A Neutralizing Anti–Fibroblast Growth Factor 8 Monoclonal Antibody Shows Potent Antitumor Activity against Androgen-Dependent Mouse Mammary Tumors In vivo

Purpose: Fibroblast growth factor 8b (FGF8b) has been implicated in oncogenesis of sex hormone–related malignancies. A murine monoclonal anti-FGF8 antibody, KM1334, has been raised against a FGF8b-derived peptide and shown to neutralize FGF8b activity in an androgen-dependent mouse mammary cell line (SC-3) in vitro growth. The purpose of this study was to evaluate KM1334 as a therapeutic agent for FGF8-dependent cancer. Experimental Design: Specificity and neutralizing activity of KM1334 were examined in vitro . In vivo therapeutic studies were done in nude mice bearing SC-3 tumors s.c. Results: KM1334 recognized FGF8b and FGF8f specifically out of four human FGF8 isoforms and showed little binding to other members of FGF family. Neutralizing activity of KM1334 was confirmed by both blocking of FGF8b binding to its three receptors (FGFR2IIIc, FGFR3IIIc, and FGFR4) and FGF8b-induced phosphorylation of FGFR substrate 2α and extracellular signal-regulated kinase 1/2 in SC-3 cells. The in vitro inhibitory effect could be extended to in vivo tumor models, where KM1334 caused rapid regression of established SC-3 tumors in nude mice. This rapid regression of tumors after KM1334 treatment was explained by two independent mechanisms: ( a ) decreased DNA synthesis, as evidenced by a decrease in uptake of 5-bromo-2′-deoxyuridine, and ( b ) induction of apoptosis as shown by the terminal deoxynucleotidyl transferase–mediated nick end labeling assay. Conclusions: KM1334 possesses strong blocking activity in vitro and antitumor activity in vivo and therefore may be an effective therapeutic candidate for the treatment of cancers that are dependent on FGF8b signaling for growth and survival.