Transdermal Delivery of 2-Arachidonoyl Glycerol (2-AG) for the Treatment of Arthritic Pain

This research proposes to improve the transdermal delivery of 2-arachidonoylglycerol (2-AG) for the adjunct treatment of osteoarthritis, rheumatoid arthritis (RA) and joint pain secondary to other autoimmune diseases, such as inflammatory bowel disease, multiple sclerosis, and systemic lupus erythematosus. Current methods of treatment for these conditions do not always provide adequate pain relief in many patients, or are associated with addiction, various side effects and/or patient noncompliance. Systemic RA treatments have drastically improved over the last decade; however, many patients 'still have substantial unrelieved joint pain and stiffness, even though their joint deterioration may be arrested by new biological agents. Thus, there is a strong need for the development of novel drug treatments for joint pain. 2-AG, an endocannabinoid, has been shown to playa strong role in alleviation of inflammatory pain via CB2 receptors. A recent study has shown that intra-articular injection of 2-AG in a preclinical model of arthritic pain decreased joint pain. Topical products are better than painful local injections in providing local therapeutic benefit, while reducing the risk of systemic adverse effects. Additionally, this product would not have the abuse liability problems of opioids that some patients use to treat joint pain. Thus, we hypothesize that a transdermal gel or patch containing a prodrug of 2-AG will be an important adjunct treatment in arthritis and joint pain associated with autoimmune diseases, and would be a significant improvement in patient care and quality of life. In our preliminary diffusion stUdies with hairless guinea pig skin, 2-AG flux was found to be 137.7±27.1 ng/cm2/h and the drug content in the skin (upper layer) was 965.2±516 j.Jg of drug/g of skin. Published data shows that the dermis concentration of hydrophobic compounds may reach only about 25-50% compared to the upper skin layer because of the difficulty in partitioning out of the stratum corneum. In a recently published 2-AG study, an initial concentration of about 1 mg/ml was needed in synovial fluid to treat joint pain with 50% efficacy. Hence, an enhancement of 2-AG diffusion by at least 2-4 fold will be needed to reach this concentration in the deeper layers of tissue and into the synovium. We aim to synthesize hydrophilic prodrugs of 2-AG to improve permeation across the skin into synovial fluid. Prod rugs should improve the delivery rates of 2-AG across the skin because of optimized physiochemical properties for faster diffusion. If prod rugs fail to improve the flux of 2-AG, microneedle assisted delivery of salts of 2-AG or its prod rugs will be carried out. The specific aims of this project include: (1) to synthesize a series of 2-AG prodrugs for transdermal flux optimization, (2) to characterize the physicochemical parameters of the drugs, including solubilities and stabilities in select solvents, (3) to measure the penetration and concurrent bioconversion of the prodrugs in hairless guinea pig and human skin in vitro, and (4) to compare the transdermal delivery of 2-AG prodrugs with methanandamide, and 0-1812, the stable analogs of anandamide.