Sn (IV) Protoporphyrin IX is an inhibitor heme oxygenase (the enzyme that catalyzes the conversion of heme to biliverdin in the heme degradation pathway) but has also been found to stimulate production of the heme oxygenase protein¹.  Contrast the activity of Co (III) Protoporphyrin which has been found to have similar activities to Sn (IV) Protoporphyrin but with a greater enhancement of heme oxygenase synthesis activity such that heme oxygenase activity is actually increase when administered in vivo while in vitro administration inhibits heme oxygenase activity¹.  Heme oxygenase has been implicated in tumor cell resistance to chemotherapy², reduction of free radical formation³ and inflammation⁴ and associated with vascular repair⁴.