TBL1 Inhibitor, Tegavivint, Supresses Cell Survival and Promotes Sensitivity to Chemotherapy in ALL and AML

BACKGROUND Abnormal wnt signaling has been linked to different forms of cancer and has been described to be critical in acute myeloblastic leukemia (AML) and acute lymphoblastic leukemia (ALL). AML is a subtype of leukemia with a poor prognosis as long-term disease-free survival is only 30~40%. While B-ALL has a better prognosis, relapse of B-ALL still has a poor overall survival rate. Aberrant Wnt pathway activation is a common feature in AML and B-ALL as Wnt/catenin activation through β-catenin is involved in self- renewal of leukemia initiating cells. In the canonical Wnt pathway, the signaling of wnt inhibits β-catenin from being degraded. β-catenin regulates transcription of several genes by its translocation into the nucleus. Recently, it has been shown that transducin β-like protein 1 (TBL1) and its highly related family member TBLR1 are required for Wnt-β-catenin-mediated transcription. Overexpression of TBL1 or TBLR1 can lead to significantly enhanced β-catenin-mediated transcription. Conversely, depletion of TBL1 or TBLR1 abolishes the activation of β-catenin. It has been shown that Tegavivint, a novel small molecule inhibitor of Wnt-ß-catenin signaling, binds to transducin ß-like protein 1 (TBL1) preventing the binding of TBL1 to ß-catenin, which results in nuclear degradation of ß-catenin in MV4-11 cells. Here we focus on the effect of Tegavivint in combination with chemotherapy: We hypothesize that interrupting the binding of TBL1 to beta-catenin abrogates not only AML, but also B-ALL cell survival and tests if Tegavivint sensitizes AML cells to AraC and B-ALL cells to chemotherapeutic agents including Vincristine, Dexamethasone or the tyrosine kinase inhibitor Nilotinib as part of preclinical evaluation in acute leukemias. RESULTS As AML is a genetically heterogenous disease, we have tested Tegavivint in vitro in six AML cell lines (THP1, KG1, MOLM14, MOLM13m U937 and MV4-11). These six AML cell lines express β-catenin and TBL1 as determined by Western Blotting. Tegavivint decreases nuclear β-catenin without affecting cytoplasmic β-catenin and decreases non-phospho β-catenin, the active form of β-catenin. We also determined that the IC50 of Tegavivint after 24 hours of incubation ranged between 5-16 nM in these 6 cell lines using AnnexinV/ DAPI staining and flow cytometry. We observed that Tegavivint can sensitize all six AML cell lines to chemotherapy (Ara-C) within 24 hours of incubation. We have also tested Tegavivint on 5 ALL cell lines with different karyotypes (RCH-ACV, NALM6, REH, SUPB15, and RS4;11). We determined that the IC50 of Tegavivint ranged between 5-6.5nM in these 5 cell lines. We also found that Tegavivint can sensitize four ALL cells to chemotherapy using Vincristine and Dexamethasone and one B-ALL cell line (SUBP-B15: BCR-ABL+) to the tyrosine kinase inhibitor Nilotinib within 24 hours of incubation. Further in vitro evaluation of patient-derived B-ALL cells and in vivo evaluation of the sensitization of B-ALL and AML to chemotherapy are in progress. CONCLUSION Our preliminary data shows that AML and B-ALL are sensitive to TBL1- β-catenin inhibition using Tegavivint as a monotherapy and can be sensitized to chemotherapy when AraC or Vincristine, dexamethasone or Nilotinib treatment is combined with Tegavivint. As our data supports our hypothesis that TBL-1- β-catenin inhibition is a new target in B-ALL and AML therapy, further studies are in progress to preclinically evaluate this approach for clinical care.