Manganese(II) complexes of quinoline derivatives: characterization, catalase activity, interaction with mitochondria and anticancer activity

Anticancer Metallocenes and Metal Complexes of Transition Elements from Groups 4 to 7

With the progression in the field of bioinorganic chemistry, the role of transition metal complexes as the most widely used therapeutics is becoming a more and more attractive research area. The complexes of transition metals possess a great variety of attractive pharmacological properties, including anticancer, anti-inflammatory, antioxidant, anti-infective, etc., activities. Transition metal complexes have proven to be potential alternatives to biologically active organic compounds, especially as antitumor agents. The performance of metal coordination compounds in living systems is anticipated to differ generally from the action of non-metal-containing drugs and may offer unique diagnostic and/or therapeutic opportunities. In this review, the rapid development and application of metallocenes and metal complexes of elements from Groups 4 to 7 in cancer diagnostics and therapy have been summarized. Most of the heavy metals discussed in the current review are newly discovered metals. That is why the use of their metal-based compounds has attracted a lot of attention concerning their organometallic and coordination chemistry. All of this imposes more systematic studies on their biological activity, biocompatibility, and toxicity and presupposes further investigations.

Effect of Lewis Acids on the Structure and Reactivity of a Mononuclear Hydroxomanganese(III) Complex

The addition of Sc(OTf)₃ and Al(OTf)₃ to the mononuclear Mn^III-hydroxo complex [Mn^III(OH)(dpaq)]⁺ (1) gives rise to new intermediates with spectroscopic properties and chemical reactivity distinct from those of [Mn^III(OH)(dpaq)]⁺. The electronic absorption spectra of [Mn^III(OH)(dpaq)]⁺ in the presence of Sc(OTf)₃ (1-Sc^III) and Al(OTf)₃ (1-Al^III) show modest perturbations in electronic transition energies, consistent with moderate changes in the Mn^III geometry. A comparison of ¹H NMR data for 1 and 1-Sc^III confirm this conclusion, as the ¹H NMR spectrum of 1-Sc^III shows the same number of hyperfine-shifted peaks as the ¹H NMR spectrum of 1. These ¹H NMR spectra, and that of 1-Al^III, share a similar chemical-shift pattern, providing firm evidence that these Lewis acids do not cause gross distortions to the structure of 1. Mn K-edge X-ray absorption data for 1-Sc^III provide evidence of elongation of the axial Mn-OH and Mn-N(amide) bonds relative to those of 1. In contrast to these modest spectroscopic perturbations, 1-Sc^III and 1-Al^III show greatly enhanced reactivity toward hydrocarbons. While 1 is unreactive toward 9,10-dihydroanthracene (DHA), 1-Sc^III and 1-Al^III react rapidly with DHA (k₂ = 0.16(1) and 0.25(2) M^-1 s^-1 at 50 °C, respectively). The 1-Sc^III species is capable of attacking the much stronger C-H bond of ethylbenzene. The basis for these perturbations to the spectroscopic properties and reactivity of 1 in the presence of these Lewis acids was elucidated by comparing properties of 1-Sc^III and 1-Al^III with the recently reported Mn^III-aqua complex [Mn^III(OH₂)(dpaq)]²⁺ ( J. Am. Chem. Soc. 2018, 140, 12695-12699). Because 1-Sc^III and 1-Al^III show ¹H NMR spectra essentially identical to that of [Mn^III(OH₂)(dpaq)]²⁺, the primary effect of these Lewis acids on 1 is protonation of the hydroxo ligand caused by an increase in the Brønsted acidity of the solution.

Oxoiron(IV) complexes as synthons for the assembly of heterobimetallic centers such as the Fe/Mn active site of Class Ic ribonucleotide reductases

Nonheme oxoiron(IV) complexes can serve as synthons for generating heterobimetallic oxo-bridged dimetal complexes by reaction with divalent metal complexes. The formation of FeIII-O-CrIII and FeIII-O-MnIII complexes is described herein. The latter complexes may serve as models for the FeIII-X-MnIII active sites of an emerging class of Fe/Mn enzymes represented by the Class 1c ribonucleotide reductase from Chlamydia trachomatis and the R2-like ligand-binding oxidase (R2lox) found in Mycobacterium tuberculosis. These synthetic complexes have been characterized by UV-Vis, resonance Raman, and X-ray absorption spectroscopy, as well as electrospray mass spectrometry. The FeIII-O-CrIII complexes exhibit a three-band UV-Vis pattern that differs from the simpler features associated with FeIII-O-FeIII complexes. The positions of these features are modulated by the nature of the supporting polydentate ligand on the iron center, and their bands intensify dramatically in two examples upon the binding of an axial cyanate or thiocyanate ligand trans to the oxo bridge. In contrast, the FeIII-O-MnIII complexes resemble FeIII-O-FeIII complexes more closely. Resonance Raman characterization of the FeIII-O-MIII complexes reveals an 18O-sensitive vibration in the range of 760-890 cm-1. This feature has been assigned to the asymmetric FeIII-O-MIII stretching mode and correlates reasonably with the Fe-O bond distance determined by EXAFS analysis. The likely binding of an acetate as a bridging ligand to the FeIII-O-MnIII complex 12 lays the foundation for further efforts to model the heterobimetallic active sites of Fe/Mn enzymes.

Characterization, catalyzed water oxidation and anticancer activities of a NIR BODIPY-Mn polymer

To obtain near-IR absorbing biomaterials as fluorescence cellular imaging and anticancer agents for hypoxic cancer cell, a nano NIR fluorescence Mn(III/IV) polymer (PMnD) was spectroscopically characterized. The PMnD shows strong emission at 661nm when excited with 643nm. Furthermore, PMnD can catalyze water oxidation to generate dioxygen when irradiated by red LED light (10W). In particular, the PMnD can enter into HepG-2 cells and mitochondria. Both anticancer activity and the inhibition of the expression of HIF-1α for PMnD were concentration dependent. Our results demonstrate that PMnD can be developed as mitochondria targeted imaging agents and new inhibitors for HIF-1 in hypoxic cancer cells.

Cefepime, a fourth-generation cephalosporin, in complex with manganese, inhibits proteasome activity and induces the apoptosis of human breast cancer cells

Cefepime (FEP), which is a member of the fourth-generation cephalosporin class, has been extensively studied as a biochemical and antimicrobial reagent in recent years. Manganese (Mn) is important in the biochemical and physiological processes of many living organisms, and it is also high expressed in some tumor tissues. In the present study, we aimed to investigate the proteasome-inhibitory and anti-proliferative properties of 8 metal complexes (FEP‑Cu, FEP-Zn, FEP-Co, FEP-Ni, FEP-Cd, FEP-Cr, FEP-Fe, FEP-Mn) in MDA-MB‑231 human breast cancer cells. The FEP-Mn complex was found to be more potent in its ability to inhibit cell proliferation and proteasome activity than the other compounds tested. Moreover, the FEP-Mn complex inhibited proteasomal chymotrypsin-like (CT-like) activity and induced the apoptosis of breast cancer cells in a dose-and time-dependent manner. Furthermore, the MCF-10A cells were much less sensitive to the FEP complexes compared with the MDA-MB-231 breast cancer cells. These results demonstrated that the FEP-Mn(II) complex has the potential to act as a proteasome inhibitor and apoptosis inducer and therefore has possible future applications in cancer chemotherapy.