Depsipeptide (FK228) Preferentially Induces Apoptosis in BCR/ABL-Expressing TF-1 Cells.
Authors: Okabe Seiichi , Tauchi Tetsuzo , Nakajima Akihiro , Sashida Goro , Sumi Masahiko , Gotoh Akihiko , Broxmeyer Hal E. , Ohyashiki Junko H. , Ohyashiki Kazuma 
Published: October 2019

Abstract
Chronic myelogenous leukemia (CML) results from transformation of hematopoietic cells by the BCR/ABL gene. Although high rates of hematologic responses to imatinib therapy, the acquired resistance to imatinib has been recognized as a major problem in the treatment of CML Histone deacetylases (HDACs) and histone acetyltransferases (HATs) regulate gene expression and cell growth. Recently, HDAC inhibitors have known as a new class of anti-cancer drugs. One of the HDAC inhibitor, depsipeptide (FK228) is now doing the clinical trial for the treatment of patients, such as peripheral T-cell lymphoma, but there was fully not known to the CML. In this study, we used the TF-1 BCR-ABL cell line, which were transfected BCR/ABL gene to the leukemia cell line, TF-1. We show here that FK228 preferentially induced apoptosis of TF-1 BCR-ABL cells, compare to the parental cell line, TF-1. IC50 of FK228 was 1.5ng/ml. BCR/ABL, intracellular molecular chaperone, heat shock protein 90 (HSP90), and p53 which regulate cell cycle, and signal-transducing activators of transcription 5 (STAT5) were acetylated after FK228 treatment, but not glycogen synthase kinase-3β (GSK-3β) and extracellular regulated kinase-1 (Erk-1). Histone H4 is also acetylated after FK228 treatment in a time and dose depend fashion. In a cell cycle analysis, TF-1 BCR-ABL cells were stopped at G2-M phase after FK228 treatment. The activity of Mitogen-activated protein kinase (MAPK) and Src kinases were blocked after FK228 treatment in a time and dose depend fashion, but p38MAPK was activated and c-jun N terminal kinase (JNK) activity was unchanged. Inhibitor of apoptosis proteins (c-IAPs) have prevented cell death by inhibiting effectors caspases. mRNA levels of IAPs especially survivin, cIAP-1, and apollon, were inhibited by FK228 treatment and moreover, caspase3, caspase9 and poly (ADP-ribose) polymerase (PARP) were activated in a time and dose depend manner. Histone acetylation, caspase activitation and cell cycle were not changed by treatment of p38 inhibitor, SB203580, indicating that p38MAPK was not involved in FK228 cell signaling directly. It has been reported human telomerase reverse transcriptase (hTERT), the catalytic subunit of telomerase, is highly expressed in most human tumors and HDAC plays a central role in the regulation of hTERT. We studied the relation of hTERT and HDAC inhibitor. We used the CML cell line which was transfected shRNA of human telomerase reverse transcriptase (hTERT). Telomerase activity was reduced shRNA transfected cells compared to the wild type. Histone H4 acetylation was not reduced after FK228 treatment compared to the wild-type and mock transfected cell, but FK228-inducing apoptosis was reduced in the cells which were transfected with shRNA of hTERT. FK228 also induced histone acetylation, caspase activation and apoptosis of primary CML blastic crisis cells which was resistant to STI571. Our study suggests that FK228 may be of use in the management of CML patients.