SUBCELLULAR-LOCALIZATION OF P-BORONOPHENYLALANINE-DELIVERED B-10 IN THE RAT 9L GLIOSARCOMA - CRYOGENIC PREPARATION IN-VITRO AND IN-VIVO

A well-characterized in vitro cryogenic preparation for ion microscopi c isotope imaging, which minimizes redistribution of diffusible specie s, was used to determine the distribution of boron in GS-9L gliosarcom a cells incubated with the boron neutron capture therapy agent, p-boro nophenylalanine (BPA). At the subcellular level, boron from BPA distri butes relatively homogeneously within the glioma cell. Boron from BPA was eliminated rapidly, indicating that most is unbound. Thus a large pool of boron is susceptible to diffusion artifact. Removal of this ar tifact increases the degree of confidence in microdosimetric results i nferred from the homogeneous subcellular distribution. The ion microsc opic imaging of boron in subcutaneous tumors cryofixed in situ was ach ieved in rats treated with BPA. Boron signals from BPA were adequate t o image microdistributions at the 1-mu m resolution level. As in the i n vitro case, boron did not localize discretely at the subcellular lev el. However, boron heterogeneity was seen at the tissue level. Physiol ogically valid cellular potassium and sodium levels were seen, which d emonstrates minimized redistribution artifact. Future tissue studies d esigned to correlate ion microscopic boron images to microscopic struc ture are feasible using cryogenic sample preparation and ion microscop y,