# Targeting Hsp70 Immunosuppressive Signaling Axis with Lipid Nanovesicles: A Novel Approach to Treat Pancreatic Cancer

## TL;DR

This study introduces a new treatment for pancreatic cancer using lipid nanovesicles to block immunosuppressive signals in the tumor environment.

## Contribution

The novel approach uses SapC-DOPG to target and inhibit secreted Hsp70, reversing immunosuppression in pancreatic cancer.

## Key findings

- PDAC cells secrete Hsp70, which promotes M2 macrophage polarization and tumor immunosuppression.
- SapC-DOPG blocks Hsp70 activity, reverses immune suppression, and reduces tumor growth in mouse models.
- High phosphatidylserine on cancer cells correlates with increased Hsp70 secretion and MΦ differentiation.

## Abstract

Pancreatic ductal adenocarcinoma (PDAC) is the twelfth most frequent cancer worldwide and the fourth leading cause of cancer-related deaths in the USA, and is projected to be ranked second by 2030. FOLFIRINOX or gemcitabine-abraxane, the current standard treatments for advanced PDAC, prolong survival by only several months in chemo-sensitive patients. Thus, there remains an urgent medical need to develop novel approaches to treat PDAC. Since the PDAC tumor microenvironment (TME) is highly immunosuppressive with M2 polarized macrophages (MΦ), inhibition of immunosuppressive M2 polarization offers a potentially robust approach to reactivate the immune system against PDAC. In this study, we developed a Saposin C (SapC)-coupled dioleoylphosphatidylglycerol (SapC-DOPG) that binds secreted heat shock protein 70 (Hsp70), which was recently shown to be secreted by PDAC cells and to be a potent mediator of TME immunosuppression. Our preclinical studies using mouse models of pancreatic cancer show that SapC-DOPG blocks Hsp70 actions and inhibits tumor growth. These preclinical studies suggest a promising immunotherapeutic approach to treat PDAC.

Background: Despite many efforts to effectively treat PDAC, PDAC carries one of the highest mortality rates of all major cancers. Thus, there is a critical unmet need to develop novel approaches to improve the clinical outcome of PDAC. It is well known that many cancers, including PDAC, generate a local TME that allows cancer to escape normal immune surveillance. Phosphatidylserine (PS), a negatively charged phospholipid that is abundant on the cancer cell membrane and with known actions to promote the secretion of immunomodulatory proteins, may provide a mechanism to regulate the TME. This study explored that possibility. Methods: MΦ differentiation and polarization were assessed by Western blotting and flow cytometric approaches. PS exposure and surface markers were analyzed by flow cytometry. Protein–protein and protein–lipid interactions were analyzed by immunofluorescence and enzyme-linked immunosorbent assay (ELISA). Phospholipid and SapC-DOPG treatment were employed to assess target protein functions in MΦ polarization, tumor growth, and survival in subcutaneous and orthotopic tumor models. The PK-PD and safety of SapC-DOPG were tested on orthotopic mouse models. Results: Our studies show that PDAC secretes Hsp70 that stimulates the MΦ polarization to the immunosuppressive M2 phenotype. We found that high surface PS on cancer cells correlates with increased secretion of Hsp70 and is associated with higher MΦ differentiation activity in vitro and in vivo. Furthermore, blocking cancer cell-secreted Hsp70 with SapC-DOPG reverses the immune suppression and reduces tumor growth. Conclusions: These preclinical results reveal a novel immunotherapeutic approach to potentially improve the outcome of PDAC treatment in humans.