Methods of preventing and/or treating cancer are disclosed. The methods comprise administering to the patient a pharmaceutically effective amount of a water-soluble, acid-stable organometallic nanoparticles, optionally in combination with another therapeutic agent. In particular, nanoparticles that consist of polymerized citric acid and various different types of metals including, but not limited to, iron, calcium, zinc, silver and magnesium. These nanoparticles are acid-stability and self-degradation leading to constituent metal release when pH rises closer to the neutral pH of 7 or higher.