Construction Of Boronic Acid-rich Protein Nanoparticles And The Anti-cancer Research

The high drug concentration and long-acting time within tumor tissues have been actively pursued over past three decades with nanoparticulate drug delivery systems. Since tumors consist of heterogeneous cells that have quite different sensitivity to drug, delivering large fraction of the administered drugs to the tumor sites will increase the possibility to kill heterogeneous cancer cells and reduce off-target toxicity. However, the abnormal architecture and composition of tumors make drug targeting considerably difficult. The challenge still lies in the design of nanoparticles that can maximally accumulate in tumor tissues and release their payload over an extended period to kill cancer cells.Due to the enhanced permeability and retention (EPR) effect and variable pore size of tumor vessels, nanoparticles can passively accumulate in the tumor tissues depending on their size. It has been reported that EPR effect can lead to a more than50-fold increase in the accumulation of nanoparticles within tumors compared with healthy tissues. However, when administered into the blood, most nanoparticles are recognized and eliminated by the mononuclear phagocytic cells in the reticuloendothelial system (RES) of the liver and spleen, which leads to insufficient accumulation at the target site. Beside this, the rapid washout of drug and nanoparticles from the tumor tissue is another major obstacle for drug delivery. Drugs and nanocarriers are rapidly metabolized or transfered back into the circulation, resulting in short drug action time to tumors. Thus, no significantly high and prolonged antitumor effects have been expected.Recently, boron-containing compounds have attracted much attention in biomedical research and applications, especially in drug delivery system. Typically, phenylboronic acid (PBA) and its derivatives are widely used in cancer treatment and diagnosis. PBA is able to reversibly react with1,2-diols and1,3-diols to form cyclic boronate esters.In general, PBA can form stable complexes with sugars only if PBA is disassociated (at pH values above the pKa value of PBA). Exceptionally, nondissociated PBA can form remarkably stable binding with sialic aicd (SA) due to special modalities. SA is an anionic monosaccharide occurring at the termini of the glycan chains. It is found that SA is overexpressed on the cell surface of many different types of malignant and metastatic cancers. Taking advantage of such feature of cancer cells, many research groups have designed different kinds of PBA-containing nanomaterials for targeting to SA residues overexpressed on cancer cells. The high affinity and selectivity of PBA to SA enhance their tumor targeting ability without affecting adversly their long circulating properties. Based on the above discussions, we prepared a series of bovine serum albumin-poly(N-3-acrylamidophenylboronic acid)(BSA-PAPBA) nanoparticles with different sizes to pick out an optimum size which shows maximal EPR effect. Then, we decorate these nanoparticles with positively charged PEI-PEG copolymer and active targeting groups, cRGD peptide. Through such integrated design in the nanoparticles, the combined effects of size and surface chemistry on cell uptake, in vivo biodistribution and antitumor activity of nanoparticles are examined. Besides, we also present the preparation of well-defined amphiphilic block copolymer poly(ethylene glycol)-block-poly(dehydroabieticethyl methacrylate)(PEG-b-PDAEMA) and their micellar nanoparticles as robust drug delivery vehicles for anticancer treatment. The detailed work is described as below:(1) We prepared boronic acid-rich protein nanoparticles composed of bovine serum albumin (BSA) and poly(N-3-acrylamidophenylboronic acid)(PAPBA), with the diameter less than50nm (40nm). We found that such protein nanoparticles have high accumulation and long retention time in liver tissue due to the size effect and significant washout-resistant ability arising from the interaction between boronic acid-containing nanoparticles and live tissue. When used to deliver antitumor agent to an orthotopic liver cancer model, the boronic acid-rich protein nanoparticles not only impede tumor growth but also induce remarked tumor regression without suffering the toxic effects. We demonstrate that these results are due to the overexpression of sialic acid group in liver cancer cell and the interaction between boronic acid-rich protein nanoparticles and sialic acid group as well as size effect of nanoparticles.(2) We present an improvement in nanoparticle design to enhance drug accumulation and prolong particle residence time at tumor site. Based on the work stated above, we prepared another three batches of bovine serum albumin-poly(N-3-acrylamidophenylboronic acid)(BSA-PAPBA) nanoparticles with diameters of70nm,110nm and150nm, and found that the nanoparticles with110nm diameter have the most desirable biodistribution and tumor targeting ability. Thanks to the interaction between the phenylboronic acid group and the SA residue overexpressed on cancer cells, the recognition ability of nanoparticles to cancer cells and the retention time of nanoparticles at tumor sites were significantly improved. Furthermore, we decorated the110nm nanoparticles with positively charged PEI-PEG copolymer and cRGD peptide successively, to optimize their cellular uptake, biodistribution and antitumor activity.(3) We prepared micellar nanoparticles by well-defined amphiphilic block copolymer poly(ethylene glycol)-block-poly(dehydroabieticethyl methacrylate)(PEG-b-PDAEMA) and further loaded anticancer natural drug PLGM into the nanoparticles using an easy and quick procedure. The in vitro and in vivo behaviors of these nanoparticles were examined by dynamic light scattering, transmission electron microscopy, cytotoxicity, near-infrared fluorescence imaging, tumor growth inhibition and biodistribution. It was found that by virtue of the stable and stealth nanoparticulate formulation, the in vivo circulation time and tumor accumulation of PLGM were significantly improved, resulting in superior efficiency in impeding tumor growth and extension of the lifetime of mice compared to free PLGM and Taxol(?) in murine hepatoma H22cancer models.