Enhancing Tumor Cell Response to Chemotherapy by Simultaneous Delivery of siRNA and Anticancer Drug Using Nanoparticles

SUMMARY We have developed an innovative nanotherapeutic approach towards utilizing polymer-lipid hybrid nanoparticles (NPs) capable of simultaneously delivering cisplatin and anti-Rev1 and Rev3L siRNA in order to sensitize prostate cancer to chemotherapy and prevent resistance arising during treatment. This approach is the first ever rationally designed delivery system to target translesion DNA polymerases. Administering these NPs revealed a synergistic effect on tumor inhibition in an LNCaP xenograft mouse model that was strikingly more effective than platinum monotherapy. INTRODUCTION Despite advances in early detection and increased understanding of the molecular basis of cancer biology, a significant percentage of patients with early-stage cancer have recurrent disease. In most cases, the relapsed tumors are metastatic and refractory to subsequent treatment of the initial drug regimen. Recent evidence has implicated that acquired resistance can arise from DNA damage chemotherapy-induced mutations and increase tumor cell capacity to either repair or tolerate DNA damage. Therefore, the depletion of crucial gene products involved in the pathways (e.g. Rev1 and Rev3L) by RNAi therapeutics may restore the tumors’ chemosensitivity to treatment. Although considerable efforts have been made to explore various delivery systems for chemotherapeutics and small interfering RNA (siRNA), there remains a pressing need towards engineering nanocarriers that are clinically relevant, biocompatible, efficient, and can be tailored to specific disease targets. The objective of this research is to develop a versatile nanocarrier platform capable of codelivering siRNA (antiRev1 and Rev3L) and cisplatin for enhanced treatment of cancer through synergistic effects (Figure 1). EXPERIMENTAL METHODS Here, we describe an integrated nanodelivery system capable of simultaneously delivering cisplatin prodrug and siRNAs against REV1 and REV3L expression to enhance chemosensitivity of tumors. PLGA-b-PEG was formulated with a cationic lipid-like molecule designated as G0-C14 into NPs that comprises three components: a siRNA inner core, a cationic and hydrophobic layer composed of PLGA and G0-C14, and a hydrophilic PEG corona (Figure 2A). The G0-C14 compound (Figure 2C) is synthesized with cationic head groups which can efficiently bind siRNA via electrostatic interactions and flexible hydrophobic tails for self-assembly with PLGAb-PEG to form Pt(IV)-prodrug encapsulating NPs. In this study, we applied a Pt(IV)-prodrug approach previously employed in our laboratory to deliver cisplatin. In this approach, a novel Pt(IV) precursor compound (1, Figure 2B) was developed to allow the release of cisplatin at a lethal dose upon intracellular reduction. The linear decanoyl chains in compound 1 also enable efficient encapsulation within the hydrophobic layer of NPs and controlled release without compromising either feature. We investigated the ability of these polymer/lipid hybrid NPs to down-regulate the expression of target genes as well as to induce Figure 2. A) Chemical structure of PLGA-b-PEG/G0C14 NPs. B) Chemical structure of the hydrophobic platinum(IV) compound 1 and cisplatin. C) Synthesis of G0-C14. D) Size distribution of the NPs containing both compound 1 and siRNA. E) Representative TEM