Session: 604. Molecular Pharmacology and Drug Resistance: Myeloid Neoplasms: Poster II
Hematology Disease Topics & Pathways:
Research, Acute Myeloid Malignancies, AML, Translational Research, Diseases, Myeloid Malignancies, Biological Processes, molecular biology, pathogenesis
Using protein degradation CRISPR-based screening technology we have identified HECT ubiquitin ligase UBR5 as a regulator of Menin protein stability. Furthermore, depletion of UBR5 partially rescues the anti-proliferative effects of MI treatments through blunting transcriptional inhibition of canonical Menin/KMT2A target genes such as MEIS1/HOXA. UBR5 colocalizes with Menin and KMT2A proteins on chromatin and contributes to transcriptional inhibition during MI treatments.
We further characterize Menin degradation by using CRISPR base editor screens coupled to FACS in an endogenously edited MEN1-mScarlet human leukemia cell line to identify key Menin residues responsible for Menin degradation after MI treatment. We found and validated, using Menin overexpression systems, residues near the KMT2A interaction interface that prevented degradation and are outside of the MI binding pocket. Our data suggests that Menin degradation necessitates MI induced KMT2A displacement and that UBR5/KMT2A possibly compete for Menin association at a putative degron.
In our recent study we identified mutations that induce resistance to Menin inhibitors via base-editor screens and these mutations were also identified in AMLs from patients (Perner et al. 2023). In that screen we also observed a mutation (D136N) that is outside the Menin MI-binding pocket and conferred a selective advantage on AML cells during MI treatment; this mutation has not been observed in patients but suggests a yet uncharacterized resistance mechanism. We generated MEN1-D136N mutated human leukemia cell lines and observed both protein degradation rescue as well as MI resistance, albeit less so than binding pocket mutations. Menin/KMT2A-FITC-peptide fluorescence polarization assays suggest that MI binding is not affected by D136N. This suggests an alternative resistance mechanism mediated by evasion of Menin degradation. We next applied our base editing technology in MEN1-M327I mutated human leukemia cell lines to ask if degradation evasive compound mutations could deepen resistance phenotypes. We observed that the D136N substitution was the top compound mutation hit conferring a selective advantage in M327I MEN1 cells during a MI treatment course in our screen.
Finally, we compared the Menin degradation potential of several MIs currently under clinical investigation and discovered variability among MIs for induced Menin degradation suggesting this is a designable feature. Additionally, we found that Menin degradation is not tightly linked to drug binding affinities opening the potential to overcome MI drug binding mutations through degradation mechanisms. Taken together our data suggests that MI induce degradation is an essential and designable feature of MI design/efficacy. Our data also suggests that degradation evasive mutations in MEN1 could be an alternative resistance mechanism to contend with going forward in clinical trials.
Disclosures: Fischer: Civetta Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Lighthorse Therapeutics: Current equity holder in private company; Proximity Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Neomorph, Inc.: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees, Other: Founder; Avilar Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Photys Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Novartis: Consultancy; Sanofi: Consultancy; EcoR1 Capital: Consultancy; Deerfield: Consultancy; Deerfield: Research Funding; Novartis: Research Funding; Ajax: Research Funding; Interline: Research Funding; Astellas: Research Funding. Ebert: Exo Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Abbvie: Consultancy; Calico: Research Funding; Neomorph Inc.: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Skyhawk Therapeutics: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; TenSixteen Bio: Current equity holder in private company, Membership on an entity's Board of Directors or advisory committees; Novartis: Research Funding. Armstrong: Syndax: Research Funding; Neomorph Inc: Consultancy, Current holder of stock options in a privately-held company; Imago Biosciences: Consultancy, Current holder of stock options in a privately-held company; Cyteir Therapeutics: Consultancy, Current holder of stock options in a privately-held company; C4 Therapeutics: Consultancy, Current holder of stock options in a privately-held company; Nimbus Therapeutics: Consultancy, Current holder of stock options in a privately-held company; Accent Therapeutics: Consultancy, Current holder of stock options in a privately-held company; Janssen: Research Funding; MENIN inhibition: Patents & Royalties: WO/2017/132398A1.
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