Mitochondrial activities play a pivotal role in regulating cell cycle in response to doxorubicin

Doxorubicin induces both DNA damage and metabolic interference. How these effects interact to modulate cellular toxicity is not completely understood but important given the widespread use of doxorubicin in cancer treatment. This study tests the hypothesis that cell cycle arrest and survival are affected by distinct mitochondrial activities during doxorubicin exposure. Parental and mutant S. cerevisiae strains deficient in selected genes with mitochondrial function were treated with doxorubicin and assayed for changes in proliferation rates, cell survival and cell cycle arrest kinetics. Mitochondrial DNA content was estimated using quantitative PCR. Mitochondrial function was assessed by measuring oxygen consumption with and without an uncoupler. Parental cells growing in a non-fermentable carbon source medium and mutants lacking mitochondria and grown in glucose medium both show abrupt cell cycle and proliferation arrest during doxorubicin exposure compared to parental cells grown in glucose. Mitochondrial DNA increases during doxorubicin exposure in S. cerevisiae and in human breast cancer cells. Yeast strains deficient in TCA cycle activity or electron transport both show more abrupt cell cycle arrest than parental cells when exposed to doxorubicin. Concurrent treatment with the mitochondrial uncoupler dinitrophenol facilitates cell cycle progression and proliferation during doxorubicin exposure. Doxorubicin exposure induces mitochondrial DNA synthesis with TCA cycle and oxidative phosphorylation activity having opposing effects on cell proliferation, survival and cell cycle kinetics. TCA cycle activity provides biosynthetic substrates to support cell cycle progression and cell proliferation while electron transport and oxidative phosphorylation facilitate cell cycle arrest and possibly increased cytotoxicity.