Peroxidase-linked anti-basic fibroblast growth factor monoclonal antibody Fab' conjugates: application for two-site enzyme immunoassay and immunohistochemical detection

Mitogenic activity toward human breast cancer cell line MCF-7 of two bFGFs purified from sera of breast cancer patients: co-operative role of cathepsin D

Mitogenic activity toward MCF-7 cells of two immunoreactive (high-molecular-weight form bFGF, HMW-bFGF; and 16-K bFGF, having the same molecular weight as recombinant bFGF) purified from pooled sera of breast cancer patients by heparin-affinity chromatography and gel filtration was investigated. The mitogenic activity of 16-K bFGF toward the cells was equal to that of recombinant bFGF, whereas the mitogenic effect of HMW-bFGF was weak. Most of the mitogenic activity of these two bFGFs was neutralized by anti-bFGF antibody. Also, the mitogenic activity of both HMW-bFGF and 16-K bFGF was markedly enhanced by aspartyl protease (cathepsin D), which is secreted in excess by breast cancer cells and is responsible for the enzymatic degradation of the extracellular matrix (ECM). By an enzyme immunoassay, we detected cathepsin D-mediated release of recombinant bFGF previously bound to the ECM of MCF-7 cells into the conditioned medium, and also observed cathepsin D-mediated proteolysis of HMW-bFGF to release free 16-K bFGF. These results suggest that 16-K bFGF is the bFGF molecule itself in the blood and that HMW-bFGF is a circulating form of bFGF in blood whose mitogenic activity is regulated by cathepsin D.

Improvement of an EIA system for basic fibroblast growth factor by use of biotinylated antibody prepared with NHS-LC-biotin

We improved our previously devised enzyme immunoassay (FIA) system for basic fibroblast growth factor (bFGF) using biotinylated antibody prepared with sulfosuccinimidyl-6-(biotinamido)hexanoate (NHS-LC-Biotin, Pierce), a water-soluble biotin analogue, with an extended spacer arm. The discriminatory detection limit of the improved EIA was found to be 5 pg/ml (0.5 pg/assay tube), sixfold more sensitive than that of the previous system. The reproducibility of within- and between-assay series was 5.10-8.61% and 5.99-8.69%, respectively; and recovery of exogenous bFGF from serum was approximately 102%. Employing the improved EIA system, we investigated by chromatofocusing chromatography the isoelectric points of two immunoreactive bFGFs (high-molecular-weight bFGF-like immunoreactive substance, designated as HMW-bFGF-LI and 16-kd bFGF-LI, having the same molecular weight as recombinant bFGF) detected in serum from a breast cancer patient. As a result, the pI value of HMW-bFGF-LI was estimated to be 7.13, and that of 16 kd bFGF-LI, 9.58.