Intracellular localization of the radiation enhancer motexafin gadolinium using interferometric Fourier fluorescence microscopy

Motexafin gadolinium (MGd) is a unique therapeutic agent that localizes in cancer cells and increases tumor response to ionizing radiation and certain chemotherapeutics. The in vitro intracellular localization, accumulation, and retention of MGd in murine EMT6 mammary sarcoma and Rif-1 fibrosarcoma cell lines were studied using interferometric Fourier fluorescence microsco py. MGd cellular uptake was semiquantified using its characteristic fluores cence emission band centered at 758 nm. Colocalization studies were perform ed using mitochondrial, endoplasmic reticulum, Golgi apparatus, nuclear, an d lysosomal fluorescent organelle probes, and verified using interferometri c Fourier spectroscopy. Cellular uptake was gradual and increased significa ntly with incubation time. MGd localized primarily within the lysosomes and endoplasmic reticulum, and to a lesser extent within the Golgi apparatus a nd mitochondria. Mitochondrial staining was increased in media without seru m. No nuclear uptake was detected in the Rif-1 cells, but after 48 h nuclea r uptake was observed in 15% of EMT6 cells. These results indicated that MG d accumulates within cytoplasmic compartments. The sustained intracellular localization of MGd may, in part, account for its unique radiation and chem otherapy enhancement properties. Interferometric Fourier fluorescence micro scopy is a potentially powerful tool in delineating and verifying localizat ion sites of therapeutic agents.