TABLE 2

Effect of Gefitinib on Radiation-Absorbed Dose to Cell Nucleus from ¹¹¹In-DTPA-hEGF Localized at Cell Membrane, Cytoplasm, or Nucleus of MDA-MB-468 EGFR-Overexpressing Human Breast Cancer Cells^*

Treatment	Cell compartment	Ā (Bq × s)^†	S ([Gy/Bq × s] × 10⁻⁴)	Radiation dose to nucleus $\text{[math]}$ , (Gy)^‡
¹¹¹In-DTPA-hEGF	Membrane	4,240	1.78	0.75
	Cytoplasm	11,307	3.18	3.4
	Nucleus	2,651	60.3	16.0
			Total	20.15
¹¹¹In-DTPA-hEGF + gefitinib	Membrane	3,432	1.78	0.61
	Cytoplasm	9,894	3.18	3.15
	Nucleus	4,735	60.3	28.55
			Total	32.31

↵* Radiation-absorbed dose ( $\text{[math]}$ ) to cell nucleus was estimated using cellular radiation dosimetry model of Goddu et al. (22): $\text{[math]}$ = Ā × S, where S is radiation-absorbed dose in nucleus (Gy) per unit of cumulated radioactivity in source compartment, Ā (Bq × s).
↵† Ā = A₀/λ, where A₀ is amount of radioactivity localized in the compartment at time 0, and λ is radioactive decay constant for ¹¹¹In (2.83 × 10⁻⁶/s). Rapid localization of ¹¹¹In-DTPA-hEGF in the compartment and rate of elimination corresponding to radioactive decay of radionuclide ¹¹¹In are assumed.
↵‡ Based on each MDA-MB-468 cell having a diameter of 10 μm and a nuclear diameter of 6 μm. Assumes targeting of a single cell with ¹¹¹In-DTPA-hEGF to receptor saturation. At receptor saturation, ∼48 mBq ¹¹¹In-DTPA-hEGF would be bound to each MDA-MB-468 cell at a specific activity of 3.7 MBq/μg.