We are developing in vivo small animal imaging techniques that can measure early effects of
photodynamic therapy (
PDT) for
prostate cancer.
PDT is an emerging therapeutic modality that continues to show promise in the treatment of
cancer. At our institution, a new second-generation photosensitizing
drug, the
silicon phthalocyanine Pc 4, has been developed and evaluated at the Case Comprehensive
Cancer Center. In this study, we are developing magnetic resonance imaging (MRI) techniques that provide
therapy monitoring and early assessment of
tumor response to
PDT. We generated human
prostate cancer xenografts in athymic nude mice. For the imaging experiments, we used a high-field 9.4-T small animal MR scanner (Bruker Biospec). High-resolution MR images were acquired from the treated and control
tumors pre- and post-
PDT and 24 hr after
PDT. We utilized multi-slice multi-echo (MSME) MR sequences. During imaging acquisitions, the animals were anesthetized with a continuous supply of 2%
isoflurane in
oxygen and were continuously monitored for respiration and temperature. After imaging experiments, we manually segmented the
tumors on each image slice for quantitative image analyses. We computed three-dimensional T2 maps for the
tumor regions from the MSME images. We plotted the histograms of the T2 maps for each
tumor pre- and post-
PDT and 24 hr after
PDT. After the imaging and
PDT experiments, we dissected the
tumor tissues and used the histologic slides to validate the MR images. In this study, six mice with human
prostate cancer tumors were imaged and treated at the Case Center for Imaging Research. The T2 values of treated
tumors increased by 24 ± 14% 24 hr after the
therapy. The control
tumors did not demonstrate significant changes of the T2 values.
Inflammation and
necrosis were observed within the treated
tumors 24 hour after the treatment. Preliminary results show that Pc 4-PDT is effective for the treatment of human
prostate cancer in mice. The small animal MR imaging provides a useful tool to evaluate early
tumor response to
photodynamic therapy in mice.