Relocalization of KIT D816V to Cell Surface After Dasatinib Treatment: Potential Clinical Implications Houcine Bougherara, 1 Sophie Georgin-Lavialle, 2,3 Gandhi Damaj, 4 Jean-Marie Launay, 5 Ludovic Lhermitte, 2,6 Christian Auclair, 1 Michel Arock, 1 Patrice Dubreuil, 7 Olivier Hermine, 1,2,8 Marie-Alix Poul 1,9 Abstract Systemic mastocytosis is a disease associated with a D816V mutation on KIT tyrosine kinase receptor KIT in mastocytes. We describe the treatment of blood samples from 28 patients with systemic mastocytosis with the tyrosine kinase inhibitor dasatinib, which enhances KIT D816V flow cytometry detection on mast cell– related cells, with a more pronounced increase on the severe forms of the disease. Background: Systemic mastocytosis (SM) is a heterogeneous disease that displays variable aggressivity. Adults with SM frequently have a D816V mutation in the tyrosine kinase (TK) receptor gene KIT. We previously reported that, in a Chinese hamster ovarian cell model expressing exogenous KIT variants, constitutive activating KIT mutations induced intracellular mislocalization of KIT reversed by inhibition of KIT TK activity. Hence, we hypothesized that inhibition of KIT kinase activity by the TK inhibitor dasatinib could be useful to increase KIT detection sensitivity in samples from patients with SM. Patients And Methods: We tested this hypothesis on a BaF/3 cell line modified to express either KIT wild-type (WT) or KIT D816V, on the human mastocytoma cell line HMC1.2, and among 28 patients with proven SM who did (n = 24) or did not (n = 4) carry the D816V KIT mutation and displayed various SM subtypes by using a simple flow cytometry assay to quantify KIT relocalization upon dasatinib treatment. Results: We confirm KIT cell surface increase upon dasatinib treatment on BaF/3 KIT D816V and HMC1.2 cell lines but not on BaF/3 KIT WT cell line. The analysis of bone marrow and peripheral blood samples of patients with SM showed KIT surface level increase for patients with the KIT D816V mutation but not for patients who had no KIT mutation. Interestingly, the extent of KIT level relocalization correlates with SM severity, with a higher relocalization for patients with aggressive forms compared with indolent forms. Conclusions: Overall, results of this study suggests that treating the peripheral blood sample with dasatinib of a patient with SM before analysis by flow cytometry could contribute to narrowing the SM diagnosis. Clinical Lymphoma, Myeloma & Leukemia, Vol. 13, No. 1, 62-9 © 2013 Elsevier Inc. All rights reserved. Keywords: Dasatinib, KIT cell surface detection, KIT mutation, Systemic mastocytosis, Tyrosine kinase inhibitor Drs Bougherara and Georgin-Lavialle contributed equally to this article. 1 CNRS UMR 8113, Laboratoire de Biologie et Pharmacologie Appliquée, École Normale Supérieure de Cachan, Cachan, France 2 CNRS UMR 8147, Hôpital Necker-Enfants malades, Université Paris Descartes, Paris, France 3 Centre de Référence des Mastocytoses, Faculté de Médecine et AP-HP Necker- Enfants Malades, Paris, France 4 Service des Maladies du Sang, Centre Hospitalier Universitaire Hôpital Sud, Amiens, France 5 Laboratoire de Biochimie et Biologie moléculaire, Hôpital Lariboisière, Université Paris VII, France 6 Laboratoire d’Hématologie, Université Paris Descartes, Paris Sorbonne Cité, Faculté de Médecine et assistance Publique Hôpitaux de Paris (AP-HP) Necker-Enfants Malades, Paris, France 7 Centre de Recherche en Cancérologie de Marseille, France, Institut National de la Sante et de la recherche Medicale U891, Laboratoire de Signalisation, Hématopoïèse et Mécanisme de l’Oncogenèse, Centre de référence des mastocytoses, Institut Paoli- Calmettes, Marseille, France 8 Service d’Hématologie Adultes, Université Paris Descartes, Paris Sorbonne Cité, Faculté de Médecine et AP-HP Necker-Enfants Malades, Paris France 9 Institut National de la Sante et de la recherche Medicale U896, CRLC Val d’Aurelle, Universités de Montpellier I et II, Montpellier, France Submitted: Aug 11, 2011; Revised: Aug 13, 2012; Accepted: Aug 23, 2012; Epub: Nov 3, 2012 Address for correspondence: Houcine Bougherara, PhD, Dèpartement d’Immunologie et d’Hématologie, Institut Cochin, 22 Rue Mechain, 75014 Paris, France. E-mail contact: houcine.bougherara@inserm.fr Original Study 62 Clinical Lymphoma, Myeloma & Leukemia February 2013 2152-2650/$ - see frontmatter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.clml.2012.08.004