Paclitaxel: What has been done and the challenges remain ahead

In recent years, the nanotechnology has offered researchers the opportunity to solve the problems caused by the vehicle of the standard and first formulation of paclitaxel (Taxol^®), while maximizing the proven antineoplastic activity of the drug against many solid tumors. Hence, different types of nanocarriers have been employed to improve the efficacy, safety, physicochemical properties and pharmacokinetic/pharmacodynamic profile of this drug. To date, paclitaxel is the unique drug that is marketed in three different nanoplatforms for its parenteral delivery: polymeric nanoparticles (Abraxane^®), liposomes (Lipusu^®), and polymeric micelles (Genexol^®, Nanoxel^® and Paclical^®). Indeed, a fourth nanocarrier might be available soon, because phase III studies of Opaxio™, a polymeric-conjugated, are near completion. Furthermore, other several nanoformulations are currently in various stages of clinical trials. Therefore, it is only through the critical analysis of clinical evidence from these studies that we can get a more concrete idea of what has been achieved with pharmaceutical nanotechnology so far. This review attempts to summarize current information available regarding the clinical status and the physicochemical characteristic of different nanocarriers for paclitaxel delivery in cancer therapy. We present an overview of the preclinical and clinical data of these systems including their pharmacokinetics, dose and administration, adverse events and clinical efficacy.