Sometimes, however, the protein expression profiles of cell lines do represent the accurate protein expression pro files of the in vivo tumor or tissues. Indeed, immortalized cell lines derived from human tumors, like HepG2 cell line, are more homogenous than solid liver tumors, as noted above. They have been extensively employed most in a wide range of in vitro disease models, and they produce large amounts of high quality DNA, mRNA and protein for analysis. Furthermore, they are Inhibitors,Modulators,Libraries excellent tools for mechanistic studies and are commercially available. Addi tionally, they afford improved reproducibility, ease of application of quantitative techniques and controlled experimental conditions. In addition, the protein profiles of cell cultures tend to give cleaner backgrounds than those of the corresponding tissues.

Wirth and co workers provide an example where a cell line reflects a true representation of the in vivo biology they reported that proteins present in non transformed cell lines Chang and WRL 68 were identical to the pro teins found in normal human liver. And, in a proteome profiling study, fresh bladder tumors showed strikingly similar protein Inhibitors,Modulators,Libraries expression profiles when compared to their primary cell cultures. Furthermore, Didonato and co workers compared the protein expressions of renal cell carcinoma tissues and patient matched normal kidney tissues with the primary RCC renal cell cul Inhibitors,Modulators,Libraries tures derived from the tissues, and found that the overall patterns of the profiles of the tissues and cell cultures were similar.

The protein spots on the 2D PAGE of the cell cul tures had much higher resolution, and the exact expres sion alterations of proteins in cancer and normal cell cultures were present in the tissue samples. Tan and co workers examined an immortalized mouse retinal cell line for markers characteristic of photorecep tor Inhibitors,Modulators,Libraries cells. Inhibitors,Modulators,Libraries they found that the 661W cell line exhibited sim ilar cellular and biochemical characteristics to those of the original cone photoreceptor cells from which they were derived. In a T cell acute lymphoblastic leukemia study, Gjerset and co workers found that, with regard to sur face markers, karyotype, and T cell receptor gene rear rangements, the cell cultures indeed closely resembled those of the patients at the time of diagnosis.

Comparative proteomics of a normal tissue against those of its tumor cell line could afford useful insights into qual itative and quantitative changes in proteins profiles fol lowing tumor development, and facilitate the discovery of novel markers of tumors. Loredana and co more information workers profiled the proteome of normal human breast tissues, and compared these with those of the corresponding 8701 BC breast cancer cell line. They found that the 8701 BC cell line retains the dominant luminal phenotype of the breast epithe lium, which expresses predominantly cytokeratins 8 and 18, and that the proteomic profile of the cell line appears highly homologous to the in vivo counterpart.