Organic anion transporter 1 (OAT1/SLC22A6) enhances bioluminescence based on d-luciferin–luciferase reaction in living cells by facilitating the intracellular accumulation of d-luciferin

Abstract Bioluminescence (BL) imaging based on d -luciferin ( d -luc)–luciferase reaction allows noninvasive and real-time monitoring of luciferase-expressing cells. Because BL intensity depends on photons generated through the d -luc–luciferase reaction, an approach to increase intracellular levels of d -luc could improve the detection sensitivity. In the present study, we showed that organic anion transporter 1 (OAT1) is useful, as a d -luc transporter, in boosting the BL intensity in luciferase-expressing cells. Functional screening of several transporters showed that the expression of OAT1 in HEK293 cells stably expressing Pyrearinus termitilluminans luciferase (HEK293/eLuc) markedly enhanced BL intensity in the presence of d -luc. When OAT1 was transiently expressed in HEK293 cells, intracellular accumulation of d -luc was higher than that in control cells, and the specific d -luc uptake mediated by OAT1 was saturable with a Michaelis constant (K m ) of 0.23 μM. The interaction between OAT1 and d -luc was verified using 6-carboxyfluorescein, a typical substrate of OAT1, which showed that d -luc inhibited the uptake of 6-carboxyfluorescein mediated by OAT1. BL intensity was concentration-dependent at steady states in HEK293/eLuc cells stably expressing OAT1, and followed Michaelis–Menten kinetics with an apparent K m of 0.36 μM. In addition, the enhanced BL was significantly inhibited by OAT1-specific inhibitors. Thus, OAT1-mediated transport of d -luc could be a rate-limiting step in the d -luc–luciferase reaction. Furthermore, we found that expressing OAT1 in HEK293/eLuc cells implanted subcutaneously in mice also significantly increased the BL after intraperitoneal injection of d -luc. Our findings suggest that because OAT1 is capable of transporting d -luc, it can also be used to improve visualization and monitoring of luciferase-expressing cells.