Mechanistic Study of The Small Molecule Inhibitor DX-52-1

Cell migration is a basic biological process that is fundamental to several normal and disease processes such as embryonic development, tissue repair, immune function, angiogenesis and cancer cell invasion and metastasis. Small organic molecules inhibiting cell migration can be used as both research probes and therapeutic agents. DX-52-1, a semisynthetic derivative of the natural product quinocarmycin (also known as quinocarcin), inhibits the migration of Madin-Darby canine kidney epithelial cells with nanomolar concentration. We have identified galectin-3, a multifunctional protein whose best-known function is its sugar binding ability, as a secondary target of DX-52-1 with functions in cell motility. In addition, we have identified HUK-921, another small molecule with antimigratory activity that has far greater selectivity for galectin-3 over radixin both in vitro and in cells. Neither of them targets the carbohydrate-binding site of galectin-3, moreover, results indicate that functions of galectin-3 required for cell migration are independent of carbohydrate binding ability. We investigated the effects of the two inhibitors on cell migration and proliferation in different cancer cell lines and discovered that DX-52-1shows promising potency in serveral of the tested ones especially triple negative human breast cancer BT20 and MDA-MB-231 cells, suggesting this small molecule has a great potential to treat cancers. Six DX-52-1 analogs were synthesized and structure-activity relationship (SAR) studies were carried out in cell migration and in vitro competitive binding assays. We provided strong evidence that the mechanism of covalent modification of galectin-3 involves elimination of the nitrile group of DX-52-1 followed by an attack of a nucleophilic amino acid side chain of galectin-3 on the resulting iminium ion. We proposed the similar mechanism for alkylation of radixin by DX-52-1. Furthermore, we demonstrated that the hydroxyl group (-OH) of DX-52-1(C-19) plays an important role in recognition of DX-52-1 and target proteins.