OBJECTIVE  To screen out small molecule MELK inhibitors on colorectal cancer through virtual screening and in vitro experiment from Macleaya cordata, a traditional Chinese medicine.

METHODS  The benzophenanthridine alkaloids from Macleaya cordata were collected through literature search and identified as a small molecule compound(ligand). By AutoDock Vina software, the potential compounds that inhibited MELK kinase were screened according to the score. The inhibition effect of the compounds on colorectal cancer cells was detected by using MTT assay. The expression of PARP, Caspase-3 and MELK proteins was analyzed by Western blotting. Cell thermal shift assay was used to evaluate the binding capacity of compounds with MELK protein.

RESULTS  Forty four compounds could stably dock with MELK protein, and 22 compounds had a relatively strong ability to bind with MELK protein. The result of in vitro experiment showed that, three compounds including 6-ethoxysanguinarine, dihydrosanguinarine and 6-acetonyldihydrosanguinarine inhibited the proliferation of colorectal cancer cells in a concentration- and time-dependent manner, bound with and down-regulated MELK protein respectively. The expression of PARP and Caspase-3 proteins was down-regulated, and the levels of Cleaved PARP and Cleaved caspase-3 were up-regulated in colorectal cancer cells treated with 6-ethoxysanguinarine.

CONCLUSION By virtual screening and in vitro experiments, three benzophenanthridine compounds that inhibited MELK protein are screened, which will provide an experimental basis for the development of new small molecule MELK inhibitors for the treatment of colorectal cancer.