Anticancer therapeutic potential of Mn porphyrin/ascorbate system

Area of Science:

• Biochemistry and Medicinal Chemistry
• Cancer Research and Therapeutics
• Nanotechnology and Drug Delivery

Background:

• Ascorbate (Asc) shows limited anticancer efficacy alone, despite generating tumoricidal hydrogen peroxide (H2O2) via endogenous catalysts.
• Optimizing H2O2 production requires exogenous catalysts with tailored properties for enhanced efficacy and tumor localization.
• Manganese porphyrins (MnPs) are investigated as potential catalysts due to their tunable redox properties, charge, and lipophilicity.

Purpose of the Study:

• To synthesize and characterize 14 Mn porphyrins (MnPs) with diverse properties to optimize ascorbate oxidation and H2O2 production.
• To evaluate the in vitro and in vivo anticancer efficacy of MnP/Asc combinations in breast cancer models.
• To elucidate the structure-activity relationships (SAR) governing MnP catalytic efficiency and anticancer effects.

Main Methods:

• Synthesis and characterization of 14 MnPs with varying redox potentials, charges, and lipophilicity.
• Spectrophotometric and electrochemical assays to determine MnP-catalyzed ascorbate oxidation rates (vo(Asc)ox).
• In vitro cytotoxicity assays on human and mouse cancer cell lines (MCF-7, MDA-MB-231, 4T1) and normal cells (HBL-100).
• In vivo efficacy studies in a 4T1 mammary mouse tumor model.
• Assessment of cellular oxidative stress, thiol levels, and redox ratios (GSH/GSSG, Cys/CySS).

Main Results:

• A bell-shaped SAR was identified between MnP redox potential (E1/2) and ascorbate oxidation rate, highlighting cationic Mn(III) N-substituted pyridylporphyrins with E1/2 > 0 mV as optimal catalysts.
• Combined MnP/Asc treatment achieved up to 95% suppression of cancer cell viability without affecting normal cells.
• The MnP/Asc system significantly increased cellular oxidative stress.
• MnTE-2-PyP(5+) was identified as the most effective catalyst, demonstrating significant tumor growth suppression in vivo when combined with Asc.
• High accumulation of MnTE-2-PyP(5+) in tumors (7-fold higher than normal tissue) contributed to its efficacy.

Conclusions:

• Optimized MnPs, particularly MnTE-2-PyP(5+), can significantly enhance the anticancer activity of ascorbate by generating tumoricidal H2O2.
• The MnP/Asc system exhibits potent anticancer effects with minimal toxicity to normal tissues, offering a promising therapeutic strategy.
• Targeted accumulation of MnPs within tumors is crucial for maximizing therapeutic benefit and minimizing systemic side effects.