Abstract 4978: Combination of a clinical stage-hedgehog inhibitor, GT1708, improves Venetoclax-induced apoptosis by down-regulating MCL-1 proteins in AML cells
Authors: Ma Liandong , Zhou Qianxiang , Yan Honghua , Dong Min , Han Xiahe , Li Jiangwie , Qu Jie , Qian Weidong , Tong Youzhi 
Published: April 2023

Abstract
Acute Myeloid Leukemia (AML) is the third hematological malignancies with the worst relative overall 5-year survival rate (11.7%) in hematological malignancies. AML is a heterogeneous disease with a broad spectrum of genomic changes and molecular mutations that lead to a poor prognosis and clinical outcome. Leukemic stem cells progress to myoblasts that continue to proliferate without differentiating, namely, immature blasts in AML. The hedgehog (HH)/glioma-associated oncogene homolog (GLI) signaling pathway is essential for embryonic and stem cell developments. This pathway has been one of the most promising targets for drug discovery and developments for AML. Although HH inhibitor Glasdegib in combo with low-dose cytarabine achieved FDA approval for AML, Venetoclax (BCL-2 inhibitor/ABT-199) plus a hypomethylating agent (HMA) have been dominating the regimens in AML recently. Here we reported GT1708, a HH inhibitor, improves ABT-199 (venetoclax)-induced apoptosis by down-regulating MCL-1 proteins in AML cells. GT1708 is a potent HH inhibitor (IC50=0.11 nM in HH pathway-driven cellular assay) and inhibited GLI expression with doses of 1, 3 and 10 mpk in a HH-dependent medulloblastoma animal models. In Molm-13 (AML) cells, GT1708 was shown to down-regulate the expression of MCL-1 proteins (anti-apoptotic proteins). In contrast, ABT-199 increased the expression of MCL-1. Furthermore, ABT+Aza (Azacidine/HMA drug) induced more MCL-1 expression than ABT-199. Importantly, GT1708 was shown to induce the expression of cleaved-PARP (c-PARP/apoptotic marker) and to increase c-PARP expression when combined with ABT-199. Due to ABT+Aza induced MCL-1 overexpression, the combination of both agents failed to induce c-PARP, suggesting MCL-1 overexpression conferring resistance to ABT+Aza therapy in Molm-13 cells. GT1708 was further evaluated in flow cytometry-based apoptotic assays. GT1708, ABT-199 and Aza were demonstrated to induce an early apoptosis by 9.98%, 47.5%, and 8.64%, respectively. In comparation, ABT+GT1708 were revealed to induce a 61% of apoptosis superior to 47% or 48.5% of apoptosis induced by either ABT or ABT+Aza in Molm-13 cells. These results confirm the role of MCL-1 overexpression in conferring resistance to ABT+Aza therapy, which can be overcome by ABT+GT1708 combo. GT1708/ABT combo were also shown a marginable superior antitumor activity than ABT along in Molm-13 animal models. GT1708 has been testing in a phase I study in AML patients with previous multiple lines of regimens. GT1708 has been shown to reduce blast counts in three of 13 AML patients treated with higher doses and demonstrated favorite PK and safety profiles. In brief, these results support the clinical development of GT1708 in combination with ABT-199 in AML patients.
Citation Format: Liandong Ma, Qianxiang Zhou, Honghua Yan, Min Dong, Xiahe Han, Jiangwie Li, Jie Qu, Weidong Qian, Youzhi Tong. Combination of a clinical stage-hedgehog inhibitor, GT1708, improves Venetoclax-induced apoptosis by down-regulating MCL-1 proteins in AML cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4978.