The serological results from apparently healthy individuals and prostate cancer patients were evaluated with a new assay called TPAcyk ELISA. This assay has a biochemical specificity for fragments of cytokeratins 8 and 18, and exhibits a low within- and between-assay imprecision. The data indicate a significant difference between the results of males and females, but no significant age-dependent relation was found. The cut-off value (95% specificity) for healthy individuals was estimated to be 1.27 ng/mL (n = 190) for males and 0.95 ng/mL (n = 81) for females. When using a cut-off value of 1.27 ng/mL, we found a sensitivity for prostate cancer patients with T2-3 N0M0 of about 20%. For patients with metastatic disease, a sensitivity of 75% was found. A higher sensitivity was obtained with patient sera analyzed with PSA than with TPAcyk, particularly in patients with early stages of the disease. We conclude that the results from this new TPAcyk assay were significantly elevated in patients initially diagnosed with poorly differentiated tumors, that patients with localized tumors exhibited low concentrations, and that patients with metastatic disease showed, on average, 8 times higher concentrations than patients with localized disease. The combination of the TPAcyk and PSA results increased the sensitivity for prostate cancer, particularly in patients with metastatic disease.
Cytokeratins 8 and 18 are most frequently co-expressed in simple epithelia and carcinomas. Fragments of these cytokeratins are released into the systemic circulation where they can be quantified and utilized as tumour markers. The present paper reports on a solid-phase sandwich monoclonal immunoassay, considered "epithelial tissue-specific", which recognizes fragments of human cytokeratins 8 and 18 of different sizes (10-50 kD). The evaluated ELISA and IRMA assays exhibited a detection limit of 0.1 microgram 1-1 and characteristically demonstrated a within-assay coefficient of variation (CV) of 1-4% and a between-assay CV of 3-5%. The long-term (300 days) repeatability of lyophilized samples tested in the assay was estimated to have a less than 10% CV. Of apparently healthy individuals, 95% were found to have serum concentrations of less than 0.95 micrograms 1-1. A highly significant difference was found between apparently healthy individuals and pancreatic cancer patients. Patients with metastatic disease showed a sensitivity of 93% and those with local disease 83%, at 95% specificity. This TPAcyk assay revealed good correlation (0.98) with the TPS assay detecting the specific M3 epitope of the tissue polypeptide antigen. The correlation with the long established polyclonal assay of tissue polypeptide antigen (TPA) was estimated to be 0.9.
The possibility of using cytokeratin antibodies for the radioimmunolocalization of urinary bladder cancer was studied. A monoclonal murine IgG antibody was raised against cytokeratin 8 and labelled with iodine-125; normal murine IgG was used for control purposes. The urothelial cancer cell line RT4 was transplanted into immunodeficient nude mice. The anti-cytokeratin 8 antibody was administered intraperitoneally and its uptake in the tumour and other organs was analyzed with a computerized gamma camera. Optimal scintigraphic visualization occurred 11 days after antibody administration. The tumour/blood ratio of the specific antibody was 5.64 (+/- 5.01 SD) on day 11, compared with 0.73 (+/- 0.35 SD) in the control. Autoradiography demonstrated antibody uptake preferentially in viable sections of the tumour. The antibody uptake is presumed to be the result mainly of binding to the released cytokeratin in and around cells lysed during natural cellular death. The monoclonal murine anti-cytokeratin antibody is of potential interest in studies aimed at improving the clinical staging of urinary bladder cancer.
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