It has been proposed that the generation of O2 during photodynamic therapy (PDT) may lead to photochemical depletion of ambient tumour oxygen, thus causing acute hypoxia and limiting treatment effectiveness. We have studied the effects of fluence rate on pO2, in the murine RIF tumour during and after PDT using 5 mg kg(-1) Photofrin and fluence rates of 30, 75 or 150 mW cm(-2). Median pO2 before PDT ranged from 2.9 to 5.2 mmHg in three treatment groups. Within the first minute of illumination, median tumour pO2 decreased with all fluence rates to values between 0.7 and 1.1 mmHg. These effects were rapidly and completely reversible if illumination was interrupted. During prolonged illumination (20-50 J cm(-2)) pO2 recovered at the 30 mW cm(-2) fluence rate to a median value of 7.4 mmHg, but remained low at the 150 mW cm(-2) fluence rate (median pO2 1.7 mmHg). Fluence rate effects were not found after PDT, and at both 30 and 150 mW cm(-2) median tumour pO2 fell from control levels to 1.0-1.8 mmHg within 1-3 h after treatment conclusion. PDT with 100 J cm(-2) at 30 mW cm(-2) caused significantly (P = 0.0004) longer median tumour regrowth times than PDT at 150 mW cm(-2), indicating that lower fluence rate can improve PDT response. Vascular perfusion studies uncovered significant fluence rate-dependent differences in the responses of the normal and tumour vasculature. These data establish a direct relationship between tumour pO2, the fluence rate applied during PDT and treatment outcome. The findings are of immediate clinical relevance.
Background and Objective
We examined tumor response to methylene blue (MB)-mediated photodynamic therapy (PDT) in a murine tumor model. The goal was to investigate the effects of drug-light interval (DLI), injection vehicle, and fluence on tumor destruction. Fluorescence and reflectance spectroscopy informed our understanding.
Materials and Methods
EMT6 tumor cells were implanted intradermally on the backs of female BALB/c mice and grown to ~ 4-mm diameter. Mice were given a 35 μL, single site, intratumor injection of 500 μg/mL MB administered in either a water or a 5% ethanol-5% Cremophor-90% saline vehicle. PDT was begun either immediately or after a 1-hour DLI with a fluence rate of 60 mW/cm2. Each animal received a fluence of 240 or 480 J/cm2. Fluorescence and reflectance spectra were captured before and during irradiation.
A protocol consisting of the Cremophor-based vehicle, 0 DLI, and a fluence of 480 J/cm2 was the most effective, with a 55% cure rate as measured by no evidence of tumor 90 days after PDT. Use of the water vehicle with this fluence and DLI reduced the cure rate to 20%. Reducing the fluence to 240 J/cm2 similarly reduced treatment efficacy with 0 and 1-h DLIs. Univariate Cox proportional hazards analysis identified increased fluence, 0 vs. 1-h DLI, and the Cremophor vs. water vehicle as highly significant independent predictors of long term tumor control (p < 0.01 in each case). Multivariate analysis with model selection revealed fluence and injection vehicle as the best predictors of survival hazards. Fluorescence spectroscopy in vivo showed that MB fluorescence decreased monotonically during a 2-h dark interval but was restored by irradiation. Reflectance spectroscopy revealed that MB at this injected concentration attenuates the treatment beam significantly.
Sensitizer delivery vehicle, drug-light interval, and fluence contribute significantly to the tumor response to MB-mediated PDT.
fluorescence spectroscopy; methylene blue; photodynamic therapy; reflectance spectroscopy
Photodynamic therapy (PDT) with low light fluence rate has rarely been studied in protocols that use short drug–light intervals and thus deliver illumination while plasma concentrations of photosensitizer are high, creating a prominent vascular response. In this study, the effects of light fluence rate on PDT response were investigated using motexafin lutetium (10 mg/kg) in combination with 730 nm light and a 180-min drug–light interval. At 180 min, the plasma level of photosensitizer was 5.7 ng/μl compared to 3.1 ng/mg in RIF tumor, and PDT-mediated vascular effects were confirmed by a spasmodic decrease in blood flow during illumination. Light delivery at 25 mW/cm2 significantly improved long-term tumor responses over that at 75 mW/cm2. This effect could not be attributed to oxygen conservation at low fluence rate, because 25 mW/cm2 PDT provided little benefit to tumor hemoglobin oxygen saturation. However, 25 mW/cm2 PDT did prolong the duration of ischemic insult during illumination and was correspondingly associated with greater decreases in perfusion immediately after PDT, followed by smaller increases in total hemoglobin concentration in the hours after PDT. Increases in blood volume suggest blood pooling from suboptimal vascular damage; thus the smaller increases after 25 mW/cm2 PDT provide evidence of more widespread vascular damage, which was accompanied by greater decreases in clonogenic survival. Further study of low fluence rate as a means to improve responses to PDT under conditions designed to predominantly damage vasculature is warranted.
Photodynamic therapy (PDT) is known to alter the expression of various genes in treated cells. This prompted us to examine the activity of genes encoding two important enzymes in sphingolipid (SL) metabolism, dihydroceramide desaturase (DES) and sphingosine kinase (SPHK), in mouse SCCVII tumor cells treated by PDT using either the porphyrin-based photosensitizer Photofrin or silicon phthalocyanine Pc4. The results revealed that PDT induced an upregulation in the expression of two major isoforms of both genes (DES1 and DES2 as well as SPHK1 and SPHK2). While the changes were generally moderate (2-3 fold gains), the increase in DES2 expression was more pronounced and it was much greater with Photofrin-PDT than with Pc4-PDT (over 23-fold vs. less than 5-fold). Combining either Photofrin-PDT or Pc4-PDT with the cationic C16-ceramide LCL30 (20 mg/kg i.p.) for treatment of subcutaneously growing SCCVII tumors rendered important differences in the therapy outcome. Photofrin-PDT, used at a dose that attained good initial response but no tumor cures, produced 50% cures when combined with a single LCL30 treatment. In contrast, the same LCL30 treatment combined with Pc4-PDT had no significant effect on tumor response. The optimal timing of LCL30 injection was immediately after Photofrin-PDT. The therapeutic benefit was lost when LCL30 was given in two 20 mg/kg injections encompassing intervals before and after PDT. LCL85, the cationic B13 ceramide analogue and SL-modulating agent, also increased cure rates of Photofrin-PDT treated tumors, but the therapeutic benefit was less pronounced than with LCL30. These results with LCL30 and LCL85, and our previous findings for LCL29 (another SL analogue), assert the potential of SLs for use as adjuvants to augment the efficacy of PDT-mediated tumor destruction.
Sphingolipid analogs; Squamous cell carcinoma SCCVII; Photodynamic therapy; Dihydroceramide desaturase; Sphingosine kinase
Background and Objective
Photodynamic therapy (PDT) is a local antineoplastic treatment with the potential for tumor cell specificity. PDT using either hematoporphyrin derivatives or 5-aminolevulinic acid (ALA) has been reported to induce brain edema indicating disruption of the blood–brain barrier (BBB). We have evaluated the ability of ALA-mediated PDT to open the BBB in rats. This will permit access of chemotherapeutic agents to brain tumor cells remaining in the resection cavity wall, but limit their penetration into normal brain remote from the site of illumination.
Study Design/Materials and Methods
ALA-PDT was performed on non-tumor bearing inbred Fischer rats at increasing fluence levels. Contrast T1-weighted high field (3 T) magnetic resonance imaging (MRI) scans were used to monitor the degree of BBB disruption which could be inferred from the intensity and volume of the contrast agent visualized.
PDT at increasing fluence levels between 9 and 26 J demonstrated an increasing contrast flow rate. A similar increased contrast volume was observed with increasing fluence rates. The BBB was found to be disrupted 2 hours following PDT and 80–100% restored 72 hours later at the lowest fluence level. No effect on the BBB was observed if 26 J of light was given in the absence of ALA.
ALA-PDT was highly effective in opening the BBB in a localized region of the brain. The degradation of the BBB was temporary in nature at fluence levels of 9 J, opening rapidly following treatment and significantly restored during the next 72 hours. No signs of tissue damage were seen on histological sections at this fluence level. However, higher fluences did demonstrate permanent tissue changes localized in the immediate vicinity of the light source.
brain edema; fischer rat; fluence; fluence rate; magnetic resonance imaging; malignant glioma
Background and Objective
Achieving local control of gliomas with photodynamic therapy (PDT) requires the delivery of adequate light fluences to depths of 1–2 cm in the resection margin where the majority of local recurrences originate. This is clinically impractical with current single-shot, intraoperative PDT treatments due to the length of time required to deliver adequate fluences. Multiple or extended treatment protocols would therefore seem to be required. The response of human glioma spheroids to 5-aminolevulinic acid (ALA)-mediated PDT using single or, repetitive light delivery protocols was investigated at both low and ultra low fluence rates.
Study Design/Materials and Methods
Human glioma spheroids (400 μm diameter) were subjected to sub-threshold light fluence (1.5, 3, or 6 J cm−2) ALA–PDT consisting of four light delivery schemes: single treatment given over either 1 or 24 hours, repetitive treatment given either as four 1 hour light treatments separated by a 4 day interval, or 24 hours light delivery, consisting of four 24 hours treatments separated by a 3 day interval. Treatment efficacy was evaluated using a growth assay. In some cases, confocal microscopy was used to image cell viability.
The repetitive and single light treatment protocols were most effective when delivered at ultra low (μW cm−2) fluence rates. In all cases, growth inhibition was light dose-dependent. The repetitive ultra low fluence rate treatment (1.5 J cm−2; irradiance = 17 μW cm−2) light delivery protocol was the most effective resulting in total growth inhibition during the 2-week observation period.
Ultra low light fluence rate ALA–PDT results in significant spheroid growth inhibition. Repeated administration of ALA was required during repetitive and/or protracted single PDT treatment protocols. The existence of a lower fluence rate limit, below which the efficacy of threshold light fluences diminish was not found in these studies.
photodynamic therapy; 5-aminolevulinic acid; human glioma spheroids; fluence; fluence rate; repetitive PDT; chronic PDT; malignant glioma
Photodynamic therapy (PDT) is a light-based treatment modality in which wavelength specific activation of a photosensitizer (PS) generates cytotoxic response in the irradiated region. PDT response is critically dependent on several parameters including light dose, PS dose, uptake time, fluence rate, and the mode of light delivery. While the systematic optimization of these treatment parameters can be complex, it also provides multiple avenues for enhancement of PDT efficacy under diverse treatment conditions, provided that a rational framework is established to quantify the impact of parameter selection upon treatment response. Here we present a theranostic technique, combining the inherent ability of the PS to serve simultaneously as a therapeutic and imaging agent, with the use of image-based treatment assessment in three dimensional (3D) in vitro tumor models, to comprise a platform to evaluate the impact of PDT parameters on treatment outcomes. We use this approach to visualize and quantify the uptake, localization, and photobleaching of the PS benzoporphyrin derivative monoacid ring-A (BPD) in a range of treatment conditions with varying uptake times as well as continuous and fractionated light delivery regimens in 3D cultures of AsPC-1 and PANC-1 cells. Informed by photobleaching patterns and correlation with cytotoxic response, asymmetric fractionated light delivery at 4 hours BPD uptake was found to be the most effective regimen assessed. Quantification of the spatial profile of cell killing within multicellular nodules revealed that these conditions also achieve the highest depth of cytotoxicity along the radial axis of 3D nodules. The framework introduced here provides a means for systematic assessment of PDT treatment parameters in biologically relevant 3D tumor models with potential for broader application to other systems.
Photodynamic therapy; PDT; photosensitizer imaging; fractionation; verteporfin; BPD; in vitro 3D tumor model.
Background and Objective
Bacterial arthritis does not respond well to antibiotics and moreover multidrug resistance is spreading. We previously tested photodynamic therapy (PDT) mediated by systemic Photofrin® in a mouse model of methicillin-resistant Staphylococcus aureus (MRSA) arthritis, but found that neutrophils were killed by PDT and therefore the infection was potentiated.
Study Design/Materials and Methods
The present study used an intra-articular injection of Photofrin® and optimized the light dosimetry in order to maximize bacterial killing and minimize killing of host neutrophils. MRSA (5 × 107 CFU) was injected into the mouse knee followed 3 days later by 1 μg of Photofrin® and 635-nm diode laser illumination with a range of fluences within 5 minutes. Synovial fluid was sampled 6 hours or 1–3, 5, and 7 days after PDT to determine MRSA colony-forming units (CFU), neutrophil numbers, and levels of cytokines.
A biphasic light dose response was observed with the greatest reduction of MRSA CFU seen with a fluence of 20 J cm−2, whereas lower antibacterial efficacy was observed with fluences that were either lower or higher. Consistent with these results, a significantly higher concentration of macrophage inflammatory protein-2, a CXC chemokine, and greater accumulation of neutrophils were seen in the infected knee joint after PDT with a fluence of 20 J cm−2 compared to fluences of 5 or 70 J cm−2.
PDT for murine MRSA arthritis requires appropriate light dosimetry to simultaneously maximize bacterial killing and neutrophil accumulation into the infected site, while too little light does not kill sufficient bacteria and too much light kills neutrophils and damages host tissue as well as bacteria and allows bacteria to grow unimpeded by host defense.
photoinactivation; antimicrobial effect; neutrophil-mediated host defense; chemokine; macrophage inflammatory protein-2
Photodynamic therapy (PDT) using Photofrin was used in combination with a hypoxic toxin (mitomycin C, MMC) to treat four patients with recurrent skin metastasis of a mammary carcinoma. In preclinical experiments an additive effect was found for the combination of MMC and PDT for treating subcutaneous RIF1 tumours in mice. When interstitial PDT was combined with a low dose of MMC (administered 15 min before illumination), the Photofrin dose or light dose could be reduced by a factor of 2 in order to obtain equivalent cure rate or growth delay. In the clinical pilot study, a low dose of Photofrin (0.75 mg kg-1) was used for PDT alone (superficial illumination) or combined with low-dose MMC (5 mg m-2). Different tumour areas were illuminated with or without a preceding infusion of MMC. Both tumour response and skin photosensitivity were scored. After 8-12 weeks of treatment, tumour cure could be achieved by administering light doses > or = 150 J cm-2 for PDT alone and similar effects were obtained when light doses of 75-87.5 J cm-2 were given after infusion with MMC. In all cases necrotic tissue of both tumour and surrounding skin was observed, which lasted for a mean of 5 months (range 2-20 months). Skin phototoxicity, tested by using a standardised illumination of skin patches on the back, lasted maximally 3 weeks. Three main conclusions could be drawn from these studies: (1) The enhanced effects of the combination of PDT and MMC observed in mouse tumours can be extrapolated to patients with mammary skin metastasis. (2) The combination of PDT and hypoxic toxins facilitates treatment by permitting lower doses of photosensitiser to be used (thereby reducing skin phototoxicity) or lower light doses (thereby reducing illumination times and allowing the possibility to treat larger tumour areas). (3) Restoration of skin after PDT in previously treated tumour areas (chemotherapy, radiation therapy and surgery) is very low.
We examined effects of fluence rate on the photobleaching of the photosensitizer Pc 4 during photodynamic therapy (PDT) and the relationship between photobleaching and tumor response to PDT. BALB/c mice with intradermal EMT6 tumors were given 0.03 mg/kg Pc 4 by intratumor injection and irradiated at 667 nm with an irradiance of 50 or 150 mW/cm2 to a fluence of 100 J/cm2. While no cures were attained, significant tumor growth delay was demonstrated at both irradiances compared to drug-only controls. There was no significant difference in tumor responses to these two irradiances (p = 0.857). Fluorescence spectroscopy was used to monitor the bleaching of Pc 4 during irradiation, with more rapid bleaching with respect to fluence shown at the higher irradiance. No significant correlation was found between fluorescence photobleaching and tumor regrowth for the data interpreted as a whole. Within each treatment group, weak associations between photobleaching and outcome were observed. In the 50 mW/cm2 group, enhanced photobleaching was associated with prolonged growth delay (p = 0.188), while at 150 mW/cm2 this trend was reversed (p = 0.308). Thus, it appears that Pc 4 photobleaching is not a strong predictor of individual tumor response to Pc4-PDT under these treatment conditions.
The efficacy of photodynamic therapy (PDT) depends upon the delivery of both photosensitizing drug and oxygen. In this study, we hypothesized that local vascular microenvironment is a determinant of tumor response to PDT. Tumor vascularization and its basement membrane (collagen) were studied as a function of supplementation with basement membrane matrix (Matrigel) at the time of tumor cell inoculation. Effects on vascular composition with consequences to tumor hypoxia, photosensitizer uptake and PDT response were measured. Matrigel-supplemented tumors developed more normalized vasculature, composed of smaller and more uniformly-spaced blood vessels than their unsupplemented counterparts, but these changes did not affect tumor oxygenation or PDT-mediated direct cytotoxicity. However, PDT-induced vascular damage increased in Matrigel-supplemented tumors, following an affinity of the photosensitizer Photofrin for collagen-containing vascular basement membrane coupled with increased collagen content in these tumors. The more highly-collagenated tumors demonstrated more vascular congestion and ischemia after PDT, along with a higher probability of curative outcome that was collagen dependent. In the presence of photosensitizer-collagen localization, PDT effects on collagen were evidenced by a decrease in its association with vessels. Together, our findings demonstrate that photosensitizer localization to collagen increases vascular damage and improves treatment efficacy in tumors with greater collagen content. The vascular basement membrane is thus identified to be a determinant of therapeutic outcome in PDT of tumors.
collagen; photodynamic therapy; microenvironment; normalization; vasculature
Singlet oxygen (1O2) is the major cytotoxic agent responsible for cell killing for type-II photodynamic therapy (PDT). An empirical four-parameter macroscopic model is proposed to calculate the “apparent reacted 1O2 concentration”, [1O2]rx, as a clinical PDT dosimetry quantity. This model incorporates light diffusion equation and a set of PDT kinetics equations, which can be applied in any clinical treatment geometry. We demonstrate that by introducing a fitting quantity “apparent singlet oxygen threshold concentration” [1O2]rx,sd, it is feasible to determine the model parameters by fitting the computed [1O2]rx to the Photofrin-mediated PDT-induced necrotic distance using interstitially-measured Photofrin concentration and optical properties within each mouse. After determining the model parameters and the [1O2]rx,sd, we expect to use this model as an explicit dosimetry to assess PDT treatment outcome for a specific photosensitizer in an in vivo environment. The results also provide evidence that the [1O2]rx, because it takes into account the oxygen consumption (or light fluence rate) effect, can be a better predictor of PDT outcome than the PDT dose defined as the energy absorbed by the photosensitizer, which is proportional to the product of photosensitizer concentration and light fluence.
photodynamic therapy; explicit dosimetry; singlet oxygen; mathematical modeling
The present study investigated the effects of 2-(1-hexyloxyethyl)-2-devinylpyro pheophorbide-a (HPPH)-mediated photodynamic therapy (PDT) on in vitro cell survival and in vivo tumor growth derived from human esophageal squamous cancer cells (Eca109). A cell counting kit 8 (CCK8) assay was used to assess the phototoxicity of HPPH-mediated PDT in cultured Eca109 cells. The inhibition of tumor growth was determined by the changes in the relative tumor volume (RTV) and tumor weight. The results revealed that HPPH, in the range of 0.005–1 μg/ml, exhibited no cytotoxicity in the Eca109 cells without light exposure and that the in vitro efficiency of HPPH-mediated PDT was higher compared with that of Photofrin®-mediated PDT. The in vivo results indicated that graded doses of HPPH-mediated PDT significantly inhibited the xenograft tumor growth derived from the Eca109 cells in a dose-dependent manner. The inhibition efficacy of 0.6 and 1.0 mg/kg HPPH-mediated PDT was similar to that of 10 mg/kg Photofrin-mediated PDT. Furthermore, HPPH possessed a lower toxicity than Photofrin at the dose that achieved the same efficacy in mice bearing Eca109 subcutaneous tumors. The histopathological findings indicated that the tumor tissues in the photosensitizer (PS)-treated mice demonstrated varying degrees of necrosis. HPPH and Photofrin exhibited vascular cytotoxicity on the treated tumors. In conclusion, the present study demonstrated that the phototoxicity of HPPH-mediated PDT is higher than that of Photofrin-mediated PDT of the same dose. HPPH possessed lower toxicity than Photofrin at the dose that achieved the same efficacy. Therefore, HPPH may be a promising agent for treating human esophageal squamous cell cancer (ESCC).
2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a photodynamic therapy; human esophageal squamous cell cancer
Photodynamic therapy (PDT) is currently under investigation in phase II and III clinical studies for the treatment of tumours in superficial localisations. Thus far, the underlying mechanisms of PDT regarding cellular responses and gene regulation are poorly understood. Photochemically generated singlet oxygen (1O2) is mainly responsible for cytotoxicity induced by PDT. If targeted cells are not disintegrated, photo-oxidative stress leads to transcription and translation of various stress response and cytokine genes. Tumour necrosis factor (TNF) alpha, interleukin (IL) 1 and IL-6 are strongly induced by photodynamic treatment, supporting inflammatory action and immunological anti-tumour responses. To investigate the first steps of gene activation, this study focused on the proto-oncogenes c-jun and c-fos, both coding for the transcription factor activator protein 1 (AP-1), which was found to mediate IL-6 gene expression. We here determine the effects of photodynamic treatment on transcriptional regulation and DNA binding of transcription factor AP-1 in order to understand the modulation of subsequent regulatory steps. Photodynamic treatment of epithelial HeLa cells was performed by incubation with Photofrin and illumination with 630 nm laser light in vitro. Expression of the c-jun and c-fos genes was determined by way of Northern blot analysis, and DNA-binding activity of the transcription factor AP-1 was evaluated by electrophoretic mobility shift assay (EMSA). Photofrin-mediated photosensitisation of HeLa cells resulted in a rapid and dose-dependent induction of both genes but preferential expression of c-jun. Compared with the transient expression of c-jun and c-fos by phorbol ester stimulation, photodynamic treatment led to a prolonged activation pattern of both immediate early genes. Furthermore, mRNA stability studies revealed an increased half-life of c-jun and c-fos transcripts resulting from photosensitisation. Although mRNA accumulation after PDT was stronger and more prolonged compared with phorbol ester stimulation, with regard to AP-1 DNA-binding activity, phorbol ester was more efficient. Surprisingly, in addition to the activation of AP-1 DNA-binding via PDT, photodynamic treatment can decrease AP-1 DNA-binding of other strong inducers, such as the protein kinase C-mediated pathway of phorbol esters and the antioxidant pyrrolidine dithiocarbamate (PDTC). This study demonstrates a strong induction of c-jun and c-fos expression by PDT, with prolonged kinetics and mRNA stabilisation as compared with activation by phorbol esters. Interestingly, this observation is not coincident with an overinduction of AP-1 DNA-binding, hence suggesting that post-translational modifications are dominant regulatory mechanisms after PDT that tightly control AP-1 activity in the nucleus thus limiting the risk of deregulated oncogene expression.
Background and Aims: Red laser light of wavelength 630 nm is usually used for Photofrin®-mediated photodynamic therapy (PDT). The 630-nm light employed in PDT corresponds to the region of the wavelength used in low-level laser therapy (LLLT) may influence on the photodynamic effect required for killing cancer cells. The aim of this in vitro study was to investigate the changes in cell viability and degree of cell proliferation after Photofrin®-mediated PDT using 630-nm pulsed laser irradiation (10 Hz repetition rate and 7–9 ns pulse width), which was clinically found to induce no remarkable cell injury.
Materials and Methods: A study has been conducted in which HeLa cells are incubated with Photofrin® for 15 min (10 µg/ml). Irradiation was carried out at an average fluence rate of 50 mW/cm2 with light doses of 1, 3, and 5 J/cm2. The cytotoxic effects on the cells are evaluated by the XTT (2,3-bis[2-methoxy-4-nitro-5-sulfophenyl]-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide) assay.
Results: The results showed that the laser irradiated cells exhibited a greater clonogenic activity than normal and PDT treated cells for a short period after the laser irradiation.
Conclusion: If the level of 630-nm pulsed laser irradiation employed in a PDT is comparatively lowered, it would have a biostimulatory effect like that of in LLLT.
PDT; LLLT; HeLa cells; Cell proliferation; 630-nm pulsed laser
We demonstrate the use of an enzyme-activatable fluorogenic probe, Neutrophil Elastase 680 FAST (NE680), for in vivo imaging of neutrophil elastase (NE) activity in tumors subjected to photodynamic therapy (PDT). NE protease activity was assayed in SCC VII and EMT6 tumors established in C3H and BALB/c mice, respectively. Four nanomoles of NE680 was injected intravenously immediately following PDT irradiation. 5 h following administration of NE680, whole-mouse fluorescence imaging was performed. At this time point, levels of NE680 fluorescence were at least threefold greater in irradiated versus unirradiated SCC VII and EMT6 tumors sensitized with Photofrin. To compare possible photosensitizer-specific differences in therapy-induced elastase activity, EMT6 tumors were also subjected to 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH)-PDT. NE levels measured in HPPH-PDT-treated tumors were twofold higher than in unirradiated controls. Ex vivo labeling of host cells using fluorophore-conjugated antibodies and confocal imaging were used to visualize Gr1+ cells in Photofrin-PDT-treated EMT6 tumors. These data were compared with recently reported analysis of Gr1+ cell accumulation in EMT6 tumors subjected to HPPH-PDT. The population density of infiltrating Gr1+ cells in treated versus unirradiated drug-only control tumors suggests that the differential in NE680 fold enhancement observed in Photofrin versus HPPH treatment may be attributed to the significantly increased inflammatory response induced by Photofrin-PDT. The in vivo imaging of NE680, which is a fluorescent reporter of NE extracellular release caused by neutrophil activation, demonstrates that PDT results in increased NE levels in treated tumors, and the accumulation of the cleaved probe tracks qualitatively with the intratumor Gr1+ cell population.
photodynamic therapy; neutrophil elastase; neutrophil elastase 680 FAST; molecular imaging; in vivo imaging; immune cell imaging; photoactivatable probe; confocal microscopy; protease activity; Photofrin; 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a
The in vitro susceptibility of pathogenic Candida species to the photodynamic effects of the clinically approved photosensitizing agent Photofrin was examined. Internalization of Photofrin by Candida was confirmed by confocal fluorescence microscopy, and the degree of uptake was dependent on incubation concentration. Uptake of Photofrin by Candida and subsequent sensitivity to irradiation was influenced by culture conditions. Photofrin uptake was poor in C. albicans blastoconidia grown in nutrient broth. However, conversion of blastoconidia to filamentous forms by incubation in defined tissue culture medium resulted in substantial Photofrin uptake. Under conditions where Photofrin was effectively taken up by Candida, irradiated organisms were damaged in a drug dose- and light-dependent manner. Uptake of Photofrin was not inhibited by azide, indicating that the mechanism of uptake was not dependent on energy provided via electron transport. Fungal damage induced by Photofrin-mediated photodynamic therapy (PDT) was determined by evaluation of metabolic activity after irradiation. A strain of C. glabrata took up Photofrin poorly and was resistant to killing after irradiation. In contrast, two different strains of C. albicans displayed comparable levels of sensitivity to PDT. Furthermore, a reference strain of C. krusei that is relatively resistant to fluconazole compared to C. albicans was equally sensitive to C. albicans at Photofrin concentrations of ≥3 μg/ml. The results indicate that photodynamic therapy may be a useful adjunct or alternative to current anti-Candida therapeutic modalities, particularly for superficial infections on surfaces amenable to illumination.
Photodynamic therapy (PDT) is efficacious in the treatment of small malignant lesions when all cells in the tumour receive sufficient drug, oxygen and light to induce a photodynamic effect capable of complete cytotoxicity. In large tumours, only partial effectiveness is observed presumably because of insufficient light penetration into the tissue. The heterogeneity of the metabolic response in mammary tumours following PDT has been followed in vivo using localised phosphorus NMR spectroscopy. Alterations in nucleoside triphosphates (NTP), inorganic phosphate (Pi) and pH within localised regions of the tumour were monitored over 24-48 h following PDT irradiation of the tumour. Reduction of NTP and increases in Pi were observed at 4-6 h after PDT irradiation in all regions of treated tumours. The uppermost regions of the tumours (those nearest the skin surface and exposed to the greatest light fluence) displayed the greatest and most prolonged reduction of NTP and concomitant increase in Pi resulting in necrosis. The metabolite concentrations in tumour regions located towards the base of the tumour returned a near pre-treatment levels by 24-48 h after irradiation. The ability to follow heterogeneous metabolic responses in situ provides one means to assess the degree of metabolic inhibition which subsequently leads to tumour necrosis.
5-Aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) (ALA-PDT) is a highly selective treatment for malignant cells. ALA-PDT has the potential to develop into a novel therapeutic strategy for various types of cancer. Recently, light-emitting diodes (LEDs), which are inexpensive, stable and easier to handle compared to lasers, have been used in PDT as a light source. However, in colorectal cancer (CRC), the efficacy of ALA-PDT in combination with LEDs has not been fully assessed. Therefore, in this study, we evaluated the antitumor effect of ALA-PDT using various LEDs in colon cancer cells. The HT-29 human colon cancer cell line was used both in vitro and in vivo. HT-29 cells were seeded in 96-well plates. Following 5-ALA administration, cells were irradiated using LEDs at different wavelengths. Three types of LEDs, blue (peak wavelength, 456 nm), white (broad-band) and red (635 nm) were used. Twenty-four hours after irradiation, the cytotoxic effects of ALA-PDT were measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In order to evaluate the antitumor effect of ALA-PDT in vivo, nude mice were inoculated with HT-29 cells. Xenograft mice were injected intraperitoneally with 5-ALA and irradiated with 3 types of LEDs at a measured fluence rate of 96 mW/cm2 and fluence of 32 J/cm2. Each group comprised 6 mice. ALA-PDT was repeated 3 times at weekly intervals. Tumor weights were measured. Compared to the controls, ALA-PDT using LEDs showed significant antitumor effects in vitro and in vivo. The blue and white LEDs demonstrated greater antitumor effects compared to the red LEDs in vitro and in vivo. In particular, tumor inhibition rates in the blue and white LED groups were approximately 88% to those of the control group in the mouse models. In conclusion, ALA-PDT using LEDs is effective and useful in the treatment of CRC cells. This method could be a novel treatment modality for CRC.
5-aminolevulinic acid; photodynamic therapy; colon cancer; light-emitting diode; protoporphyrin IX
Background and Objective
Photodynamic therapy (PDT) of thoracic malignancies involving the pleural surfaces is an active area of clinical investigation. The present report aims to characterize a model for PDT of disseminated non-small cell lung carcinoma grown orthotopically in nude mice, and to evaluate PDT effect on tumor and normal tissues.
H460 human non-small cell lung carcinoma (NSCLC) cells were injected percutaneously into the thoracic cavity of nude mice. HPPH-PDT (1 mg/kg, 24 h) was performed via the interstitial delivery (150 mW/cm) of 661 nm light to the thoracic cavity at fluences of 25-200 J/cm.
H460 tumors exhibited exponential growth within the thoracic cavity consisting of diffuse, gross nodular disease within 9 days after intrathoracic injection. Tumor volume, measured by magnetic resonance imaging (MRI), was highly correlated with the aggregate tumor mass extracted from the corresponding animal. Intrathoracic PDT at fluences of ≥ 50 J/cm produced significant decreases in tumor burden as compared to untreated controls, however mortality increased with rising fluence. Accordingly, 50 J/cm was selected for MRI studies to measure intra-animal PDT effects. Tumor distribution favored the ventral (vs. dorsal), caudal (vs. cranial), and right (vs. left) sides of the thoracic cavity by MRI; PDT did not change this spatial pattern despite an overall effect on tumor burden. Histopathology revealed edema and fibrin deposition within the pulmonary interstitium and alveoli of the PDT-treated thoracic cavity, as well as occasional evidence of vascular disruption. Prominent neutrophil infiltration with a concomitant decline in the lymphocyte compartment was also noted in the lung parenchyma within 24 hours after PDT.
HPPH-PDT of an orthotopic model of disseminated NSCLC is both feasible and effective using intracavitary light delivery. We establish this animal model, together with the treatment and monitoring approaches, as novel and valuable methods for the pre-clinical investigation of intrathoracic PDT of disseminated pleural malignancies.
HPPH; Photochlor®; 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a; interstitial illumination; magnetic resonance imaging; non-small cell lung carcinoma; photodynamic therapy; pleural malignancy
Background and Objective
We investigated the relationship among heat shock protein 70 (hsp70) promoter activation, extracellular HSP70 protein levels, and tumor cure in an animal model of meso-tetrahydroxyphenyl chlorin (mTHPC; Foscan®)-mediated photodynamic therapy (PDT).
Materials and Methods
Using Western blot analysis, we compared HSP70 protein levels in control and PDT-treated EMT6 cells with the amplitude of hsp70-promoter driven green fluorescent protein (GFP) expression in identically treated, stably transfected hsp70-GFP/EMT6 cells. A clonogenic survival assay was performed to assess the relationship among promoter activation, HSP70 levels, and cell survival in vitro. Tumor growth studies with this transfected cell line were performed to examine responses to fluences from 0.1 to 10 J cm−2, which ranged from sub-curative to curative. In vivo stereofluorescence and confocal fluorescence imaging were used to assess the temporal kinetics in hsp70 activation in tumors subjected to these fluences and the intratumor spatial correlation between hsp70 induction and extracellular levels of HSP70, respectively.
Maximum GFP expression and HSP protein levels in cells were observed at PDT doses that corresponded to 30% cell survival. The relative changes in GFP and HSP70 protein accumulation as analyzed using Western immunoblots agreed very well, thereby confirming the validity of fluorescent reporter assessment of gene expression in our studies. In vivo imaging revealed that hsp70 promoter-driven GFP expression and accumulation of extracellular HSP70 in PDT-treated tumors subjected to non-curative doses exhibit minimal spatial correlation. There is a strong correlation between mTHPC-PDT doses that result in long-term tumor cure and those that cause high levels of surface exposed or extracellularly released HSP70s.
Treatment conditions that induce strong promoter activation do not correspond to tumor cure. PDT doses that result in long-term tumor growth control also produce significant accumulation of extracellular HSP70.
photodynamic therapy; heat shock protein; HSP70; meso-tetrahydroxyphenyl chlorin; in vivo imaging; confocal fluorescence microscopy
Light fluence delivered to the tumor volume is an important dosimetry quantity in photodynamic therapy (PDT). The in vivo measurements in 4 patients showed that light fluence rates varied significantly in a prostate during PDT. The maximum and the mean fluence rates in a quadrant varied from 74 to 777 mW/cm2 and from 45 to 385 mW/cm2, respectively, among 13 quadrants of 4 patients’ prostates. To determine three-dimensional (3D) light fluence rate distribution in a heterogeneous prostate, a kernel model was developed. The accuracy of the model was examined with a finite-element-method (FEM) model calculation, a phantom measurement, and the in vivo measurements. The kernel model calculations showed good agreements with the FEM model calculation and the measurements. The maximum and the mean deviations of the kernel model calculation from the in vivo measurements in the 4 patients were 23% and 4%, respectively. The kernel model, which is based on an analytic expression of a point source in a spherical symmetrical heterogeneity, has the advantage of fast calculation and is suitable for real time PDT treatment planning.
photodynamic therapy; light fluence rate; prostate; heterogeneity; kernel model; finite element method model; cylindrical diffusing fiber
The role of nitric oxide (NO) in the response to Photofrin-based photodynamic therapy (PDT) was investigated using mouse tumour models characterized by either relatively high or low endogenous NO production (RIF and SCCVII vs EMT6 and FsaR, respectively). The NO synthase inhibitors Nω-nitro- L -arginine (L-NNA) or Nω-nitro- L -arginine methyl ester (L-NAME), administered to mice immediately after PDT light treatment of subcutaneously growing tumours, markedly enhanced the cure rate of RIF and SCCVII models, but produced no obvious benefit with the EMT6 and FsaR models. Laser Doppler flowmetry measurement revealed that both L-NNA and L-NAME strongly inhibit blood flow in RIF and SCCVII tumours, but not in EMT6 and FsaR tumours. When injected intravenously immediately after PDT light treatment, L-NAME dramatically augmented the decrease in blood flow in SCCVII tumours induced by PDT. The pattern of blood flow alterations in tumours following PDT indicates that, even with curative doses, regular circulation may be restored in some vessels after episodes of partial or complete obstruction. Such conditions are conducive to the induction of ischaemia-reperfusion injury, which is instigated by the formation of superoxide radical. The administration of superoxide dismutase immediately after PDT resulted in a decrease in tumour cure rates, thus confirming the involvement of superoxide in the anti-tumour effect. The results of this study demonstrate that NO participates in the events associated with PDT-mediated tumour destruction, particularly in the vascular response that is of critical importance for the curative outcome of this therapy. The level of endogenous production of NO in tumours appears to be one of the determinants of sensitivity to PDT. © 2000 Cancer Research Campaign
photodynamic therapy; nitric oxide; ischaemia-reperfusion injury; mouse tumour models; tumour blood flow; nitric oxide synthase inhibitors
Mechanisms for improving photodynamic therapy (PDT) were investigated in the murine RIF1 tumour using meso-tetrahydroxyphenylchlorin (m-THPC) or bacteriochlorin a (BCA) as photosensitisers and comparing these results with Photofrin-mediated PDT. The 86Rb extraction technique was used to measure changes in perfusion at various times after interstitial PDT. Non-curative combinations of light doses with m-THPC and BCA PDT markedly decreased vascular perfusion. This decrease was more pronounced for both new photosensitisers than for Photofrin. Comparison of tumour perfusion after PDT with tumour response revealed an inverse correlation for all three photosensitisers, but the relationship was less clear for m-THPC and BCA. In vivo/in vitro experiments were performed after Photofrin or m-THPC PDT in order to assess direct tumour kill (immediate plating) vs indirect vascular effects (delayed plating). For both photosensitisers, there was little direct cell killing but clonogenic survival decreased as the interval between treatment and excision increased. When m-THPC PDT was combined with mitomycin C (MMC), light doses could be decreased by a factor of 2 for equal tumour effects. Lower light and m-THPC doses could be used compared with Photofrin PDT in combination with MMC. BCA PDT with MMC did not result in a greater tumour response compared with BCA PDT alone. Reduction in both light and photosensitiser does for effective PDT regimes in combination with MMC offers substantial clinical advantages, since both treatment time and skin photosensitisation will be reduced.
Photodynamic therapy (PDT) involves the administration of a photosensitizer (PS) followed by illumination with visible light, leading to generation of reactive oxygen species. The mechanisms of resistance to PDT ascribed to the PS may be shared with the general mechanisms of drug resistance, and are related to altered drug uptake and efflux rates or altered intracellular trafficking. As a second step, an increased inactivation of oxygen reactive species is also associated to PDT resistance via antioxidant detoxifying enzymes and activation of heat shock proteins. Induction of stress response genes also occurs after PDT, resulting in modulation of proliferation, cell detachment and inducing survival pathways among other multiple extracellular signalling events. In addition, an increased repair of induced damage to proteins, membranes and occasionally to DNA may happen. PDT-induced tissue hypoxia as a result of vascular damage and photochemical oxygen consumption may also contribute to the appearance of resistant cells.
The structure of the PS is believed to be a key point in the development of resistance, being probably related to its particular subcellular localization.
Although most of the features have already been described for chemoresistance, in many cases, no cross-resistance between PDT and chemotherapy has been reported. These findings are in line with the enhancement of PDT efficacy by combination with chemotherapy. The study of cross resistance in cells with developed resistance against a particular PS challenged against other PS is also highly complex and comprises different mechanisms.
In this review we will classify the different features observed in PDT resistance, leading to a comparison with the mechanisms most commonly found in chemo resistant cells.
chemoresistance; cross resistance; PDT; photodynamic therapy; photosensitizer; resistance; apoptosis; photosensitizers; mechanisms; porphyrins; MDR