Furthermore, ATP synthase was also found on the surface of breast cancer cells and was involved in cell proliferation, which showed that it could be a target for cancer therapy. Diverse categories of ATP synthase inhibitors have been discovered and investigated, Compound Library including peptides, polyphenolic phytochemicals, polyketides, polyenic a-pyrone derivatives, and so on. One of the compounds called citreoviridin is a polyene mycotoxin produced by several molds of genera, such as Penicillium and Aspergillus. It consists of an a-pyrone ring conjugated to a furan ring. Citreoviridin inhibits the activity of ATP synthase by interacting with the b subunit of F1 ATP synthase. It was shown to affect several metabolic enzymes, including glycogen synthase, glutamic-oxaloacetic transaminase and transketolase. Citreoviridin has been proved to inhibit the proliferation of the lung adenocarcinoma cell lines A549 and CL1-0 by activating the unfolded protein response. Proteomics, which measures mature proteins, could be used to closely observe biological functions in cells. There are two major methods available for mass spectrometry quantitation, the stable isotope-based and the label-free approaches. A wellestablished and widely used stable isotope-based method is isobaric tags for relative and absolute quantitation . iTRAQ reagents are amide reactive and covalently link to the N terminus and side chain of lysine residues of peptides. It provides multiplex protein quantitation by labeling peptides from different samples with different iTRAQ reagents. One of the most significant advantages of iTRAQ quantitation is that the intensities of peptide precursor ions in MS and fragment ions in MS/MS are enhanced by combination of all iTRAQ-labeled samples prior to MS analysis, which increases the accuracy of quantitation. However, global biases can arise from the sample preparation, reducing the accuracy of protein quantitation. Therefore, a good normalization method is of significant importance and should be performed to access accurate quantitation. Another key concern about iTRAQ is the integration of peptide-level Epoxomicin information into the measurement of protein abundance. A variety of algorithms were proposed and many software packages are also available for estimation of protein expression. In this study, our major objective was to elucidate the effect induced by citreoviridin in a lung cancer xenograft model. Applying proteomic analysis, we investigated the proteomic changes and pathways leading to cell proliferation inhibition caused by citreoviridin in lung cancer. First, the reproducibility of the iTRAQ-based proteomic strategies was assessed, followed by the acquisition of the proteomic profiling of citreoviridin-treated tumors with iTRAQ proteomic experiments. For data analysis, we optimized the normalization of iTRAQ signals and quantified the expression of proteins identified. After selecting differentially expressed human proteins between control and citreoviridintreated tumors, we investigated the pathways induced by citreoviridin in lung cancer xenograft tumors.