Dynamic secondary ion mass spectrometry analysis of boron from boron neutron capture therapy drugs in co-cultures: single-cell imaging of two different cell types within the same ion microscopy field of imaging

A co-culture, cryogenic SIMS methodology is presented for the quantitative analysis of cell type-dependent accumulation of boron delivered by BPA-F and BSH, two clinically approved drugs used in boron neutron capture therapy of cancer. T98G human glioblastoma cells were co-cultured with morphologically different normal LLC-PK1 epithelial cells or GM3348 human skin fibroblasts. Our freeze-fracture method of cryogenic sample preparation successfully fractured the different cell types grown together in co-cultures. Quantitative observations revealed an active uptake of boron from BPA-F in both T98G and LLC-PK1 cells but did not show cell type-dependent differences. Accumulation of BSH in all three cell types examined also did not reveal any cell type-dependent differences in co-cultures. As this method relies on the analysis, within the same field of SIMS imaging, of two different cell types that have been maintained under identical conditions of growth, drug exposure, sample preparation, and instrumental analysis, it provides the most effective approach for comparing cell type-specific differences in boron concentrations. The most effective applications of this method will be realized in testing the selectivity of experimental boronated compounds designed to specifically target tumor cells.