Stimulator of
interferon genes (
STING) is an innate immune receptor activated by natural or synthetic agonists to elicit antitumoral immune response via type I IFNs and other inflammatory
cytokines. Bacillus Calmette-Guerin (BCG) is the standard of care as intravesical
therapy for patients with high-risk
non-muscle invasive bladder cancer (
NMIBC). There are limited options available for patients with
NMIBC who developed BCG unresponsiveness. In this study, we characterized in vitro and in vivo antitumor effects of E7766, a macrocyle-bridged
STING agonist, via
intravesical instillation in two syngeneic orthotopic murine
NMIBC tumor models resistant to therapeutic doses of BCG and anti-PD-1 agents. E7766 bound to recombinant
STING protein with a Kd value of 40 nmol/L and induced IFNβ expression in primary human peripheral blood mononuclear cells harboring any of seven major
STING genotypes with EC50 values of 0.15 to 0.79 μmol/L. Intravesical E7766 was efficacious in both
NMIBC models with induction of effective immunologic memory in the treated animals. Pharmacologic activation of the
STING pathway in the bladder resulted in IFN pathway activation, infiltration of T cells and natural killer (NK) cells, dendritic cell activation, and antigen presentation in bladder epithelium, leading to the antitumor activity and immunity. In addition, measurements of the pharmacodynamic markers, Ifnβ1 and CXCL10, in bladder, urine, and plasma, and of
STING pathway intactness in
cancer cells, supported this mode of action. Taken together, our studies reveal an antitumor immune effect of pharmacologic activation of the
STING pathway in bladder epithelium and thus provide a rationale for subsequent clinical studies in patients with
NMIBC.