Deciphering the key role of the glycosyltransferase GALNT14 in osteosarcoma tumorigenesis

Osteosarcoma (OS) is the most common primary malignant bone tumor with bimodal incidence by predominantly affecting adolescents and adults 60 years of age and older. Current treatment of OS commonly involves surgical resection and neoadjuvant and adjuvant chemotherapy, which remains insufficient to improve survival for patients with refractory or relapsed OS. We have identified the glycosyltransferase GALNT14 as a potential therapeutic target for OS by incorporating gene expression data from the NIH TARGET database and transcriptomic analysis of institutional patient-derived xenografts (PDXs) from patient tumors demonstrating chemoresistance. High expression of GALNT14 in patient tumors is associated with reduced survival likelihood and chemosensitivity compared to patient tumors with low GALNT14 expression. By comparing samples based on percent necrosis, we determined that GALNT14 is significantly upregulated in patient samples with low (<90%) necrosis, which is associated with reduced overall and relapse-free survival. To gain further insights into the role of GALNT14 in OS tumorigenesis and chemosensitivity, we have established in vitro and in vivo OS models of altered GALNT14 expression either by knock-out (KO) models in high-expressing GALNT14 OS cell lines or GALNT14 overexpression (OE) models in low-expressing GALNT14 OS cell lines. KO models were established by using CRISPR-Cas9 gRNA targets against GALNT14 in human OS cell lines. OE models were established using lentiviral transduction of human OS cell lines using a vector expressing GALNT14 . In vitro studies demonstrated that loss of GALNT14 increased chemosensitivity and decreased metastatic potential, assessed through transwell invasion and migration assays. Furthermore, sarcosphere assays demonstrated decreased stem cell properties in our GALNT14 KO models. We observed reverse effects by in vitro studies of cell lines with overexpression of GALNT14 , suggesting a specific role for GALNT14 in OS tumorigenesis. In addition, orthotopic in vivo studies using immunodeficient mice injected with GALNT14 KO cell lines displayed decreased tumor growth and metastasis. RNA sequencing comparing GALNT14 KO and OE models revealed gene signatures and biological pathways related to immune function, leading us to develop syngeneic models of GALNT14 OE in murine OS cell lines derived from genetically-engineering murine models (GEMMs). We have validated these models at the protein level and are currently assessing their in vitro and in vivo characteristics. Our results suggest a role for GALNT14 in contributing to OS tumorigenesis by mechanisms related to therapeutic resistance, metastatic potential, stem cell properties, and/or immune function. Further studies are ongoing to strengthen our mechanistic understanding of the downstream effects dependent on GALNT14 expression.