Bioreductive activation and drug chaperoning in cobalt pharmaceuticals

Exploiting Co(III)-Cyclopentadienyl Complexes To Develop Anticancer Agents

In recent years, organometallic complexes have attracted much attention as anticancer therapeutics aiming at overcoming the limitations of platinum drugs that are currently marketed. Still, the development of half-sandwich organometallic cobalt complexes remains scarcely explored. Four new cobalt(III)-cyclopentadienyl complexes containing N,N-heteroaromatic bidentate, and phosphane ligands were synthesized and fully characterized by elemental analysis, spectroscopic techniques, and DFT methods. The cytotoxicity of all complexes was determined in vitro by the MTS assay in colorectal (HCT116), ovarian (A2780), and breast (MDA-MB-231 and MCF-7) human cancer cell lines and in a healthy human cell line (fibroblasts). The complexes showed high cytotoxicity in cancer cell lines, mostly due to ROS production, apoptosis, autophagy induction, and disruption of the mitochondrial membrane. Also, these complexes were shown to be nontoxic in vivo in an ex ovo chick embryo yolk sac membrane (YSM) assay.

Synthesis, characterization, and cancer cell-selective cytotoxicity of mixed-ligand cobalt(III) complexes of 8-hydroxyquinolines and phenanthroline bases

Transition metal complexes exhibiting selective toxicity towards a broad range of cancer types are highly desirable as potential anticancer agents. Herein, we report the synthesis, characterization, and cytotoxicity studies of six new mixed-ligand cobalt(III) complexes of general formula [Co(B)2(L)](ClO4)2 (1-6), where B is a N,N-donor phenanthroline base, namely, 1,10-phenanthroline (phen in 1, 2), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 3, 4), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 5, 6), and L is the monoanion of 8-hydroxyquinoline (HQ in 1, 3, 5) and 5-chloro-7-iodo-8-hydroxyquinoline (CQ in 2, 4, 6). The X-ray single crystal structures of complexes 1 and 2 as PF6- salts revealed a distorted octahedral CoN5O coordination environment. Complexes demonstrated good stability in an aqueous buffer medium and in the presence of ascorbic acid as a reductant. Cytotoxicity studies using a panel of nine cancer cell lines showed that complex 6, with the dppz and CQ ligands, was significantly toxic against most cancer cell types, yielding IC50 values in the range of 2 to 14 μM. Complexes 1, 3, and 5, containing the HQ ligand, displayed lower toxicity compared to their CQ counterparts. The phenanthroline complexes demonstrated marginal toxicity towards the tested cell lines, while the dpq complexes exhibited moderate toxicity. Interestingly, all complexes demonstrated negligible toxicity towards normal HEK-293 kidney cells (IC50 > 100 μM). The observed cytotoxicity of the complexes correlated well with their lipophilicities (dppz > dpq > phen). The cytotoxicity of complex 6 was comparable to that of the clinical drug cisplatin under similar conditions. Notably, neither the HQ nor the CQ ligands alone demonstrated noticeable toxicity against any of the tested cell lines. The Annexin-V-FITC and DCFDA assays revealed that the cell death mechanism induced by the complexes involved apoptosis, which could be attributed to the metal-assisted generation of reactive oxygen species. Overall, the dppz complex 6, with its remarkable cytotoxicity against a broad range of cancer cells and negligible toxicity toward normal cells, holds significant potential for cancer chemotherapeutic applications.

A Comparison of In Vitro Studies between Cobalt(III) and Copper(II) Complexes with Thiosemicarbazone Ligands to Treat Triple Negative Breast Cancer

Metal complexes have gained significant attention as potential anti-cancer agents. The anti-cancer activity of [Co(phen)2(MeATSC)](NO3)3•1.5H2O•C2H5OH 1 (where phen = 1,10-phenanthroline and MeATSC = 9-anthraldehyde-N(4)-methylthiosemicarbazone) and [Cu(acetylethTSC)Cl]Cl•0.25C2H5OH 2 (where acetylethTSC = (E)-N-ethyl-2-[1-(thiazol-2-yl)ethylidene]hydrazinecarbothioamide) was investigated by analyzing DNA cleavage activity. The cytotoxic effect was analyzed using CCK-8 viability assay. The activities of caspase 3/7, 9, and 1, reactive oxygen species (ROS) production, cell cycle arrest, and mitochondrial function were further analyzed to study the cell death mechanisms. Complex 2 induced a significant increase in nicked DNA. The IC50 values of complex 1 were 17.59 μM and 61.26 μM in cancer and non-cancer cells, respectively. The IC50 values of complex 2 were 5.63 and 12.19 μM for cancer and non-cancer cells, respectively. Complex 1 induced an increase in ROS levels, mitochondrial dysfunction, and activated caspases 3/7, 9, and 1, which indicated the induction of intrinsic apoptotic pathway and pyroptosis. Complex 2 induced cell cycle arrest in the S phase, ROS generation, and caspase 3/7 activation. Thus, complex 1 induced cell death in the breast cancer cell line via activation of oxidative stress which induced apoptosis and pyroptosis while complex 2 induced cell cycle arrest through the induction of DNA cleavage.

A Breast Cancer Stem Active Cobalt(III)-Cyclam Complex Containing Flufenamic Acid with Immunogenic Potential

The cytotoxic and immunogenic-activating properties of a cobalt(III)-cyclam complex bearing the non-steroidal anti-inflammatory drug, flufenamic acid is reported within the context of anti-cancer stem cell (CSC) drug discovery. The cobalt(III)-cyclam complex 1 displays sub-micromolar potency towards breast CSCs grown in monolayers, 24-fold and 31-fold greater than salinomycin (an established anti-breast CSC agent) and cisplatin (an anticancer metallopharmaceutical), respectively. Strikingly, the cobalt(III)-cyclam complex 1 is 69-fold and 50-fold more potent than salinomycin and cisplatin towards three-dimensionally cultured breast CSC mammospheres. Mechanistic studies reveal that 1 induces DNA damage, inhibits cyclooxygenase-2 expression, and prompts caspase-dependent apoptosis. Breast CSCs treated with 1 exhibit damage-associated molecular patterns characteristic of immunogenic cell death and are phagocytosed by macrophages. As far as we are aware, 1 is the first cobalt complex of any oxidation state or geometry to display both cytotoxic and immunogenic-activating effects on breast CSCs.

Study of novel bidentate heterocyclic amine-based metal complexes and their biological activities: cytotoxicity and antimicrobial activity evaluation

Metallic antitumor drugs with heterocyclic ligands, such as novel AMI (amino methyl imidazole) complexes [Pd(AMI)Cl₂](1), [Cu(AMI)L¹](2), and [Cu(AMI)L²·2H₂O](3) where L¹ = oxalate and L² = malonate, were synthesized and characterized. Assessments included elemental analyses, mass spectrometry, Fourier transform-infrared spectroscopy, ultraviolet-visible spectroscopy, and thermal analysis. The cytotoxicity of AMI complexes compared to cisplatin was assessed using MTT (3-[4,5-dimethylthiazol-2-yl] 2,5diphenyl tetrazolium bromide) assay with breast (MCF-7) and cervical (HeLa) cancer cell lines. After treating these cells with the AMI complexes' IC₅₀ values for 48 h, malondialdehyde levels and catalase activity were used to assess oxidative stress, antioxidant activity was evaluated with DPPH radical scavenging method, comet assays assessed DNA damage, and DNA fragmentation was evaluated using the gel electrophoresis. In vitro, antimicrobial activity was assessed using a disc diffusion method. The anticancer activity results showed that IC₅₀ (half-maximal inhibitory concentration) values of complex one, two, and three against MCF-7 and HeLa cancer cells are 0.156 ± 0.0006, 0.125 ± 0.001, 0.277 ± 0.002 μM respectively for MCF-7 cells and 0.222 ± 0.0005, 0.126 ± 0.0009, 0.152 ± 0.001 μM respectively for HeLa cells. Complex two demonstrated strong anticancer activity against MCF-7 and Hela cells. The study of oxidative stress parameters revealed that Malondialdehyde levels increased in cancer cell lines treated with complexes compared to untreated cells. Catalase activity decreased in cells treated with palladium chelate. The DPPH radical scavenging assay results identified that complex one was a more potent antioxidant in MCF-7 and Hela cells than other complexes with SC₅₀ values of 227.5 ± 0.28 and 361 ± 1.2 μL/mL, respectively. The comet assay results showed that complex two caused significant DNA damage in MCF-7 and HeLa cancer cells treated. Antimicrobial assays identified complex three as the most effective. Copper complexes give better antifungal activity against A. flavus than the palladium complex. We conclude that complex two is the most active in both cell types and might be assessed as a clinically useful drug for breast cancer treatment. The significance of the current study is the synthesis of antitumor drugs containing heterocyclic ligands, such as novel AMI complexes, and the study of their biological activities.

Trivalent Cobalt Complexes with NNS Tridentate Thiosemicarbazones: Preparation, Structural Study and Investigation of Antibacterial Activity and Cytotoxicity against Human Breast Cancer Cells

New complexes of trivalent cobalt with substituted thiosemicarbazone ligands having an NNS donor system {HL1 = 4-(4-nitrophenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide and HL2 = 4-(2,5-dimethoxyphenyl)-1-((pyridin-2-yl)methylene)thiosemicarbazide} were synthesized via the in situ oxidation of divalent cobalt chloride accompanying its addition to the ligands. The complexes C1 and C2 were characterized via elemental (CHNS) analysis and 1H NMR, FT-IR and UV-Vis. spectroscopic data. Further, conductometric studies on the DMF solutions of the complexes indicated their 1:1 nature, and their diamagnetism revealed the low-spin trivalent oxidation state of the cobalt in the complexes. The X-ray diffraction analysis of complex C1 indicated that it crystallizes in the triclinic space group P-1. The metal exhibits an octahedral environment built by two anionic ligands bound via pyridine nitrogen, imine nitrogen and thiol sulfur atoms. The complex is counterbalanced by a chloride ion. In addition, two lattice water molecules were detected in the asymmetric unit of the unit cell. The ligand HL2 (20 mg/mL in DMSO) displayed inhibition zones of 10 mm against both S. aureus and E. coli, and the same concentration of the respective complex raised this activity to 15 and 12 mm against these bacterial strains, respectively. As a comparison, ampicillin inhibited these bacterial strains by 21 and 25 mm, respectively. Screening assay by HL1 on four human cancer cells revealed the most enhanced activity against the breast MCF-7 cells. The induced growth inhibitions in the MCF-7 cells by all compounds (0–100 μg/mL) have been detected. The ligands {HL1 and HL2} and complex C2 gave inhibitions with IC50 values of 52.4, 145.4 and 49.9 μM, respectively. These results are more meaningful in comparison with similar cobalt complexes, but less efficient compared with the inhibition with IC50 of 9.66 μM afforded by doxorubicin. In addition, doxorubicin, HL1 and HL2 induced cytotoxicity towards healthy BHK cells with IC50 values of 36.42, 54.8 and 110.6 μM, but surviving fractions of 66.1% and 62.7% of these cells were detected corresponding to a concentration of 100 μg/mL of the complexes (136.8 μM of C1 and 131.4 μM of C2).

Cobalt(III) Complexes for Light-Activated Delivery of Acetylacetonate-BODIPY, Cellular Imaging, and Photodynamic Therapy

Cobalt(III) complexes [Co(TPA)(L¹)](ClO₄)₂ (1), [Co(4-COOH-TPA)(L¹)](ClO₄)₂ (2), [Co(TPA)(L²)]Cl₂ (3), and [Co(4-COOH-TPA)(L²)]Cl₂ (4) having acetylacetonate-linked boron-dipyrromethene ligands (L¹, acac-BODIPY; L², acac-diiodo-BODIPY) were prepared and characterized, and their utility as bioimaging and phototherapeutic agents was evaluated (TPA, tris-(2-pyridylmethyl)amine; 4-COOH-TPA, 2-((bis-(2-pyridylmethyl)amino)methyl)isonicotinic acid). HL¹, HL², and complex 1 were structurally characterized by X-ray crystallography. Complexes 1 and 2 on photoactivation or in a reducing environment (excess GSH, ascorbic acid, and 3-mercaptopropionic acid) released the acac-BODIPY ligand. They exhibited strong absorbance near 501 nm (ε ∼ (5.2-5.8) × 10⁴ M^-1 cm^-1) and emission bands near 513 nm (Φ_F ∼ 0.13, λ_ex = 490 nm) in dimethyl sulfoxide (DMSO). Complexes 3 and 4 with absorption maxima at ∼536 and ∼538 nm (ε ∼ (1.2-1.8) × 10⁴ M^-1 cm^-1), respectively, afforded high singlet oxygen quantum yield (Φ_Δ ∼ 0.79) in DMSO. Complexes 1-4 showed Co(III)-Co(II) redox responses near -0.2 V versus saturated calomel electrode (SCE) in dimethylformamide (DMF)-0.1 M tetrabutylammonium perchlorate (TBAP). The photocleavage of pUC19 DNA by complex 4 revealed the formation of both singlet oxygen and superoxide anion radicals as the reactive oxygen species (ROS). Confocal fluorescence microscopy showed the selective accumulation of complex 1 in the endoplasmic reticulum (ER) in A-549 cells. Complex 4 exhibited a high phototherapeutic index value (PI > 7000) in HeLa cancer cells (IC₅₀ ∼ 0.007 μM in visible light of 400-700 nm, total dose ∼5 J cm^-2). The ancillary ligands in the complexes demonstrated a structure-activity relationship and modulated the Co(III)-Co(II) redox potential, the complex solubility, acac-BODIPY ligand release kinetics, and phototherapeutic efficacy.

Dithiocarbazate-FeIII, -CoIII, -NiII, and -ZnII Complexes: Design, Synthesis, Structure, and Anticancer Evaluation

Non-platinum-metal complexes show great potential as anticancer agents. Herein, a series of dithiocarbazate non-Pt-metal complexes, including [Fe^III(L)₂]·Cl·2H₂O 1, [Co^III(L)₂]·NO₃·2.5H₂O 2, [Ni^II(L)₂] 3, and [Zn^II(L)₂] 4, have been designed and evaluated for their efficacy as antineoplastic agents. Among them, complex 2 exhibited higher anticancer efficacy than complexes 1, 3, 4, and cisplatin against several cancer cell lines. Hemolysis assays revealed that complex 2 showed comparable hemolysis with cisplatin. In vivo anticancer evaluations showed that complex 2 could retard tumor xenograft growth effectively with low systemic toxicity. Further studies revealed that complex 2 suppressed cancer cells by triggering multiple mechanisms involving the simultaneous inhibition of mitochondria and glycolytic bioenergetics. Overall, our study provides new insights into the anticancer mechanism of Co complexes, which can be used as a good strategy to overcome the flexibility of cancer cells to chemotherapy adaptation.

Co(II) coordination polymer: Treatment activity on the chronic obstructive pulmonary disease by reducing the inflammatory cytokines releasing

In the current study, using a semi-flexible quadritopic N-donor ligand, 5,5′-bipyrimidine (bpym), a new azide-based coordination polymer, [Co(bpym)(N3)2]n (1), was synthesized and structurally characterized via the single crystal X-ray diffraction along with the elemental analysis. Its treatment activity on the chronic obstructive pulmonary disease (COPD) would be evaluated and the related mechanism was explored. Firstly, the ELISA (enzyme linked immunosorbent assay) detection assay was performed and the levels of the inflammatory cytokines were measured. In addition to this, the NF-κB signaling pathway activation in the lung epithelial cells was measured with the real time RT-PCR (reverse transcription-polymerase chain reaction). Both six-membered rings containing nitrogen and the azide group on the designed drug molecule were confirmed by molecular docking simulation to have activities to the NF-kappaB.

Investigation of cobalt(III)-phenylalanine complexes for hypoxia-activated drug delivery

Four cobalt(iii)-phenylalanine complexes, [Co(Phe)(py2en)](ClO4)2·H2O (1), [Co(Phe)(TPA)](ClO4)2·H2O (2), [Co(Phe)(py2enMe2)](ClO4)2·H2O (3) and [Co(bipy)2(Phe)](ClO4)2·H2O (4), were investigated as prototype models for hypoxia-activated delivery of melphalan - a phenylalanine derivative anticancer drug of the class of nitrogen mustards. Single crystal X-ray diffraction analysis provided the molecular structures of 1-4, as a single isomer/conformer. According with NMR and theoretical calculations, the solid-state structures of 2 and 4 are maintained in solutions. For complexes 1 and 3, though, a mixture of isomers was found in DMSO solutions: Λ-cisα(exo,exo) and Δ-cisβ1(exo,exo) for 1 (3 : 2 ratio), and Λ-cisα(exo,exo) and Δ-cisα(exo,exo) for 3 (5 : 1 ratio). Theoretical calculations point to a re-equilibration reaction of the solid-state Λ-cisβ1 isomer of 1 in solution. Electrochemical analysis revealed a correlation between the electron-donor capacity of the ancillary ligands and the redox potentials of the complexes. The potentials varied from +0.01 for 1 to +0.31 V vs. SHE for 4 in aqueous media and indicate that reduction should be achieved in biological media. The integrity of the complexes in pH 5.5 and 7.4 buffered solutions was confirmed by UV-Vis monitoring up to 24 h at 25 °C. Reduction by ascorbic acid (AA) shows an O2-dependent dissociation of the l-Phe for complexes 1-3, with higher conversion rates at pH 7.4. For complex 4, a fast dissociation of l-Phe was observed, with conversion rates unaffected by the pH and presence of O2.

Deciphering the effect of hydrophobicity on protein binding interaction in cobalt(II) complexes by multispectroscopic and computational methods

In the present work, we report the synthesis, characterization of two cobalt complexes (1 and 2) and their HSA binding studies by multispectroscopic methods. Hirshfeld surfaces analysis and fingerprint plot analysis were carried out to identify intermolecular interactions viz., N-H···O, O-H···O and C-H···O linkages in crystal framework of the complexes. Density functional theory (DFT) studies were carried out to ascertain the electronic structure and molecular geometry of the complexes 1 and 2, and determine the localization of HOMO and LUMO in the complexes. A comparative in vitro interaction study of complex 1 and 2 with human serum albumin protein was carried out by employing UV-vis, fluorescence, circular dichroism, FTIR and molecular docking techniques. Interestingly, the HSA binding affinity of complex 2 was found to be more than complex 1 which was evidenced from the higher binding constant values owing to its strong hydrophobic topology. Further, a significant conformational change in microenvironment of HSA was noticed upon binding with complexes 1 and 2, nevertheless more perturbations were noticed in presence of complex 1. Molecular docking studies were carried out to validate the spectroscopic results and ascertain the preferential binding mode of complexes at the specific target site of HSA.Communicated by Ramaswamy H. Sarma.

Warburg Effect Targeting Co(III) Cytotoxin Chaperone Complexes

A glucose-based vector for targeting cancer cells conjugated to a tris(methylpyridyl)amine (tpa) ligand to generate targeted chaperone and caging complexes for active anticancer agents is described. The ligand, tpa(CONHPEGglucose)₁, inhibits hexokinase, suggesting that it will be phosphorylated in the cell. A Co(III) complex incorporating this ligand and coumarin-343 hydroximate (C343ha), [Co(C343ha){tpa(CONHPEGglucose)₁}]Cl, is shown to exhibit glucose-dependent cellular accumulation in DLD-1 colon cancer cells. Cellular accumulation of [Co(C343ha){tpa(CONHPEGglucose)₁}]⁺ is slower than for the glucose null and glucosamine analogues, and the glucose complex also exhibits a lower ability to inhibit antiproliferative activity. Distributions of cobalt (X-ray fluorescence) and C343ha (visible light fluorescence) in DLD-1 cancer cell spheroids are consistent with uptake of [Co(C343ha){tpa(CONHPEGglucose)₁}]⁺ by rapidly dividing cells, followed by release and efflux of C343ha and trapping of the Co{tpa(CONHPEGglucose)₁} moiety. The Co{tpa(CONHPEGglucose)₁} moiety is shown to have potential for the caged and targeted delivery of highly toxic anticancer agents.

Synthesis, characterization and cytotoxicity studies of Co(III)-flavonolato complexes

Hypoxia activated Co(III) complexes as prodrugs may provide with a selective delivery of cytotoxic or antibacterial compounds. Whithin this field sixteen novel Co(III) ternary complexes with the general formula [Co(4N)(flav)](ClO₄)₂, where 4N = tris(2-aminoethyl)amine (tren) or tris(2-pyridylmethyl)amine (tpa) and flav = deprotonated form of differently substituted flavonols have been synthesized, characterized, and their cytotoxicity assayed under both normoxic and hypoxic conditions. Molecular structures of two free flavonols and seven complexes are also reported. In all the complexes the bioligands exhibited the expected (O,O) coordination mode and the complexes showed a slightly distorted octahedral geometry. Cyclic voltammetric studies revealed that both the substituents of the flavonoles and the type of 4N donor ligands had an impact on the reduction potential of the complex. The ones containing tren demonstrated significantly higher stability than the tpa analogues, making these former compounds promising candidates for the development of hypoxia-activated prodrug complexes. Tpa complexes showed higher activity against both selected human cancer cell lines (A549, A431) than their free ligand flavonols, indicating that the anticancer activity of the bioligand can be enhanced upon complexation. However, slight hypoxia-selectivity was found only for a tren complex (11) with moderate cytotoxicity.

Effect of the replacement of tripodal 4N donors by two 2N chelators on the redox and cytotoxic activity of maltolato and deferipronato containing Co(III) complexes

Fourteen novel Co^III ternary complexes with the general formula [Co(4N)(2O)]X₂ or [Co(2N)₂(2O)]X₂ where 4N = tris(2-aminoethyl)amine (tren) or tris(2-pyridylmethyl)amine (tpa); 2N = 1,10-phenantroline (phen), 2,2'-bipyridine (bipy), 1,2-diaminoethane (en) or 2-(aminomethyl)pyridine (ampy) and 2O = 1,2-dimethyl-3-hydroxy-4(1H)-pyridinone (dhpH), 3-hydroxy-2-methyl-4-pyrone (maltH) or 2-ethyl-3-hydroxy-4H-pyran-4-one (etmaltH) were synthesized, characterized and their redox features explored. Molecular structure of some selected [Co(2N)₂(2O)](ClO₄)₂ (2N = phen, bipy, en; 2O = dhp, malt) or [Co(4N)(2O)](ClO₄)₂ (4N = tpa; 2O = etmalt) type complexes were assessed by X-ray diffraction and showed the expected octahedral geometry. Replacement of the 4N donor ligands by two 2N donor ligands resulted in the decrease of the cathodic peak potential of the complexes indicating easier reduction and allowing therefore the tailoring of the redox properties of the complexes. Screening of selected compounds against a human derived cancer cell line, HeLa, showed that, unlike the [Co(4N)(2O)]X₂ derivatives, the complexes containing 2N = bipy or phen ligands have better anticancer activity than cisplatin or carboplatin.

A novel Schiff base cobalt(III) complex induces a synergistic effect on cervical cancer cells by arresting early apoptosis stage

A new schiff base cobalt(III) complex [N,N'-bis(2'-hydroxyphenylacetone)-o-ethanediamine] cobalt(III) (M3) has been synthesized and characterized by single X-ray crystallography. The cytotoxicity of complex M3 was evaluated against HeLa, LoVo, A549, A549/cis cancer cell lines, and the normal cell lines LO2 by MTT assays. The IC₅₀ is in the range of 6.27-22.68 μM, which is somewhat lower than cisplatin on the basis of platinum molar concentration. Furthermore, anticancer mechanistic studies showed that the complex M3 inhibited cell proliferation by blocking DNA synthesis and then acted on nuclear division of HeLa cells over time. Moreover, western blot analysis indicated M3 dramatically decreased the target protein c-Myc and KLF5 expression levels, and activated many signaling pathways including ER stress, apoptosis, cell cycle and DNA damage in HeLa. M3 did not affect proteasomal activity.