In addition, since HSPB1 contributes to chemotherapy resistance and apoptosis inhibition in gastric cancer cells, the high levels of HSPB1 observed in our GC sample might be associated with anticancer drug resistance or survival, as well as poor patient prognosis. The lack of additional information about the survival or response to any adjuvant treatment from the studied patients is one limitation of this study. After going unnoticed for decades, Warburg’s hypothesis of a glycolytic phenotype in tumors is now increasingly recognized. Particularly in highly aggressive tumors a shift from efficient ATP synthesis via oxidative phosphorylation to increased glycolysis has been observed. These changes in energy metabolism have been linked to increased angiogenesis, impaired apoptosis, and generation of an acidic tumor environment. Increased glycolysis has been shown to result from suppression of OXPHOS due to a hypoxic state in tumor areas with poor blood and oxygen supply, from mutation of key regulatory genes, or from increased reactive oxygen species levels. The latter two lead to a pseudo-hypoxic state under normoxic conditions. Hypoxia has been recognized as a predictive marker for metastatic disease, therapy resistance, and poor outcome in several types of cancer. To date, aggressive tumor behavior of PHEOs/PGLs has not been conclusively studied with respect to energy metabolism. This is Tulathromycin B partially due to several limitations, including: limited availability of SDHB-related tumors, unsuccessful establishment to date of an SDHB cell line, difficulties in maintaining primary cells from human PHEOs/PGLs in culture, and the absence of an SDHB animal model. Recently, mouse PHEO cells were established as an excellent tool for the study of the molecular biology of PHEO in vitro and in vivo. Tumors identical with PHEOs/PGLs develop after i.v. and s.c. injection of these cells into nude mice. Martiniova et al. recently developed the more aggressive mouse tumor tissue cells by bulk culture of a liver tumor that developed after tail vein injection of MPC into a nude mouse. Magnetic resonance imaging and microarray gene expression profiling comparing MPC to MTT cells revealed changes reflective of more aggressive behavior of the latter. Thus, comparison of the molecular biology of MTT cells to MPC may provide valuable insight into causes for aggressive behavior in PHEOs/PGLs. By focusing on the cell model, typical inter-patient variability in gene expression can be avoided, possibly allowing for an unbiased view onto changed molecular pathways. Therefore, we decided to run a comparative protein expression study of MPC and MTT cells as a first step to detect proteins that seem to be of importance for an aggressive PHEO/PGL phenotype. Analysis of the differentially expressed proteins focused on changes in energy metabolism related pathways. Expression changes detected in the MPC and MTT cells were then evaluated in human VHL- and SDHB-derived PHEOs/PGLs. Changes related to energy metabolism were further evaluated by measurement of OXPHOS complex activity, ROS production, and expression analysis of additional glycolysis and OXPHOS related genes. The results presented here may lead to better characterization and understanding of the pathogenesis of aggressive PHEOs/PGLs. In the present study, comparative analysis of MPC and MTT cells helped us to identify differentially expressed proteins characteristic of aggressive behavior. We chose this approach to avoid identifying differentially expressed proteins in direct comparisons of SDHB and VHL-PHEOs/PGLs that may be due to tumor location, the Butenafine hydrochloride different mutations, or other factors that are not necessarily related to the aggressive behavior of SDHB tumors.