Lipophilic triphenylphosphonium derivatives enhance radiation-induced cell killing via inhibition of mitochondrial energy metabolism in tumor cells

Publication date: 1 April 2017
Source:Cancer Letters, Volume 390
Author(s): Hironobu Yasui, Kumiko Yamamoto, Motofumi Suzuki, Yuri Sakai, Tomoki Bo, Masaki Nagane, Eri Nishimura, Tohru Yamamori, Toshihide Yamasaki, Ken-ichi Yamada, Osamu Inanami
It has recently been reported that radiation enhances mitochondrial energy metabolism in various tumor cell lines. To examine how this radiation-induced alteration in mitochondrial function influences tumor cell viability, various lipophilic triphenylphosphonium (TPP⁺) cation derivatives and related compounds such as 4-hydroxy-2,2,6,6-tetramethyl-1-oxy-piperidin (Tempol) with TPP⁺ (named “Mito-”) were designed to inhibit the mitochondrial electron transport chain. Mito-(CH2)10-Tempol (M10T) and its derivatives, Mito-(CH2)5-Tempol (M5T), Mito-(CH2)10-Tempol-Methyl (M10T-Me), Mito-C10H21 (M10), and C10H21-Tempol (10T), were prepared. In HeLa human cervical adenocarcinoma cells and A549 human lung carcinoma cells, the fractional uptake of the compound into mitochondria was highest among the TTP⁺ analogs conjugated with Tempol (M10T, M5T, and 10T). M10T, M10T-Me, and M10 exhibited strong cytotoxicity and enhanced X-irradiation-induced reproductive cell death, while 10T and M5T did not. Furthermore, M10T, M10T-Me, and M10 decreased basal mitochondrial membrane potential and intracellular ATP. M10T treatment inhibited X-ray-induced increases in ATP production. These results indicate that the TPP cation and a long hydrocarbon linker are essential for radiosensitization of tumor cells. The reduction in intracellular ATP by lipophilic TPP⁺ is partly responsible for the observed radiosensitization.



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