Epithelial ovarian cancer is the fourth leading cause of
cancer death among women. Due to the asymptomatic nature and poor survival characteristic of the disease, screening for specific
biomarkers for
ovarian cancer is a major health priority. Differentially expressed
proteins in the serum of
ovarian cancer patients have the potential to be used as
cancer-specific
biomarkers. In this study, proteomic methods were used to screen 24 serum samples from women with high-grade
ovarian cancer and compared to a control group of 11 healthy women. Affigel-Blue treated serum samples were processed either by linear (pH 4-7) or narrow range (pH 5.5-6.7) IEF strips for the first dimension.
Proteins separated in first dimension were resolved by 8-16% gradient SDS-PAGE.
Protein spots were visualized by
SYPRO Ruby staining, imaged by FX-imager and compared and analyzed by PDQuest software. Twenty-two
protein spots were consistently differentially expressed between normal and
ovarian cancer patients by resolving
proteins in a linear pH strip of 4-7 for the first dimension. Six of the
protein spots, significantly up-regulated in grade 3
ovarian cancer patients (p < 0.05), were identified by MALDI-TOF MS and Western blotting as the
isoforms of
haptoglobin precursor. When
serum proteins were resolved on narrow pH range strips (5.5-6.7), 23 spots were consistently differentially expressed between normal and grade 3
ovarian cancer patients. Of these, 4
protein spots significantly down regulated in grade 3
ovarian cancer patients (p < 0.05) were identified by MALDI-TOF MS and Western blotting, as
isoforms of
transferrin precursor. Increased expression of serum
haptoglobin and
transferrin was also identified in peritoneal
tumor fluid obtained from women diagnosed with grade 2/3
ovarian cancer (n = 7). Changes in the expression of
haptoglobin and
transferrin in the serum of women with different pathological grades of
ovarian cancer was examined by one-dimensional Western blotting method. Serum samples collected from women suffering from benign, borderline, grade 1, grade 2 and grade 3
cancer (n = 4 for
haptoglobin and n = 5 for
transferrin in each group) were analyzed and compared to the serum of normal healthy women. The mean serum
haptoglobin expression in grade 3
ovarian cancer patients was fourfold higher than in the control subjects (p < 0.05). On the other hand,
transferrin expression in grade 3
ovarian cancer patients was decreased by twofold than in normal healthy women (p < 0.05).
Haptoglobin expression in the serum of
cancer patients (n = 7) decreased following
chemotherapy (six cycles of
taxol/
carboplatin). Concomitant with the decrease of
haptoglobin,
transferrin expression remained constant in four patients, but increased in three out of seven patients included in the study. Changes in serum expression of
haptoglobin correlated with the change of CA 125 levels before and after
chemotherapy. In conclusion, proteomic profiling of differentially expressed
proteins in the sera of normal women compared to women with
ovarian cancer can greatly facilitate the discovery of a panel of
biomarkers that may aid in the detection of
ovarian cancer with greater specificity.