Nimotuzumab is an EGFR-targeting antibody that has demonstrated encouraging clinical results in the absence of severe side-effects observed with other approved anti-EGFR
antibodies. We investigated whether different clinical behavior of
nimotuzumab is related to its bivalent/monovalent binding profile. Binding properties of
nimotuzumab and
cetuximab, the most development of anti-EGFR
antibodies, were studied in vitro using chip surfaces and cells with varying EGFR expression levels. Experimental observations demonstrated that in contrast to
cetuximab, the intrinsic properties of
nimotuzumab required bivalent binding for stable attachment to the cellular surface, leading to
nimotuzumab selectively binding to cells that express moderate to high EGFR expression levels. At these conditions, both
antibodies bound bivalently, and accumulated to similar degrees. When EGFR density is low,
nimotuzumab monovalent interaction was transient, whereas
cetuximab continued to interact strongly with the receptors. We compared the in vitro anti-
tumor efficacy of
nimotuzumab and
cetuximab.
Cetuximab decreased the cell viability and induced apoptosis for all the tested cell lines, effects which did not depend on EGFR expression level. In contrast,
nimotuzumab also provoked significant anti-cellular effects, but its anti-
tumor capacity decreased together with EGFR expression level.
Cetuximab Fab fragment was able to impact
tumor cell survival, whereas
nimotuzumab fragment totally lost this effect.
Tumor-xenograft experiments using cells with a high EGFR expression revealed similar
tumor growth inhibiting effects for both
antibodies. This study suggests an explanation for
nimotuzumab clinical profile, whereby anti-
tumor activity is obtained in absence of severe toxicities due to its properties of bivalent binding to EGFR.