Validating [alpha]-particle emission from .sup.211At-labeled antibodies in single cells for cancer radioimmunotherapy using CR-39 plastic nuclear track detectors

Recently, .sup.211 At has received increasing attention as a potential radionuclide for cancer radioimmunotherapy. It is a [alpha]-particle emitter, which is extremely effective against malignant cells. We demonstrate a method to verify the efficiency of .sup.211 At-labeled trastuzumab antibodies (.sup.211 At-trastuzumab) against HER2 antigens, which has not been determined for radioimmunotherapy. A CR-39 plastic nuclear detector is used for measuring the position and the linear energy transfer (LET) of individual .sup.211 At [alpha]- particle tracks. The tracks and .sup.211 At-trastuzumab-binding cells were co-visualized by using the geometric information recorded on the CR-39. HER2-positive human gastric cancer cells (NCI-N87), labelled with .sup.211 At-trastuzumab, were dropped on the centre of the CR-39 plate. Microscope images of the cells and the corresponding [alpha]-tracks acquired by position matching were obtained. In addition, 3.5 cm x 3.5 cm macroscopic images of the whole plate were acquired. The distribution of number of [alpha]-particles emitted from single cells suggests that 80% of the .sup.211 At-trastuzumab-binding cells emitted [alpha]-particles. It also indicates that the [alpha]-particles may strike the cells several times along their path. The track-averaged LET of the [alpha]-particles is evaluated to be 131 keV/[mu]m. These results will enable quantitative evaluation of delivered doses to target cells, and will be useful for the in vitro assessment of .sup.211 At-based radioimmunotherapeutic agents.