Abstract LB-183: Anti-PD1 blunts obesity associated triple negative breast cancer progression
Authors: Pingili Ajeeth , Miller Emily , Teng Bin , Makowski Liza 
Published: August 2019

Abstract
Few targeted therapies exist for triple negative breast cancer (TNBC), resulting in elevated recurrence and metastasis and a great unmet clinical need. Immune checkpoint therapy is promising; a recent clinical trial reported improved responses with anti-PD-L1 in advanced TNBC. Obesity increases poor outcomes in TNBC due to elevated invasion, metastasis, and mortality. Despite being an inflammatory state, obesity also can increase immune checkpoint ligands PD-1 and PD-L1 in some tumors and expression on PD-L1 on T cells and adipocytes, which drive immunosuppression. Greater PD-1 and PD-L1 may be due to hypoxia and inflammatory cytokines through increased expression and stability. Critically, immune checkpoint inhibitors appear to be more effective in obese patients, but underlying mechanisms remain unclear. Thus, we hypothesize that hypoxia and inflammation may synergistically increase immune checkpoint ligands which would alter immune checkpoint inhibitor efficacy in TNBC. To address this problem, syngeneic tumors were generated via orthotopic engraftment of E0771 basal-like breast cancer cell line into age-matched immune-competent C57BL/6J female littermates made obese on high fat diet (HFD, 60% kcal from fat) or lean on low fat diet (LFD, 10% fat). Mice were started on diets at weaning. By sacrifice at 27 weeks of age, lean and obese mice weighed 24.39g or 45.54g, respectively (p value &lt;0.0001, N=15-16). Body composition showed no change in lean mass; obese mice had 48.64% adiposity (g fat/g body weight) compared to 15.99% in lean mice as 27 weeks (P=&lt;0.0001). E0771 cells (0.25 x106) were injected after 24 weeks on diet and mice were sacrificed 24 days later. Mice were treated with anti-mouse anti-PD-1 or isotype control (IgG2a) (200 ug/kg i.p.) every 3rd day until sacrifice. Eleven out of 16 obese mice developed tumors (68.8% incidence). Surprisingly, only 2 tumors arose in N=16 lean mice (12.5% incidence) despite randomized same-day cell injections of lean and obese mice. Importantly, anti-PD-1 significantly reduced tumor volume in obese mice as measured by IVIS and caliper (P=0.0147, N=4-5, 22 days after tumor implantation). Ongoing studies include comprehensive evaluation of the immune microenvironment of both the tumors and normal mammary gland by flow and RNAseq. Immunohistology quantification of tumor, immune cell, and microenvironment characteristics will determine to what extent anti-PD-1 altered modifiers of tumor progression such as proliferation, apoptosis/necrosis, angiogenesis, stem cell content, epithelial to mesenchymal transition parameters.
In conclusion, these results suggest that obesity-induced mammary microenvironmental effects augmented tumor incidence in immune intact C57BL/6J mice. Furthermore, immune checkpoint inhibitor successfully reduced tumor progression in obese mice. Potential inflammatory changes unique to the mammary gland or tumor microenvironment could be targeted in concert with checkpoint inhibitors in future interventions.
Citation Format: Ajeeth Pingili, Emily Miller, Bin Teng, Liza Makowski. Anti-PD1 blunts obesity associated triple negative breast cancer progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-183.