Gallium Porphyrin Research Articles

Erythrocyte-Mimicking Nanovesicle Targeting Porphyromonas gingivalis for Periodontitis.

Porphyromonas gingivalis has been demonstrated to have the strongest association with periodontitis. Within the host, P. gingivalis relies on acquiring iron and heme through the aggregation and lysis of erythrocytes, which are important factors in the growth and virulence of P. gingivalis. Additionally, the excess obtained heme is deposited on the surface of P. gingivalis, protecting the cells from oxidative damage. Based on these biological properties of the interaction between P. gingivalis and erythrocytes, this study developed an erythrocyte membrane nanovesicle loaded with gallium porphyrins to mimic erythrocytes. The nanovesicle can target and adhere with P. gingivalis precisely, being lysed and utilized by P. gingivalis as erythrocytes. Ingested gallium porphyrin replaces iron porphyrin in P. gingivalis, causing intracellular metabolic disruption. Deposited porphyrin generates a large amount of reactive oxygen species (ROS) under blue light, causing oxidative damage, and its lethality is enhanced by bacterial metabolic disruption, synergistically killing P. gingivalis. Our results demonstrate that this strategy can target and inhibit P. gingivalis, reduce its invasion of epithelial cells, and alleviate the progression of periodontitis.

Decrease of ESKAPE virulence with a cationic heme-mimetic gallium porphyrin photosensitizer: The Trojan horse strategy that could help address antimicrobial resistance

IntroductionEmerging antibiotic resistance among bacterial pathogens has forced an urgent need for alternative non-antibiotic strategies development that could combat drug resistant-associated infections. Suppression of virulence of ESKAPE pathogens' by targeting multiple virulence traits provides a promising approach. ObjectivesHere we propose an iron-blocking antibacterial therapy based on a cationic heme-mimetic gallium porphyrin (GaCHP), which antibacterial efficacy could be further enhanced by photodynamic inactivation. MethodsWe used gallium heme mimetic porphyrin (GaCHP) excited with light to significantly reduce microbial viability and suppress both the expression and biological activity of several virulence traits of both Gram-positive and Gram-negative ESKAPE representatives, i.e., S. aureus and P. aeruginosa. Moreover, further improvement of the proposed strategy by combining it with routinely used antimicrobials to resensitize the microbes to antibiotics and provide enhanced bactericidal efficacy was investigated. ResultsThe proposed strategy led to substantial inactivation of critical priority pathogens and has been evidenced to suppress the expression and biological activity of multiple virulence factors in S. aureus and P. aeruginosa. Finally, the combination of GaCHP phototreatment and antibiotics resulted in promising strategy to overcome antibiotic resistance of the studied microbes and to enhance disinfection of drug resistant pathogens. ConclusionLastly, considering high safety aspects of the proposed treatment toward host cells, i.e., lack of mutagenicity, no dark toxicity and mild phototoxicity, we describe an efficient alternative that simultaneously suppresses the functionality of multiple virulence factors in ESKAPE pathogens.

Glucose-Responsive Self-Healing Bilayer Drug Microneedles Promote Diabetic Wound Healing Via a Trojan-Horse Strategy.

Chronic nonhealing wounds are serious complications of diabetes with a high morbidity, and they can lead to disability or death. Conventional drug therapy is ineffective for diabetic wound healing because of the complex environment of diabetic wounds and the depth of drug penetration. Here, we developed a self-healing, dual-layer, drug-carrying microneedle (SDDMN) for diabetic wound healing. This SDDMN can realize transdermal drug delivery and broad-spectrum sterilization without drug resistance and meets the multiple needs of the diabetic wound healing process. Quaternary ammonium chitosan cografted with dihydrocaffeic acid (Da) and l-arginine and oxidized hyaluronic acid-dopamine are the main parts of the self-healing hydrogel patch. Methacrylated poly(vinyl alcohol) (methacrylated PVA) and phenylboronic acid (PBA) were used as the main part of the MN, and gallium porphyrin modified with 3-amino-1,2 propanediol (POGa) and insulin were encapsulated at its tip. Under hyperglycaemic conditions, the PBA moiety in the MN reversibly formed a glucose-boronic acid complex that promoted the rapid release of POGa and insulin. POGa is disguised as hemoglobin through a Trojan-horse strategy, which is then taken up by bacteria, allowing it to target bacteria and infected lesions. Based on the synergistic properties of these components, SDDMN-POGa patches exhibited an excellent biocompatibility, slow drug release, and antimicrobial properties. Thus, these patches provide a potential therapeutic approach for the treatment of diabetic wounds.

Efficient and Stable Air-Processed Ternary Organic Solar Cells Incorporating Gallium-Porphyrin as an Electron Cascade Material.

Two gallium porphyrins, a tetraphenyl GaCl porphyrin, termed as (TPP)GaCl, and an octaethylporphyrin GaCl porphyrin, termed as (OEP)GaCl, were synthesized to use as an electron cascade in ternary organic bulk heterojunction films. A perfect matching of both gallium porphyrins' energy levels with that of poly(3-hexylthiophene-2,5-diyl) (P3HT) or poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) polymer donor and the 6,6-phenyl C71 butyric acid methyl ester (PCBM) fullerene acceptor, forming an efficient cascade system that could facilitate electron transfer between donor and acceptor, was demonstrated. Therefore, ternary organic solar cells (OSCs) using the two porphyrins in various concentrations were fabricated where a performance enhancement was obtained. In particular, (TPP)GaCl-based ternary OSCs of low concentration (1:0.05 vv%) exhibited a ~17% increase in the power conversion efficiency (PCE) compared with the binary device due to improved exciton dissociation, electron transport and reduced recombination. On the other hand, ternary OSCs with a high concentration of (TPP)GaCl (1:0.1 vv%) and (OEP)GaCl (1:0.05 and 1:0.1 vv%) showed the poorest efficiencies due to very rough nanomorphology and suppressed crystallinity of ternary films when the GaCl porphyrin was introduced to the blend, as revealed from X-ray diffraction (XRD) and atomic force microscopy (AFM). The best performing devices also exhibited improved photostability when exposed to sunlight illumination for a period of 8 h than the binary OSCs, attributed to the suppressed photodegradation of the ternary (TPP)GaCl 1:0.05-based photoactive film.

Photoactivated Gallium Porphyrin Reduces Staphylococcus aureus Colonization on the Skin and Suppresses Its Ability to Produce Enterotoxin C and TSST-1.

Staphylococcus aureus is a key pathogen in atopic dermatitis (AD) pathogenicity. Over half of AD patients are carriers of S. aureus. Clinical isolates derived from AD patients produce various staphylococcal enterotoxins, such as staphylococcal enterotoxin C or toxic shock syndrome toxin. The production of these virulence factors is correlated with more severe AD. In this study, we propose cationic heme-mimetic gallium porphyrin (Ga3+CHP), a novel gallium metalloporphyrin, as an anti-staphylococcal agent that functions through dual mechanisms: a light-dependent mechanism (antimicrobial photodynamic inactivation, aPDI) and a light-independent mechanism (suppressing iron metabolism). Ga3+CHP has two additive quaternary ammonium groups that increase its water solubility. Furthermore, Ga3+CHP is an efficient generator of singlet oxygen and can be recognized by heme-target systems such as Isd, which improves the intracellular accumulation of this compound. Ga3+CHP activated with green light effectively reduced the survival of clinical S. aureus isolates derived from AD patients (>5 log10 CFU/mL) and affected their enterotoxin gene expression. Additionally, there was a decrease in the biological functionality of studied toxins regarding their superantigenicity. In aPDI conditions, there was no pronounced toxicity in HaCaT keratinocytes with both normal and suppressed filaggrin gene expression, which occurs in ∼50% of AD patients. Additionally, no mutagenic activity was observed. Green light-activated gallium metalloporphyrins may be a promising chemotherapeutic to reduce S. aureus colonization on the skin of AD patients.

Phototreatment with water-soluble cationic gallium porphyrin impacts Staphylococcus aureus viability and staphyloxanthanin level

Phototreatment with water-soluble cationic gallium porphyrin impacts Staphylococcus aureus viability and staphyloxanthanin level

Cobalt-catalyzed carbonylation of epoxides to β-lactones promoted by gallium porphyrin

Oxophilic Ga(III) porphyrin complexes were developed to replace Al(III) or toxic Cr(III) complexes as the Lewis acid catalyst to achieve the Co-catalyzed carbonylation of epoxides to β-lactones. Its performance is comparable to the state-of-the-art catalyst systems consisting of Al(III) or Cr(III). Large-scale reaction using the combination of (TPP)GaCl and Co2(CO)8 in low loading revealed its potential application for the preparation of β-butyrolactone from propylene oxide and CO.

Nonfouling and Antibacterial Zwitterionic Contact Lenses Loaded with Heme-Mimetic Gallium Porphyrin for Treating Keratitis.

Antifouling and antibacterial are two critical challenges in the development of contact lenses (CLs). Herein, we presented nonfouling and antibacterial bifunctionalized CLs by encapsulating cationic heme-mimetic gallium porphyrin (Ga-CHP) into zwitterionic-elastomeric-networked (ZEN) hydrogel. Results proved that the ZEN hydrogel showed excellent abilities to resist non-specific protein adsorption, bacterial adhesion, and biofilm formation. Moreover, Ga-CHP could be sustainably released and kill >99.9% planktonic bacteria and >99.9% mature biofilms. In vivo, the symptoms of bacterial keratitis in mice were significantly alleviated after wearing the CLs for 7 days via iron-blocking and photodynamic synergistic antibacterial therapy with the help of natural sunlight. This study highlights the nonfouling and antibacterial superiority of the Ga-CHP-functional zwitterionic CLs and proposes a portable yet efficient non-antibiotic keratitis treatment strategy.

Iron-blocking antibacterial therapy with cationic heme-mimetic gallium porphyrin photosensitizer for combating antibiotic resistance and enhancing photodynamic antibacterial activity

Iron is an essential nutrient for bacterial survival and replication. Interfering with iron metabolism is a potential nondrug-resistant antibacterial strategy. Here we propose an iron-blocking antibacterial therapy (IBAT) based on cationic heme-mimetic gallium porphyrin (Ga-CHP). Cations and heme bionics facilitated the uptake of Ga-CHP by bacteria through heme metabolism and are the primary motifs for its broad-spectrum antibacterial activity. Ga-CHP can rapidly kill gram-positive and gram-negative strains, even multidrug-resistant strains. Notably, unlike antibiotics, it is hard for bacteria to evolve drug resistance in terms of phenotypes and mutations. Furthermore, Ga-CHP is also a superior photosensitizer and its antibacterial capability can be further enhanced via synergistic photodynamic therapy in vitro and in vivo due to heme-assisted catalase inactivation. This work presents an innovative antibacterial strategy for addressing antibiotic resistance crisis and enhancing photodynamic antibacterial activity.

Synthesis and in vitro analysis of novel gallium tetrakis(4-methoxyphenyl)porphyrin and its long-acting nanoparticle as a potent antimycobacterial agent

Bacterial heme uptake pathways offer a novel target for antimicrobial drug discovery. Recently, gallium (Ga) porphyrin complexes were found to be effective against mycobacterial heme uptake pathways. The goal of the current study is to build on this foundation and develop a new Ga(III) porphyrin and its nanoparticles, formulated by a single emulsion-evaporation technique to inhibit the growth of Mycobacterium avium complex (MAC) with enhanced properties. Gallium 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin chloride (GaMeOTP) was synthesized from 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin and GaCl3. GaMeOTP showed enhanced antimicrobial activity against MAC104 and some clinical M. avium isolates. The synthesized Ga(III) porphyrin antimicrobial activity resulted in the overproduction of reactive oxygen species. Our study also demonstrated that F127 nanoparticles encapsulating GaMeOTP exhibited a smaller size than GaTP nanoparticles and a better duration of activity in MAC-infected macrophages compared to the free GaMeOTP. The nanoparticles were trafficked to endosomal compartments within MAC-infected macrophages, likely contributing to the antimicrobial activity of the drug.

Iron-Blocking Antibacterial Therapy with Cationic Heme-Mimetic Gallium Porphyrin Photosensitizer for Combating Antibiotic Resistance and Enhancing Photodynamic Antibacterial Activity

Iron-Blocking Antibacterial Therapy with Cationic Heme-Mimetic Gallium Porphyrin Photosensitizer for Combating Antibiotic Resistance and Enhancing Photodynamic Antibacterial Activity

Gallium Porphyrin and Gallium Nitrate Reduce the High Vancomycin Tolerance of MRSA Biofilms by Promoting Extracellular DNA-Dependent Biofilm Dispersion.

Biofilms, structured communities of bacterial cells embedded in a self-produced extracellular matrix (ECM) which consists of proteins, polysaccharide intercellular adhesins (PIAs), and extracellular DNA (eDNA), play a key role in clinical infections and are associated with an increased morbidity and mortality by protecting the embedded bacteria against drug and immune response. The high levels of antibiotic tolerance render classical antibiotic therapies impractical for biofilm-related infections. Thus, novel drugs and strategies are required to reduce biofilm tolerance and eliminate biofilm-protected bacteria. Here, we showed that gallium, an iron mimetic metal, can lead to nutritional iron starvation and act as dispersal agent triggering the reconstruction and dispersion of mature methicillin-resistant Staphylococcus aureus (MRSA) biofilms in an eDNA-dependent manner. The extracellular matrix, along with the integral bacteria themselves, establishes the integrated three-dimensional structure of the mature biofilm. The structures and compositions of gallium-treated mature biofilms differed from those of natural or antibiotic-survived mature biofilms but were similar to those of immature biofilms. Similar to immature biofilms, gallium-treated biofilms had lower levels of antibiotic tolerance, and our in vitro tests showed that treatment with gallium agents reduced the antibiotic tolerance of mature MRSA biofilms. Thus, the sequential administration of gallium agents (gallium porphyrin and gallium nitrate) and relatively low concentrations of vancomycin (16 mg/L) effectively eliminated mature MRSA biofilms and eradicated biofilm-enclosed bacteria within 1 week. Our results suggested that gallium agents may represent a potential treatment for refractory biofilm-related infections, such as prosthetic joint infections (PJI) and osteomyelitis, and provide a novel basis for future biofilm treatments based on the disruption of normal biofilm-development processes.

Gallium Porphyrin and Gallium Nitrate Synergistically Inhibit Mycobacterial Species by Targeting Different Aspects of Iron/Heme Metabolism.

There is an urgent need for new effective and safe antibiotics active against pathogenic mycobacterial species. Gallium (Ga) nitrate (Ga(NO3)3) and Ga porphyrin (GaPP) have each been shown to inhibit the growth of a variety of mycobacterial species. The Ga(III) ion derived from Ga(NO3)3 has the potential to disrupt the mycobacterial Fe(III) uptake mechanisms and utilization, including replacing iron (Fe) in the active site of enzymes, resulting in the disruption of function. Similarly, noniron metalloporphyrins such as heme mimetics, which can be transported across the bacterial membrane via heme-uptake pathways, would potentially block the acquisition of iron-containing heme and bind to heme-utilizing proteins, making them nonfunctional. Given that they likely act on different aspects of mycobacterial Fe metabolism, the efficacy of combining Ga(NO3)3 and GaPP was studied in vitro against Mycobacterium avium, Mycobacterium abscessus, and Mycobacterium tuberculosis (M. tb). The combination was then assessed in vivo in a murine pulmonary infection model of M. abscessus. We observed that Ga(NO3)3 in combination with GaPP exhibited synergistic inhibitory activity against the growth of M. avium, M. tb, and M. abscessus, being most active against M. abscessus. Activity assays indicated that Ga(NO3)3 and GaPP inhibited both catalase and aconitase at high concentrations. However, the combination showed a synergistic effect on the aconitase activity of M. abscessus. The Ga(NO3)3/GaPP combination via intranasal administration showed significant antimicrobial activity in mice infected with M. abscessus. M. abscessus CFU from the lungs of the Ga(NO3)3/GaPP-treated mice was significantly less compared to that of nontreated or single Ga(III)-treated mice. These findings suggest that combinations of different Ga(III) compounds can synergistically target multiple iron/heme-utilizing mycobacterial enzymes. The results support the potential of combination Ga therapy for development against mycobacterial pathogens.

Nonlinear optical performances of graphene oxide ternary nanohybrids functionalized by axially coordinated gallium porphyrins

A GaTPP-GO-GaTTP ternary nanohybrid possesses enhanced optical nonlinearities compared to other samples due to the efficient charge transfer effect.

Single hydroxo-bridged group 13 metalloporphyrin dimers: Solution studies and solid-state structures

The syntheses of indium, gallium and aluminum porphyrin dimers with a single hydroxo-bridge, [Formula: see text][M(Porph)]2(OH)[Formula: see text], are described. Emphasis is given to indium and gallium derivatives. The X-ray structures for [Formula: see text] [Ga(OEP)]2(OH)[Formula: see text] ClO4 and [Formula: see text] [In(OEP)]2(OH)[Formula: see text] ClO4 (two forms) are presented. The dimeric molecules can be synthesized by the acid-treatment of the corresponding hydroxo-ligated monomeric complexes [M(OEP)(OH)] and [M(TPP)(OH)]. The nature of the starting material (the hydroxo-ligated monomer) was first suggested by IR spectroscopy and further proved by proton-deuterium exchange followed by 1H NMR spectroscopy. The structure of a monomeric indium hydroxide complex, [In(OEP)(OH)], is also presented. The synthesis of the dimer for all metals can be monitored by UV-vis spectroscopy, which clearly demonstrates that a blue-shift of the Soret band accompanies formation of the dimer from the monomer. A strong [Formula: see text]–[Formula: see text]interaction between the two porphyrin rings of these [Formula: see text]-hydroxo-bridged dimers is confirmed both by solution state studies (1H NMR and UV-vis spectroscopy) and the X-ray structures of [Formula: see text] [M(OEP)]2(OH)[Formula: see text] ClO4 (M = In, Ga). In addition, exposure of methylene chloride solutions of these bridged complexes to white light afforded the corresponding chloro derivatives, [M(Porph)Cl]. The stereochemistry of a range of [Formula: see text]-hydroxo dimers is discussed and DFT simulations at the HSEH1PBE/SDD level of theory provide suitable structural models and further electronic structure insights on selected [Ga(Porph)(OH)] and [Formula: see text] [Ga(Porph)]2(OH)[Formula: see text][Formula: see text] derivatives.

Simultaneous Detection of Vanadyl, Nickel, Iron, and Gallium Porphyrins in Marine Shales from the Eagle Ford Formation, South Texas

Metalloporphyrins in immature shales of the Late Cretaceous Eagle Ford Formation from South Texas were analyzed by positive-ion electrospray ionization (ESI) Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Vanadyl, nickel, iron, and gallium porphyrins were detected in a single mass spectrum. The iron porphyrins were most abundant, followed by vanadyl, nickel, and gallium porphyrins, consistent with the metal contents determined by elemental analysis. The distribution of porphyrins shows that deoxophylloerythroetio (DPEP) porphyrins, dicyclic-deoxophylloerythroetio (di-DPEP) porphyrins, and porphyrins containing oxygen functional groups are the main components. The detection of oxygen-containing porphyrins, such as iron porphyrins with formulas of CnHmN4FeO, CnHmN4FeO2, and CnHmN5FeO2, would offer new clues of petroporphyrins formation mechanism from biological sources, such as chlorophylls and hemes. To our knowledge, this reports for the first time the presence of oxygen-containing iron porphyrins and gallium porphyrins in geological samples other than coals and lignites. The discovery of these petroporphyrins could provide additional insights into the diagenetic pathway of petroporphyrins and novel applications in petroleum geochemistry/exploration and oil refining. The composition of metalloporphyrins may potentially provide clues to decipher the redox conditions during deposition in the Eagle Ford Formation and provide better understanding of the Oceanic Anoxic Event 2 (OAE-2).

Axial Ligand Effects on the Structures of Self-Assembled Gallium-Porphyrin Monolayers on Highly Oriented Pyrolytic Graphite.

Monolayers of five-coordinate gallium octaethylporphyrin complexes (Ga(OEP)X; X = Cl, Br, I, O3SCF3, CCPh) on highly oriented pyrolytic graphite were studied at the solid-liquid (1-phenyloctane) interface using scanning tunneling microscopy (STM) to probe the dependence of their properties on the nature of the axial X ligand. Density functional theory calculations of the gas-phase structures of the free molecules reveal that the gallium atom is positioned above the plane of the porphyrin macrocycle, with this pyramidal distortion increasing in magnitude according to X = O3SCF3 (displacement = 0.35 Å) < Cl, Br, I (∼0.47 Å) < CCPh (0.54 Å). All compounds exhibit pseudohexagonal close-packed structures in which the porphyrin is oriented coplanar with the surface and the axial ligand is oriented perpendicular to it, and with unit-cell parameters that are within experimental error of each other (a, b = 1.34 (3)-1.39 (2) nm, Γ = 66 (2)-68 (1)°). In contrast to these close similarities, the stabilities of the monolayers are sensitive to the nature of the axial ligand: the monolayers of Ga(OEP)(O3SCF3) and Ga(OEP)(CCPh) exhibit damage during the STM experiment upon repeated scanning and upon toggling the sign of the bias potential, but monolayers of Ga(OEP)Cl, Ga(OEP)Br, and Ga(OEP)I do not. A second important ligand-influenced property is that Ga(OEP)I forms bilayer structures, whereas the other Ga(OEP)X compounds form monolayers exclusively under identical conditions. The top layer of the Ga(OEP)I bilayer is oriented with the iodo ligand directed away from the surface, like the bottom layer, but the molecules pack in a square, lower-density geometry. The comparatively large polarizability of the iodo ligand is suggested to be important in stabilizing the bilayer structure.

Photochemical Chlorination and Oxygenation Reaction of Cyclohexene Sensitized by Ga(III) Porphyrin–Clay Minerals System with High Durability and Usability

Abstract Photochemical chlorination and oxygenation reaction of cyclohexene sensitized by gallium(III) porphyrin–clay hybrid compound was investigated. Gallium(III) porphyrin did not aggregate on the clay surface, and thus, maintained photoactivity for the photochemical reaction. Gallium(III) porphyrin without clay decomposed immediately in the photochemical reaction. On the other hand, gallium(III) porphyrin adsorbed on clay was more stable than that without clay during the photochemical reaction and the altered porphyrin on clay still had photocatalytic ability along with original porphyrin. It was suggested that gallium(III) porphyrin was protected by clay surface during the photochemical reaction. In addition, the efficiency for the photochemical chlorination and oxygenation reaction was kept even at high porphyrin adsorption densities on clay. These findings are beneficial to construct efficient and durable photochemical reaction systems.

PET/PDT theranostics: synthesis and biological evaluation of a peptide-targeted gallium porphyrin.

The development of novel theranostic agents is an important step in the pathway towards personalised medicine, with the combination of diagnostic and therapeutic modalities into a single treatment agent naturally lending itself to the optimisation and personalisation of treatment. In pursuit of the goal of a molecular theranostic suitable for use as a PET radiotracer and a photosensitiser for PDT, a novel radiolabelled peptide-porphyrin conjugate targeting the α6β1-integrin has been developed. (69/71)Ga and (68)Ga labelling of an azide-functionalised porphyrin has been carried out in excellent yields, with subsequent bioconjugation to an alkyne-functionalised peptide demonstrated. α6β1-integrin expression of two cell lines has been evaluated by flow cytometry, and therapeutic potential of the conjugate demonstrated. Evaluation of the phototoxicity of the porphyrin-peptide theranostic conjugate in comparison to an untargeted control porphyrin in vitro, demonstrated significantly enhanced activity for a cell line with higher α6β1-integrin expression when compared with a cell line exhibiting lower α6β1-integrin expression.

Sonodynamically induced apoptosis and active oxygen generation by gallium–porphyrin complex, ATX-70

In this study, we investigated the induction of apoptosis by ultrasound in the presence of the photochemically active gallium-porphyrin complex, 7,12-bis(1-decyloxyethyl)-Ga(III)-3,8,13,17-tetramethyl-porphyrin 2,18-dipropionyl diaspartic acid (ATX-70). HL-60 cells were exposed to ultrasound for up to 3 min in the presence and absence of ATX-70, and the induction of apoptosis was examined by analyzing cell morphology, DNA fragmentation, and caspase-3 activity. Cells treated with 80 μM ATX-70 and ultrasound clearly showed membrane blebbing and cell shrinkage, whereas significant morphologic changes were not observed in cells exposed to either ultrasound or ATX-70 alone. Also, DNA ladder formation and caspase-3 activation were observed in cells treated with both ultrasound and ATX-70 but not in cells treated with ultrasound or ATX-70 alone. In addition, the combination of ATX-70 and the same acoustical arrangement of ultrasound substantially enhanced nitroxide generation by the cells. Sonodynamically induced apoptosis, caspase-3 activation, and nitroxide generation were significantly suppressed by histidine. These results indicate that the combination of ultrasound and ATX-70 induces apoptosis in HL-60 cells. The significant reduction in sonodynamically induced apoptosis, nitroxide generation, and caspase-3 activation by histidine suggests that active species such as singlet oxygen are important in the sonodynamic induction of apoptosis.