Table 1.

Normalized trastuzumab distribution with or without GA

			Endosomes and lysosomes
	Intracellular (% of total)	Tubulovesicular, <60 nm (% of intracellular)	Internal mb (% of intracellular)	Limiting mb (% of intracellular)
0 min	1.4 ± 0.3	ND	ND	ND
5 min	6.2 ± 1.0	ND	ND	ND
3 h	17.0 ± 2.5	69.2 ± 3.5	15.7 ± 2.7	11.8 ± 2.2
3 h +GA	39.3 ± 5.2a	20.1 ± 3.8a	73.1 ± 3.6a	6.3 ± 1.9

BT474 cells with surface-bound trastuzumab were incubated ± GA for the indicated time at 37°C and then fixed and processed for quantitative detection of trastuzumab by immunogold electron microscopy as described in Materials and Methods. Normalization to the number of total (left column) or intracellular gold particles (right columns) was performed individually for each cell profile prior to mean and SE calculations. Not included is a small population of endocytic 60-150-nm vesicles comprising <4% of the intracellular label. Non-normalized data are presented in Supplementary Table 1. Qualitatively similar results were observed for SKBr3 cells (unpublished data). mb, membrane; GA, geldanamycin; ND, not determined.

^ap < 0.001 in comparison with corresponding 3-h result.