| Polymeric nanomaterials can be used as drug carriers for controlling drug release and improving drug bioavailability. But most of nano-drug carriers are often accumulated in liver and spleen, which results in low concentrations of carriers and drugs in blood and poor therapeutic efficacy. There have many factors that cause the accumulation of nanocarriers in the liver and spleen, including the sizes of nanocarriers, composition, charge properties of surface and others. In our study, we found that the hydrophilic/hydrophobic behavior of nanocarriers is also important influencing factor.Isotope tracer technique is a method that using the radionuclide label and trace compounds, which has the advantage of high sensitivity and easy detection. The technique can accurately quantitate and trace compounds at molecular or atomic level. And now it has been widely used in the fields of scientific research, medicine, agriculture, and industry. This technique has also applied in the real-time and quantitative studies of in vivo biodistribution and metabolism of polymeric materials. In order to systematically study the effect of the hydrophilic/hydrophobic behavior of polymeric nanomaterials on their biodistribution, we introduce the research which can change the biodistribution, prolong the blood circulation time and decrease the accumulation in liver and spleen of polymeric materials by adjusting their hydrophilic/hydrophobic behavior. This provides new ideas and methods for the studies of effect on the in vivo distribution and metabolism of polymeric materials by their surface properties. We prepared nano-polymeric micelles through spontaneously self-assembly of block copolymers poly(ethylene glycol)-block-poly (L-lysine)(PEG-b-PLys) and poly(N-isopropylacrylamide)-block-poly (aspartic acid)(PNIPAM-b-PAsp) in aqueous medium. A series of mixed shell micelles (MSMs) with hydrophilic/hydrophobic gradient on the surface were synthesized by change the feed ratio of PEG-b-PLys and PNIPAM-b-PAsp (PEG segment to PNIPAM segment (WPEG/WPNIPAM) as10/0,7/3,5/5, and3/7, called as MSMs-0, MSMs-30, MSMs-50, and MSMs-70, respectivly). All the MSMs have the same size, charge properties of surface and composition. The molecular structure of the MSMs was detected by nuclear magnetic resonance spectroscopy (1H NMR). The particle size and electric potential of MSMs were detected by dynamic light scattering (DLS) and zeta potential analyzer, respectively. The morphology of MSMs was observed by transmission electron microscope (TEM). The biological safety of MSMs was evaluated by MTT assay. Cellular uptake was detected by flow cytometry and observed with inverted fluorescence microscope. Then the effect of the surface heterogeneity on the in vivo biodistribution was systematically investigated through in vivo tracking of the125I-labeled MSMs.The results showed that the size of all the four kinds of micelles is about100nm and the electric potential is about-8mv under physiological conditions. These results indicated that the four kinds of micelles have almost the same partical size, electric potential and inner composition, and conform to the original design of our project. The in vitro biocompatibility results showed that the four kinds of micelles have low cytotoxicity and all the cell viability is higher than75%when the concentration of MSMs up to100μg/ml. The cellular uptake efficiency has significant differences between the four kinds of micelles, the MSMs-50%has the highest cellular uptake efficiency instead of the highest hydrophilic micelle has the highest cellular uptake efficiency. The MSMs were radio-labeled by125I with chloramine-T method, and the labeling rate was33.9%～38.5%. The labeled micelles were purified with10KDa ultrafiltration tubes and the radiochemical purities were higher than96.7%. The radiolabeled MSMs were injected intravenously via the tail vein with concentration of5mg/kg, the tissue distribution results showed that MSMs-0has the highest concentration in liver and spleen (53.4%ID/g and248.0%ID/g, respectivly) at one hour after i.v. administration. While MSMs-50has the lowest concentration in liver with14.9%ID/g and MSMs-70has the lowest concentration in spleen with20.4%ID/g. The MSMs-50has highest blood concentration which is four-fold higher than three other MSMs at one hour. All the MSMs were cleared from the body at24hours after i.v. administration, this can avoid nanotoxicity which caused by long-term accumulation of nanomaterials.Overall we changed the in vivo distribution of micelles by adjusted the ratio of hydrophilic group and hydrophobic group on the micelles surface. And we screened the mixed shell micelle MSMs-50which has lower accumulation in liver and longer blood circulation time. Our results and design ideas provid theoretical basis and methodological guidance for designing and preparing polymeric nano-drug carriers with long-term blood circulation and high utilization. |
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