The Involvement of Mitochondrial Membrane Potential in Cross-Resistance Between Radiation and Docetaxel.
To 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 antimicrotubule agent, docetaxel (DTX). The involvement of reactive oxygen species (ROS) from mitochondria (mtROS) in the cross-resistance to X-rays and DTX was studied.



Sensitivity to anticancer 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 (ρ(0)) cells, the cells were cultured for 3 to 4 weeks in medium containing ethidium bromide.



Treatment with DTX increased mtROS in parental cells but not in CRR cells. DTX induced DNA double-strand breaks in parental cells. The mitochondrial membrane potential of CRR cells was lower in CRR cells than in parental cells. Depletion of mtDNA induced DTX resistance in parental cells. Treatment with dimethyl sulfoxide also induced DTX resistance in parental cells.



The 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 β-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.
Department of Radiation Biology and Medicine, Faculty of Medicine, Tohoku Medical and Pharmaceutical University, Sendai, Japan; Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
Yoshikazu
Y
Kuwahara
Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
Mehryar Habibi
MH
Roudkenar
Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
Masatoshi
M
Suzuki
Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
Yusuke
Y
Urushihara
Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan.
Motoi
M
Fukumoto
Department of Radiopharmacy, Tohoku Medical and Pharmaceutical University, Sendai, Japan.
Yohei
Y
Saito
Department of Pathology, Institute of Development, Aging and Cancer, Tohoku University, Sendai, Japan; Department of Molecular Pathology, Tokyo Medical University, Tokyo, Japan. Electronic address: manabu.fukumoto.a8@tohoku.ac.jp.
Manabu
M
Fukumoto
D000970:Antineoplastic Agents / Q000008:administration & dosage; D000077143:Docetaxel; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000528:radiation effects*; D006367:HeLa Cells; D056945:Hep G2 Cells; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects* / Q000528:radiation effects*; D008928:Mitochondria / Q000187:drug effects / Q000528:radiation effects; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects; D017382:Reactive Oxygen Species / Q000378:metabolism*; D043823:Taxoids / Q000008:administration & dosage*; D050257:Tubulin Modulators / Q000008:administration & dosage; D014965:X-Rays
D000970:Antineoplastic Agents; D017382:Reactive Oxygen Species; D043823:Taxoids; D050257:Tubulin Modulators; D000077143:Docetaxel