Performance of photodynamic therapy using multiple light sources in the rat R1 rhabdomyosarcoma tumor model

Abstract

3192 Background: Introducing photodynamic therapy (PDT) into routine clinical use will require a radical change in excitation source, and a better understanding of photosensitizer dosimetry and biological effect. Light Sciences Corporation (LSC) has designed a Light Infusion Therapy system (Litx), based on inexpensive light-emitting diode technology and the photosensitizer talaprofin sodium (LS11). One of the advantages to interstitial PDT with the system is the potential to treat patients with large tumors by simultaneous illumination using multiple light sources. Methods: WAG/Rij rat rhabdomyosarcomas were employed to assess the feasibility and safety of multiple light source (LS) treatments. Previous to the multiple LS studies, a series of single LS light dose escalation studies (5 to 40 mW/cm, 50 to 1000 J/cm) were performed using the same model. In the multiple LS studies, each tumor-bearing rat was given 5.0 mg/kg (iv) talaporfin sodium 90 minutes prior to illumination. Tumors were grown to a size sufficient for implantation of two or three 10 mm long LS. Treatments were performed at 40 mW/cm with two LS at a fluence of 400 J/cm, or three LS at 200 J/cm. The implantation geometry was chosen such that the effect zones would either overlap or abut each other, based on the tissue response from a single LS run at the same illumination parameters. The PDT effect was assessed 72 hours post-treatment, by Evans blue and TTC vital staining. Results: With a single LS in this WAG/Rij rat rhabdomyosarcoma model, the radius of Litx PDT effect zone is fluence-dependant; however, the effect zone length is related only to LS length. The kill zone radius from each LS in the two- and three- LS illuminations was equal to the radius from a single LS under the same treatment parameters. The effect zone lengths were also found to be the same as in the single LS illuminations. Conclusions: The feasibility and safety of simultaneous multiple LS illumination with the Litx system expands the treatable range to include larger tumors. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Light Sciences Corp. Light Sciences Corp. Light Sciences Corp.