A. Premji1,2, J. Link1, T. Yamao1, K. Rashid2, E. Abt2, A. Labora1, C. Chan1, T. Le2, Z. Wainberg3, C. Radu2, T. Donahue1,2 1University Of California – Los Angeles, Surgery, Los Angeles, CA, USA 2University Of California – Los Angeles, Molecular And Medical Pharmacology- Ahmanson Translational, Los Angeles, CA, USA 3University Of California – Los Angeles, Hematology/Oncology, Los Angeles, CA, USA
Introduction:
Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive and therapy-resistant cancer known for its immunosuppressive tumor microenvironment (TME). PDAC tumor and infiltrating immune cells overexpress the pro-inflammatory mediator STING (Stimulator of Interferon Genes), yet also generate abundant immunosuppressive adenosine. Strategies for harnessing STING and targeting adenosine signaling to enhance anti-tumor immunity in PDAC have remained elusive.
Methods:
In a novel Phase 1A/1B clinical trial at UCLA, we assessed drug responses and patient outcomes in 25 patients. We also conducted RNA-seq on 20 patient tumors from the trial, both before and after treatment, to quantify gene expression signatures related to immunosuppression. We evaluated the effectiveness of novel therapeutics to disrupt adenosine metabolism using a murine syngeneic implanted tumor model. We used an ex vivo fresh tissue slice model derived from patient tumors and conducted in vitro experiments using murine bone-marrow derived macrophages, a mouse macrophage cell line, and human peripheral blood mononuclear cells to elucidate the mechanisms underlying adenosine-mediated immunosuppression and drug efficacy.
Results:
Our recently completed neoadjuvant clinical trial at UCLA revealed that poor responses to FOLFIRINOX and PD-1 inhibition in borderline resectable PDAC correlated with high adenosine signaling and a lack of intratumoral plasma cells (p=0.02). In an interim analysis of the first four patients in an ongoing trial, adenosine production was effectively inhibited by targeting CD73, the ectonucleotidase enzyme responsible for converting AMP to adenosine. In a novel discovery, we found that stabilizing adenosine in vitro inhibited STING signaling and promoted immunosuppression by decreasing Type I interferon and increasing IL-6 production from tumor-conditioned macrophages (p<0.01). STING signaling was effectively restored by blocking ENPP1, the enzyme responsible for hydrolyzing ATP and the natural STING ligand, cGAMP (p<0.01). Using an ex vivo model of fresh tissue slices from patient tumors, we demonstrated that ENPP1 inhibition preserved ATP and cGAMP levels. We observed a significant reduction in tumor mass when combining FOLFIRINOX chemotherapy with ENPP1 inhibition in a syngeneic cell line graft mouse model (p < 0.05).
Conclusion:
Our research reveals that adenosine plays a pivotal role in mediating immunosuppression in PDAC by hampering STING-mediated innate immune signaling and promoting a cytokine profile that favors tumor growth. Our innovative approach, which incorporates clinical trial samples with pre-clinical mouse and human-derived models, supports that the simultaneous inhibition of ENPP1 and CD73 may effectively reverse the immunosuppressive tumor microenvironment in PDAC. This promising combination therapy, when coupled with FOLFIRINOX chemotherapy, highlights a promising and effective treatment strategy for PDAC.