Tin(Sn+4)-diiododeuteroporphyrin; an in vitro and in vivo inhibitor of heme oxygenase with substantially reduced photoactive properties.

Iodination of Sn-deuteroporphyrin (Ki = 0.185 microM) at positions C2 and C4 of the porphyrin ring results in an enhanced ability of the resulting derivative, Sn-diiododeuteroporphyrin, to inhibit (Ki = 0.069 microM) heme oxygenase activity in vitro. The potency of Sn-diiododeuteroporphyrin inhibition of bilirubin production in vivo is similar to that of Sn-protoporphyrin, but in vitro tests demonstrate that, when in solution with human serum albumin, Sn-diiododeuteroporphyrin is significantly (3-10 times, depending upon conditions) less photosensitizing than are Sn-protoporphyrin or Sn-mesoporphyrin. These findings demonstrate that halogenation of a suitable porphyrin macrocycle can substantially diminish photoactive properties of the compound whereas retaining its ability to act as a heme oxygenase inhibitor.