Mentor Name: Christopher Kuo

The lungs continue to be the most common site of relapse and metastasis for patients with osteosarcoma (OST). Despite current intensive multimodal therapy, 60% of the patients with lung metastases will die. Surgical resection of lung metastases remains the mainstay of treatment for cure. Effective targeted therapy is desperately needed. Thrombospondin-2 (THBS2) is an extracellular matrix (ECM) protein enriched in fibrotic niches that can modulate cellular differentiation, adhesion and migration. In pancreatic cancer, THBS2 is a poor prognostic biomarker, and its knockdown decreases “Don’t Eat Me” CD47 expression, thus enhancing immune detection. To date, little is known about the immunomodulatory role of THBS2 in the TME of metastatic OST. In pancreatic cancer, THBS2 recruits and polarizes TAMs to an immunosuppressive M2 state, thereby forming an immune barrier. In late-stage OST, THBS2 upregulation can increase its migratory potential. My preliminary data analyzing published spatial transcriptomics (ST) OST lung metastases demonstrated high THBS2 expression in OST tumor colocalized with high M2 TAMs expression. My hypothesis is that THBS2 has a pro-tumor role in metastatic OST through polarization of M2 TAMs, upregulating CD47, and creating a fibrotic niche, leading to immune evasion and an immunosuppressive TME.

We will address this hypothesis via the following aim:test the functional importance of THBS2 within the TME of OST in an in vivo zebrafish xenograft model of OST. The zebrafish model is a unique tool to study complex cell-cell interactions during metastatic cascade. Zebrafish are completely transparent during early stages of life, allowing unprecedented in vivo imaging of cell-cell interactions. We will first establish a lung-relevant xenograft model of metastatic osteosarcoma in zebrafish through this POST project. Once we establish a lung-relevant xenograft model, we will then investigate the macrophage dynamics and phenotypes in response to xenografted OST cells in zebrafish via live imaging and single cell RNA-sequencing and assess how THBS2 knockout alters the TME. By understanding the biology of THBS2 within OST lung metastases, we may develop novel therapeutic strategies that decrease the lung fibrotic niche, allow for immune detection and halt further metastatic spread.