Cationic Spherical Nucleic Acids for Intracellular Delivery of an Immunomodulant

Abstract

The growing epidemic of antimicrobial resistance has caused significant morbidity rates worldwide as well as increasing probabilities of cancer recurrence. Efforts to address this epidemic have turned to immunomodulators, a class of molecules which modify the immune system in order to fight off infection. Muramyl dipeptide (MDP) is an immunomodulator of interest due to its specificity for NOD2, a primary receptor involved in immunoregulation. However, use of MDP in vivo causes an overly strong immunostimulatory effect; furthermore, MDP is rapidly cleared from the body due to high solubility and low molecular weight. In order to improve the clinical outlook of MDP, multiple analogues and delivery methods have been explored, with mixed success. MDP analogues have found the most success as adjuvants, although strict FDA approval guidelines limit this approach. Delivery methods for MDP are costly and also induce cytotoxicity, thereby emphasizing the clinical challenges of MDP. Introduced in 1996, Spherical Nucleic Acids (SNAs) are radially oriented oligonucleotides on a nanoparticle surface. SNAs have been shown to readily enter cells with little to no cytotoxicity and in fact, they have found clinical success in a variety of gene delivery and vaccine applications, making them a versatile platform for drug delivery. Herein, we demonstrate that SNAs can be applied as cellular delivery vehicles for MDP. To achieve this, we synthesized dual-layer SNAs whereby two unique oligonucleotides were functionalized onto a gold nanoparticle core. We show that by modulating the surface charge of the SNAs, faster cellular uptake can be achieved, which presents promise for increasing drug delivery and reaching cell compartments of interest. Additionally, we show early evidence that conjugation of MDP to the SNA corona retains MDP activity. Taken together, this work proposes effective SNA designs to deliver muramyl-based immunostimulants, which show promise in the expansion of SNA utility into immunomodulation.