Improvement of systemic 5-aminolevulinic acid-based photodynamic therapy in vivo using light fractionation with a 75-minute interval.
We have studied different single and fractionated illumination schemes after systemic administration of 5-aminolevulinic acid (ALA) to Improve the response of nodular tumors to ALA-mediated photodynamic therapy. Tumors transplanted on the thigh of female WAG/Rij rats were transdermally illuminated with red light (633 nm) after systemic ALA administration (200 mg/kg). The effectiveness of each treatment scheme was determined from the tumor volume doubling time. A single illumination (100 J/cm2 at 100 mW/cm2, 2.5 h after ALA administration) yielded a doubling time of 6.6+/-1.2 days. This was significantly different from the untreated control (doubling time, 1.7+/-0.1 days). The only treatment scheme that yielded a significant improvement compared to all other schemes studied was illumination at both 1 and 2.5 h after ALA administration (both 100 J/cm2 at 100 mW/cm2) and resulted in a tumor volume doubling time of 18.9+/-2.9 days. A possible mechanism to explain this phenomenon is that the protoporphyrin IX formed after administration of ALA is photodegraded by the first illumination. In the 75-min interval, new porphyrin is formed enhancing the effect of the second illumination.
de Bruijn
H S
HS
Department of Radiation Oncology, Daniel den Hoed Cancer Centre, University Hospital Rotterdam, The Netherlands.
van der Veen
N
N
Robinson
D J
DJ
Star
W M
WM
D000622:Aminolevulinic Acid / Q000008:administration & dosage*; D000818:Animals; D005260:Female; D008027:Light; D009374:Neoplasms, Experimental / Q000188:drug therapy* / Q000473:pathology; D010778:Photochemotherapy / Q000379:methods*; D051381:Rats; D013997:Time Factors
D000622:Aminolevulinic Acid