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Monitoring the protein expression pattern in tumour cells by proteomics technologies offers opportunities to discover potentially new biomarkers for the early detection and diagnosis of cancer. Different proteomic tools such as 2D-PAGE, 2D-DIGE, SELDI-ToF-MS technology, protein arrays, ICAT, iTRAQ and MudPIT have been used for differential analysis of various biological samples, including cell lysates, cell secretome (conditioned medium), serum, plasma, tumour tissue and nipple aspirate fluid, to better understand the molecular basis of cancer pathogenesis and the validation and characterisation of disease-associated proteins. In recent years, there has been a large increase in cancer-related publications dealing with new biomarker discovery for cancer, therefore, in this review we have focused on the contribution of proteomics technologies in serum and conditioned medium-based oncology research particularly for lung, breast, melanoma and pancreatic cancer.

The aim of this study was to examine whether the degree to which cell lines model corresponding cells in vivo is an important aspect of their value as models in studying disease processes.The work presented here utilizes gene expression data from two published microarray datasets to compare the differences and similarities among the two systems in order to identify major transcriptional changes in the adaptation process from a tissue to a cell line.Gene ontology and pathway analyses of comparator gene lists showed that the cell cycle related genes were significantly up-regulated in cell lines and immune response related genes were significantly up-regulated in clinical specimens. Estrogen receptor analysis also indicated differences in the clustering patterns of cell lines relative to clinical specimens.These findings suggest that significant differences in gene expression exist between clinical conditions and their respective cell line models and that these differences should be taken into account when extrapolating cell line results to in vivo systems.

p53 is a tumour suppressor gene, which is mutated in more than half of all tumours. Most chemotherapeutic drugs cause DNA damage, which is sensed by p53; the cell can then try to repair the damage or induce cell suicide. If the p53 machinery is defective, effective chemotherapy is made more difficult.Wild-type p53 was transfected into lung cancer cell lines with different p53 status. The transfected cells were tested for changes in sensitivity to a range of chemotherapeutic agents.We observed only modest changes in the sensitivity to the chemotherapeutic agents adriamycin, taxol and carboplatin in the transfected cells lines. p53 protein was detected in a transfected clone of the cell line H1299, whose parent cells are p53 null. However, the protein did not accumulate after DNA damage, suggesting that this cell line utilises alternative pathways for responding to stress, and no longer has a functional p53 pathway.The results suggest that introduction of wild-type p53 alone is not sufficient to substantially alter the sensitivity of a cell line to a given chemotherapeutic agent.

We have previously shown that the selection of cancer cell lines with chemotherapeutic agents can alter the invasive potential of the cells, resulting in a superinvasive phenotype, where cells not only invade through matrigel and migrate through membrane pores, but also subsequently detach from the underside of the invasion chamber, survive in suspension and ultimately attach to and grow on the bottom of the well beneath the insert. In order to determine the significance of this in vivo, the following experiments were performed.4T1-GFP mouse mammary adenocarcinoma cells were pulse-selected with doxorubicin or paclitaxel. Three variants with differing invasiveness were isolated and their metastatic potential in vivo was compared to the parental cell line, through injection into the mammary fat pad of BALB/c mice and subsequent primary tumour growth and metastasis to the lungs measurement.Increasing superinvasiveness was inversely linked to tumour diameter (p0.005). The superinvasive status predicted the incidence of lung nodules in 2/3 variant groups, with significant differences in the number of nodules (p0.001).The in vitro superinvasive phenotype coupled with decreased adhesion may predict for metastatic potential in vivo.

A number of cellular proteins, including P-glycoprotein (P-gp) and Multiple drug Resistance Protein (MRP-1), act as drug efflux pumps and are important in the resistance of many cancers to chemotherapy. We previously reported that a small number of NSAIDs could inhibit the activity of MRP-1.We chose sulindac as a candidate agent for further investigation as it has the most favourable efficacy and toxicity profile of the agents available for a potential specific MRP-1 inhibitor. NCI H460 cells expressed MRP-1 protein (by Western blot) and also the toxicity of doxorubicin (a substrate of MRP-1) could be potentiated in this line using non-toxic concentrations of the MRP-1 substrate/inhibitor sulindac. These cells were implanted in nude mice and the animals divided into various groups which were administered doxorubicin and/or sulindac.Sulindac was shown to significantly potentiate the tumour growth inhibitor activity of doxorubicin in this MRP-1-overexpressing human tumour xenograft model.Sulindac may be clinically useful as an inhibitor of the MRP-1 cancer resistance mechanism.

Caspase-3 is a key executioner cysteine protease involved in programmed cell death or apoptosis. A ribozyme to human caspase-3 was designed, tested by in vitro cleavage, and transfected into a drug-resistant variant (DLKP-A5F) of a human lung carcinoma cell line (DLKP). By both stable and transient transfection, this ribozyme was shown to be effective at down-regulating human caspase-3 mRNA and protein levels.

Galectin-3, a beta-galactosidase-binding protein, is involved in regulating many physiological and pathological cellular processes. The significance of galectin-3 in human lung and nasal carcinoma cells has not yet been elucidated.Using RT-PCR and Western blotting techniques, the constitutive level of galectin-3 in the human non-small cell lung carcinoma cell line, DLKP, was investigated. Following galectin-3 cDNA transfection into these cells, growth, toxicity, adhesion, motility and invasion assays were used to investigate the relevance of galectin-3 over-expression.Galectin-3 over-expression did not induce a multi-drug resistance phenotype or significantly affect cell growth rate, but it did result in enhanced (i) adhesion to extracellular matrix components; (ii) cell motility; and (iii) in vitro invasiveness. Furthermore, studies of RPMI-2650 variants suggest that galectin-3 expression correlates with nasal carcinoma cell invasiveness.Our results suggest that galectin-3 expression levels in both lung and nasal tumour cells may play a role in cell motility, invasion, and metastasis.