Cristina Mari

Anticancer Profile of a Series of Gold(III) (2-phenyl)pyridine Complexes

Six phosphorescent (2‐phenyl)pyridine (ppy) gold(III) 2,4,6‐tris(trifluoromethyl)phenyl (FMes) complexes were synthesized and investigated for their anticancer potential. The compounds demonstrated strong antiproliferative activity, with EC50 values in the low micromolar range, along with significant accumulation in HeLa cancer cells after treatment for only 6 h (up to 119 ng gold per milligram of protein as measured by high‐resolution continuum source atomic spectroscopy). Enzyme inhibition studies showed interaction of the gold(III) complexes with thioredoxin reductase (TrxR), a key homeostasis‐regulation flavoprotein. TrxR was inhibited with IC50 values in the micromolar range. Furthermore, five of the complexes displayed selectivity toward TrxR against glutathione reductase (GR, a disulfide reductase structurally related to TrxR) by up to >49‐fold. Because no major differences in bioactivity were observed across the series, [(ppy)Au(FMes)(PPh3)OTf] (complex 4) was chosen for further in‐depth biological characterization. Complex 4 was also found to interact with guanosine monophosphate in 1H NMR studies under long incubation times. Interestingly, 4 induced a significant increase in intracellular levels of reactive oxygen species, which led to late apoptotic events and cytocidal effects.

Induction of Cytotoxicity through Photorelease of Aminoferrocene

Reactive oxygen species (ROS)-activated aminoferrocene-based anticancer prodrug candidates successfully take advantage of intrinsically high amounts of ROS in tumor tissues. Interestingly, the ROS-initiated activation of these prodrug candidates leads to formation of unstable aminoferrocene (Fc-NH2) derivatives, which decay to iron ions. The latter catalytically increases ROS concentration to a lethal level. In this work, we prepared light-controlled aminoferrocene prodrug candidates by derivatizing Fc-NH2 with an o-nitrophenyl and an o-nitrobiphenyl photolabile protecting group (PLPG), respectively, and by further conjugation to a mitochondria localization signal (MLS) peptide (Cys-D-Arg-Phe-Lys-NH2). The resulting bioconjugates were found to be more stable and less cytotoxic, in the dark, toward human promyelocytic leukemia cells (HL-60) compared to Fc-NH2. Upon light irradiation at 355 nm, both conjugates released Fc-NH2, albeit with very different photolysis quantum yields. The o-nitrobiphenyl photocage was in fact several orders of magnitude more efficient than the o-nitrophenyl photocage in releasing Fc-NH2. This difference was reflected by the light irradiation experiments on the HL-60 cell line, in which aminoferrocene conjugated with the o-nitrobiphenyl cage and the MLS displayed the highest phototoxicity index (2.5 ± 0.4) of all the compounds tested. The iron release assays confirmed the rise in iron ion concentrations upon light irradiation of both caged aminoferrocene derivatives. Together with the absence of phototoxicity on the nonmalignant hTERT-immortalized retinal pigment epithelial (hTERT RPE-1) cell line, these results indicate catalytic generation of ROS as possible mode of action.

Multi-stimuli responsive block copolymers as a smart release platform for a polypyridyl ruthenium complex

A variety of applications of amphiphilic block copolymers result from the control of their self-assembled structures. Herein, the synthesis and structure formation of block copolymers (BCPs) consisting of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) as one segment and poly(methyl methacrylate) (PMMA) or a statistical copolymer (PDMAEMA-co-PMMA) as a second segment, is described. The BCPs provide molar masses between 8.9 kg mol−1 and 35.6 kg mol−1 with low polydispersity index values, Đ = 1.05–1.13. BCPs are synthesized via sequential anionic polymerization strategies while structure formation in water is investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The PDMAEMA-containing micelles in water are loaded with a Ru(II) polypyridyl complex, i.e. [Ru(bipy)2-dppz-7-hydroxymethyl][PF6]2 (bipy = 2,2′-bipyridine; dppz = dipyridophenazine), which was previously shown to act as a potential photosensitizer in photodynamic therapy (PDT). Successful loading of the BCP micelles is evidenced by TEM measurements after dialysis in water. Stimulus-responsive release of the Ru(II) complex from the BCP micelles is shown using ultrasound, change of pH or temperature as external triggers. The quantification and release profiles for the Ru(II) complex are obtained by atomic absorption spectrometry (AAS). As a result, PDMAEMA-b-PMMA is not capable of releasing the Ru(II) complex in a controlled manner after application of, for instance, ultrasound or temperature change as external triggers due to the shielding (stealth effect) of the BCP. On the contrary, micelles made of BCPs featuring PDMAEMA and PDMAEMA-co-PMMA segments reveal excellent Ru(II) complex release profiles due to the tailored molecular composition of the underlying block segments as evidenced by temperature-dependent DLS and AAS measurements. Thus, these smart PDMAEMA-containing BCPs pave the way to a variety of applications for selective triggered release of small molecules.

Electrochemical, spectroscopic, magnetic and structural studies of complexes bearing ferrocenyl ligands of N-(3-hydroxypicolinoyl)picolinamide

The synthesis and in-depth characterisation including X-ray crystallography of a new hydroxy derivative of bis(2-pyridylcarbonyl)amine Hbpca, namely N-(3-hydroxypicolinoyl)picolinamide (Hbpca-OH), as well as two ferrocenyl derivatives of Hbpca-OH, namely 2-(picolinoylcarbamoyl)pyridin-3-yl ferrocenoate (HL1) and bis(2-(picolinoylcarbamoyl)pyridin-3-yl) 1,1′-ferrocenoate (H2L2), is reported. HL1 and H2L2 were complexed with five different transition metal cations, namely Fe2+, Zn2+, Ni2+, Cu2+ and Cu+, to give ten complexes with varying stoichiometries, which were characterised by different analytical methods including 1H NMR, ESI-MS, IR spectroscopy and microanalysis. The metal complexation was also confirmed by electrochemical measurements for all complexes except Zn(L1)2 and FeL2, for which the changes in formal redox potentials of ferrocene ΔE°′ observed were not significant enough. Furthermore, two X-ray structures of CuII complexes, namely [Cu2I2L12] and [Cu2I2L2]n, were determined. Both structures contain an extremely rare CuII–I2–CuII bridge. Finally, a small antiferromagnetic coupling in [Cu2I2L2]n was observed.

Insertion of organometallic moieties into peptides and peptide nucleic acids using alternative “click” strategies

The insertion of metal complexes in biologically active systems is of great interest in view of diagnostic and therapeutic applications as well as a precious tool to unveil biological mechanisms. Optimization of safe and biocompatible reactions is critical to achieve high functionalization efficiency. Herein we present the application of two modified versions of copper-catalyzed azide–alkyne cycloaddition (click) chemistry, namely a one-pot diazotransfer + azide–alkyne cycloaddition (one-pot click) and a copper-free photoactivated tetrazole–alkene cycloaddition (photoclick), for derivatization of peptides and peptide nucleic acids (PNAs) with ferrocene and cymantrene moieties. These metal fragments were chosen for their possible exploitation as redox and IR probes. We could demonstrate that one-pot click enables for efficient functionalization of propargyl-glycine and an alkyne-containing peptide with an amino-containing cymantrene precursor. In addition, we could show that photoclick allows for the insertion of maleimido-ferrocene into a peptide and a PNA sequence containing a tetrazole moiety.