Antiproliferative, antiangiogenic and proapoptotic activity of h‐R3: A humanized anti‐EGFR antibody

The epidermal growth factor receptor (EGFR) proto‐oncogene is frequently overexpressed in tumors of epithelial origin. This event is thought to be causative for tumor development and progression and henceforth associated with poor prognosis. The recent considerable interest in developing EGFR‐targeting agents resulted in derivation of the monoclonal, humanized, neutralizing antibody h‐R3, which binds to the extracellular domain of EGFR with high affinity and strongly inhibits EGFR‐dependent cellular transformation. Thus, treatment of A431 squamous cell carcinoma cells with h‐R3 in either 2‐dimensional or 3‐dimensional culture resulted in appreciable antimitotic effects through induction of the G1 arrest. Although h‐R3 does not appear to have a direct proapoptotic activity in this setting, it inhibits production of the vascular endothelial growth factor (VEGF) by A431 cells both in vitro and in vivo. In the latter case, h‐R3 treatment (0.25–1 mg/mouse; every other day per 2 weeks) not only significantly reduced VEGF mRNA expression of A431 tumors growing subcutaneously in SCID mice but also resulted in reduction of the overall microvascular density (MVD), disappearance of dilated “mother vessels,” as well as in suppression of tumor growth followed by regression of established tumors. This apparent antiangiogenic activity of h‐R3 was associated with reduction in Ki67‐positive tumor cell fraction and (unlike in vitro) also with an elevated apoptotic index, the latter indicative of a cytotoxic mode of action in vivo. Taken together, h‐R3 is a promising new antagonist of the EGFR oncogene, the anticancer properties of which are associated with combined and potent antiproliferative, antiangiogenic and proapoptotic activity. © 2002 Wiley‐Liss, Inc.