Targeting Pro-Tumoral Macrophages in Early Primary and Metastatic Breast Tumors with the CD206-Binding mUNO Peptide

Mol Pharm. 2020 Jul 6;17(7):2518-2531. doi: 10.1021/acs.molpharmaceut.0c00226. Epub 2020 Jun 1.


M2-like tumor-associated macrophages (M2 TAMs) play important roles in the resistance of tumors to immunotherapies. Selective depletion or reprogramming of M2 TAMs may sensitize the nonresponsive tumors for immune-mediated eradication. However, precision delivery of payloads to M2 TAMs, while sparing healthy tissues, has remained an unresolved challenge. Here, we studied the application of a short linear peptide (CSPGAK, "mUNO") for the delivery of molecular and nanoscale cargoes in M2 TAMs in vitro and the relevance of the peptide for in vivo targeting of early-stage primary breast tumors and metastatic lung foci. First, we performed in silico modeling and found that mUNO interacts with mouse CD206 via a binding site between lectin domains CTLD1 and CTLD2, the same site previously demonstrated to be involved in mUNO binding to human CD206. Second, we showed that cultured M2 macrophages take up fluorescein-labeled (FAM) polymersomes conjugated with mUNO using the sulfhydryl group of its N-terminal cysteine. Pulse/chase studies of FAM-mUNO in M2 macrophages suggested that the peptide avoided lysosomal entrapment and escaped from early endosomes. Third, our in vivo studies with FAM-mUNO demonstrated that intraperitoneal administration results in better pharmacokinetics and higher blood bioavailability than can be achieved with intravenous administration. Intraperitoneal FAM-mUNO, but not FAM-control, showed a robust accumulation in M2-skewed macrophages in mouse models of early primary breast tumor and lung metastasis. This targeting was specific, as no uptake was observed in nonmalignant control organs, including the liver, or other cell types in the tumor, including M1 macrophages. Collectively, our studies support the application of the CD206-binding mUNO peptide for delivery of molecular and nanoscale cargoes to M2 macrophages and manifest the relevance of this mode of targeting primary and metastatic breast tumors.

Keywords: CD206; drug delivery systems; homing peptide; immunotherapy; nanomedicine; pharmacokinetics; triple-negative breast cancer; tumor-associated macrophages.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Binding Sites
  • Cell Differentiation
  • Cell Line, Tumor
  • Drug Carriers / administration & dosage
  • Drug Carriers / chemistry
  • Drug Carriers / metabolism
  • Drug Carriers / pharmacokinetics
  • Female
  • Fluorescence
  • Humans
  • Immunotherapy / methods*
  • Lectins, C-Type / chemistry*
  • Lectins, C-Type / immunology
  • Lectins, C-Type / metabolism
  • Lung Neoplasms / diagnosis*
  • Lung Neoplasms / diagnostic imaging
  • Lung Neoplasms / pathology
  • Lung Neoplasms / secondary
  • Lymphatic Metastasis / diagnosis*
  • Lymphatic Metastasis / diagnostic imaging
  • Lymphatic Metastasis / immunology
  • Lysosomes / metabolism
  • Maleimides / chemistry
  • Mannose-Binding Lectins / chemistry*
  • Mannose-Binding Lectins / immunology
  • Mannose-Binding Lectins / metabolism
  • Mice
  • Mice, Inbred BALB C
  • Microscopy, Electron, Transmission
  • Peptides / administration & dosage
  • Peptides / chemistry*
  • Peptides / metabolism
  • Peptides / pharmacokinetics
  • Polyesters / chemistry
  • Polyethylene Glycols / chemistry
  • Polymers / administration & dosage
  • Polymers / chemistry
  • Polymers / pharmacology
  • Receptors, Cell Surface / chemistry*
  • Receptors, Cell Surface / immunology
  • Receptors, Cell Surface / metabolism
  • Triple Negative Breast Neoplasms / diagnosis*
  • Triple Negative Breast Neoplasms / diagnostic imaging
  • Triple Negative Breast Neoplasms / pathology
  • Tumor-Associated Macrophages / immunology*
  • Tumor-Associated Macrophages / metabolism


  • Drug Carriers
  • Lectins, C-Type
  • Maleimides
  • Mannose-Binding Lectins
  • Peptides
  • Polyesters
  • Polymers
  • Receptors, Cell Surface
  • mannose receptor
  • polycaprolactone
  • maleimide
  • Polyethylene Glycols