Effective delivery of STING agonist using exosomes suppresses tumor growth and enhances antitumor immunity

Kathleen M Mcandrews,Sara P.Y Che,Valerie S Lebleu,Raghu Kalluri

doi:10.1016/j.jbc.2021.100523

Abstract

The Stimulator of Interferon Genes (STING) pathway is implicated in the innate immune response and is important in both oncogenesis and cancer treatment. Specifically, activation of the cytosolic DNA sensor STING in antigen-presenting cells (APCs) induces a type I interferon response and cytokine production that facilitates antitumor immune therapy. However, use of STING agonists (STINGa) as a cancer therapeutic has been limited by unfavorable pharmacological properties and targeting inefficiency due to rapid clearance and limited uptake into the cytosol. Exosomes, a class of extracellular vesicles shed by all cells are under consideration for their use as effective carriers of drugs owing to their innate ability to be taken up by cells and their biocompatibility for optimal drug biodistribution. Therefore, we engineered exosomes to deliver the STING agonist cyclic GMP-AMP (iExoSTINGa), to exploit their favorable pharmacokinetics and pharmacodynamics. Selective targeting of the STING pathway in APCs with iExoSTINGa was associated with superior potency compared with STINGa alone in suppressing B16F10 tumor growth. Moreover, iExoSTINGa showed superior uptake of STINGa into dendritic cells compared with STINGa alone, which led to increased accumulation of activated CD8+ T-cells and an antitumor immune response. Our study highlights the potential of exosomes in general, and iExoSTINGa specifically, in enhancing cancer therapy outcomes.

Highlights

Dendritic cells (DCs) bridge innate and adaptative response, and DNA released from genomic unstable cancer cells elicits
The utility of stimulator of interferon genes (STING) agonist (STINGa), namely cyclic GMP-AMP (cGAMP) and other cyclic dinucleotides (CDNs), in the treatment of cancer is in early phase of clinical testing [7], and ongoing efforts are directed toward overcoming its unfavorable pharmacological profile and poor bioavailability [9,10,11,12]
In order to determine whether STINGa may bind to intraluminal STING, we evaluated the level of STING in exosomes

Summary

Results

We engineered exosomes containing the small-molecule STING agonist cyclic GMP-AMP (cGAMP, STINGa), thereafter referred to as iExoSTINGa. We evaluated SLC19A1 protein levels in HEK293T cells and exosomes, and SLC19A1 was not detected in exosomes (Fig. S1, C and D). In agreement with these findings, incubation with folic acid, which competes for folic acid receptors, did not alter the amount of STINGa associated with the exosomes (Fig. 1E). Treatment of exosomes with proteinase K to cleave all surface proteins and ectodomains of transmembrane proteins (Fig. S1G) that could be potentially involved in STINGa transport did not significantly alter STINGa present in the exosomes (Fig. 1F). When mice presented with 50 mm tumors, treatment was initiated, and experimental groups received three intratumoral injections of the indicated concentration of iExoSTINGa, STINGa, or just exosomes (Exo) (Fig. 2A). To ascertain the underlying mechanism associated with the antitumor activity of iExoSTINGa, the immune microenvironment

80 WT STINGa

Discussion

Experimental procedures

G Untreated