Computational Exploration of the Mechanism of Action of a Sorafenib-Containing Ruthenium Complex as an Anticancer Agent for Photoactivated Chemotherapy

Ruthenium(II) polypyridyl complexes are being tested as potential anticancer agents in different therapies, which include conventional chemotherapy and light-activated approaches. A mechanistic study on a recently synthesized dual-action Ru(II) complex [Ru(bpy)2(sora)Cl]+ is described here. It is characterized by two mono-dentate leaving ligands, namely, chloride and sorafenib ligands, which make it possible to form a di-aquo complex able to bind DNA. At the same time, while the released sorafenib can induce ferroptosis, the complex is also able to act as a photosensitizer according to type II photodynamic therapy processes, thus generating one of the most harmful cytotoxic species, 1O2. In order to clarify the mechanism of action of the drug, computational strategies based on density functional theory are exploited. The photophysical properties of the complex, which include the absorption spectrum, the kinetics of ISC, and the character of all the excited states potentially involved in 1O2 generation, as well as the pathway providing the di-aquo complex, are fully explored. Interestingly, the outcomes show that light is needed to form the mono-aquo complex, after releasing both chloride and sorafenib ligands, while the second solvent molecule enters the coordination sphere of the metal once the system has come back to the ground-state potential energy surface. In order to simulate the interaction with canonical DNA, the di-aquo complex interaction with a guanine nucleobase as a model has also been studied. The whole study aims to elucidate the intricate details of the photodissociation process, which could help with designing tailored metal complexes as potential anticancer agents.

Improving In Vivo Tumor Accumulation and Efficacy of Platinum Antitumor Agents by Electronic Tuning of the Kinetic Lability

The impact of kinetic lability or reactivity on in vitro cytotoxicity, stability in plasma, in vivo tumor and tissue accumulation, and antitumor efficacy of functional platinum(II) (Pt) anticancer agents containing a O˄O β-diketonate leaving ligand remain largely unexplored. To investigate this, we synthesized Pt complexes [(NH3 )2 Pt(L1-H)]NO3 and [(DACH)Pt(L1-H)]NO3 (L1=4,4,4-trifluoro-1-ferrocenylbutane-1,3-dione, DACH=1R,2R-cyclohexane-1,2-diamine) containing an electron deficient [L1-H]- O˄O leaving ligand and [(NH3 )2 Pt(L2-H)]NO3 and [(DACH)Pt(L2-H)]NO3 (L2=1-ferrocenylbutane-1,3-dione) containing an electron-rich [L2-H]- O˄O leaving ligand. While all four complexes have comparable lipophilicity, the presence of the electron-withdrawing CF3 group was found to dramatically enhance the reactivity of these complexes toward nucleophilic biomolecules. In vitro cellular assays revealed that the more reactive complexes have higher cellular uptake and higher anticancer potency as compared to their less reactive analogs. But the scenario is opposite in vivo, where the less reactive complex showed improved tissue and tumor accumulation and better anticancer efficacy in mice bearing ovarian xenograft when compared to its more reactive analog. Finally, in addition to demonstrating the profound but contrasting impact of kinetic lability on in vitro and in vivo antitumor potencies, we also described the impact of kinetic lability on the mechanism of action of this class of promising antitumor agents.

Cytotoxicity of Alizarine versus Tetrabromocathecol Cyclometalated Pt(II) Theranostic Agents: A Combined Experimental and Computational Investigation

Platinum compounds cytotoxicity is strictly related to their ability to be converted into active mono- and di-aquated species and consequently to the replacement of labile ligands by water molecules. This activation process makes the platinum center prone to nucleophilic substitution by DNA purines. In the present work, quantum mechanical density functional theory (DFT) computations and experimental investigations were carried out in order to shed light on the relationship between the internalization, aquation, and DNA binding of two isostructural anionic theranostic complexes previously reported by our group, NBu₄[(PhPy)Pt(Aliz)], 1 (IC₅₀ 1.9 ± 1.6 μM), and NBu₄[(PhPy)Pt(BrCat)], 2 (IC₅₀ 52.8 ± 3.9 μM). Cisplatin and a neutral compound [(NH₃)₂Pt(Aliz)], 3, were also taken as reference compounds. The computed energy barriers and the endergonicity of the hydrolysis reactions showed that the aquation rates are comparable for 1 and 2, with a slightly higher reactivity of 1. The second hydrolysis process was proved to be the rate-determining step for both 1 and 2, unlike for compound 3. The nucleophilic attack by the N7 site of guanine to both mono- and di-aquated forms of the complexes was computationally investigated as well, allowing to rationalize the observed different cytotoxicity. Computational results were supported by photostability data and biological assays, demonstrating DNA as the main target for compound 1.

An experimental−theoretical approach to study the cytotoxicity of ionic Pt(II) complexes containing (O^O) chelating ancillary ligands.

HOMO-LUMO photosensitization analyses of coronene-cytosine complexes

Photosensitization analyses of models of (–HC = CH–)n assisted coronene-cytosine complexes assigned by Cor-n-Cyt; n varying by 0, 1, 2, and 3, were investigated in this work by performing density functional theory (DFT) calculations. The investigated models were optimized and chemical descriptors were evaluated. To achieve the goal of this work, energy levels of the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) were evaluated to reach the absorption energy requirement for innovating photosensitizer (PS) compounds. The models indicated that the complex formations could help the structures to participate in interactions easier than the singular models, in which HOMO-LUMO descriptors indicated lower required absorption energy for them to increase their safety for human health level. The required absorption energies of complexes with n = 0, 1, and 2, were in ultraviolet (UV) region whereas that of complex with n = 3 was moved to visible region. In this regard, the idea of new PS compounds innovation was examined here to introduce Cor-n-Cyt complexes for possible applications in photodynamic therapy (PDT).

Computational Analysis of Photophysical Properties and Reactivity of a New Phototherapeutic Cyclometalated Au(III)-Hydride Complex

Gold(III) complexes have recently emerged as new versatile and efficacious metal containing anticancer agents. In an attempt to reconcile the specific affinity of such complexes for target sulfur containing biomolecules with their capability to strongly bind thiol-containing compounds widely distributed in non-tumoral cells, a new series of cyclometalated Au(III)-hydride complexes has been proposed as photoactivatable anticancer prodrugs. Here, the computational exploration of the photophysical properties and reactivity in dark and under light irradiation of the first member of the series, named 1 a, is reported. Complex 1 a low hydricity in dark together with facile hydride substitution leading to H₂ elimination under excitation by visible light have been examined by means of DFT and TD-DFT computations. Both singlet and triplet excited states have been characterized, allowing the identification of the active species involved in photoactivation pathways leading to the controlled detachment of the hydride ligand. Also the viable two-photon activation at the ideal phototherapeutic window has been investigated.