Multifunctional polymeric micelles for enhanced intracellular delivery of doxorubicin to metastatic cancer cells

Purposes. To develop multifunctional RGD-decorated poly(ethylene oxide)-b-poly(ester) based micelles and assess their pH-triggered core degradation and targeted drug release in tumor cells that overexpress RGD receptors. Methods. Novel poly(ethylene oxide)-b-poly(epsilon-caprolactone) (PEO-b-PCL) based copolymers modified with RGD ligands on PEO and pendent functional groups on PCL, i.e., GRGDS-PEO-b-poly(alpha-benzylcarboxylate-epsilon-caprolactone) (GRGDS-PEO-b-PBCL) and GRGDS-PEO-b-poly(alpha-carboxyl-epsilon-caprolactone) (GRGDS-PEO-b-PCCL), were synthesized. Chemical conjugation of doxorubicin (DOX) to PCCL core produced GRGDS-PEO-b-P(CL-DOX) micellar conjugates, while GRGDS-PEO-b-PBCL were used to physically encapsulate DOX. For both systems, micellar core degradation, drug release, intracellular drug uptake/disposition, and cytotoxicity against B16F10 metastatic cells were investigated. Results. The PBCL and P(CL-DOX) cores were found resistant to degradation in pH 7.2, but showed 10% and 40% loss in core molecular weight in pH 5.0 within 144 h, respectively. Preferential release of DOX and DOX derivatives from PBCL and P(CL-DOX) cores was noted in pH 5.0, respectively. The GRGDS-modified micelles showed enhanced cellular internalization through endocytosis, increased intracellular DOX release, nuclear localization, and improved cytotoxicity against metastatic B16F10 cells compared to their unmodified counterparts. Conclusions. The results clearly suggest a promise for the development of multifunctional polymeric micelles with RGD ligand decorated shell and endosomal pH-triggered degradable core for selective DOX delivery to metastatic cancer cells.