Factors Governing P-Glycoprotein-Mediated Drug–Drug Interactions at the Blood–Brain Barrier Measured with Positron Emission Tomography

Abstract

The adenosine triphosphate-binding cassette transporter P-glycoprotein (ABCB1/Abcb1a) restricts at the blood–brain barrier (BBB) brain distribution of many drugs. ABCB1 may be involved in drug–drug interactions (DDIs) at the BBB, which may lead to changes in brain distribution and central nervous system side effects of drugs. Positron emission tomography (PET) with the ABCB1 substrates (R)-[11C]verapamil and [11C]-N-desmethyl-loperamide and the ABCB1 inhibitor tariquidar has allowed direct comparison of ABCB1-mediated DDIs at the rodent and human BBB. In this work we evaluated different factors which could influence the magnitude of the interaction between tariquidar and (R)-[11C]verapamil or [11C]-N-desmethyl-loperamide at the BBB and thereby contribute to previously observed species differences between rodents and humans. We performed in vitro transport experiments with [3H]verapamil and [3H]-N-desmethyl-loperamide in ABCB1 and Abcb1a overexpressing cell lines. Moreover we conducted in vivo PET experiments and biodistribution studies with (R)-[11C]verapamil and [11C]-N-desmethyl-loperamide in wild-type mice without and with tariquidar pretreatment and in homozygous Abcb1a/1b(−/−) and heterozygous Abcb1a/1b(+/−) mice. We found no differences for in vitro transport of [3H]verapamil and [3H]-N-desmethyl-loperamide by ABCB1 and Abcb1a and its inhibition by tariquidar. [3H]-N-Desmethyl-loperamide was transported with a 5 to 9 times higher transport ratio than [3H]verapamil in ABCB1- and Abcb1a-transfected cells. In vivo, brain radioactivity concentrations were lower for [11C]-N-desmethyl-loperamide than for (R)-[11C]verapamil. Both radiotracers showed tariquidar dose dependent increases in brain distribution with tariquidar half-maximum inhibitory concentrations (IC50) of 1052 nM (95% confidence interval CI: 930–1189) for (R)-[11C]verapamil and 1329 nM (95% CI: 980–1801) for [11C]-N-desmethyl-loperamide. In homozygous Abcb1a/1b(−/−) mice brain radioactivity distribution was increased by 3.9- and 2.8-fold and in heterozygous Abcb1a/1b(+/−) mice by 1.5- and 1.1-fold, for (R)-[11C]verapamil and [11C]-N-desmethyl-loperamide, respectively, as compared with wild-type mice. For both radiotracers radiolabeled metabolites were detected in plasma and brain. When brain and plasma radioactivity concentrations were corrected for radiolabeled metabolites, brain distribution of (R)-[11C]verapamil and [11C]-N-desmethyl-loperamide was increased in tariquidar (15 mg/kg) treated animals by 14.1- and 18.3-fold, respectively, as compared with vehicle group. Isoflurane anesthesia altered [11C]-N-desmethyl-loperamide but not (R)-[11C]verapamil metabolism, and this had a direct effect on the magnitude of the increase in brain distribution following ABCB1 inhibition. Our data furthermore suggest that in the absence of ABCB1 function brain distribution of [11C]-N-desmethyl-loperamide but not (R)-[11C]verapamil may depend on cerebral blood flow. In conclusion, we have identified a number of important factors, i.e., substrate affinity to ABCB1...

Imaging the impact of cyclosporin A and dipyridamole on P-glycoprotein (ABCB1) function at the blood-brain barrier: A [11C]-N-desmethyl-loperamide PET study in nonhuman primates

“…In Human, [ 11 C]dLop was shown to be poorly metabolized, allowing for accurate estimation of the P-gp function at the BBB. [ 11 C]dLop brain distribution was shown to be sensitive to P-gp inhibition in both the human and non-human primates using prototypical P-gp inhibitors such as DCPQ (Liow et al, 2009) or tariquidar (Kreisl et al, 2010), although being less sensitive than [ 11 C]verapamil to detect partial and low degree of P-gp inhibition using tariquidar in mice (Wanek et al, 2015). Non-human primates have been shown to be more relevant than rodents to study P-gp function at the BBB, given the high differences in P-gp expression between rodents and primates (Hoshi et al, 2013).…”

“…In human, Kreisl et al reported a 5-fold increase in AUC 10-30 using tariquidar 4 mg/kg as an inhibitor and hypothesized that P-gp remained only partially inhibited in this condition (Kreisl et al, 2015). In rats, P-gp inhibition using high dose CsA (50 mg/kg) resulted in a smaller 3.5-fold increase in the brain-to-plasma concentration ratio, estimated using the total volume of distribution (V T ) in the 1-tissue compartment model (Farwell et al, 2013), although the in vitro transport of [ 11 C]dLop was shown similar in P-gp overexpressing cells transfected using either the rodent Abcb1a or the human ABCB1 gene (Wanek et al, 2015). The brain-to-plasma ratio observed in anesthetized mice was only 6 to 7-fold higher in P-gp deficient (Abcb1a/1b (-/-) ) as compared with wild-type mice (Lazarova et al, 2008;Wanek et al, 2015).…”

“…In rats, P-gp inhibition using high dose CsA (50 mg/kg) resulted in a smaller 3.5-fold increase in the brain-to-plasma concentration ratio, estimated using the total volume of distribution (V T ) in the 1-tissue compartment model (Farwell et al, 2013), although the in vitro transport of [ 11 C]dLop was shown similar in P-gp overexpressing cells transfected using either the rodent Abcb1a or the human ABCB1 gene (Wanek et al, 2015). The brain-to-plasma ratio observed in anesthetized mice was only 6 to 7-fold higher in P-gp deficient (Abcb1a/1b (-/-) ) as compared with wild-type mice (Lazarova et al, 2008;Wanek et al, 2015). Interestingly, the brain-to-plasma ratio measured in awake non-anesthetized animals was 14-fold higher in Abcb1a/1b (-/-) mice as compared to wild-type mice (Wanek et al, 2015).…”

“…Compared to [ 11 C]verapamil, [ 11 C]dLop benefits from poor metabolism and improved A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPT 5 metabolic stability in humans (Kannan et al, 2009;Kreisl et al, 2010), although extensively metabolized in mice (Wanek et al, 2015). In drug development, the use of PET in combination with [ 11 C]dLop may be an appealing approach for the non-invasive study of the potency of new chemical entities to inhibit P-gp function at the BBB (Wulkersdorfer et al, 2014).…”

Blood-brain Barrier Remodeling during Brain Metastasis Formation

“…Additionally, cells that constitute the BBB express enhanced levels of active drug efflux transporters of the ATP-binding cassette (ABC) gene family, which have been recognized as key determinants of drug distribution to, and elimination from, the CNS (58,77). The most widely characterized transporter of the ABC family is P-glycoprotein (P-gp), which has been a subject of numerous investigations and for years was considered a major obstacle in the delivery of therapeutics into the brain (78,79). Recent studies indicated P-gp function is largely supported by the breast cancer resistance protein (BCRP), and overexpression of BCRP is associated with resistance to a wide range of different anticancer agents including mitoxantrone, camptothecins, anthracyclines, flavopiridol and antifolates (80,81).…”