Paclitaxel?HSA interaction. Binding sites on HSA molecule

Abstract

It is used to treat several cancers including tumours of the breast, ovary and lung. The effect of paclitaxel on rapidly dividing cancer cells is based on the ability to bind and stabilize microtubules, thus leading to the block of cell replication in the late G 2 –M phase of the cell cycle. In the present work the interaction of paclitaxel with human serum albumin (HSA) in aqueous solution at physiological pH has been investigated through CD, fluorescence spectroscopy and by the antibody precipitate test. Binding of paclitaxel to albumin impact on protein structure and it influences considerably albumin binding of other molecules like warfarin, heme or bilirubin. The paclitaxel–HSA interaction causes the conformational changes with the loss of helical stability of protein and local perturbation in the domain IIA binding pocket. The relative fluorescence intensity of the paclitaxel-bound HSA decreased, suggesting that perturbation around the Trp 214 residue took place. This was confirmed by the destabilization of the warfarin binding site located in subdomain IIA. CD and fluorescence spectroscopic results showed marked reductions (about 50% decrease in the CD Cotton effect intensity, and ∼35% decrease of the fluorescence intensity) in the affinity of albumin for bilirubin upon paclitaxel binding. These results suggested that paclitaxel molecule is bound in the vicinity of Trp 214, which forms part of the wall in one of the two main drug-binding cavities of HSA (site I subdomain IIA). Paclitaxel (trade name Taxol ® ) is one of the world's most effective anticancer drugs. It is used to treat several cancers including tumours of the breast, ovary and lung. In the present work the interaction of paclitaxel with human serum albumin (HSA) in aqueous solution at physiological pH has been investigated through CD, fluorescence spectroscopy and by the antibody precipitate test. Binding of paclitaxel to albumin impact on protein structure and it influences considerably albumin binding of other molecules like warfarin, heme or bilirubin. The paclitaxel–HSA interaction causes the conformational changes with the loss of helical stability of protein and local perturbation in the domain IIA binding pocket. The relative fluorescence intensity of the paclitaxel-bound HSA decreased, suggesting that perturbation around the Trp 214 residue took place. This was confirmed by the destabilization of the warfarin binding site, which includes Trp 214, and high affinity bilirubin binding site located in subdomain IIA.