Abstract B016: Interrupting Hsp70–TLR2 axis to inhibit MerTK activation: A strategy for pancreatic cancer immunotherapy

Abstract Background: Despite many efforts to effectively treat pancreatic ductal adenocarcinoma (PDAC), PDAC carries the highest mortality rate of all major cancers. Thus, there remains a critical medical need to develop novel approaches to improve the clinical outcome of PDAC. It is well known that PDAC generates a localized tumor microenvironment (TME) that allows cancer to escape normal immune surveillance. Immunosuppressive M2 macrophages (MΦ) in the TME facilitate escape from immune surveillance and promote tumor growth. Therefore, TME-induced immunosuppression is a potent immunotherapeutic approach to treating PDAC cancer. In this study, we investigated the nature of a factor secreted by PDAC cells that markedly induced MΦ M2 polarization. Method: Cancer cell-secreted proteins were detected by liquid chromatography-mass spectrometry. MΦ differentiation and polarization were assessed by western blotting and flow cytometry. Protein-protein and protein-lipid interactions were analyzed by co-immunoprecipitation, immunofluorescence, and enzyme-linked immunosorbent assay (ELISA). Cancer cell surface phosphatidylserine (PS) exposures were assessed by flow cytometry. Dioleoylphosphatidylglycerol (DOPG) and Saposin C coupled dioleoylphosphatidylglycerol (SapC-DOPG) lipid vesicles (LVs) treatments were used to assess target protein functions in MΦ polarization, tumor growth, and survival in subcutaneous and orthotopic tumor models. Results: We found that PDAC cells induced MΦ M2 polarization through exosome-free secreted heat shock protein 70 (Hsp70) that acted on MΦ TLR2 to upregulate MerTK. PDAC secreted Hsp70 is tyrosine phosphorylated, whereas the intracellular form is not. Hsp70, TLR2, and MerTK were found to be associated together in a complex. Surface PS-high cancer cells secreted more Hsp70 and possessed strong M2 MΦ polarization. DOPG LVs bound to Hsp70 and blocked the M2 MΦ polarization in vitro. Furthermore, DOPG LVs inhibited intra-tumor M2 MΦ polarization and tumor growth by sequestering the cancer-released Hsp70. Furthermore, tumor-targeting SapC-DOPG LVs increased the survival of the PDAC orthotopic mouse model. Conclusions: These results reveal a novel immunotherapeutic approach to improve the outcome of PDAC treatment. Citation Format: Ahmet Kaynak, Xiaoyang Qi. Interrupting Hsp70–TLR2 axis to inhibit MerTK activation: A strategy for pancreatic cancer immunotherapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_3):Abstract nr B016.