Any eukaryotic metabolite produced during a metabolic reaction in animals that include diverse creatures from sponges, insects to mammals.
A xenobiotic (Greek, xenos "foreign"; bios "life") is a compound that is foreign to a living organism. Principal xenobiotics include: drugs, carcinogens and various compounds that have been introduced into the environment by artificial means.
A chemical compound that can be excited by light of a specific wavelength and subsequently transfer energy to a chosen reactant. This is commonly molecular oxygen within a cancer tissue, which is converted to (highly rective) singlet state oxygen. This rapidly reacts with any nearby biomolecules, ultimately killing the cancer cells.