Tegavivint directly targets TBL1 to inhibit b-catenin nuclear oncogenic activity

Tegavivint (BC2059) is a first-in-class small molecule that has demonstrated clinical activity in multiple cancer types including HCC and NSCLC. Tegavivint binds to TBL1 resulting in inhibition of Wnt/beta-catenin oncogenic activity. To further define tegavivint's mechanism of action, we performed a series of biochemical, cell-based, and structural studies to characterize its interaction with TBL1 family members and beta-catenin. TBL1, the human homologue of EBI, is a cancer driver gene and core component of the nuclear coactivator complex that regulates protooncogenic transcription factor activity. The TBL1 gene family consists of three highly conserved family members (TBL1x,TBL1xR1,TBL1Y) which are overexpressed and mutated in aggressive and invasive cancers. TBL1 deletion or silencing suppresses tumor cell growth, whereas overexpression induces invasion and EMT. Notably, TBL1 binds directly to nuclear beta-catenin to form a regulatory complex on beta-catenin target-gene promoters, positioning it as a critical node in Wnt/beta-catenin signaling. To characterize the tegavivint-TBL1 interaction we have performed structural and functional studies using recombinant purified TBL1 proteins. TBL1 was observed to self-assemble into a functional dimer, creating the beta-catenin binding site, and also spontaneously forming a larger multimeric complex of three dimers. Tegavivint binds directly to both TBL1x and TBLxR1 with nanomolar affinity. Binding of TBL1 to beta-catenin was characterized, and a low nanomolar affinity binding region in beta-catenin mapped within an armadillo domain. Cell-based studies across multiple cancer types confirmed tegavivint disrupts the TBL1/beta-catenin transcriptional complex, selectively promotes degradation of nuclear b-catenin , and impairs beta-catenin nuclear transcriptional activity. These studies also characterized the role of active WNT signaling in modulation of TBL1 function and tegavivint activity. An X-ray crystal structure of TBL1xR1 protein was resolved, enabling precise modeling of tegavivint's binding mode within the beta-catenin-binding pocket of TBL1. Further structure-guided computational screens identified multiple new structurally diverse chemical series. Similar to tegavivint, these series bind directly to TBL1, disrupt the beta-catenin/TBL1 interaction, inhibit beta-catenin dependent transcription, and promote nuclear beta-catenin degradation. These findings establish the oncogenic driver gene TBL1 as a novel, druggable target in the WNT/ beta- catenin signaling pathway and highlight tegavivint as a differentiated therapeutic strategy for Wnt-driven cancers.