WRN-targeted therapy using inhibitors NSC 19630 and NSC 617145 induce apoptosis in HTLV-1-transformed adult T-cell leukemia cells

Background: Human T-cell leukemia virus type 1 (HTLV-1) Infection is associated with adult T-cell leukemia/lymphoma (ATLL), a lymphoproliferative malignancy with a dismal prognosis and limited therapeutic options. Recent evidence shows that HTLV-1-transformed cells present defects in both DNA replication and DNA repair, suggesting that these cells might be particularly sensitive to treatment with a small helicase inhibitor. Because the "Werner syndrome ATP-dependent helicase" encoded by the WRN gene plays important roles in both cellular proliferation and DNA repair, we hypothesized that inhibition of WRN activity could be used as a new strategy to target ATLL cells.

Methods: Our analysis demonstrates an apoptotic effect induced by the WRN helicase inhibitor in HTLV-1-transformed cells in vitro and ATL-derived cell lines. Inhibition of cellular proliferation and induction of Apoptosis were demonstrated with cell cycle analysis, XTT proliferation assay, clonogenic assay, annexin V staining, and measurement of mitochondrial transmembrane potential.

Results: Targeted inhibition of the WRN helicase induced cell cycle arrest and Apoptosis in HTLV-1-transformed leukemia cells. Treatment with NSC 19630 (WRN inhibitor) induces S-phase cell cycle arrest, disruption of the mitochondrial membrane potential, and decreased expression of anti-apoptotic factor Bcl-2. These events were associated with activation of caspase-3-dependent Apoptosis in ATL cells. We identified some ATL cells, ATL-55T and LMY1, less sensitive to NSC 19630 but sensitive to another WRN inhibitor, NSC 617145.

Conclusions: WRN is essential for survival of ATL cells. Our studies suggest that targeting the WRN helicase with small inhibitors is a novel promising strategy to target HTLV-1-transformed ATL cells.