Table 1. Affinity measurements of chimeric and humanized anti-EGFR antibodies, as determined by surface plasmon resonance (Biacore), luminescent oxygen-channeling immunoassay (AlphaLISA) and flow cytometry.

	BIAcore				AlphaLISA		A431 FACS binding
	ka	kd	KD	WT/x	EC50	WT/x	EC50	WT/x
	(M−1s−1)	(s−1)	(M)		(nM)		(ug/ml)
cetuximab	6.5E+05	1.1E-03	1.7E-09	1.0	0.09	1.00	2.01	1.00
ch225	6.0E+05	1.1E-03	1.8E-09	0.9	0.08	1.13	ND	ND
hu225	5.4E+05	4.6E-03	8.5E-09	0.2	0.33	0.27	1.79	1.12

Ratio of activity for chimeric (ch225) or humanized (hu225) variants compared with cetuximab is given as WT/x. ND, not determined.