Increased expression of mitochondrial benzodiazepine receptors following low-level light treatment facilitates enhanced protoporphyrin IX production in glioma-derived cells in vitro

BACKGROUND AND OBJECTIVES

This study investigates whether low-level light treatment (LLLT) can enhance the expression of peripheral-type mitochondrial benzodiazepine receptors (PBRs) on glioma-derived tumor cells, and by doing so promote the synthesis of protoporphyrin IX (PpIX) and increase the photodynamic therapy (PDT)-induced cell kill using 5-aminolevulinic acid (ALA). The endogenous photosensitizer, PpIX and related metabolites including coproporphyrin III are known to traffic into or out of the mitochondria via the PBRs situated on the outer mitochondrial membrane. Cells of astrocytic derivation within the brain express PBRs, while neurons express the central-type of benzodiazepine receptor.

STUDY DESIGN

Astrocytoma-derived CNS-1 cells were exposed to a range of differing low-level light protocols immediately prior to PDT. LLLT involved using broad-spectrum red light of 600-800 nm or monochromatic laser light specific to 635 or 905 nm wavelength. Cells (5 x 10(5)) were exposed to a range of LLLT doses (0, 1, or 5 J/cm(2)) using a fixed intensity of 10 mW/cm(2) and subsequently harvested for cell viability, immunofluorescence, or Western blot analysis of PBR expression. The amount of PpIX within the cells was determined using chemical extraction techniques.

RESULTS

Results confirm the induction of PBR following LLLT is dependent on the dose and wavelength of light used. Broad-spectrum red light provided the greatest cell kill following PDT, although LLLT with 635 nm or 905 nm also increased cell kill as compared to PDT alone. All LLLT regimens increased PBR expression compared to controls with corresponding increases in PpIX production.

CONCLUSIONS

These data suggest that by selectively increasing PBR expression in tumor cells, LLLT facilitates enhanced tumor cell kill using ALA-PDT. This may further improve the selectivity and efficacy of PDT treatment of brain tumors.

Photodynamic therapy for the treatment of vertebral metastases in a rat model of human breast carcinoma

The feasibility and efficacy of photodynamic therapy (PDT) for the treatment of vertebral metastases using a minimally invasive surgical technique adapted from vertebroplasty was evaluated in a rodent model. Initial validation included photosensitizer (benzoporphyrin-derivative monoacid-ring A) drug uptake studies and in vitro confirmation of PDT efficacy. Intracardiac injection of human MT-1 breast cancer cells was performed in athymic rats. In 63 rats that developed vertebral metastases 21 days post-inoculation, single treatment of PDT was performed using a parapedicular approach placing an optical fiber adjacent to targeted vertebrae. Two milligrams per kilogram of photosensitizer drug was administered intravenously followed by 150 mW of 690 nm light illumination at varying drug-light intervals and light energies. Histologic and immunohistochemical analysis was performed assessing treatment effect. Local tumor viability and growth was quantified by bioluminescence imaging pre and 48 h post-treatment. PDT demonstrated an ablative effect on vertebral metastases (light energies 25-150 J). The effect varied in proportion to light energy with the greatest anti-tumor effect observed at 150 J using a 3 h drug-light interval. 9/22 rodents in the 3 h drug-light interval developed hindlimb paralysis following treatment, consistent with drug uptake studies demonstrating an increase in spinal cord uptake 3h following drug administration. The observations of paralysis following treatment highlight the importance of closely defining the therapeutic window of treatment in safety and efficacy.

Photodynamic therapy for the treatment of metastatic lesions in bone: studies in rat and porcine models

This study represents the first reported use of photodynamic therapy (PDT) for metastatic bone lesions and specifically, as a treatment for spinal metastases. A model of bone metastasis in rat confirmed the efficacy of benzoporphyrin derivative-monoacid-mediated PDT for treating lesions within the spine and appendicular bone. Fluorimetry confirmed the selective accumulation of drug into the tumor(s) at 3 h post-injection. 48 h post-light delivery into the vertebral body of the rat spine loss of bioluminescent signal and histological analyses of sectioned spine confirmed MT-1 tumor cell kill in vivo as previously confirmed in vitro using an established cell viability assay. Porcine vertebrae provided a model comparable to that of human for light propagation and PDT response. Histological examination of vertebrae 48 h post-PDT revealed a necrotic radius of 0.6 cm with an average fluence rate of 4.3 mW/cm2. Non-necrotic tissue damage was evident up to 2 cm out from the treatment fiber. Results support the application of PDT to the treatment of primary or metastatic lesions within bone.

Volume CT with a flat-panel detector on a mobile, isocentric C-arm: Pre-clinical investigation in guidance of minimally invasive surgery

A mobile isocentric C-arm (Siemens PowerMobil) has been modified in our laboratory to include a large area flat-panel detector (in place of the x-ray image intensifier), providing multi-mode fluoroscopy and cone-beam computed tomography (CT) imaging capability. This platform represents a promising technology for minimally invasive, image-guided surgical procedures where precision in the placement of interventional tools with respect to bony and soft-tissue structures is critical. The image quality and performance in surgical guidance was investigated in pre-clinical evaluation in image-guided spinal surgery. The control, acquisition, and reconstruction system are described. The reproducibility of geometric calibration, essential to achieving high three-dimensional (3D) image quality, is tested over extended time scales (7 months) and across a broad range in C-arm angulation (up to 45 degrees), quantifying the effect of improper calibration on spatial resolution, soft-tissue visibility, and image artifacts. Phantom studies were performed to investigate the precision of 3D localization (viz., fiber optic probes within a vertebral body) and effect of lateral projection truncation (limited field of view) on soft-tissue detectability in image reconstructions. Pre-clinical investigation was undertaken in a specific spinal procedure (photodynamic therapy of spinal metastases) in five animal subjects (pigs). In each procedure, placement of fiber optic catheters in two vertebrae (L1 and L2) was guided by fluoroscopy and cone-beam CT. Experience across five procedures is reported, focusing on 3D image quality, the effects of respiratory motion, limited field of view, reconstruction filter, and imaging dose. Overall, the intraoperative cone-beam CT images were sufficient for guidance of needles and catheters with respect to bony anatomy and improved surgical performance and confidence through 3D visualization and verification of transpedicular trajectories and tool placement. Future investigation includes improvement in image quality, particularly regarding x-ray scatter, motion artifacts and field of view, and integration with optical tracking and navigation systems.

Localization of chromophore absorption signals in TEM with an improved prism-mirror-prism filter

A corrected prism-mirror-prism electron energy filter with curved entrance and exit faces was designed and incorporated into a Zeiss EM902 transmission electron microscope. The installation of the new filter required little modification to the existing microscope geometry and electronics. The filter had an energy resolution of 1.1 eV over the full image plane (acceptance half angle 10 mradian). The improved energy resolution was applied in studies of the low electron energy loss region that includes molecular orbital excitations or chromophore energy absorptions. Chromophore signal behaviour under electron irradiation was characterized using embedded crystals of hematin and of the dye mercury orange. Images of these crystals confirmed the expected decrease in signal intensity on shifting the selected energy loss from the region of molecular orbital excitations (less than approximately 5 eV) to higher energy losses. Electron irradiation-induced fading of the chromophore signal from hematin and mercury orange yielded similar 1/e dose values of 1.1 x 10(5) e(-) nm(-2) and 1.4 x 10(5) e(-) nm(-2) respectively. In a cellular context, chromophore signals were obtained from energy-filtered images of RIF-1 cell sections containing the photosensitizer chlorin e6 and from sections of BS-C-1 cells with cytoskeletal labelling via FITC-conjugated antibodies. The respective signals were extracted using a dose-dependent method or a shift in selected energy. Chromophore signal distributions were in agreement with fluorescence light microscopic images, but provided detail at higher spatial resolution.

Potentiation of chlorin e6 photodynamic activity in vitro with peptide-based intracellular vehicles

Photodynamic therapy (PDT) is a targeted treatment modality where photosensitizers accumulate into cells and are selectively activated by light leading to the production of toxic species and cell death. Focusing the action of photosensitizers to a unique intracellular target may enhance their cytotoxicity. In this study, we demonstrate that the routing of the porphyrin-based photosensitizer chlorin e(6), to the nucleus of cells can significantly alter its toxicity profile. The cellular localization of chlorin e(6) was achieved by coupling the chromophore during solid-phase synthesis to a nucleus-directed linear peptide (Ce6-peptide) or a branched peptide (Ce6-loligomer) composed of eight identical arms displaying the sequence of the Ce6-peptide. These constructs incorporated signals guiding their cytoplasmic uptake and nuclear localization. Ce6-peptide and Ce6-loligomer displayed an enhanced photodynamic activity compared to unconjugated chlorin e(6), lowering the observed CD(50) values for CHO and RIF-1 cells by 1 or more orders of magnitude. The intracellular accumulation of Ce6-peptide and Ce6-loligomer was assessed by electron and confocal microscopy as well as by flow cytometry. Constructs were internalized by cells within an hour and by 6 h, the release of active oxygen species could be observed within the nucleus of cells pretreated with Ce6-loligomer. These results highlight the utility of designing peptides as vehicles for regulating the intracellular distribution of photosensitizers such as chlorin e(6) in order to maximize their efficacy in PDT.

Peptide-based intracellular shuttle able to facilitate gene transfer in mammalian cells

Loligomers are peptide-based intracellular vehicles able to penetrate cells and self-localize into distinct cellular compartments. Loligomers can be rapidly assembled by automated solid-phase approaches and were designed to act as nonviral, nonlipophilic intracellular shuttles. One nucleus-directed loligomer, termed loligomer 4, was evaluated for its ability to function as a transfection agent. Loligomer 4 readily associates with plasmids to form noncovalent complexes. The migration of loligomer 4-plasmid complexes into cells was monitored by flow cytometry and fluorescence microscopy. Populations of plasmids labeled with 7-AAD exist either free or in association with loligomer 4 inside cells and are visible throughout the cytosol and nucleus of chinese hamster ovary (CHO) cells. Loligomer 4-plasmid complexes were not cytotoxic to cells and were readily imported by most cells (>70%). CHO cells were transfected with complexes of loligomer 4 and plasmids harboring luciferase, green fluorescent protein or beta-galactosidase reporter genes. The transfection efficiency of loligomer 4-plasmid DNA complexes was greater when cells were maintained as suspensions instead of monolayers. Transfections could be performed with cells suspended in serum-containing medium. The observed levels of transfection, however, were modest with 5-10% of CHO cells expressing either a green fluorescent protein or the enzyme beta-galactosidase. Loligomers have recently been observed in vesicular compartments [Singh, D., Kiarash, R., Kawamura, K, LaCasse, E. C., and Gariépy, J. (1998) Biochemistry 37, 5798-5809] and differences between levels of cellular import and transfection efficiency may well reflect the need to optimize the release of loligomers and their complexes from these compartments in future designs. In summary, loligomer 4 behaves as a stable, soluble and effective transfection agent. These results demonstrate the feasibility of designing loligomers able to act as intracellular guided agents aimed at gene transfer applications.

Computer quantification of intracellular gold particles

We describe the use of image software programs available for both PC and Macintosh computers to quantify the accumulation and distribution of gold-labeled constructs within two-dimensional cell sections. The compartmentalization of a biotinylated-peptide was visualized in radiation-induced fibrosarcoma cells by transmission electron microscopy, using a gold particle-streptavidin conjugate. This study illustrates the ease of tabulating gold particles observed in scanned electron micrographs, using Adobe Photoshop in conjunction with the public domain NIH Image program (Version 1.61). Quantitative information regarding the localization of molecules inside cells is crucial in defining their sites of action and in developing more effective therapeutic agents.

Ruthenium complexes as nitric oxide scavengers: a potential therapeutic approach to nitric oxide-mediated diseases

1. Ruthenium(III) reacts with nitric oxide (NO) to form stable ruthenium(II) mononitrosyls. Several Ru(III) complexes were synthesized and a study made of their ability to bind NO, in vitro and also in several biological systems following expression of the inducible isoform of nitric oxide synthase (iNOS). Here we report on the properties of two, related polyaminocarboxylate-ruthenium complexes: potassium chloro[hydrogen(ethylenedinitrilo)tetraacetato]ruthenate+ ++ (=JM1226; CAS no.14741-19-6) and aqua[hydrogen(ethylenedinitrilo)tetraacetato]ruthenium (=JM6245; CAS no.15282-93-6). 2. Binding of authentic NO by aqueous solutions of JM1226 yielded a product with an infrared (IR) spectrum characteristic of an Ru(II)-NO adduct. A compound with a similar IR spectrum was obtained after reacting JM1226 with S-nitroso-N-acetylpenicillamine (SNAP). 3. The effect of JM1226 or JM6245 on nitrite (NO2-) accumulation in cultures of macrophages (RAW 264 line) 18 h after stimulating cells with lipolysaccharide (LPS) and interferon-gamma (IFNgamma) was studied. Activation of RAW264 cells increased NO2- levels in the growth medium from (mean+/-1 s.e.mean) 4.9+/-0.5 microM to 20.9+/-0.4 microM. This was blocked by actinomycin D (10 microM) or cycloheximide (5 microM). The addition of JM1226 or JM6245 (both 100 microM) to activated RAW264 cells reduced NO2- levels to 7.6+/-0.2 microM and 8.8+/-0.6 microM, respectively. N(G)-methyl-L-arginine (L-NMMA; 250 microM) similarly reduced NO2- levels, to 6.1+/-0.2 microM. 4. The effect of JM1226 or JM6245 on NO-mediated tumour cell killing by LPS+IFNgamma-activated macrophages (RAW 264) was studied in a co-culture system, using a non-adherent murine mastocytoma (P815) line as the 'target' cell. Addition of JM1226 or JM6245 (both 100 microM) to the culture medium afforded some protection from macrophage-mediated cell killing: target cell viability increased from 54.5+/-3.3% to 93.2+/-7.1% and 80.0+/-4.6%, respectively (n=6). 5. Vasodilator responses of isolated, perfused, pre-contracted rat tail arteries elicited by bolus injections (10 microl) of SNAP were attenuated by the addition of JM1226 or JM6245 (10(-4) M) to the perfusate: the ED50 increased from 6.0 microM (Krebs only) to 1.8 mM (Krebs + JM6245) and from 7 microM (Krebs only) to 132 microM (Krebs + JM1226). Oxyhaemoglobin (5 microM) increased the ED50 value for SNAP from 8 microM to 200 microM. 6. Male Wistar rats were injected with bacterial LPS (4 mg kg(-1); i.p.) to induce endotoxaemia. JM1226 and JM6245 (both 100 microM) fully reversed the hyporesponsiveness to phenylephrine of tail arteries isolated from animals previously (24 h earlier) injected with LPS. Blood pressure recordings were made in conscious LPS-treated rats using a tail cuff apparatus. A single injection of JM1226 (100 mg kg(-1), i.p.) administered 20 h after LPS (4 mg kg(-1), i.p.) reversed the hypotension associated with endotoxaemia. 7. The results show that JM1226 and JM6245 are able to scavenge NO in biological systems and suggest a role for these compounds in novel therapeutic strategies aimed at alleviating NO-mediated disease states.

An examination of some derivatives of S-nitroso-1-thiosugars as vasodilators

A number of S-nitrosated compounds derived from 1-thiosugars (glucose, galactose, xylose, maltose, and lactose) have been prepared and characterized. Most of the compounds obtained were unstable either as solids or in solution. However, S-nitroso-1-thio-2,3,4,6-tetra-O-acetylglucopyranose was stable enough to examine as a vasodilator using an isolated rat tail artery model. It also proved effective in human cutaneous vascular smooth muscle relaxation when delivered transdermally.

NADPH-diaphorase activity in activated astrocytes represents inducible nitric oxide synthase

In paraformaldehyde-fixed sections of healthy brain, glial cells at the light-microscope level do not contain measurable levels of NADPH-diaphorase. However, after a variety of lesions in the mouse brain, some reactive astrocytes express varying amounts of this enzyme. Following stab wounds, activated astrocytes or related glial cells surrounding the lesion, contained moderate to high levels of NADPH-diaphorase in the cerebellum, midbrain, thalamus, striatum, hippocampal formation and neocortex. Double-labelling experiments confirmed that this corresponds to an inducible form of nitric oxide synthase, similar to that found in activated macrophages. Within the lesion there were large numbers of macrophages which also contained NADPH-diaphorase. After 10 min of global hypoxic ischaemia, some reactive astrocytes also contained NADPH-diaphorase. These cells were confined to the dorsal part of the hippocampal formation (the dentate fascia and CA1 areas) and to the anterolateral striatum. More focal ischaemic damage, produced by dividing an arterial branch, also produced a rim of reactive astrocytes containing NADPH-diaphorase, that surrounded the area of necrosis. Low levels of NADPH-diaphorase were induced within one day of a stab wound and the enzyme activity reached near maximal levels by two days postlesion. Moderate NADPH-diaphorase activity was still present at 63 days postlesion, but only a small number of astrocytes were stained in the immediate vicinity of the lesion. These experiments confirm that NADPH-diaphorase activity represents inducible nitric oxide synthase in activated astrocytes and probably in inflammatory macrophages. We conclude that a high proportion of activated astrocytes and a small proportion of invading macrophages are induced to express moderate to high levels of nitric oxide synthase following neuronal damage. Our results indicate that following a variety of lesions reactive astrocytes are synthesizing significant levels of nitric oxide within 24 h. This nitric oxide may be involved in modulating the likelihood of epileptic seizures.