5-aminolevulinic acid photodynamic therapy for the treatment of high-grade gliomas.

INTRODUCTION: Photodynamic therapy (PDT) is a two-step treatment involving the administration of a photosensitive agent followed by its activation at a specific light wavelength for targeting of tumor cells. MATERIALS/METHODS: A comprehensive review of the literature was performed to analyze the indications for PDT, mechanisms of action, use of different photosensitizers, the immunomodulatory effects of PDT, and both preclinical and clinical studies for use in high-grade gliomas (HGGs). RESULTS: PDT has been approved by the United States Food and Drug Administration (FDA) for the treatment of premalignant and malignant diseases, such as actinic keratoses, Barrett's esophagus, esophageal cancers, and endobronchial non-small cell lung cancers, as well as for the treatment of choroidal neovascularization. In neuro-oncology, clinical trials are currently underway to demonstrate PDT efficacy against a number of malignancies that include HGGs and other brain tumors. Both photosensitizers and photosensitizing precursors have been used for PDT. 5-aminolevulinic acid (5-ALA), an intermediate in the heme synthesis pathway, is a photosensitizing precursor with FDA approval for PDT of actinic keratosis and as an intraoperative imaging agent for fluorescence-guided visualization of malignant tissue during glioma surgery. New trials are underway to utilize 5-ALA as a therapeutic agent for PDT of the intraoperative resection cavity and interstitial PDT for inoperable HGGs. CONCLUSION: PDT remains a promising therapeutic approach that requires further study in HGGs. Use of 5-ALA PDT permits selective tumor targeting due to the intracellular metabolism of 5-ALA. The immunomodulatory effects of PDT further strengthen its use for treatment of HGGs and requires a better understanding. The combination of PDT with adjuvant therapies for HGGs will need to be studied in randomized, controlled studies.

Preliminary results of interstitial motexafin lutetium-mediated PDT for prostate cancer.

BACKGROUND AND OBJECTIVES: Interstitial photodynamic therapy (PDT) is an emerging modality for the treatment of solid organ disease. Our group at the University of Pennsylvania has performed extensive studies that demonstrate the feasibility of interstitial PDT for prostate cancer. Our preclinical and clinical experience is herein detailed. STUDY DESIGN/MATERIALS AND METHODS: We have treated 16 canines in preclinical studies, and 16 human subjects in a Phase I study, using motexafin lutetium-mediated PDT for recurrent prostate adenocarcinoma. Dosimetry of light fluence, drug level and oxygen distribution for these patients were performed. RESULTS: We demonstrate the safe and comprehensive treatment of the prostate using PDT. However, there is significant variability in the dose distribution and the subsequent tissue necrosis throughout the prostate. CONCLUSIONS: PDT is an attractive option for the treatment of prostate adenocarcinoma. However, the observed variation in PDT dose distribution translates into uncertain therapeutic reproducibility. Our future focus will be on the development of an integrated system that is able to both detect and compensate for dose variations in real-time, in order to deliver a consistent overall PDT dose distribution.

Photodynamic therapy with motexafin lutetium for rectal cancer: a preclinical model in the dog.

PURPOSE: Local recurrence of rectal cancer remains a significant clinical problem despite multi-modality therapy. Photodynamic Therapy (PDT) is a cancer treatment which generates tumor kill through the production of singlet oxygen in cells containing a photosensitizing drug when exposed to laser light of a specific wavelength. PDT is a promising modality for prevention of local recurrence of rectal cancer for several reasons: tumor cells may selectively retain photosensitizer at higher levels than normal tissues, the pelvis after mesorectal excision is a fixed space amenable to intra-operative illumination, and PDT can generate toxicity in tissues up to 1 cm thick. This study evaluated the safety, tissue penetration of 730 nm light, normal tissue toxicity and surgical outcome in a dog model of rectal resection after motexafin lutetium-mediated photodynamic therapy. METHODS: Ten mixed breed dogs were used. Eight dogs underwent proctectomy and low rectal end to end stapled anastomosis. Six dogs received the photosensitizing agent motexafin lutetium (MLu, Pharmacyclics, Inc., Sunnyvale, CA) of 2 mg/kg preoperatively and underwent subsequent pelvic illumination of the transected distal rectum of 730 nm light with light doses ranging from 0.5 J/cm(2) to 10 J/cm(2) three hours after drug delivery. Two dogs received light, but no drug, and underwent proctectomy and low-rectal stapled anastomosis. Two dogs underwent midline laparotomy and pelvic illumination. Light penetration in tissues was determined for small bowel, rectum, pelvic sidewall, and skin. Clinical outcomes were recorded. Animals were sacrificed at 14 days and histological evaluation was performed. RESULTS: All dogs recovered uneventfully. No dog suffered an anastomotic leak. Severe tissue toxicity was not seen. Histological findings at necropsy revealed mild enteritis in all dogs. The excitation light penetration depths were 0.46 +/- 0.18, 0.46 +/- 0.15, and 0.69 +/- 0.39 cm, respectively, for rectum, small bowel, and peritoneum in dogs that had received MLu. For control dogs without photosensitizer MLu, the optical penetration depths were longer: 0.92 +/- 0.63, 0.67 +/- 0.10, and 1.1 +/- 0.80 cm for rectum, small bowel, and peritoneum, respectively. CONCLUSION: Low rectal stapled anastomosis is safe when performed with MLu-mediated pelvic PDT in a dog model. Significant tissue penetration of 730 nm light into the rectum and pelvic sidewall was revealed without generation of significant toxicity or histological sequelae. Penetration depths of 730 nm light in pelvic tissue suggest that microscopic residual disease of less than 5 mm are likely to be treated adequately with MLu-mediated PDT. This approach merits further investigation as an adjuvant to total mesorectal excision and chemoradiation for rectal cancer.

Effects of hyperglycemia on oxygenation, radiosensitivity and bioenergetic status of subcutaneous RIF-1 tumors.

Since tissue oxygen tension is a balance between delivery and consumption of oxygen, considerable effort has been directed at increasing the former and/or decreasing the latter. Techniques to decrease the rate of cellular oxygen consumption (increasing the distance oxygen can diffuse into tissues) include increasing glycolysis by administering supra-physiologic levels of glucose. We have examined the effect of hyperglycemia produced by intravenous glucose infusion on the tissue oxygenation and radiation response of subcutaneously implanted murine radiation induced fibrosarcomas (RIF-1). A 0.3 M glucose solution was delivered via tail vein injection according to a protocol that maintained glucose at a plasma concentration of 17+/-1 mM. The effect of this treatment on radiation response (clonogenic and growth delay studies), tumor oxygenation (needle electrode pO2 and 2-[2-nitro-1H-imidazol-1-yl]-N-(2,2,3,3,3-pentafluoropropyl) acetamide (EF5) binding), and tumor bioenergetics and pH (31P NMR spectroscopy) was examined. Systemic measurements included hematocrit and blood glucose and lactate concentrations. The results of these studies suggest that these subcutaneously implanted RIF-1 tumors are both radiobiologically and metabolically hypoxic and that intravenous glucose infusion is not an effective method of modifying this metabolic state.

Vascularity and uptake of photosensitizer in small human tumor nodules: implications for intraperitoneal photodynamic therapy.

PURPOSE: i.p. spread of cancers is a common clinical problem, with limited treatment options leading to morbidity and death. i.p. photodynamic therapy (IP-PDT) combines maximal surgical debulking of gross tumor with intraoperative light delivery to the peritoneum after preoperative i.v. injection of photosensitizer to treat residual disease. An issue of concern in IP-PDT is the potential lack of photosensitizer uptake by residual small tumor nodules (STNs) < or =5 mm in maximum diameter and by microscopic residual disease caused by incomplete development of a vascular supply. This study examined the existence of vasculature and Photofrin (PF) uptake in STNs in 12 patients in a Phase II clinical trial for IP-PDT. EXPERIMENTAL DESIGN: Patients received PF 2.5 mg/kg i.v. 48 h before surgery. STNs obtained during surgery were cryosectioned, immunostained for platelet/endothelial cell adhesion molecule 1, and analyzed by light microscopy. Mean vascular densities in STNs were determined by counting microvessels within a x200 field (0.28 mm(2) area). Sections were also examined for PF uptake by fluorescence image analysis using an epifluorescence microscope and IPLab Spectrum software. RESULTS: Data obtained showed that tumors as small as 1 mm in diameter stained positive for platelet/endothelial cell adhesion molecule 1 and contained PF. A negative control from a patient not given PF showed no detectable fluorescence. The average of all mean vascular densities in STNs was determined to be 100 +/- 29. CONCLUSIONS: We conclude that STNs, as small as 1 mm in diameter, have a functional vasculature, because these tumors show PF uptake after i.v. delivery. Both properties are crucial for the treatment of residual STNs by IP-PDT after surgical debulking.

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.

Depletion of tumor oxygenation during photodynamic therapy: detection by the hypoxia marker EF3 [2-(2-nitroimidazol-1[H]-yl)-N-(3,3,3-trifluoropropyl)acetamide ].

Photodynamic therapy (PDT) of tumors can create hypoxia when oxygen is depleted by photochemical consumption or the oxygen supply is compromised by microvascular damage. However, oxygen is a requirement for PDT, and hypoxia during illumination can lead to poorer tumor response. As such, sensitive methods of quantifying tumor oxygen and evaluating its distribution may help in the development and optimization of treatment protocols. In this study, the hypoxia marker EF3 [2-(2-nitroimidazol-1[H]-yl)-N-(3,3,3-trifluoropropyl)acetam ide] was used to evaluate the oxygenation of PDT-treated radiation-induced fibrosarcoma tumors. Tumor-bearing mice were administered Photofrin (5 mg/kg) 24 h before PDT illumination at 75 mW/cm2, 135 J/cm2 (30 min). EF3 (52 mg/kg) was injected either within 3 min before PDT illumination, with tumor excision at the conclusion of illumination, or within 3 min after illumination, with tumor excision 30 min later. Control animals received EF3 alone, EF3 plus Photofrin, or EF3 plus illumination. After tumor disaggregation, staining with a fluorochrome-conjugated monoclonal antibody, and flow cytometric analysis, control tumors demonstrated an averaged median fluorescence intensity (+/- SE) of 17.1 +/- 2.8. EF3 binding significantly (P = 0.007) increased during PDT to a median fluorescence intensity of 48.9 +/- 8.3. In the 30 min after PDT, EF3 binding returned to control levels (median, 18.3 +/- 3.3). To evaluate the oxygen concentrations corresponding to these fluorescence intensities, an in vitro standard curve was created based on the in vivo exposure conditions. From this curve, the oxygen tensions of tumors exposed to EF3 under control conditions, during PDT, or after PDT were calculated to be 3.1-5.3, 1.2-2.4, and 3.0-5.2 mm Hg, respectively. Detection of EF3 binding using a monoclonal antibody correlated well with direct detection of binding using a radioactive assay. EF3 binding was linear with drug incubation for times from 1.5 to 60 min. Overall, this work demonstrates that hypoxia during PDT illumination of radiation-induced fibrosarcoma tumors can be detected by the hypoxia marker EF3. Hypoxia during illumination can be labeled separately from that found before or after PDT. Tissue oxygen tensions corresponding to EF3 binding levels can be calculated.

Photofrin photodynamic therapy can significantly deplete or preserve oxygenation in human basal cell carcinomas during treatment, depending on fluence rate.

At high fluence rates in animal models, photodynamic therapy (PDT) can photochemically deplete ambient tumor oxygen through the generation of singlet oxygen, causing acute hypoxia and limiting treatment effectiveness. We report that standard clinical treatment conditions (1 mg/kg Photofrin, light at 630 nm and 150 mW/cm2), which are highly effective for treating human basal cell carcinomas, significantly diminished tumor oxygen levels during initial light delivery in a majority of carcinomas. Oxygen depletion could be found during at least 40% of the total light dose, but tumors appeared well oxygenated toward the end of treatment. In contrast, initial light delivery at a lower fluence rate of 30 mW/cm2 increased tumor oxygenation in a majority of carcinomas. Laser treatment caused an intensity- and treatment time-dependent increase in tumor temperature. The data suggest that high fluence rate treatment, although effective, may be inefficient.

Potentiation of photodynamic therapy antitumor activity in mice by nitric oxide synthase inhibition is fluence rate dependent.

The effects of systemic administration of the nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine (L-NNA) in combination with photodynamic therapy (PDT) on tumor response, tumor oxygenation and tumor and normal skin perfusion were studied in C3H mice bearing subcutaneous radiation-induced fibrosarcoma tumors. Photodynamic therapy was carried out using the photosensitizer Photofrin (5 mg/kg) in conjunction with a low fluence rate (30 mW/cm2) and a high fluence rate (150 mW/cm2) protocol at a total fluence of 100 J/cm2. Low fluence rate PDT produced approximately 15% tumor cures, a response not significantly altered by administration of 20 mg/kg L-NNA either 5 min before or after PDT. In contrast, high fluence rate PDT produced no tumor cures by itself, but addition of L-NNA either pre- or post-PDT resulted in approximately 30% and approximately 10% tumor cures, respectively. The L-NNA by itself tended to decrease tumor pO2 levels and perfusion, but statistically significant differences were reached only at one time point (1 h) with one of the oxygenation parameters measured (% values < 2 mm Hg). Photodynamic therapy by itself decreased tumor oxygenation and perfusion more significantly. Addition of L-NNA before PDT further potentiated this effect. The L-NNA exerted its most striking effects on the PDT response of the normal skin microvasculature. Low fluence rate PDT caused severe and lasting shut-down of skin microvascular perfusion. With high fluence rate PDT, skin perfusion was initially decreased but recovered to persistent normal levels within 1 h of treatment. Administration of L-NNA reversed this response, converting it to complete and lasting vascular shut-down identical to that achieved with low fluence rate PDT. This effect was somewhat L-NNA dose dependent but was still marked at a dose of 1 mg/kg. It occurred whether L-NNA was given before or after PDT. The L-NNA did not alter the long-term vascular response of skin to low fluence rate PDT. The ability of L-NNA to correspondingly improve tumor response and severely limit skin vascular perfusion following high fluence rate PDT, while providing no benefit for the low fluence rate protocol, suggests that vascular changes in the tumor surrounding normal tissue contribute to the enhanced tumor curability with adjuvant L-NNA treatment.