Suppression of p38-stress kinase sensitizes quiescent leukemic cells to anti-mitotic drugs by inducing proliferative responses in them

Abstract

Quiescent cells pose a formidable challenge in clinical management of leukemia, since they escape chemo-radiotherapy and become a source of post-therapy relapse. These cells may be refractory to various known growth-promoting signals, making it imperative to identify the biochemical signals necessary to coax them into mitosis. Using serum-starved cell lines as an experimental model of quiescent leukemic cells (QLCs), we demonstrate that a suppression of p38 stress kinase by pharmacological means forms a sufficient trigger to induce proliferative responses in the treated QLCs, even in the absence of any external growth-promoting stimulus. A robust expression of Ki67 and B23 was seen in treated cells, an effect clearly mediated through the activation of extra-cellular signal-regulated kinase (MEK/ERK) pathway. Commensurate with their proliferative status, the treated QLCs got sensitized to significantly low concentrations of anti-mitotic agents. Most importantly, primitive leukemic progenitors present in the mononuclear cells (MNCs) that were isolated from the peripheral blood of freshly diagnosed untreated acute myeloid leukemic (AML) patients got more efficiently killed by cytosine arabinoside (AraC) when the cells were pre-treated with a pharmacological inhibitor of p38. Our data strongly suggest that a suppression of p38 leads to the sensitization of QLCs to anti-mitotic drugs by triggering proliferative responses in them. This approach may have a potential clinical application.