Unambiguous Identification of -Tubulin as the Direct Cellular Target Responsible for the Cytotoxicity of Chalcone by Photoaffinity Labeling

摘要

Chalcone is a simple and potentially privileged structure in medicinal chemistry with a diverse repertoire of biological activities, among which cytotoxicity is of particular interest. The sharp structure-activity relationship (SAR) for chalcone's cytotoxicity suggests structure-specific target interactions. Despite the numerous putative targets proposed, evidence for direct target interactions in cells is unavailable. In this study, guided by the sharp cytotoxic SAR, we developed a cytotoxic chalcone-based photoaffinity labeling (PAL) probe, (E)-3-(3-azidophenyl)-1-[3,5-dimethoxy-4-(prop-2-yn-1-yloxy)phenyl]-2-methylprop-2-en-1-one (C95; IC50: 0.38 +/- 0.01m), along with two structurally similar non-cytotoxic probes. These probes were used to search for the direct cellular target responsible for chalcone's cytotoxicity through intact cell-based PAL experiments, in which -tubulin was identified to specifically interact with the cytotoxic probe (i.e., C95) but not the non-cytotoxic probes. A set of phenotypical and biochemical assays further reinforced -tubulin as the cytotoxic target of chalcones. Peptide mass quantitation by mass spectrometric analysis revealed one peptide potentially labeled by C95, providing information on chalcone's binding site on -tubulin.