Selective accumulation of hematoporphyrin derivative in glioma through proton-coupled folate transporter SLC46A1

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.