Potentiation of photodynamic therapy by heat: Effect of sequence and time interval between treatments in vivo

Photodynamic therapy (PDT) utilizing hematoporphyrin derivative (Hpd) as photosensitizer and an argon-dye laser as the light source was used alone and in combination with a localized microwave hyperthermia treatment to treat the SMTF mammary carcinoma in mice. A 30-min heat treatment at 44.5°C was applied 0–8 hr before or after a standard photodynamic treatment (67.5 or 135 J/cm², given 24 hr post-7.5 mg/kg Hpd). Potentiation of PDT by heat was found to be related to the sequence of the treatments and the time interval between them. When 44.5°C for 30 min was applied immediately after a 15-min PDT treatment, significant potentiation was seen (58% long-term tumor control vs 3 and 10%, respectively, for PDT and heat alone). This potentiation decreased with increasing time between PDT and heat, with tumor control values decreasing to 36, 20, and 14%, when 2, 4, and 8 hr, respectively, were allowed between treatments. Only additive effects of the independent therapies were found when this heat treatment was applied 0–8 hr before PDT. In other experiments, mice were treated with single or fractionated 30-min PDT treatments (two 15-min treatments separated by 0-,-2-, 4-, or 8-hr intervals). Decreases in tumor control were seen with increasing time interval; only minor differences in tumor control were seen when 4–8 hr was allowed between treatments compared to a single 15-min treatment.     

Synergistic enhancement of the efficacy of the bioreductively activated alkylating agent RSU-1164 in the treatment of prostatic cancer by photodynamic therapy

Bioreductively activated alkylating agents (BAA) require metabolic reduction to become cytotoxic. Hypoxia induces a massive increase in reductive metabolism activating BAA to their cytotoxic form. One of these BAA agents is cis-2,3-dimethyl 1-(2-nitro-1-imidazolyl)-3-(1-aziridinyl)-2-propanol referred to as RSU-1164. In a hypoxic environment, RSU-1164 is activated to a highly reactive bifunctional alkylating agent capable of crosslinking macromolecules which results in cell death. Photodynamic therapy (PDT) is a treatment modality which consists of the initial accumulation of hematoporphyrin derivative (HPD) within a tumor followed by the activation of the HPD by 630 nm. light to induce a cytotoxic response. The precise mechanism of PDT is not known, however, two actions of the activated HPD have been documented. The first is a direct cytotoxic effect, secondary to singlet oxygen production. The second is through vascular collapse and subsequent hypoxia. The combination of a chemotherapeutic agent like RSU-1164, which is activated by hypoxia, with PDT to produce such hypoxia, therefore, should greatly increase the efficiency and utility of RSU-1164. To test this hypothesis, Copenhagen rats bearing established Dunning R-3327 AT-2 prostate cancers were treated with PDT treatment alone (HPD 20 mg./kg. injected IP and then 24 hr. later, the tumor exposed to 630 nm. light at 400 mW/cm.2 for 30 min. [total dose 720 J/cm.2]), RSU-1164 alone (injected IP at a dose of 200 mg./kg.) or with the combination of this PDT treatment plus RSU-1164 given 30 min. before light exposure. These results demonstrated that this combinational treatment synergistically produces a greater retardation in the growth of the AT-2 tumor than either of the monotherapies of RSU-1164 or PDT alone.     

Hyperthermic potentiation of photodynamic therapy employing Photofrin I and II: comparison of results using three animal tumor models

Hyperthermia induced by a microwave source (2,450 MHz) was used alone and in combination with photodynamic therapy (PDT) to treat the SMT-F, EMT-6, and RIF animal tumors in vivo. PDT was administered using either Photofrin I or II as the photosensitizer and an argon-pumped tunable dye laser (630 nm) as the light source. Greater than additive increases in long-term tumor control were achieved when hyperthermia was given immediately post-PDT in the SMT-F and RIF tumor systems. Only additive (or independent) increases in tumor control were achieved when hyperthermia was given immediately before PDT in all these tumor systems and when heat was applied post-PDT using the EMT-6 tumor. In a series of experiments using the SMT-F tumor, it was observed that decreases in PDT drug or light doses could be offset (in terms of tumor control) by the addition of a subsequent heat treatment. This result, along with others presented, indicates the clinical potential of PDT and hyperthermia as adjuvant cancer modalities.     

Combination studies of hyperthermia induced by the neodymium: yttrium-aluminum-garnet (Nd:YAG) laser as an adjuvant to photodynamic therapy

Photodynamic therapy (PDT) and hyperthermia have been investigated as treatments for several types of tumors. Studies have been done to determine the efficacy of each modality individually and recently in combination with each other. In this study, 630-nm light was delivered by an argon-dye laser and hyperthermia was induced using an Nd:YAG laser. Both lasers offer the ability of delivering the beams through a quartz fiberoptic alone or simultaneously. This study examines the efficacy of the simultaneous administration of PDT and selective hyperthermia at 44.5 degrees C in tumor control in the spontaneous mammary tumor (SMT-F) in DBA mice. Hyperthermia alone (44.5 degrees C, 30 min) resulted in complete destruction of tumors, with no subsequent regrowth in 6.6% of the mice treated. PDT alone (5 mg/kg dihematoporphyrin ether; 135 J/cm) resulted in a cure rate of approximately 10%, and the simultaneous treatment of the modalities resulted in a 32.8% cure rate after 90 days. These values are indicative of a synergistic interaction.     

Photodynamic therapy for head and neck cancer xenografts in athymic mice

This study examines efficacy and optimal treatment variables of photodynamic therapy (PDT) for human head and neck squamous cancer (HNSC) xenografts in athymic mice. Two and four days after injection of hematoporphyrin derivative (HPD), tumors were illuminated with red light from an argon-dye laser. Sixty-three tumors were treated. With HPD dose and light intensity constant at 7.5 mg/kg and 100 mW/cm2, respectively, the extent of tumor necrosis was strongly dependent on duration of light exposure. There was no substantial difference in results for 30- and 60-minute treatment durations between animals injected with HPD 2 and 4 days before treatment. After 30 minutes treatment time, responses were seen in 8 of 10 mice (2 days post-HPD) and 11 of 12 mice (4 days post-HPD). After 60 minutes treatment time, toxicity was high. We conclude that, in this model, PDT is effective in selective killing of HNSC. For future comparison studies in this model, if the indicated HPD dose and light intensity are used we recommend a 2-day delay after HPD injection and a light exposure duration of 30 minutes.     

Photodynamic effects of SIM01, a new sensitizer, on experimental brain tumors in rats

BACKGROUND: Glioblastomas are the third most common cause of cancer death in patients between 15 and 35 years old. Literature suggests that PDT could represent a promising treatment, providing that sensitizers could accumulate within the cancer tissues despite the blood-brain barrier. METHODS: Distribution and PDT effect of SIM01, a promising photosensitizer, have been evaluated on orthotopic C6 tumor model in rats by comparison with HPD and m-THPC. Pharmacokinetics had been analyzed with fluorescence and ROS. Photodynamic treatment was done using a 630-nm light with an energy density of 100 J cm(-2) for HPD and a 652-nm light with an energy density of 20 J cm(-2) for m-THPC and SIM01. RESULTS: The correlation between fluorescence and ROS dosimetry was found to be excellent. An optimal concentration was found after 12 hours for SIM01 (4 mg/kg), 24 hours for HPD (10 mg/kg), and 48 hours for m-THPC (4 mg/kg). The best normal tissue/cancer ratio of concentration had been found after 12 hours for SIM01 and 48 hours for HPD and m-THPC. Pathological examinations after PDT showed that the criteria for histology of glioblastic origin were absent in SIM01-treated rats 12 hours after injection but were present in 50% of rats treated 24 hours after injection and in all after a 48-hour delay. Mean survival of rats treated 12 or 24 hours after SIM01 injection was significantly improved compared with controls, HPD-, or m-THPC-treated groups. Survival of rats treated 12 or 24 hours after SIM01 injection reached 20 days but decreased for longer delays. On the contrary, survival reached 18 days at the maximum for rats treated 48 hours after m-THPC or HPD injection. CONCLUSIONS: Our results confirm that PDT is a promising treatment for glioblastomas. SIM01 efficacy is as efficient as m-THPC but with much more favorable pharmacokinetics.     

Photodynamic therapy of human ocular cancer

Photodynamic therapy (PDT), also known as photoradiation therapy, was employed in five patients with ocular tumors that had been photosensitized to hematoporphyrin derivative (HPD). In each case more conventional treatment had failed to control the tumor, or the patient was considered a poor candidate for surgical intervention because of advanced age or general health. Intravenous administration of 2.5-3.0 mg/kg HPD was followed by PDT 2-4 days later, using a dye laser tuned to a wavelength of 632 nm. Laser light was delivered either by a fiber optic probe maintained at a fixed distance, or via a slit lamp system, for intervals of up to 20 minutes. The levels of energy applied were mainly below 420 Joules/cm2, but for tumors less than 1 mm diameter energy levels were as high as 3000 J/cm2 with a conservative power value as low as 20 mW/cm2. Tumor response to PDT was disappointing. Although substantial superficial tumor necrosis occurred in several cases, it did not extend to the deeper levels of tumor tissue. In each instance surgical intervention became necessary. Deficiencies in the procedure are discussed.     

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.     

Photodynamic therapy of superficial bladder tumors

Photodynamic therapy (PDT), using hematoporphyrin derivative (HPD) and the red light (wavelength 630 nm) of an argon-dye laser as the source of excitation energy was performed on 46 patients with superficial bladder tumors. Two methods of laser irradiation, (1) focal PDT using a 400 micron quartz fiber through a cystourethroscope in 22 patients with superficial bladder tumors and (2) whole bladder wall total PDT using a motor-driven laser light scattering device in 24 patients with multifocal carcinoma in situ and/or dysplasia of bladder mucosa associated with multicentric concurrent superficial tumors, were used. The patients in (2) had been referred for total cystectomy, and 19 of these 24 patients had a history of several transurethral resections, hyperthermia and/or instillation therapy. HPD 2-4 mg/kg was i.v. injected 48 to 72 hours before PDT. Judging from the results of 60 protrusions treated by focal PDT, the light power should be 200 mW/cm2 for 5-10 minutes or more and the total light energy should be 100 J/cm2 or more in tumors up to 2 cm in size. With focal PDT, 4 of the 22 patients had no recurrence with the mean tumor free time of 20.8 months. In 6 of the 24 patients treated with total PDT using 10, 20 or 30 J/cm2 of light energy, there was no recurrence with a mean tumor-free time of 7.5 months and there was no significant relationship between the recurrence rate and total light energy used.     

Photodynamic therapy for human malignant mesothelioma in the nude mouse

Photodynamic therapy (PDT) utilizes a photoactivatable preparation, Photofrin II, which selectively localizes in cancerous tissue and produces substances toxic to that tissue when activated by light. Whether PDT would be able to selectively destroy human malignant mesothelioma was investigated by using a human-derived malignant mesothelioma tumor subcutaneously implanted in nude mice. Human malignant mesothelioma was grown subcutaneously to a size of 0.2-0.4 cm3. Selective retention of Photofrin II was studied by measuring light-induced inhibition of cytochrome c oxidase activity in tumor, heart, and lung. Photofrin II was retained in greater quantities in tumor than in heart or lung at 24 hr after injection. Using laser light at 630 nm under varying conditions, tumor growth was measured every 2 days following PDT for 18 days. All PDT regimens were successful in destroying malignant mesothelioma. Photofrin II at 5 mg/kg was superior to 2 mg/kg (P less than 0.005), light delivered at 50 mW/cm2 x 2 hr was superior to that delivered at 200 mW/cm2 x 30 min (P less than 0.05), and a total fluence of 180 J/cm2 was equivalent to 360 J/cm2 in affecting tumor growth. Ten of 12 mice treated at 50 mW/cm2 became tumor-free and remained so for 30 days following treatment. We concluded that PDT was effective against human malignant mesothelioma in a nude mouse model without adversely affecting the animal. A role for PDT in treating patients with malignant mesothelioma may exist.     

Microprocessor-controlled Nd:YAG laser for hyperthermia induction in the RIF-1 tumor.

Near-infrared radiation from a Nd:YAG laser at 1,064 nm was used interstitially or superficially to induce hyperthermia in RIF-1 tumors in C3H male mice. A single 600-microns quartz fiber with a 0.5-cm cylindrical diffusor or a weakly diverging microlens at its distal end was used to deliver laser energy to tumors in the hind leg (mean volume = 100 mm3). Two thermocouples were inserted into each tumor. One thermocouple controlled a microprocessor-driven hyperthermia program (maximum output of 3.5 Watts) to maintain the desired temperature. Tumors were exposed to various temperature-time combinations (42-45 degrees C/30 min). Our initial results indicated that excellent temperature control to within 0.2 degrees C of the desired temperature at the feedback thermocouple was achievable during both superficial and interstitial heat treatments. Temperatures at the second thermocouple, however, were found to be lower by as much as 2.3 degrees C (using the cylindrical diffusor) or higher by up to 4.6 degrees C (using the microlens) when compared to the feedback thermocouple temperature. Several correlations were seen between total dose, tumor growth delay, percent skin necrosis, and temperature at the second thermocouple after several superficial and interstitial treatments. Statistically significant improvements in tumor growth delay (at 42 and 45 degrees C) and increased percent skin necrosis at all temperatures were observed after superficial versus interstitial treatment.     

Microvascular blood flow dynamics associated with photodynamic therapy, pulsed dye laser irradiation and combined regimens

BACKGROUND AND OBJECTIVES: Previous in vitro studies demonstrated the potential utility of benzoporphyrin derivative monoacid ring A (BPD) photodynamic therapy (PDT) for vascular destruction. Moreover, the effects of PDT were enhanced when this intervention was followed immediately by pulsed dye laser (PDL) irradiation (PDT/PDL). We further evaluate vascular effects of PDT alone, PDL alone and PDT/PDL in an in vivo rodent dorsal skinfold model. STUDY DESIGN/MATERIALS AND METHODS: A dorsal skinfold window chamber was installed surgically on female Sprague-Dawley rats. One milligram per kilogram of BPD solution was administered intravenously via a jugular venous catheter. Evaluated interventions were: control (no BPD, no light), PDT alone (576 nm, 16 minutes exposure time, 15 minutes post-BPD injection, 10 mm spot), PDL alone at 7 J/cm2 (585 nm, 1.5 ms pulse duration, 7 mm spot), PDL alone at 10 J/cm2, PDT/PDL (PDL at 7 J/cm2), and PDT/PDL (PDL at 10 J/cm2). To assess changes in microvascular blood flow, laser speckle imaging was performed before, immediately after, and 18 hours post-intervention. RESULTS: Epidermal irradiation was accomplished without blistering, scabbing or ulceration. A reduction in perfusion was achieved in all intervention groups. PDT/PDL at 7 J/cm2 resulted in the greatest reduction in vascular perfusion (56%). CONCLUSIONS: BPD PDT can achieve safe and selective vascular flow reduction. PDT/PDL can enhance diminution of microvascular blood flow. Our results suggest that PDT and PDT/PDL should be evaluated as alternative therapeutic options for treatment of hypervascular skin lesions including port wine stain birthmarks.     

Combined effects of hyperthermia, bleomycin, and X rays on Ehrlich ascites tumor

The combined effects of water-bath hyperthermia at 42.5 degrees C for 30 min, 1/10 LD50 Bleomycin iv, and 200 rad x irradiation were studied in DDD strain male mice with Ehrlich ascites tumor. The objective was to acquire data on the optimum regimen for a combined administration of these three modalities. The treatments were given 10 days after the inoculation of 2 X 10(6) of the cells into the right hind limb. Concomitant application of the three modalities led to an 80% regression. A single modality produced no significant effect and a 30-50% regression occurred when only two modalities were combined. To assess the influence of timing and sequence, hyperthermia was applied at 1, 2, 4, and 6 hr before, after, or simultaneously with the combination of Bleomycin and 200 rad X ray. A significant effect was obtained in the case of concomitant application of the three and hyperthermia was effective when applied within 2 hr before or after administration of Bleomycin plus irradiation. This enhancement disappeared at 4-hr intervals.     

Effect of hematoporphyrin derivative 2 on estrogen receptors in experimental mammary tumors

This study reports the effect of hematoporphyrin derivative 2 (HPD2) on estrogen receptors (ER) in the animal model used to develop the clinical ER assay. Fifty 200-g female Sprague-Dawley rats were given 20 mg of dimethylbenzanthracene by gastric intubation. Spontaneous mammary tumors occurred in 35 animals. Animals were anesthetized and 50% of each tumor was removed when the tumors were 2 cm in diameter. Animals were then randomized to receive 5 mg/kg (group A), 10 mg/kg (group B), or 0 mg/kg (group C) HPD2 intravenously 48 hours after biopsy. The remaining tumor was excised 48 hours post HPD2 injection. All samples were weighed, placed on ice, and frozen to -70 degrees C. ER assay was performed by batch run. Results (fmol/mg cytosol) were as follows: All animals (n = 35) pre HPD2 34.2 +/- 5.4, post HPD2 34.2 +/- 5.8; group A: (n = 11) pre HPD2 33.9 +/- 7.9, post HPD2 37.1 +/- 7.8; group B: (n = 13) pre HPD2 29.2 +/- 3.8, post HPD2 25.5 +/- 3.6; group C: (n = 11) pre HPD2 40.3 +/- 5.2, post HPD2 41.5 +/- 7.9. HPD2 does not affect ER in this animal model. Confirmatory studies with human tumor material must be completed.     

Fluorescence biodistribution and photosensitising activity of toluidine blue o on rat buccal mucosa

. The antimicrobial activity of toluidine blue O (TBO) in the presence of red light has been demonstrated for a wide range of microorganisms. The response of tissues to TBO-induced photosensitisation is an important factor in assessing the clinical usefulness of this technique for the treatment of infectious diseases. The aims of this study were to determine the effect of TBO-mediated photosensitisation on rat buccal mucosa and the biodistribution of the photosensitiser in this tissue. An aqueous solution of TBO was applied to one side of the buccal mucosa of the animals. A 6 mm diameter area was then exposed to light (633 nm) from a copper vapour pumped-dye laser. The opposite, untreated, side of the buccal mucosa served as a control. TBO concentrations of 25, 50 and 200 μg/ml, laser light doses of 110, 170 and 340 J/cm² were assessed. Control groups of animals were subjected to 340 J/cm² laser light alone or to 200 μg/ml TBO alone. Serial sacrifices were performed after 72 h to obtain mucosal tissue samples for histological examination. For the determination of TBO biodistribution, additional groups received the same TBO doses and were sacrificed after 1 min or 10 min. Specimens were removed and frozen immediately for digital fluorescence imaging. No necrotic or inflammatory changes were found in the buccal mucosa of the animals with any of the treatments (using up to 200 μg/ml TBO and 340 J/cm² laser light). A high TBO fluorescence in the epithelium, particularly in the keratinised layer, with almost no fluorescence in the underlying connective tissue was demonstrated by the digital imaging. The results of this study suggest that TBO-mediated PDT (within the concentrations and light doses tested) could be a safe antimicrobial approach for the oral infections without damaging the adjacent normal tissue. Paper received 2 May 2001; accepted 23 July 2001.     

Implications of a pre-existing tumor hypoxic fraction on photodynamic therapy.

The presence of oxygen in tissue is a requirement for photodynamic therapy (PDT)-induced destruction of solid tumors, otherwise no cell death occurs. Since many tumors have been shown to have significant populations of hypoxic cells, it is of clinical interest to determine if pre-existing tumor hypoxia limits phototherapy. This question was examined using RIF tumors where tumor response to PDT of completely oxygenated tumors was compared to tumors with an induced hypoxic fraction. Tumor hypoxia was induced by using vasoactive drugs (epinephrine, chlorpromazine, or isoproterenol), given 30 min prior to PDT, or by a surgical method. PDT consisted of 5 mg/kg Photofrin II ip 24 hr prior to treatment and 135 J/cm2 630-nm light. The administration of the various vasoactive agents induced hypoxic fractions of 2.2 to 10%. The surgical method induced hypoxic fractions of 35%. Tumor response and cure in animals given vasoactive agents did not differ from controls, suggesting that low levels of pre-existing tumor hypoxia do not limit photodynamic therapy in this tumor model. Animals with tumors made hypoxic by a surgical method showed significantly reduced tumor response to PDT. Only 14% of these animals had tumors which became flat and necrotic by the day following PDT, compared to nearly 100% for animals given vasoactive drugs or controls. Furthermore, no tumor cure was observed in animals treated by this method. The higher level of tumor hypoxia in these animals likely represents one point where large proportions of PDT-resistant cells can survive after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hematoporphyrin derivative photoradiation therapy of the rat 9L gliosarcoma brain tumor model

The distribution of hematoporphyrin derivative (HPD) in the rat 9L gliosarcoma intracerebral brain tumor model at 4, 24, 48, and 72 hours after intravenous administration was evaluated using a digital video fluorescence microscopy technique. Maximum tissue fluorescence in the normal brain was observed at 4 hours, whereas maximum fluorescence in the tumor regions occurred at 24 hours. Although the fluorescence counts suggested that there was significant uptake of HPD within the tumors when compared to normal brain, only 33% to 44% of each of the eight tumors surveyed showed fluorescence. In response to a laser light dose (633 nm) of 30 J/cm2, six rats that had been sensitized with HPD had a patchy coagulation necrosis involving up to 70% of the total tumor volume. In contrast, four rats given HPD only or exposed to laser only had no areas of necrosis, as observed on histological examination. In a group of 30 rats, no prolongation of survival was observed in response to photoradiation therapy.     

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.     

Effect of hematoporphyrin derivative photoradiation therapy on survival in the rat 9L gliosarcoma brain-tumor model

Intracerebral tumors were produced in 99 rats by stereotaxic implantation of 9L gliosarcoma brain-tumor cells. Hematoporphyrin derivative (HPD), 10 or 20 mg/kg, was administered as an intravenous bolus 24 or 48 hours before irradiation of the tumor region with light from an argon pumped-dye laser (632 nm). Laser light, at a dose of 30, 60, or 200 joules/sq cm, was delivered through a craniectomy 10 or 13 days after tumor implantation. Survival times were significantly prolonged in rats exposed to laser light at a dose of 200 joules/sq cm 24 hours after administration of HPD, 20 mg/kg.     

Safety assessment of oral photodynamic therapy in rats

Photodynamic therapy (PDT) is based on the synergism of a photosensitive drug (a photosensitizer) and visible light to destroy target cells (e.g., malignant, premalignant, or bacterial cells). The aim of this study was to investigate the response of normal rat tongue mucosa to PDT following the topical application of hematoporphyrin derivative (Photogem®), Photodithazine®, methylene blue (MB), and poly(lactic-co-glycolic acid) (PLGA) nanoparticles loaded with MB. One hundred and thirty three rats were randomly divided in various groups: the PDT groups were treated with the photosensitizers for 10 min followed by exposure to red light. Those in control groups received neither photosensitizer nor light, and they were subjected to light exposure alone or to photosensitizer alone. Fluorescent signals were obtained from tongue tissue immediately after the topical application of photosensitizers and 24 h following PDT. Histological changes were evaluated at baseline and at 1, 3, 7, and 15 days post-PDT treatment. Fluorescence was detected immediately after the application of the photosensitizers, but not 24 h following PDT. Histology revealed intact mucosa in all experimental groups at all evaluation time points. The results suggest that there is a therapeutic window where PDT with Photogem®, Photodithazine®, MB, and MB-loaded PLGA nanoparticles could safely target oral pathogenic bacteria without damaging normal oral tissue.