BRD4-targeting PROTACs Synergize With Chemotherapeutics Against Osteosarcoma Cell Lines

Area of Science:

• Oncology
• Epigenetics
• Pharmacology

Background:

• Advanced osteosarcoma has a poor prognosis, necessitating novel targeted therapies, especially for metastatic disease.
• Bromodomain inhibitors (BETi) are epigenetic modulators with demonstrated antitumor effects.
• Proteolysis targeting chimeras (PROTACs) offer enhanced degradation of target proteins when combined with chemotherapeutics.

Purpose of the Study:

• To investigate the efficacy of BET inhibitors (BETi), including JQ1, dBET57, and MZ1 PROTACs, in combination with cytotoxic drugs against osteosarcoma cell lines.
• To evaluate the synergistic activity and toxicity of these combined treatments.

Main Methods:

• Chemosensitivity assays were performed on osteosarcoma cell lines (HOS, Saos-2, MG-63, G292).
• Cells were treated with BET-directed agents alone or in combination with cisplatin, doxorubicin, topotecan, and gemcitabine.
• Cell viability was assessed to determine drug efficacy and synergy.

Main Results:

• BET degraders showed significant toxicity, particularly in HOS cells.
• Synergistic activity was observed between BET agents and chemotherapeutics, especially in chemoresistant Saos-2 cells and MG-63 cells.
• Combinations of BET agents with doxorubicin and the MZ1-topotecan pair demonstrated potentiation of toxicity. Protein expression of AXL, BCL-X, and others was reduced by BET agents.

Conclusions:

• The combination of novel BET PROTACs with chemotherapeutics presents a potential new therapeutic strategy for osteosarcoma.
• This approach may improve treatment outcomes for osteosarcoma patients.
• The development of orally available PROTACs entering clinical trials supports this therapeutic avenue.