Clinical Lymphoma, Myeloma & Leukemia, Vol.22, Suppl.2 - October 2022

Abstracts Clinical Lymphoma, Myeloma & Leukemia October 2022 S218 screens performed using the Brie library identified the Urod gene encoding uroporphyrinogen decarboxylase as a critical dependency in two Trp53/Bcor mutated mouse AEL cell lines. UROD is a cytosolic enzyme in the heme biosynthesis pathway involved in converting cytosolic uroporphyrinogen III into the key heme biosynthetic intermediate, coproporphyrinogen III. In an analysis of RNA-seq data from over 2,000 acute leukemia samples, UROD was significantly overexpressed and active by a data-driven network inference algorithm in AEL compared to other leukemia subtypes. We validated UROD as a dependency by electroporation of Cas9 and synthetic sgRNA ribonucleoprotein complex in the two screened cell lines, additional mouse leukemia cell lines, and two commercially available human AEL cell lines. Targeted knockout of UROD resulted in decreased tumor cell growth and viability compared to the non-targeting guide control cells. Sequencing analysis showed high editing efficiency (>85%) followed by recovery of the wild- type cells, indicating that UROD is a dependency in these cells. These results correlated with a significant increase of necrotic cells preceding loss of editing in the two tested human cell lines. We also observed an increase in ALAS1 expression, which is negatively regulated by cellular heme, indicating that UROD knockout leukemic cells cannot generate heme, leading to necrotic cell death. Moreover, mitochondrial function assays showed significant decreases in basal respiration, ATP production, maximal respiration, and spare capacity in a time-dependent manner, followed by the rescue of mitochondrial function after loss of editing efficiency and re-expression of UROD. We have recently developed homozygous UROD-dTAG engineered human AEL cell lines to perform in-vivo survival studies. Co n clusio n s: Through whole-genome CRISPR knockout screening and functional studies, we show that UROD is a dependency in AEL and provides a basis for exploring its therapeutic inhibition. Keywords: AML, AEL, UROD, heme synthesis, RNP AML-147 C-MYC Targeting by Degradation: Novel Dual c-Myc/GSPT1 Degrader GT19715 Exerts Profound Cell Kill In Vitro and In Vivo in Acute Myeloid Leukemia and Lymphomas Yuki Nishida MD, PhD 1 , Darah A Scruggs MS 1 , Edward Ayoub PhD 1 , Tallie Patsilevas BS 1 , Vivian R Ruvolo MS 1 , Po Yee Mak BS 1 , Bing Z Carter PhD 1 , Steffen Boettcher MD 2 , Abhishek Maiti MD 3 , Qianxiang Zhou PhD 4 , Zhaohui Yang PhD 4 , Honghua Yan PhD 4 , Liandong Ma PhD 4 , Michael Andreeff MD, PhD 1 1 Section of Molecular Hematology and Therapy, Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, Houston, USA. 2 Department of Medical Oncology and Hematology, University of Zurich, Zurich, Switzerland. 3 Department of Leukemia, University of Texas MD Anderson Cancer Center, Houston, USA. 4 Kintor Pharmaceutical Ltd., Suzhou, China Objecti v e: The oncoprotein c-Myc governs epigenome and transcriptome and is deregulated in 7 0% of all human cancers. MYC is highly expressed in TP53 mutant or venetoclax (ven) resistant AML (Sallman, Blood 2021, Nishida, ASH 2021). However, targeting c-Myc or the MYC pathway has not been met with success. PROTACs or cerebron E3 ligase modulators (CELMoDs) are attractive modalities to specifically target hitherto undruggable oncoproteins. D esig n a n d Setti n g: We developed the first c-Myc degrader GT19630 (GT19 7 15, the salt form of GT19630). We tested it in cell-free, cellular assays and in animal studies. Results: GT19630 effectively degraded oncogenic c-Myc protein (IC50 = 1.5 nM) in HL-60 cells. C-Myc was effectively pulled down by biotinylated GT19630 in a cell-free, in vitro affinity purification assay; and a proteasome inhibitor ixazomib completely blocked c-Myc degradation. IC50 of GT19 7 15 in HL-60 cells was 1.8 nM, being considerably lower than 40.2 nM, an IC50 of normal myeloid progenitors in CFU assay, suggesting a therapeutic window. GT19630 shares chemical properties with other CELMoDs and proteomic analyses revealed degradation of translation termination factor G1 to S phase transition proteins 1 (GSPT1), an important factor in LSC survival (Surka et al. Blood 2021). Indeed, GT19630 effectively degrades GSPT1 along with complete degradation of c-Myc in a xenograft model with HL-60 cells, and inhibits tumor growth at a dose as low as 0.3 mg/kg/bid. GT19630 had no effect on normal myeloid lineages in rats at 6 mg/kg. GT19 7 15 eliminates circulating blasts and prolongs survival in the c-Myc-driven systemic Daudi leukemia/lymphoma model. Importantly, GT19 7 15 induces cell killing independent of TP53 status, and baseline c-Myc protein levels significantly correlatedwith sensitivity toGT19 7 15 inMOLM- 13 cells with CRISPR engineered knockout or mutations of TP53 (R2 = 0.86, P = 0.02). We found that MV4;11 ven resistant (VR) cells demonstrated elevated protein levels of c-Myc, and GSPT1 and exhibited greater sensitivity to GT19 7 15compared to ven-sensitive parental cells. Finally, GT19 7 15 significantly reduced human CD45+ AML blasts compared to vehicle control in vivo in an AML PDX model. Co n clusio n s: First results with the novel dual c-Myc/ GSPT1 degrader GT19 7 15 demonstrate promising preclinical anti- lymphoma and -leukemia efficacy, providing rationale for its clinical development. Keywords: AML, Myc-driven lymphoma/leukemia, Myc degrader, CELMoDs, GSPT1 AML-151 Characteristics of Acute Promyelocytic Leukemia Hospitalizations in the United States Aditi Sharma MD 1 , Jay Yang MD 2 , Vijendra Singh MD 2 1 Wayne State University, Detroit, USA. 2 Karmanos Cancer Institute/Wayne State University, Detroit, USA Co n text: There is a paucity of contemporary population-based data on acute promyelocytic leukemia (APL) in the United States (US). Objecti v e: To determine epidemiology of APL admissions and their predictors of mortality. D esig n : Retrospective analysis utilizing National Inpatient Sample to identify APL admissions (International Classification of Diseases 10 code: C92.40 {APL