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

Abstract

The oncoprotein c-Myc governs epigenome and transcriptome and is deregulated in 70% 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. We developed the first c-Myc degrader GT19630 (GT19715, the salt form of GT19630). We tested it in cell-free, cellular assays and in animal studies. 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 GT19715 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. GT19715 eliminates circulating blasts and prolongs survival in the c-Myc-driven systemic Daudi leukemia/lymphoma model. Importantly, GT19715 induces cell killing independent of TP53 status, and baseline c-Myc protein levels significantly correlated with sensitivity to GT19715 in MOLM-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 GT19715compared to ven-sensitive parental cells. Finally, GT19715 significantly reduced human CD45+ AML blasts compared to vehicle control in vivo in an AML PDX model. First results with the novel dual c-Myc/GSPT1 degrader GT19715 demonstrate promising preclinical anti-lymphoma and -leukemia efficacy, providing rationale for its clinical development.