Differential proteomic profiling identifies novel molecular targets of paclitaxel and phytoagent deoxyelephantopin against mammary adenocarcinoma cells.

A major germacranolide sesquiterpene lactone, deoxyelephantopin, identified from Elephantopus scaber L. (known as "Didancao" in Chinese medicine) showed significant antitumor growth and antimetastatic effect on murine mammary adenocarcinoma TS/A cells in vitro and in vivo in mice. Deoxyelephantopin exhibited a superior effect to that of the paclitaxel in prolonging median survival time of tumor-bearing animals in our recent study. To investigate the molecular mechanisms underlying the difference in efficacy between deoxyelephantopin and paclitaxel, we used 2-D DIGE and LC-ESI-MS/MS to profile proteins differentially expressed in the nucleus and cytoplasm of TS/A cells and used the MetaCore database to determine the functional protein networks affected by both treatments. Deoxyelephantopin and paclitaxel treatment produced regulation of molecules involved in proteolysis and calcium ion transport, suggesting the possible effects of both drugs on proteasome and endoplasmic reticulum machinery in TS/A cells. Western blot analysis of marker proteins (e.g., PDI, GRP78, TXND5, caspase-12, caspase-3 and PARP) further verified that induction of endoplasmic reticulum stress was associated with apoptosis induced by both deoxyelephantopin and paclitaxel, but only deoxyelephantopin inhibited proteasomal proteolysis in TS/A cells. The novel effects on targeting ER machinery and suppressing proteasome activity suggest the great potential of deoxyelephantopin for mammary cancer therapy.