On the interaction of fluorophore-encapsulating PEGylated lecithin liposomes with hamster and human platelets

Metallated phthalocyanines and their hydrophilic derivatives for multi-targeted oncological photodynamic therapy

BACKGROUND AND AIM

A photosensitizer (PS) delivery and comprehensive tumor targeting platform was developed that is centered on the photosensitization of key pharmacological targets in solid tumors (cancer cells, tumor vascular endothelium, and cellular and non-cellular components of the tumor microenvironment) before photodynamic therapy (PDT). Interstitially targeted liposomes (ITLs) encapsulating zinc phthalocyanine (ZnPC) and aluminum phthalocyanine (AlPC) were formulated for passive targeting of the tumor microenvironment. In previous work it was established that the PEGylated ITLs were taken up by cultured cholangiocarcinoma cells. The aim of this study was to verify previous results in cancer cells and to determine whether the ITLs can also be used to photosensitize cells in the tumor microenvironment and vasculature. Following positive results, rudimentary in vitro and in vivo experiments were performed with ZnPC-ITLs and AlPC-ITLs as well as their water-soluble tetrasulfonated derivatives (ZnPCS4 and AlPCS4) to assemble a research dossier and bring this platform closer to clinical transition.

METHODS

Flow cytometry and confocal microscopy were employed to determine ITL uptake and PS distribution in cholangiocarcinoma (SK-ChA-1) cells, endothelial cells (HUVECs), fibroblasts (NIH-3T3), and macrophages (RAW 264.7). Uptake of ITLs by endothelial cells was verified under flow conditions in a flow chamber. Dark toxicity and PDT efficacy were determined by cell viability assays, while the mode of cell death and cell cycle arrest were assayed by flow cytometry. In vivo systemic toxicity was assessed in zebrafish and chicken embryos, whereas skin phototoxicity was determined in BALB/c nude mice. A PDT efficacy pilot was conducted in BALB/c nude mice bearing human triple-negative breast cancer (MDA-MB-231) xenografts.

RESULTS

The key findings were that (1) photodynamically active PSs (i.e., all except ZnPCS4) were able to effectively photosensitize cancer cells and non-cancerous cells; (2) following PDT, photodynamically active PSs were highly toxic-to-potent as per anti-cancer compound classification; (3) the photodynamically active PSs did not elicit notable systemic toxicity in zebrafish and chicken embryos; (4) ITL-delivered ZnPC and ZnPCS4 were associated with skin phototoxicity, while the aluminum-containing PSs did not exert detectable skin phototoxicity; and (5) ITL-delivered ZnPC and AlPC were equally effective in their tumor-killing capacity in human tumor breast cancer xenografts and superior to other non-phthalocyanine PSs when appraised on a per mole administered dose basis.

CONCLUSIONS

AlPC(S4) are the safest and most effective PSs to integrate into the comprehensive tumor targeting and PS delivery platform. Pending further in vivo validation, these third-generation PSs may be used for multi-compartmental tumor photosensitization.

Optimal Use of 2',7'-Dichlorofluorescein Diacetate in Cultured Hepatocytes

Oxidative stress is a state that arises when the production of reactive transients overwhelms the cell's capacity to neutralize the oxidants and radicals. This state often coincides with the pathogenesis and perpetuation of numerous chronic diseases. On the other hand, medical interventions such as radiation therapy and photodynamic therapy generate radicals to selectively damage and kill diseased tissue. As a result, the qualification and quantification of oxidative stress are of great interest to those studying disease mechanisms as well as therapeutic interventions. 2',7'-Dichlorodihydrofluorescein-diacetate (DCFH₂-DA) is one of the most widely used fluorogenic probes for the detection of reactive transients. The nonfluorescent DCFH₂-DA crosses the plasma membrane and is deacetylated by cytosolic esterases to 2',7'-dichlorodihydrofluorescein (DCFH₂). The nonfluorescent DCFH₂ is subsequently oxidized by reactive transients to form the fluorescent 2',7'-dichlorofluorescein (DCF). The use of DCFH₂-DA in hepatocyte-derived cell lines is more challenging because of membrane transport proteins that interfere with probe uptake and retention, among several other reasons. Cancer cells share some of the physiological and biochemical features with hepatocytes, so probe-related technical issues are applicable to cultured malignant cells as well. This study therefore analyzed the in vitro properties of DCFH₂-DA in cultured human hepatocytes (HepG2 cells and differentiated and undifferentiated HepaRG cells) to identify methodological and technical features that could impair proper data analysis and interpretation. The main issues that were found and should therefore be accounted for in experimental design include the following: (1) both DCFH₂-DA and DCF are taken up rapidly, (2) DCF is poorly retained in the cytosol and exits the cell, (3) the rate of DCFH₂ oxidation is cell type-specific, (4) DCF fluorescence intensity is pH-dependent at pH < 7, and (5) the stability of DCFH₂-DA in cell culture medium relies on medium composition. Based on the findings, the conditions for the use of DCFH₂-DA in hepatocyte cell lines were optimized. Finally, the optimized protocol was reduced to practice and DCFH₂-DA was applied to visualize and quantify oxidative stress in real time in HepG2 cells subjected to anoxia/reoxygenation as a source of reactive transients.

Analysis and Optimization of Conditions for the Use of 2',7'-Dichlorofluorescein Diacetate in Cultured Hepatocytes

Numerous liver pathologies encompass oxidative stress as molecular basis of disease. The use of 2',7'-dichlorodihydrofluorescein-diacetate (DCFH₂-DA) as fluorogenic redox probe is problematic in liver cell lines because of membrane transport proteins that interfere with probe kinetics, among other reasons. The properties of DCFH₂-DA were analyzed in hepatocytes (HepG2, HepaRG) to characterize methodological issues that could hamper data interpretation and falsely skew conclusions. Experiments were focused on probe stability in relevant media, cellular probe uptake/retention/excretion, and basal oxidant formation and metabolism. DCFH₂-DA was used under optimized experimental conditions to intravitally visualize and quantify oxidative stress in real-time in HepG2 cells subjected to anoxia/reoxygenation. The most important findings were that: (1) the non-fluorescent DCFH₂-DA and the fluorescent DCF are rapidly taken up by hepatocytes, (2) DCF is poorly retained in hepatocytes, and (3) DCFH₂ oxidation kinetics are cell type-specific. Furthermore, (4) DCF fluorescence intensity was pH-dependent at pH < 7 and (5) the stability of DCFH₂-DA in cell culture medium relied on medium composition. The use of DCFH₂-DA to measure oxidative stress in cultured hepatocytes comes with methodological and technical challenges, which were characterized and solved. Optimized in vitro and intravital imaging protocols were formulated to help researchers conduct proper experiments and draw robust conclusions.

Attritional evaluation of lipophilic and hydrophilic metallated phthalocyanines for oncological photodynamic therapy

BACKGROUND AND AIM

Oncological photodynamic therapy (PDT) relies on photosensitizers (PSs) to photo-oxidatively destroy tumor cells. Currently approved PSs yield satisfactory results in superficial and easy-to-access tumors but are less suited for solid cancers in internal organs such as the biliary system and the pancreas. For these malignancies, second-generation PSs such as metallated phthalocyanines are more appropriate. Presently it is not known which of the commonly employed metallated phtahlocyanines, namely aluminum phthalocyanine (AlPC) and zinc phthalocyanine (ZnPC) as well as their tetrasulfonated derivatives AlPCS4 and ZnPCS4, is most cytotoxic to tumor cells. This study therefore employed an attritional approach to ascertain the best metallated phthalocyanine for oncological PDT in a head-to-head comparative analysis and standardized experimental design.

METHODS

ZnPC and AlPC were encapsulated in PEGylated liposomes. Analyses were performed in cultured A431 cells as a template for tumor cells with a dysfunctional P53 tumor suppressor gene and EGFR overexpression. First, dark toxicity was assessed as a function of PS concentration using the WST-1 and sulforhodamine B assay. Second, time-dependent uptake and intracellular distribution were determined by flow cytometry and confocal microscopy, respectively, using the intrinsic fluorescence of the PSs. Third, the LC₅₀ values were established for each PS at 671 nm and a radiant exposure of 15 J/cm² following 1-h PS exposure. Finally, the mode of cell death as a function of post-PDT time and cell cycle arrest at 24 h after PDT were analyzed.

RESULTS

In the absence of illumination, AlPC and ZnPC were not toxic to cells up to a 1.5-μM PS concentration and exposure for up to 72 h. Dark toxicity was noted for AlPCS4 at 5 μM and ZnPCS4 at 2.5 μM. Uptake of all PSs was observed as early as 1 min after PS addition to cells and increased in amplitude during a 2-h incubation period. After 60 min, the entire non-nuclear space of the cell was photosensitized, with PS accumulation in multiple subcellular structures, especially in case of AlPC and AlPCS4. PDT of cells photosensitized with ZnPC, AlPC, and AlPCS4 yielded LC₅₀ values of 0.13 μM, 0.04 μM, and 0.81 μM, respectively, 24 h post-PDT (based on sulforhodamine B assay). ZnPCS4 did not induce notable phototoxicity, which was echoed in the mode of cell death and cell cycle arrest data. At 4 h post-PDT, the mode of cell death comprised mainly apoptosis for ZnPC and AlPC, the extent of which was gradually exacerbated in AlPC-photosensitized cells during 8 h. ZnPC-treated cells seemed to recover at 8 h post-PDT compared to 4 h post-PDT, which had been observed before in another cell line. AlPCS4 induced considerable necrosis in addition to apoptosis, whereby most of the cell death had already manifested at 2 h after PDT. During the course of 8 h, necrotic cell death transitioned into mainly late apoptotic cell death. Cell death signaling coincided with a reduction in cells in the G₀/G₁ phase (ZnPC, AlPC, AlPCS4) and cell cycle arrest in the S-phase (ZnPC, AlPC, AlPCS4) and G₂ phase (ZnPC and AlPC). Cell cycle arrest was most profound in cells that had been photosensitized with AlPC and subjected to PDT.

CONCLUSIONS

Liposomal AlPC is the most potent PS for oncological PDT, whereas ZnPCS4 was photodynamically inert in A431 cells. AlPC did not induce dark toxicity at PS concentrations of up to 1.5 μM, i.e., > 37 times the LC₅₀ value, which is favorable in terms of clinical phototoxicity issues. AlPC photosensitized multiple intracellular loci, which was associated with extensive, irreversible cell death signaling that is expected to benefit treatment efficacy and possibly immunological long-term tumor control, granted that sufficient AlPC will reach the tumor in vivo. Given the differential pharmacokinetics, intracellular distribution, and cell death dynamics, liposomal AlPC may be combined with AlPCS4 in a PS cocktail to further improve PDT efficacy.

In Vivo Assessment of Thermosensitive Liposomes for the Treatment of Port Wine Stains by Antifibrinolytic Site-Specific Pharmaco-Laser Therapy

Antifibrinolytic site-specific pharmaco-laser therapy (SSPLT) is an experimental treatment modality for refractory port wine stains (PWS). Conceptually, antifibrinolytic drugs encapsulated in thermosensitive liposomes are delivered to thrombi that form in semi-photocoagulated PWS blood vessels after conventional laser treatment. Local release of antifibrinolytics is induced by mild hyperthermia, resulting in hyperthrombosis and complete occlusion of the target blood vessel (clinical endpoint). In this study, 20 thermosensitive liposomal formulations containing tranexamic acid (TA) were assayed for physicochemical properties, TA:lipid ratio, encapsulation efficiency, and endovesicular TA concentration. Two candidate formulations (DPPC:DSPE-PEG, DPPC:MPPC:DSPE-PEG) were selected based on optimal properties and analyzed for heat-induced TA release at body temperature (T), phase transition temperature (T_m), and at T > T_m. The effect of plasma on liposomal stability at 37 °C was determined, and the association of liposomes with platelets was examined by flow cytometry. The accumulation of PEGylated phosphocholine liposomes in laser-induced thrombi was investigated in a hamster dorsal skinfold model and intravital fluorescence microscopy. Both formulations did not release TA at 37 °C. Near-complete TA release was achieved at T_m within 2.0–2.5 min of heating, which was accelerated at T > T_m. Plasma exerted a stabilizing effect on both formulations. Liposomes showed mild association with platelets. Despite positive in vitro results, fluorescently labeled liposomes did not sufficiently accumulate in laser-induced thrombi in hamsters to warrant their use in antifibrinolytic SSPLT, which can be solved by coupling thrombus-targeting ligands to the liposomes.

Preclinical evaluation of thermosensitive poly(N-(2-hydroxypropyl) methacrylamide mono/dilactate)-grafted liposomes for cancer thermochemotherapy

Thermosensitive liposomes grafted with cholesterol-conjugated poly(N-(2-hydroxypropyl) methacrylamide mono/dilactate) (chol-pHPMAlac) have been developed for heat-induced release of doxorubicin (DOX). These liposomes release DOX completely during mild hyperthermia, but their interaction with blood cells and cancer cells has not been studied. Following intravenous administration, liposomes may interact with plasma proteins and various types of cells (e.g., endothelial cells, platelets, and macrophages), which would reduce their disposition in the tumor stroma. Interaction between liposomes and platelets may further cause platelet activation and thrombosis, which could lead to vascular occlusion and thromboembolic complications. The aim was to investigate DOX release kinetics in the presence of serum, stability, in vitro uptake by and toxicity to cancer cells and somatic cells, and platelet activating potential of the chol-pHPMAlac liposomes. DOX release was determined spectrofluorometrically. Liposome stability was determined in buffer and serum by dynamic light scattering and nanoparticle tracking analysis. Association with/uptake by and toxicity of empty liposomes to AML-12, HepG2 (both hepatocyte-derived cancer cells), RAW 264.7 (macrophages), and HUVEC (endothelial) cells was assayed in vitro. Platelet activation was determined by analysis of P-selectin expression and fibrinogen binding. DOPE:EPC liposomes (diameter = 135 nm) grafted with 5% chol-pHPMAlac (cloud point (CP) = 16 °C; M_n = 8.5 kDa) released less than 10% DOX at 37 °C in 30 min, whereas complete release took place at 47 °C or higher within 10 min. The size of these liposomes remained stable in buffer and serum during 24 h at 37 °C. Fluorescently labeled but DOX-lacking chol-pHPMAlac-liposomes exhibited poor association with/uptake by all cells under investigation, were not cytotoxic, and did not activate platelets in both buffered solution and whole blood. In conclusion, thermosensitive chol-pHPMAlac-grafted liposomes rapidly release DOX during mild hyperthermia. The liposomes are stable in a physiological milieu, are not taken up by cells that are encountered in an in vivo setting, and are non-antagonistic towards platelets. Chol-pHPMAlac-grafted liposomes are therefore good candidates for DOX delivery to tumors and temperature-triggered release in tumor stroma.

Tranexamic Acid-Encapsulating Thermosensitive Liposomes for Site-Specific Pharmaco-Laser Therapy of Port Wine Stains

Site-specific pharmaco-laser therapy (SSPLT) is a developmental stage treatment modality designed to non-invasively remove superficial vascular pathologies such as port wine stains (PWS) by combining conventional laser therapy with the prior administration of a prothrombotic and/or antifibrinolytic pharmaceutical-containing drug delivery system. For the antifibrinolytic SSPLT component, six different PEGylated thermosensitive liposomal formulations encapsulating tranexamic acid (TA), a potent antifibrinolytic lysine analogue, were characterized for drug:lipid ratio, encapsulation efficiency, size, endovesicular TA concentration (C TA), phase transition temperature (T m), and assayed for heat-induced TA release. Assays were developed for the quantification of liposomal TA and heat-induced TA release from two candidate formulations. The outcome parameters were then combined with a 3D histological reconstruction of a port wine stain biopsy to extrapolate in vivo posologies for SSPLT. The prime formulation, DPPC:DSPE-PEG2000 (96:4 molar ratio), had a drug:lipid molar ratio of 0.82, an encapsulation efficiency of 1.29%, a diameter of 155 nm, and a C TA of 214 mM. The peak TA release from this formulation (T m = 42.3 °C) comprised 96% within 2.5 min, whereas this was 94% in 2 min for DPPC:MPPC:DSPE-PEG2000 (86:10:4) liposomes (T m = 41.5 °C). Computational analysis revealed that < 400 DPPC:DSPE-PEG2000 (96:4 molar ratio) liposomes are needed to treat a PWS of 40 cm2, compared to a three-fold greater quantity of DPPC:MPPC:DSPE-PEG2000 (86:10:4) liposomes, indicating that, in light of the assayed parameters and endovascular laser-tissue interactions, the former formulation is most suitable for antifibrinolytic SSPLT. This was further confirmed with experiments involving ex vivo and in vivo liposome-platelet and liposome-red blood cell association as well as uptake and toxicity assays with cultured endothelial cells (HUVECs), macrophages (RAW 264.7), and hepatocytes (HepG2).

Magnetic Nanoparticle Labeling of Human Platelets from Platelet Concentrates for Recovery and Survival Studies

Platelets are the smallest blood cells and important for hemostasis. Platelet concentrates (PC) are medicinal products transfused to prevent or treat bleeding. Typically, platelets in PCs are assessed by in vitro tests for their function. However, in vivo testing of these platelets is highly desirable. To distinguish transfused platelets from patients or probands own cells after PC transfusions within the scope of clinical studies, platelets need to be efficiently labeled with minimal preactivation prior to transfusion. Here we report on a method for improved cell uptake of ferucarbotran magnetic nanoparticles contained in Resovist, an FDA-approved MRI contrast agent, by modifying the nanoparticle shell with human serum albumin (HSA). Both HSA-ferucarbotran nanoparticles and magnetically labeled platelets were produced according to EU-GMP guidelines. Platelet function after labeling was evaluated by light transmission aggregometry and by determination of expression of CD62P as platelet activation marker. Magnetic labeling does not impair platelet function and platelets showed reasonable activation response to agonists. Platelet survival studies in NOD/SCID-mice resulted in comparable survival behavior of magnetically labeled and nonlabeled platelets. Additionally, labeled platelets can be recovered from whole blood by magnetic separation.

Shear-sensitive nanocapsule drug release for site-specific inhibition of occlusive thrombus formation

Essentials Vessel stenosis due to large thrombus formation increases local shear 1-2 orders of magnitude. High shear at stenotic sites was exploited to trigger eptifibatide release from nanocapsules. Local delivery of eptifibatide prevented vessel occlusion without increased tail bleeding times. Local nanocapsule delivery of eptifibatide may be safer than systemic antiplatelet therapies.

SUMMARY

Background Myocardial infarction and stroke remain the leading causes of mortality and morbidity. The major limitation of current antiplatelet therapy is that the effective concentrations are limited because of bleeding complications. Targeted delivery of antiplatelet drug to sites of thrombosis would overcome these limitations. Objectives Here, we have exploited a key biomechanical feature specific to thrombosis, i.e. significantly increased blood shear stress resulting from a reduction in the lumen of the vessel, to achieve site-directed delivery of the clinically used antiplatelet agent eptifibatide by using shear-sensitive phosphatidylcholine (PC)-based nanocapsules. Methods PC-based nanocapsules (2.8 × 1012 ) with high-dose encapsulated eptifibatide were introduced into microfluidic blood perfusion assays and into in vivo models of thrombosis and tail bleeding. Results Shear-triggered nanocapsule delivery of eptifibatide inhibited in vitro thrombus formation selectively under stenotic and high shear flow conditions above a shear rate of 1000 s-1 while leaving thrombus formation under physiologic shear rates unaffected. Thrombosis was effectively prevented in in vivo models of vessel wall damage. Importantly, mice infused with shear-sensitive antiplatelet nanocapsules did not show prolonged bleeding times. Conclusions Targeted delivery of eptifibatide by shear-sensitive nanocapsules offers site-specific antiplatelet potential, and may form a basis for developing more potent and safer antiplatelet drugs.

The effects of nanomaterials on blood coagulation in hemostasis and thrombosis

The blood coagulation balance in the organism is achieved by the interaction of the blood platelets (PLTs) with the plasma coagulation system (PCS) and the vascular endothelial cells. In healthy organism, these systems prevent thrombosis and, in events of vascular damage, enable blood clotting to stop bleeding. The dysregulation of hemostasis may cause serious thrombotic and/or hemorrhagic pathologies. Numerous engineered nanomaterials are being investigated for biomedical purposes and are unavoidably exposed to the blood. Also, nanomaterials may access vascular system after occupational, environmental, or other types of exposure. Thus, it is essential to evaluate the effects of engineered nanomaterials on hemostasis. This review focuses on investigations of nanomaterial interactions with the blood components involved in blood coagulation: the PCS and PLTs. Particular emphases include the pathophysiology of effects of nanomaterials on the PCS, including the kallikrein-kinin system, and on PLTs. Methods for investigating these interactions are briefly described, and a review of the most important studies on the interactions of nanomaterials with plasma coagulation and platelets is provided. WIREs Nanomed Nanobiotechnol 2017, 9:e1448. doi: 10.1002/wnan.1448 For further resources related to this article, please visit the WIREs website.

Development of new antiatherosclerotic and antithrombotic drugs utilizing F11 receptor (F11R/JAM-A) peptides

Peptides with enhanced resistance to proteolysis, based on the amino acid sequence of the F11 receptor molecule (F11R, aka JAM-A/Junctional adhesion molecule-A), were designed, prepared, and examined as potential candidates for the development of anti-atherosclerotic and anti-thrombotic therapeutic drugs. A sequence at the N-terminal of F11R together with another sequence located in the first Ig-loop of this protein, were identified to form a steric active-site operating in the F11R-dependent adhesion between cells that express F11R molecules on their external surface. In silico modeling of the complex between two polypeptide chains with the sequences positioned in the active-site was used to generate peptide-candidates designed to inhibit homophilic interactions between surface-located F11R molecules. The two lead F11R peptides were modified with D-Arg and D-Lys at selective sites, for attaining higher stability to proteolysis in vivo. Using molecular docking experiments we tested different conformational states and the putative binding affinity between two selected D-Arg and D-Lys-modified F11R peptides and the proposed binding pocket. The inhibitory effects of the F11R peptide 2HN-(dK)-SVT-(dR)-EDTGTYTC-CONH2 on antibody-induced platelet aggregation and on the adhesion of platelets to cytokine-inflammed endothelial cells are reported in detail, and the results point out the significant potential utilization of F11R peptides for the prevention and treatment of atherosclerotic plaques and associated thrombotic events.

Transcription and translation of human F11R gene are required for an initial step of atherogenesis induced by inflammatory cytokines

BACKGROUND

The F11 Receptor (F11R; aka JAM-A, JAM-1) is a cell adhesion protein present constitutively on the membrane surface of circulating platelets and within tight junctions of endothelial cells (ECs). Previous reports demonstrated that exposure of ECs to pro-inflammatory cytokines causes insertion of F11R molecules into the luminal surface of ECs, ensuing with homologous interactions between F11R molecules of platelets and ECs, and a resultant adhesion of platelets to the inflamed ECs. The main new finding of the present report is that the first step in this chain of events is the de-novo transcription and translation of F11R molecules, induced in ECs by exposure to inflammatory cytokines.

METHODS

The experimental approach utilized isolated, washed human platelet suspensions and cultured human venous endothelial cells (HUVEC) and human arterial endothelial cells (HAEC) exposed to the proinflammatory cytokines TNF-alpha and/or IFN-gamma, for examination of the ability of human platelets to adhere to the inflamed ECs thru the F11R. Our strategy was based on testing the effects of the following inhibitors on this activity: general mRNA synthesis inhibitors, inhibitors of the NF-kappaB and JAK/STAT pathways, and small interfering F11R-mRNA (siRNAs) to specifically silence the F11R gene.

RESULTS

Treatment of inflamed ECs with the inhibitors actinomycin, parthenolide or with AG-480 resulted in complete blockade of F11R- mRNA expression, indicating the involvement of NF-kappaB and JAK/STAT pathways in this induction. Transfection of ECs with F11R siRNAs caused complete inhibition of the cytokine-induced upregulation of F11R mRNA and inhibition of detection of the newly- translated F11R molecules in cytokine-inflamed ECs. The functional consequence of the inhibition of F11R transcription and translation was the significant blockade of the adhesion of human platelets to inflamed ECs.

CONCLUSION

These results prove that de novo synthesis of F11R in ECs is required for the adhesion of platelets to inflamed ECs. Because platelet adhesion to an inflamed endothelium is crucial for plaque formation in non-denuded blood vessels, we conclude that the de-novo translation of F11R is a crucial early step in the initiation of atherogenesis, leading to atherosclerosis, heart attacks and stroke.