Robust pancreatic tumor suppression by a novel combination treatment with anti-PD-1 immune checkpoint antibody and stroma modifying RNA oligonucleotide STNM01 in mice.
Authors: Ye Juanjuan , Suizu Futoshi , Yamakawa Keiko , Mukai Yuri , Nishiyama Akira , Yoneyama Hiroyuki , Tsuchiya Takayoshi , Kato Motohiko , Yahagi Naohisa , Kadota Kyuichi 
Published: June 2024

e14630 Background: Tumor stromal remodeling is an obstacle for immune checkpoint blockade therapies. STNM01 is a synthetic RNA oligonucleotide that represses carbohydrate sulfotransferase 15 (CHST15), which is responsible for tumor stromal remodeling. We have previously reported that STNM01 monotherapy by intratumoral injection repressed tumor stromal remodeling while increase tumor-infiltrating T lymphocytes (TILs) in pancreatic tumor-bearing mice. STNM01 was shown to increase TILs in patients with unresectable pancreatic cancer in a Phase I/IIa trial. In the present study, we investigated whether STNM01-mediated TIL enhancement improves anti-tumor effect of anti-PD-1 immune checkpoint antibody by combination treatment in murine models of pancreatic tumor. Methods: In mouse pancreatic cancer KPC and Pan02 subcutaneous syngeneic tumor models, mice were divided into 4 groups for treatment; 1) control, 2) STNM01 monotherapy, 3) anti-PD-1 antibody monotherapy, and 4) combination therapy with STNM01 and anti-PD-1 antibody. Intratumoral injections with 0.9-1.0 mg/mL of STNM01 or control and intraperitoneal administrations of anti-PD-1 antibody or control (5mg/kg) were then performed twice a week for 2 weeks. Mice were sacrificed after 2 week-treatment from baseline, and anti-tumor effects were evaluated by immunohistochemistry for KPC and flowcytometry for Pan02 model, respectively. Results: In the KPC-implanted syngeneic mouse model, combination treatment with intratumoral STNM01 and systemic anti-PD-1 antibody synergistically and robustly suppressed tumor growth as mean % tumor growth inhibition was over 80%. Tumor-infiltrating CD4+ and CD8+ T cells significantly increased in the anti-PD-1 plus STNM01 combination therapy group compared to anti-PD-1 monotherapy group. In the Pan02-implanted syngeneic mouse model, the combination treatment with STNM01 and anti-PD-1 significantly augmented necrosis area of tumor. Flowcytometry analyses showed that tumor-infiltrating CD3+, CD4+ and CD8+ T cells significantly increased in the anti-PD-1 plus STNM01 combination therapy group compared to control group. Although FoxP3+ Treg did not change, the ratio of CD8 to FoxP3 was significantly high only in the anti-PD-1 plus STNM01 combination therapy group. Notably, Ly6C+Ly6G+ granulocytic MDSCs dramatically diminished in the anti-PD-1 plus STNM01 combination therapy group, while anti-PD-1 monotherapy had no impact on tumoral MDSCs. Conclusions: The present work represents the first report of robust synergy between systemic anti-PD-1 antibody and single stroma modifying agent through intratumoral route of administration. Combination usage of STNM01 would provide a novel and clinically feasible therapeutic option to trigger remarkable effect of immune checkpoint inhibitors to this most hard-to-treat solid tumor.