Comparing desferrioxamine and light fractionation enhancement of ALA-PpIX photodynamic therapy in skin cancer

Abstract

Background: Aminolevulinic acid (ALA)-based photodynamic therapy (PDT) provides selective uptake and conversion of ALA into protoporphyrin IX (PpIX) in actinic keratosis and squamous cell carcinoma, yet large response variations in effect are common between individuals. The aim of this study was to compare pre-treatment strategies that increase the therapeutic effect, including fractionated light delivery during PDT (fPDT) and use of iron chelator desferrioxamine (DFO), separately and combined.

Methods: Optical measurements of fluorescence were used to quantify PpIX produced, and the total amount of PpIX photobleached as an implicit measure of the photodynamic dose. In addition, measurements of white light reflectance were used to quantify changes in vascular physiology throughout the PDT treatment.

Results: fPDT produced both a replenishment of PpIX and vascular re-oxygenation during a 2 h dark interval between the first and second PDT light fractions. The absolute photodynamic dose was increased 57% by fPDT, DFO and their combination, as compared with PDT group (from 0.7 to 1.1). Despite that light fractionation increased oedema and scab formation during the week after treatment, no significant difference in long-term survival has been observed between treatment groups. However, outcomes stratified on the basis of measured photodynamic dose showed a significant difference in long-term survival.

Conclusions: The assessment of implicit photodynamic dose was a more significant predictor of efficacy for ALA-PDT skin cancer treatments than prescription of an enhanced treatment strategy, likely because of high individual variation in response between subjects.

Figure 1

PpIX production for five different cell lines after incubation with ALA. Fluorescence was normalised by auto-fluorescence obtained from the cells incubated with medium (blank).

Figure 2

PpIX fluorescence measured in response to blue excitation light, and BVF and oxygen saturation determined by white light spectroscopy of skin tumours (intradermal implantation of SCC25 cells). Full-PDT meant that the animals received just one scheme illumination 3 h after ALA application (total fluence of 50 J cm⁻² and fluence rate of 50 mW cm⁻²; n=10). *Student's t-test, P-value≤0.0018. **Kruskal–Wallis test, P-value≤0.00021. The results in the table are presented as mean±s.d.

Figure 3

Treatment outcome measures. (A) A box and whisker plot of the volume measured on the first week after treatment (oedema+tumour) of skin cancer; (B) number of animals in each group that presented scab after 6 days of light treatment; (C) illustrative representation to show oedema after 1 day of treatment (left) and scab after 6 days of treatment (right). PDT groups received one scheme illumination 3 h after ALA application (total fluence of 50 J cm⁻²). fPDT groups received twofold illumination (total fluence of 10 and 40 J cm⁻², 3 and 5 h after ALA application, respectively). *P-value<0.05 (Kruskal–Wallis test). The samples were compared in terms of light fractionation effect (PDT/fPDT), iron chelation effect (PDT/DFO+PDT and fPDT/DFO+fPDT) or combination effect (DFO+PDT/DFO+fPDT).

Figure 4

Kaplan–Meier curves for survival response of skin tumour-bearing mice (SCC25 cells intradermal implantation). (A) Effect of treatment received (n=10 animals per each group; P-value=0.43, log-rank test); (B) Effect of absolute dose received (n=20 animals per each group; P-value=0.045, log-rank test).