High-field magnetic
resonance imaging of the response of human prostate
cancer to Pc 4-based photodynamic therapy in an
animal model
INTRODUCTION: High-field magnetic resonance imaging
(MRI) is an emerging technique that provides a
powerful, non-invasive tool for in vivo studies of
cancer therapy in animal models. Photodynamic
therapy (PDT) is a relatively new treatment modality
for prostate cancer, the second leading cause of
cancer mortality in American males. The goal of this
study was to evaluate the response of human prostate
tumor cells growing as xenografts in athymic nude
mice to Pc 4-sensitized PDT. MATERIALS AND METHODS:
PC-3, a cell line derived from a human prostate
malignant tumor, was injected intradermally on the
back flanks of athymic nude mice. Two tumors were
initiated on each mouse. One was treated and the
other served as the control. A second-generation
photosensitizing drug Pc 4 (0.6 mg/kg body weight)
was delivered to each animal by tail vein injection
48 hours before laser illumination (672 nm, 100 mW/cm(2),
150 J/cm(2)). A dedicated high-field (9.4 T)
small-animal MR scanner was used for image
acquisitions. A multi-slice multi-echo (MSME)
technique, permitting noninvasive in vivo assessment
of potential therapeutic effects, was used to
measure the T2 values and tumor volumes. Animals
were scanned immediately before and after PDT and 24
hours after PDT. T2 values were computed and
analyzed for the tumor regions. RESULTS: For the
treated tumors, the T2 values significantly
increased (P<0.002) 24 hours after PDT (68.2+/- 8.5
milliseconds), compared to the pre-PDT values
(55.8+/-6.6 milliseconds). For the control tumors,
there was no significant difference (P = 0.53)
between the pre-PDT (52.5+/-6.1 milliseconds) and
24-hour post-PDT (54.3+/-6.4 milliseconds) values.
Histologic analysis showed that PDT-treated tumors
demonstrated necrosis and inflammation that was not
seen in the control. DISCUSSION: Changes in tumor T2
values measured by multi-slice multi-echo MR imaging
provide an assay that could be useful for clinical
monitoring of photodynamic therapy of prostate
tumors. 2007 Wiley-Liss, Inc
PMID: 17960753
[PubMed - indexed for MEDLINE]