Zinc Protoporphyrin

Zinc Protoporphyrin (Zn(II)-protoporphyrin IX) is an orally active and competitive heme oxygenase-1 (HO-1) inhibitor. Zinc Protoporphyrin regulates expression of HO-1 at the transcriptional level. The effect of Zinc Protoporphyrin on HO-1 expression is controversial.  It was shown to induce HO-1 expression in some cells, but suppress it in others. Zinc Protoporphyrin is used as a screening marker of iron deficiency in vivo. Zinc Protoporphyrin has anti-cancer activity^{[1][2][3][4][5]}. In Vitro:to increase in Protoporphyrin (Zn(II)-protoporphyrin IX; 5 μM; 72 hours) causes the fraction of late apoptotic and necrotic cells increasing from 10.9% in controls to 30.4% after 72 h^[3].
Zinc Protoporphyrin (1.25-40 μM; 48 or 72 hours) exerts cytostatic/cytotoxic effects against tumor cells^[3].
Zinc Protoporphyrin (2.5, 5 μM; 48 or 72 hours) results in dose- and time-dependent reduction of cells in the G1 phase of the cell cycle^[3].
Zinc Protoporphyrin (1.25-40 μM; 48 hours) leads to the accumulation of cleaved (active) caspase-3^[3].
The effect of Zinc Protoporphyrin on HO-1 expression is controversial.  It was shown to induce HO-1 expression in some cells, but suppress it in others^[4][5].
For example, Zinc Protoporphyrin is shown to induce HO-1 expression in hamster fibroblast (HA-1) cells but not in Neuro-2A mouse neuroblastoma cells and primary cultures of rat cortical neurons.
Zinc Protoporphyrin suppresses the induction of HO-1 by statins or lipopolysaccharide.
Zinc Protoporphyrin induces HO-1 expression in human prostate adenocarcinoma PC-3 and breast adenocarcinoma MCF-7 cells.
In Vivo:Zinc Protoporphyrin (12.5, 25, 50 mg/kg for i.p.; 12.5, 50 mg/kg for p.o.; from day 7 to 19) exerts dose-dependent antitumor effects manifested by the retardation of tumor growth^[3].