Poster Z5 - Dissecting Nanoparticle Fate in Osteoarthritis: A Comparative Study of Fluorescence and Magnetic Particle Imaging in Surgical and Non-Surgical Models

Introduction: Understanding nanoparticle (NP) tracking and long-term NP fate are critical components in advancing novel drug delivery strategies towards translation. Specifically in osteoarthritis (OA), nanomaterial therapies are limited by poor bioavailability and poor retention in the target tissue. To engineer effective OA treatments, it is necessary to understand both where the material is localizing and how long it is retained there. Imaging modalities relying on fluorescent tracking, including IVIS, are the current gold standard for evaluating nanoparticle fate. However, these strategies are limited by tissue depth attenuation, background signal, and photobleaching, rendering them semi-quantitative. Magnetic particle imaging (MPI) is an emerging technology that enables non-invasive visualization and quantification of superparamagnetic iron oxide (SPION) tracers without depth attenuation or background, and signal is unambiguously proportional to SPINO mass, making it a promising modality to understand NP fate. The goal of this study was to engineer NPs dual labeled for MPI and IVIS imaging, and compare their outcomes for NP tracking after administration into OA joints. A secondary objective was to determine is the type of OA model (surgical vs. non-surgical) impacts NP retention, clearance, and biodistribution.

Materials and

Methods: Dual-labeled poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) were engineered by encapsulating with superparamagnetic iron oxide nanoparticles (SPIONs) and conjugating them with fluorophores (Alexaflour 750). Dual-labeled NPs were characterized by DLS for hydrodynamic diameter (Dh) and zeta potential. Characterization was compared to single-labeled NPs designed with either A750 or SPION encapsulation. Male C57bL/6 mice were subjected to either an anterior cruciate ligament transection (ACLT) surgery, a non-invasive tibial compression for ACL rupture (ACLR), or no injury (n = 10/group). To assess the effects of wound healing on particle fate, two cohorts of the study were completed with endpoints 3 or 14 days following OA-induction. 24 hours after injury 10 uL of dual-labeled NPs (10 mg/ml) were administered via intra-articular injection in the affected knee, with 10 uL saline injected into the contralateral limb as a control. NP signal was measured via MPI (info) and IVIS (info) until endpoint (day 1, 2, 3, 7, and 14). Following endpoint, the joints were removed and separated then imaged on the IVIS and MPI to measure the signal of retained NP in the joint. Major organs were also removed and imaged on IVIS and MPI to evaluate NP clearance.

Results, Conclusions, and Discussions: Dual-labeled NPs had an average hydrodynamic diameter of 201 nm ± 30.71 and a surface charge of 31 mV ± 2.56, which was similar to single-labeled NPs. However, iron mass and iron content were significantly decreased in dual-labeled NPs (0.12 mg ± 0.04, 4.0% w/w ± 2.03) compared to single-labeled NPs (0.32 mg ± 0.02, 7.2 %w/w ± .71) which resulted in significantly lower MPI signal (4.3 x 105 ± 3.7 x104 ) compared to single-labeled NPs (5.9 x 105 ± 1.6 x 105) (p = 0.04). NP retention and clearance differed based on MPI and IVIS signal. Fluorescence signal diminished by day 14 for NP retention, while MPI signal remained consistent. MPI signal was equivalent to a measure of 87% of NPs retained in the joint at endpoint, compared to non as measured by IVIS. At endpoint, fluorescent signal was detected in the spleen, lungs, kidneys, and liver. However, there was no magnetic signal detected in the organs. NP biodistribution within the joint varied between ACLT and ACLR animals at the early endpoint (day 3); however, this difference was not present at the later endpoint (day 14). Taken together, these results point to the need to carefully consider the choice of imaging system utilized when investigating drug delivery systems or therapeutics. A major advantage of MPI over IVIS is its capability to translate its signal to iron mass, as MPI signal linearly correlates with iron concentration. To our knowledge, this study represents the first application of dual-labeled NPs with MPI and IVIS capabilities in multiple OA models, providing opportunities to accurately understand the efficacy and specificity of targeted delivery using NPs as OA progresses. This study also demonstrates the MPI offers a robust method for NP tracking providing an accurate assessment of NP fate and potential therapeutics for OA.

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