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 HE 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.