Targeting CHK1 pathway to induce cytotoxic response to histone deactylase inhibitors and evaluating the synergistic effects of CHK1 and HDAC inhibitors in human soft tissue sarcoma cell lines and primary tumor xenografts.

Abstract

10049 Background: Histone deacetylase inhibitors (HDACis) are promising anticancer drugs; however, the molecular mechanisms leading to cell death by HDACis have not been well understood and no clear mechanism of resistance has been elucidated to explain limited efficacy of HDACis in clinical trials. Methods: In vitro treatment of cell lines with HDACi and Chk1 inhibitors, time course experiments, protein analysis by western blot, and ex vivo evaluation of sarcoma xenografts were performed. Results: In HDACi- treated sarcoma cell lines, Chk1 downregulation was functional as indicated by decreased inhibitory phosphorylation of cdc25c and its downstream target cdc2. Chk1 downregulation occurred upon HDACi treatment and preceded apoptosis, as assessed by poly(ADP-ribose) polymerase cleavage. Pharmacological inhibition of Chk1 showed strong synergistic effect with LBH589 in sarcoma cells in vitro. Serial sampling of mouse xenografts of these sarcoma cell lines using FNAB indicates that downregulation of Chk1 upon HDACi treatment occurs in vivo and can be used to assess and predict efficacy of treatment. Conclusions: Taken together these results suggest that Chk1 could be an early pharmacodynamic marker to assess HDACi efficacy in clinical samples. A combination of drugs targeting HDAC and Chk1 enzymes may be clinically useful for sarcoma treatment. We show that expression of checkpoint kinase 1 (Chk1), which has a major role in G2 cell cycle checkpoint regulation, was markedly reduced in multiple sarcoma cell lines both in vitro and in vivo as well as in human sarcoma samples tested ex vivo when cells were treated with the HDACi LBH589, scriptaid, valproic acid, or apicidin. No significant financial relationships to disclose.