High affinity binding of paclitaxel to human serum albumin

Abstract

Paclitaxel, a very potent antitumor agent is a hydrophobic molecule with low aqueous solubility. Its currently used formula (Taxol®) contains the drug in a 1 : 1 (v/v) mixture of ethanol and Cremophor EL. To minimize vehicle‐related toxicity, we developed a novel, water‐soluble formulation in which paclitaxel is bound noncovalently to human serum albumin. For this purpose, studies of the paclitaxel–albumin binding equilibrium were performed. Paclitaxel dissolved in ethanol was added to the aqueous solution of human serum albumin. Precipitated paclitaxel was removed and unbound drug was separated by ultrafiltration. Paclitaxel concentration was measured by RP‐HPLC. Binding data were evaluated based both on the Scatchard plot and the general binding equation describing binding equilibria with the stepwise stoichiometric binding constants. The Scatchard plot was found to be curvilinear with a slight positive slope of the final part. Parameters of high affinity specific binding were determined from the initial part of the curve (nsp = 1.3 and Ksp = 1.7 × 106 m−1). Stoichiometric binding constants were estimated by fitting the general binding equation to the experimental data (K1 = 2.4 × 106 m−1 and K2 = 1.0 × 105 m−1). Saturation of the protein with paclitaxel, similarly to other ligands of albumin, could not be reached. The greatest observed value of r (number of paclitaxel molecules bound to one albumin molecule) was 6.6.

Albumin-bound formulation of paclitaxel (Abraxane® ABI-007) in the treatment of breast cancer

“…It is a natural carrier of endogenous hydrophobic molecules (such as vitamins, hormones, and other water-insoluble plasma substances), that are bound in a reversible non-covalent manner [58][59][60] Moreover albumin seems to help endothelial transcytosis of protein-bound and unbound plasma constituents principally through binding to a cell-surface, 60-kDa glycoprotein (gp60) receptor (albondin). gp60 binds to caveolin-1 (an intracellular protein) with subsequent formation of transcytotic vesicles (caveolae) (Figure 1).…”

Noncovalent interaction-assisted drug delivery system with highly efficient uptake and release of paclitaxel for anticancer therapy

“…24 The cells were incubated with the culture medium for 30 seconds, 1 minute, 5 minutes, 30 minutes, and 24 hours, washed twice with PBS, and incubated with fresh culture medium for another 24 hours.…”

Enzymatic tumour tissue digestion coupled to SPE–UPLC–Tandem Mass Spectrometry as a tool to explore paclitaxel tumour penetration

“…Based on the strong protein binding affinity of PTX [13] and in an attempt to improve recovery and reduce the ion suppression, we decided to introduce an additional protein precipitation step prior to SPE. To this end, the 6% phosphoric acid solution was replaced by a 1:1 (v/v) mixture of 0.06 N Ba(OH) 2 and 0.06 N ZnSO 4 (both Sigma-Aldrich, Bornem, Belgium).…”