TAS-116 (pimitespib), a heat shock protein 90 inhibitor, shows efficacy in preclinical models of adult T-cell leukemia.

Adult T-cell leukemia/lymphoma (ATL) is a highly chemoresistant malignancy of peripheral T lymphocytes caused by human T-cell leukemia virus type 1 infection, for which there is an urgent need for more effective therapeutic options. The molecular chaperone heat shock protein 90 (HSP90) plays a crucial role in nuclear factor-κB (NF-κB)-mediated antiapoptosis in ATL cells, and HSP90 inhibitors are new candidate therapeutics for ATL. Accordingly, we investigated the anti-ATL effects of a novel oral HSP90 inhibitor, TAS-116 (pimitespib), and the mechanisms involved in ex vivo and in vivo preclinical models. TAS-116 achieved IC50 values of less than 0.5 µmol/L in 10 ATL-related cell lines and less than 1 µmol/L in primary peripheral blood cells of nine ATL patients; no toxicity was observed toward CD4+ lymphocytes from healthy donors, indicating the safety of this agent. Given orally, TAS-116 also showed significant inhibitory effects against tumor cell growth in ATL cell-xenografted mice. Furthermore, gene expression profiling of TAS-116-treated Tax-positive or -negative cell lines and primary ATL cells using DNA microarray and multiple pathway analysis revealed the significant downregulation of the NF-κB pathway in Tax-positive cells and cell-cycle arrest in Tax-negative cells and primary ATL cells. TAS-116 suppressed the activator protein-1 and tumor necrosis factor pathways in all examined cells. These findings strongly indicate the efficacy of TAS-116, regardless of the stage of ATL progression, and its potential application as a novel clinical anti-ATL therapeutic agent.