Targeting Activating Transcription Factor 3 by Galectin-9 Induces Apoptosis and Overcomes Various Types of Treatment Resistance in Chronic Myelogenous Leukemia

Junya Kuroda,Shigeo Horiike,Masafumi Taniwaki,Akira Yamauchi,Yuji Shimura,Mitsuomi Hirashima,Nana Sasaki,Hisao Nagoshi,Mio Yamamoto,Shinya Kimura,Tsutomu Kobayashi

doi:10.1158/1541-7786.mcr-10-0040

Abstract

Tyrosine kinase inhibitors (TKI) against Bcr-Abl are the first-line therapeutics for chronic myelogenous leukemia (CML). However, the resistance to Bcr-Abl TKIs is induced in leukemic cells not only by loss of sensitivity to TKIs through Bcr-Abl-related molecular mechanisms but also by loss of addiction to Bcr-Abl TK activity by acquiring Bcr-Abl-unrelated additional oncogenic mutations. Therefore, the identification of an additional therapeutic target has been anticipated for achievement of a complete cure and to overcome resistance to treatment. We here showed that modified human Galectin-9 (hGal9), a lectin that show specific affinity for beta-galactosides, inhibits the proliferation of five CML-derived cell lines by inducing apoptosis at their IC(50)s from 17.5 to 164.9 nmol/L. Our study revealed that activating transcription factor 3 (ATF3), a member of the ATF/cAMP-responsive element binding protein family transcription factors, is the critical mediator for cell killing by hGal9, and that Noxa is one of the downstream effector molecules of ATF3. Bim, on the other hand, the BH3-only protein essential for apoptosis by Bcr-Abl TKIs, was not associated with hGal9-induced cell death. ATF3-mediated cell death by hGal9 was not hampered by the absence of p53, the presence of mutant Abl(T315I), or by P-glycoprotein overexpression. In addition, hGal9 showed the additive growth-inhibitory effect with imatinib on CML cell lines. Collectively, hGal9 is a candidate agent that may overcome various kinds of resistance to treatment for CML and may suggest that ATF3 may be a new target molecule for the development of new treatment modalities that can overcome resistance to currently available chemotherapeutics.

Highlights

Our study showed that the cell death inducing mechanism by human Galectin-9 (hGal9) uses activating transcription factor 3 (ATF3), a member of the ATF/CREB family of transcription factors that functions as a tumor suppressor (2529), but not p53 or Bim, the major proapoptotic factors in cell death induced by conventional genotoxic agents or Bcr-Abl tyrosine kinase (TK) inhibitors (TKI)
This implies that hGal9 is effective against chronic myelogenous leukemia (CML) cells that have lost their addiction to Bcr-Abl TK activity or their functional p53
HGal9 was effective against CML cells with T315I Abl mutation, which completely impedes the binding of Bcr-Abl TKIs to drug-binding sites in Abl and K562 without functional p53

Summary

Introduction

The constitutive active fusion tyrosine kinase (TK) Bcr-Abl is responsible for deregulated cell proliferation and resistance to cytotoxic insults in chronic myelogenous leukemia (CML) cells, whereas the blockade of the BcrAbl signaling pathway by TK inhibitors (TKI) leads to the inhibition of cell proliferation and induces apoptosis. Resistance to Bcr-Abl TKIs is induced in leukemic cells by loss of sensitivity to TKIs through the acquisition of Abl mutation or the overexpression of Bcr-Abl and by loss of addiction to Bcr-Abl TK activity by acquiring Bcr-Abl–unrelated additional oncogenic mutations [7]. A new treatment approach that induces an antileukemic effect through Bcr-Abl–unrelated molecular pathways is urgently needed for the achievement of a complete cure and to overcome TKI resistance. Among 14 mammalian galectins, galectin-9 (Gal9) has been shown to possess the anticancer properties by regulating various cellular functions, such as cell adhesion, cell proliferation, or

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