Preparation Of BSA-mPEG Conjugates By "Click Chemistry" And Their Application As Drug Carriers For 5-FU

In order to improve the therapeutic effect and decrease the side-effects of anti-cancer drugs, various drug carriers have been developed. In the blood stream of the mammals, serum albumin is the major transport protein and binds a great variety of metabolities and organic compounds. Therefore, it is always of the first consideration in the research of interaction force between biological macromolecules and small molecules such as drugs, metal ions and surfactants. Employing this nonspecific binding ability, it has been used in sustaining the release of therapeutic drugs injected into the blood stream. On the other hand, PEG (poly(ethylene glycol))is a kind of polymer that is neutral and avirulent and has been certificated by the FDA as a drug which could be injected into human blood. PEGylation is a procedure of growing interest for enhancing the therapeutic and biotechnological potential of peptides and proteins. When PEG is properly linked, it modifies many of its features such as biodistribution and solubility in organic solvents, while the main biological functions may be maintained. Therefore, BSA (bovine serum albumin)-m PEG (monomethoxylated form of poly(ethylene glycol)) conjugates are employed as the carriers in our experiment. Meanwhile, a novel "click reaction" is used to realize the conjugation process in a mild environment, which has never been reported. The "click chemistry" present in this article is the special reaction between alkyne and azide groups. Afterwards, the alkyne terminated mPEG was firstly achieved by phase transfer catalyst synthesis method described by Teodorescu et al. and BSA-N₃ was prepared when BSA reacts directly with NaN₃. Coupling of the alkyne terminated mPEG to BSA-N₃ is achieved by a mild Cu¹ -mediated cycloaddition reaction and the catalyst was supplied by sodium ascorbate and CuSO₄. Then, the conjugates are used to bind the anticancer drug, 5-FU (5-Flouroricial) in the hydrophobic region of BSA. Therefore there is only physical process which would not denature the drug. The successful conjugation has been proved by many characterization methods including UV-Vis, NMR, FTIR and SDS-PAGE etc. The in vitro adsorption results provide a evidence that there is a strong interaction between BSA and 5-FU. What is more, the conjugations play a better role in the release experiment than BSA. Because the interaction between BSA and 5-FU employed here is nonspecific, the conjugates are potential for the adsorption of many other kinds of drugs.