Abstract 254: Dietary fish oil and aspirin to augment anti-PD-1 immunotherapy in metastatic melanoma
Authors: Chacon Alexander C. , Qin Shuyang S. , Melucci Alexa D. , Jackson Katherine M. , Burchard Paul R. , Dave Yatee A. , Jewell Rachel , Belt Brian A. , Tabayoyong William , Linehan David C. , Prieto Peter A. 
Published: June 2022

Abstract
Introduction: First line anti-PD-1 immune checkpoint inhibition (αPD-1 ICI) induces objective responses in less than 50% of metastatic melanoma patients. Aspirin (ASA) use is associated with improved responsiveness to ICI, with inhibition of myeloid-induced immunosuppression in the tumor microenvironment (TME) a purported mechanism. Cyclooxygenase modulators ASA (pharmacologic inhibitor) and dietary fish oil (FO, substrate) shift myeloid and T cell populations to anti-inflammatory, pro-resolution phenotypes in immunity and cancer.
Methods: C57-BL6/J mice were injected with YUMM 1.7 melanoma in the flank. Mice were fed control chow and water (CTL) or omega-3 rich (FO) chow (10% w/w, 30%kcal/kcal), given ASA in drinking water (600 ug/mL), or FO/ASA combined (COMBO) starting 12 days post tumor implantation, the same day as starting intraperitoneal αPD1 or IgG2a vehicle (q3-4 days). An alternative cohort received pre-αPD-1 treatment ASA and FO starting day 7. Tumors were assessed for growth, harvested, and characterized via flow cytometry on day 32.
Results: When diets and water were started concurrent with αPD-1/IgG2a, FO decreased tumor volume vs. CTL for both vehicle (28%) and αPD-1 (27%) treatments; ASA and COMBO (p = 0.0501) did not. Compared to CTL, FO and COMBO increased monocytes (CD45+, CD11b+, Ly6C+, Ly6G-) and PD-L1+ monocytes in the TME with no effect on tumor associated macrophages (TAMS); ASA decreased the percent of Arginase 1+, CD206+ TAMs. ASA increased PD1+ CD8 T cells, while COMBO increased CD4 and CD8 T cells including LAG3+ and PD1+ CD8 T cells.
When diets and water were started on day 7, FO + αPD-1 decreased tumor volume (21%) vs. αPD-1 controls; ASA and COMBO did not. Compared to CTL, FO and COMBO similarly altered immune populations as above, with FO additionally increasing total CD3+ T-cells, PD-L1+ CD4 T cells, and PD-1+ CD8 T cells; COMBO increased dendritic cells (CD11c+, MHCII+, F4/80-). TAMS were not assessed.
Results significant (p&lt; 0.05) by ANOVA or t-test unless specified. Food eaten, water imbibed, and weight did not vary between groups.
Conclusions: Dietary fish oil impaired in vivo melanoma tumor growth with and without αPD-1 ICI despite increases in classically deleterious monocyte populations, while aspirin decreased M2-like macrophages in the TME without alterations in tumor growth. Modulation of the cyclooxygenase axis may be a cost-effective method to skew TME immune populations to favor αPD-1 immunotherapy responses in metastatic melanoma.
Citation Format: Alexander C. Chacon, Shuyang S. Qin, Alexa D. Melucci, Katherine M. Jackson, Paul R. Burchard, Yatee A. Dave, Rachel Jewell, Brian A. Belt, William Tabayoyong, David C. Linehan, Peter A. Prieto. Dietary fish oil and aspirin to augment anti-PD-1 immunotherapy in metastatic melanoma [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 254.