An osteogenic microenvironment improves response during denosumab treatment in giant cell tumors of bone in the spine

Giant cell tumors of bone are benign but locally aggressive tumors. Typically diagnosed in individuals between the ages of 20 and 40 years, these tumors cause significant amounts of pain, and morbidity. Giant cell tumors of bone can be treated with an increased dosing regimen of denosumab, a monoclonal antibody that targets receptor activator of nuclear kappa-B ligand, which has shown promise in reducing pain and tumor size, while contributing to improved ossification of the tumor. However, the ossification response observed varies, with some patients responding rapidly with total tumor ossification, while others respond slowly, if at all. Due to gaps in our current understanding of what improves ossification in patients, we aimed to identify patient specific biomarkers that contributed to increased ossification in our patient cohort.

Pre-treatment biopsy samples from 19 patients collected from 3 North American centres were grouped based on their response to denosumab, determined from their change in Boriani ossification grade after treatment. The 19 patients pre-treatment tissue was used in gene expression analysis using RNA extraction and nanoString analysis. A subset of tissue from 6 patients and 3 healthy controls were included in protein expression analysis, where differential expression and gene set enrichment analysis was conducted to identify upregulated proteins and pathways contributing to the different treatment responses.

A distinct microenvironment was identified through both genetic and proteomic expression. Good responders demonstrated upregulation of TNFRSF11B and CX3CL1, genes that are related to bone remodeling, and a downregulation of CX3CR1. Additionally, tissue remodeling and cell proliferation markers were upregulated, while immune related markers were downregulated in our good responders (increased ossification of tumor). Genetic analysis was complemented by protein analysis which in our good responders demonstrated upregulation of bone pathways associated with bone development, bone mineralization, ossification, and osteoblast differentiation, and downregulation in bone remodeling, bone resorption, and osteoclast differentiation. Further analysis identified upregulation of LTF, FBLN5, LOX, CHAD, and OGN, and downregulation of CEBPB, CTSK, and TFRC.

Giant cell tumors of bone show varied mineralization responses to denosumab, with the biological factors associated with this variability remaining poorly understood. We used gene and protein expression analysis of pre-treatment biopsy tissue to compare good and poor mineralization responses. The good responders demonstrate a pre-treatment tumor microenvironment that favors bone formation and reduced resorption, suggesting that biomarker analysis of biopsied samples may help to understand a patient's response to denosumab and guide personalized treatment strategies.