1. Academic Validation
  2. A novel histone deacetylase 8 (HDAC8)-specific inhibitor PCI-34051 induces apoptosis in T-cell lymphomas

A novel histone deacetylase 8 (HDAC8)-specific inhibitor PCI-34051 induces apoptosis in T-cell lymphomas

  • Leukemia. 2008 May;22(5):1026-34. doi: 10.1038/leu.2008.9.
S Balasubramanian 1 J Ramos W Luo M Sirisawad E Verner J J Buggy
Affiliations

Affiliation

  • 1 Department of Cancer Biology, Pharmacyclics Inc., Sunnyvale, CA 94085, USA. sriram@pcyc.com
Abstract

We have developed a potent, histone deacetylase 8 (HDAC8)-specific inhibitor PCI-34051 with >200-fold selectivity over the other HDAC isoforms. PCI-34051 induces caspase-dependent Apoptosis in cell lines derived from T-cell lymphomas or leukemias, but not in other hematopoietic or solid tumor lines. Unlike broad-spectrum HDAC inhibitors, PCI-34051 does not cause detectable histone or tubulin acetylation. Cells defective in T-cell receptor signaling were still sensitive to PCI-34051-induced Apoptosis, whereas a Phospholipase C-gamma1 (PLCgamma1)-defective line was resistant. Jurkat cells showed a dose-dependent decrease in PCI-34051-induced Apoptosis upon treatment with a PLC inhibitor U73122, but not with an inactive analog. We found that rapid intracellular calcium mobilization from endoplasmic reticulum (ER) and later cytochrome c release from mitochondria are essential for the apoptotic mechanism. The rapid CA(2+) flux was dependent on PCI-34051 concentration, and was blocked by the PLC inhibitor U73122. Further, Apoptosis was blocked by CA(2+) Chelators (BAPTA) and enhanced by CA(2+) effectors (thapsigargin), supporting this model. These studies show that HDAC8-selective inhibitors have a unique mechanism of action involving PLCgamma1 activation and calcium-induced Apoptosis, and could offer benefits including a greater therapeutic index for treating T-cell malignancies.

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