Biosensor-expressing spheroid cultures for imaging of drug-induced effects in three dimensions.

In the past, the majority of antitumor compound-screening approaches had been performed in two-dimensional (2D) cell cultures. Although easy to standardize, this method provides results of limited significance because cells are surrounded by an artificial microenvironment, are not exposed to hypoxia gradients, and lack cell-cell contacts. These nonphysiological conditions directly affect relevant parameters such as the resistance to anticancer drugs. Multicellular tumor spheroids more closely resemble the in vivo situation in avascularized tumors. To monitor cellular reactions within this three-dimensional model system, we stably transfected a spheroid-forming glioblastoma cell line with Grx1-roGFP2, a green fluorescent protein (GFP)-based glutathione-specific redox sensor that detects alterations in the glutathione redox potential. Functionality and temporal dynamics of the sensor were verified with redox-active substances in 2D cell culture. Based on structured illumination microscopy using nonphototoxic light doses, ratio imaging was then applied to monitor the response of the glutathione system to exogenous hydrogen peroxide in optical sections of a tumor spheroid. Our approach provides a proof of concept for biosensor-based imaging in 3D cell cultures.

In vitro comparison of hypericin and 5-aminolevulinic acid-derived protoporphyrin IX for photodynamic inactivation of medulloblastoma cells.

BACKGROUND: Hypericin (HYP) is a naturally occurring photosensitizer. Cellular uptake and photodynamic inactivation after incubation with this photosensitizer have neither been examined in medulloblastoma cells in vitro, nor compared with 5-aminolevulinic acid-derived protoporphyrin IX (5-ALA-derived PpIX). METHODS: In 3 medulloblastoma cell lines (D283 Med, Daoy, and D341 Med) the time- and concentration-dependent intracellular accumulation of HYP and 5-ALA-derived PpIX was analyzed by fluorescence microscopy (FM) and FACS. Photocytotoxicity was measured after illumination at 595 nm (HYP) and 635 nm (5-ALA-derived PpIX) in D283 Med cells and compared to U373 MG glioma cells. RESULTS: All medulloblastoma cell lines exhibited concentration- and time-dependent uptake of HYP. Incubation with HYP up to 10 µM resulted in a rapid increase in fluorescence intensity, which peaked between 2 and 4 hours. 5-ALA-derived PpIX accumulation increased in D283 Med cells by 22% over baseline after 5-ALA incubation up to 1.2 mM. Photocytotoxicity of 5-ALA-derived PpIX was higher in D283 Med medulloblastoma compared to U373MG glioma. The LD50 [lethal dose (light dose that is required to reduce cell survival to 50% of control)] of 5-ALA-derived PpIX was 3.8 J/cm(2) in D283 Med cells versus 5.7 J/cm2 in U373MG glioma cells. Photocytotoxicity of HYP in D283 Med cells was determined at 2.5 µM after an incubation time of 2 h and an illumination wavelength of 595 nm. The [Formula: see text] value was 0.47 J/cm(2). CONCLUSION: By its 5-fold increase in fluorescence over autofluorescence levels HYP has excellent properties for tumor visualization in medulloblastomas. The high photocytotoxicity of HYP, compared to 5-ALA-derived PpIX, is convincingly demonstrated by its 8- to 13-fold lower LD50. Therefore HYP might be a promising molecule for intraoperative visualization and photodynamic treatment of medulloblastomas.

Live monitoring of cargo release from peptide-based hybrid nanocapsules induced by enzyme cleavage.

The miniemulsion process is used as a new route for the preparation of enzyme-responsive nanocapsules with payload-release properties. Peptide-based hybrid nanocapsules are prepared via interfacial polyaddition containing a water-soluble dye that is efficiently encapsulated inside. The influence of the synthetic parameters as the functionality of the peptide and the nature of the dispersed phase on the structure of the nanocapsules were investigated. After redispersion in water, the enzymatic cleavage of the peptide sequence and the release of the fluorescent dye are both monitored in real time. This is evidenced because of the quenching FRET system framing the recognition site in the peptide sequence, and the fluorescence recovery of the self-quenched encapsulated dye respectively.

Matrix-dependent regulation of AKT in Hepsin-overexpressing PC3 prostate cancer cells.

The serine-protease hepsin is one of the most prominently overexpressed genes in human prostate carcinoma. Forced expression of the enzyme in mice prostates is associated with matrix degradation, invasive growth, and prostate cancer progression. Conversely, hepsin overexpression in metastatic prostate cancer cell lines was reported to induce cell cycle arrest and reduction of invasive growth in vitro. We used a system for doxycycline (dox)-inducible target gene expression in metastasis-derived PC3 cells to analyze the effects of hepsin in a quantitative manner. Loss of viability and adhesion correlated with hepsin expression levels during anchorage-dependent but not anchorage-independent growth. Full expression of hepsin led to cell death and detachment and was specifically associated with reduced phosphorylation of AKT at Ser(473), which was restored by growth on matrix derived from RWPE1 normal prostatic epithelial cells. In the chorioallantoic membrane xenograft model, hepsin overexpression in PC3 cells reduced the viability of tumors but did not suppress invasive growth. The data presented here provide evidence that elevated levels of hepsin interfere with cell adhesion and viability in the background of prostate cancer as well as other tissue types, the details of which depend on the microenvironment provided. Our findings suggest that overexpression of the enzyme in prostate carcinogenesis must be spatially and temporally restricted for the efficient development of tumors and metastases.

Selective enrichment of hypericin in malignant glioma: pioneering in vivo results.

Malignant gliomas are diffuse infiltrative growing tumors with a poor prognosis despite treatment with a combination of surgery, radiotherapy and chemotherapy. It has been shown recently that complete tumor resection improves the survival time significantly. Hypericin, a component of St. Johns Wort, is one of the most powerful photosensitizers in nature. The aim of the present study was to investigate accumulation of hypericin in intracerebral implanted malignant glioma in vivo. Rats underwent stereotactic implantation of C6 glioma cells. After intravenous administration of hypericin (5 mg per kg body weight), accumulation of the compound was studied in tumor, the infiltration zone surrounding the tumor and healthy brain (contralateral hemisphere) by fluorescence microscopy between 0 and 48 h after injection. Results were compared by one-way analysis of variance. For post hoc pair-wise comparison the Tukey-Kramer HSD test was used. Accumulation of hypericin was significantly higher in C6 glioma as compared to normal tissue. Maximum hypericin uptake was achieved at 24 h after injection. Ratios of fluorescence intensity between tumor and normal tissue as well as infiltration zone and normal tissue of about 6.1:1 and 1.4:1 were found. Considering tissue auto-fluorescence, fluorescence ratios of about 19.8:1 and 2.5:1 were calculated, respectively. Therefore, hypericin seems to be quite an effective fluorescence marker for the detection of glioma in vivo. To the best of our knowledge, the present study demonstrates for the first time that hypericin accumulates selectively in intracerebral implanted C6 glioma in vivo after systemic (intravenous) administration.

Multi-dimensional fluorescence microscopy of living cells.

An overview on fluorescence microscopy with high spatial, spectral and temporal resolution is given. In addition to 3D microscopy based on confocal, structured or single plane illumination, spectral imaging and fluorescence lifetime imaging microscopy (FLIM) are used to probe the interaction of a fluorescent molecule with its micro-environment. Variable-angle total internal reflection fluorescence microscopy (TIRFM) permits selective measurements of cell membranes or cell-substrate topology in the nanometre scale and is also combined with spectral or time-resolved detection. In addition to single cells or cell monolayers, 3-dimensional cell cultures are of increasing importance, since they are more similar to tissue morphology and function. All methods reported are adapted to low dose of illumination, which is regarded as a key parameter to maintain cell viability. Applications include cancer diagnosis and cell tomography under different physiological conditions.

Light dose is a limiting factor to maintain cell viability in fluorescence microscopy and single molecule detection.

A test system for cell viability based on colony formation has been established and applied to high resolution fluorescence microscopy and single molecule detection. Living cells were irradiated either by epi-illumination or by total internal reflection (TIR) of a laser beam, and light doses where at least 90% of irradiated cells survived were determined. These light doses were in the range of a few J/cm(2) up to about 200 J/cm(2) depending on the wavelength of illumination as well as on the presence or absence of a fluorescent dye (e.g., the membrane marker laurdan). In general, cells were less sensitive to TIR than to epi-illumination. However, comparably high light doses needed for repetitive excitation of single molecules limit the application of super-resolution microscopy to living cells.

Synthesis, in vitro progesterone receptors affinity of gadolinium containing mifepristone conjugates and estimation of binding sites in human breast cancer cells.

Novel gadolinium-based mifepristone conjugates were synthesised using various synthetic routes. Moderate antiprogestagenic activity of the new conjugates was observed in human breast cancer cells (T47-D cells) using AP (alkaline phosphatase) assay. The amount of incorporated Gd determined by inductively coupled plasma mass spectroscopy (ICPMS) indicates the number of binding sites per cell. These conjugates might be important compounds to develop receptor-targeted MRI contrast agents as well as other anti-breast cancer therapeutics.

Cationic hypericin derivatives as novel agents with photobactericidal activity: synthesis and photodynamic inactivation of Propionibacterium acnes.

The present communication describes for the first time the synthesis and preliminary testing of two cationic hypericin derivatives. Uncharged hypericin derivatives with omega,omega'-attached C2-linkers leading to a pyridyl or a 4-dimethylaminophenyl residue were prepared and subsequently quaternized by means of iodomethane. Photobactericidal activity was assessed using Propionibacterium acnes. The quaternary N,N,N-trimethyl-anilinium derivative displayed a pronounced photodynamic inactivation of the bacteria at low incubation concentrations (<100 nm) and a short incubation time (1 h) after illumination with yellow light (590 nm, 20 J cm(-2)), whereas the photobactericidal efficacy of the N-methyl-pyridinium derivative was negligible under identical experimental conditions.

Syntheses and antigestagenic activity of mifepristone derivatives.

A series of mifepristone derivatives with different "linker groups" in position 4' of the phenyl ring in the 11beta-position of the steroid scaffold (2-41) have been synthesized. Their antigestagenic activites were determined in a cell-based assay (alkali phosphatase assay in T47-D breast cancer cells) and compared with that of the parent compound mifepristone. SAR and QSAR studies reveal the influence of both lipophilicity and partial charge based van der Waals surface area descriptors on biological activity. Within the series of compounds described in this study, three mifepristone derivatives are identified with considerably high antigestagenic activity. These compounds are regarded as useful starting materials for the synthesis of either physiologically stable or cleavable progesterone receptor-binding conjugates for therapeutic or diagnostic purposes.

Total internal reflection fluorescence lifetime and anisotropy screening of cell membrane dynamics.

A high content screening (HCS) system for fluorescence measurements at surfaces, in particular the plasma membrane of living cells, is described. The method is based on multiple total internal reflections (TIRs) of an incident laser beam within the glass bottom of a microtiter plate such that up to 96 individual samples could be illuminated by an evanescent electromagnetic field. Fluorescence lifetimes and time-resolved fluorescence anisotropies of these samples were assessed. While fluorescence lifetime represents a general measure for the interaction of a marker molecule with its microenvironment, the rotational diffusion time corresponds to the relaxation time of a molecule from a position with a defined orientation into a position with an arbitrary orientation. Thus, time-resolved fluorescence anisotropy reflects the viscosity of the microenvironment, i.e., membrane fluidity in the case of living cells. For all measurements in this study, either human glioblastoma cells incubated with the fluorescent membrane marker NBD-cholesterol or human breast cancer cells expressing a membrane-associating fluorescent protein were used.

Subcellular colocalization of hypericin with respect to endoplasmic reticulum and Golgi apparatus in glioblastoma cells.

BACKGROUND: To improve the poor prognosis of patients suffering from malignant glioma, hypericin (HYP)-based photodynamic therapy might be a promising approach. Intracellular localization of HYP was investigated by quantitative colocalization analysis with respect to endoplasmic reticulum (ER) and Golgi apparatus (GA) by double staining experiments with fluorescence microscopy. MATERIALS AND METHODS: U373 MG glioblastoma cells were stained with HYP and costainings were applied for specific organelle markers for ER and GA. RESULTS: In cells double-stained with HYP and ER-Tracker, 57% of HYP signals were found within the ER and 52% of the ER compartment showed HYP signals. The colocalization fraction of HYP found in the GA was 36% and 46% of the GA showed HYP signals. CONCLUSION: In glioblastoma cells, a considerable fraction of HYP is localized in the ER; in addition, a significant amount of the photosensitizer shows colocalization with the GA.

Cell-substrate topology upon ALA-PDT using variable-angle total internal reflection fluorescence microscopy (VA-TIRFM).

Because of the low penetration depth of an evanescent electromagnetic field, total internal reflection fluorescence microscopy (TIRFM) proved to be a powerful technique to examine fluorescent dyes or photosensitizers in close vicinity to the plasma membrane of living cells. In addition, on variation of the angle of incidence of exciting laser light, the penetration depth is varied, so that cell-substrate topology can be examined with nanometer resolution. Using a specific illumination device for TIRFM and a highly sensitive electron multiplying (EM) CCD camera, fluorescence of the photosensitizer protoporphyrin IX (PPIX) was studied in human cancer cells after application of 5-aminolevulinic acid (5-ALA) prior to and after irradiation with sublethal light doses (635 nm, 4 J/cm2). For cells growing on microscope cover slides, cell-substrate distances varied between approximately 20 and 250 nm with a mean distance of approximately 120 nm. On light exposure, these distances generally decreased, and a mean value below 100 nm was attained. Moreover, focal contacts visualized with a fusion protein of yellow fluorescent protein and focal adhesion kinase were maintained on light exposure, i.e., light-induced detachment of cells from their substrate was not likely to occur.

Relation between intracellular location and photodynamic efficacy of 5-aminolevulinic acid-induced protoporphyrin IX in vitro. Comparison between human glioblastoma cells and other cancer cell lines.

A promising clinical application of 5-aminolevulinic acid (5-ALA)-induced protoporphyrin IX (PP IX) is fluorescence detection and photodynamic treatment of residual tumour tissue during surgical resection of high grade malignant glioma. U373 MG human glioblastoma cells were used as a model system to study the relation between intracellular location and photodynamic efficacy of 5-ALA-induced PP IX in more detail. Therefore, ultra-sensitive fluorescence microscopy, using either optical excitation of whole cells or selective excitation of the plasma membrane by an evanescent electromagnetic field, was combined with quantitative measurements of intracellular porphyrin amount and phototoxicity. Glioblastoma cells accumulated PP IX to a moderate extent as compared to T47D breast cancer cells (high accumulation) or OV2774 ovarian cancer cells (low accumulation). Although photodynamic inactivation of the different cell lines (decreasing in the order T47D > U373 MG > OV2774) seemed to be directly related to PP IX accumulation, examination of the data in more detail revealed that photodynamic efficacy per photosensitizer molecule (PE) was about two times higher in glioblastoma and ovarian cancer cells as compared to breast cancer cells. The different photodynamic efficacy of PP IX was related to the different intracellular location. In contrast to breast cancer cells where PP IX fluorescence was localized in small granules, PP IX fluorescence in glioblastoma cells and ovarian cancer cells originated mainly from cellular membranes. Thus, the intracellular location of PP IX in a predominantly lipophilic environment, characterized by a comparably high photostability (probed by photobleaching and photoproduct formation) and a lower degree of porphyrin aggregation (probed previously by fluorescence decay kinetics), seems to be the key factor for high photodynamic efficacy of 5-ALA-induced PP IX. In the case of OV2774 ovarian cancer cells, however, a low PP IX accumulation limited cell inactivation upon irradiation, whereas the results obtained for glioblastoma cells are encouraging to develop PDT to an additional therapeutic option for the treatment of tumour margins in patients who underwent fluorescence-guided resection of high grade malignant glioma after 5-ALA administration.

Photodynamic therapy of malignant glioma with hypericin: comprehensive in vitro study in human glioblastoma cell lines.

The poor prognosis of patients suffering from malignant glioma requires further efforts. Photodynamic therapy (PDT) might be a therapeutic option to increase surgical radicality. Hypericin (HY) exhibit high phototoxicity to malignant cells and accumulates to a higher extent in glioblastoma cells as compared to neurons. Therefore, the impact of various experimental parameters on cytotoxicity, intracellular accumulation and phototoxicity of HY was quantitatively assessed in the three human glioblastoma cell lines U373 MG, LN229 and T98G. Additionally, intracellular location of HY was studied with fluorescence microscopic techniques. For all three cell lines, no cytotoxicity was found for incubation concentrations up to 5 microM. For short-time incubation (2 h), maximum HY fluorescence was achieved at an incubation concentration of about 5 microM. However, uptake kinetics of HY was dependent on its incubation concentration. Moreover, increase in HY fluorescence was negligible at 4 degrees C, which strongly indicates that the compound is taken up by an energy-dependent process. HY exhibited high phototoxicity (at 595 nm) in all three cell lines with ID50-values ranging from 0.15 J/cm(2) to 0.22 J/cm(2), but sensitivity decreased in the order U373 MG > LN229 > T98G. However, assessment of phototoxicity at different wavelengths revealed that highest cell inactivation was achieved at 600 nm. Fluorescence microscopy showed that HY fluorescence arose predominantly from the perinuclear region and the nuclear membrane. Fluorescence pattern of HY was significantly different from those observed for organelle markers staining lysosomes or mitochondria. Location of HY in the plasma membrane was proven by total internal reflection fluorescence microscopy. Thus, the present study demonstrates that glioblastoma cells can be effectively inactivated by HY-PDT after short-time incubation and exposure to low light doses. These results obtained in cell culture are encouraging and justify further evaluation HY-PDT for the treatment of malignant glioma in animal experiments.

Total internal reflectance fluorescence reader for selective investigations of cell membranes.

A novel setup for fluorescence measurements of surfaces of biological samples, in particular the plasma membrane of living cells, is described. The method is based on splitting of a laser beam and multiple total internal reflections (TIR) within the bottom of a microtiter plate (cell substrate), such that up to 96 individual samples are illuminated simultaneously by an evanescent electromagnetic field. Main prerequisites are an appropriate thickness and a high transmission of the glass bottom, which is attached to the 96-well cell culture plate by a noncytotoxic adhesive. Glass rods of rectangular cross sections are optically coupled to this bottom for TIR illumination. Fluorescence arising from the plasma membrane of living cells is detected simultaneously from all samples using an integrating charge-coupled device (CCD) camera. The TIR fluorescence reader is validated using cultivated cells incubated with different fluorescent markers, as well as stably transfected cells expressing a fluorescent membrane-associating protein. In addition, particularly with regard to potential pharmaceutical applications, the kinetics of the intracellular translocation of a fluorescent protein kinase c fusion protein upon stimulation of the cells is determined.

Autofluorescence lifetime imaging of cultivated cells using a UV picosecond laser diode.

Lifetime images of autofluorescence of cultivated endothelial cells were recorded using a novel picosecond laser diode in the near ultraviolet range (375 nm). In contrast to existing picosecond light sources this wavelength permits efficient excitation of the free and protein bound coenzyme NADH with fluorescence lifetimes of 0.4-0.5 ns and 2.0-2.5 ns, respectively. The effective fluorescence lifetime tau(eff) (depending on both lifetimes) was homogenously distributed over the cells with some shortening in the perinuclear region, possibly close to mitochondria. A slight decrease of tau(eff) was observed after inhibition of the mitochondrial respiratory chain, whereas a slight increase was observed after inhibition of the glycolytic pathway, thus indicating variations of the ratio of free and protein bound NADH. Although present applications are still limited by their low pulse energy (< or = 5 pJ), uv picosecond laser diodes have a large potential in high resolution fluorescence microscopy and fluorescence lifetime endoscopy.

Laser-assisted fluorescence microscopy for measuring cell membrane dynamics.

Membranes of living cells are characterized by laser-assisted fluorescence microscopy, in particular a combination of microspectrofluorometry, total internal reflection fluorescence microscopy (TIRFM), fluorescence lifetime imaging (FLIM) and Forster resonance energy transfer (FRET) spectroscopy. The generalized polarization (GP, characterizing a spectral shift which depends on the phase of membrane lipids) as well as the effective fluorescence lifetime (tau(eff)) of the membrane marker laurdan were revealed to be appropriate parameters for membrane stiffness and fluidity. GP decreased with temperature, but increased during cell growth and was always higher for the plasma membrane than for intracellular membranes. Microdomains of different fluorescence lifetimes tau(eff) were observed at temperatures above 30 degree C and disappeared during cell aging. Non-radiative energy transfer was used to detect laurdan selectively in close proximity to a molecular acceptor (DiI) and may present a possibility for measuring membrane dynamics in specific microenvironments.

A novel, high-affinity, fluorescent progesterone receptor antagonist. Synthesis and in vitro studies.

The present paper describes the chemical synthesis and in vitro characterization of a novel, high-affinity, fluorescent progesterone receptor (PR) antagonist. The three-step synthesis was carried out starting from mifepristone. After demethylation with calcium oxide, the methylamino group was alkylated with 6-bromohexanol, and the resulting compound was reacted with fluorescein 5-isothiocyanate, yielding the fluorescein-mifepristone conjugate. Interaction of the conjugate as well as of its precursors with PR was determined in cell culture (alkaline phosphatase assay and transactivation assay). Antiprogestagenic activity of the intermediates were comparable to that of the parent compound. Even after attachment of the bulky fluorescein moiety, considerable antiprogestagenic activity was maintained. Microscopic studies revealed that fluorescence of the conjugate was almost confined to the nuclei of steroid hormone receptor-positive cells, whereas the nuclei of steroid hormone receptor-negative cells remained unstained. To our knowledge, this is the first report on a fluorescent ligand for PR suitable for studies in living cells. It is proposed that the present fluorescent PR antagonist might serve as a lead compound for the development of contrast agents for PR imaging, e.g., by near-infrared optical imaging.

Fluorescence lifetime imaging (FLIM) of rhodamine 123 in living cells.

A novel setup for fluorescence intensity and lifetime imaging (FLIM) of living cells is reported. Time-resolving techniques are combined with total internal reflection fluorescence microscopy (TIRFM), which permits optical excitation of either plasma membranes or whole cells depending on whether the angle of incidence of the excitation light is greater or smaller than the critical angle for total internal reflection. The method is applied to BKEz-7 endothelial cells incubated with various concentrations of the well established mitochondrial marker rhodamine 123(R123). Measurements show that only at low concentrations this dye is mainly located within the mitochondria, whereas at higher concentrations an accumulation within the plasma membrane occurs as well. Concomitantly, fluorescence quenching in the mitochondria is observed at high concentrations, probably due to aggregation of the R123 molecules. Therefore, for diagnostic applications the concentration of R123 in the incubation medium should not be above 25 microM.