Complexation of Cell-Penetrating Peptide-Polymer Conjugates with Polyanions Controls Cells Uptake of HPMA Copolymers and Anti-tumor Activity

Cell penetrating peptides (CPPs) can mediate effective delivery of their associated drugs and drug carriers intracellularly, however their lack of cell specificity remains a major obstacle for their clinical development. We aimed at improving the cell specificity and therapeutic efficacy of HPMA copolymer-octaarginine (R8) conjugate (P-R8) in cells at the tumor micro-environment. To avoid premature cell-penetration, the positively charged R8 moieties were masked via electrostatic complexation with various polyanionic molecules (heparin sulfate, hyaluronic acid, fucoidan and poly-glutamic acid). We followed the kinetics of the FITC-labeled P-R8 penetration into endothelial and cancer cells over-time after its complexation in vitro and further tested whether the in situ addition of a stronger polycation can trigger the release of P-R8 from the complexes to resume cell penetration activity. A murine model of B16-F10 lung metastasis was then used as an in vivo model for assessing the therapeutic efficacy of the P-R8, loaded with doxorubicin (P-R8-DOX), after its complexation with PGA. The intracellular penetration of P-R8-FITC was reversibly inhibited by forming electrostatic interactions with counter polyanions, and can be restored either gradually over time by dissociation from the polyanions, or promptly following the addition of protamine sulfate. Mice injected with B16-F10 cells and treated with P-R8-DOX/PGA complexes, exhibited a significant prolonged survival times when compared with DOX-treated mice or relative to mice treated with either P-R8-DOX or P-DOX alone. The gradual release of P-R8 from P-R8-DOX/PGA may improve the therapeutic efficacy of water-soluble based nanomedicines for the treatment of solid lung tumors.