Mining the Ovarian Cancer Ascites Proteome for Potential Ovarian Cancer Biomarkers

Abstract

Current ovarian cancer biomarkers are inadequate because of their relatively low diagnostic sensitivity and specificity. There is a need to discover and validate novel ovarian cancer biomarkers that are suitable for early diagnosis, monitoring, and prediction of therapeutic response. We performed an in-depth proteomics analysis of ovarian cancer ascites fluid. Size exclusion chromatography and ultrafiltration were used to remove high abundance proteins with molecular mass >30 kDa. After trypsin digestion, the subproteome (<30 kDa) of ascites fluid was determined by two-dimensional liquid chromatography-tandem mass spectrometry. Filtering criteria were used to select potential ovarian cancer biomarker candidates. By combining data from different size exclusion and ultrafiltration fractionation protocols, we identified 445 proteins from the soluble ascites fraction using a two-dimensional linear ion trap mass spectrometer. Among these were 25 proteins previously identified as ovarian cancer biomarkers. After applying a set of filtering criteria to reduce the number of potential biomarker candidates, we identified 52 proteins for which further clinical validation is warranted. Our proteomics approach for discovering novel ovarian cancer biomarkers appears to be highly efficient because it was able to identify 25 known biomarkers and 52 new candidate biomarkers that warrant further validation. Molecular & Cellular Proteomics 8:661-669, 2009.Accounting for ϳ3% of all new cancer cases in 2008 (1) with a 1 in 59 (1.7%) lifetime probability of developing the disease, ovarian cancer is the most lethal gynecological malignancy deeming 5-6% of all cancer deaths (1). Hidden deep within the pelvis, ovarian cancer is relatively asymptomatic in early stages, and because of the lack of adequate screening, ovarian cancer has resulted in the majority of cases being presented with late stage disease in association with a low 5-year survival rate of 25-40%. When presented at an early stage, the 5-year survival rate exceeds 90% and most patients are cured by surgery alone (2). Although the most widely used serum marker for ovarian cancer is carbohydrate antigen 125 (CA125), 1 its utility as a screening marker is limited because of its high false positive rates and elevation in other malignancies such as uterine, fallopian, colon, and gastric cancer (3, 4) as well as in non-malignant conditions such as pregnancy and endometriosis (5). These reasons alone demonstrate the need and immediate benefit in using biomarkers with increased sensitivity and specificity for early diagnosis, prognosis, or monitoring of ovarian cancer.Many advanced stage ovarian cancer patients exhibit rapid growth of intraperitoneal tumors along with abdominal distention as a result of accumulation of ascites fluid in the peritoneal cavity. Mechanistically ascites formation occurs as malignant cells secrete proteins, growth factors, and cytokines that cause neovascularization, angiogenesis, increased fluid filtration, and/or lymphatic obstruction (6 -8) resulting...

Ascites in Ovarian Cancer Progression: Opportunities for Biomarker Discovery and New Avenues for Targeted Therapies

“…The concentration of soluble factors is usually much higher in ascites compared to serum, which increases the likelihood of detecting low abundance proteins [24,57]. In that context, proteomic/peptidomic proiling of ascites has been employed for biomarker discovery [59][60][61]. Diferent experimental approaches were used leading to the identiication of various sets of biomarkers all of which requiring further validation to determine their true potential.…”

Glycoproteomic identification of potential glycoprotein biomarkers in ovarian cancer proximal fluids

“…This is due to the fact that some well-known and previously studied proteins in the context of ovarian cancer were also identified ( Table 2 ). These include the classical ovarian cancer biomarker CA125 and others such as mesothelin, WFDC2 (HE4), α 2-macroglobulin, cathepsin D, and clusterin, which have shown promise as ovarian cancer biomarkers [ 17 ]. The glycosylation status of a number of these proteins has been studied in various contexts and some were reported to be sialylated ( Table 2 ) lending further support to our methodology.…”

Evaluation of Serum Nidogen-2 as a Screening and Diagnostic Tool for Ovarian Cancer

“…Kuk et al [3] stated that nidogen-2 was elevated in the serum of patients with ovarian carcinoma, compared to patients with benign gynecological diseases and normal controls. Statistical analysis demonstrated that nidogen-2 has a potential diagnostic value.…”

“…Based on ovarian cancer prevalence, which is 1.3% [12], the expected sensitivity of nidogen-2 based on previous study is 55% and the expected specificity is 90% [3]; CI is 95% and the desired precision in this study will be 0.05 for specificity; accordingly, the sample size was calculated as 144 cases.…”

“…Despite enormous efforts, there are no successful screening methods developed until now to decrease mortality, whether by pelvic examination, ultrasonography or by use of serum markers. Numerous possible markers have been identified, yet no currently available test gives sufficient levels of accuracy [2, 3]. …”