Abstract
CDK (cyclin-dependent kinase) inhibitors have shown remarkable activity in CLL, where its efficacy has been linked to inhibition of the transcriptional CDKs (7 and 9) and deregulation of RNA polymerase and short-lived pro-survival proteins such as MCL1. Furthermore, ER (endoplasmic reticulum) stress has been implicated in CDK inhibition in CLL. Here we conducted a pre-clinical study of a novel orally active kinase inhibitor P1446A in CLL B-cells. P1446A inhibited CDKs at nanomolar concentrations and induced rapid apoptosis of CLL cells in vitro, irrespective of chromosomal abnormalities or IGHV mutational status. Apoptosis preceded inactivation of RNA polymerase, and was accompanied by phosphorylation of stress kinases JNK (c-Jun N-terminal kinase) and p38 MAPK (mitogen-activated protein kinase). Pharmacologic inhibitors of JNK/p38 MAPK conferred protection from P1446A-mediated apoptosis. Treatment with P1446A led to a dramatic induction of NOXA in a JNK-dependent manner, and sensitized CLL cells to ABT-737, a BH3-mimetic. We observed concurrent activation of apoptosis stress-inducing kinase 1 (ASK1) and its interaction with inositol-requiring enzyme 1 (IRE1) and tumor necrosis factor receptor-associated factor 2 (TRAF2) in CLL cells treated with P1446A, providing insights into upstream regulation of JNK in this setting. Consistent with previous reports on limited functionality of ER stress mechanism in CLL cells, treatment with P1446A failed to induce an extensive unfolded protein response. This study provides rationale for additional investigations of P1446A in CLL.
Publication types
-
Research Support, Non-U.S. Gov't
MeSH terms
-
Animals
-
Apoptosis / drug effects*
-
Apoptosis / genetics
-
Cell Line, Tumor
-
Coculture Techniques
-
Cyclin-Dependent Kinases / antagonists & inhibitors*
-
Enzyme Activation / drug effects
-
Humans
-
Immunoglobulin Heavy Chains / genetics
-
JNK Mitogen-Activated Protein Kinases / metabolism*
-
Leukemia, Lymphocytic, Chronic, B-Cell / genetics
-
Leukemia, Lymphocytic, Chronic, B-Cell / metabolism*
-
Mice
-
Mutation
-
Protein Kinase Inhibitors / pharmacology*
-
Proto-Oncogene Proteins c-bcl-2 / genetics
-
Proto-Oncogene Proteins c-bcl-2 / metabolism
-
Signal Transduction / drug effects
-
Stromal Cells / drug effects
-
Stromal Cells / metabolism
-
Unfolded Protein Response / drug effects
-
p38 Mitogen-Activated Protein Kinases / metabolism*
Substances
-
Immunoglobulin Heavy Chains
-
PMAIP1 protein, human
-
Protein Kinase Inhibitors
-
Proto-Oncogene Proteins c-bcl-2
-
Cyclin-Dependent Kinases
-
JNK Mitogen-Activated Protein Kinases
-
p38 Mitogen-Activated Protein Kinases
Grants and funding
This study was in part funded by Piramal Healthcare Ltd., which provided salary support for Sreesha Srinivasa, a co-author on this study, as well as research materials. In addition, Alexey V. Danilov’s salary was in part paid by the Lymphoma Research Foundation Clinical Investigator Career development award. JRB is supported by the Leukemia Lymphoma Society and the American Cancer Society and is a Scholar in Clinical Research of the Leukemia and Lymphoma Society. The above funding organizations did not play a role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and only provided financial support in the form of authors' salaries and research materials.