Intratumor photosensitizer injection for photodynamic therapy: Pre-clinical experience with methylene blue, Pc 4, and Photofrin

摘要

Intravenous administration of some photosensitizers, including the FDA-approved Photofrin, results in significant systemic photosensitivity and a 2-3-day drug-light interval. Direct intratumor injection of photosensitizer could potentially eliminate these negative aspects of photodynamic therapy (PDT), while requiring a lower photosensitizer dose to achieve comparable drug concentration in the target tissue. We performed PDT using intratumor injection of 3 photosensitizers, methylene blue (MB), Pc 4, and Photofrin, in mouse tumor models. After a 0-15 minute drug-light interval, illumination was delivered by appropriate diode lasers. For animals receiving MB or Pc 4, surface illumination was delivered using a microlens-terminated fiber. For animals receiving Photofrin, interstitial illumination was delivered by a 1 cm diffuser. In animals receiving MB or Pc 4, tumor dimensions were measured daily post-PDT, with a cure being defined as no palpable tumor 90 days post-treatment. For Photofrin, animals were sacrificed 24 hours post-PDT and tumors were excised, with samples H&E stained to assess PDT-induced necrosis. 55% of tumors were cured with MB-PDT, and significant tumor growth delay (p=0.002) was observed for Pc 4. For Photofrin PDT, the mean necrosis radius was 3.4±0.8 mm, compared to 2.9±1.3 mm for systemic administration, which was not a significant difference (p=0.58). Intratumoral injection of the photosensitizers methylene blue, Pc 4, and Photofrin is feasible, and results in appreciable tumor response. Further investigation is necessary to optimize treatment protocols and assess the systemic photosensitivity induced by intratumor injection.