The selective protein kinase C beta inhibitor enzastaurin induces apoptosis in cutaneous T-cell lymphoma cell lines through the AKT pathway.
Enzastaurin displays pro-apoptotic properties against a spectrum of malignancies and is currently being investigated in clinical trials. We have investigated the effects of enzastaurin on the viability of the cutaneous T-cell lymphoma cell lines HuT-78 and HH by using 3-(4,5-dimethylthiazol-2-yl)-5(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay, cell cycle analysis, propidium iodide and annexin-V staining, and caspase-3-mediated proteolytic activation. Enzastaurin-treatment decreased cell viability, increased annexin V-FITC-positive cells, and increased the proportion of sub-G1 populations in both cell lines that was not reversed by the T-cell growth stimulating cytokines IL-2, IL-7, IL-15. Enzastaurin-induced cell death involved caspase-3-activated cleavage of poly(ADP-ribose) polymerase that was inhibited by the pan-caspase inhibitor ZVAD-fmk, whereas the increase in sub-G1 population was only partially inhibited by ZVAD-fmk. Furthermore, enzastaurin downregulated AKT activity and its downstream effectors GSK3beta and ribosomal protein S6. The phosphatidylinositol 3-kinase (PI3K)/AKT pathway has been implicated in the growth and survival of hematologic malignancies and inhibition of this pathway is considered as a therapeutic target. Protein kinase C activation contributes to PI3K/AKT activation, but it is unknown how enzastaurin may interfere with signaling through this pathway. These results demonstrate that enzastaurin, at clinically achievable concentrations, induces apoptosis and affects AKT signaling, and provide a rationale for further in vivo studies addressing the therapeutic efficacy in cutaneous T-cell lymphoma patients.
Querfeld
Christiane
C
Department of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA. c-querfeld@northwestern.edu
Rizvi
Mujahid A
MA
Kuzel
Timothy M
TM
Guitart
Joan
J
Rademaker
Alfred
A
Sabharwal
Simran S
SS
Krett
Nancy L
NL
Rosen
Steven T
ST
D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D020169:Caspases / Q000032:analysis / Q000502:physiology; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D016410:Lymphoma, T-Cell, Cutaneous / Q000201:enzymology / Q000473:pathology*; D010766:Phosphorylation / Q000187:drug effects; D011065:Poly(ADP-ribose) Polymerases / Q000032:analysis / Q000502:physiology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors*; D064546:Protein Kinase C beta; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000502:physiology*; D038601:Ribosomal Protein S6 / Q000032:analysis; D015398:Signal Transduction / Q000502:physiology*; D012878:Skin Neoplasms / Q000201:enzymology / Q000473:pathology*
D004791:Enzyme Inhibitors; D007211:Indoles; D038601:Ribosomal Protein S6; D011065:Poly(ADP-ribose) Polymerases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D051057:Proto-Oncogene Proteins c-akt; D011493:Protein Kinase C; D064546:Protein Kinase C beta; D038362:Glycogen Synthase Kinase 3; D020169:Caspases; C504878:enzastaurin