Deformable Nanocarrier for Systemic Delivery of siRNA or Small-Molecule to Solid Tumors

Nucleic acids are promising drug candidates as they can address diseases with few “druggable” targets. Nevertheless, nucleic acids are challenging to deliver because of their large molecular weights, dense negative charges, proinflammatory activities, and short half-lives in biological fluids. Synthetic gene carriers based on cationic polymers or lipids have been used to overcome these challenges; however, their cationic nature results in dose-limiting toxicities and accelerated removal by the filtering MPS organs after systemic administration. In the past six years, several nucleic acid-based therapeutics have been approved by the FDA, formulated as lipid nanoparticles (LNPs). Nonetheless, LNPs show extensive liver accumulation after intravenous administration and, hence, are only indicated for hepatic or local vaccine delivery applications. Therefore, there is a critical unmet need for a nanocarrier that delivers nucleic acids to the extrahepatic organs without significant toxicities. To address this need, we developed Nanosac, a deformable and non-cationic nanocarrier, to deliver siRNA to solid tumors. Deformability can improve multiple aspects of the nanoparticle biotransport, ranging from circulation time and protein corona composition to biodistribution and interactions with the target cells. Meanwhile, a non-cationic carrier avoids proinflammatory complications and rapid clearance of cationic nanoparticles. For this application, we used siRNAs targeting CD47/SIRPa and PD-l/PD-L1 immune checkpoints due to their critical roles as “don't-eat-me” and “don't-find-me” signals to immune cells, respectively, which interfere with the development of innate and adaptive antitumor immune responses.

In the same context of enhancing the tumor delivery of nanomedicine, we developed two formulations for the small-molecule chemo drug, carfilzomib (CFZ). A nanocrystal formulation with optimized particle size had high CFZ loading, adequate colloidal stability in circulation and better antitumor activity in mice than the FDA-approved CFZ formulation. Despite its improved efficacy, the stiff nanocrystals aggravated CFZ immunotoxicity due to its excessive accumulation in mice spleens. To address this issue, we employed Nanosac technology for CFZ delivery, exploiting its deformability to reduce the non-specific spleen distribution and enhance CFZ tolerability.

Our results showed that Nanosac delivered siRNA to tumor cells and silenced the target protein expression better than LNPs. In vivo, Nanosac reduced siRNA accumulation in the MPS organs and achieved greater siRNA-mediated tumor suppression than LNPs in two murine tumor models. Moreover, Nanosac achieved greater checkpoint protein silencing in tumors, but less silencing in the MPS organs than LNPs, highlighting their differential biodistribution. The superior Nanosac performance relative to LNPs after systemic delivery is likely due to the difference in their protein coronas and cellular delivery capabilities. In addition, CFZ loading in Nanosac ameliorated CFZ immune cell toxicity in vitro and improved its tolerability in mice while maintaining similar therapeutic efficacy compared to the stiff nanocrystal formulation. Collectively, these findings highlight nanocarrier deformability and corona composition as viable strategies to improve the extrahepatic delivery of nucleic acids as well as to minimize toxicities related to extensive NP distribution to the off-target MPS organs.