Background: Valproic acid (VPA) is an HDAC inhibitor (HDACI) with an anticancer
activity, but is hepatotoxic. N-(2-hydroxyphenyl)-2-propylpentanamide (o-OH-VPA) is a VPA aryl
derivative designed in silico as a selective inhibitor of HDAC8 with biological properties against
HeLa, rhabdomyosarcoma and breast cancer cell cultures.
Objective: We studied the epigenetic mechanism of o-OH-VPA as an HDACI and evaluated
whether it was toxic to normal cells.
Methods: HeLa cells and primary human fibroblasts were used for this study as carcinogenic and
normal cells, respectively. Cell survival was evaluated by MTT assay, whereas viability and doubling
time were determined by the Trypan-blue method. HDAC activity was tested using the colorimetric
HDAC activity assay. The expression of p21 was analyzed by PCR and HDAC8 expression
was also evaluated by real-time PCR. Cell cycle and caspase-3 activity were analyzed by flow cytometry
and caspase-3 colorimetric assay, respectively.
Results: o-OH-VPA (IC50 = 0.1 mM) was fifty-eight times more effective than VPA (IC50 = 5.8
mM) to reduce HeLa cell survival. Furthermore, o-OH-VPA increased the doubling time of HeLa
cells by 33% with respect to the control. o-OH-VPA acted as HDACI in HeLa cells without affecting
the HDAC8 expression, arresting the cell cycle of HeLa cells in the G0/G1 phase due to the increase
in p21 expression with the inhibition of caspase-3 activity without exhibiting toxicity toward
Conclusion: Our results revealed that o-OH-VPA is an HDACI with a selective effect against
HeLa cells but without the known toxicity exerted by most pan-HDACIs on normal cells.