A comparison between argon-dye and excimer-dye laser for photodynamic effect in transplanted mouse tumor.

Photodynamic therapy (PDT) utilizing a hematoporphyrin derivative (HpD) as a sensitizer has become a viable option for the local treatment of neoplastic disease. The argon-dye laser system is commonly used as a light source in this treatment modality. The excimer-dye laser, on the other hand, delivers high-energy red light in a pulsatile fashion. In this investigation, we treated BALB/c mice bearing mouse kidney sarcoma cell tumors with PDT using HpD at the dose of 5 mg/kg body weight as a photosensitizer and either a standard argon-dye laser or the pulsatile excimer-dye laser as the light source. At equal light energy doses (50 J/cm2), necrotic changes at depths averaging 4 mm from the tumor surface were obtained with the argon-dye laser (200 mW power output) while tumor necrosis at depths exceeding 15 mm from the tumor surface was obtained using the excimer-dye laser (6 mJ/pulse, 5 Hz). To determine the best conditions for photoirradiation with the excimer-dye laser, tumor-bearing mice were treated with different total light doses (10, 30 and 50 J/cm2), dose rates (1, 3 and 6 mJ/cm2), and frequencies (5, 15 and 50 Hz) of light exposure. Our results indicate that the optimal effects obtained with the excimer-dye laser are related to the total light dose used and the dose rate, but not to the frequency of light exposure.     

Photodynamic therapy for chest wall progression from breast carcinoma is an underutilized treatment modality

BACKGROUND: Chest wall progression of breast carcinoma after failure of salvage surgery, radiation, and chemohormonal therapy is a quagmire with limited therapeutic options. Because photodynamic therapy (PDT) offers excellent results in cutaneous lesions, PDT may play a role in this indication. However, to the authors' knowledge, published data for this subgroup of patients using the only commercially available photosensitizing agent, Photofrin, often show high treatment morbidity, limiting PDT's usefulness. The authors report the feasibility of decreasing the photosensitizer drug dose as a means of exploiting photobleaching kinetics to improve the therapeutic ratio for these individuals. METHODS: One hundred two chest wall sites were treated with PDT after failure of multimodality salvage therapy. In these 9 patients, lesion size ranged from 0.57 to 9 cm. Photodynamic therapy consisted of outpatient intravenous infusion of 0.8 mg/kg of Photofrin, followed 48 hours later by 630 nm light treatment of 135-170 J/cm2 delivered by a KTP:YAG laser coupled to dye unit. Two patients underwent a second PDT procedure due to new lesion formation. All patients were observed for a minimum of 6 months, and none was lost to follow-up. RESULTS: Photodynamic therapy was well tolerated with no photosensitivity reported. Despite all patients having failed surgery, full dose radiation and multiagent chemohormonal therapy, chest wall lesions healed with no scarring. Only 1 (9 cm) lesion took longer than 3 months to granulate over. The authors were able to evaluate all treatment sites, and complete response, defined as total lesion elimination, was noted in 89% of the lesions; reduction without regrowth occurred in 8% with no response in 3% of the lesions. CONCLUSIONS: Despite having prior treatment and fragile tissues, low dose Photofrin-induced PDT offers excellent clinical response with minimal morbidity. These results show that PDT should play an important role in the management of chest wall failure from breast carcinoma.     

Photodynamic therapy in women with cervical intraepithelial neoplasia using topically applied 5-aminolevulinic acid

Photodynamic therapy (PDT) is a novel treatment modality that produces local tissue necrosis with laser light after prior administration of a photosensitizing agent. We performed a study of topically applied 5-aminolevulinic acid (5-ALA) in the photodynamic treatment of women with high-grade cervical intraepithelial neoplasia (CIN) using fixed 5-ALA doses and application protocols derived from previous in vitro and in vivo results. Three to 5 hr prior to PDT, 10 ml of a 20% solution of 5-ALA was topically applied using a cervical cap. PDT was performed with irradiation of 100 J/cm2 at an irradiance of 100-150 mW/cm2 with an argon-ion-pumped dye laser at 635 nm. For the endocervix, a specifically designed cylindrical applicator was used. Ten treatment cycles of PDT using 5-ALA were performed in 7 patients with high-grade CIN. Non-thermal laser treatment with 100-150 mW/cm2 was well tolerated. Local toxicity was minor as several patients reported burning sensations and vaginal discharge, but no necrosis, sloughing or scarring occurred. After 3 months, a significant reduction in the size of the ectocervical CIN lesions was noted in only 3 patients, who underwent a second PDT cycle. However, no significant improvement in CIN lesions was noted since cold knife conization revealed persistent CIN in all 7 cases. Therefore, PDT after topical application of 5-ALA using an irradiation of 100 J/cm2 produces only minimal side effects. However, it does not appear to be effective in treating CIN.     

New proposal for the treatment of nodular basal cell carcinoma with intralesional 5-aminolevulinic acid

Photodynamic therapy (PDT) is a treatment modality using a photosensitizer, light and oxygen to cause photochemically-induced selective cell death. Topical PDT is most suitable for thin lesions such as superficial basal cell carcinoma and actinic keratoses in dermatology. Results with PDT as treatment of thicker lesions such as nodular basal cell carcinoma appear to have a limited role because the photosensitizer or the light cannot penetrate deeply enough into the thicker tumor volume. In this preliminary study we use intralesional administration of 5-aminolevulinic acid to enhance the efficacy of the photosensitivity of nodular basal cell carcinomas, thus improving clinical cure.     

A Comparison between Argon-dye and Excimer-dye Laser for Photodynamic Effect in Transplanted Mouse Tumor

Photodynamic therapy (PDT) utilizing a hematoporphyrin derivative (HpD) as a sensitizer has become a viable option for the local treatment of neoplastic disease. The argon-dye laser system is commonly used as a light source in this treatment modality. The excimer-dye laser, on the other hand, delivers high-energy red light in a pulsatile fashion. In this investigation, we treated BALB/c mice bearing mouse kidney sarcoma cell tumors with PDT using HpD at the dose of 5 mg/kg body weight as a photosensitizer and either a standard argon-dye laser or the pulsatile excimer-dye laser as the light source. At equal light energy doses (50 J/cm²), necrotic changes at depths averaging 4 mm from the tumor surface were obtained with the argon-dye laser (200 mW power output) while tumor necrosis at depths exceeding 15 mm from the tumor surface was obtained using the excimer-dye laser (6 mJ/pulse, 5 Hz). To determine the best conditions for photoirradiation with the excimer-dye laser, tumor-bearing mice were treated with different total light doses (10, 30 and 50 J/cm²), dose rates (1, 3 and 6 mJ/cm²), and frequencies (5,15 and 50 Hz) of light exposure. Our results indicate that the optimal effects obtained with the excimer-dye laser are related to the total light dose used and the dose rate, but not to the frequency of light exposure.     

Topical 5-aminolevulinic acid and photodynamic therapy in dermatology: a minireview.

Photodynamic therapy (PDT) is a treatment modality using a photosensitizer, light and oxygen to cause photochemically induced selective cell death. When exposed to light with the proper wavelength, the topically applied photosensitizer or photosensitizer precursor can activate a biomolecule through electron transfer to yield free radicals or produce singlet oxygen from energy transferred from the excited sensitizer to molecular oxygen. The tissue damage is the result of the activation of reactive singlet oxygen or free radical production. Photodynamic therapy with topical application of 5-aminolevulinic acid (ALA) is a new technique and although it remains largely experimental, it has potential application for treatment of malignant skin tumors, various precancerous and selected benign skin diseases. This technique yields not only a high percentage of good therapeutic results but also excellent cosmetic outcome. This paper reviews the recently published data on clinical ALA-based PDT in dermatology.     

New Proposal for the Treatment of Nodular Basal Cell Carcinoma with Intralesional 5-Aminolevulinic Acid

Abstract

Photodynamic therapy (PDT) is a treatment modality using a photosensitizer, light and oxygen to cause photochemically-induced selective cell death. Topical PDT is most suitable for thin lesions such as superficial basal cell carcinoma and actinic keratoses in dermatology. Results with PDT as treatment of thicker lesions such as nodular basal cell carcinoma appear to have a limited role because the photosensitizer or the light cannot penetrate deeply enough into the thicker tumor volume. In this preliminary study we use intralesional administration of 5-aminolevulinic acid to enhance the efficacy of the photosensitivity of nodular basal cell carcinomas, thus improving clinical cure.     

Long circulating half-life and high tumor selectivity of the photosensitizer meta-tetrahydroxyphenylchlorin conjugated to polyethylene glycol in nude mice grafted with a human colon carcinoma

In a model of nude mice bearing a human colon carcinoma xenograft, the biodistribution and tumor localization of meta-tetrahydroxyphenylchlorin (m-THPC) coupled to polyethylene glycol (PEG) were compared with those of the free form of this photosensitizer used in photodynamic therapy (PDT). At different times after i.v. injection of both forms of ¹²⁵I-labeled photosensitizer, m-THPC-PEG gave on average a 2-fold higher tumor uptake than free m-THPC. In addition, at early times after injection, m-THPC-PEG showed a 2-fold longer blood circulating half-life and a 4-fold lower liver uptake than free m-THPC. The tumor to normal tissue ratios of radioactivity concentrations were always higher for m-THPC-PEG than for free m-THPC at any time point studied from 2 to 96 hr post-injection. Significant coefficients of correlation between direct fluorescence measurements and radioactivity counting were obtained within each organ tested. Fluorescence microscopy studies showed that m-THPC-PEG was preferentially localized near the tumor vessels, whereas m-THPC was more diffusely distributed inside the tumor tissue. To verify whether m-THPC-PEG conjugate remained phototoxic in vivo, PDT experiments were performed 72 hr after injection and showed that m-THPC-PEG was as potent as free m-THPC in the induction of tumor regression provided that the irradiation dose for m-THPC-PEG conjugate was adapted to a well-tolerated 2-fold higher level. The overall results demonstrate first the possibility of improving the in vivo tumor localization of a hydrophobic dye used for PDT by coupling it to PEG and second that a photosensitizer conjugated to a macromolecule can remain phototoxic in vivo. Int. J. Cancer 76:842–850, 1998.© 1998 Wiley-Liss, Inc.     

Photoactivation of hypericin down-regulates glutathione S-transferase activity in nasopharyngeal cancer cells

Photodynamic therapy (PDT) is a new modality of treatment for cancer. Hypericin is a photosensitizer, which is known to generate reactive oxygen species upon activation with light. We observed that photoactivated hypericin induces the generation of reactive oxygen intermediates in nasopharyngeal cancer (NPC) cells in vitro. There was also significant reduction of Glutathione S-transferase (GST) activity in HK1 and CNE-2 NPC cells and in tumor tissues from the NPC/HK1 murine tumor model by hypericin-mediated PDT. As antioxidants protect cells against phototoxicity, down-regulation of GST activity would potentiate the efficacy of hypericin-PDT treatment.     

Benzochloroporphyrin Derivative Induced Cytotoxicity and Inhibition of Tumor Recurrence During Photodynamic Therapy for Osteosarcoma

Photodynamic therapy (PDT) is a promising cancer treatment modality that uses dye-sensitized photooxidationof biologic matter in target tissue. This study explored effects of the photosensitizer BCPD-17 during PDT forosteosarcoma. LM-8 osteosarcoma cells were treated with BCPD-17 and cell viability after laser irradiationwas assessed in vitro with the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. The effectsof BCPD-17 during PDT recurrence were then examined on tumor-bearing mice in vivo. BCPD-17 had dosedependentcytotoxic effects on LM-8 osteosarcoma cells after laser irradiation which also had energy-dependenteffects on the cells. The rate of local recurrence was reduced when marginal resection of mice tumors was followedby BCPD-17-mediated PDT. Our results indicated BCPD-17-mediated PDT in combination with marginalresection of tumors is a potentially new effective treatment for osteosarcoma.     

Photodynamic therapy for experimental tumors using ATX-S10(Na), a hydrophilic chlorin photosensitizer, and diode laser.

ATX-S10(Na), a hydrophilic chlorin photosensitizer having an absorption maximum at 670 nm, is a candidate second-generation photosensitizer for use in photodynamic therapy (PDT) for cancer treatment. The effectiveness of PDT using ATX-S10(Na) and a diode laser for experimental tumors was evaluated in vitro and in vivo. In-vitro PDT using ATX-S10(Na) and the diode laser showed drug concentration-, laser dose- and drug exposure time-dependent cytotoxicity to various human and mouse tumor cell lines. In Meth-A sarcoma-implanted mice, optimal PDT conditions were found where tumors were completely eliminated without any toxicity. Against human tumor xenografts in nude mice, the combined use of 5 mg / kg ATX-S10(Na) and 200 J / cm(2) laser irradiation 3 h after ATX-S10(Na) administration showed excellent anti-tumor activity, and its efficacy was almost the same as that of PDT using 20 mg / kg porfimer sodium and a 100 J / cm(2) excimer dye laser 48 h after porfimer sodium injection. Microscopic observation of tumor tissues revealed that PDT using ATX-S10(Na) and the diode laser induced congestion, thrombus and degeneration of endothelial cells in tumor vessels, indicating that a vascular shutdown effect plays an important role in the anti-tumor activity of PDT using ATX-S10(Na) and the diode laser.     

Photofrin-mediated photodynamic therapy induces vascular occlusion and apoptosis in a human sarcoma xenograft model.

Photodynamic therapy (PDT) involves light activation of a photosensitizer, resulting in oxygen-dependent, free radical-mediated cell death. Little is known about the efficacy of PDT in treating human sarcomas, despite an ongoing clinical trial treating i.p. sarcomatosis. The present study evaluates PDT treatment of a human sarcoma xenograft in nude mice and explores the mechanism of PDT-mediated antitumor effect. Athymic nude mice, 6-8 weeks of age, were s.c. injected with 5 x 10(6) cells of the A673 human sarcoma cell line. Tumors were allowed to grow to a diameter of about 10 mm. Photofrin (PF), 10 mg/kg, was injected by tail vein, and 24 h later, 630 nm light was delivered to the tumor with fluences of 50, 100, 150, or 300 J/cm2 at a fluence rate of 250 mW/cm2. To assess the efficacy of PDT in the treatment of sarcomas, photosensitizer uptake/retention studies and dose-response studies were performed. Studies carried out to determine the mechanism of tumor response included tumor temperature measurements before, during, and after treatment; tumor vascular perfusion studies with laser Doppler; electron microscopic analysis of tumor sections for vascular occlusion; and analysis of tumor cryosections for endothelial cell damage, apoptosis, and necrosis. At all time points of analysis, photosensitizer levels were greater in tumor than in muscle. Dose-response studies showed that at 100 J/cm2, five of six mice had a complete response to treatment, one of six had a partial response, and no deaths occurred. Temperature measurements indicated that thermal injury did not contribute to tumor response. Vascular perfusion studies demonstrated a significant reduction in blood flow as early as 6 h after PDT. Electron micrographs revealed erythrostasis in tumor microvessels starting as early as 2 h after treatment and complete occlusion of blood vessels by 12 h. Starting as early as 4 h after PDT, apoptosis first appeared in endothelial cells lining the occluded blood vessels and became more widespread at later time points. PDT is an effective treatment for this human sarcoma xenograft in nude mice. The mechanism of tumor destruction in this model appears to be vascular damage with initial apoptosis in tumor endothelial cells and delayed tumor cell apoptosis. This therapy may be valuable in the treatment of patients with sarcomatosis.     

Mechanisms for optimising photodynamic therapy: second-generation photosensitisers in combination with mitomycin C.

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.     

Whole bladder wall photodynamic therapy of transitional cell carcinoma rat bladder tumors using intravesically administered hypericin

Whole-bladder wall photodynamic therapy (PDT) is a promising treatment for carcinoma in situ (CIS) and diffuse premalignant changes of the bladder. After the results of our clinical studies showing that intravesical hypericin selectively accumulates in superficial bladder tumors, we investigated the hypericin-PDT efficacy in an AY-27 orthotopic transitional cell carcinoma rat bladder tumor model. After the instillation of hypericin (30 microM, 2 hr) in the bladder, tumors were irradiated (25-50 mW/cm 6-48 J/cm(2)) using 595 nm laser light. Data demonstrate that light doses of 12-48 J/cm(2) resulted in selective PDT-induced urothelial tumor damage without damaging detrusor musculature. Histological assessment of bladder sections 2 days after PDT showed tumor destruction, with tumor cells shrinking and detaching from the bladder wall. There were tumor regrowth 1-3 weeks after treatment. The in vivo/in vitro clonogenic assay results revealed up to 98% of tumor cell kill by hypericin PDT. In conclusion, hypericin PDT can be used to safely induce a selective urothelial tumor damage without damaging detrusor musculature, when optimum hypericin concentration and light fluences are used. A small percentage (2-5%) of tumor cells that survive the photodynamic treatment resulting in tumor regrowth after a prolonged period of time is likely due to oxygen depletion during light irradiation.     

Photodynamic therapy for breast cancer in a BALB/c mouse model

Objective

Photodynamic therapy (PDT) has been used for superficial neoplasms and its usage has been recently extended to deeper lesions. The purpose of this study was to observe whether or not PDT can cure breast cancer in the solid tumor model, and to define the critical point of laser amount for killing the cancer cells.

Methods

Twenty four BALB/c mouse models with subcutaneous EMT6 mammary carcinomas were prepared. Mice were divided into eight groups depending on the amount of illumination, and the tumor size was between 8 mm and 10 mm. We began by peritoneal infiltration with a photosensitizer 48 hours prior to applying the laser light, and then we applied a non-thermal laser light. The energy was from 350 J/cm² to 30 J/cm² to the cancer.

Results

Regardless of the tumor size from 8 mm to 10 mm, all mice apparently showed positive results via PDT. We also did not find any recurrence over 90 J/cm². In all models, the color of the breast cancer lesions began to vary to dark on 2 days post PDT and the tumor regression began simultaneously. Also, we confirmed the complete regression of the breast cancer 21 days after PDT.

Conclusion

We confirmed that PDT may treat breast cancers that are sized less 10 mm in mouse models. The moderate energy to destruct the breast cancer cells may be 90 J/cm². Therefore, we can expcect that PDT may be utilized to treat breast cancer, but we need more experience, skills and processing for clinical trials.     

Effect of photodynamic therapy in combination with ionizing radiation on human squamous cell carcinoma cell lines of the head and neck

Photodynamic therapy (PDT) is a promising treatment modality for head and neck, and other tumours, using drugs activated by light. A second generation drug, 5-aminolaevulinic acid (5-ALA), is a precursor of the active photosensitizer protoporphyrin IX (PpIX) and has fewer side-effects and much more transient phototoxicity than previous photosensitizers. We have investigated the effect of 5-ALA mediated PDT in combination with gamma-irradiation on the colony forming ability of several human head and neck tumour cell lines. The effect of treatments on the DNA cell cycle kinetics was also investigated. Our results indicate that the combination of 5-ALA mediated PDT and gamma-irradiation results in a level of cytotoxicity which is additive and not synergistic. 5-ALA mediated PDT had no discernible effect on DNA cell cycle distributions. gamma-irradiation-induced cell cycle arrest in G2 did not enhance the phototoxicity of 5-ALA.     

Topical 5-Aminolevulinic Acid and Photodynamic Therapy in Dermatology: a Minireview

Abstract

Photodynamic therapy (PDT) is a treatment modality using a photosensitiz-er, light and oxygen to cause photochemically induced selective cell death. When exposed to light with the proper wavelength, the topically applied photo-sensitizer or photosensitizer precursor can activate a biomolecule through electron transfer to yield free radicals or produce singlet oxygen from energy transferred from the excited sensitizer to molecular oxygen. The tissue damage is the result of the activation of reactive singlet oxygen or free radical production. Photodynamic therapy with topical application of 5-aminolevulinic acid (ALA) is a new technique and although it remains largely experimental, it has potential application for treatment of malignant skin tumors, various precancerous and selected benign skin diseases. This technique yields not only a high percentage of good therapeutic results but also excellent cosmetic outcome. This paper reviews the recently published data on clinical ALA-based PDT in dermatology.     

Preclinical evaluation of motexafin lutetium-mediated intraperitoneal photodynamic therapy in a canine model.

Intraperitoneal photodynamic therapy (IP PDT) is an experimental cancer treatment in clinical development for the treatment of peritoneal carcinomatosis and sarcomatosis. A canine study of motexafin lutetium (Lu-Tex)-mediated IP PDT was performed to evaluate normal tissue toxicities of this treatment in the presence and absence of a bowel resection and to assess the feasibility of measuring Lu-Tex fluorescence in abdominal tissues. Thirteen dogs were treated with Lu-Tex (0.2-2 mg/kg) i.v. 3 h before laparotomy and 730-nm light delivery (fluences, 0.5-2.0 J/cm2; average fluence rate <150 mW/cm2). Laparoscopy was performed 7-10 days after the procedure to assess acute toxicities. In situ fluorescence spectra were obtained from various abdominal tissues before and after light delivery using a fiber array probe with fixed-source detector distances. Lu-Tex-mediated IP PDT was well tolerated at the doses of drug and light studied. Bowel toxicity was not observed in animals treated with a bowel resection before PDT. Mild transient liver function test abnormalities without associated clinical sequelae were observed. No gross PDT-related abnormalities were observed at laparoscopy or necropsy; however, thickening in the glomerular capillary wall and the mesangium were noted microscopically in the kidneys of seven dogs. No renal function abnormalities were found. Analysis of the fluorescence spectra from intra-abdominal tissues suggests that measurements of Lu-Tex in situ are feasible and may provide a way of assessing photosensitizer concentration in vivo without the need for a biopsy. These results support the continued development of Lu-Tex as a candidate photosensitizer for IP PDT.     

Photodynamic destruction of high grade dysplasia and early carcinoma of the esophagus after the oral administration of 5-aminolevulinic acid

BACKGROUND: Photodynamic therapy (PDT) is a new local, endoscopically controlled therapeutic concept based on the selective sensitization of malignant and precancerous lesions prior to light-induced tissue destruction. 5-aminolevulinic acid (5-ALA) appears to be a promising alternative photosensitizer with a high mucosa specificity without phototoxic side effects on the skin. The authors report on their experiences with this new form of PDT in 27 patients. METHODS: Twenty-seven patients (6 females and 21 males; ages 47-79 years) with histologically proven high grade dysplasia (n = 9) and early carcinoma (normal endoultrasonography or classified as uT1N0M0; n = 19; 1 patient had 2 lesions) of the esophagus were included in this study. Approximately 4-6 hours after oral ingestion of 5-ALA in a dosage of 60 mg/kg of body weight, laser light irradiation was conducted with a dye laser system with a wavelength of 635 nanometers at a light dose of 150 J/cm(2). RESULTS: The length of the segment of the esophagus with severe dysplasia or carcinoma of the mucosa varied between 0.5-9.0 cm (mean length, 2.5 cm). High grade dysplasia was eradicated in all patients. In addition, 19 mucosal tumors in 18 patients were treated successfully in 10 of 19 cases with an average of 1.7 treatment sessions and a mean follow-up of 16.9 months (range, 3-37 months). Method-related morbidity and mortality were not observed. CONCLUSIONS: Severe dysplasia and superficial (相似文献   

Mechanistic investigation and implications of photodynamic therapy induction of vascular endothelial growth factor in prostate cancer

Photodynamic therapy (PDT) is now an approved therapeutic modality, and induction of vascular endothelial growth factor (VEGF) following subcurative PDT is of concern as VEGF may provide a survival stimulus to tumors. The processes that limit the efficacy of PDT warrant investigation so that mechanism-based interventions may be developed. This study investigates VEGF increase following subcurative PDT using the photosensitizer benzoporphyrin derivative (BPD) both in an in vitro and in an orthotopic model of prostate cancer using the human prostate cancer cell line LNCaP. The two subcurative doses used, 0.25 and 0.5 J/cm(2), mimicked subcurative PDT and elicited a 1.6- and 2.1-fold increase, respectively, in secreted VEGF 24 hours following PDT. Intracellular VEGF protein measurement and VEGF mRNA showed a 1.4- and 1.6-fold increase only at 0.5 J/cm(2). In vivo subcurative PDT showed an increase in VEGF by both immunohistochemistry and ELISA. In vitro analysis showed no activation of hypoxia-inducible factor-1alpha (HIF-1alpha) or cyclooxygenase-2 (COX-2) following subcurative PDT; furthermore, small interfering RNA inhibition of HIF-1alpha and COX-2 inhibitor treatment had no effect on PDT induction of VEGF. PDT in the presence of phosphatidylinositol 3-kinase/AKT inhibitor or mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase inhibitor still induced VEGF. However, subcurative PDT increased phosphorylated p38 and stress-activated protein kinase/c-Jun NH(2)-terminal kinase. The p38 MAPK inhibitor abolished PDT induction of VEGF. The results establish the importance of VEGF in subcurative BPD-PDT of prostate cancer and suggest possible molecular pathways for its induction. These findings should provide the basis for the development of molecular-based interventions for enhancing PDT and merit further studies.