Intra-articular drug delivery systems for joint diseases

Abstract

Intra-articular (IA) injections directly deliver high concentrations of therapeutics to the joint space and are routinely used in various musculoskeletal conditions such as osteoarthritis (OA) and rheumatoid arthritis (RA). However, current IA-injected drugs are rapidly cleared and do not significantly affect the course of joint disease. In this review, we highlight recent developments in IA therapy, with a special emphasis on current and emerging therapeutic carriers and their potential to deliver disease-modifying treatment modalities for arthritis. Recent IA approaches concentrate on platforms that are safe with efficient tissue penetration, and readily translatable for controlled and sustained delivery of therapeutic agents. Gene therapy delivered by viral or non-viral vectors and cell-based therapy for cartilage preservation and regeneration are being intensively explored.

Introduction

Intra-articular (IA) drug delivery presents many advantages as it offers direct access to the joint space, thus increasing the bioavailability of therapeutic agents at the affected site while reducing systemic exposure, potential side effects and overall cost. Although IA injections are generally considered safe, their therapeutic effectiveness remains severely limited due to rapid clearance of the drugs. IA injections are routinely used for various rheumatic diseases, especially osteoarthritis (OA), the most common form of arthritis that usually affects a few large joints but can result in severe disability, often requiring costly joint replacement [1].

The focus of current research is to move OA from a disease requiring joint replacement to one that can be managed with early detection and medical intervention. While the pathogenesis of OA remains poorly understood, post-traumatic OA (PTOA) offers a model to study early changes and provides an opportunity for intervention as the time and nature of the initial trauma are generally known [2,3]. As depicted in Figure 1, a joint trauma can set off a series of molecular-level events beginning immediately with disturbance in joint homeostasis [4,5] and, over time, leading to end-stage OA characterized by structural changes [6]. Arthroscopic strategies for meniscus and/or ligament repair do not alter the course of disease [7]. Currently, pain management and physical therapy offer short-term benefits, but they cannot prevent surgical joint replacement [8,9]. Unless, new therapeutic interventions targeting pre-OA at the onset of disease become available, OA will remain a non-curable disease resulting in higher number of joint replacement surgeries at younger age.

Figure 1.

Stages of OA after initial trauma. At the molecular level, a joint trauma can set off a series of events immediately beginning with disturbance in joint homeostasis and, over time, leading to end-stage disease. The focus of research is shifting, albeit slowly, from end-stage disease, where total joint replacement is the only solution, to pre-OA stage where early molecular markers can predict the likelihood of clinical disease. At each stage following trauma, a distinct set of biochemical changes occur.

Currently few options exist for IA treatment. Corticosteroids are often administered IA to treat pain and resolve the joint effusion associated with rheumatoid arthritis (RA) and OA. Their effect, however, is short-lived and does not modify disease progression [10,11]. Likewise, hyaluronic acid (HA), a viscosupplementation approved by the U.S. Food & Drug Administration (FDA), is commonly used to treat OA. However, there is no conclusive evidence that HA, in its original formulation, delays or prevents the need for joint replacement [12,13]. Ideal IA drug delivery platforms should offer controlled release of the therapeutic agent with extended bioavailability and joint retention, have no or minimal safety concerns, promise a disease-modifying effect and/or cartilage regeneration, and be readily translatable. Despite recent advances, no single IA drug delivery platform fulfills all these properties.

In this review, we have summarized recent developments in IA therapy (Figure 2), with a discussion on how therapeutic delivery systems are being developed to meet the above criteria.

Figure 2.

Overview of IA delivery platforms. IA injections deliver therapeutics to the joint space to treat joint disorders. The emerging trends focus is on IA delivery of disease-modifying therapeutics via: 1) sustained and controlled drug delivery platforms, 2) gene therapy using viral-mediated vectors or non-viral platforms, including nanoparticles or induced pluripotent stem cells, and 3) stem cell-based tissue-engineered products without or with scaffolds. HA-PEG = hyaluronic acid – poly(ethylene glycol).

Synthetic, controlled release drug delivery platforms

Rapid clearance of drugs from the joint limits the efficacy of many IA therapeutics such as corticosteroids and HA (reviewed in [14]), prompting the search for safe formulations that, offer sustained and extended drug availability. To this end, numerous natural and synthetic (bio)materials have been employed to achieve ideal properties such as increased articular dwell time with slow and steady (controlled) drug release and safe biodegradation of delivery vehicle. Each type of biomaterials has advantages and disadvantages as summarized in in Box I.

Highlights.

• Focus on disease-modifying approaches for intra-articular drug delivery

• Polymeric particles as platforms for sustained and controlled drug release

• In vivo delivery of nucleic acids for cartilage preservation and regeneration

• Stem cell-based tissue-engineered products for cartilage regeneration

Polymeric micelles are the most studied platforms for IA drug delivery. These nanoscale carriers are composed of amphiphilic polymers that self-assemble into nanostructures [15]. They provide several inherent properties that allow the encapsulation of a wide range of therapeutics, including poorly soluble compounds, for controlled and sustained release as well as protection of the encapsulated drugs from in vivo degradation and clearance [16]. These properties make polymeric micelles ideally suited for IA drug delivery to extend drug exposure time and to prevent rapid clearance by synovial phagocytes. Several applications of micelles have been explored for OA and RA treatment. Various hydrophobic, small molecule drugs (e.g., indomethacin, dexamethasone) have been incorporated into micelles and administered either IA or systemically [17]. Polymeric micelles have favorable toxicity profiles and could serve as extended drug delivery platforms [18].

Hydrogels represent another promising mode of IA drug delivery. It is known that HA has a short half-life (1–2 days in the tissue) and the use of unmodified HA is severely limited by high degradation rate, poor mechanical properties, and rapid clearance. To produce mechanically and chemically stable HA while retaining its biocompatibility, aqueous solutions of HA can be cross-linked to form hydrogels, increasing its retention time in the joint space. Combining HA with synthetic materials such as poly(ethylene glycol) (PEG) to form hybrid hydrogels is an alternative approach [19]. PEG is the most prevalent synthetic biomaterial used for developing hydrogels. However, PEG does not support cartilage-specific extracellular matrix synthesis to the same extent as natural biomaterials such as HA. Hybrid hydrogels promise to improve PEG bioactivity while simultaneously enhancing HA stability in the joint space [20]. The potency of HA hydrogels can be further enhanced by integrating kartogenin (KGN) into PEG as these PEG/KGN HA biodegradable hydrogels provide better chondroprotective and cartilage regenerative outcomes than HA hydrogels in experimental OA [21].

Another way to achieve sustained drug release, in the joint, is to combine natural or synthetic hydrogel materials with injectable drug delivery microspheres. Incorporation of therapeutic agents into the polymeric matrix during microsphere synthesis enables more precise and controlled drug release. For example, the homogeneous nanoporous structure of PEG microgels and the ability to precisely control pore size during microsphere synthesis leads to enhanced drug loading and more sustained release [20].

Synthetic polymeric particles, such as poly(lactic-co-glycolic acid) (PLGA), are other popular delivery platforms due to their unique characteristics such as tunable physiochemical and mechanical properties, and lack of immunogenicity [17]. In fact, they are the most widely used synthetic polymers that are obtained through reproducible industrial processes and the only FDA-approved IA delivery system since they degrade into naturally existing metabolites that are then fully resorbed. PLGA microspheres have been successfully used for IA sustained delivery of therapeutic agents to relieve pain and inflammation [22] but are less successful in targeting chondrocytes unless extremely high doses are used [23]. Nonetheless, the FDA has recently approved ZILRETTA™, a formulation that is composed of triamcinolone acetonide (TCA) embedded in a PLGA hydrogel. This extended-release corticosteroid formulation is specifically indicated for IA injection to manage OA knee pain [24]. Whether ZILRETTA™ has disease-modifying effects on OA is still being determined.

Gene therapy for cartilage preservation

Viral-based gene therapy

Adenovirus-mediated gene therapy has long been used and applied in OA (reviewed in [25,26]). One of the main impediments to gene therapy in OA is inefficient gene transduction. However, new methods such as the use of α-10 integrin antibody to conjugate the capsid of helper-dependent adenoviral-vector leads to efficient chondrocyte infection while de-targeting other cell types [27]. Likewise, gene transfer of rat Il1ra (interleukin 1 receptor antagonist) using an adeno-associated viral-vector holds promise for OA treatment, as the vector genome persists locally in the rat knee for up to a year with limited uptake by tissues outside the knee [28]. Viral-vectors, however, have several potential limitations such as immunogenicity, insertional mutagenesis, persistence and sustainability of transgene expression, and in many cases, lack of tissue and cell specificity [25,26]. To overcome the issues with cell and tissue specificity, incorporation of certain molecular adapters allows modification of adenoviruses for greater tropism toward targeted tissues. For example, the discovery of unconventional immunoglobulins derived from serum of camels and alpacas provides compatibility with the cytosolic biosynthesis of adenovirus capsid proteins, thus allowing for target cell specificity and ultimately making possible their use for directing adenovirus-mediated gene therapy to a particular tissue in the joint. Similarly, to overcome the broad negative effects of preexisting immunity to common human serotypes of adenoviruses, researchers have developed vectors based on chimpanzee-derived adenoviruses for gene therapy application (reviewed in [25]). Last year, the world’s first gene therapy product Invosaa (TissueGene) was approved for arthritis in South Korea, and Phase III studies are starting soon in the United States. The therapy targets OA by IA injection of human allogeneic chondrocytes transduced with a retrovirus encoding transforming growth factor-β1 (TGF-β1) [29]. This raises the expectation that approved genetic medicines may become a reality for arthritis in particular and musculoskeletal regenerative medicine in general.

Non-viral gene therapy

Given the shortcomings of adeno-associated viral-vectors, biocompatible and biodegradable nanomaterials are being increasingly explored for IA drug delivery since incorporation of the drug into a nanoplatform enhances its bioavailability and solubility while affording protection from biodegradation. Particle-based technologies for OA therapy have been reviewed extensively elsewhere [17,30,31]. Drug delivery into sub-compartments of cartilage, however, remains a challenging task since the avascular cartilage renders the chondrocytes inaccessible and the dense collagen-matrix prevents effective drug penetration.

Delivery systems for siRNAs and microRNAs

RNA interference (RNAi) by small interfering RNA (siRNA) is a way of ablating gene expression in cells. siRNA silences a specific gene by binding to and degrading target mRNA. Chemically modified siRNAs require no transfection reagents and can be applied to cells in vitro using relatively straightforward methods. However, critical barriers to siRNA delivery in vivo, including molecular instability and inefficient transfection of the target cells, hinder the wide application of this gene silencing approach (reviewed in [32]). Our laboratory has recently shown that modifications of the native melittin led to the formulation of a self-assembling, ~55 nm peptide-siRNA nanocomplex that deeply penetrates cartilage to specifically silence nuclear-factor kappa B (NF-κB), a signaling pathway that controls the expression of several matrix-degrading enzymes involved in the remodeling of cartilage matrix [33]. The nanocomplex persists in human cartilage explants, thus providing a clinically relevant and promising approach to overcoming the obstacles of siRNA delivery. Other key features that will likely prove advantageous for cartilage preservation include generic formulation for short nucleotide structures allowing siRNA multiplexing (i.e. targeting 3 or more pathways simultaneously) or swapping of any unmodified RNA (i.e., no need for backbone or end-piece alterations). The peptide-siRNA nanocomplex provides a favorable toxicity profile, showing no innate or adaptive immune responses to the agent after multiple IA administrations. Lastly, a simple 10-minute mixing procedure yields GMP (good manufacturing practice)-ready siRNA and peptide components for rapid self-assembly and immediate injection and thus avoiding sophisticated (i.e. expensive) processing and purification steps [33]. siRNA may also be delivered to cartilage through a chondrocyte-homing nanoparticle [34]. Along these lines, this technology has been used for delivery of many therapeutic agents such as TGF beta-activated kinase 1 (TAK1) [35], matrix metalloproteinase 13 (MMP-13) and a disintegrin and metalloproteinase with thrombospondin motif 5 (ADAMTS-5) [36] to inhibit early cartilage degeneration.

Recently, the catabolic and anabolic effects of microRNAs (miRNAs) on OA cartilage have become increasingly evident, prompting research into their IA delivery. Some emerging options include conjugation of miRNAs with lipid nanoparticles for active transportation across the adipocyte membrane and the use of liposomes. Liposomes are closed spherical vesicles composed of phospholipids that have been proposed as efficient carriers for controlled drug delivery [37]. Derived from natural, biodegradable and nontoxic lipids, liposomes can entrap a variety of hydrophilic and hydrophobic drugs and are therefore good candidates for local targeting of therapeutic agents to the site of interest [38]. However, conventional liposomal formulations are prone to rapid elimination from the bloodstream, therefore limiting therapeutic efficacy [37]. Exosomes are cell-derived vesicles that have been shown to exhibit multiple roles in inter-cellular signaling as well as transport of proteins and miRNAs. These vesicles are emerging targets for drug delivery, since they have the ability to evade the immune system and since they can directly fuse with the plasma membrane of target cell(s) for efficient delivery of therapeutic molecule directly into cytoplasm and bypassing the endosomes. While efforts to develop synthetic carriers for miRNAs are ongoing, recent studies indicate that the ideal delivery platform for miRNAs into the synovial cavity is lentivirus-mediated IA injections [39–41]. Thus, more research is still needed to develop an effective but safe miRNA delivery systems.

Inducible gene delivery systems

Transgenes can also be delivered by non-viral vectors using progenitor or differentiated cells. This cutting-edge technology stems from the concept of using inducible promoters to replace viral sequencing to drive the expression of therapeutic genes as and when needed [42,43]. While the presence of viral genes in viral vectors could potentially lower the stable expression of a transgene in the transduced cell, cellular promoters are less susceptible to promoter silencing and in fact support long-term expression in the joint. CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/CRISPR associated protein 9) genome engineering systems are now being used successfully to generate cells that antagonize inflammatory signals in an autoregulated, feedback-controlled manner. These genome-engineering systems rewire endogenous cell circuits to allow for prescribed input/output relationships between inflammatory mediators and their targets, thus providing the foundation for a rapidly responsive cell-based drug delivery system [44,45].

Delivery systems for cell-based cartilage repair

In recent years, advances in knowledge about stem cells and induced pluripotent stem cells (iPSCs) have led to promising cell–based therapies for articular cartilage repair and an apparent alternative for traditional chondrocyte implantation. Cell therapy has led to short-term improvement in symptoms and may reduce or delay arthroplasty; however, long-term data are still lacking [46]. In addition, IA injection of mesenchymal stem cells (MSCs) results in pain relief, better quality of life, and significantly improved cartilage quality with no need for hospitalization or surgery. Thus, cell transplantation appears to be a reliable alternative treatment for chronic knee OA [47,48]. However, there exist significant logistic and operational problems associated with appropriate handling, expansion, storage and delivery of stem cells to the synovial joint.

Accruing evidence suggests that the direct injection of MSCs to the joint via a syringe or through an arthroscopic port can limit cartilage damage and improve its repair, perhaps due to their anti-inflammatory function, especially if delivered at early stages in the disease process [49]. However, direct injection has some limitations, including short-term retention in the joint, and lacks a high level of evidence on the restoration of the original hyaline cartilage. Therefore, continued development of tissue engineering strategies has sought to combine cells with scaffolds with and without biological signals to boost repair response in the knee. In search of the holy grail of regenerative medicine, a number of matrix-assisted techniques have been developed and numerous natural and synthetic scaffolds have been designed [49,50]. The characteristics of an ideal scaffold include (1) functional and mechanical properties resembling the desired final tissue-engineered product, (2) enhanced viability, retention and engraftment of cells in the joint, (3) ability to withstand and function in a hostile inflammatory environment within the synovial joint and (4) absence of immunogenicity and toxicity. Research in this area is on the rise and in near future we anticipate some groundbreaking developments for viable cell delivery products.

Conclusion

In summary, the ideal properties of an IA drug delivery system depend on the nature of the delivery platforms. Hydrogels, for example, need to possess good biodegradability, superior biocompatibility, low immunogenicity and flexibility in their structure to allow for optimal loading and controlled release of a drug. For gene therapy, replication deficient vectors, non-viral vectors and vectors with tunable properties are desirable. Both for cell and gene therapy vehicles, the common characteristics are safety, efficiency, specificity and sustained presence in the tissue for cartilage preservation and repair. Ideal properties of scaffolds for cell delivery include but not limited to unique functional and mechanical attributes, cell retention potential, ability to withstand the aggressive inflammatory milieu within joints, non-immunogenicity, and toxicity.

The emerging trends indicate that new IA delivery approaches have a number of distinct characteristics. The focus on sustained and controlled drug delivery platforms is rising. Gene therapy, either by direct vector administration or cell implantation with and without biomaterials is receiving great attention. Finally, localized tissue engineering is replacing generalized systemic delivery systems. However, translation of these modalities to the clinic awaits further studies to fully assess the risks and benefits of these delivery platforms and agents.

Box I. Advantages and disadvantages of sustained-release delivery platforms.

Material type	Advantage	Disadvantage	Reference
Polymeric micelles	Easy to design Encapsulation of a wide-range of therapeutics Controlled and/or sustained release Protection of encapsulated drugs from in vivo degradation and clearance	Limited polymers for use Lack of stability Deficiency in methods for large-scale production	[15,16,18]
Poly(ethylene glycol) (PEG)	Water soluble Excellent biocompatibility Low toxicity High drug loading capacity Increased dwell time Highly permissible environment for facile diffusion FDA approved	Rapid drug release Inhibit cellular uptake Inhibit endosomal escape	[19–21]
Poly lactic-co-glycolic acid (PLGA)	Specifically tailored to be biocompatible and biodegradable Exhibits a wide-array of erosion time Modification in surface properties provide better interaction with biological materials FDA approved	Negative charge of PLGA particles is disadvantageous for particle uptake PLGA particles cannot be sterile filtered Particle size may limit crossing of biological barriers	[17,22–24]

Review criteria.

Articles to include in this Review were selected after searching PubMed database for articles published within last two years for the following terms: “osteoarthritis AND therapy” and “intra-articular AND injection”. Only English-language original publications and review articles were selected on the basis of their relevance for inclusion in the bibliography. Reference lists of the publications identified were also screened for additional relevant material.

List of abbreviations

ADAMTS-5

A disintegrin and metalloproteinase with thrombospondin motif 5

CRISPR/Cas9

Clustered regularly interspaced short palindromic repeats/ CRISPR associated protein 9

FDA

The U.S. Food & Drug administration

GMP

Good manufacturing practice

HA

Hyaluronic acid, hyaluronan

IA

Intra-articular

IL-1RA/Il1ra

Interleukin 1 receptor antagonist

iPSCs

Induced pluripotent stem cells

KGN

Kartogenin

miRNA

MicroRNA

MMP-13

Matrix metallopeptidase 13

MSCs

Mesenchymal stem cells

NF-κB

Nuclear-factor kappa B

OA

Osteoarthritis

PEG

Poly(ethylene glycol)

PLGA

Poly(lactic-co-glycolic acid)

PTOA

Post-traumatic osteoarthritis

RA

Rheumatoid arthritis

RNAi

RNA interference

siRNA

Small interfering RNA

TAK1

Transforming growth factor beta activated kinase 1

TCA

Triamcinolone acetonide

TGF-β1

Transforming growth factor beta 1