pH-responsive and charge shielded cationic micelle of poly(L-histidine)-block-short branched PEI for acidic cancer treatment.

To address cancer cell heterogeneity while endowing tumor specificity, the approach of charge shielding/deshielding was tested in vitro and in vivo with a paclitaxel loaded cationic micelle from a block copolymer of poly(L-histidine) (3.7kDa) and short branched polyethyleneimine (1.8 kDa). The cationic micelle surface was shielded by electrostatically complexing with a negatively charged mPEG (2 kDa)-block-polysulfadimethoxine (4 kDa) (mPEG-b-PSDM) at pH7.4. Unshielded micelle at pH7.4 and deshielded micelle at tumor extracellular pH were readily taken up by two wild types of human cancer cell lines, MCF-7 breast adenocarcinoma and SKOV-3 ovarian carcinoma, while the uptake of the shielded micelle at pH7.4 was minimal. The preliminary in vivo results from a mouse model xenografted with MCF-7 showed significant anticancer therapeutic efficacy and deep penetration of the micelle into tumor tissues after deshielding, supporting the unique pH-responsive mechanism to treat acidic cancer.