239-Plutonium, as extrapolated, is among the most toxic poisons of sulfur biochemistry, like thiols, known.
Vitalethine, a disulfide (VSSV), cycles in the body through its thiol, vitaletheine (VSH), and its sulfenic acid (VSOH) forms, which together appear to stimulate the humoral immune system to stop cancer at a concentration just incrementally larger than the vanishly low concentrations of Plutonium reported to cause cancer:
http://www.vitaletherapeutics.org/vtlmntox.htm
http://www.vitalethine.org/WAPFMetlTox.html