Customized Lanthanide Nanobiohybrids for Noninvasive Precise Phototheranostics of Pulmonary Biofilm Infection.

A noninvasive strategy for in situ diagnosis and precise treatment of bacterial biofilm infections is highly anticipated but still a great challenge. Currently, no in vivo biofilm-targeted theranostic agent is available. Herein, we fabricated intelligent theranostic alginate lyase (Aly)-NaNdF4 nanohybrids with a 220 nm sunflower-like structure (NaNdF4@DMS-Aly) through an enrichment-encapsulating strategy, which exhibited excellent photothermal conversion efficiency and the second near-infrared (NIR-II) luminescence. Benefiting from the site-specific targeting and biofilm-responsive Aly release from NaNdF4@DMS-Aly, we not only enabled noninvasive diagnosis but also realized Aly-photothermal synergistic therapy and real-time evaluation of therapeutic effect in mice models with Pseudomonas aeruginosa biofilm-induced pulmonary infection. Furthermore, such nanobiohybrids with a sheddable siliceous shell are capable of delaying the NaNdF4 dissolution and biodegradation upon accomplishing the therapy, which is highly beneficial for the biosafety of theranostic agents.

Lanthanide complexes facilitate wound healing by promoting fibroblast viability, migration and M2 macrophage polarization.

A tridentate ligand LH3 ((2-hydroxy-3-methoxybenzylidene)-2-(hydroxyimino)propanehydrazide) comprising o-vanillin, hydrazone and oxime donor groups has been employed to prepare a series of tetranuclear Ln(III) complexes. The reaction of ligand LH3 with Ln(NO3)3 [Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er] in MeOH yielded Ln4(LH)6(MeOH)2 (Ln = Sm(1), Eu(2), Gd(3), Tb(4), Ho (6) and Er (7))] whereas the corresponding reaction with Dy(NO3)3 afforded Dy4(LH)4(LH2)2(OH)2 (5). All complexes were characterized by various analytical techniques including single crystal X-ray diffraction, IR spectroscopy, UV-Vis spectroscopy, and elemental analysis. To investigate the potential of these lanthanide complexes for wound healing applications, their effects on fibroblast viability, migration, and M2 macrophage polarization were evaluated. The cytotoxicity assessment revealed that complexes 2(Eu), 4(Tb), 5(Dy), and 7(Er) significantly enhanced fibroblast viability compared to the negative control (NC). In vitro wound healing assay demonstrated that complexes 2(Eu) and 7(Eu) substantially promoted fibroblast migration compared to the NC. Moreover, complex 2(Eu) exhibited significant anti-inflammatory effects by reducing the phagocytic ability of lipopolysaccharide (LPS)-stimulated macrophage cells and attenuating nitric oxide (NO) production. In conclusion, among the series of complexes tested, complex 2(Eu) displayed the most potent anti-inflammatory effect on macrophage cells, while simultaneously promoting fibroblast viability and migration. This unique combination of properties renders complex 2 (Eu) highly promising for wound healing applications.

Lanthanide-Based Organic Salts: Synthesis, Characterization, and Cytotoxicity Studies.

The formulation of magnetic ionic liquids (MILs) or organic salts based on lanthanides as anions has been explored. In this work, a set of choline-family-based salts, and two other, different cation families, were combined with Gadolinium(III) and Terbium(III) anions. Synthetic methodologies were previously optimized, and all organic salts were obtained as solids with melting temperatures higher than 100 °C. The magnetic moments obtained for the Gd(III) salts were, as expected, smaller than those obtained for the Tb(III)-based compounds. The values for Gd(III) and Tb(III) magnetic salts are in the range of 6.55-7.30 MB and 8.22-9.34 MB, respectively. It is important to note a correlation between the magnetic moments obtained for lanthanides, and the structural features of the cation. The cytotoxicity of lanthanide-based salts was also evaluated using 3T3, 293T, Caco2, and HepG2 cells, and it was revealed that most of the prepared compounds are not toxic.

Structures, Antioxidant Properties, and Antimicrobial Properties of Eu(III), Gd(III), and Dy(III) Caffeinates and p-Coumarates.

In this study, we investigated the structures of lanthanide (Eu(III), Dy(III), and Gd(III)) complexes with p-coumaric (p-CAH2) and caffeic (CFAH3) acids using the FTIRKBr, FTIRATR, and Raman spectroscopic methods. The compositions of the solid phase caffeinates and p-coumarates were obtained on the basis of the amounts of hydrogen and carbon determined using an elemental analysis. The degree of hydration and the thermal decomposition of each compound were examined via a thermal analysis of TG, DTG, and DSC. Antioxidant spectroscopic tests were performed using the DPPH (1,1-diphenyl-2-picrylhydrazyl radical), FRAP (ferric reducing antioxidant activity), and ABTS (2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (diammonium salt radical cation) methods. The antimicrobial activity of each compound against Escherichia coli, Bacillus subtilis, and Candida albicans was investigated. The electrical properties of the liposomes which mimicked the microbial surfaces formed in the electrolyte containing the tested compounds were also investigated. The above biological properties of the obtained complexes were compared with the activities of p-CAH2 and CFAH3. The obtained data suggest that lanthanide complexes are much more thermally stable and have higher antimicrobial and antioxidant properties than the ligands (with the exception of CFAH3 in the case of antioxidant activity tests). The Gd(III) complexes revealed the highest biological activity among the studied lanthanide complexes.

Ecotoxicity of non- and PEG-modified lanthanide-doped nanoparticles in aquatic organisms.

Various types of nanoparticles (NPs) have been widely investigated recently and applied in areas such as industry, the energy sector, and medicine, presenting the risk of their release into the environment. The ecotoxicity of NPs depends on several factors such as their shape and surface chemistry. Polyethylene glycol (PEG) is one of the most often used compounds for functionalisation of NP surfaces, and its presence on the surfaces of NPs may affect their ecotoxicity. Therefore, the present study aimed to assess the influence of PEG modification on the toxicity of NPs. As biological model, we chose freshwater microalgae, a macrophyte and invertebrates, which to a considerable extent enable the assessment of the harmfulness of NPs to freshwater biota. SrF2:Yb3+,Er3+ NPs were used to represent the broad group of up-converting NPs, which have been intensively investigated for medical applications. We quantified the effects of the NPs on five freshwater species representing three trophic levels: the green microalgae Raphidocelis subcapitata and Chlorella vulgaris, the macrophyte Lemna minor, the cladoceran Daphnia magna and the cnidarian Hydra viridissima. Overall, H. viridissima was the most sensitive species to NPs, which affected its survival and feeding rate. In this case, PEG-modified NPs were slightly more toxic than bare ones (non-significant results). No effects were observed on the other species exposed to the two NPs at the tested concentrations. The tested NPs were successfully imaged in the body of D. magna using confocal microscopy; both NPs were detected in the D. magna gut. The results obtained reveal that SrF2:Yb3+,Er3+ NPs can be toxic to some aquatic species; however, the structures have low toxicity effects for most of the tested species.

Antileishmanial Activity, Toxicity and Mechanism of Action of Complexes of Sodium Usnate with Lanthanide Ions: Eu(III), Sm(III), Gd(III), Nd(III), La(III) and Tb(III).

Leishmaniases are neglected diseases with limited therapeutic options. Diffuse cutaneous leishmaniasis can occur in Brazil due to Leishmania amazonensis. This study details the antileishmanial activity and cytotoxicity of complexes of sodium usnate (SAU) with lanthanide ions ([LnL3 (H2O)x] (Ln = La(III), Nd(III), Gd(III), Tb(III), Eu(III) and Sm(III); L = SAU). All lanthanide complexes were highly active and more potent than SAU against L. amazonensis promastigotes and intracellular amastigotes (Pro: IC50 < 1.50 µM; Ama: IC50 < 7.52 µM). EuL3·3H2O and NdL3·3H2O were the most selective and effective on intracellular amastigotes, with a selectivity index of approximately 7.0. In silico predictions showed no evidence of mutagenicity, tumorigenicity or irritation for all complexes. Treatment with EuL3·3H2O triggered NO release even at the lowest concentration, indicating NO production as a mechanism of action against the parasite. Incubating promastigotes with the lanthanide complexes, particularly with SmL3·4H2O and GdL3·3H2O, led to a change in the mitochondrial membrane potential, indicating the ability of these complexes to target this essential organelle. The same complexes caused cell death through cell membrane disruption, but their relationship with early or late apoptotic processes remains unclear. Thus, the inclusion of lanthanide ions in SAU improves selectivity with a promising mechanism of action targeting the mitochondria.

NIR light-triggered peroxynitrite anion production via direct lanthanide-triplet photosensitization for enhanced photodynamic therapy.

Peroxynitrite anion (ONOO-), a product derived from reaction between reactive oxygen species (ROS) and nitric oxide (NO), is considered to be a more toxic reactive species than most ROS for cancer photodynamic therapy (PDT). To promote the PDT effect, a viable method is to develop rational strategies for efficient ONOO- generation at targeted tumor sites. Herein, a heterostructure nanocomposite containing ZnO-coated lanthanide nanoparticles (LnNPs) is reported for ONOO--based PDT. In this nanocomposite, Nd3+-doped LnNPs are employed to realize efficient NIR-light-triggered ROS generation by activating the triplet state of chlorin-e6 (Ce6) photosensitizers via a direct lanthanide-to-triplet sensitization mechanism. Meanwhile, ZnO in the composite catalyzes the decomposition of S-nitrosoglutathione (GSNO) to generate NO in the tumor microenvironment. The coupled system allows the combination of photo-induced ROS and NO to produce ONOO-, leading to drastically promoted cancer cell apoptosis and tumor growth inhibition. This study establishes a new apoptosis-inducing PDT agent, which is potentially active in drug resistant malignancies.

Lanthanide (III) complexes of bis-coumarins as strong inhibitors of bovine xanthine oxidase - molecular docking and SAR studies.

The gout disease is spreading worldwide and its drug target is the human xanthine oxidase. Through this work, we investigated the inhibitory effect of the ten lanthanide(III) complexes of biologically active bis-coumarins on xanthine oxidase. We achieved molecular docking studies using GOLD software to study the formed interactions in the enzyme-inhibitor complex. The results confirm the inhibitory effect of the lanthanide complexes showing the best Nd(III) complex with IC50 of 12.91 nM. The docking results confirm this inhibition. We saved nearly the same interactions between the two inhibitors allopurinol and the Nd(III) complex according to the docking results. No further studies have been found in this context. The ADMET analysis show that the three complexes are nontoxic.Communicated by Ramaswamy H. Sarma.

Estimating dynamic vascular perfusion based on Er-based lanthanide nanoprobes with enhanced down-conversion emission beyond 1500 nm.

Peripheral artery disease (PAD) is a common, yet serious, circulatory condition that can increase the risk of amputation, heart attack or stroke. Accurate identification of PAD and dynamic monitoring of the treatment efficacy of PAD in real time are crucial for optimizing therapeutic outcomes. However, current imaging techniques do not enable these requirements. Methods: A lanthanide-based nanoprobe with emission in the second near-infrared window b (NIR-IIb, 1500-1700 nm), Er-DCNPs, was utilized for continuous imaging of dynamic vascular structures and hemodynamic alterations in real time using PAD-related mouse models. The NIR-IIb imaging capability, stability, and biocompatibility of Er-DCNPs were evaluated in vitro and in vivo. Results: Owing to their high temporal-spatial resolution in the NIR-IIb imaging window, Er-DCNPs not only exhibited superior capability in visualizing anatomical and pathophysiological features of the vasculature of mice but also provided dynamic information on blood perfusion for quantitative assessment of blood recovery, thereby achieving the synergistic integration of diagnostic and therapeutic imaging functions, which is very meaningful for the successful management of PAD. Conclusion: Our findings indicate that Er-DCNPs can serve as a promising system to facilitate the diagnosis and treatment of PAD as well as other vasculature-related diseases.

Multifunctional lanthanide metal-organic framework based ratiometric fluorescence visual detection platform for alkaline phosphatase activity.

A turn-on/off ratiometric fluorescence detection platform based on multifunctional lanthanide metal-organic framework (Ln-MOF) and an enzymatic cascade reaction is proposed for alkaline phosphatase (ALP) activity assay. L-phosphotyrosine is hydrolyzed to levodopa (L-dopa) by two steps of enzymatic reaction. L-dopa further reacts with naphthoresorcinol to produce carboxyazamonardine with strong emission at 490 nm. In this process, multifunctional Ln-MOF (Cu@Eu-BTC, BTC is the 1,3,5-benzenetricarboxylic acid) acts not only as a nanozyme to catalyze the fluorogenic reaction between L-dopa and naphthoresorcinol but also as a fluorescence internal standard. The emission of Cu@Eu-BTC at 620 nm is quenched by phosphate anions, and the dual-response ratiometric fluorescence (F490/F620) can be achieved. A good linear relationship was obtained between Δ(F490/F620) and ALP activity in the range 0.3-24 U L-1 with the detection limit of 0.02 U L-1. In addition, a portable assay tube was designed for visual and point-of-care testing of ALP activity by color variation (ratiometric chromaticity). Both the ratiometric fluorescence detection and the visual detection methods were successfully applied to monitor ALP activity in human serum samples with recovery between 95.5%-109.0% and 94.0%-110.1%, and relative standard deviation less than 8.1% and 9.5%, respectively. As far as we know, this is the first report of ALP activity assay assisted by multifunctional Ln-MOF.Graphical abstract.

Low Dose Soft X-Ray Remotely Triggered Lanthanide Nanovaccine for Deep Tissue CO Gas Release and Activation of Systemic Anti-Tumor Immunoresponse.

Gas-based therapy has emerged as a new green therapy strategy for anti-tumor treatment. However, the therapeutic efficacy is still restricted by the deep tissue controlled release, poor lymphocytic infiltration, and inherent immunosuppressive tumor microenvironment (TME). Herein, a new type of nanovaccine is designed by integrating low dose soft X-ray-triggered CO releasing lanthanide scintillator nanoparticles (ScNPs: NaLuF4 :Gd,Tb@NaLuF4 ) with photo-responsive CO releasing moiety (PhotoCORM) for synergistic CO gas/immuno-therapy of tumors. The designed nanovaccine presents significantly boosted radioluminescence and enables deep tissue CO generation at unprecedented tissue depths of 5 cm under soft X-ray irradiation. Intriguingly, CO as a superior immunogenic cell death (ICD) inducer further reverses the deep tissue immunosuppressive TME and concurrently activates adaptive anti-tumor immunity through efficient reactive oxygen species (ROS) generation. More importantly, the designed nanovaccine presents efficient growth inhibition of both local and distant tumors via a soft X-ray activated systemic anti-tumor immunoresponse. This work provides a new strategy of designing anti-tumor nanovaccines for synergistic deep tissue gas-therapy and remote soft X-ray photoactivation of the immune response.

Genome-wide toxicogenomic study of the lanthanides sheds light on the selective toxicity mechanisms associated with critical materials.

Lanthanides are a series of critical elements widely used in multiple industries, such as optoelectronics and healthcare. Although initially considered to be of low toxicity, concerns have emerged during the last few decades over their impact on human health. The toxicological profile of these metals, however, has been incompletely characterized, with most studies to date solely focusing on one or two elements within the group. In the current study, we assessed potential toxicity mechanisms in the lanthanide series using a functional toxicogenomics approach in baker's yeast, which shares many cellular pathways and functions with humans. We screened the homozygous deletion pool of 4,291 Saccharomyces cerevisiae strains with the lanthanides and identified both common and unique functional effects of these metals. Three very different trends were observed within the lanthanide series, where deletions of certain proteins on membranes and organelles had no effect on the cellular response to early lanthanides while inducing yeast sensitivity and resistance to middle and late lanthanides, respectively. Vesicle-mediated transport (primarily endocytosis) was highlighted by both gene ontology and pathway enrichment analyses as one of the main functions disturbed by the majority of the metals. Protein-protein network analysis indicated that yeast response to lanthanides relied on proteins that participate in regulatory paths used for calcium (and other biologically relevant cations), and lanthanide toxicity included disruption of biosynthetic pathways by enzyme inhibition. Last, multiple genes and proteins identified in the network analysis have human orthologs, suggesting that those may also be targeted by lanthanides in humans.

Coordination-Assembled Water-Soluble Anionic Lanthanide Organic Polyhedra for Luminescent Labeling and Magnetic Resonance Imaging.

Lanthanide-containing functional complexes have found a variety of applications in materials science and biomedicine because of their unique electroptical and magnetic properties. However, the poor stability and solubility in water of multicomponent lanthanide organic assemblies significantly limit their practical applications. We report here a series of water-stable anionic Ln2nL3n-type (n = 2, 3, 4, and 5) lanthanide organic polyhedra (LOPs) constructed by deprotonation self-assembly of three fully conjugated ligands (H4L1 and H4L2a/b) featuring a 2,6-pyridine bitetrazolate chelating moiety. The outcomes of the LOPs formation reactions were found to be very sensitive toward the reaction conditions including base, metal source, solvents, and concentrations as characterized by a combination of NMR, high-resolution ESI-MS and X-ray crystallography. Ligands H4L2a/b manifested an excellent sensitization toward lanthanide ions (Ln = EuIII and TbIII), with high luminescent quantum yields for Tb8L2a12 (Φ = 11.2% in water) and Eu8L2b12 (Φ = 76.8% in DMSO) measured in polar solvents. Furthermore, due to the giant molecular weight and rigidity of the polyhedral skeleton, Gd8L2b12 showed a very high longitudinal relaxivity (r1) of 400.53 mM-1S-1. The performance of Gd8L2b12 as potential magnetic resonance imaging contrast agents (CAs) in vivo was evaluated with much longer retention time in the tumor sites compared with the commercial GdIII-based CAs. Dual-modal imaging potential has also been demonstrated with the mixed Eu/Gd LOPs. Our results not only provide a new design route toward water-stable multinuclear lanthanide organic assemblies but also offer potential candidates of supramolecular-edifices for bioimaging and drug delivery.

Photo-physical, theoretical and photo-cytotoxic evaluation of a new class of lanthanide(iii)-curcumin/diketone complexes for PDT application.

Herein we report the synthesis, characterization, photophysical and photocytotoxicity studies of a new class of curcumin-based lanthanide(iii) complexes of general molecular formula [La(1,10-phen)2(L)(NO3)2] (1-4), where L = 1-phenylbutane-1,3-dione (L1, 1), 1-(anthracen-9-yl)butane-1,3-dione (L2, 2), 1-(3a1,5a1-dihydropyren-1-yl)butane-1,3-dione (L3, 3) and curcumin (L4, 4). Complex 1 was characterized by single-crystal X-ray crystallography and it exhibited the N4O6 coordination of La(iii). The presence of the low-lying and long-lived triplet excited state enabled the luminescent complexes (2-4) to generate singlet oxygen (1O2) in high yield when the complex was activated with visible light (400-700 nm, 10 J cm-2), which could be responsible for the photo-ablation of cancer cells. Complexes (2-4) exhibited remarkable photocytotoxicity in HeLa and MCF-7 cells with photocytotoxicity index 4-50 in the presence of visible light (400-700 nm, 10 J cm-2), while they were non-toxic in the dark with an IC50 value of >100 µM. The significantly lower toxicity (IC50 > 100 µM in the dark; IC50 in visible light ∼60 µM) of the complexes in MCF-10A (normal cells) in the dark and in visible light suggested their potential for targeting anticancer activity. Further studies showed that complex 4 induced caspase-dependent apoptosis through mitochondrial damage, mitochondrial respiration inhibition and reactive oxygen species (ROS) elevation. The cytosolic localization of complex 4 in HeLa cells, having a curcumin moiety as a fluorophore, was proved from the confocal microscopic studies. The photocytotoxicity of the complexes (1-4) was directly correlated to the efficacy of the complexes to generate singlet oxygen, which resulted in the photocytotoxicity order of 4 > 3>2 ≫ 1. Photo-physical studies revealed that the chelation of curcumin by La(iii) facilitated intersystem crossing in curcumin by reducing the energy gap of the singlet to triplet excited state. Therefore, the presence of low-lying and long-lived triplet excited state was responsible for increasing the generation of singlet oxygen and, thereby, photo-cytotoxicity in HeLa and MCF-7 cells. The present study has given an overall (Chemistry to Biology) perspective on the effect of La(iii) on the photo-cytotoxicity of selected photo-active curcumin-based ß-diketonate ligands.

Luminescence imaging-guided triple-collaboratively enhanced photodynamic therapy by bioresponsive lanthanide-based nanomedicine.

Photodynamic therapy (PDT) provides a novel sight for non-invasive tumor ablation, which, however, is still limited by low converting efficiency and short life-time of produced singlet oxygen. In this work, a bioresponsive lanthanide-based nanomedicine, FeOOH-coated and toluidine blue (TB)-loaded NaLuF4:Yb,Er,Tm@NaLuF4, is constructed for tumor microenvironment-activated photodynamic therapy with triple-collaborative enhancing strategy. In response to intratumoral reducibility and acidity, coated FeOOH decomposes, eliminating reduced glutathione (GSH) and up-regulating intratumoral oxidative stress to enhance PDT. Besides, Fe2+ is also released from this redox process, which can improve intratumoral dissolved O2 for PDT by catalytic decomposition of H2O2. Lastly, quenched upconversion luminescence of lanthanide-doped nanoparticles also recovers, which allows more efficient energy transfer to TB and hence improves PDT efficiency. By the above triple-collaborative strategy, highly efficient photodynamic tumor ablation is performed in vivo. This work proposes a rigorous method to elevate photodynamic therapeutic efficiency.

Surface Modification of Luminescent LnIII Fluoride Core-Shell Nanoparticles with Acetylsalicylic acid (Aspirin): Synthesis, Spectroscopic and in Vitro Hemocompatibility Studies.

Luminescent lanthanide fluoride core-shell (LaF3 :Tb3+ ,Ce3+ @SiO2 -NH2 ) nanoparticles, with acetylsalicylic acid (aspirin) coated on the surface have been obtained. The synthesized products, which combine the potential located in the silica shell with the luminescent activity of the core, were characterized in detail with the use of luminescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and transmission electron microscopy (TEM) methods. The in vitro effects of the modified luminescent nanoparticles on human red blood cell (RBC) membrane permeability, RBC shape, and sedimentation rate were investigated to assess the hemocompatibility of the obtained compounds. This study demonstrates that LaF3 : Tb3+ 5 %, Ce3+ 10 %@SiO2 -NH2 nanoparticles with acetylsalicylic acid (aspirin) coated on the surface are very good precursors for multifunctional drug-delivery systems or bio-imaging probes that can be used safely in potential biomedical applications.

Degradable pH-responsive NIR-II imaging probes based on a polymer-lanthanide composite for chemotherapy.

In this research, a pH-sensitive degradable nanoprobe was designed by combining hydrophobic rare earth nanoparticles with biocompatible mPEG-PLGA nanomicelles for near infrared II (NIR-II) imaging-guided anti-tumor chemotherapy. The as-synthesized nanoprobes (about 300 nm) with a highly enhanced permeability and retention (EPR) effect show great potential in the diagnosis of solid tumors, providing new prospects for clinical tumor diagnosis. Then, the degradable composite probes increase the imaging sensitivity of the probe and allow for the slow release of the internal anti-tumor drugs, reducing the loss of the drug during delivery. Finally, ultra-small rare earth nanoparticles (about 6 nm) can be excreted after hydrolysis of the composite probe to reduce the enrichment of the inorganic nanoparticles in vivo. Thus, this degradable NIR-II imaging probe based on a polymer-lanthanide composite could be a promising candidate for preclinical cancer chemotherapy and surgery navigation under a single 808 nm laser.

How Lanthanide Ions Affect the Addition-Elimination Step of Methanol Dehydrogenases.

The recently discovered methanol dehydrogenase, XoxF, is a widespread enzyme used by methylotrophic bacteria to oxidize methanol for carbon and energy, and requires lanthanide ions for its activity. This enzyme represents an essential component of methanol utilization by both methanol- and methane-utilizing bacteria. The present investigation looks on the electronic, energetic and geometrical behavior of the methanol dehydrogenase from Methylacidiphilum fumariolicum SolV, which is strictly dependent on early lanthanide metals with +3 oxidation states, by examining enzyme-substrate complexes of all the lanthanides. We focus on the catalytic reaction mechanism of two methanol dehydrogenases having as cofactor europium and ytterbium belonging to the mid- and later- series of lanthanides, in comparison with the methanol dehydrogenase containing the cerium, one early lanthanide. Our results provide evidence for the influence of the lanthanide contraction effect in all the elementary steps of the catalytic reaction mechanism. This indication may prove useful for developing new catalytic machineries of enzymes that adopt new-to-nature transformations.

Lanthanide-dependent alcohol dehydrogenases require an essential aspartate residue for metal coordination and enzymatic function.

The lanthanide elements (Ln3+), those with atomic numbers 57-63 (excluding promethium, Pm3+), form a cofactor complex with pyrroloquinoline quinone (PQQ) in bacterial XoxF methanol dehydrogenases (MDHs) and ExaF ethanol dehydrogenases (EDHs), expanding the range of biological elements and opening novel areas of metabolism and ecology. Other MDHs, known as MxaFIs, are related in sequence and structure to these proteins, yet they instead possess a Ca2+-PQQ cofactor. An important missing piece of the Ln3+ puzzle is defining what features distinguish enzymes that use Ln3+-PQQ cofactors from those that do not. Here, using XoxF1 MDH from the model methylotrophic bacterium Methylorubrum extorquens AM1, we investigated the functional importance of a proposed lanthanide-coordinating aspartate residue. We report two crystal structures of XoxF1, one with and another without PQQ, both with La3+ bound in the active-site region and coordinated by Asp320 Using constructs to produce either recombinant XoxF1 or its D320A variant, we show that Asp320 is needed for in vivo catalytic function, in vitro activity, and La3+ coordination. XoxF1 and XoxF1 D320A, when produced in the absence of La3+, coordinated Ca2+ but exhibited little or no catalytic activity. We also generated the parallel substitution in ExaF to produce ExaF D319S and found that this variant loses the capacity for efficient ethanol oxidation with La3+ These results provide evidence that a Ln3+-coordinating aspartate is essential for the enzymatic functions of XoxF MDHs and ExaF EDHs, supporting the notion that sequences of these enzymes, and the genes that encode them, are markers for Ln3+ metabolism.

Mitochondria-localizing dicarbohydrazide Ln complexes and their mechanism of in vitro anticancer activity.

In this study, two novel organic ligands, bis(salicylaldehyde)pyrazino-1,10-phenanthroline-7,10-dicarbohydrazide (L) and bis(salicylaldehyde)-1,10-phenanthroline-7,10-dicarbohydrazide (L1), were synthesized. These ligands were used to react with lanthanide(iii) acetate to obtain complexes 1-6, namely, [Dy5(L)2(CH3COO)5(CH3OH)(µ3-OH)(µ2-OH)(H2O)]·2CH3OH (1), [Tb5(L)2(CH3COO)5(CH3OH)(µ3-OH)(µ2-OH)(H2O)]·3CH3OH (2), [Gd5(L)2(CH3COO)5(CH3OH)(µ3-OH)(µ2-OH)(H2O)]·3CH3OH (3), [Dy5(L1)2(µ2-OH)(µ3-OH)(CH3COO)5(CH3OH)(H2O)2]·2H2O (4), [Dy5(L1)2(µ3-OH)(CH3COO)6(CH3OH)3]·CH3OH (5), and [Dy5(L1)2(µ2-OH)2(µ3-OH)(CH3COO)4(CH3OH)(H2O)2]·CH3OH (6). Fluorescence studies demonstrated that complexes 1-6 show appreciable fluorescence in the yellow-green region. In vitro antitumor screening revealed that complex 1 exhibits better inhibitory activities than the commercial anticancer drug cisplatin against SK-OV-3 and A549 tumor cell lines, with IC50 values of 8.09 ± 1.25 and 13.26 ± 0.39 µM, respectively. All six complexes showed low cytotoxicity toward normal human liver HL-7702 cells compared with cisplatin. Complexes 1 and 3 induced the highest apoptosis rate of SK-OV-3/DDP cells. They also bind to DNA via an intercalative mode with the binding constant Kq values of 1.6 × 104 and 1.19 × 104 L mol-1, respectively. Confocal fluorescence imaging ascertained that complexes 1 and 3 are primarily localized in the mitochondria. Further studies revealed that these complexes trigger SK-OV-3/DDP cell apoptosis via a mitochondrial dysfunction pathway, which is probably caused by the reduction of the mitochondrial membrane potential and the induction of reactive oxygen species production.