Autoimmune diseases comprise of more than 80 chronic ailments, type I diabetes and Rheumatoid Arthritis (RA) being the most common ones and their prevalence rate has been increasing ever since [1]. There are multiple causes that can trigger an autoimmune disease, starting from environmental factors to epigenetic elements. The annual incidence of the world population being affected by RA is approximately one percent that is one individual in every ten thousand is being affected by this incurable malady [2].
RA commonly triggered by proinflammatory cytokines causes muscular dystrophy, swelling of the proximal interphalangeal, metacarpophalangeal or wrist joints,accompanied with immeasurable pain [3]. The disease proliferates through three checkpoints, first is the recognition of modified proteins, second, T-cell metabolic reprogramming and third, is the recognition of modified proteins and emergence of autoantibodies [4]. The inflammation caused in RA is due to the clonal expansion of auto reactive T-cells, such as T helper (Th) 17 lymphocytes and B lymphocyte [5]. These B lymphocytes mature to their end stage of plasma cells producing auto antibodies, including anti citrullinated peptide antibodies and rheumatoid factor, which is why the diagnosis includes confirmation of presence of rheumatoid factor-IGM and CRP (cyclic citrullinated protein) in blood [6]. A multitude of research is being carried out on RA and the findings suggest that JAK/STAT pathway plays a crucial role towards the onset of the disease [7].
The JAK (Janus kinase) protein is a non-receptor tyrosine kinase beholding four members in its family namely JAK 1, JAK2, JAK3 and TYK2 [8]. Delving into the history of each of the proteins of this family, JAK3 has been selected as the target to address the yet immedicable disease RA for this particular study [9]. Cytokines that are dependent on these JAK proteins are crucial regulators of immunity and inflammation and also have been found to be essential in immunopathology and autoimmune diseases such as RA Previous studies also says that JAK3 is highly expressed in lymphocytes and it predominantly mediates and participates in the formation of cytokines [10] [11]. The deficiency or disorder of JAK3 leads to malfunction of lymphocytes and in due course causes loss of immune function [12]. One of the major reasons of selecting JAK3 is that the deficiency of this particular protein could avoid the adverse toxic effect damaging other tissues whereas deficiency of JAK1 and JAK2 could be lethal to human body [13].
Treatment of RA in current times include medicines divided into four distinct groups namely NSAIDs (Non-steroidal anti-inflammatory drugs), corticosteroids, conventional DMARDs (Disease Modifying Anti Rheumatic Drugs) and biological DMARDs [14]. NSAIDs are preferable in acute stages of the disease and corticosteroids act as adjunctive therapy for active disease that persists. Synthetic DMARDs are used to reduce inflammation and pain whereas biological DMARDs are drugs that act on the TNF-α inhibitors, co-stimulant inhibitors, Interleukin (IL) inhibitors and B-cell receptors. These biological DMARD’s comprises of a special case of medicines called JAK inhibitors.
The approved medicines under this category are tofaticinib, peficitinib and baricitinib. Tofacitinib works by blocking the action of janus kinase enzymes but its long-term use caused severe pulmonary embolism and the use of this medicines was not approved in the European countries[15]. Peficitinib has only been approved in the European countries and is still under clinical trial. Baricitinib is used as a mono or combination therapy, this drug is mostly used under an emergency condition and is more specific to interactions with JAK1 protein [16]. Going by the history of these drugs and their efficacy in RA patients there is need for a new drug that could overcome these drawbacks and be more specific to JAK3 protein as JAK1 and JAK2 has other functions essential to the human body unlike JAK3 which is restricted to expression in the immune system only[17].
Conventional drug discovery is a complex, multistep, tedious and time taking process. Lead compounds need to undergo preclinical studies, clinical trials, post marketing statistics and safety monitoring studies [18]. Whereas drug repurposing also called as drug re-profiling is an unprecedented approach which is cost effective, poses reduced risk of failure and also has lesser chances of adverse reactions in patients as its efficacy and safety studies have already been performed. In this study we have included this strategy to target JAK3 protein against FDA database for RA [19]. In this study molecular docking, Density functional theory calculations and molecular dynamic simulation has been carried out to substantiate the fact that existing drugs can be redirected as therapeutics for other diseases.