Anti-proliferative and proteasome inhibitory activity of Murraya koenigii leaf extract in human cancer cell lines

Proteasome inhibition has been demonstrated to be a promising strategy for cancer therapy. The chymotrypsin-like activity of the 20S catalytic unit of the 26S proteasome is known to be critical for cancer cell survival. Inhibition of the proteasomal activity leads to tumor cell death. Murraya koenigii Spreng a medically important herb of Asian origin, is rich in phenolic content, and dietary polyphenols are known to act as proteasome inhibitors. This study was aimed at testing the cytotoxic and proteasomal inhibitory potential of M. koenigii leaf extract in four different human cell lines namely; colon, prostate, liver and cervical cancer. The cytotoxicity of M. koenigii leaf extract was tested by the MTT assay, inhibition of growth by colony formation assay and inhibition of the chymotrypsin-like (Ch-L) activity of the 26S proteasome using a specific fluorogenic substrate by fluorometry. There was a dose-dependent decrease in cell viability/proliferation with M. koenigii leaf extract treatment in all the cell lines tested. In line with the cell viability data there was a dose-dependent decrease in growth as observed by decreased colony formation in the cell lines tested. M. koenigii extract decreased the Ch-L activity of the endogenous proteasome in both intact cells and cell extracts in all the four cancer cell lines. Our results suggest that the proteasome is a target for M. koenigii leaf extract in various cancer cell lines and that inhibition of the proteasome may be one of the mechanisms responsible for its anticancer potential

Murraya <it>koenigii</it> leaf extract inhibits proteasome activity and induces cell death in breast cancer cells

<p>Abstract</p> <p>Background</p> <p>Inhibition of the proteolytic activity of 26S proteasome, the protein-degrading machine, is now considered a novel and promising approach for cancer therapy. Interestingly, proteasome inhibitors have been demonstrated to selectively kill cancer cells and also enhance the sensitivity of tumor cells to chemotherapeutic agents. Recently, polyphenols/flavonoids have been reported to inhibit proteasome activity. Murraya <it>koenigii</it> Spreng, a medicinally important herb of Indian origin, has been used for centuries in the Ayurvedic system of medicine. Here we show that Murraya <it>koenigii</it> leaves (curry leaves), a rich source of polyphenols, inhibit the proteolytic activity of the cancer cell proteasome, and cause cell death.</p> <p>Methods</p> <p>Hydro-methanolic extract of curry leaves (CLE) was prepared and its total phenolic content [TPC] determined by, the Folin-Ciocalteau’s method. Two human breast carcinoma cell lines: MCF-7 and MDA-MB-231 and a normal human lung fibroblast cell line, WI-38 were used for the studies. Cytotoxicity of the CLE was assessed by the MTT assay. We studied the effect of CLE on growth kinetics using colony formation assay. Growth arrest was assessed by cell cycle analysis and apoptosis by Annexin-V binding using flow cytometry. Inhibition of the endogenous 26S proteasome was studied in intact cells and cell extracts using substrates specific to 20S proteasomal enzymes.</p> <p>Results</p> <p>CLE decreased cell viability and altered the growth kinetics in both the breast cancer cell lines in a dose-dependent manner. It showed a significant arrest of cells in the S phase albeit in cancer cells only. Annexin V binding data suggests that cell death was via the apoptotic pathway in both the cancer cell lines. CLE treatment significantly decreased the activity of the 26S proteasome in the cancer but not normal cells.</p> <p>Conclusions</p> <p>Our study suggests M. <it>koenigii</it> leaves to be a potent source of proteasome inhibitors that lead to cancer cell death. Therefore, identification of active component(s) from the leaf extract could lead to the development of anti-cancer agents which could be useful in the treatment of different types of cancers.</p