Disclosed is a method of treating cancer in a patient comprising administering to the patient an effective amount of a diazeniumdiolated (N2O2-containing) compound or a pharmaceutically acceptable salt thereof, wherein the cancer cell has an elevated level of reactive oxygen species (ROS) and/or a decreased level of one or more of PRX1, PRX6, and OGG1, compared to a normal cell of the same tissue or tissue type. An example of a diazeniumdiolated compound is Formula (I), wherein X and Q are defined herein. Also disclosed are diazeniumdiolated compounds, pharmaceutical compositions, and methods of use including enhancing the chemotherapeutic treatment of chemotherapeutic agents and high energy radiation.