Background: everal JAKi are now used for the treatment of RA; approved doses include baricitinib (bari) 2- and/or 4-mg QD, tofacitinib (tofa) 5-mg BID, upadacitinib (upa) 15-mg QD. The JAK selectivity these agents is proposed to vary across the class.
Objectives: In vitro cellular pharmacology of bari to tofa, upa, and filgotinib (filgo) were compared.
Methods: PBMCs from 6 healthy donors were incubated with the JAKis over a 7- to 8-point concentration range. Following cytokine stimulation, levels of pSTAT were measured and IC50 calculated in gated leukocyte subpopulations. Therapeutic dose relevance was assessed using calculated mean concentration-time (CT) profiles over 24 hours for bari 2- and 4-mg QD; tofa 5- and 10-mg BID; upa 15- and 30-mg QD; filgo 100- and 200-mg QD. Average daily % inhibition of pSTAT (%SI) was calculated for each JAKi, cytokine, and cell type; filgo %SI integrated parent drug + metabolite.
Results: The cytokines did not signal in all cell types (Figure 1). When signaling was detected, IC50 and %SI for a particular JAKi were generally similar across cell types, with dose-dependent inhibition (Figures 1 & 2). Based on IC50s, upa was most and filgo/metabolite least potent across JAK2/2 or JAK2/TYK2-dependent (IL-3, GM-CSF, G-CSF), JAK1/3-dependent (IL-2, 4, 15, 21), and JAK1/2/TYK2 dependent (IL-6 & 10, IFN-α & γ) signaling pathways.
Incorporating CT profiles, no agent potently or continuously inhibited an individual cytokine signaling pathway throughout the dosing interval. Comparing bari 4-mg to tofa 5-mg BID, upa 15-mg QD, and filgo 100-mg QD, %SI of JAK2/2 or JAK2/TYK2-dependent cytokines was highest with bari 4-mg and upa. Inhibition of JAK1/2/TYK2 cytokines was highest with bari 4-mg. Inhibition of JAK2/2 or JAK2/TYK2, and of JAK1/3-dependent cytokines was lowest for filgo 100-mg QD. For bari 2-mg QD vs. these other JAKi doses, %SI of JAK2/2 or JAK2/TYK2 was highest with upa followed by bari 2-mg. The highest inhibitors of the JAK1/2/TYK2-dependent cytokines varied by cytokine / cell type though consistently included upa. Inhibition of JAK1/3 was highest for upa and tofa. Across comparisons, filgo 100-mg QD showed the least %SI of JAK2/2 or JAK2/TYK2-dependent, and of JAK1/3-dependent cytokines. Filgo reached the highest levels of %SI among agents only for 200-mg QD vs. lower doses of the other JAKi (for selected JAK1/2/TYK2-dependent cytokines).
Conclusion: JAKis display different in vitro pharmacologic profiles which, coupled to their in vivo pharmacokinetics, suggest they modulate distinct cytokine pathways to differing degrees and durations over 24 hours. Ex vivo whole cell assays seem distinct from cell free kinase inhibition assays in determining the overall cytokine modulatory potential of members of the JAKi class.
Disclosure of Interests: Iain McInnes Grant/research support from: Bristol-Myers Squibb, Celgene, Eli Lilly and Company, Janssen, and UCB, Consultant of: AbbVie, Bristol-Myers Squibb, Celgene, Eli Lilly and Company, Gilead, Janssen, Novartis, Pfizer, and UCB, Guilherme Rocha Shareholder of: Eli Lilly and Company, Employee of: Eli Lilly and Company, Richard E Higgs Shareholder of: Eli Lilly and Company, Employee of: Eli Lilly and Company, Daniel Dairaghi Shareholder of: Eli Lilly and Company, Employee of: Eli Lilly and Company, Thomas Wehrman Shareholder of: An insignificant amount in AbbVie as part of a larger portfolio, Consultant of: Primity Bio Inc. works with many pharmaceutical and biotech companies and provides CRO services., Evan Wang Shareholder of: Eli Lilly and Company, Employee of: Eli Lilly and Company, Zhang Xin Shareholder of: Eli Lilly and Company, Employee of: Eli Lilly and Company, Jorge Ross Terres Shareholder of: Eli Lilly and Company, Employee of: Eli Lilly and Company, Terence Rooney Shareholder of: Eli Lilly and Company, Employee of: Eli Lilly and Company, Peter C. Taylor Grant/research support from: Celgene, Eli Lilly and Company, Galapagos, and Gilead, Consultant of: AbbVie, Biogen, Eli Lilly and Company, Fresenius, Galapagos, Gilead, GlaxoSmithKline, Janssen, Nordic Pharma, Pfizer Roche, and UCB
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