# Structural Analysis of Tilvestamab in Complex with AXL

## TL;DR

This paper presents a structural analysis of the AXL receptor bound to the antibody tilvestamab, using multiple imaging techniques to understand their interaction and guide future drug development.

## Contribution

The study provides a low-resolution 3D model of the tilvestamab-AXL complex and identifies methods for optimizing high-resolution structural studies.

## Key findings

- AXL and tilvestamab form a complex confirmed by SAXS and cryo-EM.
- A homogeneous complex was achieved using monomeric AXL and Fab fragment.
- The structural data can guide mutation design to alter binding affinity.

## Abstract

AXL is a receptor tyrosine kinase with a significant
role in various
biological processes and important medical implications, particularly
in cancer. AXL transduces signals from the extracellular environment
into the cytoplasm by binding to its ligand, growth arrest-specific
protein 6 (GAS6). Activation of AXL leads to autophosphorylation of
its intracellular domain and subsequent activation of downstream signaling
pathways involved in cell proliferation, migration, differentiation,
and survival. Tilvestamab (also known as BGB149) is a first-in-class,
humanized, therapeutic anti-AXL function-blocking monoclonal antibody.
We carried out a structural characterization of the AXL-tilvestamab
complex using both negative-stain and cryogenic transmission electron
microscopy as well as synchrotron small-angle X-ray scattering. While
AXL-Fc was highly elongated and formed large heterogeneous complexes
with the full antibody, homogeneous samples for structural studies
could be made using the monomeric soluble AXL extracellular domain,
the Fab fragment of tilvestamab, and an anti-Fab nanobody. Both SAXS
and cryo-EM confirmed successful complex formation between the three
proteins, and a low-resolution 3D model for the tilvestamab-AXL complex
is presented. The data allow for sample optimization for high-resolution
structural biology, as well as designing mutations that could alter
binding affinity and specificity.