Trantinterol, a novel β2-adrenoceptor agonist, noncompetitively inhibits P-glycoprotein function in vitro and in vivo

Impact of molecular weight on the mechanism of cellular uptake of polyethylene glycols (PEGs) with particular reference to P-glycoprotein

Polyethylene glycols (PEGs) in general use are polydisperse molecules with molecular weight (MW) distributed around an average value applied in their designation e.g., PEG 4000. Previous research has shown that PEGs can act as P-glycoprotein (P-gp) inhibitors with the potential to affect the absorption and efflux of concomitantly administered drugs. However, questions related to the mechanism of cellular uptake of PEGs and the exact role played by P-gp has not been addressed. In this study, we examined the mechanism of uptake of PEGs by MDCK-mock cells, in particular, the effect of MW and interaction with P-gp by MDCK-hMDR1 and A549 cells. The results show that: (a) the uptake of PEGs by MDCK-hMDR1 cells is enhanced by P-gp inhibitors; (b) PEGs stimulate P-gp ATPase activity but to a much lesser extent than verapamil; and (c) uptake of PEGs of low MW (<2000 Da) occurs by passive diffusion whereas uptake of PEGs of high MW (>5000 Da) occurs by a combination of passive diffusion and caveolae-mediated endocytosis. These findings suggest that PEGs can engage in P-gp-based drug interactions which we believe should be taken into account when using PEGs as excipients and in PEGylated drugs and drug delivery systems.

Effect of treatment period with LC478, a disubstituted adamantayl derivative, on P-glycoprotein inhibition: its application to increase docetaxel absorption in rats

1. Treatment periods of P-glycoprotein (P-gp) inhibitors have revealed different efficacies. We have previously reported dose-dependent inhibition of P-gp in single-treatment with LC478. However, whether repeated treatment with LC478 can inhibit P-gp even at its ineffective single-treatment dose remains unknown. 2. Therefore, the purpose of this study was to assess the effect of repeated treatment (i.e., 7-day treatment) with LC478 on P-gp known to affect docetaxel bioavailability in rats. Effects of LC478 on P-gp mediated efflux and expression in MDCK-MDR1 cells, P-gp ATPase activity, and binding site with P-gp were evaluated.3. The 7-day treatment with LC478 increased docetaxel absorption via intestinal P-gp inhibition in rats. Intestinal concentrations of LC478 were 8.31-10.3 μM in rats after 7-day treatment of LC478. These concentrations were close to 10 μM that reduced P-gp mediated docetaxel efflux and P-gp expression in MDCK-MDR1 cells. Considering that intestinal LC478 concentrations after 1-day treatment were 2.68-4.19 μM, higher LC478 concentrations after 7-day treatment might have driven P-gp inhibition and increased docetaxel absorption. LC478 might competitively inhibit P-gp considering its stimulated ATPase activity and its binding site with nucleotide binding domain of P-gp. 4. Therefore, repeated treatment with LC478 can determine its feasibility for P-gp inhibition and changing docetaxel bioavailability.

Effects of Piperazine Derivative on Paclitaxel Pharmacokinetics

Paclitaxel (PTX) is an anticancer agent that is used to treat many cancers but it has a very low oral bioavailability due, at least in part, to the drug efflux transporter, P-glycoprotein (P-gp). Therefore, this study was performed to enhance oral bioavailability of PTX. In this study, we investigated the effects of several piperazine derivatives on P-gp function in vitro. Compound 4 was selected as the most potent P-gp inhibitor from the in vitro results for examining the pharmacokinetic (PK) changes of PTX in rats. Compound 4 increased the AUC_inf of PTX without alterations in the C_max value. The elimination half-life was extended and the oral clearance decreased. Additionally, the T_max was delayed or widened in the treatment groups. Therefore, the bioavailability (BA) of PTX was improved 2.1-fold following the co-administration of 5 mg/kg of the derivative. A piperazine derivative, compound 4, which was confirmed as a substantial P-gp inhibitor in vitro increased the BA of PTX up to 2-fold by a lingering absorption, in part due to inhibition of intestinal P-gp and a low oral clearance of PTX. These results suggest that co-administering compound 4 may change the PK profile of PTX by inhibiting P-gp activity in the body.

Inhibition of P-Glycoprotein Mediated Efflux in Caco-2 Cells by Phytic Acid

Phytic acid (IP6) is a natural phosphorylated inositol, which is abundantly present in most cereal grains and seeds. This study investigated the effects of IP6 regulation on P-glycoprotein (P-gp) and its potential mechanisms using in situ and in vitro models. The effective permeability of the typical P-gp substrate rhodamine 123 (R123) in colon was significantly increased from (1.69 ± 0.22) × 10^-5 cm/s in the control group to (3.39 ± 0.417) × 10^-5 cm/s (p < 0.01) in the 3.5 mM IP6 group. Additionally, IP6 can concentration-dependently decrease the R123 efflux ratio in both Caco-2 and MDCK II-MDR1 cell monolayers and increase intracellular R123 accumulation in Caco-2 cells. Furthermore, IP6 noncompetitively inhibited P-gp by impacting R123 efflux kinetics. The noncompetitive inhibition of P-gp by IP6 was likely due to decreases in P-gp ATPase activity and P-gp molecular conformational changes induced by IP6. In summary, IP6 is a promising P-gp inhibitor candidate.

Reversal of P-gp-mediated multidrug resistance in colon cancer by cinobufagin

Cinobufagin (CBF) is isolated from the skin and posterior auricular glands of the Asiatic toad (Bufo gargarizans). This study investigated the reversal effect of CBF on P-glycoprotein (P-gp)-mediated multidrug resistance (MDR) in colon cancer. The effect of CBF on the cytotoxicity of anticancer drugs in P-gp overexpressing LoVo/ADR, HCT116/L, Cao-2/ADR cells and their parental cells was determined using CCK-8 assay. Apoptosis of anti-cancer drugs and accumulation of doxorubicin (DOX) and Rhodamine 123 (Rho123) in P-gp overexpressing cells were evaluated by flow cytometry. Results indicated that CBF significantly enhanced the sensitivity of P-gp substrate drugs on P-gp overexpressing cells, but had no effect on their parental cells. CBF enhanced the effect of DOX against P-gp-overexpressing LoVo/ADR cell xenografts in nude mice. Moreover, CBF also increased cell apoptosis of chemotherapy agents and intracellular accumulation of DOX and Rho123 in the MDR cells. Further research on the mechanisms revealed non-competitive inhibition of P-gp ATPase activity, but without altering the expression of P-gp. These findings demonstrated that CBF could be further developed into a safe and potent P-gp modulator for combination use with anticancer drugs in cancer chemotherapy.

Effect of HM30181 mesylate salt-loaded microcapsules on the oral absorption of paclitaxel as a novel P-glycoprotein inhibitor

The purpose of this study was to develop HM30181 mesylate salt (HM30181M)-loaded microcapsules as a novel P-glycoprotein inhibitor for enhancing the oral absorption of paclitaxel. The effect of various carriers including hydrophilic polymers and solvents on the solubility of HM30181M were evaluated. Among the hydrophilic polymers and solvents tested, HPMC and methylene chloride (and ethanol) provided the highest HM30181M solubility. Numerous HM30181M-loaded microcapsules were prepared with HPMC, silicon dioxide and acidifying agents using a spray-drying technique, and their solubility, dissolution and physicochemical properties were evaluated. Furthermore, a pharmacokinetic study was performed after oral administration of paclitaxel alone, simultaneously with HM30181M powder or HM30181M-loaded microcapsules to rats. Among the acidifying agents investigated, phosphoric acid provided the best improvement in the solubility and dissolution of HM30181M. Moreover, the microcapsule composed of HM30181M, HPMC, silicon dioxide and phosphoric acid at a weight ratio of 3:6:3:2 remarkably enhanced the solubility and dissolution of HM30181M compared with the HM30181M powder alone. The microcapsules were spherical in shape, had a reduced particle size of about 7μm, and contained HM30181M in an amorphous state. Furthermore, this microcapsule significantly enhanced HM30181M absorption, making it about 1.7-fold faster and 1.6-fold greater after simultaneous administration, leading to about 70- and 2-fold improved oral bioavailability of paclitaxel compared with paclitaxel alone and the simultaneous administration with HM30181M powder, respectively. Thus, this novel microcapsule could be a potential candidate for effective P-glycoprotein inhibition during oral administration of paclitaxel.