An anti-Axl monoclonal antibody attenuates xenograft tumor growth and enhances the effect of multiple anticancer therapies.

Axl is expressed in various types of cancer and is involved in multiple processes of tumorigenesis, including promoting tumor cell growth, migration, invasion, metastasis as well as angiogenesis. To evaluate further the mechanisms involved in the expression/activation of Axl in various aspects of tumorigenesis, especially its roles in modulating tumor stromal functions, we have developed a phage-derived mAb (YW327.6S2) that recognizes both human and murine Axl. YW327.6S2 binds to both human and murine Axl with high affinity. It blocks the ligand Gas6 binding to the receptor, downregulates receptor expression, inhibits receptor activation and downstream signaling. In A549 non-small-cell lung cancer (NSCLC) and MDA-MB-231 breast cancer models, YW327.6S2 attenuates xenograft tumor growth and potentiates the effect of anti-VEGF treatment. In NSCLC models, YW327.6S2 also enhances the effect of erlotinib and chemotherapy in reducing tumor growth. Furthermore, YW327.6S2 reduces the metastasis of MDA-MB-231 breast cancer cells to distant organs. YW327.6S2 induces tumor cell apoptosis in NSCLC, reduces tumor-associated vascular density and inhibits the secretion of inflammatory cytokines and chemokines from tumor-associated macrophages in the breast cancer model. In conclusion, anti-Axl mAb can enhance the therapeutic efficacy of anti-VEGF, EGFR small-molecule inhibitors as well as chemotherapy. Axl mAb affects not only tumor cells but also tumor stroma through its modulation of tumor-associated vasculature and immune cell functions.

Axl as a potential therapeutic target in cancer: role of Axl in tumor growth, metastasis and angiogenesis.

Dysregulation of Axl and its ligand growth arrest-specific 6 is implicated in the pathogenesis of several human cancers. In this study, we have used RNAi and monoclonal antibodies to assess further the oncogenic potential of Axl. Here we show that Axl knockdown reduces growth of lung and breast cancer xenograft tumors. Inhibition of Axl expression attenuates breast cancer cell migration and inhibits metastasis to the lung in an orthotopic model, providing the first in vivo evidence that links Axl directly to cancer metastasis. Axl knockdown in endothelial cells impaired tube formation and this effect was additive with anti-vascular endothelial growth factor (VEGF). Further analysis demonstrated that Axl regulates endothelial cell functions by modulation of signaling through angiopoietin/Tie2 and Dickkopf (DKK3) pathways. We have developed and characterized Axl monoclonal antibodies that attenuate non-small cell lung carcinoma xenograft growth by downregulation of receptor expression, reducing tumor cell proliferation and inducing apoptosis. Our data demonstrate that Axl plays multiple roles in tumorigenesis and that therapeutic antibodies against Axl may block Axl functions not only in malignant tumor cells but also in the tumor stroma. The additive effect of Axl inhibition with anti-VEGF suggests that blocking Axl function could be an effective approach for enhancing antiangiogenic therapy.