Mutations in the mitochondrial genome confer resistance of cancer cells to anticancer drugs

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It has been established that the majority of cancer cells harbor homoplasmic somatic mutations in the mitochondrial genome(mtDNA).We show that somatic mutations in mtDNA are involved in anticancer drug-tolerance.We used trans-mitochondrial hybrid cells (cybrids) to reveal the role of mutations in mtDNA in the pancreatic cancer by excluding any effects of the nuclear background.Cybrids were constructed by repopulating HeLa devoid of mtDNA with mtDNA derived from enucleated the pancreatic cancer cells(CFPAC-1,CAPAN-2)harboring mtDNA mutations. We constructed several cybrids with mutations derived from the cancer cells as well as those with wild mtDNA derived healthy individuals. We compared the mutant and wild cybrids in resistance against staurosporine(STS), 5FU, CDDP in vitro.The experiment revealed mutant cybrids were more resistant against the drugs than wild cybrids except hyperthermia. Next, Sub-G1 populations were examined to estimate nuclear DNA fragmentation during apoptosis. STS treatment increased Sub-G1 populations more greatly in wild cybrids than in mutant cybrids. Notably, an inhibitor of cytchrome c oxidase prevented the increase in Sub-G1 population of wild cybrids with STS, suggesting respiratory chain activity is involved in STS-induced apoptosis. Furthermore, we investigated cyt. c release from mitochondriaby immunostaining. Most cells of wild cybrid lost m and were stained with anti-cyt. c antibody,indicating cyt. c release to the cytosol. In contrast, mutant cybrids maintained mitochondrial membrane potential and co-localization of cyt. c. These results indicate that mtDNA mutations of the pancreatic cancer inhibit cyt. c -dependent apoptosis.Our results demonstrate that mtDNA mutationscan confer chemoresistance on cancer cells.