1. ¹INSERM, Unité 837, Equipe 3, Institut de Recherche sur le Cancer de Lille, Lille, France
2. ²Institut Fédératif de Recherche 114, Université de Lille 2, Lille, France
3. ³Service des Maladies du Sang, Centre Hospitalier et Universitaire de Lille, Lille, France
4. ⁴Laboratoire d'Hématologie, Centre Hospitalier et Universitaire de Lille, Lille, France

Correspondence: Professor B Quesnel, Service des Maladies du Sang, Centre Hospitalier et Universitaire de Lille, Rue Polonovski, Lille 59037, France. E-mail: brunoquesnel@hotmail.com

Received 24 December 2007; Accepted 3 January 2008; Published online 24 January 2008.

Abstract

Patients with chronic myeloid leukemia who become resistant to the Abl kinase inhibitor imatinib can be treated with dasatinib. This sequential treatment can lead to BCR-ABL mutations conferring broad resistance to kinase inhibitors. To model the evolution of resistance, we exposed the mouse DA1-3b BCR-ABL⁺ leukemic cell line to imatinib for several months, and obtained resistant cells carrying the E255K mutation. We then exposed these cells to dasatinib, and obtained dasatinib-resistant cells with composite E255K+T315I mutations. Subcloning isolated a minor clone also carrying V299L. In co-culture, mutated cells were able to spread resistance to non-mutated cells through overexpression of interleukin 3, activation of MEK/ERK and JAK2/STAT5 pathways, and downregulation of Bim. Even the presence of less than 10% of mutated cells was sufficient to protect non-mutated cells. Blocking JAK2 and MEK1/2 inhibited the protective effect of co-culture. Mutated cells were also sensitive to JAK2 inhibition, but blocking MEK1/2 alone, or in association with kinase inhibitors, had little effect. These data indicate that sequential Abl kinase inhibitor therapy can generate sub-populations of mutated cells, which may coexist with non-mutated cells and protect them through a paracrine mechanism. Targeting JAK2 could eliminate both populations.