Liposomal Extravasation and Accumulation in Tumors as Studied by Fluorescence Microscopy and Imaging Depend on the Fluorescent Label

Guankui Wang, Markella Zannikou, Laren Lofchy, Yue Li, Hanmant Gaikwad, Irina V. Balyasnikova, Dmitri Simberg*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations

Abstract

Tumor trafficking of liposomes is routinely monitored via fluorescence microscopy and imaging. To investigate whether an accumulation of liposomes depends on the type of fluorescent label, we prepared PEGylated liposomes dual-labeled with indocarbocyanine lipids (ICLs: DiD or DiI) and fluorescent phospholipids (FPLs: Cy3-DSPE or Cy5-DSPE) with similar cyanine headgroups but different spectra. Using ex vivo confocal microscopy and imaging, we compared tumor extravasation and accumulation of ICLs and FPLs. After systemic injection in a syngeneic mouse model of 4T1 breast cancer, ICLs and FPLs initially colocalized in tumor blood vessels and perivascular space. At later time points, ICLs spread over a significantly larger tumor area and accumulated in tumor macrophages, whereas FPLs were mostly restricted to the vasculature with limited extravascular signal. This phenomenon was independent of liposomal composition and ICL/FPL type and was also observed in syngeneic intracranial GL261 glioma and LY2 head and neck cancer models. The dual-labeled liposomes were stable in plasma and delivered both dyes to tumors at early time points. Notably, while the level of ICLs increased over time, FPLs gradually disappeared from tumors and other organs in vivo, likely due to degradation of the phospholipid. These findings demonstrate that trafficking and stability of the label is of critical importance when assessing extravasation and accumulation of nanocarriers in tumors and other organs by fluorescence microscopy and imaging.

Original languageEnglish (US)
Pages (from-to)11880-11890
Number of pages11
JournalACS nano
Volume15
Issue number7
DOIs
StatePublished - Jul 27 2021

Keywords

  • confocal microscopy
  • endothelium
  • extravasation
  • fluorescence
  • lipids
  • liposome

ASJC Scopus subject areas

  • Materials Science(all)
  • Engineering(all)
  • Physics and Astronomy(all)

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