Macrophage migration inhibitory factor downregulation: a novel mechanism of resistance to anti-angiogenic therapy

Abstract

Anti-angiogenic therapies for cancer such as VEGF neutralizing antibody bevacizumab have limited durability. While mechanisms of resistance remain undefined, it is likely that acquired resistance to anti-angiogenic therapy will involve alterations of the tumor microenvironment. We confirmed increased tumor-associated macrophages in bevacizumab-resistant glioblastoma patient specimens and two novel glioblastoma xenograft models of bevacizumab resistance. Microarray analysis suggested downregulated macrophage migration inhibitory factor (MIF) to be the most pertinent mediator of increased macrophages. Bevacizumab-resistant patient glioblastomas and both novel xenograft models of resistance had less MIF than bevacizumab-naïve tumors, and harbored more M2/protumoral macrophages that specifically localized to the tumor edge. Xenografts expressing MIF-shRNA grew more rapidly with greater angiogenesis and had macrophages localizing to the tumor edge which were more prevalent and proliferative, and displayed M2 polarization, whereas bevacizumab-resistant xenografts transduced to upregulate MIF exhibited the opposite changes. Bone marrow-derived macrophage were polarized to an M2 phenotype in the presence of condition-media derived from bevacizumab-resistant xenograft-derived cells, while recombinant MIF drove M1 polarization. Media from macrophages exposed to bevacizumab-resistant tumor cell conditioned media increased glioma cell proliferation compared to media from macrophages exposed to bevacizumab-responsive tumor cell media, suggesting that macrophage polarization in bevacizumab-resistant xenografts is the source of their aggressive biology and results from a secreted factor. Two mechanisms of bevacizumab-induced MIF reduction were identified: (1) bevacizumab bound MIF and blocked MIF-induced M1 polarization of macrophages; and (2) VEGF increased glioma MIF production in a VEGFR2-dependent manner, suggesting that bevacizumab-induced VEGF depletion would downregulate MIF. Site-directed biopsies revealed enriched MIF and VEGF at the enhancing edge in bevacizumab-naïve patients. This MIF enrichment was lost in bevacizumab-resistant glioblastomas, driving a tumor edge M1-to-M2 transition. Thus, bevacizumab resistance is driven by reduced MIF at the tumor edge causing proliferative expansion of M2 macrophages, which in turn promotes tumor growth.

A novel xenograft model reveals invasive mesenchymal transition and ineffective angiogenic response during anti-angiogenic therapy resistance

“…Indeed, this devascularization succeeds despite upregulation of compensatory VEGF-independent pro-angiogenic pathways and despite enriched neurosphere yield in BRGs and bevacizumab-resistant xenografts and expression of genes associated with glioma stem cells, which have previously been shown to be capable of forming endothelial cells (22). This successful devascularization led to increased hypoxia in our resistance model, with an associated upregulation of genes involved in metabolism and inflammation, consistent with changes reported elsewhere (23)(24)(25).…”

“…The shear modulus of hydrogel formulations was measured using oscillatory rheometry (Anton Parr Physica MCR 310) as described previously. 25 Briefly, hydrogels were first crosslinked by incubation for 1 hr in a humidified 37˚C chamber.…”

The contribution of tumor-associated macrophages in glioma neo-angiogenesis and implications for anti-angiogenic strategies

“…87 Recently, reduced MIF expression was observed in bevacizumab-resistant glioma cells, which in turn increased M2-like TAM recruitment, promoting tumor progression. 88 In experimentally induced primitive neuroectodermal tumors, similar observations were made following drug-induced VEGFR2 blockade. 89 Contrasting with these data are the reported effects of the pan-VEGFR inhibitor cediranib that transiently decreases the intratumoral infiltration of macrophages.…”

How Does Continuous Renal Replacement Therapy Affect Septic Acute Kidney Injury?

“…Recent analysis of macrophage populations carefully isolated by differential expressions of Ly6C in CD11b + cells in the kidney injury [31, 32] confirmed that results of previous studies have shown that macrophages (predominantly CD11b + /Ly6C high cells) [30, 31] in the kidney early expressed proinflammatory genes, whereas macrophages within the kidney during the tubular repair phase (CD11b + /Ly6C intermediate cells) expressed more wound-healing markers [30]. It has been proved that decreased MIF concentration in cancer can induce macrophage polarization from proinflammatory macrophages (predominantly CD11b + /Ly6C high cells) to pro-wound healing macrophages (CD11b + /Ly6C intermediate cells) [33]. The MIF level decreases obviously during CRRT or hemodialysis and can improve the prognosis [23, 34]; however, how it works is still unknown and the MIF plasma pool is reconstituted early after the termination of hemodialysis from unknown sources.…”