Inhibition of 4EBP phosphorylation mediates the cytotoxic effect of mechanistic target of rapamycin kinase inhibitors in aggressive B-cell lymphomas
Chengfeng Bi,
Xuan Zhang,
Ting Lu,
Xiaoyan Zhang,
Xianhuo Wang,
Bin Meng,
Huilai Zhang,
Ping Wang,
Julie M. Vose,
Wing C. Chan,
Timothy W. McKeithan,
Kai Fu
Affiliations
Chengfeng Bi
Departments of Pathology and Microbiology and Hematology Oncology, University of Nebraska Medical Center, Omaha, NE, USA
Xuan Zhang
Departments of Pathology and Microbiology and Hematology Oncology, University of Nebraska Medical Center, Omaha, NE, USA
Ting Lu
Departments of Pathology and Microbiology and Hematology Oncology, University of Nebraska Medical Center, Omaha, NE, USA
Xiaoyan Zhang
Departments of Pathology and Microbiology and Hematology Oncology, University of Nebraska Medical Center, Omaha, NE, USA
Xianhuo Wang
Departments of Pathology and Microbiology and Hematology Oncology, University of Nebraska Medical Center, Omaha, NE, USA;The Sino-US Lymphoma Center, Tianjin Medical University Cancer Institute and Hospital, National Cancer Research Center, China
Bin Meng
The Sino-US Lymphoma Center, Tianjin Medical University Cancer Institute and Hospital, National Cancer Research Center, China
Huilai Zhang
The Sino-US Lymphoma Center, Tianjin Medical University Cancer Institute and Hospital, National Cancer Research Center, China
Ping Wang
The Sino-US Lymphoma Center, Tianjin Medical University Cancer Institute and Hospital, National Cancer Research Center, China
Julie M. Vose
Departments of Pathology and Microbiology and Hematology Oncology, University of Nebraska Medical Center, Omaha, NE, USA
Wing C. Chan
Department of Pathology, City of Hope Medical Center, Duarte, CA, USA
Timothy W. McKeithan
Department of Pathology, City of Hope Medical Center, Duarte, CA, USA
Kai Fu
Departments of Pathology and Microbiology and Hematology Oncology, University of Nebraska Medical Center, Omaha, NE, USA;The Sino-US Lymphoma Center, Tianjin Medical University Cancer Institute and Hospital, National Cancer Research Center, China
Mechanistic target of rapamycin (mTOR) complex 1 is a central integrator of nutrient and growth factor inputs that controls cell growth in eukaryotes. The second generation of mTOR kinase inhibitors (TORKi), directly targeting the mTOR catalytic site, are more effective than rapamycin and its analogs in cancer treatment, particularly in inducing apoptosis. However, the mechanism underlying the cytotoxic effect of TORKi remains elusive. Herein, we demonstrate that TORKi-induced apoptosis is predominantly dependent on the loss of mTOR complex 1-mediated 4EBP activation. Knocking out RICTOR, a key component of mTOR complex 2, or inhibiting p70S6K has little effect on TORKi-induced apoptosis. Conversely, increasing the eIF4E:4EBP ratio by either overexpressing eIF4E or knocking out 4EBP1/2 protects lymphoma cells from TORKi-induced cytotoxicity. Furthermore, downregulation of MCL1 expression plays an important role in TORKi-induced apoptosis, whereas BCL-2 overexpression confers resistance to TORKi treatment. We further show that the therapeutic effect of TORKi in aggressive B-cell lymphomas can be predicted by BH3 profiling, and improved by combining it with pro-apoptotic drugs, especially BCL-2 inhibitors, both in vitro and in vivo. Taken together, the study herein provides mechanistic insight into TORKi cytotoxicity and identified a potential way to optimize its efficacy in the clinical treatment of aggressive B-cell lymphoma.
