We demonstrate that uniform mechanical properties can be achieved in 3D printed polymer blends by using a dynamic Diels–Alder reaction.

The cytosolic innate immune sensor cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway is crucial for priming adaptive antitumour immunity through antigen-presenting cells (APCs). Natural agonists such as cyclic dinucleotides (CDNs) activate the cGAS-STING pathway, but their clinical translation is impeded by poor cytosolic entry and serum stability, low specificity, and rapid tissue clearance. Here, we developed an ultrasound (US)-guided cancer immunotherapy platform using nanocomplexes composed of 2’3’ cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) electrostatically bound to biocompatible branched cationic biopolymers that are conjugated onto APC-targeting microbubbles (MBs). The nanocomplex-conjugated MBs engaged with APCs and efficiently delivered cGAMP into the cytosol via sonoporation, resulting in activation of cGAS-STING and downstream proinflammatory pathways that efficiently prime antigen-specific T cells. This bridging of innate and adaptive immunity inhibited tumour growth in both localized and metastatic murine cancer models. Our findings demonstrate that targeted local activation of STING in APCs under spatiotemporally US stimulation results in systemic antitumour immunity and improves the therapeutic efficacy of checkpoint blockade, thus paving the way toward novel image-guided strategies for targeted immunotherapy of cancer.

Stimuli-sensitive nanomaterials with cooperative response are capable of converting subtle and gradual biological variations into robust outputs to improve the precision of diagnostic or therapeutic outcomes. In this study, we report the design, synthesis and characterization of a series of degradable ultra-pH sensitive (dUPS) polymers that amplify small acidic pH changes to efficacious therapeutic outputs. A hydrolytically active polycarbonate backbone is used to construct the polymer with pH-dependent degradation kinetics. One dUPS polymer, PSC7A, can achieve activation of the stimulator of interferon genes and antigen delivery upon endosomal pH activation, leading to T cell-mediated antitumor immunity. While a non-degradable UPS polymer induces granulomatous inflammation that persists over months at the injection site, degradable PSC7A primes a transient acute inflammatory response followed by polymer degradation and complete tissue healing. The improved therapeutic window of the dUPS polymers opens up opportunities in pH-targeted drug and protein therapy.

The innate immune sensor cyclic GMP–AMP synthase–stimulator of interferon genes (cGAS-STING) has recently emerged as a potential therapeutic target to boost antitumor immune responses. However, STING is a cytoplasmic protein, and its natural activator cGAMP is a negatively charged dinucleotide that is difficult to deliver intracellularly. We have developed a new platform called Microbubble-assisted UltraSound (US)-guided Immunotherapy of Cancer (MUSIC) to activate STING with spatio-temporal control to treat cancer. MUSIC showed greater STING activation compared to cGAMP alone in vitro. In murine models,MUSIC showed dramatic tumor growth inhibition and increased survival in both syngeneic breast cancer models. The absence of antitumor immune responses in STING-/- mice shows that MUSIC action is STING-dependent. Furthermore, 6/10 MUSIC-treated mice were tumor-free versus 2/10 cGAMP-treated mice. All the rechallenged MUSIC-treated mice remained tumor-free 30 days after rechallenge. MUSIC also resulted in a 7-fold decrease in metastatic burden when compared to cGAMP alone. In summary, MUSIC showed efficient STING activation invitro. In addition, local MUSIC treatment of primary tumors produced systemic antitumor immune responses in vivo as well as anticancer immune memory preventing tumor growth upon rechallenge. We are now exploring the use of nanobubbles for systemic administration. [Work supported by CPRIT Grants RR150010 and RP190233. R.F.M. is a CPRIT Established Investigator.]