Viral capsid delivery of cGAMP enhances STING-dependent antitumor immune response

Therapies to activate the STING immune response pathway represent promising potential anticancer treatments. However, the native STING activating molecule, 2’,3’-cGAMP, is a poor drug candidate due to its susceptibility to nuclease degradation and its relatively poor cell uptake. In this study, we present a nanoscale delivery vehicle based on the bacteriophage MS2 virus-like particle that can both protect cGAMP and deliver it into cells to access and bind cytosolic STING. MS2-delivered cGAMP achieved greatly increased STING activation potency relative to both free cGAMP and a nuclease-resistant synthetic cGAMP analog. In an in vivo murine colon carcinoma model, MS2-cGAMP elicited significant and prolonged antitumor activity in a STING-dependent manner at 50-fold lower concentrations relative to free cGAMP and synthetic analogs. These results demonstrate that MS2 delivery of cGAMP can yield a highly potent STING agonist immunotherapy with in vivo anticancer activity.