Multiple myeloma (MM) is a malignancy of terminally differentiated B-lymphocytes that accounts for 13% of all hematologic cancers. Despite a wealth of knowledge describing the molecular biology of MM as well as significant advances in therapeutics, this disease remains incurable. Since proteins govern the cellular structure and biological function, a wide selection of proteomic approaches holds great promise for increasing our understanding of this disease, such as by investigating the dynamic nature of protein expression, cellular and subcellular distribution, post-translational modifications, and interactions at both the cellular and subcellular levels. The aims of this review are to introduce the available and emerging proteomic technologies that have potential applications in the study of MM and to highlight the current status of proteomic studies of MM. To date, although there have been a limited number of proteomic studies in MM, those performed have provided valuable information with regard to MM diagnosis and therapy. The potential future application of proteomic technologies is expected to provide new avenues in MM diagnostics, individualized therapy design and therapy response surveillance for the clinician.
Current proteomics techniques are facing the limitations in terms of their capacity to analyze the entire proteome of a tissue or biological fluid in a single reaction. In bodily fluids like serum or plasma, protein concentrations vary over more than 10 orders of magnitude and the presence of high-abundant proteins invariably masks the detection of low-abundant proteins. The strategy of many researchers in the field is thus oriented towards either combining two or more complementary technical approaches and/or analyzing the sub-proteome of interest. Many techniques for de-complexion of the proteome, enrichment or depletion of particular sub-proteomes, and separation techniques for proteins/peptides have emerged in parallel with the development of mass spectrometry (MS) of high capacity, resolution, and accuracy. Excellent in-depth reviews on MS are available elsewhere.
In the past decade, proteomics technology has made great advances. And with the advent of powerful and sensitive mass spectrometers, sophisticated databases and bioinformatics software, it is now possible to investigate the protein changes that may underlie many diseases. However, the use of such technology to investigate MM remains a challenging problem. Initial proteomics studies aiming at the identification of biomarkers and molecular targets for MM are mostly small-scale gel-based approaches. In recent years, more large-scale approaches adopting MS/MS-based proteomics are reported. These studies generate large amounts of data that require extensive validation and follow-up analysis. Therefore, it is clear from a review of the literature that progress is being made in this area, but a great deal still remains to be done. No proteomics technique is currently able to reveal the complete human proteome, therefore the choice of the technique should be guided by the specific research question and ideally a combination of complementary techniques should be applied.
Invariably, with primary cells we must rely on label-free MS quantification, O labeling or iTRAQ approaches. In this respect, the increasingly sophisticated label-free quantification approaches that are coupled with sub-cellular fractionation and targeting of signaling complexes allow the possibility that critical protein changes will be identified in MM cells. The identification of such changes will provide important advances in understanding MM pathogenesis.
There are three main expectations for proteomic analysis of MM:The first is to decipher the molecular mechanisms and signaling events that lead to MM development. The second is to identify proteins that can be used for diagnosis or prognosis. The third is to identify potential targets for therapeutic intervention. It is clear from the above discussion that proteomics approaches have identified a number of proteins that can be potential targets for therapy in MM, but clearly there is still considerable scope for new discoveries. In conclusion, proteomics using advanced MS methods offers the opportunity to identify new therapeutic targets and biological mechanisms in MM. The challenge is to develop appropriate targeted, mechanistic and functional approaches that allow the identification of both novel and known protein species. However, successful proteomic studies on MM must be integrated and validated with biological and clinical studies. The challenge will be now to translate this fundamental knowledge into new prognostic, diagnostic, and therapeutic tools that can improve treatment and outcome of patients with MM.