I. Judson

Effects of the histone deacetylase inhibitor (HDACI) LAQ824 on histone acetylation, Hsp70 and c-Raf in peripheral blood lymphocytes from patients with advanced solid tumours enrolled in a phase I clinical trial.

3023 Background: Several HDACIs, including LAQ824, are now undergoing clinical evaluation. Preclinical data indicate that as well as promoting histone acetylation, these agents can also affect the activity of the molecular chaperone Hsp90 resulting in increased expression of Hsp70 and degradation of key client proteins such as c-Raf. Hsp90 represents an important target for novel therapeutics (Fuino et al. Mol. Cancer Ther. 2003). The purpose of this study was to determine whether an HDACI-mediated impact on Hsp90 could be detected clinically. The assessment was performed on peripheral blood lymphocytes (PBL) taken from patients participating in a Phase I trial of LAQ824.nnnMETHODSnA dose-escalating, open-label, Phase I trial was undertaken, with LAQ824 being administered by i.v. infusion on days 1-3 q21 days. PBL were collected at various timepoints on days 1, 3, 4, 5 and 8, lysed and assayed for acetylated histone H3 and H4, Hsp70 and c-Raf expression using Western blotting and, in some cases, ELISA. Histone extracts and whole cell lysates from two human colorectal tumour cell lines (HCT116 and HT29) either untreated or treated with LAQ824 were analysed as controls.nnnRESULTSnA consistent increase in acetylation of histones H3 and H4 in PBL lysates on days of treatment with LAQ824 was observed from doses of 36mg/m2 (50% MTD) and maintained for at least 24 hours. Additionally, in selected samples from patients treated at 36 mg/m2 and above, an effect on Hsp90 activity was demonstrated with increased expression of Hsp70 and decreased c-Raf levels over a similar time course. These results were consistent with those obtained from LAQ824 treated HCT116 and HT29 cells.nnnCONCLUSIONSnThese observed events in PBL suggest that as well as increasing histone acetylation, HDAC inhibition by LAQ824 does inhibit Hsp90 activity in patients at doses that are generally well-tolerated. Additional evaluation of these pharmacodynamic markers in tumour biopsies is ongoing. The biological importance of these non-histone mediated effects requires further study. [Table: see text].