By performing knockdown of AXL once HER cancer

By performing knockdown of AXL once HER2+ cancer CCT251545 have achieved lung colonization, we demonstrated that AXL contributes to the establishment of macrometastases. While inhibition of AXL impairs the efficiency of metastasis, the later finding has major clinical implications since pharmacological inhibition of AXL even at later stages may have the potential to reduce metastatic outgrowth. A recent study using tumor initiating cells from PyMT transgenic mouse tumors that display partial EMT (AXL+) suggested that AXL, by promoting the secretion of THBS2 and activation of fibroblasts, prepares the metastatic niche (Del Pozo Martin et al., 2015). We found that THBS2 was downregulated in the Axl−/− tumors (Figure 5D), in agreement with a role for AXL in the niche activation. These data support the notion that inhibition of AXL in HER2+ breast cancer dampens the efficiency of every step of the metastatic cascade. Most patients afflicted with HER2+ breast cancer undergo first line therapy with agents that target HER2. We tested the effect of prolonged systemic pharmacological inhibition of AXL and found that R428 treatments phenocopied the genetic deletion of AXL, i.e., a decrease in both CTCs and lung metastases with no effect on primary tumor growth. Furthermore, co-treatment with R428 and HER2 blocking agents inhibited HER2+ PDX tumorspheres growth. Collectively, our data demonstrate that anti-AXL therapy is sufficient to reduce metastasis in HER2+ cancers in experimental models. It will be key to define pre-clinical conditions to determine if co-targeting of HER2 and AXL affects tumor growth, intravasation and extravasation, and survival of the DTCs.
Experimental Procedures
Acknowledgments We thank Drs. Frédéric Charron, Mathieu Ferron, and Mélanie Laurin for critical reading of the manuscript. We thank Drs. Tatiana Smirnova and Jeffrey E. Segall (Albert Einstein College, USA) for their generous advice to measure circulating tumor cells. We thank Manon Laprise, Marie-Claude Lavallée, and Suzie Riverin for their technical assistance with mice, Dominic Filion for microscopy assistance, and Simone Terouz for histology. This work was supported by operating grants from the Canadian Institute of Health Research (MOP-142425 to J.F.C. and J.P.G and MOP-142374 to P.P.R.), the Réseau de Recherche en Cancer of the FRQS (FRQ-34787), and Quebec Breast Cancer Foundation (to M.P.). M.-A.G. is a recipient of a CIHR Doctoral studentship. L.A. is a recipient of a Cole Foundation Postdoctoral Fellowship. M.P. holds the Diane and Sal Guerrera Chair in Cancer Genomics at McGill University. J.F.C. holds the Transat Chair in Breast Cancer Research. P.P.R. and J.-F.C. are supported by FRQS Senior investigator career awards.
Introduction Apoptosis, also known as programmed cell death, is essential for the development and maintenance of tissues and the immune system (Jacobson et al., 1997). However, residual apoptotic cells may cause tissue damage as the membrane structure of the cell collapses, releasing its contents to the surroundings. Tissue macrophages play an important role in maintaining organ homeostasis by eliminating such apoptotic cells (Aderem and Underhill, 1999, deCathelineau and Henson, 2003). This process, which is known as efferocytosis, prevents the exposure of tissues to toxic enzymes, reactive oxygen species, and enzymes such as protease and caspase (deCathelineau and Henson, 2003). Impaired efferocytosis is implicated in the pathogenesis of numerous diseases such as cystic fibrosis, chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis (McCubbrey and Curtis, 2013). Phagocytes, including macrophages, recognize eat-me-signals, such as phosphatidylserine, through cell surface receptor tyrosine kinases (Poon et al., 2014). The suppression of Axl receptor tyrosine kinase (Axl) expression in macrophages or dendritic cells results in the inhibition of efferocytosis (Seitz et al., 2007). In Axl-knock out mice, recovery from inflammation following viral and bacterial infection is delayed as a result of impaired efferocytosis (Fujimori et al., 2015).