1497 Preliminary results of a phase 1 study of Decoy20, an intravenous, killed, multiple immune receptor agonist bacterial product in patients with advanced solid tumors

<h3>Background</h3> Systemic activation of multiple immune receptors, such as Toll-like (TLR), Nucleotide Oligomerization Domain (NOD) like, and Stimulator of Interferon Genes (STING) may be required for efficient anti-tumor immune responses. Decoy20 is an attenuated, killed, non-pathogenic, bacterial product with ~90% reduction of lipopolysaccharide (LPS)-endotoxin (TLR4 agonist) activity to enhance intravenous (IV) safety, also containing TLR1/2,2/6,8,9, NOD2 and STING agonists. Decoy20 produced pre-clinical single-agent and combination-mediated anti-tumor activity including innate/adaptive immune-mediated eradication of established tumors, involving combination with anti-PD-1, indomethacin, rituximab or cyclophosphamide. We hypothesized that, due to rapid clearance of systemic bacteria by the liver and spleen, Decoy20 may produce transient immune activation, suitable as monotherapy or in combination with approved agents (pulse-prime hypothesis). <h3>Methods</h3> INDP-D101 (NCT05651022) is an escalation and multi-dose expansion Phase 1 trial of Decoy20 in patients with advanced solid tumors refractory to standard therapy. Primary objectives: safety/tolerability. Secondary objectives: anti-drug immunogenicity, pharmacokinetics and preliminary efficacy. Exploratory objective: systemic immune activation. <h3>Results</h3> As of August 2024, 16 patients (9F, 7M), mean age 56, received a single dose at 7x10⁷ (n=6) or 3x10⁷ (n=7) Decoy20 cells or weekly dosing (n=3) at 3x10⁷ via 1-hour IV infusion and were evaluable for safety after a DLT period of 28 days. Grade (G) 3 treatment related adverse events (AEs) included lymphopenia (n=7), AST increase (n=3), ALT increase, IRR, bradycardia, pain, and malaise (all n=1); the only related G4 AE was lymphopenia (n=9). Bradycardia of &lt; 1 day duration (n=1 at 7x10⁷) and AST increase for &gt; 72 hours (n=1 at 3x10⁷) were dose limiting. Lymphopenia resolved in 2–3 days, an expected pharmacodynamic outcome suggesting trafficking of lymphocytes. Biomarker analysis (n=15) demonstrated immune activation, with transient ≥3-fold induction of plasma analytes, including CD40L, G-CSF, GM-CSF, IFN-γ, soluble IL-2 receptor, IL-2, 4, 6, 8, 9, 10, 12p70, 15, 18, 21, 27, 31, IP-10, I-TAC, MCP-1, MIG, MIP-1α/β, TNF-α/β and TRAIL. Decoy20 clearance occurred within 30–120 minutes. Weekly administration of Decoy20 for at least 4 weeks at 3x10⁷ (n=3) revealed no DLT’s and confirmed transient (24–72 hour) immune activation with each weekly infusion and rapid Decoy20 clearance, similar to single dose administration. One patient with MSS-colon cancer had stable disease for 6 months. <h3>Conclusions</h3> Decoy20 generated mostly G1-2 AEs as single dose or with weekly administration for at least 4 weeks. Transient systemic immune activation at a tolerable weekly dose supports the pulse-prime hypothesis. Decoy20 monotherapy weekly dosing enrollment continues. A combination is planned. <h3>Trial Registration</h3> NCT05651022. <h3>Ethics Approval</h3> This study was approved by the following institutions’ Ethics Boards: WIRB/Copernicus covering Atlantic, Hoag, Emory and Karmanos with approval number 20223025; USC approval number HS-22-00497.