**5.2 Multifunctional carrier systems**

122 Rheumatoid Arthritis – Treatment

The exploration of drug delivery systems for improved treatment of rheumatoid arthritis is still in the early stages. More advanced concepts that have been applied to other diseases, particularly cancer, are only beginning to be explored by rheumatoid arthritis researchers.

Current drug delivery systems for rheumatoid arthritis have almost exclusively been developed based upon the principles of passive targeting. Specificity and, consequently, efficacy can be further improved by employing an active targeting moiety. As indicated previously, RASFs and RASMs possess receptors that can potentially be used to increase the ability of the drug carrier systems to discern pannus tissue from healthy tissue. Those

Folate receptor β (FRβ) has been identified as a viable candidate for active targeting of RASMs. Several transport mechanisms exist whereby folate and folate antagonists, including methotrexate, can enter a cell. Numerous cell types throughout the body constitutively express the reduced folate carrier (RFC), a transmembrane protein. In contrast, membrane associated folate receptors (MFRs) are restricted in expression and facilitate uptake by endocytosis. The beta isoform of MFR (FRβ) is expressed selectively by activated macrophages within the pannus tissue (Nagayoshi et al., 2005; van der Heijden et al., 2009). Thus, folate may serve as an effective means of actively targeting the pannus tissue. In support of this, folate-tagged cationic and anionic poly(amidoamine) (PAMAM) dendrimers loaded with indomethacin were more effective at treating arthritic rats than indomethacin-loaded dendrimers that were folate-free (Chandrasekar et al., 2007a; Chandrasekar et al., 2007b; Chauhan et al., 2004). Furthermore, a recent study demonstrated that PAMAM dendrimers covalently linked to both folate and methotrexate could be used to selectively deliver methotrexate to synovial macrophages (Thomas et al., 2011). Although the antifolate MTX does not have a high affinity for any MFRs, several other folate analogs have been identified that possess high affinity for FRβ with low affinities for other MFRs and the RFC (van der Heijden et al., 2009). These analogs, therefore, have strong potential to be used as active targeting moieties in the future

RASFs also possess an active targeting receptor in the cell surface adhesion molecule CD44, the hyaluronic acid receptor. Several studies have indicated that CD44 is upregulated in the pannus tissue relative to healthy, normal tissue (Haynes et al., 1991; Johnson et al., 1993). Furthermore, RASFs express numerous CD44 alternatively spliced variants, including long isoforms CD44v3 and CD44v6 that are associated with an enhanced invasive capacity (Croft et al., 1997). CD44 is critical to rheumatoid arthritis pathogenesis, facilitating inflammatory cell migration and signaling activation of lymphocytes (Naor & Nedvetzki, 2003). Despite evidence of upregulation and/or selective expression, the CD44 receptor has not yet been used as an active target for drug delivery in the treatment of rheumatoid arthritis. Some cancer cells also upregulate CD44, and the potential for success using this active targeting strategy has previously been illustrated by anti-cancer drug carrier systems modified with

As indicated by the feasibility of passive targeting, neovascularization is a critical component of rheumatoid arthritis pathogenesis (Szekanecz & Koch, 2008). Adhesion molecules, including intercellular cell-adhesion molecule-1 (ICAM-1) and E-selectin, are upregulated within the newly formed vasculature and; therefore, the endothelium serves as

receptors that have the highest potential for success are discussed in this section.

**5. Future of drug delivery for rheumatoid arthritis** 

and may possess inherent anti-rheumatic properties.

hyaluronic acid oligomers (Ossipov, 2010).

**5.1 Active targeting strategies** 

A recent push in the realm of drug delivery for cancer treatment has been the development of multifunctional carrier systems whereby a single platform can be used for the release of multiple therapeutics in a controlled fashion or for both therapeutic release and diagnostic imaging (Jabr-Milane et al., 2008; van Vlerken & Amiji, 2006). Some of the success achieved in this "theranostic" approach to cancer treatment has spilled over into the study of improved treatment methods for rheumatoid arthritis. For example, folate-conjugated radiopharmaceuticals designed to target malignant tissue showed significant accumulation in the joints of patients who also had rheumatoid arthritis (Paulos et al., 2004). Radiolabelled biologics have provided an additional example of the potential for theranostics to improve rheumatoid arthritis treatment. 99m-technetium labelled infliximab (99mTc-infliximab) was used to show a strong correlation between the amount of infliximab taken up by inflamed tissue and a reduction in symptoms and swelling (Malviya et al., 2010).

#### **5.3 Stimuli-responsive carrier systems**

As discussed in brief above, in order to be optimally effective, the drug delivery systems must release their payloads at the desired site of action, i.e. the pannus tissue. In the realm of cancer drug delivery, numerous pH- and temperature-responsive carrier systems, in the form of conjugates, dendrimers, liposomes, and micelles, have been developed (Ganta et al., 2008). Although the same potential also exists for rheumatoid arthritis drug delivery, particularly in light of the lower pH of the pannus tissue relative to native tissue, to the authors' knowledge, only two pH-responsive systems, dexamethasone-HPMA conjugates (P-Dex) and dexamethasone-PEG conjugates (PEG-DEX), have been reported. Drug release was shown to increase as the pH decreased. *In vitro* and *in vivo* tests were used to demonstrate that P-Dex and PEG-DEX are more effective than free dexamethasone in regards to reducing the production of proinflammatory mediators, preventing joint damage, and targeting inflamed tissue (Liu et al., 2010; Quan et al., 2010). In addition to temperature and pH, other environmental triggers may be used. For example, elevated elastace levels have been closely linked with inflammation and the increased enzymatic activity maybe be used for cleavage. The upregulation in enzymes may additionally serve as a means of active targeting (Meers, 2001).

The Development of Targeted Drug Delivery Systems for Rheumatoid Arthritis Treatment 125

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#### **5.4 Gene therapy**

Given the nature of rheumatoid arthritis, gene therapy, whereby nucleic acids are introduced to a cell to either "turn off" select genes or upregulate therapeutic genes, is an attractive alternative treatment strategy (Jorgensen & Apparailly, 2010). This approach is limited, however, by the necessity for local administration and low transfection efficiency; therefore, for practical use, drug delivery systems for gene therapy will be required. Small interfering RNA (siRNA), in particular, may be used to knockdown the expression of proinflammatory proteins at the mRNA level. Cationic liposomes, referred to as lipoplexes, have been designed to facilitate systemic delivery of siRNA for rheumatoid arthritis treatment (Khoury et al., 2006, 2008). When administered intravenously to arthritic mice, anti-TNF-, anti-IL-1, anti IL-6, and anti IL-18 siRNA successfully reduced inflammation, bone and cartilage degradation, and secretion of a number of proinflammatory cytokines, including TNF-and IL-1 (Khoury et al., 2006, 2008). Similarly, intraperitoneal administration of anti-TNF- siRNA complexed with chitosan nanoparticles to arthritic mice resulted in a significant reduction in joint swelling, cartilage degradation, and inflammatory cell infiltration (Fernandes et al., 2008). Chitosan nanoparticles were also used to deliver the IL-1 receptor antagonist (IL-1Ra) gene to arthritic rats (Fernandes et al., 2008). Rats treated with the chitosan-gene delivery system showed reduced bone turnover, as well as decreased expression of IL-1and PGE2, relative to control rats. The efficacy of the chitosan-IL-1Ra nanoparticles was further improved by modification with folate for active targeting (Fernandes et al., 2008). An innovative strategy towards gene therapy was designed by encapsulating a nuclear factor kappa B (NF-B) decoy into stealth lipid-based nanoparticles that were surface modified with folate (Hattori et al., 2006). NF-B regulates proinflammatory gene expression and is, therefore, a critical component of rheumatoid arthritis pathogenesis (Brown et al., 2008; Simmonds & Foxwell, 2008). *In vitro,* the nanoparticles were shown to release the NF-B into the cytoplasm, as indicated by a reduction in NF-B translocation into the nucleus (Hattori et al., 2006), which presumably will result in a decreased expression of proinflammatory cytokines and growth factors.
