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Stiffness of targeted layer-by-layer nanoparticles impacts elimination half-life, tumor accumulation, and tumor penetration

Significance Layer-by-layer nanoparticles (LbL NPs), comprised of a charged core substrate layered sequentially with oppositely charged polyelectrolytes, are a promising class of drug delivery carriers for cancer therapeutics with demonstrated success in lowering off-target toxicity and enhancing efficacy. However, little is known about how LbL NP stiffness alters trafficking and delivery. Herein, we report that the stiffness of targeted LbL NPs, comprised of a liposome core and tumor-targeting, polymeric outer layers, can be tuned by altering the mechanical properties of its underlying liposomal core. We also show that these changes have a significant impact on in vivo NP trafficking properties; compliant LbL NPs have longer elimination times, higher organ and tumor accumulation, and higher tumor penetration. Nanoparticle (NP) stiffness has been shown to significantly impact circulation time and biodistribution in anticancer drug delivery. In particular, the relationship between particle stiffness and tumor accumulation and penetration in vivo is an important phenomenon to consider in optimizing NP-mediated tumor delivery. Layer-by-layer (LbL) NPs represent a promising class of multifunctional nanoscale drug delivery carriers. However, there has been no demonstration of the versatility of LbL systems in coating systems with different stiffnesses, and little is known about the potential role of LbL NP stiffness in modulating in vivo particle trafficking, although NP modulus has been recently studied for its impact on pharmacokinetics. LbL nanotechnology enables NPs to be functionalized with uniform coatings possessing molecular tumor-targeting properties, independent of the NP core stiffness. Here, we report that the stiffness of LbL NPs is directly influenced by the mechanical properties of its underlying liposomal core, enabling the modulation and optimization of LbL NP stiffness while preserving LbL NP outer layer tumor-targeting and stealth properties. We demonstrate that the stiffness of LbL NPs has a direct impact on NP pharmacokinetics, organ and tumor accumulation, and tumor penetration—with compliant LbL NPs having longer elimination half-life, higher tumor accumulation, and higher tumor penetration. Our findings underscore the importance of NP stiffness as a design parameter in enhancing the delivery of LbL NP formulations.