Homoharringtonine reduced Mcl-1 expression and induced apoptosis in chronic lymphocytic leukemia.
Homoharringtonine (HHT) is a plant alkaloid that inhibits the elongation phase of translation that is currently in clinical trials. Because the intrinsically short-lived antiapoptotic protein myeloid cell leukemia-1 (Mcl-1) has been reported to support the survival of chronic lymphocytic leukemia (CLL) cells, we hypothesized that inhibition of protein synthesis by HHT would decrease Mcl-1 expression and induce apoptosis in CLL. In primary CLL cells, HHT induced significant apoptosis independent of the prognostic characteristics of the patients. This was associated with inhibition of translation and decreased Mcl-1 levels in CLL cells. Mcl-1 reduction was evident as early as 2 hours and continued to decrease in the next 6-8 hours, whereas cell death started in 2 hours and continued to increase for 24 hours. Reduction of the Mcl-1 level was due to translation inhibition and proteasome degradation rather than to transcription inhibition or caspase cleavage. HHT and the transcription inhibitor SNS-032 induced synergistic cell killing. Although stromal cells induced Mcl-1 expression and protected CLL cells from the toxicity of fludarabine, this induction was reversed by HHT, which overcame stromal cell-mediated protection. Thus, these results provide a rationale for clinical development of HHT in CLL as single agent or in combinations.
Chen
Rong
R
Department of Experimental Therapeutics, The University of Texas M D Anderson Cancer Center, Houston, TX 77030, USA.
Guo
Lei
L
Chen
Yuling
Y
Jiang
Yingjun
Y
Wierda
William G
WG
Plunkett
William
W
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D049109:Cell Proliferation / Q000187:drug effects; D004357:Drug Synergism; D004359:Drug Therapy, Combination; D006248:Harringtonines / Q000494:pharmacology*; D000077863:Homoharringtonine; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy / Q000378:metabolism / Q000473:pathology*; D008214:Lymphocytes / Q000187:drug effects; D008875:Middle Aged; D051336:Mitochondrial Membranes / Q000187:drug effects; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D010080:Oxazoles / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017154:Stromal Cells / Q000187:drug effects; D013844:Thiazoles / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D000972:Antineoplastic Agents, Phytogenic; D006248:Harringtonines; D064549:Myeloid Cell Leukemia Sequence 1 Protein; C484864:N-(5-(((5-(1,1-dimethylethyl)-2-oxazolyl)methyl)thio)-2-thiazolyl)-4-piperidinecarboxamide; D010080:Oxazoles; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D013844:Thiazoles; D000077863:Homoharringtonine