Achieving Elongated Circulation Time and Reduced Cytotoxicity By Tuning the Surface Charge of the Doxorubicin Zwitterionic Polymer Conjugate

Polymers conjugated with doxorubicin (DOX) via hydrozne linkage have been extensively explored as nano drug vehicles (NDVs) to delivery DOX; some conjugates are currently under the clinic trail evaluation. However zwitterionic polymer poly(carboxybetaine methacrylate) (pCBMA) as the hydrophilic polymer conjugated DOX using this method, the amino groups on the DOX and the residue hydrazine groups make the final conjugate positively charged, which cause the nonspecific protein adsorption and activation, thus of cellular uptakes and other severe problems in vivo application. Hence, random copolymers of carboxybetaine methacrylate (CBMA) and methacrylohydrazide (MAH) with or without sodium methacrylate (SMA) were prepared as the polymer precursors to conjugate the DOX. The DOX conjugated NDV without SMA component was positive charged and the mice intravenously injected this type NDV all died in two hours. The toxicity mostly caused by the positive charge of the NDV, since it may lead to the severe protein absorption and blood clotting. Hence, SMA was introduced in to the polymer to counter the positive charge of the final NDV. NDV with a layer of highly protein resistant pCBMA shell and negative surface charge was prepared. Excellent stability of this NDV in physiological solution was achieved. No size increase and aggregation were observed during 4days dynamic light scattering (DLS) analysis in either fibrinogen or fetal bovine serum solution. The DNV showed an accelerated DOX release behavior under mild acid condition. Its release rate of the DOX at pH 5.0 buffer solution was almost the same as its in pH 3.0 buffer solution. It released 70% of the DOX during the 7days’ incubation at pH 5.0, while it releases less than 10% DOX at pH 7.4. Elongated circulation time was achieved owning to the excellent stability in complex protein solution. And most importantly, the NDV showed lowered invitro or invivo cytotoxicity but still remain good anticancer therapeutic efficacy. A 55% tumor-inhibition rate (TIR) was achieved in the mice treated with the NDV, while around 10% body weight increase was observed. Thus, the results indicates the necessity of a negative component to counter the positive charge of the DOX conjugate, and a promising future of the NDV with pCBMA shell and slightly negative charge to delivery DOX.

Acknowledgements

The authors would like to thank Professors Guping Tang, Hongwei Yu and Youqing Shen for use of their facilities. This work is supported by the National Nature Science Foundation of China (20974095, 20936005, 21174127) and the Ph.D. Programs Foundation of Ministry of Education of China (20110101110034).