The Significance of MALDI-TOF in Protein Identifications and Detection of Cancer - Literature review Example

About 7.6 million or 13% of global mortality is attributed to cancer. Since the majority of currently available screening tests forcancers lack high sensitivity and specificity, the routine screening to differentiate between some benign and malignant tumors is very difficult. Malignant transformation of cells involves protein expression alterations with subsequent clonal proliferation of the altered cells. Matrix-assisted laser desorption-ionization, time-of-flight (MALDI-TOF) mass spectrometry (MS) is a leading technology in proteomics. MALDI-TOF allows the direct measurement of expression signature of tissue, serum, plasma, or other biological specimens. MALDI-TOF has shown the potential in various studies by demonstrating a good total recognition rate, sensitivity and specificity in colorectal cancer, breast cancer, ovarian cancer, diagnosing leptomeningeal metastasis in patients with breast cancer, endometrial cancer and other cancers. Review of literature Maciel et al., 2005, investigated whether serum proteins could differentiate lung adenocarcinoma patients from healthy donors; this was based on the assumption that proteins can emanate from tumor to serum. The results of 2-DE/MALDI-TOF showed 5 up-regulated proteins: immunoglobulin lambda chain, transthyretin monomer, haptoglobin-alfa 2, and 2 isoforms of serum amyloid protein, and 1 down-regulated protein, fragment of apolipoprotein A-I in lung adenocarcinoma patients (Maciel et al, 2005). Ahmed et al., 2005, used proteomic methods in a study to screen 24 serum samples from women with high-grade ovarian cancer and compared it to a control group of 11 healthy women. Twenty-two protein spots were consistently differentially expressed between the control group and patients with ovarian cancer by resolving proteins in a linear pH strip of 4-7 for the first dimension. MALDI-TOF MS and Western blotting were able to identify six of the protein spots, significantly up-regulated in grade 3 ovarian cancer patients, as the isoforms of haptoglobin precursor. When the serum proteins were resolved on narrow pH range strips (5.5-6.7), 23 spots were consistently differentially expressed between the control group and grade 3 ovarian cancer patients. Of these, MALDI-TOF MS and Western blotting identified 4 protein spots, significantly down regulated in grade 3 ovarian cancer patients, as isoforms of transferrin precursor. A correlation was observed between changes in serum expression of haptoglobin with the change of CA-125 levels before and after chemotherapy. More importantly, this technique worked well even in patients with early stage disease; this would allow early diagnosis and a successful treatment outcome (Ahmed et al., 2005). Colorectal cancer (CRC) ranks amongst the most common malignancies and a leading cause of morbidity and mortality due to cancer. A sequence of genetic alterations transforms normal mucosa to a precursor adenoma and ultimately to carcinoma. In order to reduce mortality, early diagnosis is very important. However, currently, there is no diagnostic test with high sensitivity, specificity and positive predictive value to detect CRC early. New biomarkers can help in the early diagnosis, monitor disease progression, therapeutic response, detect disease recurrence, and give indications for targets for novel therapeutic strategies. De Noo et al., 2006, aimed to assess the feasibility of mass spectrometry based protein profiling to differentiate colorectal cancer patients from healthy individuals. The study used blinded tests and a randomized block design experimentation. Pre-operative serum samples were obtained from 66 colorectal cancer patients and 50 controls to generate MALDI-TOF protein profiles. Protein profiles were classified using a linear discriminant analysis with double cross-validation after pre-processing of the spectra. The results showed a total recognition rate of 92.6%, sensitivity of 95.2%, and specificity of 90.0% for the detection of CRC. This study supports the hypothesis that serum protein profiles can discriminate a normal from a malignant state. A classifier could also be constructed for the detection of CRC based upon the information in MALDI-TOF serum spectra (De Noo et al., 2006 ). Mazzanti et al., 2006, obtained colon cancer samples confined to the intestinal wall, analyzed it with expression proteomics, and compared with matched samples from normal colon tissue. Samples were processed by two-dimensional gel electrophoresis, and spots differentially expressed and consistent across all patients were identified by MALDI-TOF and by Western blot analyses. The following main observations were made for tumor tissue after an analysis of differentially expressed proteins and their metabolic pathways: (1) a shift from beta-oxidation, as the main source of energy, to anaerobic glycolysis due to the alteration of nuclear-versus mitochondrial-encoded proteins and other proteins related to fatty acid and carbohydrate metabolism; (2) lower capacity for Na (+) and K (+) cycling; and (3) operativity of the apoptosis pathway, especially mitochondrial. This study of the human colon cancer proteome, therefore, gives a better understanding of the metabolomics of early colon cancer confined to the intestinal wall. Changes in diet, and inclusion of vegetables in the diet have been shown to have a protective effect against CRC. However, not much is known about the effects that vegetable consumption has at the proteome level. Breikers et al., 2006, aimed to identify the proteins that are differentially expressed by increased vegetable consumption and their possible role in the protection against colorectal cancer. Four different vegetable diets were given to mice, followed by analysis of total cellular protein from colonic mucosal cells by a combination of 2-DE and MS. Thirty proteins were found to be differentially expressed in one or more diets as compared to the control diet; of these, 6 proteins were identified by MALDI-TOF MS: myosin regulatory light chain 2, carbonic anhydrase I, high-mobility group protein 1, pancreatitis-associated protein 3, glyceraldehyde-3-phosphate dehydrogenase and ATP synthase oligomycin sensitivity conferral protein. The study concluded that these proteins are suitable markers and alterations in the levels of these proteins have a role in the protection against colon cancer. About 5% of patients with breast cancer develop leptomeningeal metastasis (LM) as a complication. Although early diagnosis and treatment are important, 25% of cerebrospinal fluid (CSF) samples produce false-negative results at first cytological examination, which makes early diagnosis of LM difficult. Dekker et al., 2005, investigated the protein expression patterns in the CSF of patients with breast cancer, with and without LM. CSF samples of 106 patients with active breast cancer (54 with LM and 52 without LM) and 45 control subjects were digested with trypsin, and MALDI-TOF MS was used to measure the resulting peptides. Following this, the mass spectra were analyzed and compared between patient groups. One hundred and sixty four peaks were detected out of a possible 895 peak positions. After the discriminatory masses were clustered, a classifier was built to differentiate between patients with breast cancer with and without LM. The classifier had 77% maximum accuracy, 79% sensitivity, and 76% specificity. It was concluded from this that direct MALDI-TOF analysis of tryptic digests of CSF could give reproducible peptide profiles, which helps in diagnosing LM in patients with breast cancer. De Noo et al., 2006, used a randomized block design study and obtained pre-operative serum samples from 78 patients with breast cancer and 29 controls. High-resolution MALDI-TOF protein profiles were generated. This was followed by linear discriminant analysis with double cross-validation to classify protein profiles. The results showed 99% total recognition rate, 100% sensitivity, and 97.0% specificity for breast cancer detection. Endometrial tissue sampling is associated with a relatively high incidence of complications and low diagnostic sensitivity; therefore, there is an urgent need for a diagnostic method, which is both safe and non-invasive (Kikuchi et al., 2007.) Kikuchi et al., 2007, used MALDI-TOF to obtain the proteomic spectrum of albumin-associated peptides from a total of 125 serum samples (92 patients with endometrial cancer and 33 controls). The Mann–Whitney U-test and receiver operator characteristics analysis were used to select the candidate markers. Endometrial cancer was detected with a sensitivity of 65.2% (60.3% for stage I early endometrial cancer) using the combination of the three peptides. However, the three peptides were also detected in 44.6% of myoma uteri patients. This indicated that these are not specific to endometrial cancer. A large-scale study is required to confirm the clinical significance of the peptide biomarkers revealed in this study, but nevertheless, direct profiling of serum-albumin-bound peptides by MALDI-TOF is a potential use to identifying biomarkers in this condition. Discussion Oncoproteomics is the study of proteins and their interactions in a cancer cell by the use of proteomic technologies. The problem with the majority of currently available screening tests for cancers is the lack of high sensitivity and specificity; this makes the routine screening to differentiate between some benign and malignant tumors very difficult. With the advent of oncoproteomics, a new hope of discovering novel biomarkers has emerged in the screening, early diagnosis, and predicting response to cancer therapy. Matrix-assisted laser desorption-ionization, time-of-flight (MALDI-TOF) mass spectrometry (MS) is one such leading technology in proteomics. MALDI-TOF allows the direct measurement of expression signature of tissue, serum, plasma, or other biological specimens. MALDI-TOF has shown the potential in various studies by demonstrating a good total recognition rate, sensitivity and specificity in colorectal cancer, breast cancer, ovarian cancer, diagnosing leptomeningeal metastasis in patients with breast cancer, and of slightly less sensitive value in endometrial cancer. Application of direct tissue MALDI-TOF MS has also identified protein patterns with high sensitivity and specificity, which enables to distinguish primary gliomas from normal brain tissue and the different grades of gliomas (Cho, 2007). References Ahmed, N, Oliva, KT, Barker, G, Hoffmann, P, Reeve, S, Smith, IA, Quinn, MA, Rice, GE (2005). Proteomic tracking of serum protein isoforms as screening biomarkers of ovarian cancer. Proteomics. 5:4625-4636. Breikers, G, van Breda, SG, Bouwman, FG, van Herwijnen, MH, Renes, J, Mariman, EC, Kleinjans, JC, van Delft, JH (2006). Potential protein markers for nutritional health effects on colorectal cancer in the mouse as revealed by proteomics analysis. Proteomics. 6:2844-2852. Cho, WCS (2007). Contribution of oncoproteomics to cancer biomarker discovery. Molecular Cancer. 6:25. De Noo, ME, Merten, BJA, Ozalp, A, Bladergroen, MR, van der Werff, MPJ, van de Velde, CJH, Deelder, AM, Tollenaar, RAEM (2006). Detection of colorectal cancer using MALDI-TOF serum protein profiling. European Journal of Cancer. 42:1068-1076. De Noo, ME, Deelder, A, van der Werff, M, Ozalp, A, Mertens, B, Tollenaar, R (2006). MALDI-TOF serum protein profiling for the detection of breast cancer. Onkologie. 29(11):501-6. Dekker, LJ, Boogerd, W, Stockhammer, G, Dalebout, JC, Siccama, I, Zheng, P, Bonfrer, JM, Verschuuren, JJ, Jenster, G, Verbeek, MM, Luider, TM, Smitt, PA (2005). MALDI-TOF mass spectrometry analysis of cerebrospinal fluid tryptic peptide profiles to diagnose leptomeningeal metastases in patients with breast cancer. Mol Cell Proteomics. 4(9):1341-9. Kikuchi, S, Honda, K, Handa, Y, Kato, H, Yamashita, K, Umaki, T, Shitashige, M, Ono, M, Tsuchida, A, Aoki, T, Hirohashi, S, Yamada, T (2007). Serum albumin-associated peptides of patients with uterine endometrial cancer. Cancer Science. 98 (6): 822–829. Maciel, CM, Junqueira, M, Paschoal, ME, Kawamura, MT, Duarte, RL, Carvalho Mda, G, Domont GB (2005). Differential proteomic serum pattern of low molecular weight proteins expressed by adenocarcinoma lung cancer patients. J Exp Ther Oncol. 5:31-38 Mazzanti, R, Solazzo, M, Fantappie, O, Elfering, S, Pantaleo, P, Bechi, P, Cianchi, F, Ettl, A, Giulivi, C (2006). Differential expression proteomics of human colon cancer. Am J Physiol Gastrointest Liver Physiol. 290:G1329-G1338. Read More