Tumor tropic delivery of doxorubicin-polymer conjugates using mesenchymal stem cells for glioma therapy

Abstract

Mesenchymal stem cells (MSCs) possess inherent tropism to malignant cells and home to disseminated tumor foci, making MSCs an ideal candidate as targeting vehicle for drug delivery. Our previously synthesized doxorubicin (DOX)-polymer conjugates (PPCD) modified by RGD (RGD-PPCD) harness tremendous potential with active targeting and sustained release. To further enhance the conjugates penetrability and tumor tracking capability, MSCs-mediated RGD-/PPCD delivery system was created and constructed by spontaneous incorporation. The present study investigated the anti-tumor activities of MSCs loaded with RGD-/PPCD (MSCsRGD-/PPCD), compared to their corresponding RGD-/PPCD and MSCs loaded with DOX (MSCsDOX), especially. MTT assay demonstrated that although RGD-/PPCD could inhibit MSCs proliferation, there was no direct cytotoxicity to MSCs. After optimization, maximum drug loading amount was obtained by incubating MSCs for 12 h at the drug concentration of 50 μg/mL (DOX-equiv.). Further drug release and intracellular retention proved that, compared to MSCsDOX, MSCsRGD-/PPCD delayed the release peak to 12-48 h with continuous drug liberation more than 5 days, declaring the time dependent release behavior and lasting stability of conjugates in MSCs for cell-directed tumoritropic delivery. For MSCsRGD-/PPCD, intrinsic cell functions without compromise were verified by cell cycle analysis, transmigration assay and tumor penetration, while MSCsDOX showed observable but not significant suppression. As for in vivo studies, among all groups, mice intracranially administrated with MSCsPPCD and MSCsRGD-PPCD acquired the longest survival time with median being 41 and 45 days, and increased life span with 34% and 46.8% versus RGD-PPCD treatment group, respectively. Additionally, MSCsRGD-/PPCD exhibited more extensive penetration and enhanced tumor cell apoptosis than MSCsDOX. As proof of the concept, without any genetic manipulation and chemical modification, a novel modality integrating MSCs and DOX-polymer conjugates could vigorously ship therapeutics for efficient glioma therapy.

Keywords: Conjugates; Doxorubicin; Mesenchymal stem cells; Spontaneous incorporation; Tumor-tropic delivery.