Anti-angiogenic therapy leads to devascularization that limits tumor growth. However, the benefits of angiogenesis inhibitors are typically transient and resistance often develops. In this study, we explored the hypothesis that hypoxia caused by anti-angiogenic therapy induces tumor cell autophagy as a cytoprotective adaptive response, thereby promoting treatment resistance. Hypoxia-induced autophagy was dependent on signaling through the HIF-1α/AMPK pathway, and treatment of hypoxic cells with autophagy inhibitors caused a shift from autophagic to apoptotic cell death in vitro. In glioblastomas clinically resistant to the VEGF neutralizing antibody bevacizumab, increased regions of hypoxia and higher levels of autophagy-mediating BNIP3 were found when compared to pre-treatment specimens from the same patients. When treated with bevacizumab alone, human glioblastoma xenografts showed increased BNIP3 expression and hypoxia-associated growth, which could be prevented by addition of the autophagy inhibitor chloroquine. In vivo targeting of the essential autophagy gene ATG7 also disrupted tumor growth when combined with bevacizumab treatment. Together, our findings elucidate a novel mechanism of resistance to anti-angiogenic therapy in which hypoxia-mediated autophagy promotes tumor cell survival. One strong implication of our findings is that autophagy inhibitors may help prevent resistance to anti-angiogenic therapy used in the clinic.

Purpose To identify mediators of glioblastoma anti-angiogenic therapy resistance and target these mediators in xenografts. Experimental Design We performed microarray analysis comparing bevacizumab-resistant glioblastomas (BRGs) to pre-treatment tumors from the same patients. We established novel xenograft models of anti-angiogenic therapy resistance to target candidate resistance mediator(s). Results BRG microarray analysis revealed upregulation versus pre-treatment of receptor tyrosine kinase c-Met, which underwent further investigation because of its prior biologic plausibility as a bevacizumab resistance mediator. BRGs exhibited increased hypoxia versus pre-treatment in a manner correlating with their c-Met upregulation, increased c-Met phosphorylation, and increased phosphorylation of c-Met-activated focal adhesion kinase (FAK) and STAT3. We developed two novel xenograft models of anti-angiogenic therapy resistance. In the first model, serial bevacizumab treatment of an initially responsive xenograft generated a xenograft with acquired bevacizumab resistance, which exhibited upregulated c-Met expression versus pre-treatment. In the second model, a BRG-derived xenograft maintained refractoriness to the MRI tumor vasculature alterations and survival-promoting effects of bevacizumab. Growth of this BRG-derived xenograft was inhibited by a c-Met inhibitor. Transducing these xenograft cells with c-Met shRNA inhibited their invasion and survival in hypoxia, disrupted their mesenchymal morphology, and converted them from bevacizumab-resistant to bevacizumab-responsive. Engineering bevacizumab-responsive cells to express constitutively active c-Met caused these cells to form bevacizumab-resistant xenografts. Conclusion These findings support the role of c-Met in survival in hypoxia and invasion, features associated with anti-angiogenic therapy resistance; and growth and therapeutic resistance of xenografts resistant to anti-angiogenic therapy. Therapeutically targeting c-Met could prevent or overcome anti-angiogenic therapy resistance.

The homeobox gene Hoxa-9 is normally expressed in primitive bone marrow cells, and overexpression of Hoxa-9 markedly expands hematopoietic stem cells, suggesting a function in early hematopoiesis. We present evidence for major functional defects in Hoxa-9 ؊/؊ hematopoietic stem cells.

These results demonstrate that TLR2 ligands induced cardioprotection, which is mediated through a TLR2/PI3K/Akt-dependent mechanism.

Autophagy is a lysosomal degradation pathway that can sequester cytosolic material including organelles nonspecifically in a process called nonselective macroautophagy, or can target specific protein aggregates designated for destruction in a process called selective autophagy. Autophagy is one mechanism that enables tumor cells to survive stressors in the tumor microenvironment, as well as injuries caused by treatments like chemotherapy or radiation therapy. The complexity of the role of autophagy in cancer is underscored by evidence that autophagy can allow premalignant cells to escape the genotoxic stress and inflammation that promote tumorigenesis, and by evidence that some tumor cells exhibit loss of autophagy capacity altogether through molecular mechanisms that have not yet been defined. Efforts to understand and modulate the autophagy pathway will be crucial to maximize the full therapeutic potential of cancer therapies which are currently hindered by tumor cell autophagy as a resistance mechanism.

Purpose To identify mechanisms and mediators of resistance to anti-angiogenic therapy in human glioblastoma. Experimental Design We performed microarray gene expression analysis and immunohistochemistry comparing 21 recurrent glioblastomas progressing during anti-angiogenic treatment with VEGF neutralizing antibody bevacizumab to paired pre-treatment tumors from the same patients. Results Microarray analysis revealed that bevacizumab-resistant glioblastomas (BRGs) had 2 clustering patterns defining subtypes that reflect radiographic growth patterns. Enhancing BRGs (EBRGs) exhibited MRI enhancement, a long-established criterion for glioblastoma progression, and expressed mitogen-activated protein kinases, neural cell adhesion molecule-1 (NCAM-1), and aquaporin 4. Compared to their paired pre-treatment tumors, EBRGs had unchanged vascularity and hypoxia, with increased proliferation. Non-enhancing BRGs (NBRGs) exhibited minimal MRI enhancement but had FLAIR-bright expansion, a newer criterion for glioblastoma recurrence since the advent of anti-angiogenic therapy, and expressed integrin α5, laminin, fibronectin1, and PDGFRβ. NBRGs had less vascularity, more hypoxia, and unchanged proliferation than their paired pre-treatment tumors. Primary NBRG cells exhibited more stellate morphology with a 3-fold increased shape factor and were nearly 4-fold more invasive in matrigel chambers than primary cells form EBRGs or bevacizumab-naïve glioblastomas (P<0.05). Conclusion Using microarray analysis, we found two resistance patterns during anti-angiogenic therapy with distinct molecular profiles and radiographic growth patterns. These studies provide valuable biologic insight into the resistance that has limited anti-angiogenic therapy to date.

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The PicTar program predicted that microRNA-126 (miR-126), miR-145, and let-7s target highly conserved sites within the Hoxa9 homeobox. There are increased nucleotide constraints in the three microRNA seed sites among Hoxa9 genes beyond that required to maintain protein identity, suggesting additional functional conservation. In preliminary experiments, forced expression of these microRNAs in Hoxa9