Novel Mechanism of Cytotoxicity for the Selective Selenosemicarbazone, 2-Acetylpyridine 4,4-Dimethyl-3-selenosemicarbazone (Ap44mSe): Lysosomal Membrane Permeabilization

Desulfurization of thiosemicarbazones: the role of metal ions and biological implications

Thiosemicarbazones are biologically active substances whose structural formula is formed by an azomethine, an hydrazine, and a thioamide fragments, to generate a R2C=N-NR-C(=S)-NR2 backbone. These compounds often act as ligands to generate highly stable metal-organic complexes. In certain experimental conditions, however, thiosemicarbazones undergo reactions leading to the cleavage of the chain. Sometimes, the breakage involves desulfurization processes. The present work summarizes the different chemical factors that influence the desulfurization reactions of thiosemicarbazones, such as pH, the presence of oxidant reactants or the establishment of redox processes as those electrochemically induced, the effects of the solvent, the temperature, and the electromagnetic radiation. Many of these reactions require coordination of thiosemicarbazones to metal ions, even those present in the intracellular environment. The nature of the products generated in these reactions, their detection in vivo and in vitro, together with the relevance for the biological activity of these compounds, mainly as antineoplastic agents, is discussed.

Differential transmetallation of complexes of the anti-cancer thiosemicarbazone, Dp4e4mT: effects on anti-proliferative efficacy, redox activity, oxy-myoglobin and oxy-hemoglobin oxidation

The di-2-pyridylthiosemicarbazone (DpT) analogs demonstrate potent and selective anti-proliferative activity against human tumors. The current investigation reports the synthesis and chemical and biological characterization of the Fe(iii), Co(iii), Ni(ii), Cu(ii), Zn(ii), Ga(iii), and Pd(ii) complexes of the promising second generation DpT analog, di-2-pyridylketone-4-ethyl-4-methyl-3-thiosemicarbazone (Dp4e4mT). These studies demonstrate that the Dp4e4mT Co(iii), Ni(ii), and Pd(ii) complexes display distinct biological activity versus those with Cu(ii), Zn(ii), and Ga(iii) regarding anti-proliferative efficacy against cancer cells and a detrimental off-target effect involving oxidation of oxy-myoglobin (oxy-Mb) and oxy-hemoglobin (oxy-Hb). With regards to anti-proliferative activity, the Zn(ii) and Ga(iii) Dp4e4mT complexes demonstrate facile transmetallation with Cu(ii), resulting in efficacy against tumor cells that is strikingly similar to the Dp4e4mT Cu(ii) complex (IC50: 0.003-0.006 μM and 72 h). Relative to the Zn(ii) and Ga(iii) Dp4e4mT complexes, the Dp4e4mT Ni(ii) complex demonstrates kinetically slow transmetallation with Cu(ii) and intermediate anti-proliferative effects (IC50: 0.018-0.076 μM after 72 h). In contrast, the Co(iii) and Pd(ii) complexes demonstrate poor anti-proliferative activity (IC50: 0.262-1.570 μM after 72 h), probably due to a lack of transmetallation with Cu(ii). The poor efficacy of the Dp4e4mT Co(iii), Ni(ii), and Pd(ii) complexes to transmetallate with Fe(iii) markedly suppresses the oxidation of oxy-Mb and oxy-Hb. In contrast, the 2 : 1 Dp4e4mT: Cu(ii), Zn(ii), and Ga(iii) complexes demonstrate facile reactions with Fe(iii), leading to the redox active Dp4e4mT Fe(iii) complex and oxy-Mb and oxy-Hb oxidation. This study demonstrates the key role of differential transmetallation of Dp4e4mT complexes that has therapeutic ramifications for their use as anti-cancer agents.

Steric Blockade of Oxy-Myoglobin Oxidation by Thiosemicarbazones: Structure-Activity Relationships of the Novel PPP4pT Series

The di-2-pyridylketone thiosemicarbazones demonstrated marked anticancer efficacy, prompting progression of DpC to clinical trials. However, DpC induced deleterious oxy-myoglobin oxidation, stifling development. To address this, novel substituted phenyl thiosemicarbazone (PPP4pT) analogues and their Fe(III), Cu(II), and Zn(II) complexes were prepared. The PPP4pT analogues demonstrated potent antiproliferative activity (IC50: 0.009-0.066 μM), with the 1:1 Cu:L complexes showing the greatest efficacy. Substitutions leading to decreased redox potential of the PPP4pT:Cu(II) complexes were associated with higher antiproliferative activity, while increasing potential correlated with increased redox activity. Surprisingly, there was no correlation between redox activity and antiproliferative efficacy. The PPP4pT:Fe(III) complexes attenuated oxy-myoglobin oxidation significantly more than the clinically trialed thiosemicarbazones, Triapine, COTI-2, and DpC, or earlier thiosemicarbazone series. Incorporation of phenyl- and styryl-substituents led to steric blockade, preventing approach of the PPP4pT:Fe(III) complexes to the heme plane and its oxidation. The 1:1 Cu(II):PPP4pT complexes were inert to transmetalation and did not induce oxy-myoglobin oxidation.

Lysosome blockade induces divergent metabolic programs in macrophages and tumours for cancer immunotherapy

BACKGROUND

Platinum-drugs based chemotherapy in clinic increases the potency of tumor cells to produce M2 macrophages, thus leading to poor anti-metastatic activity and immunosuppression. Lysosome metabolism is critical for cancer cell migration and invasion, but how it promotes antitumor immunity in tumours and macrophages is poorly understood and the underlying mechanisms are elusive. The present study aimed to explore a synergistic strategy to dismantle the immunosuppressive microenvironment of tumours and metallodrugs discovery by using the herent metabolic plasticity.

METHODS

Naphplatin was prepared by coordinating an active alkaline moiety to cisplatin, which can regulate the lysosomal functions. Colorectal carcinoma cells were selected to perform the in vivo biological assays. Blood, tumour and spleen tissues were collected and analyzed by flow cytometry to further explore the relationship between anti-tumour activity and immune cells. Transformations of bone marrow derived macrophage (BMDM) and M2-BMDM to the M1 phenotype was confirmed after treatment with naphplatin. The key mechanisms of lysosome-mediated mucolipin-1(Mcoln1) and mitogen-activated protein kinase (MAPK) activation in M2 macrophage polarization have been unveiled. RNA sequencing (RNA-seq) was used to further explore the key mechanism underlying high-mobility group box 1(HMGB1)-mediated Cathepsin L(CTSL)-lysosome function blockade.

RESULTS

We demonstrated that naphplatin induces divergent lysosomal metabolic programs and reprograms macrophages in tumor cells to terminate the vicious tumour-associated macrophages (TAMs)-MDSCs-Treg triangle. Mechanistically, macrophages treated with naphplatin cause lysosome metabolic activation by triggering Ca2+ release via Mcoln1, which induces the activation of p38 and nuclear factor-κB (NF-κB) and finally results in polarizing M2 macrophages. In contrast, HMGB1-mediated lysosome metabolic blockade in cancer cells is strongly linked to antitumor effects by promoting cytoplasmic translocation of HMGB1.

CONCLUSIONS

This study reveals the crucial strategies of macrophage-based metallodrugs discovery that are able to treat both immunologically "hot" and "cold" cancers. Different from traditional platinum-based antitumour drugs by inhibition of DNAs, we also deliver a strong antitumour strategy by targeting lysosome to induce divergent metabolic programs in macrophages and tumours for cancer immunotherapy.

Developing an Anticancer Platinum(II) Compound Based on the Uniqueness of Human Serum Albumin

To develop the next-generation Pt drug with remarkable activity and low toxicity to maximally inhibit tumor growth, we optimized a Pt(II) thiosemicarbazone compound (C4) with remarkable cytotoxicity to SK-N-MC cells and then constructed a new human serum albumin-C4 (HSA-C4) complex delivery system. The in vivo results showed that C4 and the HSA-C4 complex have remarkable therapeutic efficiency and almost no toxicity; they induced apoptosis and inhibited tumor angiogenesis. This system showed potential as a practical Pt drug. This study could pave the way for developing next-generation dual-targeted Pt drugs and achieving their targeting therapy for cancer.

Designing Tailored Thiosemicarbazones with Bespoke Properties: The Styrene Moiety Imparts Potent Activity, Inhibits Heme Center Oxidation, and Results in a Novel "Stealth Zinc(II) Complex"

A novel, potent, and selective antitumor agent, namely (E)-3-phenyl-1-(2-pyridinyl)-2-propen-1-one 4,4-dimethyl-3-thiosemicarbazone (PPP44mT), and its analogues were synthesized and characterized and displayed strikingly distinctive properties. This activity was mediated by the inclusion of a styrene moiety, which through steric and electrochemical mechanisms prevented deleterious oxy-myoglobin or oxy-hemoglobin oxidation relative to other potent thiosemicarbazones, i.e., di-2-pyridylketone-4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) or di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT). Structure-activity relationship analysis demonstrated specific tuning of PPP44mT electrochemistry further inhibited oxy-myoglobin or oxy-hemoglobin oxidation. Both PPP44mT and its Cu(II) complexes showed conspicuous almost immediate cytotoxicity against SK-N-MC tumor cells (within 3 h). In contrast, [Zn(PPP44mT)₂] demonstrated a pronounced delay in activity, taking 48 h before marked antiproliferative efficacy was apparent. As such, [Zn(PPP44mT)₂] was designated as a "stealth Zn(II) complex" that overcomes the near immediate cytotoxicity of PPP44mT or its copper complexes. Upon examination of the suppression of oncogenic signaling, [Zn(PPP44mT)₂] was superior at inhibiting cyclin D1 expression compared to DpC or Dp44mT.

Synthesis, characterization and antitubercular activities of heterocyclic selenosemicarbazones

Reaction of cyclohexanoneselenosemicarbazone with aldehydes and ketones containing heterocyclic rings (2-oxindole, 6-cholro-2-oxindole, 3-methyl-2-oxindole, isatin, 1-methyl isatin, furfural, pyrrole-2-carboxldehyde) in ethanol yielded, respective, selenosemicarbazones {2-oxindoleselenosemicarbazone (2-HOxsesc,H¹L), 6-chloro-2-oxindole selenosemicarbazone (6-ClHOxsesc, H²L), 3-methyl-2-oxindole selenosemicarbazone (3-MeHOxses, H³L), isatinselenosemicarbazone (HIstsesc, H⁴L), 1-methyl isatinselenosemicarbazone (1-MeHIstsesc, H⁵L), 2-thiopheneselenosemicarbazone (2-Hthiosesc, H⁶L), 2-furfuralselenosemicarbazone (2-Hfursesc, H⁷L) and 2-pyrrole selenosemicarbazone (2-Hpysesc, H⁸L)}. However the similar reaction with aldehyde containing single aromatic ring (3-chlorobenzaldehyde and 4-chlorobenzaldehyde) formed 1, 2-bis(3-chlorobenzylidiene) hydrazine (A) and 1, 2-bis(4-chlorobenzylidiene) hydrazine (B) rather than selenosemicarbazone. All the synthesized compounds were characterized using IR and NMR (¹H, ¹³C) spectroscopy. Structure of A and B were confirmed by single crystal X-ray crystallography. The synthesized selenosemicarbazones were tested for their anti-tubercular activities and H¹L, H³L, H⁵L and H⁶L are found to exhibit excellent anti-TB activity. The experimental data will give an opportunity to examine their anti-tubercular activities and identify the lead molecule.

Acylselenoureas, selenosemicarbazones and selenocarbamate esters: Versatile ligands in coordination chemistry

Acylselenoureas, selenosemicarbazones and selenocarbamate esters from complexes with various transition- and main-group-metals, adopting several coordination modes.

Synthesis, crystal structures, anticancer activities and molecular docking studies of novel thiazolidinone Cu(II) and Fe(III) complexes targeting lysosomes: special emphasis on their binding to DNA/BSA

Novel [CuL₂Cl]Cl·H₂O (1) and [FeL₂Cl₂]Cl·MeOH·CHCl₃·H₂O (2) complexes of (Z)-N'-((E)-3-methyl-4-oxothiazolidin-2-ylidene)picolinohydrazonamide (L) as antitumor agents were designed and synthesized in order to explore DNA and serum albumin interaction. X-ray diffraction revealed that both 1 and 2 were a triclinic crystal system with P1̄ space group, which consisted of a positive electric main unit, a negative chloride ion and some solvent molecules. The complexes with DNA and bovine serum albumin (BSA) were studied by fluorescence and electronic absorption spectrometry. The results indicated that there was moderate intercalative binding mode between the complexes and DNA with K_app values of 2.40 × 10⁵ M^-1 (1) and 6.49 × 10⁵ M^-1 (2). Agarose gel electrophoresis experiment showed that both 1 and 2 exhibited obvious DNA cleavage activity via an oxidative DNA damage pathway, and the cleavage activities of 1 were stronger than those of 2. Cytotoxicity assay showed that 1 had a more effective antitumor activity than 2. The two complexes were bound to BSA by a high affinity and quenched the fluorescence of BSA through a static mechanism. The thermodynamic parameters suggested that hydrophobic interactions played a key role in the binding process. The binding energy xpscore of 1 and 2 were -10.529 kcal mol^-1 and -10.826 kcal mol^-1 by docking studies, and this suggested that the binding process was spontaneous. Complex 1 displayed a lysosome-specific targeting behavior with a Pearson coefficient value of 0.82 by confocal laser scanning microscopy (CLSM), and accumulated in the lysosomes, followed by the disruption of lysosomal integrity.

Complex formation and cytotoxicity of Triapine derivatives: a comparative solution study on the effect of the chalcogen atom and NH-methylation

α-N-Heterocyclic thiosemicarbazones are an important class of investigational anticancer drugs. The most prominent representative is 3-aminopyridine-2-carboxaldehyde thiosemicarbazone (Triapine), which has shown promising results in clinical trials and is currently evaluated in phase III. In this study, we investigated the influence of a chalcogen atom exchange from S (Triapine) to O (O-Triapine) and Se (Se-Triapine) and the methylation of the hydrazonic NH moiety (Me-Triapine) on their complexation with Fe(ii), Fe(iii) and Cu(ii) ions and their cytotoxicity. The main aim of this study was to characterize and compare the most feasible chemical forms in solution, their stability and redox properties, as well as to reveal the relationships of the solution speciation and kinetic data with cytotoxic activity. The complex equilibria and redox properties of the complexes were characterized by the combined use of pH-potentiometry, UV-visible spectrophotometry, electron paramagnetic resonance spectroscopy, and cyclic voltammetry. These revealed that Se-Triapine forms Cu(ii) complexes with higher, and O-Triapine with lower stability as compared with Triapine. Me-Triapine, which is not able to coordinate via the typical (N,N,S-) donor set, nevertheless coordinates to Cu(ii) with unexpected high stability. The Cu(ii) complexes of Se-Triapine and Me-Triapine can be relatively slowly reduced by glutathione at pH 7.4 (but not by ascorbate), similarly to Cu(ii)-Triapine. In contrast, the Cu(ii)-O-Triapine complex can be reduced by both reducing agents in rapid redox reactions. Se-Triapine and Triapine form high stability complexes with both Fe(ii) and Fe(iii) ions, while O-Triapine has a much stronger preference towards Fe(iii) and Me-Triapine towards Fe(ii). This difference in the iron preference of the ligands seems to have a strong impact on their cytotoxic effects, which was measured in a human uterine sarcoma cell line (MES-SA) and its multidrug-resistant subline (MES-SA/Dx5). The Cu(ii) complexes of these calcogensemicarbazones are moderately toxic, and the highest level of ROS generation was found for the Cu(ii) complex of O-Triapine, which is the most reducible.

Oxidative damage of lysosomes in regulated cell death systems: Pathophysiology and pharmacologic interventions

Lysosomes are small specialized organelles containing a variety of different hydrolase enzymes that are responsible for degradation of all macromolecules, entering the cells through the endosomal system or originated from the internal sources. This allows for transport and recycling of nutrients and internalization of surface proteins for antigen presentation as well as maintaining cellular homeostasis. Lysosomes are also important storage compartments for metal ions and nutrients. The integrity of lysosomal membrane is central to maintaining their normal function, but like other cellular membranes, lysosomal membrane is subject to damage mediated by reactive oxygen species. This results in spillage of lysosomal enzymes into the cytoplasm, leading to proteolytic damage to cellular systems and organelles. Several forms of lysosomal dependent cell death have been identified in diseases. Examination of these events are important for finding treatment strategies relevant to cancer or neurodegenerative diseases as well as autoimmune deficiencies. In this review, we have examined the current literature on involvement of lysosomes in induction of programed cell death and have provided an extensive list of therapeutic approaches that can modulate cell death. Exploitation of these mechanisms can lead to novel therapies for cancer and neurodegenerative diseases.

Unprecedented formation of palladium(II)-pyrazole based thiourea from chromone thiosemicarbazone and [PdCl2(PPh3)2]: Interaction with biomolecules and apoptosis through mitochondrial signaling pathway

Two novel pyrazole based thiourea palladium(II) complexes, [PdCl(PPh₃)(C₉H₈NO₂S-pz)] (1) and [PdCl(PPh₃)(C₁₄H₁₀NO₂S-pz)] (2) [pz = pyrazole (C₃H₂N₂)] have been obtained unexpectedly from chromone thiosemicarbazones (L1 and L2) and [PdCl₂(PPh₃)₂]. The compounds have been fully characterized by physicochemical studies. The single crystal X-ray diffraction and spectral studies revealed square planar geometry for the complexes. The conversion of chromone thiosemicarbazone into pyrazole based thiourea might have happened through coordination to palladium(II) ion after enolization, Michael addition and ring opening followed by cyclization. To the best of our knowledge, this is the first report for the conversion of chromone thiosemicarbazone into pyrazole based thiourea moiety. Plausible mechanism was proposed based on the spectroscopic studies. Calf thymus (CT) DNA binding of the compounds was explored using various spectroscopic and molecular docking methods. DNA cleavage studies suggested that complexes 1 and 2 had the capacity to cleave the supercoiled DNA (pUC19) to its naked form. In vitro cytotoxic property of the ligands and complexes has been evaluated against three human cancer cells such as A549, HepG-2 and U937. Complex 2 exhibited potent cytotoxic activity against HepG-2 cells with the IC₅₀ value of 10.4 μM. In addition, mechanistic studies showed that complex 2 induced apoptosis through mitochondrial signaling pathway in HepG-2 cells. Beneficially, complex 2 showed less toxicity against human lung (IMR90) normal cells and hence it emerges as a potential candidate for further studies.

BODIPY-Decorated Nanoscale Covalent Organic Frameworks for Photodynamic Therapy

Covalent organic frameworks (COFs), an emerging class of organic porous materials, have attracted intense attention due to their versatile applications. However, the deliberate fabrication of COF-based nanomaterials for nanomedical application remains challenging due to difficulty in their size- and structure-controlled synthesis and poor aqueous dispersibility. Herein, we report two boron-dipyrromethene (BODIPY)-decorated nanoscale COFs (NCOFs), which were prepared by the Schiff-base condensation of the free end -CHO (bonding defects in COFs) on the established imine-based NCOFs with the amino-substituted organic photosensitizer BODIPY via "bonding defects functionalization" approach. Thus BODIPY has been successfully nanocrystallized via the NCOF platform, and can be used for photodynamic therapy (PDT) to treat tumors. These NCOF-based PDT agents featured nanometer size (∼110 nm), low dark toxicity, and high phototoxicity as evidenced by in vitro and in vivo experiments. Moreover, the "bonding defects functionalization" approach might open up new avenues for the fabrication of additional COF-based platforms for biomedical treatment.

Novel Nitric Oxide Donors of Phenylsulfonylfuroxan and 3-Benzyl Coumarin Derivatives as Potent Antitumor Agents

In this work, five new hybrids of phenylsulfonylfuroxan merging 3-benzyl coumarin and their seco-B-ring derivatives 2-6 were designed and synthesized. Among them, compound 3 showed the most potent antiproliferation activities with IC₅₀ values range from 0.5 to 143 nM against nine drug-sensitive and four drug-resistant cancer cell lines. Preliminary pharmacologic studies showed that these compounds displayed lower toxicities than that of lead compound 1. Compound 3 obviously induced the early apoptosis and hardly affected the cell cycle of A2780, which was significantly different from compound 1. Especially, it gave 559- and 294-fold selectivity antiproliferation activity in P-gp overexpressed drug-resistant cancer cell lines MCF-7/ADR and KB-V compared to their drug-sensitive ones MCF-7 and KB, implying that compounds 2-6 might have an extra mechanism of anti-MDR-cancer with P-gp overexpression.

Novel chelators based on adamantane-derived semicarbazones and hydrazones that target multiple hallmarks of Alzheimer's disease

Novel adamantane-derived semicarbazones and hydrazones show multi-functional activity as potential therapeutics for Alzheimer's disease.

Mitochondria-localizing BODIPY–copper(ii) conjugates for cellular imaging and photo-activated cytotoxicity forming singlet oxygen

BODIPY–copper(ii) conjugates are prepared and characterized and the complexes showed mitochondrial localization with singlet oxygen mediated visible light-induced apoptotic cell death.

Co(iii) complexes of (1,3-selenazol-2-yl)hydrazones and their sulphur analogues

The first Co(iii) complexes with (1,3-selenazol-2-yl)hydrazones as an unexplored class of ligands were prepared and characterized by NMR spectroscopy and X-ray diffraction analysis. The novel ligands act as NNN tridentate chelators forming octahedral Co(iii) complexes. The impact of structural changes on ligands' periphery as well as that of isosteric replacement of sulphur with selenium on the electrochemical and electronic absorption features of complexes are explored. To support the experimental data, density functional theory (DFT) calculations were also conducted. Theoretical NMR chemical shifts, the relative energies and natural bond orbital (NBO) analysis are calculated within the DFT approach, while the singlet excited state energies and HOMO-LUMO energy gap were calculated with time-dependent density functional theory (TD-DFT). The electrophilic f^- and nucleophilic f⁺ Fukui functions are well adapted to find the electrophile and nucleophile centres in the molecules. Both (1,3-selenazol-2-yl)- and (1,3-thiazol-2-yl)hydrazone Co(iii) complexes showed potent antimicrobial and antioxidant activity. A significant difference among them was a smaller cytotoxicity of selenium compounds.

Structure-Activity Relationships of Di-2-pyridylketone, 2-Benzoylpyridine, and 2-Acetylpyridine Thiosemicarbazones for Overcoming Pgp-Mediated Drug Resistance

Multidrug resistance (MDR) mediated by P-glycoprotein (Pgp) represents a significant impediment to successful cancer treatment. The compound, di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT), has been shown to induce greater cytotoxicity against resistant cells than their nonresistant counterparts. Herein, the structure-activity relationships of selected thiosemicarbazones are explored and the novel mechanism underlying their ability to overcome resistance is further elucidated. Only thiosemicarbazones with electron-withdrawing substituents at the imine carbon mediated Pgp-dependent potentiated cytotoxicity, which was reversed by Pgp inhibition. Treatment of resistant cells with these thiosemicarbazones resulted in Pgp-dependent lysosomal membrane permeabilization (LMP) that relied on copper (Cu) chelation, reactive oxygen species generation, and increased relative lipophilicity. Hence, this study is the first to demonstrate the structural requirements of these thiosemicarbazones necessary to overcome MDR. We also demonstrate the mechanism that enables the targeting of resistant tumors, whereby thiosemicarbazones "hijack" lysosomal Pgp and form redox-active Cu complexes that mediate LMP and potentiate cytotoxicity.

Pro-apoptotic and pro-differentiation induction by 8-quinolinecarboxaldehyde selenosemicarbazone and its Co(iii) complex in human cancer cell lines

The ligand initiated reprogramming of cancer stem cells phenotype in AsPC-1 cells. The complex digested plasmid DNA which might be the cause of its cytotoxic activity.