Differential Pathway Coupling of the Activated Insulin Receptor Drives Signaling Selectivity by XMetA, an Allosteric Partial Agonist Antibody

Abstract

The monoclonal antibody XMetA is an allosteric partial agonist of the insulin receptor (IR), which activates the metabolic Akt kinase signaling pathway while having little or no effect on the mitogenic extracellular signal-regulated kinase (ERK) signaling pathway. To investigate the nature of this selective signaling, we have conducted a detailed investigation of XMetA to evaluate specific phosphorylation and activation of IR, Akt, and ERK in Chinese hamster ovary cell lines expressing either the short or long isoform of the human IR. Insulin activated both pathways, but the phosphorylation of Akt was more sensitive to the hormone than the phosphorylation of ERK. Maximally effective concentrations of XMetA elicited phosphorylation patterns similar to 40-100 pM insulin, which were sufficient for robust Akt phosphorylation, but had little effect on ERK phosphorylation. These data indicate that the preferential signaling of XMetA is due to an innate difference in pathway sensitivity of Akt versus ERK responses to IR activation and partial agonism by XMetA, rather than a separate pathwaybiased mechanism. The metabolic selectivity of partial IR agonists like XMetA, if recapitulated in vivo, may be a desirable feature of therapeutic agents designed to regulate blood glucose levels while minimizing undesirable outcomes of excessive IR mitogenic activation.

Unique pharmacology of a novel allosteric agonist/sensitizer insulin receptor monoclonal antibody

“…We hypothesize that this unique signaling profile of IRAB-A may be due to the binding kinetics of the mAb or a result of some structural changes induced by the antibody that are different from ligand. In accord with our findings, XMetA was reported to induce signaling pathway differences compared to insulin suggesting that allosteric engagement of the IR may lead to novel activation mechanisms [21] . This would need to be addressed through intensive structural studies.…”

“…This group has also reported two positive allosteric IR mAbs: XMetA, which activates IR in the absence and presence of ligand and another antibody, and XMetS, which acts as an insulin sensitizer. Both of these antibodies both lower blood glucose levels in mice [7] , [21] , [22] , [23] , [24] , [25] .…”

Evaluation of anti insulin receptor antibodies as potential novel therapies for human insulin receptoropathy

“…As activation of the RAS/RAF/MEK/ERK pathway is mitogenic, this is an encouraging property of antibodies for translational purposes, suggesting that they may exert metabolic benefits without undue mitogenic activity. Similar dissociation between activation of AKT and ERK has also been observed following INSR activation by the peptide ligand S597 (39) and in previous studies with anti-receptor antibodies (40). The mechanism underlying such pathway-specific activation is poorly understood, although IRS proteins may be preferentially phosphorylated by plasma membrane-associated receptor (41,42), whereas receptor internalization is required for full ERK activation (42,43).…”

Evaluation of anti-insulin receptor antibodies as potential novel therapies for human insulin receptoropathy using cell culture models

“…As activation of the RAS/RAF/MEK/ERK pathway is mitogenic, this is an encouraging property of antibodies for translational purposes, suggesting that they may exert metabolic benefits without undue mitogenic activity. Similar dissociation between activation of Akt and ERK has also been observed following INSR activation by the peptide ligand S597 [39] and in previous studies with antireceptor antibodies [40]. The mechanism underlying such biased agonism is poorly understood, although IRS proteins may be preferentially phosphorylated by plasma membrane-associated receptor [33,41], whereas receptor internalisation is required for full ERK activation [33,42].…”