Complete inhibition of ABCB1 and ABCG2 at the blood-brain barrier by co-infusion of erlotinib and tariquidar to improve brain delivery of the model ABCB1/ABCG2 substrate [11C]erlotinib

Abstract

P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) restrict at the blood-brain barrier (BBB) the brain distribution of the majority of currently known molecularly targeted anticancer drugs. To improve brain delivery of dual ABCB1/ABCG2 substrates, both ABCB1 and ABCG2 need to be inhibited simultaneously at the BBB. We examined the feasibility of simultaneous ABCB1/ABCG2 inhibition with i.v. co-infusion of erlotinib and tariquidar by studying brain distribution of the model ABCB1/ABCG2 substrate [¹¹C]erlotinib in mice and rhesus macaques with PET. Tolerability of the erlotinib/tariquidar combination was assessed in human embryonic stem cell-derived cerebral organoids. In mice and macaques, baseline brain distribution of [¹¹C]erlotinib was low (brain distribution volume, V_T,brain < 0.3 mL/cm³). Co-infusion of erlotinib and tariquidar increased V_T,brain in mice by 3.0-fold and in macaques by 3.4- to 5.0-fold, while infusion of erlotinib alone or tariquidar alone led to less pronounced V_T,brain increases in both species. Treatment of cerebral organoids with erlotinib/tariquidar led to an induction of Caspase-3-dependent apoptosis. Co-infusion of erlotinib/tariquidar may potentially allow for complete ABCB1/ABCG2 inhibition at the BBB, while simultaneously achieving brain-targeted EGFR inhibition. Our protocol may be applicable to enhance brain delivery of molecularly targeted anticancer drugs for a more effective treatment of brain tumors.

Keywords: Blood–brain barrier; P-glycoprotein; brain delivery; breast cancer resistance protein; transporter inhibition.

Figure 1.

Kinetics of [¹¹C]erlotinib in mice. Total radioactivity concentration in venous plasma collected at the end of the PET scan, measured in a gamma counter in all examined mouse groups (a). Time-activity curves (mean ± SD) in whole brain (b), AUC_brain values (c) and V_T,brain values (d) for all examined mouse groups. For comparison, AUC_brain and V_T,brain values are also shown for Abcb1a/b^(−/−)Abcg2^(−/−) mice measured in a previous study. **p < 0.01; ***p < 0.001; ****p < 0.0001, one-way ANOVA with Dunnett’s multiple comparisons test.

Figure 2.

[¹¹C]Erlotinib PET images in nonhuman primate. Representative coronal, axial and sagittal [¹¹C]erlotinib PET summation images (0–60 min) obtained in macaques without (a) or with treatment with erlotinib infusion alone (b), tariquidar infusion alone (c) or combined erlotinib/tariquidar infusion (d).

Figure 3.

Kinetics of [¹¹C]erlotinib in nonhuman primates. Metabolite-corrected arterial input function of parent [¹¹C]erlotinib in arterial plasma (a) and time-activity curves in the brain (b) and muscle tissue surrounding the brain (c) in macaques under the different tested conditions. Data are presented as individual values or mean ± SD (n = 2).

Figure 4.

Caspase-3 activation in hESC-derived cerebral organoids. Organoids were incubated for 24 h with medium with 0.1% DMSO (DMSO control), erlotinib hydrochloride (10 µg/mL, erlotinib), tariquidar dimesylate (5 µg/mL, tariquidar) and a combination of erlotinib hydrochloride (10 µg/mL) and tariquidar dimesylate (5 µg/mL) (erlotinib/tariquidar) (n = 1 cerebral organoid per treatment with eight slices analyzed per cerebral organoid). Results are expressed as percent of DMSO control. ***p < 0.001, one-way ANOVA with Dunnett’s multiple comparisons test.