Photolon™, a chlorin e6 derivative, triggers ROS production and light-dependent cell death via necrosis

Research Progress of Natural Product Photosensitizers in Photodynamic Therapy

Photodynamic therapy is a noninvasive cancer treatment that utilizes photosensitizers to generate reactive oxygen species upon light exposure, leading to tumor cell apoptosis. Although photosensitizers have shown efficacy in clinical practice, they are associated with certain disadvantages, such as a certain degree of toxicity and limited availability. Recent studies have shown that natural product photosensitizers offer promising options due to their low toxicity and potential therapeutic effects. In this review, we provide a summary and evaluation of the current clinical photosensitizers that are commonly used and delve into the anticancer potential of natural product photosensitizers like psoralens, quinonoids, chlorophyll derivatives, curcumin, chrysophanol, doxorubicin, tetracyclines, Leguminosae extracts, and Lonicera japonica extract. The emphasis is on their phototoxicity, pharmacological benefits, and effectiveness against different types of diseases. Novel and more effective natural product photosensitizers for future clinical application are yet to be explored in further research. In conclusion, natural product photosensitizers have potential in photodynamic therapy and represent a promising area of research for cancer treatment.

Photolon Nanoporous Photoactive Material with Antibacterial Activity and Label-Free Noncontact Method for Free Radical Detection

The worldwide increase in bacterial resistance and healthcare-associated bacterial infections pose a serious threat to human health. The antimicrobial photodynamic method reveals the opportunity for a new therapeutic approach that is based on the limited delivery of photosensitizer from the material surface. Nanoporous inorganic–organic composites were obtained by entrapment of photosensitizer Photolon in polysiloxanes that was prepared by the sol–gel method. The material was characterized by its porosity, optical properties (fluorescence and absorbance), and laser-induced antimicrobial activity against Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. The permanent encapsulation of Photolon in the silica coating and the antimicrobial efficiency was confirmed by confocal microscope and digital holotomography. The generation of free radicals from nanoporous surfaces was proved by scanning Kelvin probe microscopy. For the first time, it was confirmed that Kelvin probe microscopy can be a label-free, noncontact alternative to other conventional methods based on fluorescence or chemiluminescence probes, etc. It was confirmed that the proposed photoactive coating enables the antibacterial photodynamic effect based on free radicals released from the surface of the coating. The highest bactericidal efficiency of the proposed coating was 87.16%. This coating can selectively limit the multiplication of bacterial cells, while protecting the environment and reducing the risk of surface contamination.

Probing the Interactions of Porphyrins with Macromolecules Using NMR Spectroscopy Techniques

Porphyrinic compounds are widespread in nature and play key roles in biological processes such as oxygen transport in blood, enzymatic redox reactions or photosynthesis. In addition, both naturally derived as well as synthetic porphyrinic compounds are extensively explored for biomedical and technical applications such as photodynamic therapy (PDT) or photovoltaic systems, respectively. Their unique electronic structures and photophysical properties make this class of compounds so interesting for the multiple functions encountered. It is therefore not surprising that optical methods are typically the prevalent analytical tool applied in characterization and processes involving porphyrinic compounds. However, a wealth of complementary information can be obtained from NMR spectroscopic techniques. Based on the advantage of providing structural and dynamic information with atomic resolution simultaneously, NMR spectroscopy is a powerful method for studying molecular interactions between porphyrinic compounds and macromolecules. Such interactions are of special interest in medical applications of porphyrinic photosensitizers that are mostly combined with macromolecular carrier systems. The macromolecular surrounding typically stabilizes the encapsulated drug and may also modify its physical properties. Moreover, the interaction with macromolecular physiological components needs to be explored to understand and control mechanisms of action and therapeutic efficacy. This review focuses on such non-covalent interactions of porphyrinic drugs with synthetic polymers as well as with biomolecules such as phospholipids or proteins. A brief introduction into various NMR spectroscopic techniques is given including chemical shift perturbation methods, NOE enhancement spectroscopy, relaxation time measurements and diffusion-ordered spectroscopy. How these NMR tools are used to address porphyrin-macromolecule interactions with respect to their function in biomedical applications is the central point of the current review.

Sonodynamic Therapy for the Treatment of Intracranial Gliomas

High-grade gliomas are the most common and aggressive malignant primary brain tumors. Current therapeutic schemes include a combination of surgical resection, radiotherapy and chemotherapy; even if major advances have been achieved in Progression Free Survival and Overall Survival for patients harboring high-grade gliomas, prognosis still remains poor; hence, new therapeutic options for malignant gliomas are currently researched. Sonodynamic Therapy (SDT) has proven to be a promising treatment combining the effects of low-intensity ultrasound waves with various sound-sensitive compounds, whose activation leads to increased immunogenicity of tumor cells, increased apoptotic rates and decreased angiogenetic potential. In addition, this therapeutic technique only exerts its cytotoxic effects on tumor cells, while both ultrasound waves and sensitizing compound are non-toxic per se. This review summarizes the present knowledge regarding mechanisms of action of SDT and currently available sonosensitizers and focuses on the preclinical and clinical studies that have investigated its efficacy on malignant gliomas. To date, preclinical studies implying various sonosensitizers and different treatment protocols all seem to confirm the anti-tumoral properties of SDT, while first clinical trials will soon start recruiting patients. Accordingly, it is crucial to conduct further investigations regarding the clinical applications of SDT as a therapeutic option in the management of intracranial gliomas.

Synthesis, Characterization and Photodynamic Activity against Bladder Cancer Cells of Novel Triazole-Porphyrin Derivatives

Novel triazole-porphyrin derivatives (TZ-PORs) were synthesized through the Heck reaction and then incorporated into polyvinylpyrrolidone (PVP) micelles. After verifying that this incorporation did not compromise the photophysical and chemical features of TZ-PORs as photosensitizers, the phototoxicity of the formulations towards cancer cells was screened. Biological studies show high photodynamic activity of all PVP-TZ-POR formulations against a bladder cancer cell line with a particular highlight to PVP-TZ-POR 7e and 7f that are able to significantly reduce HT-1376 cell viability, while they had no effect on control ARPE-19 cells.

Visible-Light-Activated Molecular Nanomachines Kill Pancreatic Cancer Cells

Recently, synthetic molecular nanomachines (MNMs) that rotate unidirectionally in response to UV light excitation have been used to produce nanomechanical action on live cells to kill them through the drilling of holes in their cell membranes. In the work here, visible-light-absorbing MNMs are designed and synthesized to enable nanomechanical activation by 405 nm light, thereby using a wavelength of light that is less phototoxic than the previously employed UV wavelengths. Visible-light-absorbing MNMs that kill pancreatic cancer cells upon response to light activation are demonstrated. Evidence is presented to support the conclusion that MNMs do not kill cancer cells by the photothermal effect when used at low optical density. In addition, MNMs suppress the formation of reactive oxygen species, leaving nanomechanical action as the most plausible working mechanism for cell killing under the experimental conditions.

High Affinity of Chlorin e6 to Immunoglobulin G for Intraoperative Fluorescence Image-Guided Cancer Photodynamic and Checkpoint Blockade Therapy

Cancer photodynamic therapy (PDT) represents an attractive local treatment in combination with immunotherapy. Successful cancer PDT relies on image guidance to ensure the treatment accuracy. However, existing nanotechnology for co-delivery of photosensitizers and image contrast agents slows the clearance of PDT agents from the body and causes a disparity between the release profiles of the imaging and PDT agents. We have found that the photosensitizer Chlorin e6 (Ce6) is inherently bound to immunoglobulin G (IgG) in a nanomolarity range of affinity. Ce6 and IgG self-assemble to form the nanocomplexes termed Chloringlobulin (Chlorin e6 + immunoglobulin G). Chloringlobulin enhances the Ce6 concentration in the tumor without changing its elimination half-life in blood. Utilizing the immune checkpoint inhibitor antiprogrammed death ligand 1 (PD-L1) (αPD-L1) to prepare αPD-L1 Chloringlobulin, we have demonstrated a combination of Ce6-based red-light fluorescence image-guided surgery, stereotactic PDT, and PD-L1 blockade therapy of mice bearing orthotopic glioma. In mice bearing an orthotopic colon cancer model, we have prepared another Chloringlobulin that allows intraoperative fluorescence image-guided PDT in combination with PD-L1 and cytotoxic T lymphocyte antigen 4 (CTLA-4) dual checkpoint blockade therapy. The Chloringlobulin technology shows great potential for clinical translation of combinatorial intraoperative fluorescence image-guided PDT and checkpoint blockade therapy.

Novel hydrophilic galactose-conjugated chlorin e6 derivatives for photodynamic therapy and fluorescence imaging

We synthesized new hydrophilic chlorin e₆ derivatives with two and four galactose fragments conjugated to the macrocycle via carbon atom in position 6 of the galactose fragment. Galactose fragments were inserted by alkylation of the amino groups of chlorin e₆ amides with one and two ethylene diamine fragments on the macrocycle periphery with triflate of diacetone galactose, followed by removal of diisopropylidene protection by 70% aqueous trifluoroacetic acid. The synthesized compounds were shown to be capable of penetrating the membrane of HeLa cells; they have intense red fluorescence inside the cell and have phototoxic properties towards HeLa cells (upon LED irradiation at 660 nm and light exposure value of 12 J/cm²). These properties, along with water solubility, allow us to consider the synthesized compounds to be promising as potential antitumor PSs and diagnostic compounds for visualizing malignant tumors and creating on their basis preparations for simultaneous diagnostics and therapy of oncological diseases.

Development of chlorin e6-conjugated poly(ethylene glycol)-poly(d,l-lactide) nanoparticles for photodynamic therapy

Aim: In this study, we developed a chlorin e6-conjugated methoxy-poly(ethylene glycol)-poly(d,l-lactide) (mPEG-PLA-Ce6) amphiphilic polymer, which self-assembled to form stable nanoparticles. Materials & methods: The nanoparticles were characterized for particle size, ζ-potential and singlet oxygen (1O2) generation. Cellular internalization and phototoxicity were investigated against monolayer and 3D spheroids of human lung adenocarcinoma cells (A549). Results & conclusion: mPEG-PLA-Ce6 exhibited a size of 149.72 ± 3.51 nm and ζ-potential of -24.82 ± 2.94 mV. The 1O2 generation by mPEG-PLA-Ce6 in water was considerably higher than free chlorin e6. The nanoparticles showed enhanced cellular internalization and phototoxicity in monolayer and 3D spheroids. The developed mPEG-PLA-Ce6 has potential application as a nanocarrier of chlorin e6 for photodynamic therapy of solid tumors.

DNA directed damage using a brominated DAPI derivative

Conversion of a DNA-binding fluorophore (DAPI) to a photosensitizer via bromination retains high fluorescence and high affinity DNA binding but now produces light-induced reactive oxygen species directed towards DNA resulting in rapid cancer cell death.

Endoscopic ultrasonography-guided tumor ablation

Real-time guidance of needle advancement has transformed endoscopic ultrasound (EUS) from a diagnostic to an interventional procedure. EUS-guided fine-needle puncture has application in various interventional procedures (drainage of pseudocyst, biliary intervention, and injection of drugs). Celiac plexus or ganglion neurolysis for pain control is the major current EUS-guided fine-needle injection procedure. Feasibility and safety to accurately position needle devices and/or inject under real-time EUS imaging with precise delivery of interventional agent have expanded the use of EUS to ablate tumors. These include radiofrequency ablation, or delivery of fiducial markers, potential antitumor agents, or radioactive seeds, in the cancer mass. Minimally invasive EUS-guided antitumor therapy is primarily used for pancreatic cancer because of better anatomic access (vs other imaging modality) and the dismal prognosis (despite improvements in surgery and chemoradiation). Also, the response to parenteral chemotherapy in pancreatic cancer is poor because of suboptimal drug delivery resulting from hypovascularity and abundant desmoplasia. Other targets for EUS-guided tumor ablation are pancreatic neuroendocrine tumor and pancreatic cyst lesion, which are less aggressive and curable by resection. However, patients non-eligible for surgery may benefit from local EUS-guided ablation.

Dark and Photoinduced Cytotoxic Activity of the New Chlorophyll-a Derivatives with Oligoethylene Glycol Substituents on the Periphery of Their Macrocycles

In the present work, we investigated the dark and photoinduced cytotoxic activity of the new chlorophyll-a derivatives which contain the substituents of oligoethylene glycol on the periphery of their macrocycles. These compounds were tested using human cell lines to estimate their potential as photosensitizers for photodynamic therapy of cancer. It was shown that all the tested compounds have expressed photoinduced cytotoxic activity in vitro. Detailed study of the biological activity of one of the most perspective compound in this series—pyropheophorbide-a 17-diethylene glycol ester (Compound 21) was performed. This new compound is characterized by lower dark cytotoxicity and higher photoinduced cytotoxicity than previously described in a similar compound (DH-I-180-3) and clinically used Photolon^TM. Using fluorescent microscopy, it was shown that Compound 21 quickly penetrates the cells. Analysis of caspase-3 activity indicated an apoptosis induction 40 min after exposure to red light (λ = 660 nm). The induction of DNA damages and apoptosis was shown using Comet assay. The results of expression analysis of the stress-response genes indicate an activation of the genes which control the cell cycle and detoxification of the free radicals after an exposure of HeLa cells to Compound 21 and to red light. High photodynamic activity of this compound and the ability to oxidize biomolecules was demonstrated on nuclear-free mice erythrocytes. In addition, it was shown that Compound 21 is effectively activated with low energy 700 nm light, which can penetrate deep into the tissue. Thus, Compound 21 is a prospective substance for development of the new drugs for photodynamic therapy of cancer.

Upconversion nanoparticle-mediated photodynamic therapy induces THP-1 macrophage apoptosis via ROS bursts and activation of the mitochondrial caspase pathway

Atherosclerosis (AS) is the most vital cardiovascular disease, which poses a great threat to human health. Macrophages play an important role in the progression of AS. Photodynamic therapy (PDT) has emerged as a useful therapeutic modality not only in the treatment of cancer but also in the treatment of AS. The purpose of this study was to determine the molecular mechanisms underlying the activity of PDT, using mesoporous-silica-coated upconversion fluorescent nanoparticles encapsulating chlorin e6 (UCNPs-Ce6) in the induction of apoptosis in THP-1 macrophages. Here, we investigated the ability of UCNPs-Ce6-mediated PDT to induce THP-1 macrophage apoptosis by facilitating the induction of reactive oxygen species (ROS) and regulation of mitochondrial permeability transition pore (MPTP) to depolarize mitochondrial membrane potential (MMP). Both Bax translocation and the release of cytochrome C were examined using immunofluorescence and Western blotting. Our results indicated that the levels of ROS were significantly increased in the PDT group, resulting in both MPTP opening and MMP depolarization, which led to apoptosis. In addition, immunofluorescence and Western blotting revealed that PDT induced both Bax translocation and the release of cytochrome C, as well as upregulation of cleaved caspase-9, cleaved caspase-3, and cleaved poly(ADP-ribose) polymerase. Therefore, we demonstrated that UCNPs-Ce6-mediated PDT induces apoptosis in THP-1 macrophages via ROS bursts. The proapoptotic factor Bax subsequently translocates from the cytosol to the mitochondria, resulting in the MPTP opening and cytochrome C release. This study demonstrated the great potential of UCNPs-Ce6-mediated PDT in the treatment of AS.

Genotoxic effect of photodynamic therapy mediated by curcumin on Candida albicans

Photodynamic therapy (PDT) is a promising method for localized and specific inactivation of fungi and bacteria. A nontoxic light-sensitive compound is taken up by cells, which are then exposed selectively to light, which activates toxicity of the compound. We investigated the potential of sublethal PDT using light-sensitive curcumin (CUR) in combination with blue (455 nm) light to promote reactive oxygen species (ROS) formation in the form of singlet oxygen and DNA damage of Candida albicans. Surprisingly, CUR-mediated PDT but also light alone caused significantly longer comet tails, an indication of DNA damage of C. albicans when compared with the negative control. The intracellular ROS production was also significantly higher for the group treated only with light. However, PDT compared to blue light alone significantly slowed DNA repair. Comet tails decreased during 30 min visualized as a 90% reduction in length in the absence of light for cells treated with light alone, while comet tails of cells treated with PDT only diminished in size about 45%. These results indicate that complex mechanisms may result in PDT in a way that should be considered when choosing the photosensitive compound and other aspects of the treatment design.

Photodynamic inactivation of clinical isolates of Candida using Photodithazine®

This study evaluated the photodynamic inactivation (PDI) mediated by Photodithazine(®) (PDZ) against 15 clinical isolates of Candida albicans, Candida glabrata and Candida tropicalis. Each isolate, in planktonic and biofilm form, was exposed to PDI by assessing a range of PDZ concentrations and light emitting diode fluences. Cell survival of the planktonic suspensions was determined by colony forming units (CFU ml(-1)). The antifungal effects of PDI against biofilms were evaluated by CFU ml(-1) and metabolic assay. Data were analyzed by non-parametric tests (α = 0.05). Regardless of the species, PDI promoted a significant viability reduction of planktonic yeasts. The highest reduction in cell viability of the biofilms was equivalent to 0.9 log10 (CFU ml(-1)) for C. albicans, while 1.4 and 1.5 log10 reductions were obtained for C. tropicalis and C. glabrata, respectively. PDI reduced the metabolic activity of biofilms by 62.1, 76.0, and 76.9% for C. albicans, C. tropicalis, and C. glabrata, respectively. PDZ-mediated PDI promoted significant reduction in the viability of Candida isolates.

Ultrasound enhances the efficacy of chlorin E6-mediated photodynamic therapy in MDA-MB-231 cells

Sono-photodynamic therapy (SPDT) is a new modality for cancer treatment. Some studies have reported enhanced tumor cytotoxicity when sonodynamic therapy (SDT) is combined with photodynamic therapy (PDT). In this study, we investigated the cytotoxic effect of SPDT-activated chlorin e6 (Ce6) on MDA-MB-231 cells. Ce6 was found to localize mainly in mitochondria, with maximal uptake within 4 h. Cell survival was estimated by MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltertrazolium bromide tetrazolium) assay 24 h after irradiation; the combined therapy enhanced cytotoxicity to a greater extent. Apoptosis was analyzed using annexin V-PE/7-ADD (7-aminoactinomycin D) staining as well as DAPI (4', 6-diamidino-2-phenylindole) staining, and the results indicated that the cells with apoptotic characteristics were significantly increased in groups given combined therapy. Rhodamine-123 staining and cytochrome c release revealed more serious damage of mitochondria after combined treatment. The generation of reactive oxygen species detected by flow cytometry was greatly increased in cells treated with the combination therapy, and the loss in cell viability could be effectively rescued with the reactive oxygen species inhibitor N-acetylcysteine. Moreover, enhancement of cell membrane permeability after ultrasound treatment was evaluated using FD-500, and it was found that the much higher uptake of Ce6 might be involved in PDT therapy with pre-treatment ultrasound. These results suggest that ultrasound enhances the cytotoxicity of Ce6-mediated PDT, possibly because of the increased intracellular Ce6 level and ROS formation by ultrasound pre-treatment.

Susceptibility of clinical isolates of Candida to photodynamic effects of curcumin

BACKGROUND AND OBJECTIVE

The resistance of Candida species to antifungals represents a major challenge for therapeutic and prophylactic strategies. This study evaluated photodynamic therapy (PDT) mediated by Curcumin (CUR) against clinical isolates of C. albicans, C. tropicalis, and C. glabrata, both in planktonic and biofilm forms.

STUDY DESIGN/MATERIALS AND METHODS

Suspensions of Candida were treated with three CUR concentrations and exposed to four LED fluences. The protocol that showed the best outcomes for inactivation of the planktonic phase was selected to be evaluated against Candida biofilms. In addition, two higher CUR concentrations were tested. The metabolic activity of biofilms was evaluated by means of XTT reduction assay and the biofilm biomass was evaluated using crystal violet (CV) staining assay. Data were analyzed in a mixed model nested ANOVA, Wilcoxon's nonparametric tests, and the Kruskal-Wallis test (α = 5%).

RESULTS

The use of CUR in association with light was able to promote a significant antifungal effect against the planktonic form of the yeasts. When using 40 µM of CUR, the metabolic activity of C. albicans, C. glabrata, and C. tropicalis biofilms was reduced by 85%, 85%, and 73%, respectively, at 18 J/cm(2) . CUR-mediated PDT also decreased the biofilm biomass of all species evaluated. In addition, CV staining showed that C. albicans isolates were strong biofilm-forming strains, when compared with C. glabrata and C. tropicalis isolates.

CONCLUSION

The results from the present investigation showed that low CUR concentrations can be highly effective for inactivating Candida isolates when associated with light excitation.

Targeting of T/Tn antigens with a plant lectin to kill human leukemia cells by photochemotherapy

Photochemotherapy is used both for solid tumors and in extracorporeal treatment of various hematologic disorders. Nevertheless, its development in oncology remains limited, because of the low selectivity of photosensitizers (PS) towards human tumor cells. To enhance PS efficiency, we recently covalently linked a porphyrin (TrMPyP) to a plant lectin (Morniga G), known to recognize with high affinity tumor-associated T and Tn antigens. The conjugation allowed a quick uptake of PS by Tn-positive Jurkat leukemia cells and efficient PS-induced phototoxicity. The present study was performed: (i) to evaluate the targeting potential of the conjugate towards tumor and normal cells and its phototoxicity on various leukemia cells, (ii) to investigate the mechanism of conjugate-mediated cell death. The conjugate: (i) strongly increased (×1000) the PS phototoxicity towards leukemic Jurkat T cells through an O-glycan-dependent process; (ii) specifically purged tumor cells from a 1∶1 mixture of Jurkat leukemia (Tn-positive) and healthy (Tn-negative) lymphocytes, preserving the activation potential of healthy lymphocytes; (iii) was effective against various leukemic cell lines with distinct phenotypes, as well as fresh human primary acute and chronic lymphoid leukemia cells; (iv) induced mostly a caspase-independent cell death, which might be an advantage as tumor cells often resist caspase-dependent cell death. Altogether, the present observations suggest that conjugation with plant lectins can allow targeting of photosensitizers towards aberrant glycosylation of tumor cells, e.g. to purge leukemia cells from blood and to preserve the normal leukocytes in extracorporeal photochemotherapy.

The application and challenges of clinical PD-PDT in the head and neck region: a short review

We review current clinical applications of photodiagnosis (PD) and photodynamic therapy (PDT) in the head and neck field and highlight the actual status, problems, challenges as well as the future of this emerging treatment modality. In recent years literature presented input from many new developments and their applications. This is due to better awareness and developing knowledge about PD-PDT from the clinical staff, both nurses and doctors. But it is also a result of improved drug and hardware development such as lasers, LEDs and related optical devices. Current photo-medical applications in the head and neck region range from diagnostics, treatment of premalignant and malignant lesions, aesthetic and cosmetic applications to the ever expanding anti-microbial applications. Although treatment of premalignant and early malignant lesions of the oropharyngeal cavity have long been the favourite lesions to treat with PDT patients with unsalvageable tumors have also been responding remarkably well to PDT, adding significant quality of life. There is growing interest in anti-microbiological PDT and recent progress has shown that this application is able to significantly reduce the number or even eradicate specific microbial pathogens. During many surgical treatments better control of microbiological activity through PDT may lead to a better outcome. Despite progressive development in this field a few problems remain: prolonged phototoxicity, limited penetration of the photosensitizer and light, inadequate specificity, PDT-related pain as well as the lack of uniformly accepted protocols both for light application as well as photosensitizers. Recent studies have shown that PDT based pain can be separated from other forms of pain, offering hope that a specific management of pain will be possible. If PDT will become fully accepted by patients and doctors we must care about the negative factors such as pain and prolonged phototoxicity.

Inhibition of Rac1 decreases the severity of pancreatitis and pancreatitis-associated lung injury in mice

Pancreatitis is a disease with high morbidity and mortality. In vitro experiments on pancreatic acini showed that supramaximal but not submaximal cholecystokinin (CCK) stimulation induces effects in the acinar cell that can be correlated with acinar morphological changes observed in the in vivo experimental model of cerulein-induced pancreatitis. The GTPase Rac1 was previously reported to be involved in CCK-evoked amylase release from pancreatic acinar cells. Here, we demonstrate that pretreatment with the Rac1 inhibitor NSC23766 (100 microM, 2 h) effectively blocked Rac1 translocation and activation in CCK-stimulated pancreatic acini, without affecting activation of its closely related GTPase, RhoA. This specific Rac1 inhibition decreased supramaximal (10 nM) CCK-stimulated acinar amylase release (27.% reduction), which seems to be connected to the reduction observed in serum amylase (46.6% reduction) and lipase levels (46.1% reduction) from cerulein-treated mice receiving NSC23766 (100 nmol h(-1)). The lack of Rac1 activation also reduced formation of reactive oxygen species (ROS; 20.8% reduction) and lactate dehydrogenase release (LDH; 24.3% reduction), but did not alter calcium signaling or trypsinogen activation in 10 nM CCK-stimulated acini. In the in vivo model, the cerulein-treated mice receiving NSC23766 also presented a decrease in both pancreatic and lung histopathological scores (reduction in oedema, 32.4 and 66.4%; haemorrhage, 48.3 and 60.2%; and leukocyte infiltrate, 53.5 and 43.6%, respectively; reduction in pancreatic necrosis, 65.6%) and inflammatory parameters [reduction in myeloperoxidase, 52.2 and 38.9%; nuclear factor kappaB (p65), 61.3 and 48.6%; and nuclear factor kappaB (p50), 46.9 and 44.9%, respectively], together with lower serum levels for inflammatory (TNF-alpha, 40.4% reduction) and cellular damage metabolites (LDH, 52.7% reduction). Collectively, these results suggest that pharmacological Rac1 inhibition ameliorates the severity of pancreatitis and pancreatitis-associated lung injury through the reduction of pancreatic acinar damage induced by pathological digestive enzyme secretion and overproduction of ROS.