Pristimerin induces apoptosis in imatinib-resistant chronic myelogenous leukemia cells harboring T315I mutation by blocking NF-κB signaling and depleting Bcr-Abl

Zhongzheng Lu,Yanli Jin,Chun Chen,Juan Li,Jingxuan Pan,Qi Cao

doi:10.1186/1476-4598-9-112

Abstract

BackgroundChronic myelogenous leukemia (CML) is characterized by the chimeric tyrosine kinase Bcr-Abl. Bcr-Abl-T315I is the notorious point mutation that causes resistance to imatinib and the second generation tyrosine kinase inhibitors, leading to poor prognosis. CML blasts have constitutive p65 (RelA NF-κB) transcriptional activity, and NF-κB may be a potential target for molecular therapies in CML that may also be effective against CML cells with Bcr-Abl-T315I.ResultsIn this report, we discovered that pristimerin, a quinonemethide triterpenoid isolated from Celastraceae and Hippocrateaceae, inhibited growth and induced apoptosis in CML cells, including the cells harboring Bcr-Abl-T315I mutation. Additionally, pristimerin inhibited the growth of imatinib-resistant Bcr-Abl-T315I xenografts in nude mice. Pristimerin blocked the TNFα-induced IκBα phosphorylation, translocation of p65, and expression of NF-κB-regulated genes. Pristimerin inhibited two steps in NF-κB signaling: TAK1→IKK and IKK→IκBα. Pristimerin potently inhibited two pairs of CML cell lines (KBM5 versus KBM5-T315I, 32D-Bcr-Abl versus 32D-Bcr-Abl-T315I) and primary cells from a CML patient with acquired resistance to imatinib. The mRNA and protein levels of Bcr-Abl in imatinib-sensitive (KBM5) or imatinib-resistant (KBM5-T315I) CML cells were reduced after pristimerin treatment. Further, inactivation of Bcr-Abl by imatinib pretreatment did not abrogate the TNFα-induced NF-κB activation while silencing p65 by siRNA did not affect the levels of Bcr-Abl, both results together indicating that NF-κB inactivation and Bcr-Abl inhibition may be parallel independent pathways.ConclusionTo our knowledge, this is the first report to show that pristimerin is effective in vitro and in vivo against CML cells, including those with the T315I mutation. The mechanisms may involve inhibition of NF-κB and Bcr-Abl. We concluded that pristimerin could be a lead compound for further drug development to overcome imatinib resistance in CML patients.

Highlights

Chronic myelogenous leukemia (CML) is characterized by the chimeric tyrosine kinase Bcr-Abl
Pristimerin inhibits TNF-induced nuclear factor κB (NF-κB)-dependent reporter gene transcription We first examined whether pristimerin affected the tumor necrosis factor α (TNFα)-induced NF-κB-dependent reporter gene transcription
The luciferase activity detected was increased by TNFα (Figure 1B); but pristimerin inhibited the TNFα-induced NF-κB reporter activity in a dose- and time-dependent manner (Figure 1B and 1C)

Summary

Introduction

Chronic myelogenous leukemia (CML) is characterized by the chimeric tyrosine kinase Bcr-Abl. Bcr-AblT315I is the notorious point mutation that causes resistance to imatinib and the second generation tyrosine kinase inhibitors, leading to poor prognosis. CML blasts have constitutive p65 (RelA NF-κB) transcriptional activity, and NF-κB may be a potential target for molecular therapies in CML that may be effective against CML cells with Bcr-AblT315I. NF-κB may be a potential therapeutic target for the selective eradication of leukemia stem cells. CML blasts have constitutive p65 (RelA NF-κB) transcriptional activity, and NF-κB may be a potential target for molecular therapies in CML [16]. Pharmacological inhibition of NF-κB was effective in killing CML cells [17]

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Results

Conclusion