title: Macrophages inhibit human osteosarcoma cell growth after activation with the bacterial cell wall derivative liposomal muramyl tripeptide in combination with interferon-γ.
abstract: BACKGROUND
  In osteosarcoma, the presence of tumor-infiltrating macrophages positively correlates with patient survival in contrast to the negative effect of tumor-associated macrophages in patients with other tumors. Liposome-encapsulated muramyl tripeptide (L-MTP-PE) has been introduced in the treatment of osteosarcoma patients, which may enhance the potential anti-tumor activity of macrophages. Direct anti-tumor activity of human macrophages against human osteosarcoma cells has not been described so far. Hence, we assessed osteosarcoma cell growth after co-culture with human macrophages.
  
  
  METHODS
  Monocyte-derived M1-like and M2-like macrophages were polarized with LPS + IFN-γ, L-MTP-PE +/- IFN-γ or IL-10 and incubated with osteosarcoma cells. Two days later, viable tumor cell numbers were analyzed. Antibody-dependent effects were investigated using the therapeutic anti-EGFR antibody cetuximab.
  
  
  RESULTS
  M1-like macrophages inhibited osteosarcoma cell growth when activated with LPS + IFN-γ. Likewise, stimulation of M1-like macrophages with liposomal muramyl tripeptide (L-MTP-PE) inhibited tumor growth, but only when combined with IFN-γ. Addition of the tumor-reactive anti-EGFR antibody cetuximab did not further improve the anti-tumor activity of activated M1-like macrophages. The inhibition was mediated by supernatants of activated M1-like macrophages, containing TNF-α and IL-1β. However, specific blockage of these cytokines, nitric oxide or reactive oxygen species did not inhibit the anti-tumor effect, suggesting the involvement of other soluble factors released upon macrophage activation. While LPS + IFN-γ-activated M2-like macrophages had low anti-tumor activity, IL-10-polarized M2-like macrophages were able to reduce osteosarcoma cell growth in the presence of the anti-EGFR cetuximab involving antibody-dependent tumor cell phagocytosis.
  
  
  CONCLUSIONS
  This study demonstrates that human macrophages can be induced to exert direct anti-tumor activity against osteosarcoma cells. Our observation that the induction of macrophage anti-tumor activity by L-MTP-PE required IFN-γ may be of relevance for the optimization of L-MTP-PE therapy in osteosarcoma patients.
authors.forename: Jens H W
authors.initials: JH
authors.lastname: Pahl
authors.forename: Kitty M C
authors.initials: KM
authors.lastname: Kwappenberg
authors.forename: Eleni M
authors.initials: EM
authors.lastname: Varypataki
authors.forename: Susy J
authors.initials: SJ
authors.lastname: Santos
authors.forename: Marieke L
authors.initials: ML
authors.lastname: Kuijjer
authors.forename: Susan
authors.initials: S
authors.lastname: Mohamed
authors.forename: Juul T
authors.initials: JT
authors.lastname: Wijnen
authors.forename: Maarten J D
authors.initials: MJ
authors.lastname: van Tol
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Cleton-Jansen
authors.forename: R Maarten
authors.initials: RM
authors.lastname: Egeler
authors.forename: Wim
authors.initials: W
authors.lastname: Jiskoot
authors.forename: Arjan C
authors.initials: AC
authors.lastname: Lankester
authors.affiliation: Department of Pediatrics, Leiden University Medical Center, Leiden, the Netherlands. M.W.Schilham@lumc.nl.
authors.forename: Marco W
authors.initials: MW
authors.lastname: Schilham
mesh_terms: D000119:Acetylmuramyl-Alanyl-Isoglutamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001859:Bone Neoplasms / Q000188:drug therapy / Q000276:immunology* / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D018920:Coculture Techniques; D004354:Drug Screening Assays, Antitumor; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D016753:Interleukin-10 / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D008081:Liposomes; D008264:Macrophages / Q000276:immunology*; D012516:Osteosarcoma / Q000188:drug therapy / Q000276:immunology* / Q000473:pathology; D010714:Phosphatidylethanolamines / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; C508609:IL10 protein, human; D008070:Lipopolysaccharides; D008081:Liposomes; D010714:Phosphatidylethanolamines; D016753:Interleukin-10; C037144:mifamurtide; D000119:Acetylmuramyl-Alanyl-Isoglutamine; D007371:Interferon-gamma