Mechanistic Computational Modeling of Bispecific Antibodies Targeting IL6R/IL8R in Cancer Metastasis

Introduction:: Bispecific antibodies (BsAbs), antibodies with two different antigen-binding sites in one molecule, are a promising avenue for drug delivery due to their enhanced avidity interactions and dual targeting effects. However, while their ability to simultaneously affect two targets opens an array of novel therapeutic strategies, understanding the mechanisms underpinning their binding and inhibition will be crucial for maximizing the efficacy of new BsAbs treatments. Here, we describe a quantitative, computational model of a novel BsAb targeting the interleukin-6 (IL6) and interleukin-8 (IL8) receptors in cancer metastasis, demonstrating how modeling of multivalent binding provides key insight into antibody affinity and avidity effects and guides therapeutic design.

The IL6/IL8 system is an ideal target for a BsAb therapeutic because IL6 and IL8 synergize to enhance cancer metastasis in a cell-density-dependent manner, and it was recently demonstrated that blockade of the IL6 and IL8 receptors (IL6R and IL8R) with targeted therapies significantly reduced metastatic burden in pre-clinical mouse models of multiple cancer types. Here, we present detailed simulations of the monovalent and bivalent binding interactions between different antibody constructs and the IL6 and IL8 receptors to establish how binary and ternary complex formation drives receptor inhibition and predicts important considerations for in vivo therapeutic design.


Materials and Methods:: The computational model of the IL6/IL8 system consists of a system of coupled ordinary differential equations (ODEs) describing the monovalent and bivalent surface binding interactions between the antibodies of interest for inhibiting the system—tocilizumab (anti-IL6R), 10H2 (anti-IL8R), and two novel bispecific antibodies BS1 and BS2 (both anti-IL6R/anti-IL8R). Parameter values for the ligand-receptor kinetics are based on previously published data¹. We newly parameterized the antibody-receptor binding kinetics using our model, optimization algorithms, and in vitro cell surface binding and binding inhibition assays in HEK 293T cells that had been transfected to express IL6 receptors, IL8 receptors, both, or neither.

We simulated the formation of binary antibody-receptor and ternary receptor-antibody-receptor complexes over a wide range of therapeutically relevant antibody concentrations and receptor densities, and we performed a global sensitivity analysis to identify model parameters with the largest impact on receptor inhibition.

Results, Conclusions, and Discussions:: We fully parameterized the mechanistic, computational IL6R/IL8R/antibodies model, and our simulations successfully predict bound complex formation over the range of experimental data. Simulations of tocilizumab, 10H2, BS1, and BS2 binding over a range of antibody concentrations demonstrate intricate dynamics between the binary and ternary complexes.

The model predicts that the ratio between the expression levels of IL6R and IL8R is crucial to the bispecific antibody binding; in particular, it shows that the bispecific antibody binds similarly to monospecific antibodies but shows substantially different behavior when one receptor is in large excess. In addition, simulations predict that the most stable antibody-receptor complex formation occurs at high receptor concentrations and intermediate antibody concentrations. At high antibody concentrations, the antibody is in such large excess relative to the receptor that ternary complexes are unable to form in substantial amounts, and most of the receptor is bound in the less stable binary complexes (Figure 1). This phenomenon has significant implications for therapeutic dosing, and our simulations quantify and provide insight into these binding mechanisms. Finally, local and global parameter sensitivity analysis determine that the rate limiting step in the antibody binding is the formation of the initial binary complex, with subsequent ternary complex formation proceeding quickly due to the high avidity.

Our quantitative, coupled ODE model of the IL6R/IL8R/antibodies system provides clear mechanistic insight into the binding dynamics of bispecific antibodies and leads to impactful predictions for optimal targeting of the pathway to prevent cancer metastasis. Ongoing model development includes pharmacokinetic modeling of antibody transport, distribution, and elimination to complete a multiscale mechanistic model of the targeted bispecific antibody therapy against the IL6/IL8 system.

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References (Optional): : ¹Yang, Huilin, et al. "Engineered bispecific antibodies targeting the interleukin-6 and-8 receptors potently inhibit cancer cell migration and tumor metastasis." Molecular Therapy 30.11 (2022): 3430-3449.