Repurposing Brigatinib for the Treatment of Colorectal Cancer Based on Inhibition of ER-phagy

Abstract

<b>Rationale</b>: The sustained and severe endoplasmic reticulum (ER) stress in cancer cells may contribute to apoptotic cell death, thus representing a potential target for cancer therapy. Brigatinib is an anaplastic lymphoma kinase (ALK) inhibitor approved for the treatment of ALK-positive non-small-cell lung cancer (NSCLC). However, it remains unclear if brigatinib has alternative model of action to exert antitumor effect in ALK-negative cancers. <b>Methods</b>: ALK-positive NSCLC cells and various human ALK-negative cancer cells, especially human colorectal cancer (CRC) cells were used to examine the tumor suppression effect of brigatinib alone or in combination with autophagy inhibitors <i>in vitro</i> and <i>in vivo</i>. A variety of biochemical assays were conducted to elucidate the underlying mechanisms of brigatinib in CRC cells. <b>Results</b>: Here, we show the significant anti-cancer effect of brigatinib in CRC through induction of apoptosis by sustained ER stress. Mechanistically, brigatinib induces ER stress via promoting the interaction between ubiquitin-specific peptidase 5 (USP5), a deubiquitinase, and oxysterol-binding protein-related protein 8 (ORP8), leading to ORP8 deubiquitination, accumulation and growth inhibition. Furthermore, we find that brigatinib-mediated ER stress simultaneously induces autophagic response via ER-phagy that acts as a protective mechanism to relieve excessive ER stress. As such, combination of brigatinib with autophagy inhibitors significantly enhances the anti-CRC effect of brigatinib both <i>in vitro</i> and <i>in vivo</i>, supporting the repurposing of brigatinib in CRC, independently of ALK. <b>Conclusion</b>: The unearthed new molecular action of brigatinib suggests that therapeutic modulation of ER stress and autophagy might represent a valid strategy to treat CRC and perhaps other ALK-negative cancers.