Photodynamic therapy for the treatment of periocular squamous cell carcinoma in horses: a pilot study

Abstract

Objective Local photodynamic therapy (PDT) is a novel cancer therapy in veterinary ophthalmology. A prospective pilot study seeking to demonstrate proof of principle and safety for the treatment of equine periocular squamous cell carcinoma (PSCC) was therefore conducted. We hypothesized that surgical excision with adjunctive local PDT is an effective and safe treatment for equine PSCC. Procedures Nine horses (10 eyes) with PSCC were treated with surgical resection, local infiltration of resulting wound beds with 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a (HPPH) and irradiation with 665-nm wavelength diode laser. Regular follow-up ophthalmic examinations were performed. Results Surgical resection and PDT yielded disease-free intervals of 25-68 months in our study horses as of January, 2008. These results were obtained following a single treatment in seven horses and two treatments in one horse. In one horse, carcinoma in situ developed 2.5 months after partial surgical excision and PDT, requiring local excision under standing sedation. Conclusions Preliminary results suggest that surgical resection and adjunctive local PDT is a safe and effective novel treatment for PSCC in horses. More research is needed before PDT for the treatment of equine PSCC can be adequately compared with other current modalities. Important to future investigations regarding PDT, tumor recurrence rate, length of hospitalization, number of treatment episodes required to effect tumor remission, and total treatment costs should be examined in a controlled manner. Our present results and experiences suggest that this treatment may be useful in the treatment of equine PSCC.

Mitomycin C, with or without surgery, for the treatment of ocular squamous cell carcinoma in horses

“…Draught horse breeds, horses with a light coat colour, and those with reduced or absent pigmentation in the conjunctiva and nictitans appear to be at greater risk of developing the disease (Schwink 1987, Dugan and others 1991a, Mosunic and others 2004, Gearhart and others 2007, Kafarnik and others 2009). Numerous treatment modalities have been described, including surgery, cryotherapy, radiotherapy, immunotherapy, photodynamic therapy, radiofrequency hyperthermia, laser ablation and chemotherapy (Rebhun 1990 , Wilkie and Burt 1990, Dugan and others 1991b, King and others 1991, McCalla and others 1992, Théon and Pascoe 1995, Chahory and others 2002, Mosunic and others 2004, Hewes and Sullins 2006, Giuliano and others 2008). The reported tumour recurrence rates vary from 11.9 to 66.7 per cent depending on the treatment modality (Schwink 1987, Dugan and others 1991b, King and others 1991, Mosunic and others 2004, Plummer and others 2007).…”

Pheophorbide a as a photosensitizer in photodynamic therapy: In vivo considerations

“…Notably, a derivative of pheophorbide a, 2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide-a (HPPH) or Photoclor, has been studied in animals for numerous PDT applications, including the treatment of equine periocular squamous cell carcinoma, 23 rodent colon carcinoma 24,25 and xenografts of human glioma; 26 furthermore, Photoclor is currently in clinical trials of PDT of lung and head and neck cancers. 27,28 The development of pheophorbide a as a photosensitizer for PDT applications in uterine, colon, hepatic and pancreatic cancers will be greatly benefited through continued in vivo investigation, including in the areas of drug pharmacokinetics, drug selectivity, light distribution and microenvironmental effects.…”

Photo activation of HPPH encapsulated in “Pocket” liposomes triggers multiple drug release and tumor cell killing in mouse breast cancer xenografts

“…Furthermore, HPPH has been shown to generate high yields of singlet oxygen. [33][34][35][36][37] We hypothesized that HPPH (shown in red color, Figure 1) would preferentially partition into the boundary regions ("Pockets") within the lipid bilayer containing DPPC (cyan) and pockets of DC 8,9 PC (brown, Figure 1). Photoactivation of HPPH (that modifies this molecule, indicated by orange) is hypothesized to cause destabilization of pockets (indicated by dark brown circles) resulting in defects in the liposome bilayer.…”