Background: Combination therapy employing siRNAs and antitumor drugs is a promising method for the treatment of solid tumors. However, regarding combined treatments involving siRNAs and chemotherapeutic reagents, most prior research has focused on the enhanced cytotoxicity against tumor cells conferred by downregulation of the targeted protein.
Purpose: We developed D-α-tocopherol polyethylene glycol 1000 succinate (TPGS)-modified cationic liposomes (LPs) to simultaneously deliver doxorubicin (Dox) and the Bcl-2 siRNA (siBcl-2) for synergistic chemotherapy. The co-loading of siBcl-2 onto the Dox-loaded cationic LPs (siBcl-2/Dox-TPGS-LPs) could promote cellular uptake, cytotoxicity against 3D H22 tumor spheroids, circulation in the blood, drug accumulation at tumor sites, and synergistic chemotherapy in vivo.
Methods: The siBcl-2/Dox-TPGS-LPs were constructed by co-loading siBcl-2 onto the Dox-loaded TPGS-modified cationic LPs (Dox-TPGS-LPs), and Dox entrapment into the LPs was achieved using an ammonium sulfate gradient method. The antitumor effects of siBcl-2/Dox-TPGS-LPs were studied in murine hepatic carcinoma H22 cells, 3D H22 tumor spheroids, and H22 tumor-bearing mice.
Results: Dynamic light scattering technique and transmission electron microscopy images revealed that siBcl-2 loaded onto the Dox-TPGS-LPs formed a prominent corona at an nitrogen to phosphorus (N/P) ratio of 4:1, resulting in particle size increase from 155 to 210 nm and a weak positive zeta potential (+12.5 mV). The siBcl-2/Dox-TPGS-LPs enhanced the cellular uptake of Dox, promoted toxicity against 3D H22 tumor spheroids via tumor priming, prolonged Dox circulation in the blood, and increased accumulation of Dox at tumor sites, thereby enhancing the cytotoxicity of Dox in vitro and its chemotherapeutic efficacy in vivo.
Conclusion: The siBcl-2/Dox-TPGS-LPs demonstrated a strong potential for application in synergistic chemotherapy. The co-loading of siRNAs both sensitized cells toward antitumor drugs by downregulating the expression level of a specific protein and influenced the pharmacokinetic behavior of the co-delivery system in vitro and in vivo.
Keywords: Bcl-2; cationic liposomes; co-delivery; siRNA corona; synergistic chemotherapy; tumor priming.