Reports concerning hepatic mitochondrial toxicity of
sunitinib are conflicting. We therefore decided to conduct a toxicological study in mice. After having determined the highest dose that did not affect nutrient ingestion and
body weight, we treated mice orally with
sunitinib (7.5 mg/kg/day) for 2 weeks. At the end of treatment, peak
sunitinib plasma concentrations were comparable to those achieved in humans and liver concentrations were approximately 25-fold higher than in plasma.
Sunitinib did not affect
body weight, but increased plasma ALT activity 6-fold. The activity of
enzyme complexes of the electron transport chain (ETC) was decreased numerically in freshly isolated and
complex III activity significantly in previously frozen liver mitochondria. In previously frozen mitochondria,
sunitinib decreased
NADH oxidase activity concentration-dependently in both treatment groups. The hepatic mitochondrial
reactive oxygen species (ROS) content and
superoxide dismutase 2 expression were increased in
sunitinib-treated mice.
Protein and
mRNA expression of several subunits of mitochondrial
enzyme complexes were decreased in mitochondria from
sunitinib-treated mice.
Protein expression of PGC-1α,
citrate synthase activity and
mtDNA copy number were all decreased in livers of
sunitinib-treated mice, indicating impaired mitochondrial proliferation.
Caspase 3 activation and TUNEL-positive hepatocytes were increased in livers of
sunitinib-treated mice, indicating hepatocyte apoptosis. In conclusion,
sunitinib caused concentration-dependent toxicity in isolated mitochondria at concentrations reached in livers in vivo and inhibited hepatic mitochondrial proliferation. Daily mitochondrial insults and impaired mitochondrial proliferation most likely explain hepatocellular injury observed in mice treated with
sunitinib.