A pentaaza macrocyclic ring complex represented by formulae,, or: wherein X and Y represent suitable ligands which are derived from any monodentate or polydentate coordinating ligand or ligand system or the corresponding anion thereof; and R A, R B, R C, and R D are independently hydrogen, hydrocarbyl, substituted hydrocarbyl, heterocyclyl, an amino acid side chain moiety, or a moiety selected from the group consisting of -OR 11, -NR 11 R 12, -COR 11, -CO 2 R 11, -CONR 11 R 12, -SR 11, -SOR 11, -SO 2 R 11, -SO 2 NR 11 R 12, -N(OR 11)(R 12), -P (OR 11)(OR 12), -P (OR 11)(R 12), and -OP (OR 11)(OR 12), wherein R 11 and R 12 are independently hydrogen or alkyl, for use in a method of treating a cancer in a mammalian subject afflicted with the cancer, the method comprising: administering to the subject an active agent selected from the group consisting of ascorbic acid, an ascorbic acid derivative, wherein the ascorbic acid derivative is selected from: ascorbic acid esters; phosphorylated ascorbic acid compounds; ascorbic acid having one or more substitutions at the 2, 3, 4, 5 and/or 6 carbon of the ascorbic acid, wherein the substitutions are selected from the group of amino, sulfato, fatty acid, isopropylidene, deoxy, fluoro, chloro, bromo, iodo, phenyl, nitrophenyl and trifluorophenyl substitutions: stereoisomers of ascorbic acid, such as erythorbic acid (D-isoascorbic acid); and lipophilic analogs of ascorbic acid comprising 4-benzoyl-3-hydroxyfuran-2- -ones and 4-acetyl-5-aryl-3,4-dihydro-furan-2 -ones, and/or a pharmaceutically acceptable salt thereof; and administering to the subject the pentaaza macrocyclic ring complex corresponding to any of formulas - above. X and Y represent suitable ligands which are derived from any monodentate or polydentate coordinating ligand or ligand system or the corresponding anion thereof; and R A, R B, R C, and R D are independently hydrogen, hydrocarbyl, substituted hydrocarbyl, heterocyclyl, an amino acid side chain moiety, or a moiety selected from the group consisting of -OR 11, -NR 11 R 12, -COR 11, -CO 2 R 11, -CONR 11 R 12, -SR 11, -SOR 11, -SO 2 R 11, -SO 2 NR 11 R 12, -N(OR 11)(R 12), -P (OR 11)(OR 12), -P (OR 11)(R 12), and -OP (OR 11)(OR 12), wherein R 11 and R 12 are independently hydrogen or alkyl, for use in a method of treating a cancer in a mammalian subject afflicted with the cancer, the method comprising: administering to the subject an active agent selected from the group consisting of ascorbic acid, an ascorbic acid derivative, wherein the ascorbic acid derivative is selected from: ascorbic acid esters; phosphorylated ascorbic acid compounds; ascorbic acid having one or more substitutions at the 2, 3, 4, 5 and/or 6 carbon of the ascorbic acid, wherein the substitutions are selected from the group of amino, sulfato, fatty acid, isopropylidene, deoxy, fluoro, chloro, bromo, iodo, phenyl, nitrophenyl and trifluorophenyl substitutions: stereoisomers of ascorbic acid, such as erythorbic acid (D-isoascorbic acid); and lipophilic analogs of ascorbic acid comprising 4-benzoyl-3-hydroxyfuran-2- -ones and 4-acetyl-5-aryl-3,4-dihydro-furan-2 -ones, and/or a pharmaceutically acceptable salt thereof; and administering to the subject the pentaaza macrocyclic ring complex corresponding to any of formulas - above. administering to the subject an active agent selected from the group consisting of ascorbic acid, an ascorbic acid derivative, wherein the ascorbic acid derivative is selected from: ascorbic acid esters; phosphorylated ascorbic acid compounds; ascorbic acid having one or more substitutions at the 2, 3, 4, 5 and/or 6 carbon of the ascorbic acid, wherein the substitutions are selected from the group of amino, sulfato, fatty acid, isopropylidene, deoxy, fluoro, chloro, bromo, iodo, phenyl, nitrophenyl and trifluorophenyl substitutions: stereoisomers of ascorbic acid, such as erythorbic acid (D-isoascorbic acid); and lipophilic analogs of ascorbic acid comprising 4-benzoyl-3-hydroxyfuran-2- -ones and 4-acetyl-5-aryl-3,4-dihydro-furan-2 -ones, and/or a pharmaceutically acceptable salt thereof; and administering to the subject the pentaaza macrocyclic ring complex corresponding to any of formulas - above.