PGP and ovarian cancer: Immunohistochemistry analysis of HA-PEI/HA-PEG/MDR1 siRNA CD44 targeted nanoparticle on Pgp staining in ovarian cancer MDR tumor tissues further confirmed downregulation of Pgp as compared with either saline alone, MDR1 alone or HA-PEI/HA-PEG/non-specific siRNA nanoparticle treatment (Fig. 5B).