Current Status of Novel Multifunctional Targeted Pt(IV) Compounds and Their Reductive Release Properties

Platinum-based drugs are widely used in chemotherapy for various types of cancer and are considered crucial. Tetravalent platinum (Pt(IV)) compounds have gained significant attention and have been extensively researched among these drugs. Traditionally, Pt(IV) compounds are reduced to divalent platinum (Pt(II)) after entering cells, causing DNA lesions and exhibiting their anti-tumor effect. However, the available evidence indicates that some Pt(IV) derivatives may differ from the traditional mechanism and exert their anti-tumor effect through their overall structure. This review primarily focuses on the existing literature regarding targeted Pt(II) and Pt(IV) compounds, with a specific emphasis on their in vivo mode of action and the properties of reduction release in multifunctional Pt(IV) compounds. This review provides a comprehensive summary of the design and synthesis strategies employed for Pt(II) derivatives that selectively target various enzymes (glucose receptor, folate, telomerase, etc.) or substances (mitochondria, oleic acid, etc.). Furthermore, it thoroughly examines and summarizes the rational design, anti-tumor mechanism of action, and reductive release capacity of novel multifunctional Pt(IV) compounds, such as those targeting p53-MDM2, COX-2, lipid metabolism, dual drugs, and drug delivery systems. Finally, this review aims to provide theoretical support for the rational design and development of new targeted Pt(IV) compounds.

Anticancer Activity, Reduction Mechanism and G-Quadruplex DNA Binding of a Redox-Activated Platinum(IV)-Salphen Complex

Aiming at reducing the unselective cytotoxicity of Pt(II) chemotherapeutics, a great deal of effort has been concentrated into the design of metal-containing drugs with different anticancer mechanisms of action. Inert Pt(IV) prodrugs have been proposed to be a valid alternative as they are activated by reduction directly into the cell releasing active Pt(II) species. On the other hand, a promising strategy for designing metallodrugs is to explore new potential biological targets rather than canonical B-DNA. G-quadruplex nucleic acid, obtained by self-assembly of guanine-rich nucleic acid sequences, has recently been considered an attractive target for anticancer drug design. Therefore, compounds capable of binding and stabilizing this type of DNA structure would be greatly beneficial in anticancer therapy. Here, computational analysis reports the mechanism of action of a recently synthesized Pt(IV)-salphen complex conjugating the inertness of Pt(IV) prodrugs with the ability to bind G-quadruplexes of the corresponding Pt(II) complex. The reduction mechanism of the Pt(IV) complex with a biological reducing agent was investigated in depth by means of DFT, whereas classical MD simulations were carried out to shed light into the binding mechanism of the released Pt(II) complex. The results show that the Pt(IV) prodrug may be reduced by both inner- and outer-sphere mechanisms, and the active Pt(II) complex, as a function of its protonation state, stabilizes the G-quadruplex DNA prevalently, either establishing π-stacking interactions with the terminal G-tetrad or through electrostatic interactions along with H-bonds formation.

Computational Exploration of the Synergistic Anticancer Effect of a Multi-Action Ru(II)-Pt(IV) Conjugate

An in-depth computational study of the ability of a recently proposed multi-action Ru(II)–Pt(IV) conjugate to act as a photosensitizer in photodynamic therapy (PDT) and chemotherapeutic drugs is presented here. The investigated complex is characterized by a polypyridyl Ru(II) chromophore linked to a Pt(IV) complex that, acting as a prodrug, should be activated by reduction releasing the Ru-based chromophore that can absorb light of proper wavelength to be used in PDT. The reaction mechanism for active species formation has been fully elucidated by means of density functional theory and its time-dependent extension. The reduction mechanism, assisted by ascorbate, of the Pt(IV) prodrug to the Pt(II) active species has been explored, taking into consideration all the possible modes of attack of the reductant for releasing the axial ligands and affording active cisplatin. Given the similarity in the photophysical properties of the chromophore linked or not to the Pt(IV) complex, both the Ru(II)–Pt(IV) conjugate precursor and the Ru(II) chromophore should be able to act as PDT photosensitizers according to type I and type II photoprocesses. In particular, they are able to generate singlet oxygen cytotoxic species as well as auto-ionize to form highly reactive O₂^–• species.

A computational study on the ability of a multi-action Ru(II)−Pt(IV) conjugate to act as a photosensitizer in photodynamic therapy (PDT) and chemotherapeutic drugs is presented here. The reduction mechanism of the Pt(IV) complex along with the photophysical properties of both the prodrug Ru(II)−Pt(IV) conjugate and Ru(II) complex is provided. The mechanism of action has been fully elucidated by means of density functional theory and its time-dependent extension.

Catalytic role of amines in activation of PhICl2 from a computational point of view

We thoroughly investigated mechanistic features of dichlorination of diazoacetates using PhICl₂ catalysed by pyridine. We found that the pyridine serves as a catalyst for decomposition of PhICl₂ to PhI and Cl₂, leading to the dichlorination step being driven by the in situ generated Cl₂. This type of activation was found to be applicable to other amine-catalysed chlorination reactions using PhICl₂.

Iodido equatorial ligands influence on the mechanism of action of Pt(IV) and Pt(II) anti-cancer complexes: A DFT computational study

A detailed computational exploration of the most relevant steps of iodido Pt(IV) complexes reduction and Pt(II) drugs mechanism of action and eventual deactivation is presented here inspired by the recent findings on iodido Pt(II) complexes and surprising re-evaluation of their cytotoxic activity. Pt(II) and Pt(IV) model systems are investigated and compared with cisplatin and its Pt(IV) derivative. Both monodeprotonated ascorbic acid and l-cysteine are used as reducing agents in the inner-sphere reduction mechanism of Pt(IV) complexes. Aquation mechanism of iodido Pt(II) complexes, interaction with guanine and sulfur containing compounds and reaction with the model protein hen egg white lysozyme are explored, due to a detected different behavior with respect to classical platinum drugs. The outcomes of such exploration allow to shed light on the role that the increased soft character together with bridging and leaving abilities of iodide over chloride could play in determining the cytotoxic profile of iodido Pt drugs.

Theoretical Prediction of Dual-Potency Anti-Tumor Agents: Combination of Oxoplatin with Other FDA-Approved Oncology Drugs

Although Pt(II)-based drugs are widely used to treat cancer, very few molecules have been approved for routine use in chemotherapy due to their side-effects on healthy tissues. A new approach to reducing the toxicity of these drugs is generating a prodrug by increasing the oxidation state of the metallic center to Pt(IV), a less reactive form that is only activated once it enters a cell. We used theoretical tools to combine the parent Pt(IV) prodrug, oxoplatin, with the most recent FDA-approved anti-cancer drug set published by the National Institute of Health (NIH). The only prerequisite imposed for the latter was the presence of one carboxylic group in the structure, a chemical feature that ensures a link to the coordination sphere via a simple esterification procedure. Our calculations led to a series of bifunctional prodrugs ranked according to their relative stabilities and activation profiles. Of all the designed molecules, the combination of oxoplatin with aminolevulinic acid as the bioactive ligand emerged as the most promising strategy by which to design enhanced dual-potency oncology drugs.

A metadynamics perspective on the reduction mechanism of the Pt(IV) asplatin prodrug

Enhanced sampling molecular dynamics has been used to model the reduction mechanism of the antitumoral Asplatin Pt(IV) complex, c,c,t-[PtCl2(NH3)2(OH)(aspirin)] in the presence of l-ascorbic acid as reducing agent. In order to overcome the timescale problem, characteristic of many chemical reactions, we enhanced the sampling of the free energy landscape using Metadynamics. To achieve such a goal, the selection of adequate collective variables is crucial for the application of the method. Recently, a new method called Multi-Class Harmonic Linear Discriminant Analysis (MC-HLDA) has been proposed as a tool for constructing collective variables (CVs) for complex chemical processes. The method reduces the dimensionality of the variable space by generating appropriate linear combinations of several relevant chemical descriptors. The aim of this work is to assess the ability and performance of this method in describing the fundamental features of complex chemical reactions such as the Asplatin reduction mechanism in a compact, simple, and physically transparent manner. © 2019 Wiley Periodicals, Inc.

A Computational Mechanistic Investigation into Reduction of Gold(III) Complexes by Amino Acid Glycine: A New Variant for Amine Oxidation

Density functional theory (DFT) was utilized to explore the reduction of gold(III) complexes by the amino acid glycine (Gly). Interestingly, when the nitrogen atom of Gly coordinates to the gold(III) center, its C^α -hydrogen atom becomes so acidic that it can be easily deprotonated by a mild base like water. The deprotonation converts the amino acid into a potent reductant by which gold(III) is reduced to gold(I) with a moderate activation energy. To our knowledge, this is the first contribution suggesting that primary amines are oxidized to imines via direct α-carbon deprotonation. This finding may provide new insights into the mechanistic interpretation of amine oxidations catalyzed/mediated by a center with high cathodic reduction potential. This work also provides a rationalization behind why gold(III) complexes with amine-based polydentate ligands are reluctant to undergo a redox process. Gold(III) reduction occurs most efficiently if the C^α proton leaves in the plane of the C^α , N and Au atoms. Chelation prevents this alignment, resulting in the gold(III) complex being unreactive toward reduction. It has been experimentally found that gold(III) is capable of oxidizing Gly to glyoxylic acid (GA) as the initial product. The latter, in the presence of another gold(III) complex, has been reported to undergo oxidative decarboxylation to afford CO₂ and HCOOH. This process is found to be mediated by formation of a geminal diol intermediate produced by reaction of water with the aldehyde functional group of the coordinated GA.

Reduction of ormaplatin by an extended series of thiols unravels a remarkable correlation

Reduction of the Pt(iv) anticancer active prodrug ormaplatin by an extended series of thiols has been studied, revealing a remarkable linear free-energy correlation.

Reduction of a platinum(iv) prodrug model by sulfur containing biological reductants: computational mechanistic elucidation

In order for the usual l-Cys zwitterion to reduce Pt^IV, it is first required to tautomerise into its unusual form.

Exploring the Hydrolytic Behavior of the Platinum(IV) Complexes with Axial Acetato Ligands

Platinum(IV) complexes are generally thought to be kinetically inert, and are expected to be stable enough to resist premature aquation before entering the cancer cells. Nevertheless, in this work, complex 2 with axial acetato ligands can hydrolyze relatively quickly under biologically relevant conditions with a half-life of 91.7 min, resulting in the loss of the equatorial chlorido ligand. Further study indicated that the fast hydrolysis of complex 2 may be attributed to the strong σ-donor ability of N-isopropyl-1R,2R-diaminocyclohexane, and an increasing σ-donor ability of the amine group can promote the hydrolysis rate of the corresponding platinum(IV) complex. The experiment results were proven by the corresponding DFT calculation. Our study can help to re-evaluate the aqueous properties of the platinum(IV) complexes with axial acetate, which may be less inert to hydrolysis than expected under biologically relevant conditions.