A Bifunctional PARP-HDAC Inhibitor with Activity in Ewing Sarcoma

Area of Science:

• Oncology
• Molecular Biology
• Drug Discovery

Background:

• Histone deacetylase (HDAC) inhibition can induce "BRCAness," a state of synthetic lethality in cancers with proficient DNA repair.
• Combining HDAC and poly (ADP-ribose) polymerase (PARP) inhibitors is a strategy for cancers resistant to single-agent PARP inhibitors (PARPi).

Purpose of the Study:

• To report the development and characterization of a novel bifunctional inhibitor, kt-3283, with dual PARP1/2 and HDAC activity.
• To evaluate the efficacy of kt-3283 in Ewing sarcoma models.

Main Methods:

• Assays for PARP1/2, HDAC activity, and PAR formation.
• Cytotoxicity, cell-cycle, and DNA damage assessments (γH2AX, comet assay).
• Evaluation of metastatic potential using an ex vivo pulmonary metastasis assay (PuMA).

Main Results:

• Kt-3283 demonstrated superior cytotoxicity compared to FDA-approved PARPi (olaparib) and HDAC inhibitors (vorinostat) in Ewing sarcoma models.
• Kt-3283 induced significant S and G2-M cell-cycle arrest and elevated DNA damage at nanomolar concentrations.
• Kt-3283 inhibited Ewing sarcoma cell colonization in the ex vivo PuMA model.

Conclusions:

• Kt-3283 provides preclinical justification for a clinical trial of dual PARP and HDAC inhibition in Ewing sarcoma.
• This study presents proof-of-concept for a single-molecule bifunctional therapeutic strategy targeting Ewing sarcoma.