Improvements in the Oral Absorption and Anticancer Efficacy of an Oxaliplatin-Loaded Solid Formulation: Pharmacokinetic Properties in Rats and Nonhuman Primates and the Effects of Oral Metronomic Dosing on Colorectal Cancer

OBJECTIVE: The anticancer efficacy of orally administered chemotherapeutics is often constrained by low intestinal membrane permeability and oral bioavailability. In this context, we designed a solid oral formulation of oxaliplatin (OP), a third-generation cisplatin analog, to improve oral bioavailability and investigate its application in metronomic chemotherapy. METHODS: An ion-pairing complex of OP with a permeation enhancer, N(α)-deoxycholyl-l-lysyl-methylester (DLM), was successfully prepared and then mixed with dispersing agents (including poloxamer 188 and Labrasol) to form the solid, amorphous oral formulation OP/DLM (OP/DLM-SF; hereafter, ODSF). RESULTS: The optimized powder formulation was sized in the nanoscale range (133±1.47 nm). The effective permeability of OP increased by 12.4-fold after ionic complex formation with DLM and was further increased by 24.0-fold after incorporation into ODSF. ODSF exhibited respective increases of 128% and 1010% in apparent permeability across a Caco-2 monolayer, compared to OP/DLM and OP. Furthermore, inhibition of bile acid transporters by actinomycin D and caveola-mediated uptake by brefeldin in Caco-2 cell monolayers reduced the apparent permeability values of ODSF by 58.4% and 51.1%, respectively, suggesting predominant roles for bile acid transporters and caveola-mediated transport in intestinal absorption of ODSF. In addition, macropinocytosis and paracellular and transcellular passive transport significantly influenced the intestinal permeation of ODSF. The oral bioavailabilities of ODSF in rats and monkeys were 68.2% and 277% higher, respectively, than the oral bioavailability of free OP. In vivo analyses of anticancer efficacy in CT26 and HCT116 cell-bearing mice treated with ODSF demonstrated significant suppression of tumor growth, with respective maximal tumor volume reductions of 7.77-fold and 4.07-fold, compared to controls. CONCLUSION: ODSF exhibits therapeutic potential, constituting an effective delivery system that increases oral bioavailability, with applications to metronomic chemotherapy.