The mechanism of
tumor-specific
porphyrin accumulation is not clear. We investigated the expression of
proton-coupled folate transporter SLC46A1 in
glioma and aimed to clarify the relationship between
tumor fluorescence and SLC46A1 expression.We confirmed the expression of SLC46A1 in surgical specimens from 24
glioma patients by immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR). We also investigated SLC46A1 expression in
glioma cell lines by RT-PCR. The cellular uptake of
hematoporphyrin derivative in vitro was measured with a microplate reader and fluorescence microscope. In these experiments, we used three human
malignant glioma cell lines: U87, U251 and T98G. Immunohistochemistry showed SLC46A1 positivity in the malignant
tumor lesion of each specimen. Strong positive SLC46A1 expression was observed in 33% of grade IV, 22% of grade III and 17% of grade II
gliomas. All four randomly obtained
malignant glioma frozen sections expressed SLC46A1
mRNA by RT-PCR. In vitro, U87 showed the least SLC46A1 expression, U251 was intermediate, and T98G showed the most expression. The amount of
hematoporphyrin derivative (HpD) cellular uptake correlated with SLC46A1 expression. These results suggest that the accumulation of HpD in
glioma cells is related to SLC46A1 function and SLC46A1 is involved in the mechanism of
glioma fluorescence.