Cellular accumulation and retention of the technetium-99m-labelled hypoxia markers BRU59-21 and butylene amine oxime

BRU59-21 and ^99mTc-butylene amine oxime (BnAO, HL91) are being evaluated for imaging hypoxia in tumors. Both tracers: 1) rapidly reached a plateau in aerobic Chinese hamster ovary cells in vitro but continuously accumulated in hypoxic cells; 2) ceased to accumulate when hypoxic cells were exposed to air; 3) showed 40% retention upon washing the cells; 4) showed selective hypoxic accumulation only at 37°C; 5) accumulation could be modulated by addition of electron-affinic compounds; and 6) exhibited higher accumulation in cells which overexpress cytochrome P450 reductase. Both BRU59-21 and ^99mTc-BnAO share properties making them suitable for hypoxia imaging.