Optimized intratumoral delivery of a STING agonist results in improvements in local tumor immune activation.

38 Background: There has been a renaissance in the concept of promoting the immune-responsiveness of the tumor immune microenvironment via intratumoral (IT) delivery of immunostimulatory agents. As with any invasive intervention, though, outcomes following intratumoral drug delivery depend on procedural technique. We have previously shown that multi-sidehole needles (MSHNs) provide a 3-fold improvement in intratumoral drug delivery and retention relative to conventional end-hole needles (EHNs). The purpose of this study was to characterize how variations in drug delivery affect drug efficacy by evaluating immune activation following the IT delivery of a STING agonist using conventional end-hole needles (EHNs) versus multi-sidehole needles (MSHNs). Methods: Syngeneic McArdle RH-7777 (ATCC) hepatoma cells were implanted in the flank of Buffalo rats (n=20). Once tumors reached 15-20 mm in size, a STING agonist (50 ug ML RR-S2 CDA, Sigma Aldrich) vs saline (control) was injected under ultrasound visualization using either a 22G EHN or a 21G MSHN (ProFusion, Cook Regentec). Tumor tissue was harvested at 24 and 48 hours post-injection. Immune profiling was performed using flow cytometry and single cell RNA sequencing (scRNAseq). Results: There was a significant increase in tumor necrosis with MSHN injections compared to EHN or control injections (tumor viability 32%, 54%, and 82% at 48 hours, respectively). Gene expression profiling demonstrated a significant increase in interferon sensitive genes as well as STING-TBK1-IRF3 axis genes within dendritic cells with MSHN injections compared to EHN or control injections (Table). This signaling upregulation was greater at 24 hours than at 48 hours. MSHN injected tumors also exhibited fewer macrophages with immunosuppressive gene signatures and fewer T cells with exhaustion gene signatures relative to EHN or control tumors. Conclusions: Variations in IT delivery technique have a significant impact on subsequent immune activation following the injection of a STING agonist in an animal model of HCC. [Table: see text]