Tf-PEG-PLL-PLGA nanoparticles enhanced chemosensitivity for hypoxia-responsive tumor cells.

Hypoxia is an inseparable component of the solid tumor as well as the bone marrow microenvironment. In this study, we investigated the effect of the novel polyethylene glycol (PEG)-poly L-lysine (PLL)-poly lactic-co-glycolic acid (PLGA) based nanoparticles (NPs) modified by transferrin (Tf) loaded with daunorubicin (DNR) (DNR-Tf-PEG-PLL-PLGA-NPs, abbreviated as DNR-Tf-NPs) on leukemia cells (K562) under hypoxia. In vitro and in vivo tests to determine the effect of the enhanced chemosensitivity were evaluated using the immunofluorescence, flow cytometry, 3,-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-tetrazoliumbromide assay, Western blot analysis, histopathological examination, and immunohistochemistry analysis. Under hypoxia, K562 cells were hypoxia-responsive with the inhibitory concentration 50% (IC50) of DNR increased, resulting in chemotherapy insensitivity. By targeting the transferrin receptor (TfR) on the surface of K562 cells, DNR-Tf-NPs led to an increased intracellular DNR level, enhancing drug sensitivity of K562 cells to DNR with a decreased IC50, even under hypoxia. We further detected the protein levels of hypoxia-inducible factor-1α (HIF-1α), Bcl-2, Bax, and caspase-3 in K562 cells. The results indicated that DNR-Tf-NPs downregulated HIF-1α and induced apoptosis to overcome hypoxia. In the xenograft model, injection of DNR-Tf-NPs significantly suppressed tumor growth, and the immunosignals of Ki67 in DNR-Tf-NPs group was significantly lower than the other groups. It was therefore concluded that DNR-Tf-NPs could be a promising candidate for enhancing drug sensitivity under hypoxia in tumor treatment.