The involvement of mitochondrial membrane potential in cross-resistance between radiation and docetaxel

Publication date: Available online 13 July 2016
Source:International Journal of Radiation Oncology*Biology*Physics
Author(s): Yoshikazu Kuwahara, Mehryar Habibi Roudkenar, Masatoshi Suzuki, Yusuke Urushihara, Motoi Fukumoto, Yohei Saito, Manabu Fukumoto
PurposeTo understand the molecular mechanisms underlying cancer cell radioresistance, clinically relevant radioresistant (CRR) cells that continue to proliferate during exposure to 2 Gy/day X-rays for more than 30 days were established. A modified high-density survival assay for anticancer-drug screening revealed that CRR cells were resistant to an anti-microtubule agent, docetaxel (DTX). The involvement of reactive oxygen species (ROS) from mitochondria (mtROS) in the cross-resistance to X-rays and DTX was studied.Methods and MaterialsSensitivity to anti-cancer agents was determined by a modified high-density cell survival or water-soluble tetrazolium salt assay. DTX induced mtROS generation was determined by MitoSOX red staining. JC-1 staining was used to visualize mitochondrial membrane potential. DTX induced DNA double-strand breaks were determined by γ-H2AX staining. To obtain mitochondrial DNA-lacking (ρ0) cells, the cells were cultured for 3 to 4 weeks in medium containing ethidium bromide.ResultsTreatment with DTX increased mtROS in parental but not in CRR cells. DTX induced DNA double-strand breaks in parental cells. Mitochondrial membrane potential of CRR cells was lower in CRR cells than that in parental cells. Depletion of mtDNA induced DTX resistance in parental cells. Treatment with dimethyl sulfoxide also induced DTX resistance in parental cells.ConclusionsThe mitochondrial dysfunction observed in CRR cells contributes to X-ray and DTX cross-resistance. The activation of oxidative phosphorylation in CRR cells may represent an effective approach to overcome radioresistant cancers. In general, the overexpression of beta-tubulin or multidrug efflux pumps is thought to be involved in DTX resistance. In the present study, we discovered another DTX resistant mechanism by investigating CRR cells. (260/300 words)

Teaser

Clinically relevant radioresistant (CRR) cells were resistant to an anti-microtubule agent, docetaxel (DTX). After treatment with DTX or exposure to X-rays reactive oxygen species from mitochondria (mtROS) were generated in parental cells but not in CRR cells, suggesting an involvement of mtROS in the cross-resistance to DTX and X-rays. In the present study, novel DTX resistant mechanism was found by investigating CRR cells and ρ0 cells which lack mitochondrial DNA.


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