Comparison between HuT78 parental and romidpepsin-selected cell lines

Gene expression values were determined for HuT78 parental cells and cells selected with romidpesin in the presence of P-glycoprotein inhibitors. HuT78 DpVp35 cells are maintained in 35 ng/ml romidepsin with 2.5 µg/ml verapamil and HuT78 DpP100 cells are maintained in 100 ng/ml romidepsin with 1 µM valspodar To identify molecular determinants of histone deacetylase inhibitor (HDI) resistance, we selected HuT78 cutaneous T-cell lymphoma (CTCL) cells with romidepsin in the presence of P-glycoprotein (Pgp) inhibitors to prevent transporter upregulation. Resistant sublines were 250- to 385-fold resistant to romidepsin and were resistant to apoptosis induced by apicidin, entinostat, panobinostat, belinostat and vorinostat. A custom Taqman array identified increased insulin receptor (INSR) gene expression; immunoblot analysis confirmed increased expression and a 4- to 8-fold increase in mitogen activated protein kinase (MAPK) kinase (MEK) phosphorylation in resistant cells compared to parental cells. Resistant cells were exquisitely sensitive to MEK inhibitors and apoptosis correlated with restoration of proapoptotic Bim. Romidepsin combined with MEK inhibitors yielded greater apoptosis in cells expressing mutant KRAS compared to romidepsin treatment alone. Gene expression analysis of samples obtained from patients with CTCL enrolled on the NCI1312 Phase II study of romidepsin in T-cell lymphoma suggested perturbation of the MAPK pathway by romidepsin. Immunohistochemical analysis of Bim expression demonstrated decreased expression in some skin biopsies at disease progression. These findings implicate increased activation of MEK and decreased Bim expression as a resistance mechanism to HDIs, supporting combination of romidepsin with MEK inhibitors in clinical trials. Gene expression in resistant lines was compared to parental lines