High-dose etoposide formulations do not saturate intestinal P-glycoprotein: Development, stability, and pharmacokinetics in Sprague-Dawley rats

Abstract

It has been suggested that oral absorption of low-permeable P-glycoprotein (P-gp) substrates can be increased through saturation of P-gp. For BCS class IV drug substances, saturating P-gp is challenging due to low aqueous solubility. The present study investigated if the BCS IV drug substance etoposide could be solubilized to a concentration saturating P-gp after oral administration.A formulation consisting of 10% (w/v) of pluronic ® F-127 and polyvinylpyrrolidone/vinyl acetate (PVP/VA), and 57% (v/v) ethanol enhanced etoposide's solubility approximately 100 times (16 mg mL -1 ) compared to its aqueous solubility. In vitro, this formulation was stable upon dilution in simulated intestinal fluid. In male Sprague-Dawley rats, oral administration of increasing solubilized etoposide doses using the formulation matrix increased the AUC0-∞ of etoposide dose-proportionally but resulted in a lower absolute oral bioavailability (F) and rate of absorption as compared to control.At the highest investigated dose (100 mg kg -1 ), AUC0-∞ and Cmax were significantly increased by 2.9and 1.4-fold, respectively, compared to control dosed at 20 mg kg -1 . A single oral dose of 20 mg kg -1 zosuquidar followed by 20 mg kg -1 oral etoposide increased F 8.6-fold. In conclusion, a stable formulation with improved etoposide solubility was developed, yet the formulation did not result in increased oral bioavailability of etoposide.

Oral etoposide and zosuquidar bioavailability in rats: Effect of co-administration and in vitro-in vivo correlation of P-glycoprotein inhibition

“…In the case of 20 mg/kg zosuquidar co-administration, the bioavailability increased in a statistically significant manner to 20.5 ± 2.7%, however, it was lower than the groups that received 6.3 and 2.0 mg/kg zosuquidar co-administrations. Al-Ali et al (2020) conducted a study under similar conditions in the same facilities, where 20 mg/kg etoposide was dosed orally in 7 mL/kg 57% ethanol, corresponding to the same dose of etoposide and ethanol as in the present study. The resulting etoposide bioavailability was 34.5 ± 0.2% (shown as a square in Fig.…”

“…5 ), where 20 mg/kg zosuquidar was not included (R 2 = 0.656). Etoposide bioavailability after oral co-administration of 20 mg/kg etoposide and 20 mg/kg zosuquidar from Al-Ali et al, 2020 reprinted for comparison. Shown as mean ± SEM, n = 6, SEMs smaller than the symbol size are not shown.…”

“…In oral absorption studies, zosuquidar has been dosed at maximally two different doses, and consequently, systematic investigations of the dose-response relationship of zosuquidar on the oral absorption and oral pharmacokinetics of P-gp substrates are lacking. For example, 20 mg/kg oral zosuquidar increased the oral bioavailability of etoposide from 4.0% to 34.5% ( Al-Ali et al, 2020 ), which was significant, but still far from the 92% oral etoposide bioavailability reported in mdr1a(−/−) knockout rats ( Al-Ali et al, 2018a ). These findings indicated that a 20 mg/kg dose of zosuquidar did not completely inhibit the P-gp function.…”

“…Although zosuquidar is not marketed as a P-gp inhibitor, it has been heavily utilised as a model inhibitor in the research of ADME properties of potential P-gp substrates. For instance, zosuquidar has commonly been applied to alter the distribution of P-gp substrates to the CNS by inhibition of P-gp mediated cellular efflux in the blood-brain barrier ( Bihorel et al, 2007 ; Chen et al, 2009 ; Choo et al, 2000 ; Dai et al, 2003 ; Karssen et al, 2002 ; Mittapalli et al, 2012 ; Nagaya et al, 2020 ) and to a lesser extent to increase the oral absorption of P-gp substrates ( Adane et al, 2012 ; Al-Ali et al, 2020 ; Bardelmeijer et al, 2004 ; Matsuda et al, 2013 ; Mouly et al, 2004 ; Kono et al, 2021 ; Tsukimoto et al, 2015 ). Recently, the influence of factors such as sex, dosing time, and food intake on P-gp expression and function in the small intestine has also been investigated ( Dou et al, 2020 ; Mai et al, 2019 ; Mai et al, 2018 ; Mai et al, 2021 ), and zosuquidar has been applied as an inhibitor in this context as well ( Kara et al, 2021 ).…”

Combinational Inhibition of P-Glycoprotein-Mediated Etoposide Transport by Zosuquidar and Polysorbate 20

“…Several formulation approaches have been attempted to increase oral etoposide absorption by either inhibiting P-gp with inhibitors or increasing the solubility of etoposide in the intestine to saturate P-gp. The formulations were, e.g., an oral solution containing surfactants [ 7 ], oral supersaturated solutions containing surfactants [ 10 ], and amorphous solid dispersions of etoposide:copovidon:eudragit L-100 [ 8 ]. There is, however, still a need to develop formulations that can increase the bioavailability of P-gp substrates.…”