Abstract 5285: DKK1 blockade inhibits progression of bone metastases via multiple mechanisms and synergize with zoledronate treatment
Authors: Shi Tao , Liang Kaijie , Zhang Yipeng , Zhou Xiaoyu , Liu Baorui , Wei Jia 
Published: March 2024

Abstract
Background: Despite the important breakthroughs of immune checkpoint blockade (ICB) therapy in multiple primary cancers, responses of ICB therapy in bone metastases remain extremely poor, largely due to the highly immunosuppressive bone metastasis microenvironment. However, the current understanding of bone metastasis microenvironment is still incomplete, and specific treatment targets for patients with bone metastasis are still lacking.
Methods: Transcriptome sequencing data of gastric and breast cancer bone metastasis samples from The TCGA and GEO databases were obtained. The correlation between DKK1 expression and prognosis, intertumoral immune infiltration of bone-metastatic patients was analyzed. Mouse bone metastasis models from gastric, breast and lung cancer were established, and in vivo treatment efficacy of DKK1 and/or zoledronic acid was evaluated by micro-computed tomography (CT), micro-magnetic resonance imaging (MRI) and immunohistochemistry (IHC) staining. The changes of immune components wthin bone-tumor microenvironment were explored via flow cytometry, CyTOF and scRNA-seq analysis. The impact of DKK1 on different immune cell types was analyzed via in vitro co-culture models.
Results: Serum detection of gastric cancer patients from our center showed that compared with non-metastatic patients, DKK1 concentration in patients with bone metastasis was the significantly increased (p&lt;0.0001); and compared with other metastatic sites of breast cancer patients, bone metastases had the highest level of DKK1 mRNA expression (p&lt;0.05). Using multiple bone metastasis mouse models, we found that DKK1 blockade significantly controlled the tumor burden of bone metastases. Results of micro-CT and TRAP staining showed that the bone destruction and osteoclast activity within bone lesions were significantly inhibited after DKK1 blockade. In addition, results of flow cytometry and immunofluorescence staining on bone metastasis samples showed that both innate and adaptive anti-immune responses were obviously improved after DKK1 blockade, including increased infiltration of CD8+ T cells, M1 macrophages and decreased infiltration of M2 macrophages. Mechanistically, DKK1 directly induced inhibition of CD8+ T cell activation, M2 polarization of macrophages and maturation of osteoclasts, which all contributes to the immune suppression in the bone metastasis microenvironment. Finally, combined therapy of DKK1 blockade and zoledronic acid had synergistic treatment effects in bone metastases.
Conclusion: Our study provides novel insights into the multiple role of DKK1 in the bone metastasis immune microenvironment. DKK1 is a potential immunotherapeutic target for bone metastases, and dual blockade of DKK1 and zoledronic acid is a promising combination immunotherapy strategy for patients with bone metastasis.
Citation Format: Tao Shi, Kaijie Liang, Yipeng Zhang, Xiaoyu Zhou, Baorui Liu, Jia Wei. DKK1 blockade inhibits progression of bone metastases via multiple mechanisms and synergize with zoledronate treatment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5285.