Oxidative stress accelerates the pathogenesis of a number of
chronic diseases including
cancer growth and its
metastasis.
Transcription factor NF-E2-related factor-2 (Nrf2), which regulates the cellular defense system against oxidative stress, elicits essential protection against chemical-induced carcinogenic insults. We recently demonstrate that the systemic deletion of Nrf2 leads to an increased susceptibility to
cancer metastasis, which is associated with aberrant
reactive oxygen species (ROS) accumulation in myeloid-derived suppressor cells (MDSC). However, it remains elusive whether cellular
antioxidant defense system in the myeloid lineage cells plays indispensable roles for metastatic
cancer progression. We herein found that myeloid lineage-specific Nrf2-deficient mice exhibited an increased susceptibility to pulmonary
metastasis of the mouse
Lewis lung carcinoma cells, and ROS level was more highly elevated in MDSCs of
cancer-bearing Nrf2-deficient mice. Similarly, myeloid lineage-specific deletion of
selenocysteine-tRNA gene (Trsp), which is essential for synthesis of
antioxidant selenoenzymes, resulted in increased number of metastatic nodules along with ROS accumulation in MDSCs of
cancer-bearing mice. These results thus indicate that the
antioxidant systems directed by Nrf2 and selenoenzymes contribute to the clearance of ROS in MDSCs, efficiently preventing
cancer cell
metastasis. Consistent with this notion, a synthetic
triterpenoid 1-[2-cyano-3,12-dioxooleana-1,9(11)-dien-28-oyl]
imidazole (
CDDO-Im), a potent Nrf2 inducer, attenuated the ROS production in MDSCs, and thereafter reduced metastatic nodules. Taken together, this study provides compelling lines of evidence that Nrf2 inducer retains therapeutic efficacy against
cancer cell
metastasis.