The active form of vitamin B3 and a component of the coenzyme nicotinamide adenine dinucleotide (NAD). Niacinamide acts as a chemo- and radio-sensitizing agent by enhancing tumor blood flow, thereby reducing tumor hypoxia. This agent also inhibits poly(ADP-ribose) polymerases, enzymes involved in the rejoining of DNA strand breaks induced by radiation or chemotherapy. or A form of niacin (vitamin B3) that the body needs in small amounts to function and stay healthy. Nicotinamide is found in many plant and animal products and in dietary supplements. It is water-soluble (can dissolve in water) and must be taken in every day. Nicotinamide may be used to treat diabetes and certain skin conditions and is being studied in the treatment of some types of cancer. It may increase blood flow to cancer cells and block certain enzymes they need to repair damage to their DNA. This may make cancer cells easier to kill with radiation therapy and chemotherapy. Nicotinamide is a type of radiosensitizing agent and a type of chemosensitizing agent. Also called niacinamide.