Table 2. Total and in vivo biotin accessible HER2 receptor in BT474 tumors, with (+) and without (−) iRGD pre-injection.

HER2	pmol/g tumor	# receptors/cell (×104)	% accessible receptors
Total	1850 ± 150	111.4 ± 9.1	-
Biotin-labeled(−iRGD)	105 ± 13	6.3 ± 0.8	5.7
Biotin-labeled (+iRGD)	613 ± 85	36.8 ± 4.8	33.1

The accessible and total receptors were measured by ELISA as described under “Materials and Methods”. Data are presented as the mean ± SD (n = 3).