Radical Chemistry and Cytotoxicity of Bioreductive 3‑Substituted Quinoxaline Di‑<i>N</i>‑Oxides

The radical chemistry and cytotoxicity of a series of quinoxaline di-<i>N</i>-oxide (QDO) compounds has been investigated to explore the mechanism of action of this class of bioreductive drugs. A series of water-soluble 3-trifluoromethyl (<b>4</b>–<b>10</b>), 3-phenyl (<b>11</b>–<b>19</b>), and 3-methyl (<b>20</b>-<b>21</b>) substituted QDO compounds were designed to span a range of electron affinities consistent with bioreduction. The stoichiometry of loss of QDOs by steady-state radiolysis of anaerobic aqueous formate buffer indicated that one-electron reduction of QDOs generates radicals able to initiate chain reactions by oxidation of formate. The 3-trifluoromethyl analogues exhibited long chain reactions consistent with the release of the HO^•, as identified in EPR spin trapping experiments. Several carbon-centered radical intermediates, produced by anaerobic incubation of the QDO compounds with N-terminal truncated cytochrome P450 reductase (POR), were characterized using <i>N</i>-<i>tert</i>-butyl-α-phenylnitrone (PBN) and 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-<i>N</i>-oxide (DEPMPO) spin traps and were observed by EPR. Experimental data were well simulated for the production of strongly oxidizing radicals, capable of H atom abstraction from methyl groups. The kinetics of formation and decay of the radicals produced following one-electron reduction of the parent compounds, both in oxic and anoxic solutions, were determined using pulse radiolysis. Back oxidation of the initially formed radical anions by molecular oxygen did not compete effectively with the breakdown of the radical anions to form oxidizing radicals. The QDO compounds displayed low hypoxic selectivity when tested against oxic and hypoxic cancer cell lines <i>in vitro</i>. The results from this study form a kinetic description and explanation of the low hypoxia-selective cytotoxicity of QDOs against cancer cells compared to the related benzotriazine 1,4-dioxide (BTO) class of compounds

Anticancer Ruthenium(η⁶‑<i>p</i>‑cymene) Complexes of Nonsteroidal Anti-inflammatory Drug Derivatives

Oxicams are a versatile family of heterocyclic compounds, and the two representatives meloxicam and piroxicam are widely used drugs for the treatment of a variety of inflammatory and rheumatic diseases in humans. As cancer-associated inflammation is known to occur in carcinogenesis, we aimed to combine compounds carrying bioactive oxicam moieties with ruthenium­(arene) fragments, known for anticancer activity. Ru^II(arene) complexes with methyl ester derivatives of the oxicam scaffold were prepared and characterized by standard methods and crystallographically. The organoruthenium compounds formed from Ru^II(η⁶-<i>p</i>-cymene) chlorido moieties and oxicam-based ligands were subjected to bioanalytical investigations to establish their physicochemical properties with regard to stability in DMSO and water as well as reactivity toward the amino acids l-histidine (His), l-methionine (Met), and l-cysteine (Cys) and the DNA model compound guanosine 5′-monophosphate (5′-GMP). The compounds hydrolyzed rapidly in water to give the respective aqua complexes, formed amino acid complexes with Met and His, but decompose with Cys, while interaction with 5′-GMP was through its phosphate residue. The anticancer activity of the complexes against the colon carcinoma HCT116 and breast cancer MDA MB 231 cancer cell lines was established using an <i>in vitro</i> assay. The cytotoxicity was found strongly dependent on the lipophilicity of the compound, as was shown through correlation with log<i> k</i>_w and clog<i> P</i> values of the ligands. The most lipophilic compound [chlorido­(methyl 4-oxido-2-benzyl-2<i>H</i>-1,2-benzothiazine-3-carboxylate-1,1-dioxide)­(η⁶-<i>p</i>-cymene)­ruthenium­(II)] was the most active in the cell assays, with an IC₅₀ of 80 μM in HCT116 cells

New Iminodiacetate–Thiosemicarbazone Hybrids and Their Copper(II) Complexes Are Potential Ribonucleotide Reductase R2 Inhibitors with High Antiproliferative Activity

As ribonucleotide reductase (RNR) plays a crucial role in nucleic acid metabolism, it is an important target for anticancer therapy. The thiosemicarbazone Triapine is an efficient R2 inhibitor, which has entered ∼20 clinical trials. Thiosemicarbazones are supposed to exert their biological effects through effectively binding transition-metal ions. In this study, six iminodiacetate–thiosemicarbazones able to form transition-metal complexes, as well as six dicopper­(II) complexes, were synthesized and fully characterized by analytical, spectroscopic techniques (IR, UV–vis; ¹H and ¹³C NMR), electrospray ionization mass spectrometry, and X-ray diffraction. The antiproliferative effects were examined in several human cancer and one noncancerous cell lines. Several of the compounds showed high cytotoxicity and marked selectivity for cancer cells. On the basis of this, and on molecular docking calculations one lead dicopper­(II) complex and one thiosemicarbazone were chosen for in vitro analysis as potential R2 inhibitors. Their interaction with R2 and effect on the Fe­(III)₂-Y· cofactor were characterized by microscale thermophoresis, and two spectroscopic techniques, namely, electron paramagnetic resonance and UV–vis spectroscopy. Our findings suggest that several of the synthesized proligands and copper­(II) complexes are effective antiproliferative agents in several cancer cell lines, targeting RNR, which deserve further investigation as potential anticancer drugs

New Iminodiacetate–Thiosemicarbazone Hybrids and Their Copper(II) Complexes Are Potential Ribonucleotide Reductase R2 Inhibitors with High Antiproliferative Activity

As ribonucleotide reductase (RNR) plays a crucial role in nucleic acid metabolism, it is an important target for anticancer therapy. The thiosemicarbazone Triapine is an efficient R2 inhibitor, which has entered ∼20 clinical trials. Thiosemicarbazones are supposed to exert their biological effects through effectively binding transition-metal ions. In this study, six iminodiacetate–thiosemicarbazones able to form transition-metal complexes, as well as six dicopper­(II) complexes, were synthesized and fully characterized by analytical, spectroscopic techniques (IR, UV–vis; ¹H and ¹³C NMR), electrospray ionization mass spectrometry, and X-ray diffraction. The antiproliferative effects were examined in several human cancer and one noncancerous cell lines. Several of the compounds showed high cytotoxicity and marked selectivity for cancer cells. On the basis of this, and on molecular docking calculations one lead dicopper­(II) complex and one thiosemicarbazone were chosen for in vitro analysis as potential R2 inhibitors. Their interaction with R2 and effect on the Fe­(III)₂-Y· cofactor were characterized by microscale thermophoresis, and two spectroscopic techniques, namely, electron paramagnetic resonance and UV–vis spectroscopy. Our findings suggest that several of the synthesized proligands and copper­(II) complexes are effective antiproliferative agents in several cancer cell lines, targeting RNR, which deserve further investigation as potential anticancer drugs

New Iminodiacetate–Thiosemicarbazone Hybrids and Their Copper(II) Complexes Are Potential Ribonucleotide Reductase R2 Inhibitors with High Antiproliferative Activity

As ribonucleotide reductase (RNR) plays a crucial role in nucleic acid metabolism, it is an important target for anticancer therapy. The thiosemicarbazone Triapine is an efficient R2 inhibitor, which has entered ∼20 clinical trials. Thiosemicarbazones are supposed to exert their biological effects through effectively binding transition-metal ions. In this study, six iminodiacetate–thiosemicarbazones able to form transition-metal complexes, as well as six dicopper­(II) complexes, were synthesized and fully characterized by analytical, spectroscopic techniques (IR, UV–vis; ¹H and ¹³C NMR), electrospray ionization mass spectrometry, and X-ray diffraction. The antiproliferative effects were examined in several human cancer and one noncancerous cell lines. Several of the compounds showed high cytotoxicity and marked selectivity for cancer cells. On the basis of this, and on molecular docking calculations one lead dicopper­(II) complex and one thiosemicarbazone were chosen for in vitro analysis as potential R2 inhibitors. Their interaction with R2 and effect on the Fe­(III)₂-Y· cofactor were characterized by microscale thermophoresis, and two spectroscopic techniques, namely, electron paramagnetic resonance and UV–vis spectroscopy. Our findings suggest that several of the synthesized proligands and copper­(II) complexes are effective antiproliferative agents in several cancer cell lines, targeting RNR, which deserve further investigation as potential anticancer drugs

From Catalysis to Cancer: Toward Structure–Activity Relationships for Benzimidazol-2-ylidene-Derived <i>N</i>‑Heterocyclic-Carbene Complexes as Anticancer Agents

The promise of the metal­(arene) structure as an anticancer pharmacophore has prompted intensive exploration of this chemical space. While <i>N</i>-heterocyclic carbene (NHC) ligands are widely used in catalysis, they have only recently been considered in metal complexes for medicinal applications. Surprisingly, a comparatively small number of studies have been reported in which the NHC ligand was coordinated to the Ru^II(arene) pharmacophore and even less with an Os^II(arene) pharmacophore. Here, we present a systematic study in which we compared symmetrically substituted methyl and benzyl derivatives with the nonsymmetric methyl/benzyl analogues. Through variation of the metal center and the halido ligands, an in-depth study was conducted on ligand exchange properties of these complexes and their biomolecule binding, noting in particular the stability of the M–C_NHC bond. In addition, we demonstrated the ability of the complexes to inhibit the selenoenzyme thioredoxin reductase (TrxR), suggested as an important target for anticancer metal–NHC complexes, and their cytotoxicity in human tumor cells. It was found that the most potent TrxR inhibitor diiodido­(1,3-dibenzylbenzimidazol-2-ylidene)­(η⁶-p-cymene)­ruthenium­(II) <b>1b</b>^<b>I</b> was also the most cytotoxic compound of the series, with the antiproliferative effects in general in the low to middle micromolar range. However, since there was no clear correlation between TrxR inhibition and antiproliferative potency across the compounds, TrxR inhibition is unlikely to be the main mode of action for the compound type and other target interactions must be considered in future