Sustained Tumour Response to Repeated STING Activation Assessed by Diffusion Weighted MRI

Motivation: Cancer immunotherapy with cyclic GMP-AMP synthase (cGAS)-stimulator of interferon gene (STING) agonists aims to generate an immune response by T cell priming, activation and infiltration into the tumour microenvironment leading to cell death. Goal(s): The clinical development of STING agonists would benefit from imaging biomarkers that inform on intratumoural pharmacodynamics and potentially anti-tumour response. Approach: Longitudinal diffusion-weighted MRI in a thyroid xenograft model indicated sustained increase in ADC as an imaging biomarker of tumour microenvironment changes following treatment with a STING agonist. Results: The potential use of MRI as an indicator of early STING pathway related pharmacodynamic effects in situ is demonstrated. Impact: Increased ADC is a sensitive, clinically-translatable imaging biomarker of tumour response to a STING agonist.