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.