Background

Photodynamic therapy with 5-aminolevulinic acid (5-ALA PDT) is a promising novel therapeutic approach in the therapy of malignant brain tumors. 5-ALA occurs as a natural precursor of protoporphyrin IX (PpIX), a tumor-selective photosensitizer. The ATP-binding cassette transporter ABCG2 plays a physiologically significant role in porphyrin efflux from living cells. ABCG2 is also associated with stemness properties. Here we investigate the role of ABCG2 on the susceptibility of glioblastoma cells to 5-ALA PDT.

Methods

Accumulation of PpIX in doxycycline-inducible U251MG glioblastoma cells with or without induction of ABCG2 expression or ABCG2 inhibition by KO143 was analyzed using flow cytometry. In U251MG cells, ABCG2 was inducible by doxycycline after stable transfection with a tet-on expression plasmid. U251MG cells with high expression of ABCG2 were enriched and used for further experiments (sU251MG-V). PDT was performed on monolayer cell cultures by irradiation with laser light at 635 nm.

Results

Elevated levels of ABCG2 in doxycycline induced sU251MG-V cells led to a diminished accumulation of PpIX and higher light doses were needed to reduce cell viability. By inhibiting the ABCG2 transporter with the efficient and non-toxic ABCG2 inhibitor KO143, PpIX accumulation and PDT efficiency could be strongly enhanced.

Conclusion

Glioblastoma cells with high ABCG2 expression accumulate less photosensitizer and require higher light doses to be eliminated. Inhibition of ABCG2 during photosensitizer accumulation and irradiation promises to restore full susceptibility of this crucial tumor cell population to photodynamic treatment.

中文翻译：

---

ABCG2影响胶质母细胞瘤细胞中光动力治疗的效率。

背景

5-氨基乙酰丙酸（5-ALA PDT）的光动力疗法是治疗恶性脑肿瘤的一种有前途的新型治疗方法。5-ALA作为原卟啉IX（PpIX）（一种肿瘤选择性光敏剂）的天然前体存在。ATP结合盒转运蛋白ABCG2在活细胞的卟啉流出中起着重要的生理作用。ABCG2也与茎特性相关。在这里，我们研究了ABCG2对成胶质细胞瘤细胞对5-ALA PDT敏感性的作用。

方法

使用流式细胞术分析了强力霉素诱导的U251MG胶质母细胞瘤细胞中PpIX的积累，无论是否通过KO143诱导ABCG2表达或ABCG2抑制。在U251MG细胞中，用tet-on表达质粒稳定转染后，强力霉素可诱导ABCG2。富含ABCG2高表达的U251MG细胞并用于进一步实验（sU251MG-V）。通过用635 nm的激光照射对单层细胞培养物进行PDT。

结果

强力霉素诱导的sU251MG-V细胞中ABCG2的水平升高导致PpIX的积累减少，需要更高的光剂量以降低细胞活力。通过用有效且无毒的ABCG2抑制剂KO143抑制ABCG2转运蛋白，可以大大提高PpIX的积累和PDT的效率。

结论

具有高ABCG2表达的胶质母细胞瘤细胞积累的光敏剂较少，因此需要更高的光剂量才能消除。在光敏剂积累和照射过程中对ABCG2的抑制有望恢复该关键肿瘤细胞群体对光动力治疗的完全敏感性。