Abstract LB-111: GT19077, a c-Myc/Max protein-protein interaction (PPI) small molecule inhibitor, selectively targets c-Myc-additive B-cell and myeloid malignancies
Authors: Ma Liandong , Tong Youzhi , Yang Zhaohui , Zhou Qian Xiang , Chen Jie , Chen Ye , Bi Honglei , Pan Jie , Sun Qi , Xu Ru , Lai Luhua 
Published: September 2020

Abstract
c-Myc is a transcriptional factor and an oncogene driver which plays a major role in tumor initiation, progression and poor prognosis in 80% of all tumor types, especially in c-Myc-additive B-cell and myeloid malignancies. c-Myc's critical role as an oncoprotein makes it an attractive target for pharmacological inhibition. However, c-Myc has been considered as “an undruggable” target since it is an intrinsically disordered protein and regulates key physiological functions in normal cells, which can be a liability for effectively pharmacological intervention. Thus, effective and selective c-Myc targeted molecules are highly warranted, but no such inhibitors are now in clinical testing. c-Myc is dependent on the heterodimerization with Max for the stability and activation of transcription. Here we describes a c-Myc/Max PPI small molecule inhibitor, GT-19077, selectively degrades c-Myc and inhibits the proliferation of c-Myc-addictive B-cell and myeloid malignant cells, but spares c-Myc and the cell proliferation in JAK2-STAT5 dependent erythroblast cells. Through the conformation generation/binding site predication, virtual screening of molecules (&gt;200K), optimization and experimental validation, a leading c-Myc binding molecule series was identified. GT19077 was then discovered and optimized as a leading molecule that exhibited a direct c-Myc binding activity in HL-60 myeloid leukemia cells as shown in Cellular Thermal Shift Assay (CETSA). Importantly, GT19077 selectively degraded c-Myc in HL-60 cells with DC50 of 0.40 µM vs. DC50 of 2.31 µM in GM-CSF-JAK2-STAT5 dependent TF-1 erythroblast cells (&gt;5 fold) as measured by ELISA assays. Consistently, GT19077 also selectively inhibited the proliferation of HL-60 cells with the IC50 of 0.34 µM vs. IC50 of 1.6 µM in GM-CSF stimulated TF-1 cells (&gt;5 fold). Profiling on the proliferation of a selected 14 hematologic malignant cell panel with c-Myc overexpression, GT19077 selectively inhibited the proliferation of all seven B-cell malignant cell lines tested, which include three carrying Myc-IGH translocations and two expressing Kras G12A mutations, with IC50s as low as 160 nM. In addition, two myeloblast cell lines and one monoblast cell line were also sensitive to GT19077 with IC50 of 300-700 nM. In contrast, GT19077 showed almost no effect on the proliferation of four leukemia cell lines with known oncogene drivers, including two erythroblasts (JAK2-STAT5 dependent), one macrophage (FGFR1OP2-FGFR1) and one myeloblast (AML-ETO). These results suggest that c-Myc inhibitor GT19077 can selectively target c-Myc-addictive B-cell and myeloid malignancies, but spares the liability on JAK2-STAT5 driven erythroblasts. Moreover, GT19077 has almost no effect on hematologic malignancies with different oncogene drivers that can be used as biomarkers for patient stratification. Further, GT19077 demonstrated a favorable PK profile with the bioavailability of 57.3% in rat by intraperitoneal (IP) administration. Currently GT19077 is being evaluated in B-cell and myeloid malignant animal efficacy models. Since this novel c-Myc inhibitor demonstrates a superior potency and a unique electivity profile, as compared to many experimental c-Myc inhibitors, it has potential for the drug development for targeting c-Myc-addictive B-cell and myeloid malignancies.
Citation Format: Liandong Ma, Youzhi Tong, Zhaohui Yang, Qian Xiang Zhou, Jie Chen, Ye Chen, Honglei Bi, Jie Pan, Qi Sun, Ru Xu, Luhua Lai. GT19077, a c-Myc/Max protein-protein interaction (PPI) small molecule inhibitor, selectively targets c-Myc-additive B-cell and myeloid malignancies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-111.