Inhibition of proteasome activity by the dietary flavonoid apigenin is associated with growth inhibition in cultured breast cancer cells and xenografts

Abstract Introduction Proteasome inhibition is an attractive approach to anticancer therapy and may have relevancy in breast cancer treatment. Natural products, such as dietary flavonoids, have been suggested as natural proteasome inhibitors with potential use for cancer prevention and therapeutics. We previously reported that apigenin, a flavonoid widely distributed in many fruits and vegetables, can inhibit proteasome activity and can induce apoptosis in cultured leukemia Jurkat T cells. Whether apigenin has proteasome-inhibitory activity in the highly metastatic human breast MDA-MB-231 cells and xenografts, however, is unknown. Methods MDA-MB-231 breast cancer cell cultures and xenografts were treated with apigenin, followed by measurement of reduced cellular viability/proliferation, proteasome inhibition, and apoptosis induction. Inhibition of the proteasome was determined by levels of the proteasomal chymotrypsin-like activity, by ubiquitinated proteins, and by accumulation of proteasome target proteins in extracts of the treated cells or tumors. Apoptotic cell death was measured by capase-3/caspase-7 activation, poly(ADP-ribose) polymerase cleavage, and immunohistochemistry for terminal nucleotidyl transferase-mediated nick end labeling positivity. Results We report for the first time that apigenin inhibits the proteasomal chymotrypsin-like activity and induces apoptosis not only in cultured MDA-MB-231 cells but also in MDA-MB-231 xenografts. Furthermore, while apigenin has antibreast tumor activity, no apparent toxicity to the tested animals was observed. Conclusion We have shown that apigenin is an effective proteasome inhibitor in cultured breast cancer cells and in breast cancer xenografts. Furthermore, apigenin induces apoptotic cell death in human breast cancer cells and exhibits anticancer activities in tumors. The results suggest its potential benefits in breast cancer prevention and treatment

(−)-epigallocatechin gallate derivatives for inhibiting proteasome

A method of reducing tumor cell growth, the method including administering an effective amount of a compound having the formula

(−)-epigallocatechin gallate derivatives for inhibiting proteasome

(−)-EGCG, the most abundant catechin, was found to be chemopreventive and anticancer agent. However, (−)-EGCG has at least one limitation: it gives poor bioavailability. This invention provides compounds of generally formulae below, wherein R11, R12, R13, R21, R22, R2, R3, and R4 are each independently selected from the group consisting of —H, and C1 to C10 acyloxyl group; and R5 is selected from the group consisting of —H, C1-C10-alkyl, C2-C10-alkenyl, C2-C10-alkynyl, C3-C7-cycloalkyl, phenyl, benzyl and C3-C7-cycloalkenyl, whereas each of the last mentioned 7 groups can be substituted with any combination of one to six halogen atoms; at least one of R11, R12, R13, R21, R22, R2, R3 and R4 is —H, which were found to be more potent than their non-protected counterparts, which can be used as proteasome inhibitors to reduce tumor cell growth

Tea polyphenols, their biological effects and potential molecular targets

Tea is the most popular beverage in the world, second only to water. Tea contains an infusion of the leaves from the Camellia sinensis plant rich in polyphenolic compounds known as catechins, the most abundant of which is (-)-EGCG. Although tea has been consumed for centuries, it has only recently been studied extensively as a health-promoting beverage that may act to prevent a number of chronic diseases and cancers. The results of several investigations indicate that green tea consumption may be of modest benefit in reducing the plasma concentration of cholesterol and preventing atherosclerosis. Additionally, the cancer-preventive effects of green tea are widely supported by results from epidemiological, cell culture, animal and clinical studies. In vitro cell culture studies show that tea polyphenols potently induce apoptotic cell death and cell cycle arrest in tumor cells but not in their normal cell counterparts. Green tea polyphenols were shown to affect several biological pathways, including growth factor-mediated pathway, the mitogen-activated protein (MAP) kinasedependent pathway, and ubiquitin/proteasome degradation pathways. Various animal studies have revealed that treatment with green tea inhibits tumor incidence and multiplicity in different organ sites such as skin, lung, liver, stomach, mammary gland and colon. Recently, phase I and II clinical trials have been conducted to explore the anticancer effects of green tea in humans. A major challenge of cancer prevention is to integrate new molecular findings into clinical practice. Therefore, identification of more molecular targets and biomarkers for tea polyphenols is essential for improving the design of green tea trials and will greatly assist in a better understanding of the mechanisms underlying its anti-cancer activity