Verification of the unique functionality of ATOR-1017 by 3D structure determination

Important results from the project

Alligator Bioscience, a biotech company developing antibody-based therapies against cancer, sought to obtain, through 3D crystallography, detailed binding information on potentially therapeutic antibodies that bind and activate the receptor CD137. Two antibodies known to activate T cells by binding to CD137 were studied. These antibodies have been shown to have good antitumor effects in preclinical models and a good safety profile. An additional goal with the project has been to increase insight around the use of synchroton facilities for the development of protein based drugs.

Expected long term effects

The project has been successful and shows the benefit of using crystallography when developing antibody drug candidates. The structures of two antibodies bound to CD137 have been determined by crystallography to a relatively high level. These show that two different ways of binding CD137 are possible for CD137 activating antibodies. This information increases the understanding of how drug candidates targeting CD137 can activate immune cells. The results help Alligator in the differentiation and positioning of ATOR-1017 and may contribute in the outlicensing of this asset.

Approach and implementation

For this project Alligator collaborated with SARomics Biostructures. The binding parts of two antibodies and the target protein CD137 were produced in mammalian or bacterial cultures. Protein complexes of antibody fragments bound to CD137 were purified and used to form crystals. Data were collected at the synchroton facilities Diamond Light Source in the UK and MAXIV (beamlines i03 and i04 and Biomax resp.). Two complexes of antibody fragments and CD137 were determined to 2.3 Å and 3.1 Å. A third structure determined to 3.5 Å involved a complex of both antibody binding domains and CD137.