Elraglusib induces cytotoxicity via direct microtubule destabilisation independently of GSK3 inhibition

Abstract

AO_SCPLOWBSTRACTC_SCPLOWElraglusib (9-ING-41) is an ATP-competitive inhibitor of glycogen synthase kinase-3 (GSK3) with pre-clinical studies demonstrating broad activity against many tumour types. Promising early-phase clinical trial data led to FDA orphan drug status, and a randomized phase 2 study in combination with cytotoxic chemotherapy in pancreatic cancer has recently completed its recruitment. Similarly, single-agent responses in adult T-cell leukaemia/lymphoma and melanoma, and combination treatment data in several other tumour types have been encouraging. The elraglusib mechanism of action is unknown, but it is unlikely to act through GSK3 inhibition because cytotoxicity is observed below the IC50 for GSK3 and other small molecule GSK3 inhibitors do not produce cytotoxic effects, at least in lymphoma cells. We show here that elraglusib perturbs chromosomal alignment to cause a mitotic arrest in multiple tumour lines. This arrest is caused by direct microtubule depolymerisation, which prevents the attachment of kinetochores to microtubules. At clinically relevant doses, these mitotically arrested cells eventually undergo mitotic slippage, leading to gross chromosome missegregation, DNA damage and apoptosis. These effects explain the cytotoxicity of elraglusib because temporarily pausing cell cycle progression with the CDK4/6 inhibitor palbociclib abolishes any drug-induced genotoxicity and apoptosis. In summary, elraglusib acts as a potent direct microtubule destabilizer both in vitro and across multiple cancer types, resulting in mitotic arrest, DNA damage and apoptosis. These effects likely account for its broad pan-cancer activity, which does not rely upon GSK3 inhibition as they are not replicated by other GSK3 inhibitors.