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

Objective: Biallelic loss-of-function mutations in the insulin receptor (INSR) commonly cause extreme insulin resistance and early mortality. Therapeutic options are limited, but anti-INSR antibodies have previously been shown to activate two mutant receptors, S323L and F382V. This study evaluates four well characterised murine anti-INSR monoclonal antibodies with distinct epitopes (83-7, 83-14, 18-44, 18-146) as surrogate agonists for potential targeted treatment of severe insulin resistance arising from insulin receptoropathies.
Methods: Ten naturally occurring mutant human INSRs with defects affecting different aspects of receptor function were modelled and assessed for response to insulin and anti-INSR antibodies. A novel 3T3-L1 adipocyte model of insulin receptoropathy was generated permitting conditional knockdown of endogenous mouse Insr by lentiviral expression of species-specific shRNAs with simultaneous expression of human mutant INSR transgenes.
Results: All expressed mutant INSR bound to all antibodies tested. Eight mutants showed antibodyinduced autophosphorylation while co-treatment with antibody and insulin increased maximal phosphorylation compared to insulin alone. After knockdown of mouse Insr and expression of mutant INSR in 3T3-L1 adipocytes two antibodies (83-7 and 83-14) activated signalling via AKT preferentially over signalling via ERK1/2 for seven mutants. These antibodies stimulated glucose
uptake via P193L, S323L, F382V, and D707A mutant INSR, with antibody response greater than insulin response for D707A
Conclusions: Anti-insulin receptor monoclonal antibodies can activate selected naturally occurring mutant human insulin receptors, bringing the prospect of novel therapy for severe insulin resistance caused by recessive mutations closer.