Treating knee osteoarthritis by sPLA2 inhibitor-loaded micellar nanoparticles

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ABSTRACT Knee osteoarthritis (OA) is a painful and debilitating joint disease that can result in joint pain, loss of joint function, and deleterious effects on the quality of daily life. Despite recent advances in drug development, there is no disease-modifying drug available to delay OA progression or reverse the disease. Over 600,000 knee replacements are performed each year in the US. Many preclinical and clinical studies have revealed that various inflammatory mediators have been implicated in OA pathogenesis. Despite the strong association between inflammation and OA, a major challenge is how to resolve the inflammatory state since common anti-inflammatory drugs have demonstrated limited utility to slow or reverse OA progression. Moreover, rapid joint clearance and poor penetration into avascular cartilage tissues further limit the clinical application of many promising OA drugs. Therefore, there remains a critical need to identify new therapeutic targets and to develop effective drug delivery systems for OA patients. Secreted phospholipase A2 (sPLA2) enzyme specifically hydrolyzes the sn-2 ester bond of phospholipids, releasing free fatty acids and lysophospholipids. These products are well-known upstream inflammation mediators in many chronic inflammatory diseases. However, few studies have explored the role of sPLA2 in OA and the cause-effect relationship between sPLA2 upregulation and OA progression. Our recent studies found that sPLA2 level is drastically increased in full-thickness articular cartilage from both human patients and animal models of OA. To explore the potential of targeting sPLA2 pathway (i.e. by sPLA2 inhibitor, sPLA2i) for OA treatment and overcome the challenges of small sPLA2i delivery within joints (i.e. rapid clearance and poor cartilage penetration), we engineered sPLA2i (thioetheramide-PC)-loaded phospholipid micellar nanoparticles (thioetheramide-NPs) and provided the first evidence that thioetheramide-NPs, but not free sPLA2i, can effectively reduce joint inflammation, alleviate join pain and prevent OA progression in a mouse OA model. While these data are promising, thioetheramide-PC is not a clinically-approved drug and has a rather poor IC50 (~2 μM). The overall goal of this proposal is to use a clinically tested and more potent sPLA,i varespladib (~210-fold lower IC50 than thioetheramide-PC) to construct sPLA2-responsive varespladib-NPs and test their efficacy in clinically relevant animal models. We believe the proposed work will result in a clinically translatable nanotechnology that could alter the standard of care for knee OA. The specific aims for the proposal are 1) synthesize and optimize sPLA2-responsive varespladib-NPs; 2) evaluate the efficacy of varespladib-NPs in injury-induced mouse OA models; and 3) evaluate the efficacy of varespladib-NPs in the guinea pig model of spontaneous OA.