ABSTRACT
Since the introduction of technetium-99m (99mTc) and its rapid acceptance as a tool in nuclear medicine, very little information is available about is biological action as 99mTc-radiopharmaceuticals. We have determined if cyclophosphamide, an alkylating agent, used in oncology as a chemotherapeutic drug, modifies the binding of 99mTCO-4 and 99mTc-MDP (99mTc-metylenediphosphonic acid) to blood cells and to plasma proteins. The radiopharmaceuticals were injected intravenously (iv) into SW-55 mice (male and female, weight 25 g) and samples of plasma and blood cells were separated. Cyclophosphamide (50 µg) was injected iv 1 h before the radipharmaceuticals. Samples of plasma and blood cells were also precipitated with 5 per cent trichloroacetic acid and soluble and insoluble fractions were isolated. The following results were obtained: 1) cyclophosphamide did not alter (0.25 to 8h) percent radioactivity of 99m TcO04 in plasma or blood cells but increased the binding of 99m Tc-MDP to blood cells; 2) cyclophosphamide did not alter (o.25 to 8h) 6the binding of 99m TcO-4 in insoluble fraction of plasma and decreasde (1 to 4h) percent radioactivity of 99mTc-MDP in the insoluble fraction of plasma; 3) cyclophosphamide increased (0.25 to 4h) percent radioactivity of 99mTcO-4 in the insoluble fraction of blood cells but did not alter the binding of 99m Tc-MDP. Cyclophosphamide and/ or its methabolities modified the effective half-life of these radiopharmaceuticals (to 99TcO-4 was increased 2.3 to 3.4h and to 99mTc-MDP was decreased 3.3 to 2.1 h) and possibly increased the permeability of blood cells to 99m TcO-4