Investigation of the role of breast cancer resistance protein (Bcrp/Abcg2) on pharmacokinetics and central nervous system penetration of abacavir and zidovudine in the mouse

Abstract

Many anti-human immunodeficiency virus 1 nucleoside reverse-transcriptase inhibitors have low central nervous system (CNS) distribution due in part to active efflux transport at the blood-brain barrier. We have previously shown that zidovudine (AZT) and abacavir (ABC) are in vitro substrates for the efflux transport protein breast cancer resistance protein (Bcrp) 1. We evaluated the influence of Bcrp1 on plasma pharmacokinetics and brain penetration of zidovudine and abacavir in wild-type and Bcrp1-deficient (Bcrp1-/-) FVB mice. There was no difference in either area under the concentration-time profiles for plasma (AUC(plasma)) or brain (AUC(brain)) for zidovudine between the wild-type and Bcrp1-/- mice. The AUC(plasma) of abacavir was 20% lower in the Bcrp1-/- mice, whereas the AUC(brain) was 20% greater. This difference resulted in a 1.5-fold increase in abacavir brain exposure in the Bcrp1-/- mice. The effect of selective and nonselective transport inhibitors on the ABC brain/plasma ratio at a single time point was evaluated. 3-(6-Isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6, 7,12,12a-octahydropyrazino[1',2':1,6]pyrido[3,4-b]indol-3-yl)-propionicacid tert-butyl ester (Ko143), N[4[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)ethyl]phenyl]-5-methoxy-9-oxo-10H-acridine-4-carboxamide (GF120918), probenecid, and Pluronic P85 increased abacavir plasma concentrations in the wild-type mice. Abacavir plasma concentrations in Bcrp1-/- mice were increased by (R)-4-((1aR,6R,10bS)-1,2-difluoro-1,1a,6,10b-tetrahydrodibenzo (a,e)cyclopropa(c)cycloheptan-6-yl)-alpha-((5-quinoloyloxy)methyl)-1-piperazineethanol trihydrochloride (LY335979), GF120918, and probenecid, but not by Ko143. Brain/plasma concentration ratios in both the wild-type and Bcrp1-/- mice were increased by the P-glycoprotein inhibitors LY335979 and GF120918, but not by BCRP-selective inhibitors. These data indicate that deletion of Bcrp1 has little influence on the pharmacokinetics or brain penetration of AZT. However, for abacavir, deletion of Bcrp1 reduces plasma exposure and enhances brain penetration. These findings suggest that Bcrp1 does not play a significant role in limiting the CNS distribution of zidovudine and abacavir; however, brain penetration of abacavir is dependent on P-glycoprotein-mediated efflux.

Fig. 1

Structures of nucleoside substrates AZT and abacavir ABC.

Fig. 2

Accumulation of [¹⁴C]AZT, [³H]ABC, [³H]3TC, [³H]d4T, [³H]ddI, and [³H]ddC in the wild-type (□) and Bcrp1-transfected () MDCKII cells. Results are expressed as means ± S.D.; n = 3. ***, p < 0.001, compared with the wild-type control group.

Fig. 3

Concentration-time profile of AZT in Bcrp1^−/− and wild-type FVB mice after i.v. dosing (15 mg/kg). A, concentration-time profiles of AZT in plasma of Bcrp1^−/− (◊) and wild-type (♦) FVB mice. B, concentration-time profiles in brain tissue of Bcrp1^−/− (○) and wild-type (●) FVB mice. Data are represented as means ± S.D.

Fig. 4

Comparison of the C^b/C^p ratios between wild-type and Bcrp1-deficient FVB mice at different sampling time points. A, the C^b/C^p ratio for AZT in the Bcrp1-deficient mice was not different from that in the wild-type mice at any time points. n = 5–6 per time point. B, the C^b/C^p ratio for ABC in the Bcrp1-deficient mice was significantly higher than that in the wild-type mice at 5, 10, and 40 min postdose. **, p < 0.01. n = 4–5 per time point. The results are expressed as means ± S.D.

Fig. 5

Concentration-time profile of ABC in Bcrp1^−/− and wild-type FVB mice after i.v. dosing (10 mg/kg). A, concentration-time profiles of ABC in plasma of Bcrp1^−/− (◊) and wild-type (♦) FVB mice. B, concentration-time profiles in brain tissue of Bcrp1^−/− (○) and wild-type (●) FVB mice. Data are represented as means ± S.D.

Fig. 6

Effect of inhibitors on the plasma (A) and brain (B) concentrations of ABC in wild-type FVB mice after i.v. dosing. □, control (10 mg/kg); , 25 mg/kg LY335979; ▨, 1 mg/kg Ko413; is ▩, 10 mg/kg GF120918; ▤, 200 mg/kg probenecid; ▦, 20 mg/kg Pluronic P85. Results are expressed as means ± S.D.; n = 4. ***, p < 0.001; **, p < 0.01 compared with the respective wild-type controls.

Fig. 7

Effect of inhibitors on the C^b/C^p ratios 20 min postdose in wild-type (A) and Bcrp1^−/− (B) FVB mice after i.v. □, control (10 mg/kg); , 25 mg/kg LY335979; ▨, 1 mg/kg Ko413; ▩, 10 mg/kg GF120918; ▤, 200 mg/kg probenecid; ▦, 20 mg/kg Pluronic P85. Results are expressed as means ± S.D.; n = 4. ***, p < 0.001. compared with the respective wild-type and Bcrp1^−/− controls.

Fig. 8

Effect of inhibitors on the plasma (A) and brain (B) concentrations of ABC in Bcrp1^−/− FVB mice after i.v. dosing. □, control (10 mg/kg); , 25 mg/kg LY335979; ▨, 1 mg/kg Ko413; ▩, 10 mg/kg GF120918; ▤, 200 mg/kg probenecid; ▦, 20 mg/kg Pluronic P85. Results are expressed as means ± S.D.; n = 4. ***, p < 0.001; **, p < 0.01 compared with the respective Bcrp1^−/− controls.