An inhalable nanoparticulate STING agonist synergizes with radiotherapy to confer long-term control of lung metastases

Yang Liu,Amyn A Habib,Lulu Wang,Dawen Zhao,W Jeffrey Petty,William N Crowe,Yong Lu

doi:10.1038/s41467-019-13094-5

Abstract

Mounting evidence suggests that the tumor microenvironment is profoundly immunosuppressive. Thus, mitigating tumor immunosuppression is crucial for inducing sustained antitumor immunity. Whereas previous studies involved intratumoral injection, we report here an inhalable nanoparticle-immunotherapy system targeting pulmonary antigen presenting cells (APCs) to enhance anticancer immunity against lung metastases. Inhalation of phosphatidylserine coated liposome loaded with STING agonist cyclic guanosine monophosphate–adenosine monophosphate (NP-cGAMP) in mouse models of lung metastases enables rapid distribution of NP-cGAMP to both lungs and subsequent uptake by APCs without causing immunopathology. NP-cGAMP designed for enhanced cytosolic release of cGAMP stimulates STING signaling and type I interferons production in APCs, resulting in the pro-inflammatory tumor microenvironment in multifocal lung metastases. Furthermore, fractionated radiation delivered to one tumor-bearing lung synergizes with inhaled NP-cGAMP, eliciting systemic anticancer immunity, controlling metastases in both lungs, and conferring long-term survival in mice with lung metastases and with repeated tumor challenge.

Highlights

Mounting evidence suggests that the tumor microenvironment is profoundly immunosuppressive
Both layers of liposome membrane are composed of anionic PS, of which PS exposed on the outer layer serves as the “eat me” signal for antigen presenting cells (APCs), while the inner PS interacts with excessive cationic Ca2+ of calcium phosphate (CaP) to complex with cyclic guanosine monophosphate–adenosine monophosphate (cGAMP) in the core
NP-cGAMP exhibited little cGAMP release at pH 7.4, but an acidic pH-responsive release (~40% at pH 6.5 and ~80% at pH 5.0 after 12 h). These data demonstrate that NPcGAMP is stable at pH 7.4, but releases cGAMP in a pHdependent manner

Summary

Introduction

Mounting evidence suggests that the tumor microenvironment is profoundly immunosuppressive. Several studies have shown that intratumoral immunostimulants generally induce local immune response at the injected site, but have limited effect on distant, uninjected tumor sites, implying that the local approach may be inadequate to elicit systemic immunity, or that the systemic response even if induced, may be rendered inactive when exposed to the immunosuppressive tumor microenvironment (TME) at distant naive tumor sites[3,10,17] To overcome these limitations, we set out to develop a nanotechnological strategy that enables targeted delivery of immunostimulants to intratumoral APCs. Here, we assemble phosphatidylserine (PS) on the surface of nanoparticle-cGAMP (NP-cGAMP) because membrane-exposed PS can be recognized and engulfed by macrophages and dendritic cells through their PS receptors[18,19]. These data demonstrate that inhalation of NP-cGAMP may represent a pharmacological approach to enhance APCmediated adaptive immune response against lung metastases

Methods

Results

Conclusion