Discovery of GT19077, a c-Myc/Max Protein-Protein Interaction (PPI) Small Molecule Inhibitor, for Targeting c-Myc-Driven Blood Cancers

c-Myc is an oncogenic transcriptional factor, which plays important roles in tumor initiation, progression and poor prognosis in 80% of all tumor types. IGH/Myc genomic translocations have been identified in 100% Burkitt Lymphoma (BL) and 10-15% of other Non-Hodgkin lymphoma (NHL) including Diffuse large B-cell lymphoma (DLBCL), Mantle cell lymphoma (MCL) as well as B-cell multiple myeloma (MM) and myeloid malignancies (AML) with c-Myc genetic alterations. c-Myc genomic alterations and dysregulation have been directly linked to the poor clinical outcome in these blood cancers, which make c-Myc an attractive target for pharmacological inhibition as an urgent unmet medical need. However, c-Myc has been considered as “an undruggable” target since it is an intrinsically disordered protein and tightly regulates key physiological functions under normal conditions. Therefore, novel c-Myc inhibitors with selectivity of targeting c-Myc dependent NHL, MM and acceptable therapeutic index are highly warranted.

c-Myc dimerizes with Max to activate its oncogenic transcription activity. Here we described a c-Myc/Max PPI small molecule inhibitor GT-19077, which disrupted c-Myc/Max dimer with an IC₅₀ of 1.0 µM in PPI assays and inhibited c-Myc transcription activity in reporter assays with an IC₅₀ of 0.50 µM . The disruption of c-Myc/Max complex induced c-Myc instability and degradation with IC₅₀ of 0.34 µM in c-Myc-dependent HL-60 AML cells measured by ELISA assays. The effective degradation of c-Myc was then confirmed in both HL-60 and Ramos (BL) cells by Western Blotting (WB). In contrast, GT19077 was six-fold less potent for c-Myc degradation in GM-CSF-stimulated TF-1 erythroid progenitor cells with an IC₅₀ of 2.31 µM, which was defined as a 6-fold selectivity and considered as a criterion for in vivo tolerability studies. GT19077 was also much less active at degrading c-Myc in GM-CSF-stimulated TF-1 or IL-2-stimulated lymphoid progenitor NK-92 cells assayed by WB. Dysregulated c-Myc is one of major oncogene drivers in B-cell lymphoma, MM and AML. Therefore, GT19077 was evaluated in a panel of 14 hematologic malignant cell lines expressing dysregulated c-Myc or other oncogene drivers. The results showed that GT19077 selectively inhibited the proliferation of all seven B-cell malignant cell lines tested, carrying IGH/Myc translocations (6/7) or Kras G12A mutation (1/7), 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 the rest of three leukemia cell lines carrying other oncogene drivers, including JAK2V617F in HEL cells, AML-ETO in Kasumi-1 cells and FGFR fusion in KG-1 cells. These results suggest GT19077 effectively inhibits c-Myc-dependent blood cancers, but has less effect on the blood cancer cells expressing other oncogene drivers. Moreover, GT19077 inhibited c-Myc-driven tumor biology, which included inducing cell cycle arrest at G2/M and down-regulating immune oncology targets CD-47 and PD-L1 in c-Myc-dependent HL-60 cells. Furthermore, GT19077 demonstrated a favorable PK profile in vivo and degraded c-Myc proteins in HL-60 and Ramos xenograft tumor models.

In conclusion, GT19077 is a potent c-Myc/Max PPI inhibitor Lead molecule with the desired selectivity of targeting c-Myc in c-Myc dysregulated blood cancers, but sparing c-Myc in growth factor/cytokine regulated blood progenitor cells. Importantly, GT19077 effectively inhibits the proliferation of B-cell lymphoma, MM and AML cells carrying c-Myc genetic alterations, including IGH/Myc translocations, but lacks activity in blood cancer cells expressing other oncogene drivers. These results can help develop biomarkers for patient tailoring strategy. Finally, GT19077 demonstrates PK-dependent target engagement in vivo and is currently being evaluated in in vivo efficacy studies.