Selected polyoxopalladates as promising and selective antitumor drug candidates

All-Inorganic Polyoxometalates Act as Superchaotropic Membrane Carriers

Polyoxometalates (POMs) are known antitumoral, antibacterial, antiviral, and anticancer agents and considered as next-generation metallodrugs. Herein, a new biological functionality in neutral physiological media, where selected mixed-metal POMs are sufficiently stable and able to affect membrane transport of impermeable, hydrophilic, and cationic peptides (heptaarginine, heptalysine, protamine, and polyarginine) is reported. The uptake is observed in both, model membranes as well as cells, and attributed to the superchaotropic properties of the polyoxoanions. In view of the structural diversity of POMs these findings pave the way toward their biomedical application in drug delivery or for cell-biological uptake studies with biological effector molecules or staining agents.

Binary Heterogroup-Templated Scaffolds of Polyoxopalladates as Precatalysts for Plasma-Assisted Ammonia Synthesis

In addition to improving the synthetic efficiency, the template method can do a lot more in the chemistry of polyoxopalladates (POPs), such as the establishment of novel metal-oxo scaffolds. In this endeavor, a binary system comprising heterogroups of nonmetallic {As/SiO4} and metallic {VO4/5} successfully fulfills the templated growth of two POPs with unprecedented seesaw- and spindle-like prototypes. Of these, self-aggregation of heterogroups beacons an effective route to break the highly symmetrical PdII-oxo matrix and to force the arrangement of addenda in a nonconventional manner. Aside from the interest in their structural features, the as-made POPs are available for immobilization on the mesoporous SBA-15 as precatalysts for ammonia synthesis. The outer cover of heterogroups in the POP precursors contributes to the ultrafine size and uniform distribution of derived Pd0 nanoparticles (PdNPs). With the help of plasma activation on H2 and N2, such PdNPs-SBA15 catalysts significantly improve the production performance of NH3, showcasing the maximum synthesis rate of 64.42 μmol/(min·gcat) with the corresponding energy yield as high as 4.38 g-NH3/kWh.

Gallium(III)- and Thallium(III)-Encapsulated Polyoxopalladates: Synthesis, Structure, Multinuclear NMR, and Biological Activity Studies

Three gallium(III)- and thallium(III)-containing polyoxopalladates (POPs) have been synthesized and structurally characterized in the solid state and in solution, namely, the phosphate-capped 12-palladate nanocubes [XPd12O8(PO4)8]13- (X = GaIII, GaPd12P8; X = TlIII, TlPd12P8) and the 23-palladate double-cube [Tl2IIIPd23P14O70(OH)2]20- (Tl2Pd23P14). The cuboid POPs, GaPd12P8 and TlPd12P8, are solution stable as verified by the respective 31P, 71Ga, and 205Tl nuclear magnetic resonance (NMR) spectra. Of prime interest, the spin-spin coupling schemes allowed for an intimate study of the solution behavior of the TlIII-containing POPs via a combination of 31P and 205Tl NMR, including the stoichiometry of the major fragments of Tl2Pd23P14. Moreover, biological studies demonstrated the antitumor and antiviral activity of GaPd12P8 and TlPd12P8, which were validated to be as efficient as cis-platinum against human melanoma and acute promyelocytic leukemia cells. Furthermore, GaPd12P8 and TlPd12P8 exerted inhibitory activity against two herpetic viruses, HSV-2 and HCMV, in a dose-response manner.

Polyoxometalates Impact as Anticancer Agents

Polyoxometalates (POMs) are oxoanions of transition metal ions, such as V, Mo, W, Nb, and Pd, forming a variety of structures with a wide range of applications. Herein, we analyzed recent studies on the effects of polyoxometalates as anticancer agents, particularly their effects on the cell cycle. To this end, a literature search was carried out between March and June 2022, using the keywords "polyoxometalates" and "cell cycle". The effects of POMs on selected cell lines can be diverse, such as their effects in the cell cycle, protein expression, mitochondrial effects, reactive oxygen species (ROS) production, cell death and cell viability. The present study focused on cell viability and cell cycle arrest. Cell viability was analyzed by dividing the POMs into sections according to the constituent compound, namely polyoxovanadates (POVs), polyoxomolybdates (POMos), polyoxopaladates (POPds) and polyoxotungstates (POTs). When comparing and sorting the IC₅₀ values in ascending order, we obtained first POVs, then POTs, POPds and, finally, POMos. When comparing clinically approved drugs and POMs, better results of POMs in relation to drugs were observed in many cases, since the dose required to have an inhibitory concentration of 50% is 2 to 200 times less, depending on the POMs, highlighting that these compounds could become in the future an alternative to existing drugs in cancer therapy.

Coordination of Pt(IV) by {P8W48} Macrocyclic Inorganic Cavitand: Structural, Solution, and Electrochemical Studies

Hydrothermal reaction of a macrocyclic inorganic POM cavitand Li₁₇(NH₄)₂₁H₂[P₈W₄₈O₁₈₄] with [Pt(H₂O)₂(OH)₄] results in coordination of up to six {Pt(H₂O)_x(OH)_4-x} fragments to the internal surface of the polyoxoanion. The product was isolated as K₂₂(NH₄)₉H₃[{Pt(OH)₃(H₂O)}₆P₈W₄₈O₁₈₄]·79H₂O (1) and characterized by multiple techniques in the solid state (SCXRD, XRPD, XPS, FTIR, and TGA) and in solution (NMR, ESI-MS, and HPLC-ICP-AES). Electrochemical properties were studied both in solution and as components of the paste electrode. The complex shows electrocatalytic activity in water oxidation.

Promising application of polyoxometalates in the treatment of cancer, infectious diseases and Alzheimer's disease

As shown in studies conducted in recent decades, polyoxometalates (POMs), as inorganic metal oxides, have promising biological activities, including antitumor, anti-infectious and anti-Alzheimer’s activities, due to their special structures and properties. However, some side effects impede their clinical applications to a certain extent. Compared with unmodified POMs, POM-based inorganic–organic hybrids and POM-based nanocomposite structures show significantly enhanced bioactivity and reduced side effects. In this review, we introduce the biological activities of POMs and their derivatives and highlight the side effects of POMs on normal cells and organisms and their possible mechanisms of action. We then propose a development direction for overcoming their side effects. POMs are expected to constitute a new generation of inorganic metal drugs for the treatment of cancer, infectious diseases, and Alzheimer's disease.

Graphical abstract