Molecular Switch For the Assembly of Lipophilic Drug Incorporated Plasma Protein Nanoparticles and In Vivo image Guangming Gong, Yan Xu, Yuanyuan Zhou, Zhengjie Meng, Guoyan Ren, Yang Zhao, Xiang Zhang, Jinhui Wu,* and Yiqiao Hu* State Key Laboratory of Pharmaceutical Biotechnology, Nanjing University, Nanjing 210093, P. R. China * S Supporting Information ABSTRACT: A strategy to manipulate the disulfide bond breaking triggered unfolding, and subsequently assembly of human serum albumin (HSA) in a lipophilic drug-dependent manner is present. In this study, the hydrophobic region, a molecular switch of the HSA, was regulated to form HSA-paclitaxel (HSA-PTX) nanoparticles by a facile route. High-resolution transmission electron microscopy and fluorescence quenching indicate that HSA coassembled with PTX, which acts as a bridge to form core-shell nanoparticles about 50-240 nm in size, and that PTX might bind to the subdomain IIA sites of HSA. Change of ultraviolet absorption and circular dichroism spectra reveal the formation of HSA-PTX nanoparticles, which is a safety, injectable pharmaceutic nanocarrier system for tumor target. This method to prepare nanocarrier systems for hydrophobic guest molecules reveals a general principle of self-assembly for other plasma proteins and other pharmacologically active substances with poor water solubility. It also provides a basis for developing nanocarrier systems for a wide range of applications in nanomedicine, from drug delivery to bioimaging systems. ■ INTRODUCTION Protein assemblies are ubiquitous in nature. Proteins such as silk proteins, viral capsids, and amyloid proteins have been widely used as building blocks to study the assembly of macromolecular complexes, 1,2 smart biomaterials, 3,4 and models of human diseases in vitro. 5-8 Recently, simulation of the hydrophobic effect in protein-protein interactions 9,10 and drug-protein interactions 11,12 to fabricate protein nanocarrier systems for lipophilic drugs has engaged the attention of research efforts. 13,14 The employment of plasma protein as building block to fabricate nanocarrier systems for lipophilic drugs and fluorescent probes has attracted much attention because of their biocompatibility, nongenetic, and safety. Among these, albumin has been widely used for nanoparticles prepara- tion. 15,16 Human serum albumin (HSA), a kind of plasma protein that has 585 amino acids, 17 disulfide bridges, three subdomain sites (I, II, III), and hydrophobic cavities, 17 can accommodate and transport lots of hydrophobic and hydrophilic molecules to target organs and tissues. 18 Its nanoparticles can preferentially accumulate at tumor and inflamed tissues because of passive targeting by enhanced permeable reaction (EPR) effects and the active targeting mediated by gp60 receptors expressed on these tissues. 19-21 Therefore, HSA is a versatile tool to fabricate nanocarrier systems. Furthermore, the safety of HSA-based formulation has been clinically proved, 22,23 and it is of great value to fabricate HSA as the vehicles of therapeutic drugs and fluorescent probes. PTX is a widely clinical used chemotherapeutical drug, which is highly efficient in treating breast and other cancers. Because of its poor water solubility (0.3 ug mL -1 ), Cremophor EL (CrmEL)/ethanol is used to enhance its solubility, but the latter, a component of the formulation, is toxic to human body and can cause negative side effects. Some PTX formulations including liposomes, nanoparticles, emulsions, microspheres, micelles, PEG-PTX, and nanoshells have been widely explored to acquire improved physicochemical properties and biodis- tribution of PTX. 24-29 Among these, Abraxane is a novel PTX formulation for the therapy of metastatic breast cancer. 30 However, this nanocarrier system is fabricated by mechanical force, which is independent of the natural characteristic of HSA, that is, the amphipathicity, with low drug loading efficiency. We want to take on the challenge of fabricating a nanocarrier system by finely modulating the molecular switch of proteins. In previous work, we developed a strategy for fabrication of blank nanoparticles consisting of β-mercaptoethanol (β-ME)- HSA molecules. 31 In this study, HSA and PTX were arranged as two components. PTX was entrapped noncovalently in the hydrophobic cavity of HSA to form HSA-PTX nanoparticles. This was accomplished using β-ME to regulate the “exposed- hidden” switch, that is, the hydrophobic region, of HSA. The morphology and physical states of the nanoparticles were explored, and the spectrum was used to characterize the structural changes and the molecular mechanism of the assembly. Furthermore, fluorescence-probe-labeled HSA-PTX nanoparticles were fabricated to explore the biodistribution and tumor targeting capability of this nanocarrier system in vivo. Received: June 6, 2011 Published: October 27, 2011 Article pubs.acs.org/Biomac © 2011 American Chemical Society 23 dx.doi.org/10.1021/bm201401s | Biomacromolecules 2012, 13, 23-28