Targeted Blockage of Signal Transducer and Activator of Transcription 5 Signaling Pathway with Decoy Oligodeoxynucleotides Suppresses Leukemic K562 Cell Growth

Abstract

The protein signal transducer and activator of transcription 5 (STAT5) of the JAK/STAT pathway is constitutively activated because of its phosphorylation by tyrosine kinase activity of fusion protein BCR-ABL in chronic myelogenous leukemia (CML) cells. This study investigated the potential therapeutic effect of STAT5 decoy oligodeoxynucleotides (ODN) using leukemia K562 cells as a model. Our results showed that transfection of 21-mer-long STAT5 decoy ODN into K562 cells effectively inhibited cell proliferation and induced cell apoptosis. Further, STAT5 decoy ODN downregulated STAT5 targets bcl-xL, cyclinD1, and c-myc at both mRNA and protein levels in a sequence-specific manner. Collectively, these data demonstrate the therapeutic effect of blocking the STAT5 signal pathway by cis-element decoy for cancer characterized by constitutive STAT5 activation. Thus, our study provides support for STAT5 as a potential target downstream of BCR-ABL for CML treatment and helps establish the concept of targeting STAT5 by decoy ODN as a novel therapy approach for imatinib-resistant CML.

Therapeutic modulators of STAT signalling for human diseases

“…CD40 is a STAT1 target gene that is involved in T-cell activation, and suppression of its expression by the STAT1 ODN may account for the protective effects of the STAT1 ODN against atherosclerosis development 199 . Additionally, in a myelogenous leukaemia cell line (K562), treatment with a 21-bp ODN element containing a modified version of the GAS element that binds STAT5 suppressed STAT5 transcriptional activity, which led to cell cycle arrest and apoptosis 200 . This result suggests that blocking STAT5, which is downstream of the constitutively activated BCR–ABL, with an ODN decoy can be a promising therapeutic approach to overcome imatinib resistance in chronic myelogenous leukaemia 200 .…”

Therapeutic targeting of IL-7Rα signaling pathways in ALL treatment

“…Alternative efforts to target STAT5B include the use of decoy oligonucleotides in chronic myeloid leukemia and potentially the use of siRNA. 70,71 In an experimental model of BCP-ALL, STAT5B gene expression was targeted by epigenetics-based therapy using BET bromodomain inhibitors. The study indicated that bromodomain inhibition induces apoptosis in vitro, improves survival in a xenograft model, and promotes downregulation of IL-7Ra.…”

Progress towards direct inhibitors of Stat5 protein

“…To overcome this problem, the more stable short hairpin RNA (shRNA) was introduced using viral vectors and plasmids, which were then processed into siRNA [27] . Alternatively, the delivery of asODNs to target Stat5 isoforms do not suffer from nonspecifi c effects, although a two-fold greater molar excess is required compared with the corresponding siRNA to achieve effective knock-down [25,28] .…”

“…Decoy ODNs have been established as an effi cient approach to block gene expression by competing with the binding of the transcription factor to the DNA cis-element [28,29] . This sequesters the transcription factor within the cytoplasm and prevents its target gene expression [30] .…”

“…This sequesters the transcription factor within the cytoplasm and prevents its target gene expression [30] . This approach has been successful with the downregulation of Stat5 target genes in various cancer cell lines (K562 [28] , HL-60 [31] ), with no observation of non-specifi c effects. Although decoy ODNs provide an effective approach over siRNA or asODNs for inhibition, their delivery through transfection or other methods limits their subcellular compartmentalization, which may restrict their ability to inhibit Stat5 in the cytoplasm.…”