Photodynamic therapy with mTHPC and polyethylene glycol-derived mTHPC: a comparative study on human tumour xenografts.
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The photosensitizing properties of m-tetrahydroxyphenylchlorin (mTHPC) and polyethylene glycol-derivatized mTHPC (pegylated mTHPC) were compared in nude mice bearing human malignant mesothelioma, squamous cell carcinoma and adenocarcinoma xenografts. Laser light (20 J/cm2) at 652 nm was delivered to the tumour (surface irradiance) and to an equal-sized area of the hind leg of the animals after i.p. administration of 0.1 mg/kg body weight mTHPC and an equimolar dose of pegylated mTHPC, respectively. The extent of tumour necrosis and normal tissue injury was assessed by histology. Both mTHPC and pegylated mTHPC catalyse photosensitized necrosis in mesothelioma xenografts at drug-light intervals of 1-4 days. The onset of action of pegylated mTHPC seemed slower but significantly exceeds that of mTHPC by days 3 and 4 with the greatest difference being noted at day 4. Pegylated mTHPC also induced significantly larger photonecrosis than mTHPC in squamous cell xenografts but not in adenocarcinoma at day 4, where mTHPC showed greatest activity. The degree of necrosis induced by pegylated mTHPC was the same for all three xenografts. mTHPC led to necrosis of skin and underlying muscle at a drug-light interval of 1 day but minor histological changes only at drug-light intervals from 2-4 days. In contrast, pegylated mTHPC did not result in histologically detectable changes in normal tissues under the same treatment conditions at any drug-light interval assessed. In this study, pegylated mTHPC had advantages as a photosensitizer compared to mTHPC. Tissue concentrations of mTHPC and pegylated mTHPC were measured by high-performance liquid chromatography in non-irradiated animals 4 days after administration. There was no significant difference in tumour uptake between the two sensitizers in mesothelioma, adenocarcinoma and squamous cell carcinoma xenografts. Tissue concentration measurements were of limited use for predicting photosensitization in this model. (+info)
Development of meta-tetrahydroxyphenylchlorin-monoclonal antibody conjugates for photoimmunotherapy.
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A limitation of photodynamic therapy is the lack of tumor selectivity of the photosensitizer. To overcome this problem, a protocol was developed for coupling of meta-tetrahydroxyphenylchlorin (mTHPC), one of the most promising photosensitizers, to tumor-selective monoclonal antibodies (MAbs). mTHPC was radiolabeled with 131I to facilitate the assessment of the in vitro and in vivo behavior. After the modification to 131I-mTHPC-(CH2COOH)4, thus increasing the water solubility and creating a functional moiety suitable for coupling, conjugation was performed using a labile ester. Insoluble aggregates were not formed when mTHPC-MAb conjugates with a molar ratio of up to 4 were prepared. These conjugates showed a minimal impairment of the integrity on SDS-PAGE, full stability in serum in vitro, and an optimal immunoreactivity. To test the in vivo behavior of the mTHPC-MAb conjugates, the head and neck squamous cell carcinoma-selective chimeric MAb U36 was used in head and neck squamous cell carcinoma-bearing nude mice. Biodistribution data showed that the tumor selectivity of cMAb U36-conjugated mTHPC was increased in comparison with free mTHPC, despite the fact that conjugates with a higher mTHPC:MAb ratio were more rapidly cleared from the blood. Preliminary results on the in vitro efficacy of photodynamic therapy with MAb-conjugated mTHPC showed that mTHPC coupled to the internalizing murine MAb 425 exhibited more phototoxicity than when coupled to the noninternalizing chimeric MAb U36. (+info)
Contribution of endogenous carbon monoxide to regulation of diameter in resistance vessels.
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Endogenous carbon monoxide was proposed to subserve vasodepressor functions. If so, inhibition of heme oxygenase may be expected to promote vascular contraction. This hypothesis was examined in large and small arteries and in isolated first-order gracilis muscle arterioles of rat. The heme oxygenase inhibitors chromium mesoporphyrin (CrMP) and cobalt protoporphyrin (0.175-102 micromol/l) decreased the diameter of pressurized (80 mmHg) gracilis muscle arterioles, whereas magnesium protoporphyrin, a weak heme oxygenase inhibitor, did not. CrMP also elicited development of isometric tension in the muscular branch of the femoral artery but not in the aorta or femoral artery. Arteriolar constrictor responses to CrMP varied in relation to the intravascular pressure, were blunted in preparations exposed to exogenous carbon monoxide (100 micromol/l), and were unaffected by an endothelin receptor antagonist. Importantly, CrMP amplified the constrictor response to increases of pressure in gracilis arterioles. Accordingly, the constrictor effect of heme oxygenase inhibitors is attributable to magnification of myogenic tone due to withdrawal of a vasodilatory mechanism mediated by endogenous carbon monoxide. The study suggests that the vascular carbon monoxide system plays a role in the regulation of basal tone in resistance vessels. (+info)
Carbon monoxide and cerebral microvascular tone in newborn pigs.
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The present study addresses the hypothesis that CO produced from endogenous heme oxygenase (HO) can dilate newborn cerebral arterioles. HO-2 protein was highly expressed in large and small blood vessels, as well as parenchyma, of newborn pig cerebrum. Topically applied CO dose-dependently dilated piglet pial arterioles in vivo over the range 10(-11)-10(-9) M (maximal response). CO-induced cerebrovascular dilation was abolished by treatment with the Ca2+-activated K+ channel inhibitors tetraethylammonium chloride and iberiotoxin. The HO substrate heme-L-lysinate also produced tetraethylammonium-inhibitable, dose-dependent dilation from 5 x 10(-8) to 5 x 10(-7) M (maximal). The HO inhibitor chromium mesoporphyrin blocked dilation of pial arterioles in response to heme-L-lysinate. In addition to inhibiting dilation to heme-L-lysinate, chromium mesoporphyrin also blocked pial arteriolar dilations in response to hypoxia but did not alter responses to hypercapnia or isoproterenol. We conclude that CO dilates pial arterioles via activation of Ca2+-activated K+ channels and that endogenous HO-2 potentially can produce sufficient CO to produce the dilation. (+info)
Short- and long-term normal tissue damage with photodynamic therapy in pig trachea: a fluence-response pilot study comparing Photofrin and mTHPC.
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The damage to normal pig bronchial mucosa caused by photodynamic therapy (PDT) using mTHPC and Photofrin as photosensitizers was evaluated. An endobronchial applicator was used to deliver the light with a linear diffuser and to measure the light fluence in situ. The applied fluences were varied, based on existing clinical protocols. A fluence finding experiment with short-term (1-2 days) response as an end point showed considerable damage to the mucosa with the use of Photofrin (fluences 50-275 J cm(-2), drug dose 2 mg kg(-1)) with oedema and blood vessel damage as most important features. In the short-term mTHPC experiment the damage found was slight (fluences 12.5-50 J cm(-2), drug dose 0.15 mg kg(-1)). For both sensitizers, atrophy and acute inflammation of the epithelium and the submucosal glands was observed. The damage was confined to the mucosa and submucosa leaving the cartilage intact. A long-term response experiment showed that fluences of 50 J cm(-2) for mTHPC and 65 J cm(-2) for Photofrin-treated animals caused damage that recovered within 14 days, with sporadic slight fibrosis and occasional inflammation of the submucosal glands. Limited data on the pharmacokinetics of mTHPC show that drug levels in the trachea are similar at 6 and 20 days post injection, indicating a broad time window for treatment. The importance of in situ light dosimetry was stressed by the inter-animal variations in fluence rate for comparable illumination conditions. (+info)
PO2 measurements in the rat intestinal microcirculation.
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Microvascular partial oxygen pressure (PO2) data measured with the quenched phosphorescence of palladium-porphyrin (Pd-porphyrin) with the use of optical fibers have provided new insight into the behavior of the microvascular oxygenation in models of shock. However, the actual microcirculatory compartment measured by this fiber technique has not yet been demonstrated. The purpose of this study was to investigate whether the PO2 of the intestines, as measured using a fiber phosphorometer, reflects the microvascular compartment. To this end, a new intravital phosphorometer with an improved sensitivity to high-PO2 levels (up to 180 mmHg) was developed and validated. With this setup, PO2 values were measured at different inspired oxygen fractions (15, 25, and 50% oxygen) in first-order arterioles, capillaries, and venules of the ileum of rats. Simultaneously, the PO2 was measured with an optical fiber attached to another phosphorometer. PO2 measurements with the fiber phosphorometer show excellent correlation with the PO2 in the capillaries and first-order venule vessels (r2 = 0.94, slope 0.99). We therefore conclude that values measured with the fiber phosphorometer correlate with the capillary and venular PO2. (+info)
The effect of mesoporphyrin on the production of cytokines by inflammatory cells in vitro.
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This study was conducted to investigate a mechanism of the anti-inflammatory action of mesoporphyrin, especially the effect on the production of cytokines by some cultured inflammatory cells. Mesoporphyrin had no effect on lipopolysaccharide-induced tumor necrosis factor-alpha production by RAW 264.7 cells (murine macrophage-like cells). Mesoporphyrin inhibited interferon-gamma production by 1E10.H2 cells (murine T helper-1 cells), but not interleukin-4 production by D10.G4.1 cells (murine T helper-2 cells). Mesoporphyrin inhibited interleukin-6 production by human osteoblast-like MG-63 cells. This inhibition of interleukin-6 production is closely related to the suppression of prostaglandin E2 generation by interfering cyclooxygenase 1 and 2 enzyme activities. These data suggest that the inhibition of cytokine production is one of the anti-inflammatory mechanisms of mesoporphyrin. (+info)
Foscan (mTHPC) photosensitized macrophage activation: enhancement of phagocytosis, nitric oxide release and tumour necrosis factor-alpha-mediated cytolytic activity.
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Photodynamic activation of macrophage-like cells contributes to an effective outcome of photodynamic therapy (PDT) treatment. The possibility for an enhancement of macrophage activity by photosensitization with meta-tetra(hydroxyphenyl)chlorin (mTHPC) (1 microg ml(-1)) was studied in U937, monocyte cell line differentiated into macrophages (U937) cells). Phagocytic activity of U937phi cells was evaluated by flow-cytometry monitoring of ingestion of fluorescein-labelled Escherichia coli particles. Increase in irradiation fluence up to 3.45 mJ cm(-2) (corresponding irradiation time 15 s) resulted in significant increase in fluorescence signal (145%), while at higher light fluences the signal lowered down to the untreated control values. A light energy-dependent production of tumour necrosis factor-alpha (TNF-alpha) by photosensitized macrophages was further demonstrated using the L929 assay. The maximum TNF-alpha mediated cytolysis was observed at 28 mJ cm(-2) and was 1.7-fold greater than that in control. In addition, we demonstrated a fluence-dependent increase in nitric oxide (NO) production by mTHPC-photosensitized macrophages. NO release increased gradually and reached a plateau after irradiation fluence of 6.9 mJ cm(-2). Cytotoxicity measurements indicated that the observed manifestations of mTHPC-photosensitized macrophage activation took place under the sublethal light doses. The relevance of the present findings to clinical mTHPC-PDT is discussed. (+info)