*3.7. Cell Viability Assay*

The cytotoxic effect on HEP-G2, PC-3, and fibroblast cells after treatment with (a) <sup>225</sup>Ac-rHDL and (b) <sup>225</sup>Ac-DOTA-benzene-p-SCN was evaluated by performing an assay of mitochondrial dehydrogenase activity using the XTT kit (Roche Holding AG, Rotkreuz, Switzerland). Briefly, HEP-G2, PC-3, and fibroblast cells (1 <sup>×</sup> <sup>10</sup><sup>4</sup> cells/well) were seeded in 96-well microtiter plates. The medium was removed after overnight incubation and the cells were incubated for 1 h with each treatment (4 kBq/200 µL). After removing the treatments, the cells were kept at 37 ◦C, 5% carbon dioxide, and 85% relative humidity. Cell viability was assessed at 3, 24, 48, and 192 h by spectrophotometric measurements (microplate absorbance reader, EpochTM, BioTek) at 450 nm. Fibroblast cells that did not receive treatment were considered as the control group with 100% cell viability at the different time points.
