Mn(II) Promoted Divergent-Convergent Domino Reaction Giving Dinuclear Tetrasubstituted Pyrrole Complex

Domino reaction of benzo[d]thiazole-2-methylamine (S1) has been developed in the presence of MnCl2 ⋅ 4H2O, leading to tetrasubstituted pyrrole coordinated dinuclear Mn(II) complex 1 ([MnClP]2, P-=2,3,4,5-tetrakis(benzo[d]thiazol-2-yl)pyrrol-1-ide). The reaction process has been studied by assigning a series of intermediates based on time-dependent mass spectrometry, control experiments, crystallography, and density functional theory (DFT) theoretical calculation. A plausible mechanism involving an unprecedented divergent-convergent domino sequence has been proposed. Compound S1 could be activated by MnCl2 ⋅ 4H2O via coordination, which divergently produces two intermediates imine II (1-(benzo[d]thiazol-2-yl)-N-(benzo[d]thiazol-2-ylmethyl)methanimine) and alkene C (1,2-bis(benzo[d]thiazol-2-yl)ethene) through oxidative self-condensation and free radical coupling followed by elimination, respectively. They could then react with each other convergently via formal [3+2] cycloaddition to give deprotonated tetrasubstituted pyrrole coordinated intermediate [MnClP] after aromatization. Dimerization of [MnClP] produces the final product 1. Three C-C bonds and one C-N bond are formed through this six-step domino sequence. The corresponding organic skeleton (HP: 2,2',2'',2'''-(1H-pyrrole-2,3,4,5-tetrayl)tetrakis(benzo[d]thiazole)) has been obtained from 1 and shows a higher fluorescent quantum yield (52 %) than the reported 3,4-diphenyl substituted analogue 2,2'-(3,4-diphenyl-1H-pyrrole-2,5-diyl)bis(benzo[d]thiazole) (DPB) (42 %).

In vivo acute toxicity evaluation and in vitro molecular mechanism study of antiproliferative activity of a novel indole Schiff base β-diiminato manganeseIII complex in hormone-dependent and triple negative breast cancer cells

Breast cancer is the most frequently diagnosed cancer among women worldwide. Recently, increasing attention has been paid to the anticancer effects of transition metal complexes of indole Schiff bases. β-diiminato Manganese^III complex has shown promising cell cycle arrest and apoptosis induction against MCF-7 and MDA-MB-231 breast cancer cells. In this study, time- and dose- dependent inhibitory activity were evaluated using MTT assay after 48 h and 72 h exposure time. In addition, median effect analysis was conducted according to Chou-Talalay method to investigate whether Mn^III complex has synergistic effect in combination with chemotherapeutic drugs on inhibiting breast cancer cell growth. The molecular mechanisms underlying its potent antiproliferative effect was determined through bioluminescent caspase-3/7, -8 and -9 activity assays and quantitative expression analysis of cell cycle- and apoptosis-related genes. Furthermore, safety evaluation of Mn^III complex was assessed through the acute oral toxicity test in in vivo model. The MTT assay results revealed that it potently reduced the viability of MCF-7 (IC₅₀ of 0.63 ± 0.07 µg/mL for 48 h and 0.39 ± 0.08 µg/mL for 72 h) and MDA-MB-231 (1.17 ± 0.06 µg/mL for 48 h, 1.03 ± 0.15 µg/mL for 72 h) cells in dose- and time-dependent manner. Combination treatment also enhanced the cytotoxic effects of doxorubicin but not tamoxifen on inhibiting breast cancer cell growth. The involvement of intrinsic and extrinsic pathway in apoptosis induction was exhibited through the increased activity of caspase-9 and caspase-8, respectively, leading to enhanced downstream executioner caspase-3/7 activity in treated MCF-7 and MDA-MB-231 cells. In addition, gene expression analysis revealed that Mn^III complex exerts its antiproliferative effect via up-and down-regulation of p21 and cyclin D1, respectively, along with increased expression of Bax/Bcl-2 ratio, TNF-α, initiator caspase-8 and -10 and effector caspase-3 in MCF-7 and MDA-MB-231 cells. However, the results did not show increased caspase-8 activity in treated MCF-7 cells. Furthermore, in vivo acute oral toxicity test revealed no signs of toxicity and mortality in treated animal models compared to the control group. Collectively, the promising inhibitory effect and molecular and mechanistic evidence of antiproliferative activity of Mn^III complex and its safety characterization have demonstrated that it may have therapeutic value in breast cancer treatment worthy of further investigation and development.

Intercalation of manganese-mefenamic acid complex into double stranded of calf thymus DNA

The interaction of the [Mn(mef)₂(phen)H₂O] complex in which mef is mefenamic acid drug and phen is 1,10 phenanthrolin ligand with calf thymus DNA (ct-DNA) was studied by using different spectroscopic methods, molecular docking and viscometery. The competitive fluorescence and UV-Vis absorption spectroscopy indicated that the complex interacted with ctDNA via intercalating binding mode with the binding constant of 1.16 × 10⁴ Lmol^-1. The thermodynamic studies showed that the reaction between the complex and ctDNA is exothermic. Furthermore, the complex induced changes in DNA viscosity. Circular dichroism spectroscopy (CD) was employed to measure the conformational changes of ctDNA in the presence of the complex and verified intercalation binding mode. The molecular modeling results illustrated that the complex interacted via intercalation by relative binding energy of -28.45 kJ mol^-1.

Mitochondrial dysfunction is responsible for fatty acid synthase inhibition-induced apoptosis in breast cancer cells by PdpaMn

Targeting cellular metabolism is becoming a hallmark to overcome drug resistance in breast cancer treatment. Activation of fatty acid synthase (FASN) has been shown to promote breast cancer cell growth. However, there is no concrete report underlying the mechanism associated with mitochondrial dysfunction in relation to fatty acid synthase inhibition-induced apoptosis in breast cancer cells. The current study is aimed at exploring the effect of the novel manganese (Mn) complex, labeled as PdpaMn, on lipid metabolism and mitochondrial function in breast cancer cells. Herein, we observed that PdpaMn displayed strong cytotoxicity on breast cancer cell lines and selectively targeted the tumor without affecting the normal organs or cells in vivo. We also observed that PdpaMn could bind to TE domain of FASN and decrease the activity and the level of expression of FASN, which is an indication that FASN could serve as a target of PdpaMn. In addition, we demonstrated that PdpaMn increased intrinsic apoptosis in breast cancer cells relayed by a suppressed the level of expression of FASN, followed by the release of mitochondrial cytochrome c and the activation of caspases-9. Instigated by the above observations, we hypothesized that PdpaMn-induced apoptosis events are dependent on mitochondrial dysfunction. Indeed, we found that mitochondrial membrane potential (MMP) collapse, mitochondrial oxygen consumption reduction and adenosine triphosphate (ATP) release were deeply repressed. Furthermore, our results showed that PdpaMn significantly increased the reactive oxygen species (ROS) production, and the protection conferred by the free radical scavenger N-acetyl-cysteine (NAC) indicates that PdpaMn-induced apoptosis through an oxidative stress-associated mechanism. More so, the above results have demonstrated that mitochondrial dysfunction participated in FASN inhibition-induce apoptosis in breast cancer cells by PdpaMn. Therefore, PdpaMn may be considered as a good candidate for anti-breast cancer therapeutic option.

Distribution of manganese species in an oxidative dimerization reaction of a bis-terpyridine mononuclear manganese (II) complex and their heterogeneous water oxidation activities

Heterogeneous water oxidation catalyses were studied as a synthetic model of oxygen evolving complex (OEC) in photosynthesis using mica adsorbing various manganese species. Distribution of manganese species formed in the oxidative dimerization reaction of [Mn(II)(terpy)2](2+) (terpy=2,2':6',2″-terpyridine) (1') with various oxidants in water was revealed. 1' was stoichiometrically oxidized to form di-μ-oxo dinuclear manganese complex, [(OH2)(terpy)Mn(III)(μ-O)2Mn(IV)(terpy)(OH2)](3+) (1) by KMnO4 as an oxidant. When Oxone and Ce(IV) oxidants were used, the further oxidation of 1 to [(OH2)(terpy)Mn(IV)(μ-O)2Mn(IV)(terpy)(OH2)](4+) (2) was observed after the oxidative dimerization reaction of 1'. The mica adsorbates with various composition of 1', 1 and 2 were prepared by adding mica suspension to the various oxidant-treated solutions followed by filtration. The heterogeneous water oxidation catalysis by the mica adsorbates was examined using a Ce(IV) oxidant. The observed catalytic activity of the mica adsorbates corresponded to a content of 1 (1ads) adsorbed on mica for KMnO4- and Oxone-treated systems, indicating that 1' (1'ads) and 2 (2ads) adsorbed on mica do not work for the catalysis. The kinetic analysis suggested that 1ads works for the catalysis through cooperation with adjacent 1ads or 2ads, meaning that 2ads assists the cooperative catalysis by 1ads though 2ads is not able to work for the catalysis alone. For the Ce(IV)-treated system, O2 evolution was hardly observed although the sufficient amount of 1ads was contained in the mica adsorbates. This was explained by the impeded penetration of Ce(IV) ions (as an oxidant for water oxidation) into mica by Ce(3+) cations (generated in oxidative dimerization of 1') co-adsorbed with 1ads.

Enhanced intra-cutaneous delivery of a Mn-containing antioxidant drug by high-frequency ultrasounds

This study was carried out to evaluate whether high-frequency ultrasounds, a commonly used aesthetic medicine treatment for skin rejuvenation, may enhance the penetration of the Mn-containing compound Mn(II)(Me2DO2A) (manganese(II) 4,10-dimethyl-1,4,7,10-tetraazacyclododecane-1,7-diacetate) biologically active as a superoxide anion scavenger, in the cutaneous layers of ex vivo human skin explants. Although its antioxidant properties are well known and the compound is basically not toxic in animal models, its trans-cutaneous permeation and its toxicological profile at a systemic level have not yet fully analyzed. Therefore, its possible penetration in the deep cutaneous layers was also evaluated. To this purpose, Mn(II)(Me2DO2A) was formulated as emulsion-gel, lipogel and hydrogel. These different formulations were also tested in combination with high-frequency ultrasounds (10-3500 Hz frequency modulation on a 5 MHz main frequency) used as physical permeation enhancers, delivered by a MedVisage™ device (General Project, Montespertoli, Italy) currently used for aesthetic medicine purposes. The permeation of the Mn-containing compound from the formulations was evaluated by inductively coupled plasma atomic emission spectrometry (ICP-AES) measurements of Mn in horizontal cryosections of the skin samples cut at different depths to separate the epidermis, papillary and reticular dermis, as well as by vertical Franz diffusion cells. The results show that the hydrogel formulation yielded the highest transepidermal delivery of Mn(II)(Me2DO2A) and that the application of ultrasounds (3 W, FM 100 Hz, 2×10 s) significantly enhanced its penetration into the epidermis and upper dermal layers. Of note, nearly undetectable amounts of Mn(II)(Me2DO2A) were detected in the reticular dermis and the Franz cell fluid. Although an in vivo confirmation of these results will be necessary, this method may allow to minimize undesired drug passage to the bloodstream and undesired delivery to non-target internal organs and avoiding its renal excretion and release into the environment.

Eight- and six-coordinated Mn(II) complexes of heteroaromatic alcohol and aldehyde: crystal structure, spectral, magnetic, thermal and antibacterial activity studies

Crystal, molecular and electronic structure of new manganese(II) compounds: [Mn(2-CH2OHpy)2(NO3)2] (1), [Mn(4-CHO-5-MeIm)2(NO3)2] (2) and [Mn(4-CHO-5-MeIm)2Cl2] (3), where 2-hydroxymethylpyridine (2-CH2OHpy) and 5(4)-carbaldehyde-4(5)-methylimidazole (5(4)-CHO-4(5)-MeIm), have been characterised using X-ray, spectroscopic, magnetic and TG/DTG data. In compounds 1 and 2, the Mn(II) ion is eight-coordinated forming distorted pseudo-dodecahedron, that is rather unusual for the manganese(II) complexes, whereas in 3 the Mn(II) ion environment is a distorted octahedron. The high coordination number (CN=8) of 1 and 2 results from bidentate character of the nitrate ligands. The X-band EPR spectra of compounds 2 and 3 exhibit fine structure signals resulting from zero-field splitting (ZFS) of the spin states for high spin d(5) Mn(II), whereas for 1 the broad isotropic signals were observed. The estimation of ZFS for individual Mn(II) ions was carried out for all compounds using DFT calculations. The free ligands and their manganese(II) complexes have been tested in vitro against gram-positive and gram-negative bacteria in order to assess their antimicrobial properties.

A novel manganese complex, Mn-(II) N-(2-hydroxy acetophenone) glycinate overcomes multidrug-resistance in cancer

Multidrug resistance (MDR) remains a significant problem for effective cancer chemotherapy. In spite of considerable advances in drug discovery, most of the cancer cases still stay incurable because of resistance to chemotherapy. We synthesized a novel, Mn (II) complex (chelate), viz., manganese N-(2-hydroxy acetophenone) glycinate (MnNG) that exhibits considerable efficacy to overcome drug resistant cancer. The antiproliferative activity of MnNG was studied on doxorubicin resistant and sensitive human T lymphoblastic leukemia cells (CEM/ADR 5000 and CCRF/CEM). MnNG induced apoptosis significantly in CEM/ADR 5000 cells probably through generation of reactive oxygen species. Moreover, intraperitoneal (i.p.) application of MnNG at non-toxic doses caused significant increase in the life-span of Swiss albino mice bearing sensitive and doxorubicin resistant subline of Ehrlich ascites carcinoma cells.