Phenolhexyl Isothiocyanate, a New Histone Deacetylase Inhibitor, Can Prevent Tumor Formation and Inhibit Leukemia Cell Growth In Vivo.

We have demonstrated that phenolhexyl isothiocyanate (PHI) induces growth arrest and apoptosis in leukemia cells HL-60 through inhibition of the activity of histone deacetylases (HDAC), the enhancement of histone acetylation and activation of p21. In this study, we examined the effects of PHI on the growth of HL-60 leukemic xenograft in immunodeficient mice. The PHI was given to the mice by gavage. The maximum tolerated dose by the mice was determined following standard design. To determine the in vivo effect of PHI on leukemia growth, a sub-MTD dose was given to the control and the treatment groups with 17 mice in each group after injection of 1.0 x 10e6 HL-60 cells per mouse. There was a significant reduction in the incidence of tumor formation (94.1% control group vs 58.5% PHI group, p=0.004). In addition, there was also a significant difference in the tumor size between the two groups. Determined at autopsy, the mean weight of control tumors was 0.8 g vs. the tumors of the experimental group 0.35g, revealing a significant reduction of 44.4% (P<0.03). There were no detectable toxicity as evaluated by body and organ weight, and necropsy examination. The histology of the tumor showed increased apoptotic cell death. Apoptosis in the tumors was further confirmed by the cleavage of poly ADP-ribose polymerase (PARP), the target of proteolysis of caspases that execute apoptosis with Western blot analyses. The results suggest that PHI can prevent tumor formation and inhibit leukemia cell growth in vivo without significant toxicity that is routinely associated with conventional chemotherapeutic agents.