Objective: (1) To identify and (2) validate genes that are up-regulated in ovarian cancer, and (3) to investigate whether the activity of a candidate gene, creatine kinase B (CKB) is elevated in pre-operative sera from ovarian cancer patients compared to patients with benign pelvic masses and normal controls.
Methods: MICROMAX cDNA microarray system and RNA derived from pooled ovarian cancer cell lines and normal ovary surface epithelial cells (HOSE) were used to identify differentially expressed genes. Using RNA from both cell lines and from tissue obtained through laser capture microdissection (LCM), we performed quantitative PCR in order to validate up-regulation of one of these genes, creatine kinase B (CKB). Using a commercially available enzyme assay, CKB activity was measured in pre-operative serum samples obtained from 45 ovarian cancer patients, 49 patients with a benign pelvic mass, as well as 37 normal controls. Statistical analysis was preformed using an unpaired Student's t test.
Results: Microarray technology revealed that CKB gene expression had a cancer to HOSE ratio of 18. RNA levels of CKB, measured by real-time PCR, were elevated a mean (and standard error) of 36-fold (8.4) in cancer cell lines compared with HOSE cells and 22.75-fold (10.45) in microdissected ovarian cancer epithelial cells compared with normal ovarian epithelial cells. In serum, the mean (+/-standard error) of CKB enzyme activity in cancer cases was 24.7 U/L units (+/- 5.1) compared to 9.6 U/L (+/- 1.6) for benign mass cases (P = 0.0088) and to 8.5 U/L (1.7) for normal controls (P = 0.0096).
Conclusions: Microarray technology offers a method to identify tumor biomarkers with potential clinical usefulness. Our data indicated that CKB gene expression is up-regulated in ovarian cancer cells in vitro and in vivo and that CKB enzyme activity is significantly elevated in sera from ovarian cancer patients, including those with stage I disease. These findings suggest a potential role for CKB as a marker for early diagnosis.