Ritlecitinib is an orally administered, covalent small-molecule selective dual inhibitor of JAK3 and the TEC kinase family. In vitro studies showed ritlecitinib covalently binds to JAK3 and is more than 10 000 times more potent against JAK3 than against JAK1, JAK2, and tyrosine kinase. Ritlecitinib also inhibits the five members of the TEC kinase family. Ritlecitinib irreversibly inhibits Janus kinase 3 (JAK3) and TEC kinase family by blocking the adenosine triphosphate (ATP) binding site. In cellular settings, ritlecitinib inhibits cytokine induced STAT phosphorylation mediated by JAK3-dependent receptors. Additionally, ritlecitinib inhibits signaling of immune receptors dependent on TEC kinase family members.The FDA has approved ritlecitinib (LITFULO; Pfizer Inc), a once daily oral treatment, for individuals aged 12 years and older with severe alopecia areata. This makes ritlecitinib, in the 50 mg dosage, the first and only treatment approved by the FDA for adolescents with severe alopecia areata. The approval was based on the results of the ALLEGRO phase 2b/3 trial (NCT03732807), which included 718 individuals who had 50% or more scalp hair loss measured by the Severity of Alopecia Tool. Investigators of the study evaluated the safety and efficacy of ritlecitinib at 118 different sites in 18 different countries. Regulatory applications for LITFULO in alopecia areata have been submitted to countries around the world for review, including China, the European Union, Japan, and the United Kingdom. The European Medicines Agency (EMA) has accepted the Marketing Authorization Application (MAA) for ritlecitinib with a decision anticipated in the third quarter of 2023. LITFULO is also being evaluated for vitiligo, Crohn’s disease, and ulcerative colitis.

Baricitinib (trade name Olumiant) is an investigational drug for rheumatoid arthritis (RA), being developed by Incyte and Eli Lilly. Baricitinib is a selective JAK1 and JAK2 inhibitor with IC50 of 5.9 nM and 5.7 nM in cell-free assays. In February 2017 Baricitinib was approved for use in the European Union as a second-line therapy for moderate to severe active rheumatoid arthritis in adults, either alone or in combination with methotrexate. On 31 May 2018 FDA approved Barictinib for the treatment of adult patients with moderately to severely active rheumatoid arthritis who have had an inadequate response to one or more TNF antagonist therapies.

Tofacitinib is an orally available inhibitor of Janus kinases (JAK), with immunomodulatory and anti-inflammatory activities. Upon administration, tofacitinib binds to JAK and prevents the activation of the JAK-signal transducers and activators of transcription (STAT) signaling pathway. This may decrease the production of pro-inflammatory cytokines, such as interleukin (IL)-6, -7, -15, -21, interferon-alpha and -beta, and may prevent both an inflammatory response and the inflammation-induced damage caused by certain immunological diseases. JAK kinases are intracellular enzymes involved in signaling pathways affecting hematopoiesis, immunity and inflammation. Tofacitinib was discovered and developed by the National Institutes of Health and Pfizer. Besides rheumatoid arthritis, tofacitinib has also been studied in clinical trials for the prevention of organ transplant rejection, and the treatment of psoriasis and ulcerative colitis. Patients treated with tofacitinib (XELJANZ) are at increased risk for developing serious infections that may lead to hospitalization or death and adverse reactions. Most patients who developed these infections were taking concomitant immunosuppressants such as methotrexate or corticosteroids.

Filgotinib (GLPG0634) is a highly selective JAK1 inhibitor. GLPG0634 is a promising drug candidate for the future treatment of autoimmune and inflammatory disorders. It is in phase III clinical trials (initiated mid-2016) for the treatment of rheumatoid arthritis, Crohn's disease and ulcerative colitis. Most common adverse events observed were infections, gastrointestinal disorders and nervous system disorders.

NS-018 is a potent inhibitor of Janus kinase 2 (JAK2) enzyme activity and Src-family kinases. It was developed as an oral therapy for the treatment of myelofibrosis. Overall NS-018 has been used in trials studying the treatment of primary myelofibrosis, post-polycythemia vera myelofibrosis, and post-essential thrombocythemia. NS-018 is a highly active JAK2 inhibitor, with an IC50 of 0.72 nM, 46-, 54-, and 31-fold selectivity for JAK2 over JAK1 (IC50, 33 nM), JAK3 (IC50, 39 nM), and Tyk2 (IC50, 22 nM). NS-018 also inhibits Src-family kinases, especially SRC and FYN, and weakly inhibits ABL and FLT3 with 45- and 90-fold selectivity for JAK2, respectively. NS-018 shows potent inhibitory activity against cell lines JAK2V617F or MPLW515L mutations or the TEL-JAK2 fusion gene.

Decernotinib is an oral JAK3 kinase inhibitor developed by Vertex for the treatment of rheumatoid arthritis. Although the drug demonstrated a good potency in vitro and in phases I and II of clinical trials, its development was terminated.

AT-9283 was being developed by Astex Pharmaceuticals as a treatment for cancer and myelofibrosis. AT-9283 is an inhibitor of mitosis (cell division) and is the second most progressed drug candidate in the Astex portfolio of novel molecularly targeted cancer drugs. All of Astex’s current products have been discovered internally using its proprietary drug discovery approach. AT9283 is a potent inhibitor of the Aurora A and B kinases and has been shown to arrest tumour growth in a range of tumour models. Aurora kinases play a key role in mitotic checkpoint control in cell division. Both Aurora A and B are over-expressed in many human tumours and are believed to be excellent targets for anti-cancer therapy.

Cerdulatinib is an oral, dual spleen tyrosine kinase (Syk) and janus kinase (JAK) inhibitor that uniquely inhibits two key cell signaling pathways that promote cancer cell growth in certain hematologic malignancies – the B-cell receptor pathway via Syk and key cytokine receptors via JAK Being developed to treat patients with hematologic cancers, specifically those who have relapsed or who have not responded to prior therapies. Cerdulatinib is in Phase 2 study evaluating the safety and efficacy of cerdulatinib in patients with relapsed/refractory B-cell malignancies who have failed multiple therapies.

Peficitinib (formerly known as ASP015K) is a pyrrolo[2,3-b]pyridine derivative orally administered once-daily JAK inhibitor in development for the treatment of Rheumatoid Arthritis. In preclinical studied Peficitinib inhibited JAK1 and JAK3 with IC50 of 3.9 and 0.7 nM, respectively. Peficitinib also inhibited IL-2-dependent T cell proliferation in vitro and STAT5 phosphorylation in vitro and ex vivo. Furthermore, Peficitinib dose-dependently suppressed bone destruction and paw swelling in an adjuvant-induced arthritis model in rats via prophylactic or therapeutic oral dosing regimens.In clinical trials, Peficitinib treatment prescribed at 50, 100 and 150 mg amounts each showed statistically significantly higher ACR20 response rates compared to the placebo and response rates increased up to the 150 mg dosage. Adverse events included neutropenia, headache, and abdominal pain. The treatment-emergent adverse events occurring more frequently in the Peficitinib group compared with the placebo group included diarrhea, nasopharyngitis, and increased serum creatine phosphokinase activity. No cases of serious infections were reported. Herpes zoster occurred in four patients (two each in the peficitinib 25 and 100 mg cohorts). The authors concluded that treatment with peficitinib as monotherapy for 12 weeks in Japanese patients with moderate to severe RA is efficacious and showed an acceptable safety profile.

CEP-33779 is a selective JAK2 inhibitor (IC50 of 1.8 nM) developed by Cephalon, Inc for treating autoimmune disease (rheumatoid arthritis, lupus nephritis) and cancer. CEP-33779 orally administrated with 55 mg/kg inhibits phosphorylation of STAT5 in HEL92 tumor extracts from HEL92 xenograft mice. CEP33779 orally administered twice daily at the dose of 55 mg/kg reduces mean paw edema and clinical scores in mice with collagen-antibody-induced arthritis (CAIA) or collagen-induced arthritis (CIA). CEP-33779 orally administered twice daily at the dose of 55 mg/kg totally inhibits paw phospho-STAT3 expression in CAIA or CIA mice, associated with decreased cytokines including IL-12, IFNγ, IL-2, IL-1β, TNFα, and GM-CSF. CEP33779 results in reduced bone degradation, reduced tissue destruction, and reduced osteoarthritis in a dose-dependent manner in CAIA or CIA mice. CEP33779 orally administrated at 100 mg/kg extends survival and reduces splenomegaly/lymphomegaly in MRL/lpr systemic lupus erythematosus mice, thus protect mice from developing glomerulonephritis. CEP-33779 orally administrated at 100 mg/kg decreases several SLE-associated proinflammatory cytokines and reduces levels of a bone resorption biomarker associated with increased osteoclast activity in MRL/lpr systemic lupus erythematosus mice. CEP33779 orally administered twice daily at the dose of 55 mg/kg induces regression of established colorectal tumors, reduces angiogenesis, and reduces proliferation of tumor cells in a mouse model of colitis-induced colorectal cancer. Tumor regression correlated with inhibition of STAT3 and NF-κB (RelA/p65) activation, and decreased the expression of proinflammatory, tumor-promoting cytokines interleukin (IL)-6 and IL-1β