Objectives: To examine therapeutic effects of 5-aminolevulinate (ALA)-mediated photodynamic
therapy (PDT) on UVB-induced cutaneous squamous cell carcinomas (SCCs) in a mouse model.
Materials and methods: Cutaneous SCCs were established by UVB (280-320 nm) irradiation of
hairless mice. In situ fluorescence measurement was used to monitor PpIX formation after the
topical application of various concentrations of ALA cream to determine the optimal ALA dose.
Therapeutic responses of SCCs to multiple sessions of ALA PDT were examined histologically
and quantitatively. TUNEL staining was used to examine apoptosis caused by PDT. Results: After
repeated exposure for 18 to 22 weeks (4-5 days/week), multiple nodular and verrucous hyperplasia
lesions of various sizes developed at the exposed area. After four sessions of ALA PDT (8% ALA,
3 h incubation, 30 J/cm2 at 20 mW/cm2) a total of 84% of complete response was achieved for
small SCCs (1-4 mm, thickness <2.5 mm). TUNEL staining showed that PDT-induced apoptotic
cells were distributed evenly from the basal to stratum corneum layers. Conclusions: Topical ALA
PDT can trigger apoptosis in SCCs, inhibit SCC growth, and reduce the size and number of tumors
in the hairless mouse model. The true clinical value of ALA PDT for the treatment of cutaneous
SCC deserves further investigation.
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