Nanoparticle albumin-bound (nab™)-paclitaxel: improving efficacy and tolerability by targeted drug delivery in metastatic breast cancer

Breast cancer deaths in western countries are falling due to screening and adjuvant therapy, but the treatment of metastatic breast cancer (MBC) has not shown comparable advances. The most active single agents are taxanes, which extend both disease-free and overall survival. However, opportunities remain for improving outcome. Nanoparticle technology is proving a valuable addition to the pharmaceutical armamentarium, particularly in oncology. Its use to bind paclitaxel to human albumin (nanoparticle albumin-bound paclitaxel; nab-paclitaxel; Abraxane®) ensures solubility of the taxane without the use of solvents and minimizes the risk of hypersensitivity reactions without premedication. The homogeneous colloidal suspension created allows rapid dispersal of unbound drug and linear pharmacokinetics. Albumin-mediated transport of paclitaxel across the endothelium facilitates uptake of drug, and a degree of tumour selectivity is achieved by the albumin-binding propensity of SPARC (Secreted Protein Acidic Rich in Cysteine), a substance expressed on and around many breast tumours. Clinical trials in first- and second-line MBC show that nab-paclitaxel is both more effective than solvent-based taxanes and associated with less severe neutropenia. Sensory neuropathy occurs but improves rapidly when compared with that caused by conventional taxanes. A clinical development programme is investigating nab-paclitaxel in the adjuvant and neoadjuvant settings. The low incidence of neutropenia makes nab-paclitaxel a good candidate for combination with other cytotoxics. It is also being assessed when given with biologic agents such as trastuzumab and bevacizumab.