Abstract

Cyclodextrins are well-characterized barrel-shaped molecules that can solubilize organic small molecules in aqueous solution via host-guest interactions. As such, cyclodextrins are used as excipients for experimental therapeutics in vivo. We observed unanticipated modifications to bioluminescence imaging (BLI) signal intensity when 2-hydroxy-propyl-β-cyclodextrin (HPCD) was co-injected as an excipient. We hypothesized that HPCD binds D-luciferin and interferes with the BLI signal. Using luciferase-expressing cell lines, we showed that HPCD lowers the BLI signal in a concentration-dependent manner. Flow cytometry revealed that HPCD resulted in reduced cellular accumulation of D-luciferin, and mass spectrometry revealed D-luciferin-HPCD species, confirming a direct interaction. In vivo imaging using a luciferase mouse model demonstrated that HPCD reduced luciferin-mediated BLI compared with luciferin alone. The implications of using HPCD as an excipient in BLI studies is discussed.