Abstract 257: Normalization of tumor stroma improves the anti-tumor activity of anti-PD-L1 peptides in pancreatic cancer

Abstract

Abstract Pancreatic ductal adenocarcinoma (PDAC) is characterized by the abundant fibrotic stroma surrounding malignant epithelial cells. The tumor stroma is composed of extracellular matrix proteins, myofibroblasts, stellate cells, and immune cells, and comprises up to 80% of the tumor mass. The stroma promotes the progression and metastasis of tumors and the development of chemoresistance. However, the strategies of completed depletion of the stroma resulted in a more aggressive tumor and a poor survival rate in clinical trials. We discovered that silencing the RNA binding protein αCP2, which is encoded by the poly(rC)-binding protein 2 (PCBP2) gene, could destabilize the type I collagen mRNA in human pancreatic stellate cells and mouse NIH/3T3 fibroblasts, leading to the normalization of the tumor stroma. We recently discovered an anti-PD-L1 peptide that effectively blocks the PD1/PD-L1 pathway. We hypothesize that silencing αCP2 modulates the PDAC stroma, thus improving the therapeutic efficacy of immunotherapy. Therefore, the objective of this study is to develop a combination therapy strategy to treat PDAC with PCBP2 siRNA nanoparticles and the anti-PD-L1 peptide. A mixture of 1×106 PANC02 tumor cells and NIH/313 fibroblast cells was subcutaneously implanted into C57BL/6 mice to establish the desmoplastic PDAC model. The mice were treated with saline, PCBP2 siRNA nanoparticles, the anti-PD-L1 peptide, and PCBP2 siRNA nanoparticles plus the anti-PD-L1 peptide. The results showed that the combination of PCBP2 siRNA nanoparticles with the anti-PD-L1 peptide reduced tumor growth. PCBP2 siRNA decreased type I collagen expression in the tumor. The normalized stroma showed increased infiltration of effective immune cells. This approach provides a new strategy to improve the therapeutic efficacy of immunotherapy in PDAC by normalizing the tumor stroma with the PCBP2 siRNA nanoparticle. Citation Format: Chien-Yu Lin, Kun Cheng. Normalization of tumor stroma improves the anti-tumor activity of anti-PD-L1 peptides in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 257.