1. ¹Department of Dermatology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
2. ²Department of Medicine, Division of Hematology/Oncology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
3. ³Department of Preventive Medicine, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
4. ⁴Robert H. Lurie Comprehensive Cancer Center, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA

Correspondence: Dr Christiane Querfeld, Robert H. Lurie Comprehensive Cancer Center, 3-250, 303 E Superior Avenue, Chicago, Illinois 60611, USA. E-mail: c-querfeld@northwestern.edu

Received 8 November 2005; Revised 10 February 2006; Accepted 9 March 2006; Published online 27 April 2006.

Abstract

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 GSK3 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.