Abstract
Sorafenib (Nexavar) is a broad-spectrum multikinase inhibitor that proves effective in treating advanced renal-cell carcinoma and liver cancer. Despite its well-characterized mechanism of action on several established cancer-related protein kinases, sorafenib causes variable responses among human tumors, although the cause for this variation is unknown. In an unbiased screening of an oncology drug library, we found that sorafenib activates recruitment of the ubiquitin E3 ligase Parkin to damaged mitochondria. We show that sorafenib inhibits the activity of both complex II/III of the electron transport chain and ATP synthase. Dual inhibition of these complexes, but not inhibition of each individual complex, stabilizes the serine-threonine protein kinase PINK1 on the mitochondrial outer membrane and activates Parkin. Unlike the protonophore carbonyl cyanide m-chlorophenylhydrazone, which activates the mitophagy response, sorafenib treatment triggers PINK1/Parkin-dependent cellular apoptosis, which is attenuated upon Bcl-2 overexpression. In summary, our results reveal a new mechanism of action for sorafenib as a mitocan and suggest that high Parkin activity levels could make tumor cells more sensitive to sorafenib's actions, providing one possible explanation why Parkin may be a tumor suppressor gene. These insights could be useful in developing new rationally designed combination therapies with sorafenib.
Highlights
Sorafenib (Nexavar) is a broad-spectrum multikinase inhibitor that proves effective in treating advanced renal-cell carcinoma and liver cancer
Previous studies have shown that Parkin relocates from cytosol to outer mitochondrial membrane in response to treatment with the protonophore CCCP or the potassium ionophore valinomycin but not rotenone or paraquat [17]
To further investigate differential cellular responses mediated by different chemicals, we performed a high content screening for Parkin mitochondrial recruitment response with the FDAapproved oncology drug set
Summary
Previous studies have shown that Parkin relocates from cytosol to outer mitochondrial membrane in response to treatment with the protonophore CCCP or the potassium ionophore valinomycin but not rotenone or paraquat [17]. When Venus–Parkin–WT and mTurquoise– ParkinS65A were co-expressed together in HeLa cells, sorafenib could trigger both proteins to mitochondria (Fig. 2, F–H) These data suggest Parkin is activated by an autocatalytic mechanism by sorafenib in a similar manner to CCCP. Sorafenib induces PINK1/Parkin-dependent apoptosis by suppressing the Bcl-2 family of proteins Both CCCP and sorafenib cause PINK1 induction and mitochondrial localization of Parkin, yet the biological outcomes are distinct (mitophagy versus apoptosis). When sorafenib and ABT-737 were added together, both the wild-type and the Bcl-2-overexpressing cells were completely eliminated by apoptosis (Fig. 7A) This result suggests that the combination of the Bcl-2 inhibitor ABT-737 with sorafenib synergistically triggers robust apoptosis of cancer cells. When CCCP and ABT-737 were added together, robust apoptotic activity was observed (Fig. 7B) This result suggests that cancer cells with a robust PINK1–Parkin pathway are more susceptible to combined treatment with sorafenib and Bcl-2 inhibitors.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
