Photodynamic therapy of C3H tumours in mice: Effect of drug/light dose fractionation and misonidazole

C3H mammary carcinomas transplanted to the feet of mice were treated with haematoporphyrin derivative (HPD) or Photofrin II(PII) and laser light at 630 nm. While fluence rates lower than 100 mW cm⁻² gave minimal hyperthermic effects, a slight but significant growth delay was observed in unsensitized tumours exposed to a fluence rate of 150 mW cm⁻² which induced tumour temperatures in the range 40–50°C. Different modes of fractionation of the light fluence and of the HPD dose were tested but were found to give poorer rather than better results than the application of a single light exposure 24 h after intraperitoneal injection of HPD. Different PII doses were applied together with different light fluences, keeping the product of the drug dose and light fluence constant. In the dose range 6.25–50 mg/kg body weight the resulting effect on tumours was constant, allowing for a slight effect of hyperthermia at the highest light fluences, and possibly a photodegradation of PII. Misonidazole given before photodynamic treatment (PDT) slightly reduced the effect of PDT on the tumour growth. When given after PDT, however, misonidazole improved the therapeutic results significantly.     

Safety studies for intraoperative photodynamic therapy

A new adjunctive therapy is needed for colorectal carcinoma surgery to decrease local recurrence rates. Photodynamic therapy (PDT) may be able to fulfil this role by activating the selective photosensitizer haematoporphyrin derivative (HPD) intraoperatively with laser light. This technique would necessitate the irradiation of normal tissues and therefore safety studies have been carried out in miniature pigs. Animals were photosensitized with HPD (5 mg kg⁻¹), then 48 h later colonic anastomoses and ureters were irradiated with 50 J cm⁻² of 510 nm-equivalent light. Anatomical, physiological and biochemical analyses were carried out, investigating both structure and function. Our results show that PDT applied in a potentially useful biological dose has no detrimental effect on the healing of anastomoses and ureteric structure and function. This work paves the way for intraoperative adjunctive PDT to be used effectively in man.     

Photodynamic laser cyclodestruction with chloroaluminum sulfonated Phthalocyanine (CASPc) or photofrin®(PII) Vs. Nd:YAG laser cyclodestruction in a pigmented rabbit model

Background and Objective: To investigate Photofrin® (PII) and CASPc for photodynamic therapy (PDT) of the ciliary body in rabbits. Study Design/Materials and Methods: PII (10 mg/kg) or CASPc (1 mg/kg) was given by ear vein. Pharmacokinetics were studied in frozen sections by fluorescence microscopy (CCD camera based low light detection system with digital image processing) at 1 and 24 h (8 rabbits;16 eyes). Laser light was delivered (argon pumped dye laser;630 and 675 nm;8 rabbits;16 eyes) by contact fiberoptic. To compensate for iris attenuation, irradiance was 125 mW/cm² (20, 40, 80, or 160 J/cm²). Controls (4 rabbits;8 eyes) received laser light without photochemicals (OD) and for comparison, continuous wave Nd:YAG laser by fiberoptic (0.8–1.2J;OS). Results: Localization studies showed intravascular distribution with some selective ciliary body distribution at 24 h (PII > CASPc). Rabbits treated with PII or CASPc exhibited variable amounts of gross ciliary body edema, infarction, and necrosis by 24–48 h. This response was not seen in PDT control tissues;damage was seen in the iris and ciliary body, with partial vacuolization of the pigment epithelium. Conclusion: PDT may offer a more selective approach to ciliary body destruction. A small but significant thermal effect was seen during PDT from melanin photon uptake with damage to iris and ciliary body. Thermal damage and potential interaction with ocular visual pigments may limit use of these photochemicals and wavelengths for PDT of the ciliary body © 1995 Wiley-Liss, Inc.     

Effect of photodynamic therapy on urinary bladder function: an experimental study with rats

Photodynamic therapy (PDT) produces localized necrosis with light after prior administration of a photosensitizing drug. The problems with laser light dosimetry and complications relating to bladder function appear to be important limiting factors of PDT in urology. Photodynamic therapy on urinary bladder with normal epithelium of rats was performed using an argon ion laser as an energy source, with aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) photosensitizer. Four hours after ALA intravenous administration, the bladders were intravesically radiated with light doses 20, 40, or 80 J/cm². Animals in the control group did not receive ALA and were radiated with 20 J/cm² light dose. Three weeks prior to PDT, the bladder capacity and pressure changes during filling cystometry were assessed. Cystometrics were repeated 1, 3, 7, or 21 days after laser therapy. The light dose 20 J/cm² and 40 J/cm² together with the used ALA dose caused no reduction in bladder capacity, whereas 80 J/cm² light dose produced up to 50% reduction in the capacity at 3 weeks postoperatively. In control group without ALA, the animals did not regain more than 34% of the capacity of their control values at 3 weeks. The light dose of 20 J/cm² and 40 J/cm² with ALA induced functional changes that subsided after day 1. Our results indicate that with proper dosing of photosensitizing drug and light energy, the functional impairment of urinary bladder may be reduced as transient. These findings support the use of PDT as safe therapy of superficial bladder cancer. Received: 10 April 2000 / Accepted: 16 November 2000     

Post-acute response of 9L gliosarcoma to Photofrin™-mediated PDT in athymic nude mice

The objective of this study is to measure the chronic responses of 9L glioma and normal brain to photodynamic therapy (PDT). Tumor size, proliferation activity of glioma cells, and vascular endothelial growth factor (VEGF) expression in both the tumor area and the brain adjacent to tumor (BAT) were observed 7 days after clinically relevant doses of PDT treatment. 9L Gliosarcoma cells were implanted into the brain of 20 athymic nude mice. Fifteen mice were injected intraperitoneally with Photofrin™ at a dose of 2 mg/kg on day 6 after tumor implantation and were treated with laser at different optical doses of 40 J/cm² (n = 5), 80 J/cm² (n = 5), and 120 J/cm² (n = 5) at 24 h after Photofrin injection, respectively. The remaining five tumor-bearing mice served as a tumor-only control. All animals were killed 14 days after tumor implantation. Hematoxylin and eosin and immunostaining were performed to assess tumor volume, VEGF expression in the tumor and the BAT, as well as Ki67 expression in the tumor area. The tumor volume of the mice receiving 80 or 120 J/cm² group was significantly smaller than the control group (p < 0.01). VEGF immunoreactivity in the BAT was significantly increased in the 120 J/cm² PDT-treated mice (p < 0.001), compared with the immunoreactivity seen in untreated mice and those receiving Photofrin and lower optical doses. No significant differences were detected in the proliferation of glioma cells and VEGF expression in the tumor area between these groups. These data indicate that PDT can shrink tumor, especially at the high light dose, and that PDT induces expression of VEGF in the BAT, which is associated with tumor recurrence. Therefore, PDT combined with anti-angiogenic agents may be an effective treatment strategy for glioma.     

Use of photodynamic therapy in the treatment of oral and maxillofacial cancer and precancer: Report of 104 cases and preliminary observation on the mechanism

This paper describes the use of photodynamic therapy (PDT) in the treatment of 104 patients with premalignant or malignant disease of the oral cavity and maxillofacial regions. The tumours in 10 patients were submitted to detailed histological examination following resection 24 hours after PDT. In all patients the photosensitizer was haematoporphyrin derivative given in a dose of 2.5–5.0 mg/kg body weight, 48–72h before photoirradiation. Einghteen patients were treated with the helium-neon laser, with a power density of 120–200 mW/cm² and a total energy dose of 200–500 J/cm², but in this group a complete response was obtained in only 39% of patients. However, when the argon-pumped dye laser was used in the remaining cases, with a power density of 400–800 mW/cm² and a total energy dose of 720–1440 J/cm², the complete response rate rose to 72%. In the latter group, 15 patients were treated by fibre-optic implantation between the tumour and underlying normal tissues. From the histological study it would appear that PDT acts both on the blood vessels of the stroma and also at a cellular level, with some possible enhancement of immune function. Indications for PDT, based on this study, are defined.     

The effect of low-power laser light at different doses on gastric mucosa sensitized with methylene blue, haematoporphyrin derivative or toluidine blue

Helicobacter pylori has been associated with peptic ulcers, gastric cancer and various other gastroduodenal pathologies. Conventional antibiotic treatment is not entirely satisfactory, whereas photodynamic therapy (PDT) is a possible alternative. Although PDT has been shown to be effective in killing helicobacter on native gastric mucosa, the success of the technique will depend upon the mucosa underlying the bacteria remaining unharmed. This study examined the effect of increasing doses of low-power laser light on rat gastric mucosa, sensitized with either methylene blue (MB), haematoporphyrin derivative (HpD) or toluidine blue (TBO). No damage was detectable with any of the photosensitizers when a light dose of 250 Jcm^-2 was used. Mucosal damage was seen consistently with TBO (1 mg ml^-1) and a light dose of 500 J cm^-2. The same light dose of 500 J cm^-2 using MB caused inconsistent damage to the mucosa, whereas HpD had no effect even with the highest dose of laser light (500 J cm^-2). As the energy doses required to kill bacteria (50 and 200 Jcm^-2 for MB and TBO, respectively) are well below the levels shown to damage normal gastric mucosa, PDT forH. pylori should not be harmful to the underlying epithelium.     

Photodynamic therapy inhibits transforming growth factor β activity associated with vascular smooth muscle cell injury

Purpose: The multifunctional cytokine, transforming growth factor β1 (TGF-β), plays an important role in the development of injury-associated intimal hyperplasia (IH). Strategies to suppress local TGF-β activity may have a clinical potential to prevent restenosis caused by IH. Photodynamic therapy (PDT) involves the local generation of cytotoxic free radicals by light activation of photosensitizer dyes and has been shown to inhibit experimental IH. This study investigated whether PDT-generated free radicals can affect TGF-β activity in a biologic system using vascular smooth muscle cells (SMCs).Methods: The release and activation of TGF-β by injured SMCs in culture was compared between mechanical injury and PDT. Mechanical injury was induced with a rubber policeman, and PDT was performed with the photosensitizer chloroaluminum sulfonated phthalocyanine (5 μg/ml) and 675 nm laser light at subtherapeutic 10 J/cm² and the in vivo therapeutic dose of 100 J/cm². Cell viability was assessed by the tetrazolium salt conversion assay, and active and total (active + latent) TGF-β was determined by enzyme-linked immunosorbent assay in the conditioned media of SMCs 24 hours after treatment. Functional TGF-β activity was assessed by inhibition of endothelial cell mitogenesis.Results: Both forms of injury severely reduced (p < 0.0005) SMC viability to less than 15%. In untreated SMC conditioned media, only 14.5% of the total TGF-β was active (27.7 ± 8.7 pg per 1 × 10⁵ cells). However, after mechanical injury and PDT with 10 J/cm², there was a significant increase (p < 0.02) in active TGF-β (60.1 ± 10.1 pg and 48.6 ± 21.0 pg, respectively), despite a total reduction of approximately 50%. In contrast to this result, PDT with 100 J/cm² did not result in increased levels of active TGF-β (8.1 ± 3.5 pg), despite having similar levels of total TGF-β. Consequently, the conditioned media of SMCs that had 100 J/cm² PDT did not inhibit endothelial cell mitogenesis as compared with the conditioned media of SMCs with mechanical injury and 10 J/cm² PDT (p < 0.0002).Conclusions: This report describes two novel findings: (1) injury to SMCs in vitro induces the conversion of biologically latent TGF-β to active TGF-β; and (2) the therapeutic PDT dose interferes with this injury activation process. This study substantiates the concept of local cytokine inhibition by PDT in a biologic system and provides new insights into the mechanisms of PDT-mediated inhibition of experimental IH. (J Vasc Surg 1997;25:1033-43.)     

Photodetection and photodynamic therapy of ‘early’ squamous cell carcinomas of the pharynx,oesophagus and tracheo-bronchial tree

The efficacy of photodynamic therapy (PDT) alone was evaluated on 41 early squamous cell carcinomas of the pharynx (10), oesophagus (15) and tracheo-bronchial tree (16). All lesions but two were synchronous second primaries in ENT-patients suffering from a more extensive cancer, governing the overall oncological prognosis.Photofrin I (3 mg/kg) or Photofrin II (2 mg/kg) were injected 72 h prior to the red light irradiation, supplied by an argon pumped dye laser. A diffusing cylinder was used to obtain a homogeneous light distribution at the tumour site (60 J to 150 J/cm²). In the oesophagus and bronchi, the results are good for cancers staged in situ or microinvasive at endoscopy (two recurrencies for 23 lesions treated). For more advanced cancers (submucosal in the oesophagus or invading the bronchial cartilage), the results are less satisfactory (three recurrencies for eight lesions treated). In the pharynx where light dosimetry is more difficult, the rate of recurrencies is higher (3/10 lesions treated). In the bronchi (one case) and oesophagus (one case), the longest disease-free survival is now 5 years.The irradiation of a non-cancerous zone of normal buccal mucosa on 25 patients having received HPD showed necrosis in all cases with light doses as low as 50mW/cm² for 20 min (60 J cm^–2), even with Photofrin II.We encountered six complications (three cicatricial stenosis, two fistulae, one severe sunburn), most of them resulting from the lack of selectivity of HPD. According to these experiments, PDT is efficient at destroying early squamous cell carcinomas in the pharynx, oesophagus and bronchi, but the tumour selectivity of HPD is poor in the digestive tract lined with squamous cell epithelium. The only hope for the future lies in the synthesis of a more selective and more stable photosensitizer. This discussion reviews possible directions of research for the development of new dyes (cationic dyes, dyes attached to monoclonal antibodies, etc), for PDT and hyperthermia, for photodetection of early cancers using a fluoro-endoscope, and finally, for tumour depth profiling in hollow organs using lasers of different wavelengths.     

In vitro and in vivo effects of photodynamic therapy on murine malignant melanoma

Background: The role of photodynamic therapy (PDT) in the treatment of malignant melanoma is not well defined, nor is it known whether the dark melanoma cells absorb the light used in PDT. Methods: In vitro studies: 2×10⁵ B16 murine melanoma cells were incubated with aluminum phthalocyanine (AlpcS₄, 2.5 mg/kg) and were then subjected to photoradiation (50, 100 or 200 J/cm²). Viability was then assessed.In vivo studies: Histology: C57/B1 mice received 2×10⁵ B16 cells subcutaneously and were randomized into study (PDT) and three control groups. AlpcS₄ 2.5 mg/kg was injected intraperitoneally and the mice were exposed to light (100 J/cm²). After 24 hours they were sacrificed and underwent autopsies. Survival: 40 mice were randomized into PDT (40 J/cm²) and control groups and were monitored for 50 days. Tumor growth: 40 mice were randomized into one control and three treatment groups (PDT on day 3, 6, or 12 after injection with B16 cells), and were monitored for 50 days. Temperature: Tumor temperatures before and at the end of PDT were recorded. Results: In vitro studies: PDT caused a decrease in cell viability to 15.5±0.7%, 11.5±2.1%, and 1.5±0.7% (at 50, 100, and 200 J/cm², respectively;P<.001). A significant reduction in thymidine incorporation was noted at all energy levels.In vivo studies: Histology: PDT caused massive tumor necrosis. Survival: PDT prolonged the survival of mice (41±13.4 days) compared to controls (15.8±3.8 days,P<.001). Tumor growth: 31 days after injection with B16 cells, the tumor size was 2.6±0.3 cm in the control group and 1.6±0.2, 0.9±0.3, and 1.0±0.4 cm in the PDT groups (days 3, 6 and 12, respectively;P<.01). Temperature: PDT increased skin temperature to 42.8°C±1.3°C, 45.3°C±3.5°C, and 51.7°C±2.7°C at 40, 60, and 100 J/cm², respectively (P<.01). Conclusions: Photodynamic therapy was found to have significant effects in experimental melanoma in mice. The role of PDT in human melanoma remains to be studied.Presented at the 50th Annual Cancer Symposium of The Society of Surgical Oncology, Chicago, Illinois, March 20–23, 1997.     

Photodynamic therapy for the treatment of advanced gastrointestinal tumours

In the study, 120 patients with advanced gastrointestinal tumours were treated by PDT; 5 mg/kg of HpD was intravenously given 48–72 h prior to PDT. The light source was an argon dye laser with an output beam of 630 nm. The irradiation time varied from 15–25 min with a power of 100–350 mW cm^–2. The entire tumour was irradiated with a light dose of 100–250 J cm^–2. Of the 120 patients, 20 had cancer of esophagus, 72 had cancer of the gastric cardia, 18 had cancer of the stomach and 10 had cancer of the rectum. Eighty-eight patients (73.3%) had a response to PDT. Twelve patients with CR were followed up for one to five years, two patients died during the two years after PDT.     

Development of an alternative light source to lasers for photodynamic therapy: 2. Comparative in vivo tumour response characteristics

The performance of a low cost, table-top/portable light source was tested against an argon ion pumped dye laser for in vivo photodynamic therapy (PDT). The prototype delivers up to 1 W via a 4 mm flexible lightguide within a 30 nm bandwidth centred at any wavelength from 300 nm to 1200 nm at fluence rates of up to 8 W cm^–2. An in situ bioassay using regrowth delay of tumour T50/80 was used to quantify the relative efficacy of the prototype with a laser. The tumours were sensitized with haematoporphyrin derivative (HpD) and externally irradiated. There was no significant difference in the response of the tumour to treatment between the two light sources (p = 0.69). Mean growth delays ranged from 2 days (light dose 10 J cm^–2) to 20 days (light dose 100 J cm^–2). The estimate for the difference in means (laser minus prototype growth delay) was only 0.66 days and was not statistically significant. This in vivo study demonstrates that the prototype is equivalent to a laser in PDT effect. The device has low capital/running cost, is simple to use and is one of the most powerful, spectrally efficient non-laser PDT sources available.     

Tolerance of small bowel anastomoses in rabbits to photodynamic therapy with dihematoporphyrin ethers and 630 nm red light

Photodynamic therapy (PDT) is being evaluated in experimental clinical trials in patients with peritoneal malignancies. Some patients require partial small bowel resection with re-anastomosis prior to PDT because of bulky tumor or focal involvement of the small bowel by tumor. To assess the safety of PDT in this setting, the tolerance of small bowel anastomoses in New Zealand white rabbits to PDT with dihematoporphyrin ethers (DHE) and 630 nm light was studied. With conventional DHE doses of 1.5–2.5 mg/kg given 24 hours prior to surgery and light doses of 0–20 J/cm² of 630 nm light, no adverse effects were seen on the healing of small bowel anastomoses. Higher photosensitizer doses of 10 mg/kg and 20 mg/kg in conjunction with 20 J/cm², however, induced failure and breakdown of fresh anastomoses in 2/3 and 4/4 animals, respectively. © 1993 Wiley-Liss, Inc.     

Low-dose photodynamic therapy increases endothelial cell proliferation and VEGF expression in nude mice brain

We tested whether low-dose photodynamic therapy (PDT) induces an angiogenic response in the normal brain of nude mice (n=20). Normal brains of nude mice were subjected to PDT at low doses (Photofrin: 2 mg/kg; optical: 2 J/cm² and 4 J/cm²). BrdU (50 mg/kg) was injected (intraperitoneally, i.p.) daily from PDT treatment to sacrifice (1 and 2 weeks after PDT). Laser scanning confocal microscopy, immunohistochemistry, and immunofluorescence staining were performed to assay angiogenic response. Morphological results show no significant tissue damage induced by PDT and two- and three-dimensional image analyses revealed no significant difference in vascular structure between the areas of exposure to PDT and contralateral areas in all mice. However, the number of BrdU immunoreactive cells were significantly increased in the areas of PDT treatment compared with contralateral hemisphere in both groups, and the number of BrdU-positive cells increased in a PDT-dose-dependent manner. Furthermore, immunohistochemical data indicate that PDT at these low doses significantly induces the expression of the vascular endothelial growth factor (VEGF) in PDT-treated regions in the 1-week group, but not in the 2-week group. These data indicate that low-dose PDT results in increased VEGF expression and endothelial cell proliferation in normal brains.     

Endoscopic photodynamic therapy in lung cancer

The main purpose of cancer therapy is to treat malignant tissue with the least damage to normal surrounding structures. Photodynamic therapy (PDT) seems to be able to fulfil this simple but fundamental premise.The mechanism of action of the photosensitizer—light system can be summarized in two main points. Chiefly, it seems to be a photodynamic process, with energy transfer from the light to the photosensitizer and from it to the oxygen molecules. Oxygen is excited and becomes singlet oxygen, which is extremely reactive and very noxious for tissues in which it develops. Secondly, a thermal mechanism related to light absorption and consequent temperature rise also seems to be involved in malignant necrosis by PDT.Thirteen males were submitted to endoscopic PDT. A total of 15 treatments were given: 2 patients were submitted to 2 sessions of PDT. Forty-eight hours after HPD administration (72 h in a few cases), the lesions were exposed to a 630 nm light from an argon-dye laser system.The total estimated energy dose delivered to the tumour surface was 90–150 J/cm² in 11 cases. All cases treated responded well and total disappearance was obtained. Median follow-up was 9.5 months (1–20 months) and the estimated energy delivered from 90–600 J/cm². No major complications were reported.     

Interstitial photodynamic therapy in the Dunning R3327-AT6 prostatic carcinoma

Interstitial photodynamic therapy (PDT) could be an alternative radical treatment for prostate cancer. The ability to predict the depth of necrosis is necessary for light treatment planning using multiple optical fibres. The extent of PDT necrosis was studied in subcutaneously implanted R3327-AT6 Dunning prostate tumours which had similar optical characteristics to human prostate. Tumour-bearing subjects were given 20 mg kg^–1 Haematoporphyrin esters (HPE) and irradiated 24 h later with 630 nm laser light. Five subjects per group were treated with increasing light doses (50–450 J cm^–1) delivered interstitially via a single 2 cm long cylindrical diffuser. After 450 J cm^–1 of irradiation, 4.3±0.8 cm³ [standard error of the mean (s.e.m.)] of tumour tissue was necrosed to a depth of 10.5±0.8 mm around the diffuser. There was an approximately linear correlation between the volume of PDT necrosis around the fibre and prescribed light dose. The mean threshold light dose for PDT effect was 18±2 J cm^–2. In this tumour with a mean photosensitizer concentration of 16±1.5g g^–1, low light doses produced tumour necrosis. PDT using multiple diffusers could destroy a relatively large tumour volume and the diffusion theory model reliably predicted the depth of necrosis.     

Experimental Research Photodynamic Effects in Perifocal, Oedematous Brain Tissue

Summary. Summary.   Background: Photodynamic therapy (PDT) has been under discussion as additional treatment option for malignant gliomas. However, damage not only to tumour tissue but also to normal brain has been demonstrated. The mechanisms of this unwanted side effect have not yet been clearly identified. Spreading of photosensitiser with oedema after disruption of the blood-brain-barrier and potential sensitisation of normal tissue has been found previously. The present study investigates the time- and dose-dependency of normal tissue damage to photodynamic therapy using Photofrin II^? after disruption of the blood-brain-barrier.   Methods: Male wistar rats anaesthetised with chloral hydrate were subjected to focal, cerebral cold lesions. Simultaneously, Photofrin II^? (PFII) was injected (2,5 or 5 mg/kg b.w.). Laser irradiation (630 nm) was performed after 4 h, 12 h and 24 h with varying light doses. Control groups were subjected to focal cold lesion alone, cold lesion with laser irradiation, PFII followed by laser irradiation, or laser irradiation alone (n=6 all groups). 24 h later, brains were removed for assessment of necrosis in coronal sections.   Findings: Light dose had a significant impact on the extent of necrosis. Compared to control animals (lesion only: 0.84±0.2 mm²; lesion and irradiation alone: 0.7±0.3 mm²), the area of necrosis was increased to 2.8±0.5 (50 J/cm²), 3.5±1,1 (100 J/cm²) and 4.3±0.7 mm² (200 J/cm², 5 mg/kg b.w.; p<0.01). This effect was time-dependent. Maximal necrosis (6.3±1,6 mm²) was observed when brains were irradiated 12 h after PFII injection, with less necrosis occurring at 24 h (2.8±0.4 mm², p<0.01). Reducing sensitiser dose to 2.5 mg/kg b.w. resulted in a reduction of necrosis (2.09±0.2 mm², p<0.05).   Interpretations: Damage to oedematous tissue after photodynamic therapy using i.v. PFII and laser light at 630 nm depends on laser dose, sensitiser dose and the time point of laser irradiation. The time point of PDT should be considered to prevent unwanted tissue reactions. In the clinical setting however, defined damage to peritumoural tissue may be advantageous. This should be achievable by optimised timing and dosage of photodynamic therapy.     

The photodynamic effect of a pulsed dye laser on human bladder carcinoma cells in vitro

Summary The photodynamic effect of a pulsed flashlamp pumped dye laser on cultured human bladder carcinoma cells was studied. MGH-U1 cells were incubated for 1 h in dihaematoporphyrin ether (DHE) and then exposed to green laser light (504 nm, 20 Hz) for varying laser power densities (50–100 mW/cm² and exposure times (2–15 s), representing incident pulse energy fluences of 2.5–5 mJ/cm² and energy densities of 0.1–1.5 J/cm². The cell survival was measured by clonogenic assay and controls exposed to either laser light alone or DHE in the dark showed no cytotoxicity. Sensitised cells were killed by energy densities of less than 1 J/cm² (LD₉₀=0.54 J/cm²). This demonstrates the probable effectiveness of a pulsed dye laser for photodynamic therapy provided that pulse fluence are below the saturation threshold of the photosensitiser (10 mJ/cm²).     

Antimicrobial effect of photodynamic therapy using a highly pure chlorin e6

The aim of the present study is to evaluate the antimicrobial effect of photodynamic therapy (PDT) using a highly pure chlorin e₆ (Ce₆), against various pathogenic bacteria. To examine the antimicrobial effect of Ce₆-mediated PDT against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Salmonella enterica serovar Typhimurium, inhibition zone formation, CFU quantification, and bacterial viability were evaluated. Inhibition zone analysis showed that Ce₆-mediated PDT is very effective to inhibit the growth of S. aureus and P. aeruginosa, but has only minor effect to E. coli and S. Typhimurium, which was dependent on the energy density of laser and dose of Ce₆. Ce₆-mediated PDT also nearly inhibited the colony formation of S. aureus and P. aeruginosa, and partially inhibited that of E. coli and S. Typhimurium. In addition, the number of viable bacteria decreased greatly after PDT application with LS-chlorin e6 of 10 μM and laser and energy density of 20 J/cm². These results show that Ce₆-mediated PDT can be an effective alternative for antimicrobial treatment.     

Development of an alternative light source to lasers for photodynamic therapy: 1. Comparative in vitro dose response characteristics

The relative performances of a prototype lamp, a pulsed laser and a continous wave laser, were compared for photodynamic therapy (PDT). Recent advances in short are technology and lamp miniaturization coupled with improvements in the effciency, of optical filter coatings have led to the design and construction of a table-top light source prototype; the first viable and cost-effective alternative to a laser, particularly in the field of PDT. The device can deliver over 1 W directly or 0.5W via a light guide within a 30 nm band centred at any wavelength from the ultra-violet to the near infra-red at fluence rates of over 1 W cm⁻², in excess of that required for PDT. Its relative biological effectiveness (RBE), in vitro, has been proven alongside two PDT laser systems, an argon pumped dye laser and a copper vapour pumped dye laser. These first in vitro tests showed an efficiency of haematoporphyrin derivative, (HPD) induced cellular photoinactivation close to that of the argon/dye laser (RBE 100%), with a mean RBE for the lamp of 87±3% (p<0.05). The lamp proved to be superior, to that of the copper/dye laser system with an RBE of up to 150% at fluence rates above 50 m W cm⁻². Transient photobleaching of the photosensitizer was the probable cause for the relative ineffectiveness of the copper/dye laser for PDT at high fluence rates.