QUANTIFICATION OF CREATINE-KINASE BB ISOENZYME IN TUMOR CYTOSOLS AND SERUM WITH AN ULTRASENSITIVE TIME-RESOLVED IMMUNOFLUOROMETRIC TECHNIQUE

Objectives: To develop a highly sensitive immunofluorometric procedure for creatine kinase BB isoenzyme and use it to measure CK-BB in tumor cytosolic extracts and serum of cancer patients and healthy volunteer s. Design and Methods: For assay development, we used two monoclonal a ntibodies in combination with time-resolved fluorometry and the biotin -avidin system. We measured CK-BB in breast tumor cytosols and studied its association with steroid hormone receptors. We also measured CK-B B in the serum of healthy subjects and patients with prostate cancer. We have examined the molecular weight of CK-BB in serum using high per formance liquid chromatography. Results: The evaluation of the method revealed good precision and accuracy. Study of 336 breast tumor cytoso ls and 9 normal breast cytosols has shown that CK-BB is overexpressed by 95% of breast tumors and that CK-BB is present in its 80 kDa form. A close association between CK-BB and estrogen but not progesterone re ceptors was found, suggesting that CK-BB overexpression is another mar ker of estrogen sensitivity of these tumors. Previous studies, using C K-BB radioimmunoassay could not detect CK-BB in the serum of about 50% of healthy subjects. We have assessed CK-BB levels in 80 male volunte ers, detected CK-BB in all sera and provided a detailed distribution o f values. We further demonstrated that 30% of prostate cancer patients in remission (PSA < 0.4 mu g/L) post radical prostatectomy and 50% of patients with active prostate cancer (PSA > 20 mu g/L) have elevated serum CK-BB levels. The patients with highly elevated CK-BB also had h ighly elevated serum PSA. We have demonstrated that some patients who have elevated serum CK-BB also have macromolecular CK complexes in the ir serum with molecular weights of 700 and 350 kDa as well as the 80 k Da CK-BB isoenzyme. Only the latter was recognized by the assay develo ped. Conclusions: CK-BB is a marker of estrogen sensitivity in breast cancer; Patients with prostate cancer have elevated CK-BB in their ser um; The new highly specific and sensitive assay may be further used to study the role of CK-BB in various malignancies.