Overcoming PGE2-mediated suppression of stem cell-derived NK cells’ anti-tumor functionality for improved treatment of cancer
Cancer patients displaying high frequencies of intratumoral natural killer (NK) cells have shown improved prognosis. Therefore, therapies based on the adoptive transfer of NK cells might be a promising strategy to ultimately reach long-lasting progression-free survival in cancer patients. In this context, our department has designed a protocol for the generation of allogeneic NK cells from cord blood-isolated hematopoietic progenitor cells (HPC-NK). These HPC-NK cells have shown to be safe for the treatment of hematological and solid tumors in clinical trials. However, full efficacy of NK cell therapy is hampered by the suppressive microenvironment found in tumors. One of the factors known to inhibit NK cell function is prostaglandin E2 (PGE2), which is commonly secreted by tumors.
To improve efficacy of our HPC-NK cells for these cancer patients, we propose to block the EP2 and EP4 surface receptors that recognize PGE2. This blockade was investigated using EP2/4-specific inhibitors or by CRISPR-knockout of both receptors. HPC-NK cell functionality was studied in vitro in presence/absence of PGE2 by measuring cytokine secretion with ELISA, NK cell proliferation and tumor recognition in potency assays in co-culture with tumor cells.
Treatment of HPC-NK cells with PGE2 suppressed cytokine-induced proliferative capacity >20%, IFNg secretion by 2-fold, and TNF secretion about 20%. However, blockade of EP2/4 receptors with antagonists almost completely restored HPC-NK cell cytokine production and proliferation. Likewise, the antagonists almost completely rescued degranulation and IFNg production when cultured with hematological and solid tumor cells in presence of PGE2. Furthermore, extensive screening of EP2/4-targeting guide RNAs yielded up to 97% of receptor knockout. Most importantly, tumor cell recognition mechanisms were also improved more than 2-fold with CRISPR/Cas9-KO of the EP2/4 receptors.
These finding demonstrate that blocking or genetic deletion of EP receptors is an attractive strategy to rescue NK cell functionality in PGE2-enriched tumor microenvironments. Reduced PGE2 sensitivity upon adoptive transfer of HPC-NK cells could significantly improve the therapeutic benefit of these cells for the treatment of cancer patients.