Curcumin, An Active Ingredient Extracted From Chinese Herbs, Regulates Autophagic And Endoplasmic Reticulum Stress Pathways In Human Breast Cancer Cells

With more rapid urbanization, more aged population and higher economic development, the mortality and morbidity rates of breast cancer have sharply increased globally during recent decades. According to statistics issued by International Agency for Research on Cancer(IARC), breast cancer accounts for 23% total female cancers in the world, and is the first cause of death in the women. In China, the age-standardized morbidity rate of breast cancer reached to 18.7/100,000. More progress have been made in understanding of breast cancer oncology and the efficacy and prognosis of breast cancer have also been improved by in-depth clinical practice and study. Treatment of breast cancer with western medicine has effectively applied, but its practice has been limited by the chemotherapy resistance, adverse effects caused by anticancer drugs and the impaired quality of life by surgical resection. However, the traditional Chinese medicine has played more important roles in improving efficacy of chemotherapy and surgical operation and opened a new avenue to prevent and treat breast cancer. In fact, with modernization of traditional Chinese medicine and herbs, Chinese herbs have been widely used in the clinics; especially the combination of Western drugs with Chinese herbs becomes the first choice in caner therapy. Among these herbs or active components, curcumin, extracted from Curcuma longa, has been shown the promising actions on breast cancer therapy, but exact underlying molecular and cellular mechanisms remain unclear. During carcinogenesis, growth, proliferation, invasion and metastasis, more evidence have found that autophagy and endoplasmic reticulum stress were regulated in breast cancer, and more attention has been paid by physicians and scientists. The present study is designed to explore the effects of curcumin on autophgy and endoplasmic reticulum stress in two human breast cancer cells. Our findings will provide scientific bases for clinical application of curcumin and developing more new analogues.Study Objective1. To assess the role of curcumin in clinical application for breast cancer therapy and rational traditional Chinese medical bases of combination of curcumin with chemotherapy drugs.2. To explore the novel mechanism of actions of curcumin in breast cancer cells with focus on regulation of autophagy and endoplasmic reticulum stress. These results will be beneficial to developing of new regiments and resulting in improvement of quality of patients.Main methodsThis study has been conducted by combining of theoretic analysis and experimental assessment.1. Theoretical analysis1.1 Comprehensively collect, sort Chinese and overseas ancient and current medical literatures, then assess the develop and prognosis of breast cancer. The main data have obtained from epidemiological survey, genetical study, identified risk factors and preventive principles.1.2 With concept of evidence-based medicine, critically summarize the theoretic traditional Chinese medicine foundation for breast cancer treatment, and then analyze the strength and weakness of traditional Chinese medicine and Western medicine to recommend optional choice for clinical practice.2. Experimental exploration2.1 Confirm the anti-proliferation of curcumin on two human breast cancer cells. One is MCF-7 and the other MDA-MB-231. The two cell lines were treated with different concentration of curcumin. The proliferation was evaluated with MTT assay.2.2 The markers of autophagy and endoplasmic reticulum stress response were measured with Western blotting. These markers include LC3B, beclin, GRP78, p-PERK, p-eIF2alpha and IRE1.2.3 Effects of pharmacological inhibition of autophagy on proliferation inhibition of curcumin. The two autophagy-specific inhibitors, chloroquine(CQ) and 3-methyladenine (3-MA) were used to pre-treat the cells and then cells were treated with curcumin at various concentrations for 24h.The LC3B and beclin 1 were also applied to confirm the blockage of autopagy.2.4 Effects of genetically knockdown of atg5, one key gene to initiate autophagy on proliferation inhibition of curcumin. The following measures were the same as 2.3.2.5 The preconditioning of endoplasmic reticulum stress and its effects on curcumin inhibition of breast cancer cells. The two inhibitors,4-PBA and Sal and inducers,2-DG and DDTox, were used to pre-treat cells and than treated with curcumin at various concentrations for 24 h. The MTT assay was used to assess cell viability and GRP78 and p-PERK were measured for confirmation of alteration of endoplasmic reticulum stress.Main results:1. Curcumin concentration and dependently inhibits proliferation of both MCF-7 and MDA-MB-231 cells.2. Curcumin enhances expression of Beclinl and promotes transvering ratios of LC3-I to LC3-II.3. Pretreatment of CQ exaggerates the accumulation of LC3B-I caused by curcumin alone both in MCF-7 and MDA-MB-231.4. Pretreatment of 3-MA attenuated the reduction of cell viability caused by curcumin alone both in MCF-7 and MDA-MB-231.5. GRP78, p-PERK and p-eIF2alpha were all overexpressed or enhanced in both MCF-7 and MDA-MB-231 treated with curcumin at various concentrations.6. The two inhibitors,4-PBA and Sal and inducers,2-DG and DDTox, changed the expression of marker of endoplasmic reticulum stress. The inhibitor pretreatment enhance proliferation inhibition caused by curcumin and inducer preconditioning decreases anti-proliferation of curcumin in both MCF-7 and MDA-MB-231, though differences did not reach significance.ConclusionCurcumin inhibits proliferation of two human breast cancer cells via induction of cytotoxic autophagy. In addition, endoplasmic reticulum stress was also activated as adaptive response and blocking endoplasmic reticulum stress may enhance sensitiveness of breast cancer cells to curcumin.