Cytotoxic double arene ruthenium metalla-cycles that overcome cisplatin resistance

Rhenium Tricarbonyl Complexes of Azodicarboxylate Ligands

The excellent π-accepting azodicarboxylic esters adcOR (R = Et, iPr, tBu, Bn (CH₂-C₆H₅) and Ph) and the piperidinyl amide derivative adcpip were used as bridging chelate ligands in dinuclear Re(CO)₃ complexes [{Re(CO)₃Cl}₂(µ-adcOR)] and [{Re(CO)₃Cl}₂(µ-adcpip)]. From the adcpip ligand the mononuclear derivatives [Re(CO)₃Cl(adcpip)] and [Re(CO)₃(PPh₃)(µ-adcpip)]Cl were also obtained. Optimised geometries from density functional theory (DFT) calculations show syn and anti isomers for the dinuclear fac-Re(CO)₃ complexes at slightly different energies but they were not distinguishable from experimental IR or UV-Vis absorption spectroscopy. The electrochemistry of the adc complexes showed reduction potentials slightly below 0.0 V vs. the ferrocene/ferrocenium couple. Attempts to generate the radicals [{Re(CO)₃Cl}₂(µ-adcOR)]^•- failed as they are inherently unstable, losing very probably first the Cl^- coligand and then rapidly cleaving one [Re(CO)₃] fragment. Consequently, we found signals in EPR very probably due to mononuclear radical complexes [Re(CO)₃(solv)(adc)]^•. The underlying Cl^-→solvent exchange was modelled for the mononuclear [Re(CO)₃Cl(adcpip)] using DFT calculations and showed a markedly enhanced Re-Cl labilisation for the reduced compared with the neutral complex. Both the easy reduction with potentials ranging roughly from -0.2 to -0.1 V for the adc ligands and the low-energy NIR absorptions in the 700 to 850 nm range place the adc ligands with their lowest-lying π* orbital being localised on the azo function, amongst comparable bridging chelate N^N coordinating ligands with low-lying π* orbitals of central azo, tetrazine or pyrazine functions. Comparative (TD)DFT-calculations on the Re(CO)₃Cl complexes of the adcpip ligand using the quite established basis set and functionals M06-2X/def2TZVP/LANL2DZ/CPCM(THF) and the more advanced TPSSh/def2-TZVP(+def2-ECP for Re)/CPCMC(THF) for single-point calculations with BP86/def2-TZVP(+def2-ECP for Re)/CPCMC(THF) optimised geometries showed a markedly better agreement of the latter with the experimental XRD, IR and UV-Vis absorption data.

pH-Responsive Release of Ruthenium Metallotherapeutics from Mesoporous Silica-Based Nanocarriers

Ruthenium complexes are attracting interest in cancer treatment due to their potent cytotoxic activity. However, as their high toxicity may also affect healthy tissues, efficient and selective drug delivery systems to tumour tissues are needed. Our study focuses on the construction of such drug delivery systems for the delivery of cytotoxic Ru(II) complexes upon exposure to a weakly acidic environment of tumours. As nanocarriers, mesoporous silica nanoparticles (MSN) are utilized, whose surface is functionalized with two types of ligands, (2-thienylmethyl)hydrazine hydrochloride (H1) and (5,6-dimethylthieno[2,3-d]pyrimidin-4-yl)hydrazine (H2), which were attached to MSN through a pH-responsive hydrazone linkage. Further coordination to ruthenium(II) center yielded two types of nanomaterials MSN-H1[Ru] and MSN-H2[Ru]. Spectrophotometric measurements of the drug release kinetics at different pH (5.0, 6.0 and 7.4) confirm the enhanced release of Ru(II) complexes at lower pH values, which is further supported by inductively coupled plasma optical emission spectrometry (ICP-OES) measurements. Furthermore, the cytotoxicity effect of the released metallotherapeutics is evaluated in vitro on metastatic B16F1 melanoma cells and enhanced cancer cell-killing efficacy is demonstrated upon exposure of the nanomaterials to weakly acidic conditions. The obtained results showcase the promising capabilities of the designed MSN nanocarriers for the pH-responsive delivery of metallotherapeutics and targeted treatment of cancer.

Biomedically Relevant Self-Assembled Metallacycles and Metallacages

Diverse metal-organic complexes (MOCs), shaped as rectangles, triangles, hexagons, prisms, and cages, can be formed by coordination between metal ions (Pt, Pd, Ru, Rh, Ir, Zn, Co, and Cd) and organic ligands, with potential applications as alternatives to conventional biomedical materials for therapeutic, sensing, and imaging purposes. MOCs have been investigated as anticancer drugs in the treatment of malignant tumors in lung, cervical, breast, colon, liver, prostate, ovarian, brain, stomach, bone, skin, mouth, thyroid, and other cancers. MOCs with one, two, and three cavities have also been investigated as drug carriers and prepared for the loading and release of different drugs. In addition, MOCs can target proteins by the shape effect and recognize sugars and DNA by electrostatic interactions, as well as estradiol by host-guest interactions, etc. This Perspective mainly covers achievements in the biomedical application of MOCs. We aim to identify some key trends in the reported MOC structures in relation to their biomedical activity and potential applications.

Coordination-Driven Self-Assembly of Triazole-Based Apoptosis-Inducible Metallomacrocycles

Ru(II)-metallomacrocycles containing 4-pyridyl-1,2,3-triazole moiety were realized by coordination-driven self-assembly. All new compounds were characterized by electrospray ionisation mass spectrometry, elemental analysis, and 1H and 13C NMR spectroscopic techniques. The molecular structure of metallomacrocycle 8 was determined by single-crystal X-ray crystallography. The anticancer activities of metallomacrocycles 5-8 were evaluated by cytotoxicity, cell cycle analysis, and related protein expression. Metallomacrocycle 7 showed the highest cytotoxicity in HepG2 human hepatocellular carcinoma cells. In addition, apoptotic HepG2 cells were analyzed when metallomacrocycle 7 was treated. Our results suggest that metallomacrocycle 7 induces liver cancer cell death by increasing apoptosis and cell cycle arrest and that it has potential use as an agent for the treatment of human hepatocellular carcinoma.

Self-Assembled Multinuclear Complexes Incorporating 99m Tc

Multinuclear complexes or clusters are rarely investigated in medicinal inorganic chemistry although they represent structural intermediates between molecules and nanomaterials. We present in this report two strategies towards ^99m Tc-containing clusters. In a pre-assembly approach, the preformed but incomplete cluster fragment [Re₃ (μ₂ -OH)₃ (μ₃ -OH)(CO)₉ ]^- reacts with [^99m Tc(CO)₃ ]⁺ to the highly stable [^99m TcRe₃ (μ₃ -OH)₄ (CO)₁₂ ] cube. The same structure self-assembles when reacting the mononuclear Re and ^99m Tc precursors in one pot. Integrating the coordinating OH groups from Schiff bases in this concept leads straight to dinuclear, mixed-metal complexes of the type [^99m TcRe(μ₂ -O^N-R¹ )₂ (CO)₆ ] in quantitative yields. Both strategies are unprecedented and open a future path towards clusters, incorporating a ^99m Tc radiolabel while being decorated with targeting or cytotoxic moieties.