Visible-Light-Activated Quinolone Carbon-Monoxide-Releasing Molecule: Prodrug and Albumin-Assisted Delivery Enables Anticancer and Potent Anti-Inflammatory Effects

Abstract

The delivery of controlled amounts of carbon monoxide (CO) to biological targets is of significant current interest. Very few CO-releasing compounds are currently known that can be rigorously controlled in terms of the location and amount of CO released. To address this deficiency, we report herein a new metal-free, visible-light-induced CO-releasing molecule (photoCORM) and its prodrug oxidized form, which offer new approaches to controlled, localized CO delivery. The new photoCORM, based on a 3-hydroxybenzo[ g]quinolone framework, releases 1 equiv of CO upon visible-light illumination under a variety of biologically relevant conditions. This nontoxic compound can be tracked prior to CO release using fluorescence microscopy and produces a nontoxic byproduct following CO release. An oxidized prodrug form of the photoCORM is reduced by cellular thiols, providing an approach toward activation in the reducing environment of cancer cells. Strong noncovalent affinity of the nonmetal photoCORM to albumin enables use of an albumin:photoCORM complex for targeted CO delivery to cancer cells. This approach produced cytotoxicity IC values among the lowest reported to date for CO delivery to cancer cells by a photoCORM. This albumin:photoCORM complex is also the first CO delivery system to produce significant anti-inflammatory effects when introduced at nanomolar photoCORM concentration.

Emerging Delivery Strategies of Carbon Monoxide for Therapeutic Applications: from CO Gas to CO Releasing Nanomaterials

“…In a carrageenan‐induced rat paw edema model, CORM‐2‐loaded lipid nanoparticles with extended CO release half‐life and improved water solubility displayed higher anti‐inflammatory effects compared to both indomethacin and CORM‐2 solution (Figure a) . Recently, a metal‐free 3‐hydroxybenzo[g]quinolone photoCORM has been used in combination with BSA to exert anticancer and potent anti‐inflammatory activities (Figure d) . The anti‐inflammatory feature of this complex is noteworthy as the complex can attenuate LPS‐induced murine macrophage cells inflammation at unprecedented nanomolar concentrations.…”

Tracking CO Release in Cells via the Luminescence of Donor Molecules and/or their By‐Products

“…This difference may result from variances in protein binding and/or cellular uptake. It is worth noting that 20 is the first photoCORM to show nanomolar anti‐inflammatory effects . The CO release byproduct 21 is non‐toxic up to 100 μM.…”

“…Notably, 20 is best delivered to cells using bovine serum albumin (BSA) as a carrier protein. The binding constant for 20 to BSA is more than >900‐fold stronger than that of 19 , with both binding to the protein in a 1 : 1 stoichiometry ,. In the absence of visible light and in the presence of a physiologically relevant amount of BSA (0.6 mM) 20 exhibits no toxicity up to 100 μM in A549 cells whereas 19 is mildly toxic (IC 50 =82 μM).…”

“…The 3‐hydroxyquinolone photoCORM 20 (Figure ) exhibits many properties similar to its flavone analog 18 , including quantitative, visible‐light induced CO release followed by fluorescence turn‐off that can be detected using the GFP channel . Notably, 20 is best delivered to cells using bovine serum albumin (BSA) as a carrier protein.…”

“…[13] Other scaffolds have been used to develop metal-free photoCORMs, including cyclic a-diketones, a xanthene carboxylic acid, mesocarboxy BODIPYs, and 3-hydroxyflavone and 3-hydroxyquinolone motifs ( Figure 2(middle and bottom)). [14] CORMs and photoCORMs that can be tracked via luminescence offer the advantage of providing insight into cellular uptake and distribution, as well as the CO release process in living cells. [1,15] This is an important and timely issue as the reactivity of CO with known and yet unidentified cellular targets may be impacted by the proximity of CO delivery.…”