Advantageous Reactivity of Unstable Metal Complexes: Potential Applications of Metal-Based Anticancer Drugs for Intratumoral Injections

Approaches to selective and potent inhibition of glioblastoma by vanadyl complexes: Inducing mitotic catastrophe and methuosis

Drug resistance has been a major problem for cancer chemotherapy, especially for glioblastoma multiforme that is aggressive, heterogeneous and recurrent with <3% of a five-year survival and limited methods of clinical treatment. To overcome the problem, great efforts have recently been put in searching for agents inducing death of tumor cells via various non-apoptotic pathways. In the present work, we report for the first time that vanadyl complexes, i.e. bis(acetylacetonato)oxidovanadium (IV) (VO(acac)2), can cause mitotic catastrophe and methuotic death featured by catastrophic macropinocytic vacuole accumulation particularly in glioblastoma cells (GCs). Hence, VO(acac)2 strongly suppressed growth of GCs with both in vitro (IC50 = 4-6 μM) and in vivo models, and is much more potent than the current standard-of-care drug Temozolomide. The selective index is as high as ∼10 or more on GCs over normal neural cells. Importantly, GCs respond well to vanadium treatment regardless whether they are carrying IDH1 wild type gene that causes drug resistance. VO(acac)2 may induce methuosis via the Rac-Mitogen-activated protein kinase kinase 4 (MKK4)-c-Jun N-terminal kinase (JNK) signaling pathway. Furthermore, VO(acac)2-induced methuosis is not through a immunogenicity mechanism, making vanadyl complexes safe for interventional therapy. Overall, our results may encourage development of novel vanadium complexes promising for treatment of neural malignant tumor cells.

One-pot synthesis, structural investigation, antitumor activity and molecular docking approach of two decavanadate compounds

Two bases-decavanadates coordination compounds [(C6H13N4)2][Mg(H2O)6]2[O28V10].6H2O (1) and [(C7H11N2)4][Mg(H2O)6][O28V10].4H2O (2) have been synthesized and well characterized using vibrational spectroscopy (infrared), UV-Visible analysis and single crystal X-ray diffraction technique. The formula unit, for both compounds, is composed by the decavanadate [V10O28]6-, hydrated magnesium ion, a counter anion and free water molecules. The transition metal adopts octahedral geometries in both compound (1) and (2). The existence of a multitude of hydrogen bonding interactions for both compounds provides a stable three-dimensional supramolecular structure. Optical absorption reveals a band gap energy indicating the semi-conductive nature of the compound. In this study, the cytotoxic and the anti-proliferative activities of compounds (1) and (2) on human cancer cells (U87 and MDA-MB-231) were investigated. Both compounds demonstrated dose-dependent anti-proliferative activity on U87 and MDA-MB-231 with respective IC50 values of 0.82 and 0.31 μM and 1.4 and 1.75 μM. These data provide evidence on the potential anticancer activity of [(C6H13N4)2][Mg(H2O)6]2[O28V10].6H2O and [(C7H11N2)4][Mg(H2O)2][O28V10].4H2O. Molecular docking of the compounds was also examined. Molecular docking studies were performed for both compounds against four target receptors and revealed better binding affinity with these targets in comparison to Cisplatin. Moreover, molecular docking investigations suggest that these compounds may function as potential inhibitors of proteins in brain and breast cells, exhibiting greater efficiency compared to Cisplatin.

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.

Vanadium Complexes with Thioanilide Derivatives of Amino Acids: Inhibition of Human Phosphatases and Specificity in Various Cell Models of Metabolic Disturbances

In the text, the synthesis and characteristics of the novel ONS-type vanadium (V) complexes with thioanilide derivatives of amino acids are described. They showed the inhibition of human protein tyrosine phosphatases (PTP1B, LAR, SHP1, and SHP2) in the submicromolar range, as well as the inhibition of non-tyrosine phosphatases (CDC25A and PPA2) similar to bis(maltolato)oxidovanadium(IV) (BMOV). The ONS complexes increased [14C]-deoxy-D-glucose transport into C2C12 myocytes, and one of them, VC070, also enhanced this transport in 3T3-L1 adipocytes. These complexes inhibited gluconeogenesis in hepatocytes HepG2, but none of them decreased lipid accumulation in the non-alcoholic fatty liver disease model using the same cells. Compared to the tested ONO-type vanadium complexes with 5-bromosalicylaldehyde and substituted benzhydrazides as Schiff base ligand components, the ONS complexes revealed stronger inhibition of protein tyrosine phosphatases, but the ONO complexes showed greater activity in the cell models in general. Moreover, the majority of the active complexes from both groups showed better effects than VOSO4 and BMOV. Complexes from both groups activated AKT and ERK signaling pathways in hepatocytes to a comparable extent. One of the ONO complexes, VC068, showed activity in all of the above models, including also glucose utilizatiand ONO Complexes are Inhibitors ofon in the myocytes and glucose transport in insulin-resistant hepatocytes. The discussion section explicates the results within the wider scope of the knowledge about vanadium complexes.

Vanadium(V) Pyridine-Containing Schiff Base Catecholate Complexes are Lipophilic, Redox-Active and Selectively Cytotoxic in Glioblastoma (T98G) Cells

Two new series of complexes with pyridine-containing Schiff bases, [VV O(SALIEP)L] and [VV O(Cl-SALIEP)L] (SALIEP=N-(salicylideneaminato)-2-(2-aminoethylpyridine; Cl-SALIEP=N-(5-chlorosalicylideneaminato)-2-(2-aminoethyl)pyridine, L=catecholato(2-) ligand) have been synthesized. Characterization by 1 H and 51 V NMR and UV-Vis spectroscopies confirmed that: 1) most complexes form two major geometric isomers in solution, and [VV O(SALIEP)(DTB)] (DTB=3,5-di-tert-butylcatecholato(2-)) forms two isomers that equilibrate in solution; and 2) tert-butyl substituents were necessary to stabilize the reduced VIV species (EPR spectroscopy and cyclic voltammetry). The pyridine moiety within the Schiff base ligands significantly changed their chemical properties with unsubstituted catecholate ligands compared with the parent HSHED (N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine) Schiff base complexes. Immediate reduction to VIV occurred for the unsubstituted-catecholato VV complexes on dissolution in DMSO. By contrast, the pyridine moiety within the Schiff base significantly improved the hydrolytic stability of [VV O(SALIEP)(DTB)] compared with [VV O(HSHED)(DTB)]. [VV O(SALIEP)(DTB)] had moderate stability in cell culture media. There was significant cellular uptake of the intact complex by T98G (human glioblastoma) cells and very good anti-proliferative activity (IC50 6.7±0.9 μM, 72 h), which was approximately five times higher than for the non-cancerous human cell line, HFF-1 (IC50 34±10 μM). This made [VV O(SALIEP)(DTB)] a potential drug candidate for the treatment of advanced gliomas by intracranial injection.

Substitution Kinetics, Albumin and Transferrin Affinities, and Hypoxia All Affect the Biological Activities of Anticancer Vanadium(V) Complexes

Limited stability of most transition-metal complexes in biological media has hampered their medicinal applications but also created a potential for novel cancer treatments, such as intratumoral injections of cytotoxic but short-lived anticancer drugs. Two related V(V) complexes, [VO(Hshed)(dtb)] (1) and [VO(Hshed)(cat)] (2), where H2shed = N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine, H2dtb = 3,5-di-tert-butylcatechol, and H2cat = 1,2-catechol, decomposed within minutes in cell culture medium at 310 K (t1/2 = 43 and 9 s for 1 and 2, respectively). Despite this, both complexes showed high antiproliferative activities in triple-negative human breast cancer (MDA-MB-231) cells, but the mechanisms of their activities were radically different. Complex 1 formed noncovalent adducts with human serum albumin, rapidly entered cells via passive diffusion, and was nearly as active in a short-term treatment (IC50 = 1.9 ± 0.2 μM at 30 min) compared with a long-term treatment (IC50 = 1.3 ± 0.2 μM at 72 h). The activity of 1 decreased about 20-fold after its decomposition in cell culture medium for 30 min at 310 K. Complex 2 showed similar activities (IC50 ≈ 12 μM at 72 h) in both fresh and decomposed solutions and was inactive in a short-term treatment. The activity of 2 was mainly due to the reactions among V(V) decomposition products, free catechol, and O2 in cell culture medium. As a result, the activity of 1 was less sensitive than that of 2 to the effects of hypoxic conditions that are characteristic of solid tumors and to the presence of apo-transferrin that acts as a scavenger of V(V/IV) decomposition products in blood serum. In summary, complex 1, but not 2, is a suitable candidate for further development as an anticancer drug delivered via intratumoral injections. These results demonstrate the importance of fine-tuning the ligand properties for the optimization of biological activities of metal complexes.

Antimalarial Agents Derived from Metal-Amodiaquine Complexes with Activity in Multiple Stages of the Plasmodium Life Cycle

Malaria is the one of the deadliest infectious diseases worldwide. Chemically, quinolines are excellent ligands for metal coordination and are deployed as drugs for malaria treatment. There is a growing body of evidence indicating that metal complexes can be conjugated with antimalarial quinolines to be used as chemical tools to overcome the disadvantages of quinolines, improving their bioactive speciation, cellular distribution, and subsequently broadening the spectrum of activity to multiple stages of the complex Plasmodium life cycle. In this study, four novel complexes of ruthenium(II)- and gold(I)-containing amodiaquine (AQ) were synthesized, and a careful chemical characterization revealed the precise coordination site of AQ to the metals. Their speciation in solution was investigated, demonstrating the stability of the quinoline-metal bond. RuII - and AuI -AQ complexes were demonstrated to be potent and efficacious in inhibiting parasite growth in multiple stages of the Plasmodium life cycle as assayed in vitro and in vivo. These properties could be attributed to the ability of the metal-AQ complexes to reproduce the suppression of heme detoxification induced by AQ, while also inhibiting other processes in the parasite life cycle; this can be attributed to the action of the metallic species. Altogether, these findings indicate that metal coordination with antimalarial quinolines is a potential chemical tool for drug design and discovery in malaria and other infectious diseases susceptible to quinoline treatment.

Anti-Migratory and Cytotoxic Activities of [Ga(8-hydroxyquinolinato)3 ]: Roles of Endogenous Cu(II) and Drug-Induced Phenotypic Changes

As shown by IncuCyte Zoom imaging proliferation assays, invasive triple-negative human breast MDA-MB-231 cancer cells treated with sub-toxic doses (5.0-20 μM, 72 h) of [GaQ3 ] (Q=8-hydroxyquinolinato) caused profound morphological changes and inhibition of cell migration, which were likely due to terminal cell differentiation or similar phenotypical change. This is the first demonstration of potential use of a metal complex in differentiation anti-cancer therapy. Additionally, a trace amount of Cu(II) (0.20 μM) added to the medium dramatically increased [GaQ3 ] cytotoxicity (IC50 ~2 μM, 72 h) due to its partial dissociation and the action of the HQ ligand as a Cu(II) ionophore, as shown with electrospray mass spectrometry and fluorescence spectroscopy assays in the medium. Hence, cytotoxicity of [GaQ3 ] is strongly linked to ligand binding of essential metal ions in the medium, for example, Cu(II). Appropriate delivery mechanisms of such complexes and their ligands could enable a powerful new triple therapeutic approach for cancer chemotherapy, including cytotoxicity against primary tumour, arrest of metastases, and activation of innate and adaptive immune responses.

Synthesis and the photophysical and biological properties of tricarbonyl Re(I) diimine complexes bound to thiotetrazolato ligands

Twelve Re(I) tricarbonyl diimine (2,2'-bipyridine and 1,10-phenanthroline) complexes with thiotetrazolato ligands have been synthesised and fully characterised. Structural characterisation revealed the capacity of the tetrazolato ligand to bind to the Re(I) centre through either the S atom or the N atom with crystallography revealing most complexes being bound to the N atom. However, an example where the Re(I) centre is linked via the S atom has been identified. In solution, the complexes exist as an equilibrating mixture of linkage isomers, as suggested by comparison of their NMR spectra at room temperature and 373 K, as well as 2D exchange spectroscopy. The complexes are photoluminescent in fluid solution at room temperature, with emission either at 625 or 640 nm from the metal-to-ligand charge transfer excited states of triplet multiplicity, which seems to be exclusively dependent on the nature of the diimine ligand. The oxygen-sensitive excited state lifetime decay ranges between 12.5 and 27.5 ns for the complexes bound to 2,2'-bipyrdine, or between 130.6 and 155.2 ns for those bound to 1.10-phenanthroline. Quantum yields were measured within 0.4 and 1.5%. The complexes were incubated with human lung (A549), brain (T98g), and breast (MDA-MB-231) cancer cells, as well as with normal human skin fibroblasts (HFF-1), revealing low to moderate cytotoxicity, which for some compounds exceeded that of a standard anti-cancer drug, cisplatin. Low cytotoxicity combined with significant cellular uptake and photoluminescence properties provides potential for their use as cellular imaging agents. Furthermore, the complexes were assessed in disc diffusion and broth microdilution assays against methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Escherichia coli (E. coli), and Pseudomonas aeruginosa (P. aeruginosa) bacterial strains, which revealed negligible antibacterial activity in the dark or after irradiation.

Vanadium Chloro-Substituted Schiff Base Catecholate Complexes are Reducible, Lipophilic, Water Stable, and Have Anticancer Activities

A hydrophobic Schiff base catecholate vanadium complex was recently discovered to have anticancer properties superior to cisplatin and suited for intratumoral administration. This [VO(HSHED)(DTB)] complex, where HSHED is N-(salicylideneaminato)-N'-(2-hydroxyethyl)-1,2-ethanediamine and the non-innocent catecholato ligand is di-t-butylcatecholato (DTB), has higher stability compared to simpler catecholato complexes. Three new chloro-substituted Schiff base complexes of vanadium(V) with substituted catecholates as co-ligands were synthesized for comparison with their non-chlorinated Schiff base vanadium complexes, and their properties were characterized. Up to four geometric isomers for each complex were identified in organic solvents using ⁵¹V and ¹H NMR spectroscopies. Spectroscopy was used to characterize the structure of the major isomer in solution and to demonstrate that the observed isomers are exchanged in solution. All three chloro-substituted Schiff base vanadium(V) complexes with substituted catecholates were also characterized by UV-vis spectroscopy, mass spectrometry, and electrochemistry. Upon testing in human glioblastoma multiforme (T98g) cells as an in vitro model of brain gliomas, the most sterically hindered, hydrophobic, and stable compound [t_1/2 (298 K) = 15 min in cell medium] was better than the two other complexes (IC₅₀ = 4.1 ± 0.5 μM DTB, 34 ± 7 μM 3-MeCat, and 19 ± 2 μM Cat). Furthermore, upon aging, the complexes formed less toxic decomposition products (IC₅₀ = 9 ± 1 μM DTB, 18 ± 3 μM 3-MeCat, and 8.1 ± 0.6 μM Cat). The vanadium complexes with the chloro-substituted Schiff base were more hydrophobic, more hydrolytically stable, more easily reduced compared to their corresponding parent counterparts, and the most sterically hindered complex of this series is only the second non-innocent vanadium Schiff base complex with a potent in vitro anticancer activity that is an order of magnitude more potent than cisplatin under the same conditions.

Do bioactive 8-hydroxyquinolines oxidovanadium(IV) and (V) complexes inhibit the growth of M. smegmatis?

The antiproliferative effects of four series of V^IVO- and V^VO-based compounds containing 8-hydroxyquinoline ligands on the bacterium Mycolicibacterium smegmatis (M. smeg) were investigated. The effects on M. smeg were compared to the antiproliferative effects on the protozoan parasite Trypanosoma cruzi (T. cruzi), the causative agent for Chagas disease. In this study, we investigate the speciation of these compounds under physiological conditions as well as the antiproliferative effects on the bacterium M. smeg. We find that the complexes are more stable the less H₂O is present, and that the stability increases in lipid-like environments. Only one heteroleptic complex and two homoleptic complexes were found to show similar antiproliferative effects on M. smeg as reported for T. cruzi so the responses generally observed by M.smeg. is less than observed by the pathogen. In summary, we find that M. smeg is more sensitive to the detailed structure of the V-complex but overall these complexes are less effective against M. smeg compared to T. cruzi.

Controversial Role of Transferrin in the Transport of Ruthenium Anticancer Drugs

Ruthenium complexes are at the forefront of developments in metal-based anticancer drugs, but many questions remain open regarding their reactivity in biological media, including the role of transferrin (Tf) in their transport and cellular uptake. A well-known anticancer drug, KP1019 ((IndH)[Ru^IIICl₄(Ind)₂], where Ind = indazole) and a reference complex, [Ru^III(nta)₂]^3- (nta = nitrilotriacetato(3-)) interacted differently with human apoTf, monoFeTf, or Fe₂Tf. These reactions were studied by biolayer interferometry (BLI) measurements of Ru-Fe-Tf binding to recombinant human transferrin receptor 1 (TfR1) in conjunction with UV-vis spectroscopy and particle size analysis. Cellular Ru uptake in human hepatoma (HepG2) cells was measured under the conditions of the BLI assays. The mode of Tf binding and cellular Ru uptake were critically dependent on the nature of Ru complex, availability of Fe(III) binding sites of Tf, and the presence of proteins that competed for metal binding, particularly serum albumin. Cellular uptake of KP1019 was not Tf-mediated and occurred mostly by passive diffusion, which may also be suitable for treatments of inoperable cancers by intratumoral injections. High cellular Ru uptake from a combination of [Ru^III(nta)₂]^3- and Fe₂Tf in the absence of significant Ru-Tf binding was likely to be due to trapping of Ru(III) species into the endosome during TfR1-mediated endocytosis of Fe₂Tf.

Dithiocarbazate-copper complex loaded thermosensitive hydrogel for lung cancer therapy via tumor in situ sustained-release

The Pluronic F127 thermosensitive hydrogels containing copper complex 3 were constructed, which could delay A549 tumor xenograft growth effectively with lower systemic toxicity.