(525b) Optimization of Calcium Phosphate-Polymer Nanoparticle System for Co-Delivery of microRNA-21 Inhibitor and Doxorubicin

The development of nano-scaled carriers as a drug delivery platform has made a tremendous progress in the fight against cancer. Despite the progress, drug resistance remains one of the major challenges of nanotechnology-based cancer therapeutics. Due to gradually developed resistance of traditional anti-cancer drugs, new drugs that can target specific carcinogenic pathways are being sought based on molecular biology, such as small molecules, antibodies, RNAs, and DNAs. Among these, microRNA inhibitors (miRi) hold great promise in cancer therapeutics by down-regulating the proteins promoting multi-drug resistance. miRNA is a short non-coding RNA that can effectively inhibit protein translation or degrade specific mRNA transcripts. One unique feature of miRNA is that one miRNA can regulate multiple gene expressions. A key miRNA can act as a master switch for multiple pathways. An approach of a NP design carrying miRNA-21 inhibitor (miR-21i) and chemotherapeutic agent is expected to effectively treat the current challenges of drug resistance. However, the synthesis of a co-delivery system encapsulating miRNA inhibitor and chemotherapeutic agent is quite challenging, due to the opposite nature of the hydrophilicity of RNAs and the hydrophobicity of anti-cancer drugs.

In this study, a NP drug delivery system using biocompatible poly (l-lactic acid) (PLLA) was used to encapsulate doxorubicin (Dox). In order to increase the hydrophilicity, the NP system was coated with both 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino(polyethylene glycol) (DSPE-PEG) and dioleoylphosphatydic acid (DOPA), an anionic lipid. Negatively charged RNAs can condense with positively charged calcium ions to form a precipitated solid complex by the electrostatic interactions. Then an excess amount of the positive charges is neutralized by coating the complex with an anionic lipid DOPA. Thus the surface coating of the CaP/RNA complex with the hydrophilic head of the anionic lipid protects hydrophilic RNA from hydrophobic polymer, and the hydrophobic tail end allows the complex to be encapsulated along with Dox inside the hydrophobic polymeric NP structure. By delivering miR-21i and Dox simultaneously, the miR-21i upregulated tumor suppressor genes such as PTEN and PDCD4, thereby sensitizing the cells towards Dox. The optimization of the NP system with respect to particle size, polydispersity, drug loading as a function of different ratios of DOPA and DSPE-PEG is studied and will be presented. The optimum lipid to polymer ratio was found to be >50% (wt.) while a molar ratio of 1 to 9 for DOPA to DSPE-PEG gave the most stable particle with a size of ~75 nm. This NP system is tested against the two breast cancer cells of MCF7 and MDA-MB-231, and their cytotoxic efficacy would be presented. The results show that this combination therapy can improve the therapeutic index.