Evaluation of ¹¹C-glyburide as a PET probe for P-gp and Bcrp transport imaging at the mouse BBB

Objectives The role and regulation of the efflux transporter Breast Cancer Resistance Protein (BCRP) at the BBB are not well known compared to the P-glycoprotein (P-gp, MDR1). The hypoglycaemic sulfonylurea glyburide (GLB) has been described has a specific substrate of BCRP. Moreover, this widely prescribed drug can be radiolabeled with carbone-11.

Methods ³H-GLB uptake in human BCRP- and MDR1-MDCKII transfected cells was measured (n=4) with or without addition of specific inhibitors: Fumitremorgin C 10 µM and PSC833 5µM, respectively. The brain transport of ³H-GLB was measured independently from peripheral metabolism or distribution by in situ brain perfusion method in wild-type (WT) mice with or without transport inhibitors (n= 4-7 mice) and in triple deficient Mdr_1a/1b^(-/-;-/-)Bcrp^(-/-) mice. ¹¹C-GLB was obtained by radiomethylation of its O-desmethyl precursor using ¹¹C-methyl-triflate. A PET dynamic acquisition was performed in this P-gp/Bcrp deficient strain and WT mice (n=2 and 3) using a microPET scanner following an IV injection of ¹¹C-GLB (~10 MBq). Brain uptake is reported as mean brain SUV measured at equilibrium from 10 to 18 min post-injection (SUV_(10-18)).

Results The uptake of ³H-GLB was increased 3.8 and 2.1-fold in BCRP and MDR1 cells, respectively, in the presence of respective inhibitors. The brain transport of ³H-GLB in WT mice was low (K_in = 0.40 ± 0.05 µL/g/s) and was significantly increased (~1.5-fold) in the presence of P-gp or BCRP chemical inhibitor. In triple deficient mice, K_in was 1.3 ± 0.18 µL/g/s. PET data also revealed a low brain uptake of ¹¹C-GLB with SUV_(10-18)= 0.014 ± 0.002 in WT mice. However, this uptake was only increased up to ~1.5-fold in triple deficient mice.

Conclusions GLB is efficiently transported by P-gp and BCRP, both decreasing its brain uptake at the mouse BBB. However, the net brain uptake of ¹¹C-GLB in triple deficient mice is not sufficiently enhanced to consider this tracer as a suitable probe to study P-gp and/or Bcrp efflux at the BBB