We chose to study the role of p53 status in determining the cytotoxicity of AH54 and AH63 in colorectal cancer cells on account of the importance of p53 to colorectal cancer33, the central role of p53 in dictating radiosensitivity34 and previous observations that the effects of certain arene-Ru(II) diamines on cancer cells can be influenced by p53 status35, 36. The gene discussed is TP53; the disease is colorectal cancer.