The radiation bio-effects of gallum-72 on leukemic cells via a gallium-transferrin complex

Abstract

Improved methods for treatment of leukemia would be advantageous for patients and the medical community. This thesis reports results of a study of the cytotoxicity of radiolabeled transferrin in cultured leukemic cells. K-562 cells, from an erythroleukemic cell line, were grown and growth curves were plotted for characterization. K-562 cells grew logarithmically from approximately 250,000 cells mL⁻¹ to 700,000 cells mL⁻¹ and display a doubling time of approximately 20-21 hours. K-562 cells were exposed to x rays at an absorbed dose of 0, 1, 2, and 4 gray. Growth curves were plotted to create a dose response curve. Percent-cell survival in this experiment, and all subsequent experiments, was determined based on the extrapolation of the growth curves to time zero, as compared to a control. An absorbed dose of 1, 2, and 4 gray corresponded to a survival of 77([]14)%, 45([]7.4)% and 20([]2.4)%, respectively. This cell line is relatively resistant to radiation. K-562 cells were exposed to a radioactive gallium-72/stable gallium nitrate mixture to determine the effect gallium-72 decay has on cell survival . Simultaneously, K-562 cells were exposed to a concentration of stable gallium nitrate equivalent to the total gallium concentration, radioactive and stable, of the gallium-72/stable gallium mixture. This allowed a comparison of radioactive and chemotoxic effects due to gallium-72 and stable gallium, respectively. Exposures to gallium-72, at an activity of 184.0 kBq mL⁻¹, and stable gallium nitrate, at a concentration of 116.7 []M, resulted in a cell survival of 61([]10.5)% and 75([]12. 1)%, respectively. The difference is small when error is taken into consideration. Therefore radioactivity had little effect on cell survival at a specific activity of 6.3 MBq mg⁻¹. To properly assess the cytotoxicity of gallium-72 the specific activity must be increased. To determine the effect of ape-transferrin on the cytotoxicity of gallium nitrate, K-562 cells were exposed to stable gallium nitrate and increasing amounts of apo-transferrin. Cells exposed to 115.0 []M gallium nitrate exhibited an 82([]8.8)% cell survival compared to 54([]6.9)% following exposure to 115.0 []M gallium nitrate and 3.75 []M apo-transferrin. Apo-transferrin presumably increases cellular uptake of gallium nitrate thereby increasing its cyctotoxic effects.