin light chain kinases. It is neither sensitive to conventional calmodulin-antagonists nor usual kinase inhibitors. Among the compounds from Kyowa Hakko, some compounds, suggested to be bound to ATP-binding site, showed some inhibitory activity in the purified enzyme. Using isolated glands, two of them showed inhibitory activity on the acid secretion (IC50 was about 10μM). These results are promising that clinically applicable drugs could be developed using these as lead compounds.