Photodynamic Therapy as Novel Nephron Sparing Treatment Option for Small Renal Masses

Purpose: Photodynamic therapy has great potential as nephron sparing therapy for small renal masses. Using mTHPC [meso-tetra(hydroxyphenyl) chlorin] (Bio-Litec Pharma, Dublin, Ireland), a photosensitizer that targets vasculature and tissue, we determined whether renal tumors could be ablated using mTHPC mediated photodynamic therapy in a translational renal carcinoma mouse model. Materials and Methods: We administered mTHPC intravenously in kidney tumor bearing mice. Tumor diameter was about 7 mm. At several drug-light intervals a cylindrical laser fiber was placed intratumorally for interstitial illumination using a wavelength of 652 nm. We determined mTHPC biodistribution up to 48 hours after administration and tumor destruction after mTHPC mediated photodynamic therapy. In vitro mTHPC uptake and photodynamic therapy induced cytotoxicity were studied in human endothelial, renal and renal cell carcinoma cell lines. Results: Ablated regions with a maximum diameter of 9.3 mm and complete loss of cell viability were observed at a drug-light interval of 4 hours, when mTHPC was increased in blood and tissue. Viable renal tissue remained detectable outside the illuminated area. In endothelial cells mTHPC uptake and sensitivity to photodynamic therapy were increased compared to those in renal cell carcinoma and renal cells. Conclusions: mTHPC mediated photodynamic therapy is a nephron sparing therapy. The extent of renal tumor destruction is adequate for clinical translation. Localization of mTHPC in tumor vasculature and tissue produces a strong combined effect. Our findings justify further preclinical studies of the applicability of photodynamic therapy for renal cell carcinoma before photodynamic therapy can become a valuable addition to current minimally invasive treatments of small renal masses.