Background/Purpose: Therapeutic anti-TNF biologic agents can be distinct in their structure and/or in their binding to TNF.  Whether these differences affect the functional properties of these biologics in direct comparison to each other has not been thoroughly investigated.  Our objective was to determine the equivalency of all anti-TNF biologic agents approved for RA in preventing a variety of TNF-induced effects on human monocytes in vitro.

Methods: Human monocytic U937 NF-kB luciferase reporter cells and human RA PBMC were incubated with 100 ng/mL TNF +/- biologic [adalimumab (ADA), etanercept (ETN), infliximab (IFX), golimumab (GOL) or certolizumab pegol (CZP)] as pre-formed complexes.  Surface TNF-RI and –RII levels were monitored by flow cytometry after 1h. Luciferase activity was measured after 4 h. to assess NF-kB activation.  After 24 h., U937 cells and CD14+ monocytes from human RA PBMC cultures were analyzed for surface levels of ICAM-1, an adhesion molecule shown to contribute to monocyte migration and arthritis. Apoptosis was assessed using caspase 3/7 fluorescent substrate.  Alpha-2,6 sialylation (Sia), a glycosylation modification shown to regulate TNF-RI internalization and apoptosis, was evaluated using FITC-labeled Sambucus nigra lectin (SNA).

Results: Surface levels of TNF-RI and –RII on U937 cells were both reduced by 2.4-fold in presence of TNF. TNF-RI was maintained at baseline levels by 16.7 nM ADA or CZP as pre-formed complexes with TNF; however, those complexes with ETN, IFX or GOL could only preserve a fraction of TNF-RI on the surface (43%, 52% & 62%, respectively).  All anti-TNF biologics were equally effective in preventing loss of TNF-RII.  TNF stimulation of U937 NF-kB reporter cells led to a 122-fold increase in luciferase activity which was reduced to baseline by only ADA or CZP at a 38 nM conc.  Partial inhibition by 65%, 77% or 88% was observed with ETN, IFX or GOL, respectively.  TNF-enhanced ICAM-1 surface expression on U937 cells and on CD14+ monocytes from RA PBMC was reduced to baseline by 16.7 nM ADA or CZP, whereas ETN, IFX or GOL were only partially effective (69%, 83% & 86% reduction, respectively).  Both ADA:TNF and CZP:TNF complexes also completely inhibited TNF-induced apoptosis in a dose dependent manner unlike ETN, IFX and GOL, which were less effective (42%, 32% & 42% reduction, respectively).  According to SNA staining, alpha-2,6 Sia surface levels dropped in presence of TNF specifically on the subset of cells undergoing apoptosis, and this subset was reduced proportionately to the inhibitory properties of anti-TNF biologics on apoptosis.

Conclusion: For each of the conditions tested in vitro, many resembling features associated with RA, the pre-formed complexes of ADA:TNF and CZP:TNF were significantly more effective in preventing the TNF-induced effects (decrease of surface TNF-RI and alpha-2,6 Sia; increase in NF-kB activation, ICAM-1 surface levels and apoptosis) on human monocytes than those complexes of TNF with ETN, IFX or GOL. Additional in vitro and in vivo studies need to be done to further elucidate these mechanistic differences.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/therapeutic-anti-tnf-biologic-agents-exhibit-functional-differences-in-blocking-tnf-induced-effects-on-human-monocytes-in-vitro/