Mechanistic Basis of Cabotegravir–Glucuronide Disposition in Humans

Abstract

Cabotegravir, a novel integrase inhibitor under development for treatment and prevention of HIV, is primarily metabolized by UGT1A1 and UGT1A9 to a direct ether glucuronide metabolite. The aim of these studies was to elucidate the mechanistic basis of cabotegravir-glucuronide disposition in humans. Cabotegravir glucuronidation was predominantly hepatic (.95%) with minimal intestinal and renal contribution. Rat liver perfusions demonstrated that cabotegravir-glucuronide formed in the liver undergoes comparable biliary and sinusoidal excretion, consistent with high concentrations of the glucuronide in human bile and urine. Cabotegravir-glucuronide biliary excretion was mediated by MRP2 (not transported by BCRP or P-gp), whereas hepatic basolateral excretion into sinusoidal blood was via both MRP3 (Ft 5 0.81) and MRP4 (Ft 5 0.19). Surprisingly, despite high urinary recovery of hepatically-formed cabotegravir-glucuronide, metabolite levels in circulation were negligible, a phenomenon consistent with rapid metabolite clearance. Cabotegravir-glucuronide was transported by hepatic uptake transporters OATP1B1 and OATP1B3; however, metabolite clearance by hepatic uptake from circulation was low (2.7% of hepatic blood flow) and unable to explain the minimal systemic exposure. Instead, circulating cabotegravir-glucuronide undergoes efficient renal clearance, where uptake into the proximal tubule would be mediated by OAT3 (not transported by OAT1), and subsequent secretion into urine by MRP2 (Ft 5 0.66) and MRP4 (Ft 5 0.34). These studies provide mechanistic insight into the disposition of cabotegravir-glucuronide, a hepatically-formed metabolite with appreciable urinary recovery and minimal systemic exposure, including fractional contribution of redundant transporters to any given process based on quantitative proteomics. SIGNIFICANCE STATEMENT The role of membrane transporters in metabolite disposition, especially glucuronides, and as sites of unexpected drug-drug interactions, which alter drug efficacy and safety, has been established. Cabotegravir-glucuronide, formed predominantly by direct glucuronidation of parent drug in liver, was the major metabolite recovered in human urine (27% of oral dose) but was surprisingly not detected in systemic circulation. To our knowledge, this is the first mechanistic description of this phenomenon for a major hepatically-formed metabolite to be excreted in the urine to a large extent, but not circulate at detectable levels. The present study elucidates the mechanistic basis of cabotegravir-glucuronide disposition in humans. Specific hepatic and renal transporters involved in the disposition of cabotegravir-glucuronide, with their fractional contribution, have been provided.

The Role of Uptake and Efflux Transporters in the Disposition of Glucuronide and Sulfate Conjugates

“…However, MRP3 and MRP4 levels have been shown to increase in several liver diseases ( Drozdzik et al, 2020 ; Vildhede et al, 2020 ), possibly as an alternative efflux route in hepatocytes in the case of dysfunctional MRP2. MRP3/MRP4 efflux is also a likely prerequisite for hydrophilic conjugates, such as diclofenac-AG, cabotegavir-G and sulfonyloxyaristolactam, formed in the liver, to reach the blood circulation and be excreted into urine ( Zhang et al, 2016 ; Chang et al, 2017 ; Patel et al, 2019 ). The interplay between basolateral efflux and uptake transporters in the liver results in a phenomenon called hepatocyte hopping, where transporter substrates are shuttled back and forth between the sinusoidal blood and hepatocytes along the sinusoids ( Iusuf et al, 2012 ).…”

“…On the apical membranes of the proximal tubules, MATE1, MRP2, MRP4 and P-gp, are responsible for efflux into urine ( Prasad et al, 2016 ). For example, MRP2 and MRP4 participate in the renal excretion of endogenous glucuronide and sulfate conjugates and may also facilitate excretion of drug conjugates such as glucuronides of non-steroidal anti-inflammatory drugs (NSAIDs), cabotegravir-G and mycophenolic acid glucuronide (MPA-G) ( Regan et al, 2010 ; Matsunaga et al, 2014 ; Järvinen et al, 2018 ; Li et al, 2019a ; Patel et al, 2019 ). BCRP, MRP3, MATE2/2K ( SLC47A2 ) and OAT2 are present only at low levels, but may contribute to active renal secretion ( Fallon et al, 2016 ; Prasad et al, 2016 ; Li et al, 2019b ; Cheung et al, 2019 ; Oswald et al, 2019 ).…”

“…Morinidazole-S, edaravone-S and diclofenac-AG are transported by both OAT1 and OAT3 ( Mizuno et al, 2007a ; Zhong et al, 2014 ; Zhang et al, 2016 ; Huo et al, 2020 ). On the other hand, OAT3, but not OAT1, transports ethinylestradiol-S and glucuronides such as of cabotegravir-G, curcumin-G, genistein-7-G, steviol-G and MPA-G ( Uwai et al, 2007 ; Han et al, 2010a ; Wong et al, 2011b ; Wang M. et al, 2015 ; Zhou et al, 2017 ; Patel et al, 2019 ). Moreover, OAT3, but not OAT1, transports endogenous sulfates estrone-S and DHEAS ( Ueo et al, 2005 ) and relebactam, which is a drug molecule containing a sulfate group ( Chan et al, 2019 ).…”

“…Approximately 20% of the oral dose is recovered in urine as cabotegravir-G, but cabotegravir-G levels in the systemic circulation are negligible ( Bowers et al, 2016 ). This behavior is explained by efficient renal elimination of cabotegravir-G that is mediated by OAT3 on the apical and MRP2 and MRP4 on the basolateral membranes of renal proximal tubule cells ( Patel et al, 2019 ). In addition, renal glucuronidation of cabotegravir by UGT1A9 and direct efflux of the metabolite into urine may contribute to the renal excretion of cabotegravir-G.…”

Identification of Novel UGT1A1 Variants Including UGT1A1 454C>A through the Genotyping of Healthy Participants of the HPTN 077 Study

“…Specific transporters (both efflux and uptake) involved in the disposition of CAB-glucuronide in humans have been identified. 38 Therefore, the differences in expression of transporters such as multidrug resistance-associated protein 2 (MRP2), MRP3, MRP4, organic anion transporting polypeptide 1B1 (OATP1B1), OATP1B3, and organic anion transporter 3 (OAT3) may contribute to the observed interindividual differences in CAB-glucuronide levels.…”