(P 259) LOVASTATIN INDUCES NOVEL CELL DEATH THROUGH THE IMPAIRED MITOCHONDRIA IRON UTILIZATION IN OSTEOASRCOMA CELLS.

Objective: It has been reported that the mechanism of tumor-specific cell death caused by metabolic regulation has been different from normal cells. In this study, we report the effect of lovastatin, a fat-soluble statin, which we have found from screening of 400 agents, that specifically cause mitochondrial damage leading the cell death in human osteosarcoma cell lines.

Methods: The action of lovastatin was investigated using human osteosarcoma cells SaOS2, U2OS, MG63 and MSC. Cell viability was evaluated by MTS assay.　Mitochondria divalent iron was evaluated by Mito-Ferro Green staining.　Mitochondria function was evaluated by TMRE staining. Mitochondria ROS were observed as super oxide, H2O2, and hydroxyl radical, respectively, with fluorescent dyes. Mitophagy and iron metabolism-related proteins were evaluated by RT-PCR and western blot.

Results: IC50 was 10-15μM in osteosarcoma cells compared to 30μM in MSCs. Iron chelator, deferoxamine (DFO) increased cell death among various cell death inhibitors under 10μM lovastatin treatment (Figure 1), and this cell death was rescued by iron sulfide administration (Figure 2). Lovastatin administration reduced mitochondria membrane potential and decreased mitochondrial volumes, but increased superoxide, •OH and mitophagy, and all of which were also rescued by iron administration. In addition, the expression levels of transferrin and DMT1 increased with lovastatin administration, and excessive accumulation of iron and divalent iron, and a relative decrease of trivalent iron were observed in mitochondria. Since statin inhibits HMG-CoA reductase, administration of mevalonate, downstream of HMG-CoA, also rescued cell death and mitochondrial impairment as well as iron administration.

Conclusion: Although the induction of ferreoptosis by statin has been reported previously, the current results from our study suggest that cell death enhanced in osteosarcoma cells by DFO under lovastatin treatment could be a different effect from the known cell death pathway through the impaired conversion of iron from divalent to trivalent in mitochondria, since if ferreoptosis is the cause of the cell death, DFO should rescue it. In addition, CoQ deficiency is supposed to increase the superoxide that rapidly converts trivalent iron to divalent iron, and from these results, it is considered that lovastatin causes iron utilization disorder mediated by CoQ synthesis impairment, and induces cell death of a novel mechanism specific to osteosarcoma.