Abstract 6534: Overcoming B regulatory cell induced STING resistance by dual functional albumin nanomedicine to prolong survival of pancreatic cancer
Authors: Li Chengyi , Mao Shuai , Zhao Hongyi , Mahamadou Djibo , Liu Zhongwei , Wen Hanning , He Miao , Wang Meilin , Tao Jinsong , Wen Bo , Hoang Trang , Jacobovitz Binyamin , Wen Fei , Gao Wei , Sun Duxin 
Published: March 2024

Abstract
Pancreatic cancer is the most lethal form of cancer with a 5-year survival at 11% and lacks treatment options. Immunotherapy, specifically anti-PD-1/PD-L1 antibody, proves ineffective for pancreatic cancer patients due to the immunosuppressive tumor microenvironment (TME). STING agonist has emerged as the most effective immune modulator to regulate immunosuppressive TME to enhance the efficacy of immunotherapy across many different cancer types. However, two challenges hinder the use of STING agonist in pancreatic cancer: (A) STING agonist strongly stimulates induction of B regulatory cells (Bregs) in pancreatic tumor and lymph node, leading to an intrinsic resistance to STING agonist and a severe compromised efficacy. (B) Most STING agonists are used by local intra-tumor injection in clinical trials, which only shrinks the local tumors without inhibiting distal tumors or metastasis, whereas it is also not feasible for intra-tumor injection for pancreatic cancer in clinical trials. In response, we developed a first-in-class dual functional drug (SH-273) to overcome STING resistance by eliminating Bregs in both tumors and lymph nodes for long-term efficacy in pancreatic cancer. SH-273 has dual function to stimulates STING function (EC50 100 nM) and inhibits PI3Kγ (IC50 7 nM) that eliminate Bregs to overcome STING resistance. Interestingly, SH-273 achieved dual function with an opposite mechanism in regulating IRF3 phosphorylation in myeloid cells (increase) vs. in Bregs (decrease). In addition, we developed an albumin nanoparticle of SH-273 (Nano-273) for systemic delivery to enhance drug targeting to tumor and lymph node to activate systemic anticancer immunity. 3D imaging results indicated that albumin nano formulation greatly enhanced drug lymphoid draining and pancreatic tumor penetrating. Nano-273, combined with anti-PD-1, achieved long-term median survival of 200 days in LSL-KrasG12D; LSL-Trp53R172H/+; Pdx1cre/+ (KPC) mice (a substantial 67% increase from 120 days without treatment). The 80-day survival extension is significant as KPC mice mimic human pancreatic cancers with Kras/P53 mutations that are unresponsive to other available therapies. Single cell RNA-sequencing and flow cytometry revealed that Nano-273, combined with anti-PD-1, reduces Bregs by 5 to 7-fold while increasing other B cell subtypes by 4-fold in both pancreatic tumors and lymph nodes, compared to control group or group treated with STING agonist alone. These findings suggest that Nano-273 overcomes STING resistance by eliminating Bregs and induced systemic immunity to achieve long-term anti-tumor efficacy in pancreatic cancer.
Citation Format: Chengyi Li, Shuai Mao, Hongyi Zhao, Djibo Mahamadou, Zhongwei Liu, Hanning Wen, Miao He, Meilin Wang, Jinsong Tao, Bo Wen, Trang Hoang, Binyamin Jacobovitz, Fei Wen, Wei Gao, Duxin Sun. Overcoming B regulatory cell induced STING resistance by dual functional albumin nanomedicine to prolong survival of pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6534.