Development and in vivo evaluation of an oral drug delivery system for paclitaxel

The aim of the present study was to investigate the effect of poly(acrylic acid)-cysteine (PAA-cysteine) exhibiting a molecular mass of 100 and 250 kDa and reduced glutathione (GSH) on the absorption of the P-glycoprotein (P-gp) and cytochrome P450 (CYP450) substrate paclitaxel in vitro and in vivo. In vitro transport studies were performed with Caco-2 monolayers. Furthermore, the delivery system based on PAA-cysteine, GSH and paclitaxel was evaluated in vivo in rats. In vitro, the formulation comprising 0.5% (m/v) PAA-cysteine (100 kDa)/0.5% (m/v) GSH improved the transport of paclitaxel 6.7-fold (Papp = 8.7 ± 1.3 × 10−6 cm/s) in comparison to paclitaxel itself serving as buffer only control (Papp = 1.3 ± 0.4 × 10−6 cm/s). Moreover, in the presence of the formulation containing 0.5% (m/v) PAA-cysteine (250 kDa)/0.5% (m/v) GSH paclitaxel absorption was even 7.4-fold (Papp = 9.7 ± 0.3 × 10−6 cm/s) improved in comparison to the buffer only control. In vivo, the oral administration of formulations containing 1 mg of paclitaxel, 1 mg of GSH and 8 mg of PAA-cysteine (100 kDa or 250 kDa) resulted in an improved paclitaxel plasma concentration and bioavailability. The area under the plasma concentration-time curve (AUC0–8) of paclitaxel was 4.7-fold and 5.7-fold improved in comparison to the oral formulation containing paclitaxel alone, respectively. Moreover, cmax was improved by 6.3-fold and even 7.3-fold in comparison to the oral formulation containing paclitaxel alone, respectively. Thus, according to the achieved results it is suggested that PAA-cysteine in combination with GSH would be a potentially valuable tool for improving the oral bioavailability of P-gp and CYP450 substrates such as paclitaxel.