Combined inhibition of aurora kinases and Bcl-xL induces apoptosis through select BH3-only proteins

Abstract

Aurora Kinases (AURK) are mitotic kinases important for regulating cell cycle progression. Small molecule inhibitors of AURK have shown promising antitumor effects in multiple cancers; however, the utility of these inhibitors as inducers of cancer cell death has thus far been limited. Here, we examined the role of the Bcl-2 family proteins in AURK inhibition-induced apoptosis in colon cancer cells. We found that Alisertib and Danusertib, two small molecule inhibitors of AURK, are inefficient inducers of apoptosis in HCT116 and DLD-1 colon cancer cells, the survival of which requires at least one of the two anti-apoptotic Bcl-2 family proteins, Bcl-xL and Mcl-1. We further identified Bcl-xL as a major suppressor of Alisertib or Danusertib-induced apoptosis in HCT116 cells. We demonstrate that combination of a BH3-mimetic inhibitor (ABT-737), a selective inhibitor of Bcl-xL, Bcl-2, and Bcl-w, with Alisertib or Danusertib potently induces apoptosis through the Bcl-2 family effector protein Bax. In addition, we identified Bid, Puma, and Noxa, three of the BH3-only proteins of the Bcl-2 family, as mediators of Alisertib/ABT-737-induced apoptosis. We show while Noxa promotes apoptosis by constitutively sequestering Mcl-1, Puma becomes associated with Mcl-1 upon Alisertib treatment. On the other hand, we found Alisertib treatment causes activation of caspase-2, which promotes apoptosis by cleaving Bid into tBid, a suppressor of both Bcl-xL and Mcl-1. Together, these results define the Bcl-2 protein network critically involved in AURK inhibitor-induced apoptosis, and suggest that BH3-mimetics targeting Bcl-xL may help overcome resistance to AURK inhibitors in cancer cells.