Journal of Clinical Medicine Review Challenges and Opportunities in the Clinical Development of STING Agonists for Cancer Immunotherapy Leila Motedayen Aval 1, James E. Pease 2 , Rohini Sharma 1 and David J. Pinato 1,* 1 Department of Surgery & Cancer, Imperial College London, Hammersmith Hospital, Du Cane Road, London W120HS, UK;
[email protected] (L.M.A.);
[email protected] (R.S.) 2 Inflammation, Repair & Development, National Heart & Lung Institute, Imperial College London, London SW7 2AZ, UK;
[email protected] * Correspondence:
[email protected]; Tel.: +44-(0)20-7594-2799 Received: 16 September 2020; Accepted: 12 October 2020; Published: 16 October 2020 Abstract: Immune checkpoint inhibitors (ICI) have revolutionised cancer therapy. However, they have been effective in only a small subset of patients and a principal mechanism underlying immune-refractoriness is a ‘cold’ tumour microenvironment, that is, lack of a T-cell-rich, spontaneously inflamed phenotype. As such, there is a demand to develop strategies to transform the tumour milieu of non-responsive patients to one supporting T-cell-based inflammation. The cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING) pathway is a fundamental regulator of innate immune sensing of cancer, with potential to enhance tumour rejection through the induction of a pro-inflammatory response dominated by Type I interferons. Recognition of these positive immune-modulatory properties has rapidly elevated the STING pathway as a putative target for immunotherapy, leading to a myriad of preclinical and clinical studies assessing natural and synthetic cyclic dinucleotides and non-nucleotidyl STING agonists. Despite pre-clinical evidence of efficacy, clinical translation has resulted into disappointingly modest efficacy.