title: 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-naive 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 with 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-naive 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.
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: B A
authors.initials: BA
authors.lastname: Castro
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: P
authors.initials: P
authors.lastname: Flanigan
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: A
authors.initials: A
authors.lastname: Jahangiri
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: D
authors.initials: D
authors.lastname: Hoffman
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: W
authors.initials: W
authors.lastname: Chen
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: R
authors.initials: R
authors.lastname: Kuang
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: M
authors.initials: M
authors.lastname: De Lay
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: G
authors.initials: G
authors.lastname: Yagnik
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Wagner
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: S
authors.initials: S
authors.lastname: Mascharak
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: M
authors.initials: M
authors.lastname: Sidorov
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: S
authors.initials: S
authors.lastname: Shrivastav
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: G
authors.initials: G
authors.lastname: Kohanbash
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: H
authors.initials: H
authors.lastname: Okada
authors.affiliation: Department of Neurological Surgery, University of California San Francisco (UCSF), San Francisco, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Aghi
mesh_terms: D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D000818:Animals; D000068258:Bevacizumab / Q000494:pharmacology; D001932:Brain Neoplasms / Q000098:blood supply* / Q000188:drug therapy* / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D005260:Female; D005909:Glioblastoma / Q000098:blood supply* / Q000188:drug therapy* / Q000378:metabolism; D006801:Humans; D008263:Macrophage Migration-Inhibitory Factors / Q000378:metabolism*; D008264:Macrophages; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays
chemical_list: D020533:Angiogenesis Inhibitors; D008263:Macrophage Migration-Inhibitory Factors; D000068258:Bevacizumab