Targeting of RAGE-ligand signaling impairs breast cancer cell invasion and metastasis.

The receptor for advanced glycation end products (RAGE) is highly expressed in various cancers and is correlated with poorer outcome in breast and other cancers. Here we tested the role of targeting RAGE by multiple approaches in the tumor and tumor microenvironment, to inhibit the metastatic process. We first tested how RAGE impacts tumor cell-intrinsic mechanisms using either RAGE overexpression or knockdown with short hairpin RNAs (shRNAs). RAGE ectopic overexpression in breast cancer cells increased MEK-EMT (MEK-epithelial-to-mesenchymal transition) signaling, transwell invasion and soft agar colony formation, and in vivo promoted lung metastasis independent of tumor growth. RAGE knockdown with multiple independent shRNAs in breast cancer cells led to decreased transwell invasion and soft agar colony formation, without affecting proliferation. In vivo, targeting RAGE shRNA knockdown in human and mouse breast cancer cells, decreased orthotopic tumor growth, reduced tumor angiogenesis and recruitment of inflammatory cells, and markedly decreased metastasis to the lung and liver in multiple xenograft and syngeneic mouse models. To test the non-tumor cell microenvironment role of RAGE, we performed syngeneic studies with orthotopically injected breast cancer cells in wild-type and RAGE-knockout C57BL6 mice. RAGE-knockout mice displayed striking impairment of tumor cell growth compared with wild-type mice, along with decreased mitogen-activated protein kinase signaling, tumor angiogenesis and inflammatory cell recruitment. To test the combined inhibition of RAGE in both tumor cell-intrinsic and non-tumor cells of the microenvironment, we performed in vivo treatment of xenografted tumors with FPS-ZM1 (1 mg/kg, two times per week). Compared with vehicle, FPS-ZM1 inhibited primary tumor growth, inhibited tumor angiogenesis and inflammatory cell recruitment and, most importantly, prevented metastasis to the lung and liver. These data demonstrate that RAGE drives tumor progression and metastasis through distinct tumor cell-intrinsic and -extrinsic mechanisms, and may represent a novel and therapeutically viable approach for treating metastatic cancers.

VEGF drives cancer-initiating stem cells through VEGFR-2/Stat3 signaling to upregulate Myc and Sox2.

Vascular endothelial growth factor-A (VEGF), a potent angiogenic factor, is also implicated in self-renewal in several normal tissue types. VEGF has been shown to drive malignant stem cells but mechanisms thereof and tumor types affected are not fully characterized. Here, we show VEGF promotes breast and lung cancer stem cell (CSC) self-renewal via VEGF receptor-2 (VEGFR-2)/STAT3-mediated upregulation of Myc and Sox2. VEGF increased tumor spheres and aldehyde dehydrogenase activity, both proxies for stem cell function in vitro, in triple-negative breast cancer (TNBC) lines and dissociated primary cancers, and in lung cancer lines. VEGF exposure before injection increased breast cancer-initiating cell abundance in vivo yielding increased orthotopic tumors, and increased metastasis from orthotopic primaries and following tail vein injection without further VEGF treatment. VEGF rapidly stimulated VEGFR-2/JAK2/STAT3 binding and activated STAT3 to bind MYC and SOX2 promoters and induce their expression. VEGFR-2 knockdown or inhibition abrogated VEGF-mediated STAT3 activation, MYC and SOX2 induction and sphere formation. Notably, knockdown of either STAT3, MYC or SOX2 impaired VEGF-upregulation of pSTAT3, MYC and SOX2 expression and sphere formation. Each transcription factor, once upregulated, appears to promote sustained activation of the others, creating a feed-forward loop to drive self-renewal. Thus, in addition to angiogenic effects, VEGF promotes tumor-initiating cell self-renewal through VEGFR-2/STAT3 signaling. Analysis of primary breast and lung cancers (>1300 each) showed high VEGF expression, was prognostic of poor outcome and strongly associated with STAT3 and MYC expression, supporting the link between VEGF and CSC self-renewal. High-VEGF tumors may be most likely to escape anti-angiogenics by upregulating VEGF, driving CSC self-renewal to re-populate post-treatment. Our work highlights the need to better define VEGF-driven cancer subsets and supports further investigation of combined therapeutic blockade of VEGF or VEGFR-2 and JAK2/STAT3.