Targeting GSK3B in refractory B-cell malignancies

摘要

Abstract GSK3E functions as essential negative regulator of E-catenin, while E-catenin accumulation represents a central oncogenic driver in cancer. In solid tumors, E-catenin forms complexes with TCF7-factors for transcriptional activation of MYC1-5. In striking contrast to solid tumors, we found that B-cell leukemias and lymphomas are not only exempt from activating E-catenin lesions but highly sensitive to E-catenin accumulation and critically depend on its negative regulation by GSK3E-mediated degradation: Unlike other cancer types, inducible activation of E- catenin in B-cell malignancies suppressed MYC-expression and rapidly induced cell death. Instead of the transcriptional activator TCF7, our interactome studies in B-cell malignancies revealed that E-catenin formed a repressive complex with lymphoid-specific Ikaros zinc finger (IKZF)6-8 factors. Instead of MYC-activation, E- catenin assembled lymphoid-specific Ikaros factors and multiple members of the repressive nucleosome remodeling and deacetylation (NuRD)9-10 complex for transcriptional repression of MYC. GSK3E phosphorylates S/T-residues in E-catenin exon 3, to initiate E-catenin- degradation. To leverage lymphoid-specific repressive E-catenin-complexes as previously unrecognized therapeutic vulnerability, we examined GSK3E small molecule inhibitors. Strikingly, established GSK3E-inhibitors that are currently in clinical trials for the neurological disorders and solid tumors, were effective at low nanomolar concentrations in B-cell malignancies, induced massive accumulation of E-catenin, repression of MYC and acute cell death. Preclinical experiments based on patient-derived xenografts validated small molecule GSK3E-inhibitors for targeted engagement of lymphoid-specific repressive E-catenin-complexes to overcome drug-resistance in refractory B- cell malignancies in vivo. Based on this discovery, the central goal of this proposal is to repurpose GSK3E-inhibitors for targeted engagement of repressive E-catenin-complexes in refractory B-cell malignancies. Given that four GSK3E- inhibitors have already undergone full clinical development and demonstrated favorable safety profiles in eighteen clinical trials, we anticipate that this powerful new approach can rapidly be developed to benefit patients with refractory B-cell malignancies and be further extended to T-cell malignancies in the future. We propose two Aims to (1) elucidate the mechanistic basis of E-catenin-mediated tumor suppression and to (2) develop concepts to leverage targeted activation of E-catenin-Ikaros complexes for therapeutic intervention in refractory B-cell malignancies.