Methoxy-derivatization of alkyl chains increases the in vivo efficacy of cationic Mn porphyrins. Synthesis, characterization, SOD-like activity, and SOD-deficient E. coli study of meta Mn(III) N-methoxyalkylpyridylporphyrins.


Cationic Mn(III) N-alkylpyridylporphyrins (MnPs) are potent SOD mimics and peroxynitrite scavengers and diminish oxidative stress in a variety of animal models of central nervous system (CNS) injuries, cancer, radiation, diabetes, etc. Recently, properties other than antioxidant potency, such as lipophilicity, size, shape, and bulkiness, which influence the bioavailability and the toxicity of MnPs, have been addressed as they affect their in vivo efficacy and therapeutic utility. Porphyrin bearing longer alkyl substituents at pyridyl ring, MnTnHex-2-PyP(5+), is more lipophilic, thus more efficacious in vivo, particularly in CNS injuries, than the shorter alkyl-chained analog, MnTE-2-PyP(5+). Its enhanced lipophilicity allows it to accumulate in mitochondria (relative to cytosol) and to cross the blood-brain barrier to a much higher extent than MnTE-2-PyP(5+). Mn(III) N-alkylpyridylporphyrins of longer alkyl chains, however, bear micellar character, and when used at higher levels, become toxic. Recently we showed that meta isomers are ∼10-fold more lipophilic than ortho species, which enhances their cellular accumulation, and thus reportedly compensates for their somewhat inferior SOD-like activity. Herein, we modified the alkyl chains of the lipophilic meta compound, MnTnHex-3-PyP(5+) via introduction of a methoxy group, to diminish its toxicity (and/or enhance its efficacy), while maintaining high SOD-like activity and lipophilicity. We compared the lipophilic Mn(III) meso-tetrakis(N-(6'-methoxyhexyl)pyridinium-3-yl)porphyrin, MnTMOHex-3-PyP(5+), to a hydrophilic Mn(III) meso-tetrakis(N-(2'-methoxyethyl)pyridinium-3-yl)porphyrin, MnTMOE-3-PyP(5+). The compounds were characterized by uv-vis spectroscopy, mass spectrometry, elemental analysis, electrochemistry, and ability to dismute O(2)˙(-). Also, the lipophilicity was characterized by thin-layer chromatographic retention factor, R(f). The SOD-like activities and metal-centered reduction potentials for the Mn(III)P/Mn(II)P redox couple were similar-to-identical to those of N-alkylpyridyl analogs: log k(cat) = 6.78, and E(1/2) = +68 mV vs. NHE (MnTMOHex-3-PyP(5+)), and log k(cat) = 6.72, and E(1/2) = +64 mV vs. NHE (MnTMOE-3-PyP(5+)). The compounds were tested in a superoxide-specific in vivo model: aerobic growth of SOD-deficient E. coli, JI132. Both MnTMOHex-3-PyP(5+) and MnTMOE-3-PyP(5+) were more efficacious than their alkyl analogs. MnTMOE-3-PyP(5+) is further significantly more efficacious than the most explored compound in vivo, MnTE-2-PyP(5+). Such a beneficial effect of MnTMOE-3-PyP(5+) on diminished toxicity, improved efficacy and transport across the cell wall may originate from the favorable interplay of the size, length of pyridyl substituents, rotational flexibility (the ortho isomer, MnTE-2-PyP(5+), is more rigid, while MnTMOE-3-PyP(5+) is a more flexible meta isomer), bulkiness and presence of oxygen.





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Publication Info

Tovmasyan, Artak G, Zrinka Rajic, Ivan Spasojevic, Julio S Reboucas, Xin Chen, Daniela Salvemini, Huaxin Sheng, David S Warner, et al. (2011). Methoxy-derivatization of alkyl chains increases the in vivo efficacy of cationic Mn porphyrins. Synthesis, characterization, SOD-like activity, and SOD-deficient E. coli study of meta Mn(III) N-methoxyalkylpyridylporphyrins. Dalton transactions (Cambridge, England : 2003), 40(16). pp. 4111–4121. 10.1039/c0dt01321h Retrieved from

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Ivan Spasojevic

Associate Professor in Medicine

Ines Batinic-Haberle

Professor Emeritus of Radiation Oncology

            A major interest of mine has been in the design and synthesis of Mn porphyrin(MnP)-based powerful catalytic antioxidants which helped establish structure-activity relationship (SAR). It relates the redox property of metalloporphyrins to their ability to remove superoxide. SAR has facilitated the design of redox-active therapeutics and served as a tool for mechanistic considerations. Importantly SAR parallels the magnitude of the therapeutic potential of SOD mimics and is valid for all classes of redox-active compounds. Two lead Mn porphyrins are already in five Phase II clinical trials (reviewed in Batinic-Haberle et al, Oxid Med Cell Longevity 2021). Recent research suggests immense potential of MnPs in cardiac diseases. MnTE-2-PyP (AEOL10113, BMX-010) prevents and treats cardiac arrhythmia, while MnTnBuOE-2-PyP (BMX-001) fully suppressed the development of aortic sclerosis in mice. The latter result is relevant to the cancer patients undergoing chemotherapy. In addition to breast cancer, in collaboration with Angeles Alvarez Secord, MD, MHSc, we have recently shown the anticancer effects of Mn porphyrin/ascorbate in cellular and mouse models of ovarian cancer.

            In parallel with synthetic efforts, I have also been interested in the mechanistic aspects of differential actions of Mn porphyrins in normal vs tumor tissue. In-depth studies of chemistry and biology of the reactions of MnPs with redox-active agents relevant to cancer therapy – ascorbate, chemotherapy and radiation – set ground for understanding the role of thermodynamics and kinetics in the mechanism of action of Mn porphyrins. Mechanistic studies have been revealed in Batinic-Haberle et al, Antioxidant Redox Signal 2018, Batinic-Haberle and Tome, Redox Biology 2019 and Batinic-Haberle et al Oxidative Medicine and Cellular Longevity 2021. My research has resulted in over 230 publications, 18 268 citations and an h-index of 64. For my achievements, I have been awarded the 2021 Discovery Award from the Society for Redox Biology and Medicine, SfRBM.

Additional Training

  • Postdoctoral fellowship with Professor Alvin Crumbliss in the field of Bioinorganic Chemistry, Department of Chemistry, Duke University
  • Postdoctoral fellowship with Professor Irwin Fridovich in the field of Redox Biology, Department of Biochemistry, Duke University School of Medicine

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