Modification of Death receptor-mediated cell death in osteosarcoma cell lines using epigenetic modifiers

Osteosarcoma is a bone malignancy most prevalent in adolescent populations. Despite advances in multi-agent chemotherapies and surgical procedures, the survival rate remains <30% for patients with metastasis. Tumour necrosis factor-related apoptosis inducing ligand (TRAIL) is a promising anti-cancer agent, but when used as a single-agent, TRAIL-resistance occurs. Anti-Death receptor-4 and -5 agonistic mAbs are TRAIL mimetics proven to have higher specificity towards DR4 and DR5 receptor thus avoiding decoy receptors. However, their efficacy is also limited due to rapid development of resistance. In this study, the epigenetic modifiers Trichostatin A, GSK343 and BIX-01294 were explored in combination with an anti-DR5 agonistic mAb (DR5 mAb) to evaluate their anti-cancer efficacy in osteosarcoma cell lines Saos-2 and MG63. These cell lines are known to be insensitive TRAIL-induced apoptosis due to overexpression of membrane-bound and soluble decoy receptors to TRAIL, but are more sensitive to DR5 mAbs. Trichostatin A, a Histone deacetylase inhibitor (HDACi) demonstrated a synergistic effect in sensitising osteosarcoma cells to DR5 mAb. Conversely, inhibitors of the Histone methyltransferase GSK343 (EZH2i) and BIX-01294 (G9ai) in combination with DR5 mAb had an antagonistic effect on apoptosis induction. The drug combinations were also evaluated in 3D alginate tumour spheroids, and both GSK343 and BIX-01294 inhibited DR5 mAb-mediated apoptosis.