Various natural agents, including grape seed extract (GSE), have shown considerable chemopreventive and
anti-cancer efficacy against different cancers in pre-clinical studies; however, their specific protein targets are largely
unknown and thus, their clinical usefulness is marred by limited scientific evidences about their direct cellular targets.
Accordingly, herein, employing, for the first time, the recently developed drug affinity responsive target stability
(DARTS) technique, we aimed to profile the potential protein targets of GSE in human colorectal cancer (CRC) cells.
Unlike other methods, which can cause chemical alteration of the drug components to allow for detection, this approach
relies on the fact that a drug bound protein may become less susceptible to proteolysis and hence the enriched proteins can
be detected by Mass Spectroscopy methods. Our results, utilizing the DARTS technique followed by examination of the
spectral output by LC/MS and the MASCOT data, revealed that GSE targets endoplasmic reticulum (ER) stress response
proteins resulting in overall down regulation of proteins involved in translation and that GSE also causes oxidative protein
modifications, specifically on methionine amino acids residues on its protein targets. Corroborating these findings,
mechanistic studies revealed that GSE indeed caused ER stress and strongly inhibited PI3k-Akt–mTOR pathway for its
biological effects in CRC cells. Furthermore, bioenergetics studies indicated that GSE also interferes with glycolysis and
mitochondrial metabolism in CRC cells. Together, the present study identifying GSE molecular targets in CRC cells,
combined with its efficacy in vast pre-clinical CRC models, further supports its usefulness for CRC prevention and