Fluorescein and radiolabeled Function-Spacer-Lipid constructs allow for simple in vitro and in vivo bioimaging of enveloped virions

Tools that can aid in vitro and in vivo imaging and also noninvasively determine half-life and biodistribution are required to advance clinical developments. A Function-Spacer-Lipid construct (FSL) incorporating fluorescein (FSL-FLRO4) was used to label vesicular stomatitis virus (VSV), measles virus MV–NIS (MV) and influenza virus (H1N1). The ability of FSL constructs to label these virions was established directly by FACScan of FSL-FLRO4 labeled VSV and MV, and indirectly following labeled H1N1 and MV binding to a cells. FSL-FLRO4 labeling of H1N1 was shown to maintain higher infectivity of the virus when compared with direct fluorescein virus labeling. A novel tyrosine 125I radioiodinated FSL construct was synthesized (FSL-125I) from FSL-tyrosine. This was used to label VSV (VSV-FSL-125I), which was infused into the peritoneal cavity of laboratory mice. Bioscanning showed VSV-FSL-125I to localize in the liver, spleen and bloodstream in contrast to the free labels FSL-125I or 125I, which localized predominantly in the liver and thyroid respectively. This is a proof-of-principle novel and rapid method for modifying virions and demonstrates the potential of FSL constructs to improve in vivo imaging of virions and noninvasively observe in vivo biodistribution.

► Novel Function-Spacer-Lipid (FSL) constructs were used to label virions. ► FSL constructs labeled virions in a dose dependent manner. ► FSL fluorescein allowed for direct and indirect virion visualization. ► Radioiodinated FSL allowed for noninvasive in vivo imaging of virions.