In Vitro Evaluation of pH-Responsive Nanoscale Hydrogels for the Oral Delivery of Hydrophobic Therapeutics

About 70% of pharmaceutical drug candidates are poorly soluble and suffer from low oral bioavailability. Additionally, a large number of therapeutics are also substrates for P-glycoprotein (P-gp) receptors present on the intestinal cell lining and undergo efflux that further reduces their oral bioavailability drastically. Nanoscale hydrogels are promising candidates for oral delivery of hydrophobic therapeutics as they hold immense potential in improving solubility and increasing intestinal permeability of such therapeutics. In this report, we describe the in vitro evaluation and comparison of four novel, pH-responsive poly(methacrylic acid-g-polyethylene glycol-co-hydrophobic monomer) nanoscale hydrogels for their capacity to load and release chemotherapeutic doxorubicin, as well as their ability to modulate permeability in vitro for improving doxorubicin transport. The resulting nanoscale formulations showed appreciable loading, and in vitro release studies demonstrated excellent pH-triggered release kinetics. These nanoscale hydrogels can serve as carriers for oral delivery of doxorubicin, achieving drug loading efficiencies of 56-70%, and releasing up to 95% of drug within 6 h. Powder X-ray diffraction studies revealed a change from the crystalline nature of doxorubicin to an amorphous form when encapsulated within formulations, illustrating their potential of enhancing solubility and stability for oral delivery of the hydrophobic therapeutic. Furthermore, their ability to modulate in vitro intestinal permeability was also studied using transport studies with Caco-2 cells, and was complemented by assessing their antitumor activity against P-gp overexpressing, DOX-resistant H69/LX4 cancer cells. In vitro cell culture tests demonstrated up to 50% reduction in cellular proliferation in the case of poly(methacrylic acid-g-polyethylene glycol-co-methyl methacrylate), suggesting that these carriers are most suitable as hydrophobic drug carriers that can potentially overcome solubility and permeability limitations typically faced by hydrophobic therapeutics in the gastrointestinal (GI) tract.