JAK-STAT Pathway Inhibition And Their Implications: In COVID-19 Therapy

The emergence of SARS CoV-2 in December 2019 in Wuhan city, Hubei province, China is the present global pandemic. SARS CoV was the first CoV to be outbreaked on 2003 in China with fatality rate of 9.5%.According to WHO’s coronavirus situation reports of August 10, US (United States), Brazil and India remained to be the top 3 countries for past 7 days, being affected with COVID – 19. The onset of COVID- 19 is sudden, 2-4 days after exposure is considered as the incubation period and takes about 2-8 weeks for recovery, where the patient is presented with symptoms like fever, cough, shortness of breath and more.

Major cells involved in SARS –COV-2

1.Pneumocytes

Ø SARS-COV-2 infects type 2 pneumocytes in the alveolar epithelium, since they are rich in ACE-2 in the lung tissue

 2.Endothelial cells

Ø SARS CoV resulted in endothelial cell dysfunction leading to micro circulation disorder

Ø Capillary leak, hemodynamic   instability and consumptive coagulopathy occurs as a result of endothelial activation in CSS

3.Macrophages, Monocytes and Neutrophils

Ø  Macrophage is the potent source of inflammatory cytokine

Ø Macrophages and neutrophils are responsible for the destruction and phagocytosis of infected cell. Neutrophils entrap and kill microbes through neutrophils extracellular traps (NET) and this leads to demise of neutrophil., which is called “NETosis.”

4.Lymphoctes

Ø In COVID-19 patients 80% of them revealed peripheral blood lymphopenia and unexpected infiltration in the airways due to the dysfunction of innate T cells

5.NK Cells and Dendritic Cells

Ø In severe COVID-19 patient, NK cells in peripheral blood were declined

Ø NK cells destroy virus infected cells by degranulation, receptor mediated apoptosis, and antibody-dependent cell-mediated cytotoxicity

Ø Dendritic cells help to release pro-inflammatory mediators like TNFα, and aid in activation of T Lymphocyte and B Lymphocyte

SARS-CoV-2 and cytokine storm

Cytokines are necessary for combating viral infections but hyper inflammation conditions created by SARS-CoV-2 infection due to cytokine storm could lead to ARDS and even death. Cytokine storm created by SARS-CoV-2 infection also known as cytokine release syndrome (CRS)/hypercytokinemia characterized by the hyper production of inflammatory cytokines which results in the immune cells biological activity(infection) and at the same time, immune systemic negative feedback gets lost. Cytokine storm releases inflammatory responses that results in local initiation, systematic spreading, and tissue damage.

COVID -19 patients are identified with CSS, based on:

 (i) Unexpected or quick development with multiple organ collaboration (liver, Cardiac, renal injury); 

(ii) Systematic inflammatory indicators (serum ferritin, ESR, CRP) gets elevated considerably;

 (iii) Remarkable deterioration of peripheral blood lymphocyte counts; and

(iv)  Multiple cytokines (IL-1b, IL-2R, IL-6, IFN-c, IP-10, MCP-1, TNF-a) gets upraised

Small Molecules Modulating Jak/Stat Signaling Pathway

Manipulation of JAK/STAT pathway with specific inhibitors or drugs for its regulation is a promise for the upcoming therapeutic intervention for the treatment of numerous diseases.Various regulatory agencies now uphold JAK inhibitors (JAKinibs) for the treatment of immune mediated diseases. It is FERM and SH2 like domains of JAKs that regulate the kinase activity whereas classic transcription factors STAT1-4, STAT5A, STAT5B, STAT6 modulate gene transcription. Inhibitory mechanism of SOCS protein family or auto inhibition of JH1-JH2 interactions are few driving techniques in controlling the anomalous activation of the pathway. Another mechanism of regulation includes the dephosphorylation of activated JAKs and STATs by multiple Protein Tyrosine Phosphates (PTP) including SHP1; SHP2 (both activator and suppressor) and TC-PTP for STAT1, STAT3, STAT5; PTPRT for STAT3; CD45 for JAKs. Upon evidence, inhibition of activated STAT dimers by Protein Inhibitors of Activated STATs (PIAS)- PIAS1, PIAS2 (PIASx), PIAS3, PIAS4 (PIASy)- also play an important role in modulating JAK/STAT signaling. Existing evidence suggest that both activating and inactivating mutation of JAKs and STATs can impair the pathway resulting in numerous pathological conditions including malignancies and immune mediated diseases.The role of cytokines in COVID-19 has been a contributor to the worsening of the disease and inhibiting these cytokines to reduce inflammation has been a strategy to keep the disease under check.The JAK/STAT signaling inhibition looks to be a promising approach to reduce inflammation in COVID-19 patients yet falls short of concrete conclusions due to a lack of understanding of mechanism occurring at molecular levels thus warranting further studies.

Ruxolitinib, Baricitinib, Tofacitinib In Clinical Trial Against Covid-19

Ruxolitinib : It is both JAK 1 & JAK 2 inhibitor that act by terminating the kinase activity, thereby preventing nuclear translocation and STAT activation. Studies proved that inhibition of IL6/JAK/STAT3 pathway by the same can result in significant reduction of IL-6 level.                                                               Side-effects like purpuric lesions on the skin of limbs and erythrodermic rashes were identified from the examination of two SARs-Cov-2 infected patients. Anemia was also observed. Common side effects include black tarry stools, bladder pain, bleeding gum, blood in the urine or stool, coughing up blood and more.

Baricitinib is a kinase inhibitor that competes with ATP to effectively and reversibly inhibit both JAK1 and JAK2 with high selectivity hindering the pro-inflammatory signals of several cytokines like IL-6, IL-12, IL-23. It also plays a vital role in blocking proteins of the host cell responsible for the viral reproduction, and being an anti-inflammatory agent, also reduces the inflammation in ARDS patients as well. Side effects like headache, upper respiratory tract infection, nasopharyngitis are common. Long term use may increase the risks of developing serious infections and thromboembolic events in patients.

Tofacitinib inhibits JAK1, JAK3 initially & then JAK 2 at a lesser extent to modulate both immune &inflammatory responses. Common side effects include Abdominal pain, acne vulgaris, anemia, angioedema, diarrhea, dehydration, dyspepsia, headache, hepatotoxicity, hyperlipidemia, hepatitis, lymphoma, lymphopenia, nausea, neutropenia, pulmonary embolism, rashes, vomiting, blood clots, GI perforations.

 Ms. ROSHITHA ANN SHAJI, AAJA ALOSIOUS, MARIYA LUVIS- Vth PHARM -D