开题报告内容：（包括拟研究或解决的问题、采用的研究手段及文献综述，不少于2000字）
1.The reason or significance of the topic selection and research objective:
Chemotherapy, as one of the anticancer therapies, plays an important role in improving survival among cancer patients. However, multidrug resistance (MDR), whether inherent or acquired, greatly threatens clinical outcomes and patientsrsquo; lives. They are closely correlated with poor chemosensitivity. Also, chemo-drugs are not able to distinguish normal cells from cancer cells, resulting in serious side effects due to the lack of selectivity. An advanced therapy with enhanced therapeutic efficiency and safety is necessary to overcome MDR and minimize severe side effects. In recent years, combination therapy (chemo-photodynamic) has been suggested as an alternative strategy to reverse MDR and minimize side effects through different mechanisms of action, enhancing anticancer efficacy. Photodynamic therapy (PDT) is a widely used therapy in clinics to treat various cancers and is approved by the United States Federal Drug Administration(USFDA). PDT is light-activated cancer therapy, and it involves a PS, a light source, and intracellular molecular oxygen. In the process of PDT, light irradiation of the PS at a specific wavelength in the presence of molecular oxygen produces highly cytotoxic reactive oxygen species (ROS), especially reactive singlet oxygen (1O2). These species live only for a short time (lt;0.1ms) in cells and interact with lipid membranes and DNA, which can destroy tumors by three different effects:(1) tumor cell death (apoptosis/ necrosis); (2) coagulation of micro-vessels resulting in vascular shut down (nutritional cutoff); (3) stimulation of the host immune system, causing cellular apoptosis and/or necrosis in targeted sites. Thus, due to these light-activated properties, the PS can selectively attack cancer cells by ROS generation, thereby not damaging normal cells and minimizing side effects in PDT. And my graduation project aims to acquire the anti-cancer activity of TPP-PEG as the PDT agent by MTT assay.
2.MTT assay(cell-based assay) principles:
The MTT assay is a colorimetric assay for assessing cell metabolic activity. NAD(P)H-dependent cellular oxidoreductase enzymes may, under defined conditions, reflect the number of viable cells present. These enzymes are capable of reducing the tetrazolium dye MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide to its insoluble formazan, which has a purple color. Other closely related tetrazolium dyes including XTT, MTS and the WSTs, are used in conjunction with the intermediate electron acceptor,1-methoxy phenazine methosulfate(PMS). With WST-1, which is cell-impermeable, reduction occurs outside the cell via plasma membrane electron transport. However, this traditionally assumed explanation is currently contended as proof has also been found of MTT reduction to formazan in lipidic cellular structures without apparent involvement of oxidoreductases. Tetrazolium dye assays can also be used to measure cytotoxicity (loss of viable cells) or cytostatic activity (shift from proliferation to quiescence) of potential medicinal agents and toxic materials. MTT assays are usually done in the dark since the MTT reagent is sensitive to light.
3.Cell culture:
I use the human breast cancer cell line MCF-7, the cell line is grown in Dulbeccorsquo;s modified Eaglersquo;s medium (DMEM; GIBCO, USA) supplemented with 10%(v/v) heat-inactivated fetal bovine serum (FBS; GIBCO, USA) and 100 IU/ml-1 penicillin
and 100 ug/ml-1 streptomycin (GIBCO, USA) at 37°C in a 5% CO2 atmosphere.
4.Cytotoxicity assay:
4.1 Approximately 25*104 MCF-7 cells were seeded into a 96-well plate and incubated at 37°C in 5% CO2 overnight.
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