A Novel Ex Vivo Tumor Spheroid-Tissue Model for Investigating Microvascular Remodeling and Lymphatic Blood Vessel Plasticity.

Biomimetic tumor microenvironment models bridge the gap between in vitro and in vivo systems and serve as a useful way to address the modeling challenge of how to recreate the cell and system complexity associated with real tissues. Our laboratory has developed an ex vivo rat mesentery culture model, which allows for simultaneous investigation of blood and lymphatic microvascular network remodeling in an intact tissue environment. Given that angiogenesis and lymphangiogenesis are key contributors to the progression of cancer, the objective of this study was to combine tissue and tumor spheroid culture methods to establish a novel ex vivo tumor spheroid-tissue model by verifying its use for evaluating the effects of cancer cell behavior on the local microvascular environment. H1299 or A549 tumor spheroids were formed via hanging drop culture and seeded onto rat mesenteric tissues harvested from adult male Wistar rats. Tissues with transplanted spheroids were cultured in serum-free media for 3 to 5 days. PECAM, NG2, CD11b, and αSMA labeling identified endothelial cells, pericytes, immune cells, and smooth muscle cells, respectively. Time-lapse imaging confirmed cancer cell type specific migration. In addition to increasing PECAM positive capillary sprouting and LYVE-1 positive endothelial cell extensions indicative of lymphangiogenesis, tumor spheroid presence induced the formation of lymphatic/blood vessel connections and the formation of hybrid, mosaic vessels that were characterized by discontinuous LYVE-1 labeling. The results support the application of a novel tumor spheroid microenvironment model for investigating cancer cell-microvascular interactions.

Natural Killer Cell Mechanosensing in Solid Tumors.

Natural killer (NK) cells, which are an exciting alternative cell source for cancer immunotherapies, must sense and respond to their physical environment to traffic to and eliminate cancer cells. Herein, we review the mechanisms by which NK cells receive mechanical signals and explore recent key findings regarding the impact of the physical characteristics of solid tumors on NK cell functions. Data suggest that different mechanical stresses present in solid tumors facilitate NK cell functions, especially infiltration and degranulation. Moreover, we review recent engineering advances that can be used to systemically study the role of mechanical forces on NK cell activity. Understanding the mechanisms by which NK cells interpret their environment presents potential targets to enhance NK cell immunotherapies for the treatment of solid tumors.

Drug Delivery Strategies and Nanozyme Technologies to Overcome Limitations for Targeting Oxidative Stress in Osteoarthritis.

Oxidative stress is an important, but elusive, therapeutic target for osteoarthritis (OA). Antioxidant strategies that target oxidative stress through the elimination of reactive oxygen species (ROS) have been widely evaluated for OA but are limited by the physiological characteristics of the joint. Current hallmarks in antioxidant treatment strategies include poor bioavailability, poor stability, and poor retention in the joint. For example, oral intake of exogenous antioxidants has limited access to the joint space, and intra-articular injections require frequent dosing to provide therapeutic effects. Advancements in ROS-scavenging nanomaterials, also known as nanozymes, leverage bioactive material properties to improve delivery and retention. Material properties of nanozymes can be tuned to overcome physiological barriers in the knee. However, the clinical application of these nanozymes is still limited, and studies to understand their utility in treating OA are still in their infancy. The objective of this review is to evaluate current antioxidant treatment strategies and the development of nanozymes as a potential alternative to conventional small molecules and enzymes.

Functional Interrogation of Ca2+ Signals in Human Cancer Cells In Vitro and Ex Vivo by Fluorescent Microscopy and Molecular Tools.

Genetically encoded calcium indicators (GECIs) and high-resolution confocal microscopy enable dynamic visualization of calcium signals in cells and tissues. Two-dimensional and 3D biocompatible materials mimic the mechanical microenvironments of tumor and healthy tissues in a programmable manner. Cancer xenograft models and ex vivo functional imaging of tumor slices reveal physiologically relevant functions of calcium dynamics in tumors at different progression stages. Integration of these powerful techniques allows us to quantify, diagnose, model, and understand cancer pathobiology. Here, we describe detailed materials and methods used to establish this integrated interrogation platform, from generating transduced cancer cell lines that stably express CaViar (GCaMP5G + QuasAr2) to in vitro and ex vivo calcium imaging of the cells in 2D/3D hydrogels and tumor tissues. These tools open the possibility for detailed explorations of mechano-electro-chemical network dynamics in living systems.

Application of magnetic particle imaging to evaluate nanoparticle fate in rodent joints.

Nanoparticles are a promising approach for improving intra-articular drug delivery and tissue targeting. However, techniques to non-invasively track and quantify their concentration in vivo are limited, resulting in an inadequate understanding of their retention, clearance, and biodistribution in the joint. Currently, fluorescence imaging is often used to track nanoparticle fate in animal models; however, this approach has limitations that impede long-term quantitative assessment of nanoparticles over time. The goal of this work was to evaluate an emerging imaging modality, magnetic particle imaging (MPI), for intra-articular tracking of nanoparticles. MPI provides 3D visualization and depth-independent quantification of superparamagnetic iron oxide nanoparticle (SPION) tracers. Here, we developed and characterized a polymer-based magnetic nanoparticle system incorporated with SPION tracers and cartilage targeting properties. MPI was then used to longitudinally assess nanoparticle fate after intra-articular injection. Magnetic nanoparticles were injected into the joints of healthy mice, and evaluated for nanoparticle retention, biodistribution, and clearance over 6 weeks using MPI. In parallel, the fate of fluorescently tagged nanoparticles was tracked using in vivo fluorescence imaging. The study was concluded at day 42, and MPI and fluorescence imaging demonstrated different profiles in nanoparticle retention and clearance from the joint. MPI signal was persistent over the study duration, suggesting NP retention of at least 42 days, much longer than the 14 days observed based on fluorescence signal. These data suggest that the type of tracer - SPIONs or fluorophores - and modality of imaging can affect interpretation of nanoparticle fate in the joint. Given that understanding particle fate over time is paramount for attaining insights about therapeutic profiles in vivo, our data suggest MPI may yield a quantitative and robust method to non-invasively track nanoparticles following intra-articular injection on an extended timeline.

PRDX-1 Supports the Survival and Antitumor Activity of Primary and CAR-Modified NK Cells under Oxidative Stress.

Oxidative stress, caused by the imbalance between reactive species generation and the dysfunctional capacity of antioxidant defenses, is one of the characteristic features of cancer. Here, we quantified hydrogen peroxide in the tumor microenvironment (TME) and demonstrated that hydrogen peroxide concentrations are elevated in tumor interstitial fluid isolated from murine breast cancers in vivo, when compared with blood or normal subcutaneous fluid. Therefore, we investigated the effects of increased hydrogen peroxide concentration on immune cell functions. NK cells were more susceptible to hydrogen peroxide than T cells or B cells, and by comparing T, B, and NK cells' sensitivities to redox stress and their antioxidant capacities, we identified peroxiredoxin-1 (PRDX1) as a lacking element of NK cells' antioxidative defense. We observed that priming with IL15 protected NK cells' functions in the presence of high hydrogen peroxide and simultaneously upregulated PRDX1 expression. However, the effect of IL15 on PRDX1 expression was transient and strictly dependent on the presence of the cytokine. Therefore, we genetically modified NK cells to stably overexpress PRDX1, which led to increased survival and NK cell activity in redox stress conditions. Finally, we generated PD-L1-CAR NK cells overexpressing PRDX1 that displayed potent antitumor activity against breast cancer cells under oxidative stress. These results demonstrate that hydrogen peroxide, at concentrations detected in the TME, suppresses NK cell function and that genetic modification strategies can improve CAR NK cells' resistance and potency against solid tumors.

Innovation-Oriented Medical School Curricula: Review of the Literature.

Innovation and entrepreneurship (I&E) programs in medical education have become available as medical schools recognize the need to train forward-thinking physicians. There is considerable diversity in the design and implementation of these curricula, which represents a challenge and possibly serves as a deterrent for the development of additional I&E programs. A comprehensive search of medical school I&E programs and review of all Association of American Medical Colleges member websites (n = 171) were conducted. This review sought to (1) identify all American and Canadian allopathic medical schools with I&E curricula, (2) evaluate their structure/integration in the context of medical education, (3) outline core learning themes, and (4) describe the evaluative metrics. Information was collected through published or publicly available websites and through a questionnaire sent to identified I&E program leaders. Twenty-eight I&E-oriented medical education programs were identified from 26 schools; all of the programs integrated faculty leadership with backgrounds in medicine, engineering, and/or business/entrepreneurship. Of the programs, 57% (16/28) had been launched within the past four years and 75% (21/28) based program enrollment on a selective application process. Nearly all (27/28) incorporated lecture series and/or hands-on modules as a teaching technique. The most prevalent metric was completion of a capstone project (22/28; 79%). At least 15.2% (26/171) of American and Canadian allopathic medical schools include the option for students to participate in an I&E curriculum-based program. This review can be used to help medical school faculty with developing I&E curricula.

Magnetically Responsive Polymeric Microparticles for the Triggered Delivery of a Complex Mixture of Human Placental Proteins.

Bone loss through traumatic injury is a significant clinical issue. Researchers have created many scaffold types to mimic an extracellular matrix to provide structural support for the formation of new bone, however functional regeneration of larger scaffolds has not been fully achieved. Newer scaffolds aim to deliver bioactive molecules to improve tissue regeneration. To achieve a more comprehensive regenerative response, a magnetically triggerable polymeric microparticle platform is developed for the on-demand release of a complex mixture of isolated human placental proteins. This system is composed of polycaprolactone (PCL) microparticles, encapsulating magnetic nanoparticles (MNPs), and placental proteins. When subjected to an alternating magnetic field (AMF), the MNPs heat and melt the PCL, enhancing the diffusion of proteins from microparticles. When the field is off, the PCL re-solidifies. This potentially allows for cyclic drug delivery. Here the design, synthesis, and proof-of-concept experiments for this system are reported. In addition, it is shown that the proteins retain function after being magnetically released. The ability to trigger the release of complex protein mixtures on-demand may provide a significant advantage with wounds where stagnation of healing processes can occur (e.g., large segmented bone defects).

Leveraging Electrostatic Interactions for Drug Delivery to the Joint.

Arthritis is a debilitating joint disease with a high economic burden and prevalence. There are many challenges delivering therapeutics to the joint, including low bioavailability when administered systemically and low joint retention after intra-articular injection. Therefore, drug delivery systems such as nanoparticles, liposomes, dendrimers, and carrier proteins have been utilized to overcome some of these limitations. To enhance joint tissue localization and retention, there are opportunities to leverage electrostatic interactions between drug carriers and various tissues and cells. These opportunities, as they pertain to specific joint tissues, are explored in this review. Further, the impact that electrostatic interactions has on various drug delivery parameters, such as the formation of a protein corona, the uptake and cytotoxicity, and the biodistribution of the drug delivery systems, is discussed. Lastly, this review summarizes key findings from studies that have investigated the use of electrostatic interactions to increase targeting of specific joint tissues and limitations in preclinical investigations are identified. As more novel targets are discovered in treating arthritis, there will be a continued need to localize therapeutics to specific tissues for greater therapeutic outcomes and hence attention must be paid in designing the drug delivery systems.

Engineered Three-Dimensional Tumor Models to Study Natural Killer Cell Suppression.

A critical hurdle associated with natural killer (NK) cell immunotherapies is inadequate infiltration and function in the solid tumor microenvironment. Well-controlled 3D culture systems could advance our understanding of the role of various biophysical and biochemical cues that impact NK cell migration in solid tumors. The objectives of this study were to establish a biomaterial which (i) supports NK cell migration and (ii) recapitulates features of the in vivo solid tumor microenvironment, to study NK infiltration and function in a 3D system. Using peptide-functionalized poly(ethylene glycol)-based hydrogels, the extent of NK-92 cell migration was observed to be largely dependent on the density of integrin binding sites and the presence of matrix metalloproteinase degradable sites. When lung cancer cells were encapsulated into the hydrogels to create tumor microenvironments, the extent of NK-92 cell migration and functional activity was dependent on the cancer cell type and duration of 3D culture. NK-92 cells showed greater migration into the models consisting of nonmetastatic A549 cells relative to metastatic H1299 cells, and reduced migration in both models when cancer cells were cultured for 7 days versus 1 day. In addition, the production of NK cell-related pro-inflammatory cytokines and chemokines was reduced in H1299 models relative to A549 models. These differences in NK-92 cell migration and cytokine/chemokine production corresponded to differences in the production of various immunomodulatory molecules by the different cancer cells, namely, the H1299 models showed increased stress ligand shedding and immunosuppressive cytokine production, particularly TGF-ß. Indeed, inhibition of TGF-ß receptor I in NK-92 cells restored their infiltration in H1299 models to levels similar to that in A549 models and increased overall infiltration in both models. Relative to conventional 2D cocultures, NK-92 cell mediated cytotoxicity was reduced in the 3D tumor models, suggesting the hydrogel serves to mimic some features of the biophysical barriers in in vivo tumor microenvironments. This study demonstrates the feasibility of a synthetic hydrogel system for investigating the biophysical and biochemical cues impacting NK cell infiltration and NK cell-cancer cell interactions in the solid tumor microenvironment.

Characterization of Post-Traumatic Osteoarthritis in Rats Following Anterior Cruciate Ligament Rupture by Non-Invasive Knee Injury (NIKI).

Small animal models are essential for studying anterior cruciate ligament (ACL) injury, one of the leading risk factors for post-traumatic osteoarthritis (PTOA). Non-surgical models of ACL rupture have recently surged as a new tool to study PTOA, as they circumvent the confounding effects of surgical disruption of the joint. These models primarily have been explored in mice and rabbits, but are relatively understudied in rats. The purpose of this work was to establish a non-invasive, mechanical overload model of ACL rupture in the rat and to study the disease pathogenesis following the injury. ACL rupture was induced via non-invasive tibial compression in Lewis rats. Disease state was characterized for 4 months after ACL rupture via histology, computed tomography, and biomarker capture from the synovial fluid. The non-invasive knee injury (NIKI) model created consistent ACL ruptures without direct damage to other tissues and resulted in conventional OA pathology. NIKI knees exhibited structural changes as early as 4 weeks post-injury, including regional structural changes to cartilage, chondrocyte and cartilage disorganization, changes to the bone architecture, synovial hyperplasia, and the increased presence of biomarkers of cartilage fragmentation and pro-inflammatory cytokines. These results suggest that this model can be a valuable tool to study PTOA. By establishing the fundamental pathogenesis of this injury, additional opportunities are created to evaluate unique contributing factors and potential therapeutic interventions for this disease. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:356-367, 2020.

Two-Year Follow-Up and Remodeling Kinetics of ChonDux Hydrogel for Full-Thickness Cartilage Defect Repair in the Knee.

OBJECTIVE: To determine performance and repair kinetics of the ChonDux hydrogel scaffold for treating focal articular cartilage defects in the knee over 24 months. DESIGN: This assessor-blinded trial evaluates ChonDux hydrogel scaffold implantation in combination with microfracture in 18 patients across 6 sites. Male and female patients 18 to 65 years of age with full-thickness femoral condyle defects 2 to 4 cm2 in area were enrolled. Eligible patients received ChonDux treatment followed by rehabilitation. Defect volume fill was evaluated after 3, 6 (primary outcome), 12, 18, and 24 months by assessor blinded magnetic resonance imaging (MRI) analysis. Secondary outcomes were T2-weighted MRI relaxation time and patient surveys via visual analogue scale (VAS) pain and International Knee Documentation Committee (IKDC) knee function scoring. RESULTS: ChonDux maintained durable tissue restoration over 24 months with final defect percent fill of 94.2% ± 16.3% and no significant loss of fill volume at any time points. Tissues treated with ChonDux maintained T2 relaxation times similar to uninjured cartilage between 12 and 24 months. VAS pain scoring decreased between 1 and 6 weeks, and IKDC knee function scores improved by approximately 30.1 with ChonDux over 24 months. CONCLUSION: ChonDux treatment is a safe adjunct to microfracture therapy and promotes stable restoration of full thickness articular cartilage defects for at least 24 months.

Effects of cartilage-targeting moieties on nanoparticle biodistribution in healthy and osteoarthritic joints.

Understanding intra-articular biodistribution is imperative as candidate osteoarthritis (OA) drugs become increasingly site-specific. Cartilage has been identified as opportunistic for therapeutic intervention, but poses numerous barriers to drug delivery. To facilitate drug delivery to cartilage, nanoscale vehicles have been designed with different features that target the tissue's matrix. However, it is unclear if these targeting strategies are influenced by OA and the associated structural changes that occur in cartilage. The goal of this work was to study the effectiveness of different cartilage-targeting nanomaterials with respect to cartilage localization and retention, and to determine how these outcomes change in OA. To address these questions, a nanoparticle (NP) system was developed, and the formulation was tuned to possess three distinct cartilage-targeting strategies: (1) passive targeting cationic NPs for electrostatic attraction to cartilage, (2) active targeting NPs with binding peptides for collagen type II, and (3) untargeted neutrally-charged NPs. Ex vivo analyses with bovine cartilage explants demonstrated that targeting strategies significantly improved NP associations with both healthy and OA-like cartilage. In vivo studies with collagenase-induced OA in rats revealed that disease state influenced joint biodistribution for all three NP formulations. Importantly, the extent of cartilage accumulation for each NP system was affected by disease differently; with active NPs, but not passive NPs, cartilage accumulation was increased in OA relative to healthy knees. Together, this work suggests that NPs can be strategically designed for site-specific OA drug delivery, but the biodistribution of the NPs are influenced by the disease conditions into which they are delivered. STATEMENT OF SIGNIFICANCE: As emerging drugs for osteoarthritis are becoming increasingly site-specific, the need for targeted intra-articular drug delivery has evolved. To improve drug delivery to cartilage, targeting strategies for nanomaterials have been developed, but the manner in which these targeted systems accumulate at different sites within the joint remains poorly understood. Moreover, it is unclear how nanomaterial-tissue interactions change in osteoarthritic conditions, as tissue structure and composition change after disease onset. By understanding how nanomaterials distribute within healthy and disease joints, we can advance targeted drug delivery strategies and improve therapeutic outcomes for emerging drugs.

Manganese dioxide nanoparticles protect cartilage from inflammation-induced oxidative stress.

Oxidative stress has been implicated in the pathogenesis of osteoarthritis and has become an important therapeutic target. Investigations of various antioxidant supplements, reactive oxidative species (ROS) pathway mediators, and free radical scavengers for treating osteoarthritis have demonstrated common disadvantages including poor bioavailability and stability, as well as rapid joint clearance or release profiles from delivery vehicles. Moreover, these therapies do not target cartilage, which irreversibly degenerates in the presence of oxidative stress. The goal of this study was to engineer a nanoparticle system capable of sustained retention in the joint space, localization to cartilage, and mitigation of oxidative stress. Towards this goal, ROS scavenging manganese dioxide nanoparticles with physicochemical properties (less than 20 nm and cationic) that facilitate their uptake into cartilage were developed and characterized. These particles penetrated through the depth of cartilage explants and were found both in the extracellular matrix as well as intracellularly within the resident chondrocytes. Furthermore, the particles demonstrated chondroprotection of cytokine-challenged cartilage explants by reducing the loss of glycosaminoglycans and release of nitric oxide. Quantitative PCR analysis revealed that the particles mitigated impacts of oxidative stress related genes in cytokine-challenged chondrocytes. When injected intra-articularly into rats, the particles persisted in the joint space over one week, with 75% of the initial signal remaining in the joint. Biodistribution and histological analysis revealed accumulation of particles at the chondral surfaces and colocalization of the particles with the lacunae of chondrocytes. The results suggest that the manganese dioxide nanoparticles could be a promising approach for the chondroprotection of osteoarthritic cartilage.

Intra-articular targeting of nanomaterials for the treatment of osteoarthritis.

Osteoarthritis is a prevalent and debilitating disease that involves pathological contributions from numerous joint tissues and cells. The joint is a challenging arena for drug delivery, since the joint has poor bioavailability for systemically administered drugs and experiences rapid clearance of therapeutics after intra-articular injection. Moreover, each tissue within the joint presents unique barriers to drug localization. In this review, the various applications of nanotechnology to overcome these drug delivery limitations are investigated. Nanomaterials have reliably shown improvements to retention profiles of drugs within the joint space relative to injected free drugs. Additionally, nanomaterials have been modified through active and passive targeting strategies to facilitate interactions with and localization within specific joint tissues such as cartilage and synovium. Last, the limitations of drawing cross-study comparisons, the implications of synovial fluid, and the potential importance of multi-modal therapeutic strategies are discussed. As emerging, cell-specific disease modifying osteoarthritis drugs continue to be developed, the need for targeted nanomaterial delivery will likely become critical for effective clinical translation of therapeutics for osteoarthritis. STATEMENT OF SIGNIFICANCE: Improving drug delivery to the joint is a pressing clinical need. Over 27 million Americans live with osteoarthritis, and this figure is continuously expanding. Numerous drugs have been investigated but have failed in clinical trials, likely related to poor bioavailability to target cells. This article comprehensively reviews the advances in nano-scale delivery vehicles designed to overcome the delivery barriers in the joint. This is the first review to analyze active and passive targeting strategies systematically for different target sites while also delineating between tissue homing and whole joint retention. By bringing together the lessons learned across numerous nano-scale platforms, researchers may be able to hone future nanomaterial designs, allowing emerging therapeutics to perform with clinically relevant efficacy and disease modifying potential.

Multifunctional nanoparticles for intracellular drug delivery and photoacoustic imaging of mesenchymal stem cells.

Strategies that control the differentiation of mesenchymal stem cells (MSC) and enable image-guided cell implantation and longitudinal monitoring could advance MSC-based therapies for bone defects and injuries. Here we demonstrate a multifunctional nanoparticle system that delivers resveratrol (RESV) intracellularly to improve osteogenesis and enables photoacoustic imaging of MSCs. RESV-loaded nanoparticles (RESV-NPs), formulated from poly (lactic-co-glycolic) acid and iron oxide, enhanced the stability of RESV by 18-fold and served as photoacoustic tomography (PAT) contrast for MSCs. Pre-loading MSCs with RESV-NP upregulated RUNX2 expression with a resultant increase in mineralization by 27% and 45% compared to supplementation with RESV-NP and free RESV, respectively, in 2-dimensional cultures. When grown in polyethylene glycol-based hydrogels, MSCs pre-loaded with RESV-NPs increased the overall level and homogeneity of mineralization compared to those supplemented with free RESV or RESV-NP. The PAT detected RESV-NP-loaded MSCs with a resolution of 1500 cells/µL, which ensured imaging of MSCs upon encapsulation in a PEG-based hydrogel and implantation within the rodent cranium. Significantly, RESV-NP-loaded MSCs in hydrogels did not show PAT signal dilution over time or a reduction in signal upon osteogenic differentiation. This multifunctional NP platform has the potential to advance translation of stem cell-based therapies, by improving stem cell function and consistency via intracellular drug delivery, and enabling the use of a promising emerging technology to monitor cells in a clinically relevant manner.

Nanoparticle Properties for Delivery to Cartilage: The Implications of Disease State, Synovial Fluid, and Off-Target Uptake.

A major hurdle limiting the ability to treat and cure osteoarthritis, a common and debilitating disease, is rapid joint clearance and limited cartilage targeting of intra-articular therapies. Nanoscale drug carriers have the potential to improve therapeutic targeting and retention in the joint after direct injection; however, there still lacks a fundamental understanding of how the physicochemical properties of nanoparticles (NPs) influence localization to the degenerating cartilage and how joint conditions such as disease state and synovial fluid impact NP biodistribution. The goal of this study was to assess how physicochemical properties of NPs influence their interactions with joint tissues and, ultimately, cartilage localization. Ex vivo models of joint tissues were used to study how poly(lactide- co-glycolide) (PLGA) and polystyrene (PS) NP size, charge, and surface chemistry influence cartilage retention under normal and disease-mimicking conditions. Of the particles investigated, PLGA NPs surface-modified with a quaternary ammonium cation had the greatest retention within cartilage explants; however, retention was diminished 2- to 2.9-fold in arthritic tissue and in the presence of synovial fluid. Interactions with synovial fluid induced changes to NP surface properties and colloidal stability in vitro. The impact of NP charge on "off-target" synoviocyte uptake was also dependent on synovial fluid interactions. The results suggest that the design of nanocarriers for targeted drug delivery within the joint cannot be based on a single parameter such as zeta potential or size, and that the fate of injected delivery systems will likely be influenced by the disease state of the joint and the presence of synovial fluid.

Targeted Nanomedicine to Treat Bone Metastasis.

Bone metastases are common complications of solid tumors, particularly those of the prostate, breast, and lungs. Bone metastases can lead to painful and devastating skeletal-related events (SREs), such as pathological fractures and nerve compressions. Despite advances in treatment for cancers in general, options for bone metastases remain inadequate and generally palliative. Anticancer drugs (chemotherapy and radiopharmaceuticals) do not achieve therapeutic concentrations in the bone and are associated with dose-limiting side effects to healthy tissues. Nanomedicines, with their tunable characteristics, have the potential to improve drug targeting to bone metastases while decreasing side effects for their effective treatment. In this review, we present the current state of the art for nanomedicines to treat bone metastases. We also discuss new treatment modalities enhanced by nanomedicine and their effects on SREs and disease progression.

Inhibition of bone loss with surface-modulated, drug-loaded nanoparticles in an intraosseous model of prostate cancer.

Advanced-stage prostate cancer usually metastasizes to bone and is untreatable due to poor biodistribution of intravenously administered anticancer drugs to bone. In this study, we modulated the surface charge/composition of biodegradable nanoparticles (NPs) to sustain their blood circulation time and made them small enough to extravasate through the openings of the bone's sinusoidal capillaries and thus localize into marrow. NPs with a neutral surface charge, achieved by modulating the NP surface-associated emulsifier composition, were more effective at localizing to bone marrow than NPs with a cationic or anionic surface charge. These small neutral NPs (~150nm vs. the more usual ~320nm) were also ~7-fold more effective in localizing in bone marrow than large NPs. We hypothesized that NPs that effectively localize to marrow could improve NP-mediated anticancer drug delivery to sites of bone metastasis, thereby inhibiting cancer progression and preventing bone loss. In a PC-3M-luc cell-induced osteolytic intraosseous model of prostate cancer, these small neutral NPs demonstrated greater accumulation in bone within metastatic sites than in normal contralateral bone as well as co-localization with the tumor mass in marrow. Significantly, a single-dose intravenous administration of these small neutral NPs loaded with paclitaxel (PTX-NPs), but not anionic PTX-NPs, slowed the progression of bone metastasis. In addition, neutral PTX-NPs prevented bone loss, whereas animals treated with the rapid-release drug formulation Cremophor EL (PTX-CrEL) or saline (control) showed >50% bone loss. Neutral PTX-NPs did not cause acute toxicity, whereas animals treated with PTX-CrEL experienced weight loss. These results indicate that NPs with appropriate physical and sustained drug-release characteristics could be explored to treat bone metastasis, a significant clinical issue in prostate and other cancers.