Analysis of Renal Cell Carcinoma Cell Response to the Enhancement of 5‐aminolevulinic Acid‐mediated Protoporphyrin <scp>IX</scp> Fluorescence by Iron Chelator Deferoxamine^†

Abstract

ABSTRACT As a tumor photodiagnostic agent, 5‐aminolevulinic acid (ALA) is metabolized in the heme biosynthesis pathway to produce protoporphyrin IX (PpIX) with fluorescence. ALA‐PpIX fluorescence was evaluated in human renal cell carcinoma (RCC) cell lines and non‐tumor HK‐2 cell lines. We found that extracellular PpIX level was correlated with ABCG2 activity, illustrating its importance as a PpIX efflux transporter. Extracellular PpIX was also related to the K m of ferrochelatase (FECH) that chelates PpIX with ferrous iron to form heme. The V max of FECH was higher in all RCC cell lines tested than in the HK‐2 cell line. TCGA dataset analysis indicates a positive correlation between FECH expression and RCC patient survival. These findings suggest FECH as an important biomarker in RCC. Effects of iron chelator deferoxamine (DFO) on the enhancement of PpIX fluorescence were assessed. DFO increased intracellular PpIX in both tumor and non‐tumor cells, resulting in no gain in tumor/non‐tumor fluorescence ratios. DFO appeared to increase ALA‐PpIX more at 1‐h than at 4‐h treatment. There was an inverse correlation between ALA‐PpIX fluorescence and the enhancement effect of DFO. These results suggest that enhancement of ALA‐PpIX by DFO may be limited by the availability of ferrous iron in mitochondria following ALA administration.