Trafficking of a Single Photosensitizing Molecule to Different Intracellular Organelles Demonstrates Effective Hydroxyl Radical-Mediated Photodynamic Therapy in the Endoplasmic Reticulum
作者:Rebecca C. Gilson、Rui Tang、Krishna Sharmah Gautam、Dorota Grabowska、Samuel Achilefu
DOI:10.1021/acs.bioconjchem.9b00192
日期:2019.5.15
Photodynamic therapy (PDT) is often used in preclinical and clinical treatment regimens. Reactive oxygen species (ROS) generated by photosensitizers (PSs) upon exposure to light induce cell death via diverse mechanisms. PSs can exert therapeutic effects in different cellular organelles, although the efficacy of organelle-specific PDT has yet to be determined as most previous studies use different PSs in different organelles. Here, we explored how a single PS, chlorin e6 (Ce6), targeted to different organelles altered the effectiveness of PDT. Ce6 intrinsically localizes to the ER after 4 h of incubation. Modification of Ce6 via conjugation with an octapeptide (LS765), a monosubstituted triphenylphosphonium (TPP) derivative (LS897), or a disubstituted TPP derivative (LS909) altered the intrinsic localization. We determined that LS765 and LS9897 predominantly accumulated in the lysosomes, but LS909 trafficked equally to both the mitochondria and the lysosomes. Moreover, the conjugation altered the type of ROS produced by Ce6, increasing the ratio of hydrogen peroxide to hydroxyl radicals. Irradiation of identical concentrations of the PSs in solution with 650 nm, 0.84 mW/cm2 light for 10 min showed that the TPP conjugates nearly doubled the hydrogen peroxide production from ∼0.2 μM for Ce6 and LS765 to ∼0.37 μM for LS897 and LS909. In contrast, Ce6 produced ∼1.5-fold higher hydroxyl radicals than its conjugates. To compare the effect of each PS on cell death, we normalized the intracellular concentration of each PS. Hydrogen peroxide-producing PSs are effective PDT agents in the lysosomes while the hydroxyl-generating PSs are very effective in the ER. Compared to the PSs that accumulated in the lysosomes, only the ER-targeted Ce6 exerted >50% cell death at either low light power or low intracellular concentration. By delineating the contributions of cellular organelles and types of ROS produced, our work suggests that targeting hydroxyl radical-producing PSs to the ER is an exciting strategy to improve the therapeutic outcome of PDT.
光动力疗法(PDT)经常被用于临床前和临床治疗方案。光敏剂(PSs)在光照射下产生的活性氧(ROS)可通过多种机制诱导细胞死亡。光敏剂可在不同细胞器中发挥治疗作用,但细胞器特异性 PDT 的疗效尚待确定,因为之前的大多数研究在不同细胞器中使用了不同的光敏剂。在这里,我们探讨了针对不同细胞器的单个 PS--氯素 e6(Ce6)如何改变了 PDT 的有效性。培养 4 小时后,Ce6 本质上定位于 ER。通过与八肽(LS765)、单取代三苯基膦(TPP)衍生物(LS897)或二取代三苯基膦衍生物(LS909)共轭对 Ce6 进行修饰可改变其固有定位。我们确定 LS765 和 LS9897 主要在溶酶体中积累,但 LS909 在线粒体和溶酶体中的迁移量相同。此外,共轭改变了 Ce6 产生的 ROS 类型,增加了过氧化氢与羟自由基的比例。用 650 nm、0.84 mW/cm2 的光照射溶液中相同浓度的 PSs 10 分钟后发现,TPP 共轭物几乎使过氧化氢的产生量增加了一倍,从 Ce6 和 LS765 的 0.2 μM 增加到 LS897 和 LS909 的 0.37 μM。相比之下,Ce6 产生的羟自由基是其共轭物的 1.5 倍。为了比较每种 PS 对细胞死亡的影响,我们对每种 PS 的细胞内浓度进行了归一化处理。产生过氧化氢的 PS 在溶酶体中是有效的 PDT 药剂,而产生羟基的 PS 在 ER 中非常有效。与积聚在溶酶体中的 PSs 相比,在低光功率或低细胞内浓度条件下,只有以 ER 为靶标的 Ce6 能使细胞死亡超过 50%。通过划分细胞器的贡献和产生的 ROS 类型,我们的研究表明,将产生羟基自由基的 PSs 靶向到 ER 是一种令人兴奋的策略,可以提高光导光疗的治疗效果。