Investigating the Combined Toxicity of Cu(II) and Carbon Monoxide (CO); Cellular CO Delivery Using a Cu(II) Flavonolato Complex.

Carbon monoxide (CO) delivery molecules are of significant current interest as potential therapeutics, including for anticancer applications. A recent approach toward generating new types of materials-based anticancer agents involves combining the Fenton reactivity of a redox active metal ion with CO delivery. However, small molecule examples of these types of entities have not been systematically studied to evaluate the combined effect on cellular toxicity. Herein we describe a Cu(II) flavonolato complex which produces anticancer effects through a combination of copper-mediated reactive oxygen species (ROS) generation and light-induced flavonol CO release. Confocal microscopy studies provide evidence of enhanced flavonol uptake in the copper flavonolato system relative to the free flavonol, which leads to an increased amount of CO delivery within cells. Importantly, this work demonstrates that a metal flavonolato species can be used to produce enhanced toxicity effects resulting from both metal ion-induced Fenton reactivity and increased cellular uptake of a flavonol CO donor.

Mechanistic studies of visible light-induced CO release from a 3-hydroxybenzo[g]quinolone.

Organic compounds that can be triggered using light to release CO in biological environments are of significant current interest to probe the role of CO in biology and as potential therapeutics. We recently reported that a 3-hydroxybenzo[g]quinolone (5) can be used as a CO delivery molecule to produce anticancer and potent anti-inflammatory effects. Herein we report mechanistic studies of the visible light-induced CO release reaction of this compound. In wet CH3CN under aerobic conditions, 5 releases 0.90(2) equivalents of CO upon illumination with visible light (419 nm) to give a single depside product. Performing the same reaction under an 18O2 atmosphere results in quantitative incorporation of two labeled oxygen atoms in the depside product. Monitoring via 1H NMR and UV-vis during the illumination of 5 in CH3CN using 419 nm light revealed the substoichiometric formation of a diketone (6) in the reaction mixture. H2O2 formation was detected in the same reaction mixtures. DFT studies indicate that upon light absorption an efficient pathway exists for the formation of a triplet excited state species (5b) that can undergo reaction with 3O2 resulting in CO release. DFT investigations also provide insight into diketone (6) and H2O2 formation and subsequent reactivity. The presence of water and exposure to visible light play an important role in lowering activation barriers in the reaction between 6 and H2O2 to give CO. Overall, two reaction pathways have been identified for CO release from a 3-hydroxybenzo[g]quinolone.

Flavonol-Based Carbon Monoxide Delivery Molecule with Endoplasmic Reticulum, Mitochondria, And Lysosome Localization.

Light-triggered carbon monoxide (CO) delivery molecules are of significant current interest for evaluating the role of CO in biology and as potential therapeutics. Herein we report the first example of a metal free CO delivery molecule that can be tracked via confocal microscopy at low micromolar concentrations in cells prior to CO release. The NEt2-appended extended flavonol (4) localizes to the endoplasmic reticulum, mitochondria, and lysosomes. Subcellular localization of 4 results in CO-induced toxicity effects that are distinct as compared to a nonlocalized analog. Anti-inflammatory effects of 4, as measured by TNF-α suppression, occur at the nanomolar level in the absence of CO release, and are enhanced with visible-light-induced CO release. Overall, the highly trackable nature of 4 enables studies of the biological effects of both a localized flavonol and CO release at low micromolar to nanomolar concentrations.