The most efficacious Mn(III) porphyrinic (MnPs) scavengers of reactive species have positive charges close to the Mn site, whereby they afford thermodynamic and electrostatic facilitation for the reaction with negatively charged species such as O (2) (•-) and ONOO(-). Those are Mn(III) meso tetrakis(N-alkylpyridinium-2-yl)porphyrins, more specifically MnTE-2-PyP(5+) (
AEOL10113) and MnTnHex-2-PyP(5+) (where alkyls are ethyl and n-hexyl, respectively), and their imidazolium analog, MnTDE-2-
ImP(5+) (
AEOL10150, Mn(III) meso tetrakis(N,N'-diethylimidazolium-2-yl)
porphyrin). The efficacy of MnPs in vivo is determined not only by the compound
antioxidant potency, but also by its bioavailability. The former is greatly affected by the lipophilicity, size, structure, and overall shape of the compound. These
porphyrins have the ability to both eliminate
reactive oxygen species and impact the progression of oxidative stress-dependent signaling events. This will effectively lead to the regulation of redox-dependent
transcription factors and the suppression of secondary inflammatory- and oxidative stress-mediated immune responses. We have reported on the inhibition of major
transcription factors HIF-1α,
AP-1, SP-1, and NF-κB by Mn
porphyrins. While the prevailing mechanistic view of the suppression of
transcription factors activation is via antioxidative action (presumably in cytosol), the pro-oxidative action of MnPs in suppressing NF-κB activation in nucleus has been substantiated. The magnitude of the effect is dependent upon the electrostatic (
porphyrin charges) and thermodynamic factors (
porphyrin redox ability). The pro-oxidative action of MnPs has been suggested to contribute at least in part to the in vitro anticancer action of MnTE-2-PyP(5+) in the presence of ascorbate, and in vivo when combined with
chemotherapy of
lymphoma. Given the remarkable therapeutic potential of
metalloporphyrins, future studies are warranted to further our understanding of in vivo action/s of Mn
porphyrins, particularly with respect to their subcellular distribution.