Photochemical Sensitization by Azathioprine and Its Metabolites—i. 6‐mercaptopurine

Azathioprine is used as an immunosuppressant for renal transplant recipients, but is frequently associated with severe skin cancer as a side effect. 6‐Mercaptopurine, the primary metabolite of azathioprine. absorbs strongly in the UVA region and displays substantial photochemical reactivity. The primary photochemical processes in aqueous solution are triplet state formation and photoionization, as shown by flash photolysis. In oxygenated solution, singlet oxygen and superoxide are produced, and ground state 6MP appears to react with these species. Glutathione inhibits this reaction and is itself oxidized. In deoxygenated solution, reactions implicating the thiyl radical and hydrogen atom and electron transfer occur as shown by reaction with histidine and p‐nitrosodimethylaniline. Nitro Blue Tetrazolium or acrylamide.