Photodynamic Therapy of Colorectal Cancer Using a New Light Source From In Vitro Studies to a Patient Treatment Hanoch Kashtan, M.D.,* Riad Haddad, M.D.,* Yoseph Yossiphov, M.D.,t Shoshana Bar-On, B.Sc.,t Yehuda Skornick, M.D.* From the *Department of Surgery and tlnstitute of Pathology, Tel-Aviv Medical Center, and the Sackler School of Medicine, Tel-Aviv, Israel PURPOSE: Photodynamic therapy (PDT) is a relatively new alternative modality for palliation of rectal cancer. Current source of light for PDT are laser systems that are expensive and not necessarily needed for PDT. We evaluated a new nonlaser light source for PDT, Versa-Light| METHODS AND RESULTS: In vitro PDT--CT26 murine colon carci- noma cells were incubated with aluminum phthalocyanine (AIPcS4) for 48 hours and subjected to photoradiation using Versa-Light| and viability was assessed. There was a signif- icant decrease in viability of treated cells compared with controls. In vivo PDT--BALB/c mice were injected either subcutaneously or intrarectally with CT26 cancer cells. IP AlPcS 4 (2.5 n'lg/kg) was injected when tumors were visible. After 24 hours, mice were subjected to photoradiation. Massive tumor necrosis in response to PDT was observed. PDT also prolonged survival of treated mice. Patient treat- ment--A 70-year-old woman with recurrent local rectal carcinoma received intravenous Photofrin II | (2 mg/kg). After 48 and 96 hours, she was subjected to direct photo- radiation. After the first light session, there was complete macroscopic disappearance of the tumor. Biopsies up to 10 weeks after the treatment showed no cancer cells in the treated area. Sixteen weeks later, a randomized biopsy from previous tumor site showed carcinoma cells. CONCLU- SIONS: We believe that Versa-Light| is a good light source for PDT. It was effective in both in vitro and animal studies. It can also be safely used for clinical PDT. [Key words: Photodynamic therapy (PDT); Colon cancer; In vitro stud- ies; In vivo studies; Light source] Kashtan H, Haddad R, Yossiphov Y, Bar-On S, Skornick Y. Photodynamic therapy of colorectal cancer using a new light source: from in vitro studies to a patient treatment. Dis Colon Rectum 1996;39:379-383. C olorectal cancer is one of the most common internal malignancies of Western society. Esti- mated number of new cases in the United States for 1995 is 138,200, and estimated number of deaths is 55,300.1 In Israel, it is the most common internal malignancy, with almost 2,000 new cases per year. 2 Rectal cancer exhibits some difficult therapeutic Supported by the Roni Udassin Memorial Fund of the Israel Cancer Society. Address reprint requests to Dr. Kashtan: Department of Surgery A, Ichilov Hospital, 6 Weizman Street, Tel-Aviv 64239, Israel. 379 problems. Primary treatment is surgical excision. Ad- juvant modalities have been studied extensively in recent years because the natural history of disease dictates a high incidence of recurrent disease. 3 Local recurrence in rectal cancer is frequently a most dev- astating problem in terms of symptoms that are most difficult to treat. These symptoms of pain, obstruction, and bleeding related to local recurrence have stimu- lated many investigators to examine novel methods of palliation, particularly in surgery and radiation-failed patients. Photodynamic therapy (PDT) refers to the use of photosensitizing drugs in conjunction with light to treat tumors. Current source of light for PDT are laser systems. In 1972, Dougherty and his associates 4 be- gan working with PDT using laser as the source of light. They used an argon dye laser containing rho- damine B dye, which was thought to afford only fair absorption but excellent tissue penetration. Since then, several laser systems have been used with sim- ilar results. These include argon ion dye lasers, gold vapor lasers, and copper vapor dye lasers. 5 Light source should meet several requirements to be used in photodynamic therapy. Wavelength must match the absorption feature of the photosensitizer. It must have sufficient beam quality and enough power to deliver the necessary power to the tissues. Finally, the system should be practical, efficient, and at cost- effective. We used Versa-Light | (Medic Lightech Ltd., Tech- nion City, Haifa, Israel) as a new light source, which was developed in accordance with the specific de- mands for photodynamic therapy. Versa-Light | gen- erates the wavelength and energy level that are re- quired for photodynamic therapy. 6 Here, we present initial in vitro and in vivo mice studies using this light source and the first treatment of a patient with recur- rent rectal cancer.