Curcumin "Drug" Stabilized in Oxidovanadium(IV)-BODIPY Conjugates for Mitochondria-Targeted Photocytotoxicity

Mitochondria-targeted BODIPY dyes for small molecule recognition, bio-imaging and photodynamic therapy

Mitochondria are essential for a diverse array of biological functions. There is increasing research focus on developing efficient tools for mitochondria-targeted detection and treatment. BODIPY dyes, known for their structural versatility and excellent spectroscopic properties, are being actively explored in this context. Numerous studies have focused on developing innovative BODIPYs that utilize optical signals for imaging mitochondria. This review presents a comprehensive overview of the progress made in this field, aiming to investigate mitochondria-related biological events. It covers key factors such as design strategies, spectroscopic properties, and cytotoxicity, as well as mechanism to facilitate their future application in organelle imaging and targeted therapy. This work is anticipated to provide valuable insights for guiding future development and facilitating further investigation into mitochondria-related biological sensing and phototherapy.

Antibacterial and antioxidant activities of curcumin/Zn metal complex with its chemical characterization and spectroscopic studies

Curcumin is an active component of the rhizome turmeric. Curcumin/zinc (Cur/Zn) complex was synthesized and characterized using the elemental analysis, the molar conductance, FT-IR, UV-Vis,¹HNMR, scanning (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The molar conductance value is very low, referring to the absence of Cl^- ions inside or outside chelate sphere confirming non electrolytic nature. Based on IR and electronic spectra curcumin C[bond, double bond]O group in enol form chelated to Zn (II) ion. The surface morphology of curcumin chelate with Zn showed elevated in particle size and irregular grains shaped with elongated morphology. Transmission electron microscopy revealed that the curcumin chelate with Zn has spherical black spots like shape with particle size range from (33-97 nm). The antioxidant activities of curcumin and Cur/Zn complex were assessed. Results showed that the Cur/Zn complex showed potent antioxidant activities than curcumin. For antibacterial activity, Curcumin/Zn showed inhibitory effect against both (+ve and -ve) gram bacteria (Bacillus subtilis and Escherichia coli) at very low concentration. Cur/Zn recorded antibacterial and inhibition activity at 0.009 against E. coli and at 0.625 against B. subtilis. Cur/Zn complex showed higher capacity in scavenging the ABTS radical, FARAP capacity and metal chelating activity than curcumin itself and it showed more scavenging and inhibition activity for DPPH. The synthesized complex of Cur/Zn showed potent antioxidant and antibacterial activities than curcumin itself and it may benefit in treatment of aging and degenerative diseases with elevated and excessive production of free radicals.

Identification of a luminescent platinum(II) complex with BODIPY derivative as novel photodynamic therapy agent for triple negative breast cancer cells

Triple-negative breast cancer (TNBC) is one of the most malignant breast tumors for its poor prognosis and high tumor recurrence. It is urgent to develop new strategy or effective agents to overcome resistance and improve therapeutic effectiveness. Boron-dipyrromethene (BODIPY) based photosensitizers possess exciting photophysical features suitable for theranostic applications, namely, photodynamic therapy (PDT). We have designed a luminescent monofunctional platinum(II) complex with BODIPY derivative, namely I₂BC-Pt, as novel high PDT agent against triple negative breast cancer (TNBC). The di-iodinated BODIPY complex I₂BC-Pt showed excellent PDT effect against TNBC cells in green light (520 nm) giving IC₅₀ values of 0.11-0.13 μM in MDA-MB-231 and MDA-MB-468 cells. I₂BC-Pt predominately aggregated in the mitochondria of MDA-MB-231 cells and emitted green fluorescence. Besides, the anticancer mechanism studies demonstrated that I₂BC-Pt could help DNA repair through attenuating RAD51, FoxM1 and BRCA1/2, and induce p53-mediated apoptosis of TNBC cells. Taken together, I₂BC-Pt could be potentially developed as a BODIPY-based photosensitizers for TNBC therapy.

Metal Complexes with Naphthalene-Based Acetic Acids as Ligands: Structure and Biological Activity

Naproxen (6-methoxy-α-methyl-2-naphthaleneacetic acid), 1-naphthylacetic acid, 2-naphthylacetic acid and 1-pyreneacetic acid are derivatives of acetic acid bearing a naphthalene-based ring. In the present review, the coordination compounds of naproxen, 1- or 2-naphthylacetato and 1-pyreneacetato ligands are discussed in regard to their structural features (nature and nuclearity of metal ions and coordination mode of ligands), their spectroscopic and physicochemical properties and their biological activities.

Multifunctional BODIPY embedded non-woven fabric for CO release and singlet oxygen generation

Materials that can simultaneously release CO and generate singlet oxygen upon visible light irradiation under ambient conditions are highly desirable for therapeutic applications. Furthermore, materials that can sequester the undesirable side products into the matrix without affecting the release of CO and singlet oxygen generation would allow them to be used for practical applications. Focussing on these aspects, we prepared two dipicolylamine appended BODIPY‑manganese(I) tricarbonyl complexes wherein the metal core was systematically tethered at 5- and 8- positions of the BODIPY core. The complexes were embedded into a polymer matrix via electrospinning and the resulting non-woven fabrics showed CO release as well as singlet oxygen generation upon irradiation. While the hybrid materials were non-toxic in dark, they were strongly photocytotoxic to c6 cancer cells when exposed to light. Rapid CO release alongside significant singlet oxygen generation, indefinite dark stability, good biocompatibility and negligible dark toxicity makes these fabrics a potent candidate for phototherapeutic applications.

Antioxidant conjugated metal complexes and their medicinal applications

Antioxidants are naturally available and man-made substances have the ability to protect cells from damage due to a number of intracellular redox activities. Moreover, Antioxidants such as α-lipoic acid, curcumin and catechin are good anticancer agents. In recent years, the usage of metal complexes as therapeutic agents is gaining importance due to their useful biological properties. Most of the metal ions act as the essential components in building drug molecules that serve as medicines for cancer and neurodegenerative diseases. In particular, metals like copper, gold, ruthenium, and platinum have adequate anticancer properties at both micro- and nano-levels. Hence, conjugation of antioxidants with metals and metal-based compounds results in hybrid bioactive materials with improved anticancer properties. In this chapter, medicinal applications of antioxidant conjugated metal complexes are reviewed and discussed.

Diketo-Ketoenol Tautomers in Curcuminoids: Synthesis, Separation of Tautomers, and Kinetic and Structural Studies

Curcumin and its congeners exist in an equilibrium between diketo and ketoenol tautomers, which have different potencies to bind biomolecules. This work describes procedures for the preparation of 4-alkylated curcumin derivatives and the separation of their two tautomeric forms. Comprehensive NMR studies of the tautomer equilibria in various solvents have been accomplished. Additionally, a pure ketoenol tautomeric form of the active pharmaceutical ingredient (API) ASC-JM17 has been unequivocally determined by X-ray crystallography. Two different polymorphs of this API have been microscopically identified in the X-ray sample and manually separated, and a solid-state NMR study of the two polymorphs has also been performed. This work reports on the slow kinetics of diketo-ketoenol tautomerization in particular solvents that allow the separation and full characterization of both curcuminoids' tautomers.

BODIPY Conjugates as Functional Compounds for Medical Diagnostics and Treatment

Fluorescent dyes absorbing and emitting in the visible and near-IR regions are promising for the development of fluorescent probes for labeling and bio-visualization of body cells. The ability to absorb and emit in the long-wavelength region increases the efficiency of recording the spectral signals of the probes due to the higher permeability of the skin layers. Compared to other fluorescent dyes, BODIPYs are attractive due to their excellent photophysical properties-narrow absorption and emission, intense fluorescence, simple signal modulation for the practical applications. As part of conjugates with biomolecules, BODIPY could act as a biomarker, but as therapeutic agent, which allows solving several problems at once-labeling or bioimaging and treatment based on the suppression of pathogenic microflora and cancer cells, which provides a huge potential for practical application of BODIPY conjugates in medicine. The review is devoted to the discussion of the recent, promising directions of BODIPY application in the field of conjugation with biomolecules. The first direction is associated with the development of BODIPY conjugates with drugs, including compounds of platinum, paclitaxel, chlorambucil, isoxazole, capsaicin, etc. The second direction is devoted to the labeling of vitamins, hormones, lipids, and other biomolecules to control the processes of their transport, localization in target cells, and metabolism. Within the framework of the third direction, the problem of obtaining functional optically active materials by conjugating BODIPY with other colored and fluorescent particles, in particular, phthalocyanines, is being solved.

Evaluation of anticancer activity in vitro of a stable copper(I) complex with phosphine-peptide conjugate

[CuI(2,9-dimethyl-1,10-phenanthroline)P(p-OCH₃-Ph)₂CH₂SarcosineGlycine] (1-MPSG), highly stable in physiological media phosphino copper(I) complex—is proposed herein as a viable alternative to anticancer platinum-based drugs. It is noteworthy that, 1-MPSG significantly and selectively reduced cell viability in a 3D spheroidal model of human lung adenocarcinoma (A549), in comparison with non-cancerous HaCaT cells. Confocal microscopy and an ICP-MS analysis showed that 1-MPSG effectively accumulates inside A549 cells with colocalization in mitochondria and nuclei. A precise cytometric analysis revealed a predominance of apoptosis over the other types of cell death. In the case of HaCaT cells, the overall cytotoxicity was significantly lower, indicating the selective activity of 1-MPSG towards cancer cells. Apoptosis also manifested itself in a decrease in mitochondrial membrane potential along with the activation of caspases-3/9. Moreover, the caspase inhibitor (Z-VAD-FMK) pretreatment led to decreased level of apoptosis (more pronouncedly in A549 cells than in non-cancerous HaCaT cells) and further validated the caspases dependence in 1-MPSG-induced apoptosis. Furthermore, the 1-MPSG complex presumably induces the changes in the cell cycle leading to G2/M phase arrest in a dose-dependent manner. It was also observed that the 1-MPSG mediated intracellular ROS alterations in A549 and HaCaT cells. These results, proved by fluorescence spectroscopy, and flow cytometry, suggest that investigated Cu(I) compound may trigger apoptosis also through ROS generation.

Recent Strategies to Develop Innovative Photosensitizers for Enhanced Photodynamic Therapy

This review presents a robust strategy to design photosensitizers (PSs) for various species. Photodynamic therapy (PDT) is a photochemical-based treatment approach that involves the use of light combined with a light-activated chemical, referred to as a PS. Attractively, PDT is one of the alternatives to conventional cancer treatment due to its noninvasive nature, high cure rates, and low side effects. PSs play an important factor in photoinduced reactive oxygen species (ROS) generation. Although the concept of photosensitizer-based photodynamic therapy has been widely adopted for clinical trials and bioimaging, until now, to our surprise, there has been no relevant review article on rational designs of organic PSs for PDT. Furthermore, most of published review articles in PDT focused on nanomaterials and nanotechnology based on traditional PSs. Therefore, this review aimed at reporting recent strategies to develop innovative organic photosensitizers for enhanced photodynamic therapy, with each example described in detail instead of providing only a general overview, as is typically done in previous reviews of PDT, to provide intuitive, vivid, and specific insights to the readers.

Photoactivated Osmium Arene Anticancer Complexes

Half-sandwich Os-arene complexes exhibit promising anticancer activity, but their photochemistry has hardly been explored. To exploit the photocytotoxicity and photochemistry of Os-arenes, O,O-chelated complexes [Os(η⁶-p-cymene)(Curc)Cl] (OsCUR-1, Curc = curcumin) and [Os(η⁶-biphenyl)(Curc)Cl] (OsCUR-2), and N,N-chelated complexes [Os(η⁶-biphenyl)(dpq)I]PF₆ (OsDPQ-2, dpq = pyrazino[2,3-f][1,10]phenanthroline) and [Os(η⁶-biphenyl)(bpy)I]PF₆ (OsBPY-2, bpy = 2,2'-bipyridine), have been investigated. The Os-arene curcumin complexes showed remarkable photocytotoxicity toward a range of cancer cell lines (blue light IC₅₀: 2.6-5.8 μM, photocytotoxicity index PI = 23-34), especially toward cisplatin-resistant cancer cells, but were nontoxic to normal cells. They localized mainly in mitochondria in the dark but translocated to the nucleus upon photoirradiation, generating DNA and mitochondrial damage, which might contribute toward overcoming cisplatin resistance. Mitochondrial damage, apoptosis, ROS generation, DNA damage, angiogenesis inhibition, and colony formation were observed when A549 lung cancer cells were treated with OsCUR-2. The photochemistry of these Os-arene complexes was investigated by a combination of NMR, HPLC-MS, high energy resolution fluorescence detected (HERFD), X-ray adsorption near edge structure (XANES) spectroscopy, total fluorescence yield (TFY) XANES spectra, and theoretical computation. Selective photodissociation of the arene ligand and oxidation of Os(II) to Os(III) occurred under blue light or UVA excitation. This new approach to the design of novel Os-arene complexes as phototherapeutic agents suggests that the novel curcumin complex OsCUR-2, in particular, is a potential candidate for further development as a photosensitizer for anticancer photoactivated chemotherapy (PACT).

Metal-Curcumin Complexes in Therapeutics: An Approach to Enhance Pharmacological Effects of Curcumin

Curcumin, an active component of the rhizome turmeric, has gained much attention as a plant-based compound with pleiotropic pharmacological properties. It possesses anti-inflammatory, antioxidant, hypoglycemic, antimicrobial, neuroprotective, and immunomodulatory activities. However, the health-promoting utility of curcumin is constrained due to its hydrophobic nature, water insolubility, poor bioavailability, rapid metabolism, and systemic elimination. Therefore, an innovative stride was taken, and complexes of metals with curcumin have been synthesized. Curcumin usually reacts with metals through the β-diketone moiety to generate metal–curcumin complexes. It is well established that curcumin strongly chelates several metal ions, including boron, cobalt, copper, gallium, gadolinium, gold, lanthanum, manganese, nickel, iron, palladium, platinum, ruthenium, silver, vanadium, and zinc. In this review, the pharmacological, chemopreventive, and therapeutic activities of metal–curcumin complexes are discussed. Metal–curcumin complexes increase the solubility, cellular uptake, and bioavailability and improve the antioxidant, anti-inflammatory, antimicrobial, and antiviral effects of curcumin. Metal–curcumin complexes have also demonstrated efficacy against various chronic diseases, including cancer, arthritis, osteoporosis, and neurological disorders such as Alzheimer’s disease. These biological activities of metal–curcumin complexes were associated with the modulation of inflammatory mediators, transcription factors, protein kinases, antiapoptotic proteins, lipid peroxidation, and antioxidant enzymes. In addition, metal–curcumin complexes have shown usefulness in biological imaging and radioimaging. The future use of metal–curcumin complexes may represent a new approach in the prevention and treatment of chronic diseases.

BODIPY-attached zinc(II) complexes of curcumin drug for visible light assisted photo-sensitization, cellular imaging and targeted PDT

Boron-dipyrromethene (BODIPY) based photosensitizers as porphyrinoids and curcumin as natural product possess exciting photophysical features suitable for theranostic applications, namely, imaging and photodynamic therapy (PDT). Limited aqueous solubility and insufficient physiological stability, however, reduce their efficacy significantly. We have designed a novel strategy to deliver these two unusable cytotoxins simultaneously in cancer cells and herein, report the synthesis, characterization and imaging-assisted photocytotoxicity of three zinc(II) complexes containing N³-donor dipicolylamine (dpa) ligands (L^1-3) and O,O-donor curcumin (Hcur) viz. [Zn(L¹)(cur)]Cl (1), [Zn(L²)(cur)]Cl (2) and [Zn(L³)(cur)]Cl (3), where L² and L³ have pendant fluorescent BODIPY and non-emissive di-iodo-BODIPY moieties. Metal chelation imparted remarkable biological stability (pH ∼7.4) to the respective ligands and induces significant aqueous solubility. These ternary complexes could act as replacements of the existing metalloporphyrin-based PDT photosensitizers as their visible-light photosensitizing ability is reinforced by the dual presence of blue light absorbing curcumin and green light harvesting BODIPY units. Complex 2 having emissive BODIPY unit L² and curcumin, showed mitochondria selective localization in HeLa, MCF-7 cancer cells and complex 3, the di-iodinated analogue of complex 2, exhibited type-I/II PDT activity via inducing apoptosis through mitochondrial membrane disruption in cancer cells while being significantly nontoxic in dark and to the healthy cells.

Dithiocarbazate-Copper Complexes for Bioimaging and Treatment of Pancreatic Cancer

Anticancer agents that present nonapoptotic cell death pathways are required for treating apoptosis-resistant pancreatic cancer. Here, we synthesized three fluorescent dithiocarbazate-copper complexes, {[Cu^II(L)(Cl)] 1, [Cu^II₂(L)₂(NO₃)₂] 2, and [Cu^II₂Cu^I(L)₂(Br)₃] 3}, to assess their antipancreatic cancer activities. Complexes 1-3 showed significantly greater cytotoxicity toward several pancreatic cancer cell lines with better IC₅₀ than those of the HL ligand and cisplatin. Confocal fluorescence imaging showed that complex 3 was primarily localized in the mitochondria. Primarily, compound 3 also can be applied to in vivo imaging. Further studies revealed that complex 3 kills pancreatic cancer cells by triggering multiple mechanisms, including ferroptosis. Complex 3 is the first copper complex to evoke cellular events consistent with ferroptosis in cancer cells. Finally, it significantly retarded the ASPC-1 cells' growth in a mouse xenograft model.

Mixed-Ligand Cobalt(III) Complexes of a Naturally Occurring Coumarin and Phenanthroline Bases as Mitochondria-Targeted Dual-Purpose Photochemotherapeutics

The bioessential nature of cobalt and the rich photochemistry of its coordination complexes can be exploited to develop potential next-generation photochemotherapeutics. A series of six novel mixed-ligand cobalt(III) complexes of the formulation [Co(B)₂(L)]ClO₄ (1-6), where B is an N,N-donor phenanthroline base, namely, 1,10-phenanthroline (phen in 1 and 4), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 2 and 5), and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 3 and 6), and L is an O,O-donor dianionic ligand derived from catechol (1,2-dihydroxybenzene, cat^2-, in 1-3) or esculetin (6,7-dihydoxycoumarin, esc^2-, in 4-6), have been prepared and characterized, and their light-triggered cytotoxicity has been studied in cancer cells. The single-crystal X-ray diffraction structures of complexes 1 (as PF₆^- salt, 1a) and 2 show distorted octahedral geometries around the cobalt(III) center formed by the set of N₄O₂ donor atoms. The low-spin and 1:1 electrolytic complexes 1-6 display a d-d transition around 700 nm. Complexes 4-6 with a coordinated esc^2- ligand additionally display a π → π* intraligand transition centered at 403 nm. Complexes 4-6 possessing a naturally occurring and photoactive esc^2- ligand show high visible-light-triggered cytotoxicity against HeLa and MCF-7 cancer cells, yielding remarkably low micromolar IC₅₀ values while being much less toxic under dark conditions. Control complexes 1-3 possessing the photoinactive cat^2- ligand show significantly less cytotoxicity either in the presence of light or in the dark. The complex-induced cell death is apoptotic in nature caused by the formation of reactive oxygen species via a type 1 photoredox pathway. Fluorescence microscopy of HeLa cells treated with complex 6 reveals mitochondrial localization of the complex. A significant decrease in the dark toxicity of free esculetin and dppz base is observed upon coordination to cobalt(III). Complexes bind to calf-thymus DNA with significant affinity, but 6 binds with the greatest affinity. Complex 6 efficiently photocleaves supercoiled DNA to its nicked circular form when irradiated with visible light via a photoredox type 1 pathway involving hydroxyl radicals (HO^•). Thus, complex 6 showing remarkable visible-light-triggered cytotoxicity but negligible toxicity in the dark is a good candidate for cancer photochemotherapy applications.

Structure and biological profile of transition metal complexes with (E)-4-(2-(pyridin-2-ylmethylene)hydrazinyl)quinazoline

The interaction of the recently reported quinazoline derivative (E)-4-(2-(pyridin-2-ylmethylene)hydrazinyl)quinazoline (L) with a series of metal(II) (= copper(II), nickel(II), cobalt(II) and cadmium(II)) chlorides or nitrates resulted in the formation of mononuclear complexes which were characterized by spectroscopic techniques and single-crystal X-ray crystallography, i.e. [Cu(L)₂]Cl₂·4H₂O (1·4H₂O), [Ni(L)₂]Cl₂·4H₂O (2·4H₂O), [Ni(L)₂](NO₃)₂·MeOH (3·MeOH), [Co(L)₂]Cl₂·4H₂O (4·4H₂O), [Co(L)₂](NO₃)₂·H₂O (5·H₂O), [Co(L)₂](NO₃)₃·2.5H₂O (6·2.5H₂O), [Cd(L)(Cl)₂]·H₂O (7·H₂O) and [Cd(L)(CH₃OH)(H₂O)(NO₃)](NO₃) (8). The biological profile of the complexes was further assessed in regard to their binding affinity with calf-thymus DNA, their cleavage ability towards pBluescript II KS plasmid DNA in the absence or presence of irradiation of various wavelengths, their interaction with bovine serum albumin and finally, their ability to scavenge 1,1-diphenyl-picrylhydrazyl and 2,2΄-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radicals and to reduce H₂O₂.

Unraveling the binding mechanism of an Oxovanadium(IV) - Curcumin complex on albumin, DNA and DNA gyrase by in vitro and in silico studies and evaluation of its hemocompatibility

An oxovanadium(IV) - curcumin based complex, viz. [VO(cur)(2,2´-bipy)(H₂O)] where cur is curcumin and bipy is bipyridine, previously synthesized, has been studied for interaction with albumin and DNA. Fluorescence emission spectroscopy was used to evaluate the interaction of the complex with bovine serum albumin (BSA) and the BSA-binding constant (K_b) was calculated to be 2.56 x 10⁵ M^-1, whereas a single great-affinity binding site was revealed. Moreover, the hemocompatibility test demonstrated that the complex presented low hemolytic fraction (mostly below 1%), in all concentrations tested (0-250 μΜ of complex, 5% DMSO) assuring a safe application in interaction with blood. The binding of the complex to DNA was also investigated using absorption, fluorescence, and viscometry methods indicating a binding through a minor groove mode. From competitive studies with ethidium bromide the apparent binding constant value to DNA was estimated to be 4.82 x 10⁶ M^-1. Stern-Volmer quenching phenomenon gave a Κ_SV constant [1.92 (± 0.05) x 10⁴ M^-1] and k_q constant [8.33 (± 0.2) x 10¹¹ M^-1s^-1]. Molecular docking simulations on the crystal structure of BSA, calf thymus DNA, and DNA gyrase, as well as pharmacophore analysis for BSA target, were also employed to study in silico the ability of [VO(cur)(2,2´-bipy)(H₂O)] to bind to these target bio-macromolecules and explain the observed in vitro activity.

Synthesis, characterization and photodynamic activity of half-sandwich rhodium(III) complexes with curcuminoids

Half-sandwich Cp*-Rh complexes containing curcuminoids ([Rh(η⁵-Cp*)(L)(Py)]PF₆, 1-3, L = curcuminoid ligands L¹-L³) were prepared, characterized and studied for anticancer activity. Complex 1 was structurally characterized by single-crystal X-ray crystallography. Complex 3 presented excellent photodynamic anticancer effect in light (>400 nm) showing IC₅₀ values of 7.5 and 4.3 μM against HepG2, SKOV3 and HeLa, respectively, along with the 12.4, 7.9 and 4.7-fold lower toxicity in the dark. Confocal fluorescence images show that the complex primarily targeted mitochondrial localization. These results suggest that the complex 3 was a valuable agent with higher efficacy for chemotherapy and photodynamic therapy, which can achieve real-time image guidance in cancer therapy for the fluorescence of the complex as imaging signals. This investigation provides a valuable route to design novel half-sandwich Cp*-Rh complexes with higher efficacy for photodynamic anticancer chemotherapy.

Therapeutic role of curcumin and its novel formulations in gynecological cancers

Gynecological cancers are among the leading causes of cancer-associated mortality worldwide. While the number of cases are rising, current therapeutic approaches are not efficient enough. There are considerable side-effects as well as treatment resistant types. In addition, which all make the treatment complicated for afflicted cases. Therefore, in order to improve efficacy of the treatment process and patients’ quality of life, searching for novel adjuvant treatments is highly warranted. Curcumin, a promising natural compound, is endowed with numerous therapeutic potentials including significant anticancer effects. Recently, various investigations have demonstrated the anticancer effects of curcumin and its novel analogues on gynecological cancers. Moreover, novel formulations of curcumin have resulted in further propitious effects. This review discusses these studies and highlights the possible underlying mechanisms of the observed effects.

Antibacterial Mechanism of Curcumin: A Review

Curcumin is a plant-derived polyphenolic active substance with broad-spectrum antibacterial properties. Curcumin blocks bacterial growth owing to its structural characteristics and the generation of antioxidation products. Curcumin can inhibit bacterial virulence factors, inhibit bacterial biofilm formation and prevent bacterial adhesion to host receptors through the bacterial quorum sensing regulation system. As a photosensitizer, curcumin acts under blue light irradiation to induce phototoxicity and inhibit bacterial growth. Moreover, it can exert a synergistic antibacterial effect with other antibacterial substances. In this review, we summarize the research progress on the antibacterial mechanism of curcumin based on five targeting structures and two modes of action. Our discussion provides a theoretical basis and technical foundation for the development and application of natural antibacterial agents.

Structurally Characterized BODIPY-Appended Oxidovanadium(IV) β-Diketonates for Mitochondria-Targeted Photocytotoxicity

Mixed-ligand oxidovanadium(IV) β-diketonates having NNN-donor dipicolylamine-conjugated to boron-dipyrromethene (BODIPY in L₁) and diiodo-BODIPY (in L₂) moieties, namely, [VO(L₁)(acac)]Cl (1), [VO(L₂)(acac)]Cl (2), and [VO(L₁)(dbm)]Cl (3), where acac and dbm are monoanionic O,O-donor acetylacetone and 1,3-diphenyl-1,3-propanedione, were prepared, characterized, and tested for their photoinduced anticancer activity in visible light. Complexes 1 and 2 were structurally characterized as their PF₆ ^- salts (1a and 2a) by X-ray crystallography. They showed V^IVN₃O₃ six-coordinate geometry with dipicolylamine base as the facial ligand. The non-iodinated BODIPY complexes displayed absorption maxima at ∼501 nm, while it is ∼535 nm for the di-iodinated 2 in 10% DMSO-PBS buffer medium (pH = 7.2). Complexes 1 and 3 being green emissive (λ_em, ∼512 nm; λ_ex, 470 nm; Φ_F, ∼0.10) in 10% aqueous DMSO were used for cellular imaging studies. Complex 3 localized primarily in the mitochondria of the cervical HeLa cells with a co-localization coefficient value of 0.7. The non-emissive diiodo-BODIPY complex 2 showed generation of singlet oxygen (Φ_Δ ≈ 0.47) on light activation. Annexin-V assay showed singlet oxygen-mediated cellular apoptosis, making this complex a targeted PDT agent.

Synthesis, characterization, DNA binding, topoisomerase inhibition, and apoptosis induction studies of a novel cobalt(III) complex with a thiosemicarbazone ligand

In this study, 9-anthraldehyde-N(4)-methylthiosemicarbazone (MeATSC) 1 and [Co(phen)2(O2CO)]Cl·6H2O 2 (where phen = 1,10-phenanthroline) were synthesized. [Co(phen)2(O2CO)]Cl·6H2O 2 was used to produce anhydrous [Co(phen)2(H2O)2](NO3)33. Subsequently, anhydrous [Co(phen)2(H2O)2](NO3)33 was reacted with MeATSC 1 to produce [Co(phen)2(MeATSC)](NO3)3·1.5H2O·C2H5OH 4. The ligand, MeATSC 1 and all complexes were characterized by elemental analysis, FT IR, UV-visible, and multinuclear NMR (1H, 13C, and 59Co) spectroscopy, along with HRMS, and conductivity measurements, where appropriate. Interactions of MeATSC 1 and complex 4 with calf thymus DNA (ctDNA) were investigated by carrying out UV-visible spectrophotometric studies. UV-visible spectrophotometric studies revealed weak interactions between ctDNA and the analytes, MeATSC 1 and complex 4 (Kb = 8.1 × 105 and 1.6 × 104 M-1, respectively). Topoisomerase inhibition assays and cleavage studies proved that complex 4 was an efficient catalytic inhibitor of human topoisomerases I and IIα. Based upon the results obtained from the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay on 4T1-luc metastatic mammary breast cancer cells (IC50 = 34.4 ± 5.2 μM when compared to IC50 = 13.75 ± 1.08 μM for the control, cisplatin), further investigations into the molecular events initiated by exposure to complex 4 were investigated. Studies have shown that complex 4 activated both the apoptotic and autophagic signaling pathways in addition to causing dissipation of the mitochondrial membrane potential (ΔΨm). Furthermore, activation of cysteine-aspartic proteases3 (caspase 3) in a time- and concentration-dependent manner coupled with the ΔΨm, studies implicated the intrinsic apoptotic pathway as the major regulator of cell death mechanism.

Evaluation of curcumin-mediated photodynamic therapy on the reverse of multidrug resistance in tumor cells

Curcumin (CUR) possesses photosensitive anti-tumor activity. However, photoactive CUR mainly targets tumor cells sensitive to chemotherapy, whereas the effect on multi-drug resistant cancer cells has not been fully investigated. The study aimed to investigate the anti-tumor activity of CUR on resistant MCF-7/ADM cells and its underlying mechanism providing insights into CUR-mediated PDT and a reference for reversing multidrug resistance. Cell apoptosis and morphological changes were detected by Annexin V-FITC/PI double staining and immunofluorescence, respectively. The apoptosis mechanism of CUR-mediated PDT was investigated by detecting the levels of reactive oxygen species (ROS), mitochondrial membrane potential, and related proteins. MTT and apoptosis results showed that CUR-mediated PDT significantly enhanced cytotoxicity and induced considerable cell apoptosis. After treatment with CUR-mediated PDT, cells became round in shape and shrunk, F-actin was loosely arranged, and the nucleus decreased in size. In addition, the level of ROS increased over time compared to the control and peaked at 6 h. CUR-mediated PDT induced alterations in the mitochondrial membrane potential, increased the release of mitochondrial cytochrome C (Cyt-c), and downregulated caspase-3/7/9, PARP, and P-gp. In conclusion, CUR-PDT induced apoptosis in resistant MCF-7/ADM cells primarily through endogenous mitochondrial apoptosis pathway. Besides apoptosis activation in resistant cells, the reverse of multidrug resistance was ascribed to the downregulation of P-gp expression to a degree.

The Apoptosis of resistant tumor cells reduced by curcumin-mediated photodynamic therapy.

Ruthenium(II) Conjugates of Boron-Dipyrromethene and Biotin for Targeted Photodynamic Therapy in Red Light

The ruthenium(II) complexes [RuCl(L¹)(L³)]Cl (1), [RuCl(L¹)(L⁴)]Cl (2), [RuCl(L²)(L⁴)]Cl (3), [RuCl(L¹)(L⁵)]Cl (4), and [RuCl(L²)(L⁵)]Cl (5) of NNN-donor dipicolylamine (dpa) bases (L⁴, L⁵) having BODIPY (boron-dipyrromethene) moieties, NN-donor phenanthroline derivatives (L¹, L²), and benzyldipicolylamine (bzdpa, L³) were prepared and characterized by spectroscopic techniques and their cellular localization/uptake and photocytotoxicity studied. Complex 1, as its PF₆ salt (1a), has been structurally characterized with help of a single-crystal X-ray diffraction technique. It has a RuN₅Cl core with the Cl bonded trans to the amine nitrogen atom of bzdpa. The complexes showed intense absorption spectral bands near 500 nm (ε ≈ 58000 M^-1 cm^-1) in 2 and 3 and 654 nm (ε ≈ 80000 M^-1 cm^-1) in 4 and 5 in 1/1 DMSO/DPBS (v/v). Complex 5 having biotin and PEGylated-disteryl BODIPY gave a singlet oxygen quantum yield (Φ_Δ) of ∼0.65 in DMSO. Complex 5 exhibited remarkable PDT (photodynamic therapy) activity (IC₅₀ ≈ 0.02 μM) with a photocytotoxicity index (PI) value of >5000 in red light of 600-720 nm in A549 cancer cells. The biotin-conjugated complexes showed better photocytotoxicity in comparison to nonbiotinylated analogues in A549 cells. The complexes displayed less toxicity in HPL1D normal cells in comparison to A549 cancer cells. The emissive BODIPY complexes 3 and 5 (Φ_F ≈ 0.07 in DMSO) showed significant mitochondrial localization.

Zn(II) Curcuminate Complexes with 2,2'-bipyridine and Carboxylates

Two novel zinc(II) compounds with curcuminate (abbreviated as cur-), [Zn(CH3COO)(cur)(bpy)](1)·CH3OH·2H2O (bpy = 2,2'-bipyridine) and [Zn(PhCOO)(cur)(bpy)] (2)·CH3OH, have been synthesized and characterized. Their composition has been determined by single-crystal X-ray structure analysis. Complexes 1 and 2 are similar: in both a five-fold coordination environment of zinc(II) consists of a monodentate carboxylate, a chelating bidentate 2,2'-bipyridine, and curcuminate, which is bound via a deprotonated 1,3-dione moiety. In 1, 2,2'-bipyridine nitrogen atoms and curcuminate oxygen atoms form the base of a square pyramid, whereas the acetate oxygen occupies its apex. The O3N2 donor set in 2 defines a polyhedron which more closely resembles a trigonal bipyramid. The packing in the crystal lattices of both compounds is governed by hydrogen-bonds. Complexes 1 and 2 display higher stability than curcumin in buffered media at pH = 7.0, however, the degradation of coordinated cur- is comparable to that of yellow pigment curcumin (curH) when the pH is raised to 7.2. Both complexes 1 and 2 in DMSO exhibit fluorescence with Stokes shifts of 5367 and 4634 cm-1, respectively.

Photocytotoxic copper(II) complexes of N-salicylyl-l-tryptophan and phenanthroline bases

Four ternary copper(II) complexes of N-salicylyl-l-Tryptophan (Sal-TrpH) and phenanthroline bases of general formula [Cu(Sal-Trp)(L)], where L is 1,10-phenanthroline (phen, 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq, 2), dipyrido[3,2-a:2',3'-c]phenazine (dppz, 3) and 2-(anthracen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (aip, 4), were synthesized and fully characterized. The complexes were evaluated for their affinity for biomolecules and photocytotoxic activities. Single crystal X-ray diffraction studies of complex 1 revealed that it has a square pyramidal CuN₃O₂ core with the phenolate oxygen of salicylaldehyde occupying the axial coordination site in the solid state. Complexes 1-4 displayed the Cu(II)-Cu(I) redox couples at ~-0.3 V vs. Ag/AgCl reference electrode in DMF-0.1 M [Buⁿ₄N](ClO₄). A Cu(II)-based weak d-d band ~650 nm and a moderately strong ligand to metal charge transfer band at ~430 nm were observed in DMF-Tris-HCl buffer (pH 7.2) (1:4 v/v). The complexes are efficient binders to calf thymus DNA and model proteins such as bovine serum albumin and lysozyme. They cleave supercoiled plasmid DNA efficiently when exposed to 446 and 660 nm laser radiation. They are cytotoxic to HeLa (human cervical cancer) and MCF-7 (human breast cancer) cells showing significant enhancement of cytotoxicity upon photo-excitation with low energy visible light. The complexes are found to kill cancer cells through generation of reactive oxygen species (ROS) as confirmed by DCFDA (2',7'-dichlorofluorescin diacetate) assay. The apoptotic cell death induced by complex 4 was confirmed by Annexin V-Fluorescein isothiocyanate-Propidium iodide assay. Confocal microscopic images using 4 showed its primary cytosolic localization in the HeLa and MCF-7 cells.

Photochemotherapy of Infrared Active BODIPY-Appended Iron(III) Catecholates for in Vivo Tumor Growth Inhibition

Iron(III) catecholates of BODIPY (boron-dipyrromethene)-conjugated dipicolylamine ligands, viz. [Fe(L¹)(cat)Cl] (1) and [Fe(L²)(cat)Cl] (2) (H₂cat = catechol), with a ligand-to-metal charge transfer band at ∼800 nm were studied for their in vivo activity in dark and infrared light in luciferase-expressing human breast adenocarcinoma (BT474luc) cells. Complex 2 displayed in vitro photocytotoxicity in BT474luc cells (IC₅₀: 6 μM) in infrared light of 600-720 nm with moderate dark toxicity (IC₅₀: 18 μM) as evidenced from the MTT and Annexin-V FITC/PI staining assays. The mitochondria-localizing complexes showed apoptotic cell death involving reactive oxygen species whose generation was evidenced from 2,7-dichlorofluorescein diacetate assay. In vivo studies showed tumor growth inhibition in mice with an optimized complex 2 dose of 5 mg per kg body weight on exposure to infrared light of 685 nm (dose of 20 mW/cm²). The in vivo results exemplify complex 2 as a unique iron-based infrared-active photochemotherapeutic agent.

Fully Functionalizable β,β'-BODIPY Dimer: Synthesis, Structure, and Photophysical Signatures

The versatility in the synthesis of BODIPY derivatives in terms of functionalization is further demonstrated. In particular, in this work β-β'-BODIPY dimers with varied functional groups in the meso positions were synthesized in very efficient yields and short reaction times from a single platform. A photophysical study was carried out in all of the compounds. The resultant dimers show absorption bands at around 600 nm as a consequence of electronically coupled monomers disposed with a dihedral angle of around 30°, which is supported by theoretical simulations. The emission properties of these molecules are distinguished by the appearance of an ICT state as the polarity of the solvent increases.

Recent strategies to improve boron dipyrromethene (BODIPY) for photodynamic cancer therapy: an updated review

BODIPYs are photosensitizers activatable by light to generate highly reactive singlet oxygen (¹O₂) from molecular oxygen, leading to tissue damage in the photoirradiated region. Despite their extraordinary photophysical characteristics, they are not featured in clinical photodynamic therapy. This review discusses the recent advances in the design and/or modifications of BODIPYs since 2013, to improve their potential in photodynamic cancer therapy and related areas.

Self-assembled organic nanorods for dual chemo-photodynamic therapies

Photodynamic therapy (PDT) and chemotherapy have been extensively developed as effective approaches against cancer. Herein, we constructed organic nanorods by rational co-assembly of photosensitizer, di-iodinated borondipyrromethene (BDP-I2), and chemical anticancer drug, paclitaxel (PTX). The physico- and photochemical properties of the obtained nanorods were carefully investigated. BDP-I2 was selected for its high singlet oxygen (1O2) quantum yields. And the corresponding 1O2 generation ability and photodynamic effect were evaluated both in vitro and in vivo. The accelerated endosomal escape of the nanorods induced by the photodynamic effect enhanced the chemotherapeutic efficacy of PTX. We believe that this synergetic nanomedicine represents a new development for antitumor chemophotodynamic therapy.

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.