Abstract 662: Local and systemic effects of Dickkopf-1 during breast cancer progression by limiting NK cell-mediated killing

Abstract While most breast cancer patients are diagnosed early, approximately 10-20% recur with the metastatic disease within 10 years. Unfortunately, cures are limited once recur, especially if the tumor spreads to the bone, a site resistant to therapies. Elevated levels of the Wnt inhibitor dickkopf-1 (Dkk1) are detected in breast cancer patients and correlate with the progression of bone metastases. We also find that breast cancer patients with progressive metastatic bone disease unresponsive to standard-of-care therapies have higher Dkk1 levels than patients with stable disease. Intriguingly, serum Dkk1 levels do not always correlate with Dkk1 expression in cancer cells. Thus, it is important to understand the source and role of Dkk1 in breast cancer. In this study, we used mice orthotopically injected with PyMT, EO771, and 4T1 breast cancer lines. Although Dkk1 was not expressed in the tumor cells, Dkk1 serum levels were upregulated in all models. To determine the role of Dkk1 in tumor progression, we used a Dkk1 neutralizing antibody (α-Dkk1) and found a significant reduction in primary tumor growth and in the bone of mice intratibially injected with PyMT tumor cells compared to IgG. To understand the source of Dkk1, we isolated the tumor mass and the bones from tumor-bearing mice. Dkk1 was highly expressed by the osteoblasts (OBs) in the bone and to a less extent by the cancer-associated fibroblasts (CAFs) in the tumor stroma. To address the role of bone- versus CAF-derived Dkk1, we generated mice with specific deletion of Dkk1 in the OBs (OsxCre;Dkk1fl/fl), or CAFs (Fsp1Cre;Dkk1fl/fl and aSMACreERT2;Dkk1fl/fl). To our surprise, all our mouse models showed a significant reduction in primary tumor growth, suggesting systemic and local effects of Dkk1. Further supporting direct local effects of Dkk1, WT mice co-injected with PyMT and Dkk1 deficient CAFs showed reduced tumor growth compared to mice co-injected with Dkk1 sufficient CAFs. To understand how Dkk1 exerts its pro-tumorigenic effects, we performed bulk RNAseq of tumor cells isolated from IgG and α-Dkk1 treated mice. To our surprise, we did not detect changes in pathways related to cell proliferation, survival, apoptosis, and cytoskeletal reorganization. However, pathways related to immune responses were upregulated in the α-Dkk1 treated tumors. Indeed, Dkk1 neutralization did not reduce tumor growth in the NSG immune-compromised mice. To investigate which immune population was targeted by Dkk1, we treated tumor-bearing mice with α-Dkk1 in combination with depletion of T, NK cells, or macrophages. Surprisingly, only NK cell depletion abrogated α-Dkk1 anti-tumor effects. In vitro assays further confirmed reduced NK cell killing efficiency against PyMT tumor cells in the presence of recombinant Dkk1. Our data show that Dkk1 exerts local and systemic effects to promote tumor progression by modulating the killing efficiency of NK cells. Citation Format: Seunghyun Lee, Biancamaria Ricci, Roberta Faccio. Local and systemic effects of Dickkopf-1 during breast cancer progression by limiting NK cell-mediated killing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 662.