Influence of light delivery on photodynamic synovectomy in an antigen-induced arthritis model for rheumatoid arthritis.

BACKGROUND AND OBJECTIVE: Minimally invasive synovectomy techniques have been unsuccessful due to lack of selectivity. The purpose of this study was to evaluate the potential of photodynamic therapy to destroy diseased synovium in an antigen-induced arthritis model. STUDY DESIGN/MATERIALS AND METHODS: Three sets of experiments evaluated the biodistribution and treatment effects of Photofrin (PF) in rabbits with bilateral knee antigen-induced arthritis. The first set of experiments evaluated the biodistribution of PF in articular tissues of 30 rabbits from 6-72 hours after systemic injection of 2 mg/kg. In the second series of experiments, light was delivered to the knee joint via cleaved optical fibers, whereas for the third, light was delivered via a 600 microm diffusion tip fiber. Tissues were harvested at 2 and 4 weeks posttreatment. RESULTS: The biodistribution experiments demonstrated maximal uptake in inflamed synovium at 48 hours and a lack of uptake in normal tissues. With bare cleaved fibers, necrosis was observed in one specimen at 2 weeks and was absent in all specimens at 4 weeks. In the third experiment, synovial necrosis was observed in 3 of 7 specimens at 2 weeks and 3 of 8 at 4 weeks. No damage to articular cartilage or periarticular tissues was seen with either mode of light delivery. CONCLUSION: These studies indicate that selective destruction of synovium can be achieved with PF and suggest that optimization of light delivery techniques will play an important role in development of this new technique.

Photodynamic therapy of facial squamous cell carcinoma in cats using a new photosensitizer.

BACKGROUND AND OBJECTIVE: Photodynamic therapy has been shown to be an effective treatment modality for surface-oriented neoplasms of the skin, respiratory, gastrointestinal, and urogenital systems. The purpose of this study was to assess the safety and efficacy of photodynamic therapy using a new photosensitizer in the treatment of squamous cell carcinomas of the feline facial skin. STUDY DESIGN/MATERIALS AND METHODS: Cats with naturally occurring squamous cell carcinomas of the facial skin were entered into the study. Tumors were staged using a modification of the World Health Organization (WHO) system for classification of feline tumors of epidermal origin. Photodynamic therapy was delivered to the tumors using an argon-pumped dye laser 24 hours after the administration of the photosensitizer pyropheophorbide-alpha-hexyl-ether (HPPH-23). Following treatment, tumors were evaluated for complete response rates and local control durations. RESULTS: Fifteen tumors were staged T1a (< 1.5 cm diameter, noninvasive), 18 T1b (< 1.5 cm, invasive), and 28 T2B (> 1.5 cm, invasive). Complete response rates as well as local control durations were significantly (P < 0.05) related to stage. Complete response was achieved in 100% of T1a tumors, 56% of T1b tumors, and 18% of T2b tumors. One-year local control rates were 100% for T1a tumors and 53% for T1b tumors; overall 1-year local control rate for all treated tumors was 62%. Clinical, hematological, and biochemical evidence of toxicity was not seen in any cat following drug administration. However, morbidity was observed following treatment of large, invasive tumors of the nasal plane. CONCLUSION: Photodynamic therapy with the photosensitizer HPPH-23 was safe and effective in treating early stage squamous cell carcinomas of the feline nasal plane and facial skin. However, toxicity was encountered following treatment of large neoplasms.

In vitro photodynamic effects of lysyl chlorin p6: cell survival, localization and ultrastructural changes.

The in vitro cell survival, localization and ultrastructural changes following irradiation were examined in 9L glioma cells sensitized with a new photosensitizer, lysyl chlorin p6 (LCP). In clonogenic assays, LCP was 10-100-fold more phototoxic than photofrin II on a microgram/mL basis. Lysyl chlorin p6 uptake was blocked when cells were incubated at 2 degrees C. In view of the chemical properties of LCP, this finding indicates that uptake probably occurred through the endocytic pathway. Fluorescence studies showed LCP localized in a region of the endocytic compartment similar in size, shape and distribution to that labeled by lucifer yellow CH (LY), as well as localizing diffusely throughout the perinuclear cytoplasm. Cells stained with both LY and LCP, however, had distinctly separate regions of staining. Lysyl chlorin p6 localization differed from that of fluorescent probes labeling the mitochondria, Golgi apparatus and endoplasmic reticulum. Ultrastructural changes at both 2 and 30 min after laser irradiation were similar. Mitochondria were often condensed or swollen and also had constrictions and cytoplasmic invaginations. The Golgi apparatus, perinuclear space and rough endoplasmic reticulum (RER) were dilated. These data demonstrate that LCP localizes in a portion of the endosomal compartment, but that morphologic damage initially occurs in the mitochondria, Golgi apparatus and RER.

Normal brain tissue response to photodynamic therapy using aluminum phthalocyanine tetrasulfonate in the rat.

The effects of photodynamic therapy (PDT) on normal brain tissue and depth of brain necrosis were evaluated in rats receiving 2.5 mg/kg aluminum phthalocyanine tetrasulfonate. Twenty-four hours later brains were irradiated with 675 nm light at a power density of 50 mW/cm2 and energy doses ranging from 1.6 to 121.5 J/cm2. Brains were removed 24 h after PDT and evaluated microscopically. When present, brain lesions consisted of well-demarcated areas of coagulation necrosis. When plotting the depth of necrosis against the natural log of energy dose, the data fit a piecewise linear model, with a changepoint at 54.6 J/cm2 and an x intercept of 7.85 J/cm2. The slopes before and after the changepoint were 2.04 and 0.21 mm/ln J cm-2, respectively. The x intercept suggests a minimum light dose below which necrosis of normal brain will not occur, whereas the changepoint indicates the energy density corresponding to an approximate maximum depth of necrosis.

Effectiveness of a lysyl chlorin p6/chlorin p6 mixture in photodynamic therapy of the subcutaneous 9L glioma in the rat.

A new photosensitizer, LCP, a combination of lysyl chlorin p6 and chlorin p6, was synthesized and tested for effectiveness in photodynamic therapy using s.c. implanted 9L glioma tumors in rats. Tumors were irradiated with 664-nm light 4 h after LCP injection. Mean intratumoral temperature elevations were less than 4 degrees C using a power density of 50 mW/cm2 for 33.3 min (100 J/cm2). Subsequent experiments examining histological changes and tumor regrowth used a power density of 50 mW/cm2 and total energy densities of 25, 50, and 100 J/cm2. Microscopically, an energy density-dependent coagulation necrosis of tumor cells occurred in treated tumors. Long term inhibition of tumor growth was achieved only at an energy density of 100 J/cm2. Side effects of treatment were seen only in the irradiated area and consisted of coagulation necrosis of normal tissues in rats treated at 50 and 100 J/cm2, including severe skin necrosis. Exposure of rats to fluorescent room light did not cause any macroscopically detectable skin damage. Our data indicate that photodynamic destruction of s.c. 9L glioma tumors using LCP as a photosensitizer results in significant tumor growth inhibition and that further study of LCP is warranted.