Synthesis and stability studies of Ga-67 labeled phosphonium salts.

Delocalized lipophilic cations such as tri- and tetra-arylphosphonium are able to diffuse across the mitochondrial membrane, which allows them to selectively accumulate in cells with a high transmembrane potential (ΔΨm ). The mitochondrial membrane potential of cancer cells and cardiomyocytes has been reported to be significantly higher than that of normal epithelial cells. This feature can be exploited for the selective accumulation of phosphonium derivatives for the purposes of molecular imaging using radionuclides. Four structurally related Ga(III)-phosphonium salts were synthesized and fully characterized and found to be modest in toxicity toward T98G human glioblastoma cells (IC50  > 4 mM). High-activity (100 MBq) analogs containing Ga-67 were also synthesized and their stabilities in phosphate-buffered saline and human serum were determined.

Tumor cell uptake and selectivity of gadolinium(III)-phosphonium complexes: The role of delocalisation at the phosphonium centre.

The synthesis of a series of bifunctional Gd(III) complexes 1-3 covalently bound to arylphosphonium cations possessing a varying degree of delocalisation at the phosphonium centre is presented. The influence of the degree of delocalisation was investigated with regards to in vitro cytotoxicity, cellular uptake of Gd, tumor-cell selectivity and intracellular localisation of Gd within human glioblastoma (T98G) and human glial (SVG p12) cells. Cellular uptake and selectivity studies for the Gd(III) complexes indicate that a reduced delocalisation at the phosphonium centre can lead to an enhanced Gd uptake into SVG p12 cells which results in a decrease in the overall tumor cell selectivity. Synchrotron X-ray fluorescence (microbeam XRF) imaging has demonstrated for the first time that uniform uptake of Gd(III) complex 2 within a population of T98G cells increased as a function of increasing Gd incubation times. The Gd maps show dispersed spots of high intensity which are consistent with mitochondrial uptake.