These observations suggest that both wavelength and cell type influence the cell proliferation response to low-intensity laser irradiation.

As a prelude to photodynamic therapy, 5-aminolevulinic acid (ALA) was given orally to healthy dogs. ALA-induced protoporphyrin IX (PpIX) fluorescence significantly increased in the mucosa of the urinary bladder in an ALA dose-dependent fashion. Vomiting occurred after ALA administration in 70% of the dogs but did not affect PpIX fluorescence. ALA-based photodynamic therapy (PDT) of the urinary bladder in healthy dogs caused only submucosal oedema within the bladder wall. No haematologic or serum biochemistry abnormalities were observed after ALA administration. Microscopic haematuria was observed in all the dogs after PDT but was mild and self limiting. ALA-based PDT was administered to six dogs with transitional cell carcinoma (TCC) of the lower urinary tract. ALA-based PDT resulted in tumour progression-free intervals from 4 to 34 weeks in five dogs; one dog with pre-existing hydronephrosis died shortly after PDT. Dogs with TCC represent an outbred, spontaneous, tumour model for developing PDT protocols for humans with bladder cancer.

Three dogs and 1 cat with intranasal tumors were treated with pyropheophorbide-a-hexyl ether-based photodynamic therapy (PDT). PDT was well tolerated by all the animals, and no adverse effects from photosensitizer injection, such as cutaneous photosensitization, were observed. Facial swelling was observed in all animals after each PDT treatment but resolved spontaneously within 72 hours after treatment. All animals had a decrease in severity of epistaxis, frequency of sneezing, and amount of nasal discharge after PDT. Clinical signs were controlled for variable time, although long-term responses were comparable with radiation therapy in 2 animals. This small case series demonstrates another application for PDT in veterinary medicine. On the basis of these findings. further studies are warranted to define the role of PDT in the management of intranasal tumors in dogs and cats.

Cultured 9L cells were incubated with varying concentrations of pheophorbide-a-hexyl ether (HPPH) and then exposed to 665-nm red light from a non-coherent light source or a dye laser. Cell death was produced by both light sources, with the non-coherent light being most effective at the highest HPPH concentrations. To assess the feasibility of using the non-coherent light source for clinical photodynamic therapy (PDT), four dogs and three cats presenting with spontaneous superficial tumours were injected intravenously with 0.15 mg kg(-1) of HPPH, 1 h before their tumours were irradiated with 665-nm non-coherent light (50 mW cm(-2), 100 J cm(-2)). Of the nine tumours treated, there were eight complete responses, all occurring in animals with squamous cell carcinoma. After 68 weeks of follow-up, the median initial disease-free interval had not been reached. These data suggest that non-coherent light sources may be efficacious for photodynamic therapy of spontaneous superficial tumours in animals, representing a cost-effective alternative to medical lasers in both veterinary and human oncology.

ALA is an effective photosensitizer for in vitro photodynamic treatment of K9TCC cells. Further studies are warranted to assess the safety and efficacy of ALA as a photosensitizer for use in treating dogs with TCC. Impact for Human Medicine-On the basis of this study, dogs with TCC may be useful in the development of protocols for ALA-based photodynamic therapy of humans affected with muscle-invasive bladder cancer.