François-Xavier Mahon

Publications of François-Xavier Mahon

• Imatinib triggers mesenchymal-like conversion of CML cells associated with increased aggressiveness.

  Authors: Alexandre Puissant, Maeva Dufies, Nina Fenouille, Issam Ben Sahra, Arnaud Jacquel, Guillaume Robert, Thomas Cluzeau, Marcel Deckert, Mélanie Tichet, Yann Chéli, Jill-Patrice Cassuto, Sophie Raynaud, Laurence Legros, Jean-Max Pasquet, François-Xavier Mahon, Frédéric Luciano, Patrick Auberger

  Journal of molecular cell biology. 03/2012;

  Chronic myelogenous leukemia (CML) is a cytogenetic disorder resulting from the expression of p210BCR-ABL. Imatinib, an inhibitor of BCR-ABL, has emerged as the leading compound to treat CMLChronic myelogenous leukemia (CML) is a cytogenetic disorder resulting from the expression of p210BCR-ABL. Imatinib, an inhibitor of BCR-ABL, has emerged as the leading compound to treat CML patients. Despite encouraging clinical results, resistance to imatinib represents a major drawback for therapy, as a substantial proportion of patients are refractory to this treatment. Recent publications have described the existence of a small cancer cell population with the potential to exhibit the phenotypic switch responsible for chemoresistance. To investigate the existence of such a chemoresistant cellular subpopulation in CML, we used a two-step approach of pulse and continuous selection by imatinib in different CML cell lines that allowed the emergence of a subpopulation of adherent cells (IM-R Adh) displaying an epithelial-mesenchymal transition (EMT)-like phenotype. Overexpression of several EMT markers was observed in this CML subpopulation, as well as in CD34(+) CML primary cells from patients who responded poorly to imatinib treatment. In response to imatinib, this CD44(high)/CD24(low) IM-R Adh subpopulation exhibited increased adhesion, transmigration and invasion in vitro and in vivo through specific overexpression of the αVβ3 receptor. FAK/Akt pathway activation following integrin β3 (ITGβ3) engagement mediated the migration and invasion of IM-R Adh cells, whereas persistent activation of ERK counteracted BCR-ABL inhibition by imatinib, promoting cell adhesion-mediated resistance.

• Curing Chronic Myeloid Leukemia.

  Authors: Delphine Rea, Philippe Rousselot, Joelle Guilhot, François Guilhot, François-Xavier Mahon

  Current hematologic malignancy reports. 03/2012;

  The use of tyrosine kinase inhibitors (TKIs) targeted against the BCR-ABL1 oncoprotein has proven remarkably successful in chronic myeloid leukemia (CML) and long-term survival has become a reality.The use of tyrosine kinase inhibitors (TKIs) targeted against the BCR-ABL1 oncoprotein has proven remarkably successful in chronic myeloid leukemia (CML) and long-term survival has become a reality. Despite this outstanding progress, detection of minimal residual disease precludes therapy termination in most TKI-receiving patients. CML has thus turned into a chronic illness, raising concerns about long-term safety, medication adherence, and health care costs. Although treatment cessation may be feasible in few selected patients achieving deep molecular responses, a definitive cure remains elusive owing to the discovery that TKIs spare quiescent leukemic stem cells (LSC). Understanding mechanisms underlying LSC behavior in TKI-treated patients may provide important clues to develop an array of strategies that ensure the complete destruction of LSC reservoirs and thereby offer CML patients a definitive cure.

• ABT-737 increases tyrosine kinase inhibitor-induced apoptosis in chronic myeloid leukemia cells through XIAP downregulation and sensitizes CD34(+) CD38(-) population to imatinib.

  Authors: Kelly Airiau, François-Xavier Mahon, Marina Josselin, Marie Jeanneteau, Beatrice Turcq, Francis Belloc

  Experimental hematology. 01/2012;

  Chronic myeloid leukemia (CML) tumorigenicity is driven by the oncogenic BCR-ABL tyrosine kinase. Specific tyrosine kinase inhibitors (TKI) have been designed and are now used for the treatment ofChronic myeloid leukemia (CML) tumorigenicity is driven by the oncogenic BCR-ABL tyrosine kinase. Specific tyrosine kinase inhibitors (TKI) have been designed and are now used for the treatment of CML. These TKI induce apoptosis in leukemic cells in a BIM-dependent mechanism. We hypothesized that an increase in BIM activity could sensitize CML cells to TKI. We blocked the anti-apoptotic proteins of the Bcl-2 family by using ABT-737, a Bcl-2 and Bcl-XL inhibitor. ABT-737 modified Bcl-2 protein interactions toward a pro-apoptotic phenotype. Its combination with TKI resulted in a strong synergism in CML cell lines. The association also induced a large decrease in X-linked inhibitor of apoptosis (XIAP), followed by caspase-3 activation. This XIAP decrease was due to post-translational events. The mitochondrial serine protease HtrA2/Omi was identified as being responsible for this off-target effect. Then, ABT-737 and TKI cooperate at several levels to induce apoptosis of CML cells lines, and the benefit of this association was also observed in CML hematopoietic progenitors. Interestingly, a lethal effect was also observed in the more immature CD34(+)CD38(-) TKI-insensitive population. Combination therapy might by an interesting strategy for the treatment of CML patients.

• Quantitative phosphoproteomics revealed interplay between Syk and Lyn in the resistance to nilotinib in chronic myeloid leukemia cells.

  Authors: Romain Gioia, Cédric Leroy, Claire Drullion, Valérie Lagarde, Gabriel Etienne, Stéphanie Dulucq, Eric Lippert, Serge Roche, François-Xavier Mahon, Jean-Max Pasquet

  Blood. 07/2011; 118(8):2211-21.

  In this study, we have addressed how Lyn kinase signaling mediates nilotinib-resistance by quantitative phospho-proteomics using Stable Isotope Labeling with Amino acid in Cell culture. We have foundIn this study, we have addressed how Lyn kinase signaling mediates nilotinib-resistance by quantitative phospho-proteomics using Stable Isotope Labeling with Amino acid in Cell culture. We have found an increased tyrosine phosphorylation of 2 additional tyrosine kinases in nilotinib-resistant cells: the spleen tyrosine kinase Syk and the UFO family receptor tyrosine kinase Axl. This increased tyrosine phosphorylation involved an interaction of these tyrosine kinases with Lyn. Inhibition of Syk by the inhibitors R406 or BAY 61-3606 or by RNA interference restored the capacity of nilotinib to inhibit cell proliferation. Conversely, coexpression of Lyn and Syk were required to fully induce resistance to nilotinib in drug-sensitive cells. Surprisingly, the knockdown of Syk also strongly decreased tyrosine phosphorylation of Lyn and Axl, thus uncovering interplay between Syk and Lyn. We have shown the involvement of the adaptor protein CDCP-1 in resistance to nilotinib. Interestingly, the expression of Axl and CDCP1 were found increased both in a nilotinib-resistant cell line and in nilotinib-resistant CML patients. We conclude that an oncogenic signaling mediated by Lyn and Syk can bypass the need of Bcr-Abl in CML cells. Thus, targeting these kinases may be of therapeutic value to override imatinib or nilotinib resistance in CML.

• Identification of a transforming MYB-GATA1 fusion gene in acute basophilic leukemia: a new entity in male infants.

  Authors: Cathy Quelen, Eric Lippert, Stephanie Struski, Cécile Demur, Gwendoline Soler, Nais Prade, Eric Delabesse, Cyril Broccardo, Nicole Dastugue, François-Xavier Mahon, Pierre Brousset

  Blood. 05/2011; 117(21):5719-22.

  Acute basophilic leukemia (ABL) is a rare subtype of acute leukemia with clinical features and symptoms related to hyperhistaminemia because of excessive growth of basophils. No known recurrentAcute basophilic leukemia (ABL) is a rare subtype of acute leukemia with clinical features and symptoms related to hyperhistaminemia because of excessive growth of basophils. No known recurrent cytogenetic abnormality is associated with this leukemia. Rare cases of t(X;6)(p11;q23) translocation have been described but these were sporadic. We report here 4 cases of ABL with a t(X;6)(p11;q23) translocation occurring in male infants. Because of its location on chromosome 6q23, MYB was a good candidate gene. Our molecular investigations, based on fluorescence in situ hybridization and rapid amplification of cDNA ends, revealed that the translocation generated a MYB-GATA1 fusion gene. Expression of MYB-GATA1 in mouse lineage-negative cells committed them to the granulocyte lineage and blocked at an early stage of differentiation. Taken together, these results establish, for the first time, a link between a recurrent chromosomal translocation and the development of this particular subtype of infant leukemia.

• Multicenter independent assessment of outcomes in chronic myeloid leukemia patients treated with imatinib.

  Authors: Carlo Gambacorti-Passerini, Laura Antolini, François-Xavier Mahon, Francois Guilhot, Michael Deininger, Carmen Fava, Arnon Nagler, Chiara Maria Della Casa, Enrica Morra, Elisabetta Abruzzese [......] Pilar Giraldo, Sarit Assouline, Muheez A Durosinmi, Onno Leeksma, Enrico Maria Pogliani, Miriam Puttini, Eunjung Jang, Josy Reiffers, Maria Grazia Valsecchi, Dong-Wook Kim

  Journal of the National Cancer Institute. 03/2011; 103(7):553-61.

  Imatinib slows development of chronic myeloid leukemia (CML). However, available information on morbidity and mortality is largely based on sponsored trials, whereas independent long-term fieldImatinib slows development of chronic myeloid leukemia (CML). However, available information on morbidity and mortality is largely based on sponsored trials, whereas independent long-term field studies are lacking. Consecutive CML patients who started imatinib treatment before 2005 and who were in complete cytogenetic remission (CCyR) after 2 years (± 3 months) were eligible for enrollment in the independent multicenter Imatinib Long-Term (Side) Effects (ILTE) study. Incidence of the first serious and nonserious adverse events and loss of CCyR were estimated according to the Kaplan-Meier method and compared with the standard log-rank test. Attainment of negative Philadelphia chromosome hematopoiesis was assessed with cytogenetics and quantitative polymerase chain reaction. Cumulative incidence of death related or unrelated to CML progression was estimated, accounting for competing risks, according to the Kalbleisch-Prentice method. Standardized incidence ratios were calculated based on population rates specific for sex and age classes. Confidence intervals were calculated by the exact method based on the χ(2) distribution. All statistical tests were two-sided. A total of 832 patients who were treated for a median of 5.8 years were enrolled. There were 139 recorded serious adverse events, of which 19.4% were imatinib-related. A total of 830 nonserious adverse events were observed in 53% of patients; 560 (68%) were imatinib-related. The most frequent were muscle cramps, asthenia, edema, skin fragility, diarrhea, tendon, or ligament lesions. Nineteen patients (2.3%) discontinued imatinib because of drug-related toxic effects. Forty-five patients lost CCyR, at a rate of 1.4 per 100 person-years. Durable (>1 year) negative Philadelphia chromosome hematopoiesis was attained by 179 patients. Twenty deaths were observed, with a 4.8% mortality incidence rate (standardized incidence ratio = 0.7; 95% confidence interval = 0.40 to 1.10, P = .08), with only six (30%) associated with CML progression. In this study, CML-related deaths were uncommon in CML patients who were in CCyR 2 years after starting imatinib, and survival was not statistically significantly different from that of the general population.

• Deregulation of TWIST-1 in the CD34+ compartment represents a novel prognostic factor in chronic myeloid leukemia.

  Authors: Erika Cosset, Ghassan Hamdan, Sandrine Jeanpierre, Thibault Voeltzel, Karen Sagorny, Sandrine Hayette, François-Xavier Mahon, Charles Dumontet, Alain Puisieux, Franck E Nicolini, Véronique Maguer-Satta

  Blood. 02/2011; 117(5):1673-6.

  The mechanisms of resistance to tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML) often remain obscure. Analysis of patient samples during disease progression revealed theThe mechanisms of resistance to tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML) often remain obscure. Analysis of patient samples during disease progression revealed the up-regulation of the oncogene TWIST-1, also measured in primary samples from TKI-resistant patients. Moreover, we found that TWIST-1 was overexpressed in CML diagnostic samples of patients who later developed cytogenetic resistance to imatinib, even those without any detectable resistance mechanism. We confirmed the up-regulation of TWIST-1 at both RNA and protein levels in imatinib-resistant cell lines, irrespective of any other resistance mechanism. Analysis with specific small interfering RNA suggested TWIST-1 involvement in the resistance phenotype. Finally, the kinetics of TWIST-1 expression during the individual medical histories of CML patients indicated that TWIST-1 expression is down-regulated by TKIs and up-regulated with TKI resistance. We hypothesize that the overexpression of the TWIST-1 oncogene represents a novel key prognostic factor potentially useful for optimizing CML management in the TKI era.

• α-defensin 1-3 and α-defensin 4 as predictive markers of imatinib resistance and relapse in CML patients.

  Authors: Gabriel Etienne, Maryse Dupouy, Patricia Costaglioli, Claudine Chollet, Valérie Lagarde, Jean-Max Pasquet, Josy Reiffers, Bertrand Garbay, François-Xavier Mahon, Béatrice Turcq

  Disease markers. 01/2011; 30(5):221-7.

  Imatinib mesylate is a tyrosine kinase inhibitor used as first line treatment in chronic myeloid leukaemia. Despite a remarkable effectiveness, treatment failure cases have been reported in 20Imatinib mesylate is a tyrosine kinase inhibitor used as first line treatment in chronic myeloid leukaemia. Despite a remarkable effectiveness, treatment failure cases have been reported in 20 percent of CML patients. The identification of biomarkers which can predict the response to imatinib is our point of interest. Gene expression profiling microarray was carried out on secondary imatinib resistant patients. Longitudinal studies were performed on imatinib treated responder/resistant patients. Then, Q-RT/PCR studies were realized on patients prior imatinib initiation. For imatinib responder patients, we observed a strong and lasting decrease of α-defensin 1-3 and α-defensin 4 expression. For relapse patients, we observed a dramatic increase of α-defensin 1-3 and α-defensin 4 expression before BCR-ABL transcript increase. Moreover, before imatinib initiation, α-defensin 1-3 and α-defensin 4 expression was significantly lower in the resistant group than in the responder group. The variation of expression of α-defensin 1-3 and α-defensin 4 in peripheral blood is associated with imatinib resistance and may reflect an adequate immune control of the disease. Monitoring of α-defensin 1-3 and α-defensin 4 could be helpful to predict the patients who are not going to respond to the treatment.

• Persistent activation of the Fyn/ERK kinase signaling axis mediates imatinib resistance in chronic myelogenous leukemia cells through upregulation of intracellular SPARC.

  Authors: Nina Fenouille, Alexandre Puissant, Maeva Dufies, Guillaume Robert, Arnaud Jacquel, Mickaël Ohanna, Marcel Deckert, Jean-Max Pasquet, François-Xavier Mahon, Jill-Patrice Cassuto, Sophie Raynaud, Sophie Tartare-Deckert, Patrick Auberger

  Cancer research. 12/2010; 70(23):9659-70.

  SPARC is an extracellular matrix protein that exerts pleiotropic effects on extracellular matrix organization, growth factor availability, cell adhesion, differentiation, and immunity in cancer.SPARC is an extracellular matrix protein that exerts pleiotropic effects on extracellular matrix organization, growth factor availability, cell adhesion, differentiation, and immunity in cancer. Chronic myelogenous leukemia (CML) cells resistant to the BCR-ABL inhibitor imatinib (IM-R cells) were found to overexpress SPARC mRNA. In this study, we show that imatinib triggers SPARC accumulation in a variety of tyrosine kinase inhibitor (TKI)-resistant CML cell lines. SPARC silencing in IM-R cells restored imatinib sensitivity, whereas enforced SPARC expression in imatinib-sensitive cells promoted viability as well as protection against imatinib-mediated apoptosis. Notably, we found that the protective effect of SPARC required intracellular retention inside cells. Accordingly, SPARC was not secreted into the culture medium of IM-R cells. Increased SPARC expression was intimately linked to persistent activation of the Fyn/ERK kinase signaling axis. Pharmacologic inhibition of this pathway or siRNA-mediated knockdown of Fyn kinase resensitized IM-R cells to imatinib. In support of our findings, increased levels of SPARC mRNA were documented in blood cells from CML patients after 1 year of imatinib therapy compared with initial diagnosis. Taken together, our results highlight an important role for the Fyn/ERK signaling pathway in imatinib-resistant cells that is driven by accumulation of intracellular SPARC.

• The addition of daunorubicin to imatinib mesylate in combination with cytarabine improves the response rate and the survival of patients with myeloid blast crisis chronic myelogenous leukemia (AFR01 study).

  Authors: Bénédicte Deau, Franck E Nicolini, Joelle Guilhot, Françoise Huguet, Agnès Guerci, Laurence Legros, Cécile Pautas, Christian Berthou, Denis Guyotat, Pascale Cony-Makhoul, Martine Gardembas, Mauricette Michallet, Sandrine Hayette, Jean Michel Cayuela, Isabelle Radford Weiss, Delphine Réa, Sylvie Castaigne, François-Xavier Mahon, François Guilhot, Philippe Rousselot

  Leukemia research. 12/2010; 35(6):777-82.

  The median survival of patients with chronic myelogenous leukemia in myeloid blast crisis (MBC-CML) is poor even for patients treated with tyrosine kinase inhibitors (TKIs). We conducted aThe median survival of patients with chronic myelogenous leukemia in myeloid blast crisis (MBC-CML) is poor even for patients treated with tyrosine kinase inhibitors (TKIs). We conducted a dose-escalating study of daunorubicin combined to fixed doses of IM (imatinib mesylate, 600 mg/d) and cytarabine (200 mg/d for 7 days), followed by hematopoietic stem cell transplantation or maintenance therapy with single-agent IM in patients with MBC-CML at onset or after failure of therapy excluding TKIs. Thirty-six patients were evaluated. Median follow-up is 6.1 years. Daunorubicin was escaladed up to 45 mg/m(2)/d 3 days. Twenty eight patients (77.7%) had hematologic response including 20 patients (55.5%) in complete hematologic response (CHR). Patients who received daunorubicin at 30-45 mg/m(2)/d had higher CHR rates compared to other patients. Median overall survival was 16 months. Overall survival in patients with hematological response was 35.4 months. Better results were observed in patients diagnosed with MBC-CML at onset. The combination of IM with a standard "3+7" regiment was well tolerated and provided a high response rate. More than 55% of the patients achieved CHR and hematopoietic stem cell transplantation (SCT) was feasible in half of the cases. This trial was registered at www.clinicaltrials.gov as # NCT00219765.

• Imatinib plus peginterferon alfa-2a in chronic myeloid leukemia.

  Authors: Claude Preudhomme, Joëlle Guilhot, Franck Emmanuel Nicolini, Agnès Guerci-Bresler, Françoise Rigal-Huguet, Frederic Maloisel, Valérie Coiteux, Martine Gardembas, Christian Berthou, Anne Vekhoff [......] Alain Delmer, Philippe Rousselot, Laurence Legros, Marc Berger, Selim Corm, Gabriel Etienne, Catherine Roche-Lestienne, Virginie Eclache, François-Xavier Mahon, François Guilhot

  The New England journal of medicine. 12/2010; 363(26):2511-21.

  Imatinib (400 mg daily) is considered the best initial therapy for patients with newly diagnosed chronic myeloid leukemia (CML) in the chronic phase. However, only a minority of patients treated withImatinib (400 mg daily) is considered the best initial therapy for patients with newly diagnosed chronic myeloid leukemia (CML) in the chronic phase. However, only a minority of patients treated with imatinib have a complete molecular remission. We randomly assigned 636 patients with untreated chronic-phase CML to receive imatinib alone at a dose of 400 mg daily, imatinib (400 mg daily) plus cytarabine (20 mg per square meter of body-surface area per day on days 15 through 28 of each 28-day cycle) or pegylated interferon (peginterferon) alfa-2a (90 μg weekly), or imatinib alone at a dose of 600 mg daily. Molecular and cytogenetic responses, time to treatment failure, overall and event-free survival, and adverse events were assessed. An analysis of molecular response at 12 months was planned. A superior molecular response was defined as a decrease in the ratio of transcripts of the tyrosine kinase gene BCR-ABL to transcripts of ABL of 0.01% or less, corresponding to a reduction of 4 log(10) units or more from the baseline level, as assessed by means of a real-time quantitative polymerase-chain-reaction assay. At 12 months, the rates of cytogenetic response were similar among the four groups. The rate of a superior molecular response was significantly higher among patients receiving imatinib and peginterferon alfa-2a (30%) than among patients receiving 400 mg of imatinib alone (14%) (P=0.001). The rate was significantly higher among patients treated for more than 12 months than among those treated for 12 months or less. Gastrointestinal events were more frequent among patients receiving cytarabine, whereas rash and depression were more frequent among patients receiving peginterferon alfa-2a. As compared with other treatments, the addition of peginterferon alfa-2a to imatinib therapy resulted in significantly higher rates of molecular response in patients with chronic-phase CML. (Funded by the French Ministry of Health and others; ClinicalTrials.gov number, NCT00219739.).

• Discontinuation of imatinib in patients with chronic myeloid leukaemia who have maintained complete molecular remission for at least 2 years: the prospective, multicentre Stop Imatinib (STIM) trial.

  Authors: François-Xavier Mahon, Delphine Réa, Joëlle Guilhot, François Guilhot, Françoise Huguet, Franck Nicolini, Laurence Legros, Aude Charbonnier, Agnès Guerci, Bruno Varet, Gabriel Etienne, Josy Reiffers, Philippe Rousselot

  The lancet oncology. 10/2010; 11(11):1029-35.

  Imatinib treatment significantly improves survival in patients with chronic myeloid leukaemia (CML), but little is known about whether treatment can safely be discontinued in the long term. We aimedImatinib treatment significantly improves survival in patients with chronic myeloid leukaemia (CML), but little is known about whether treatment can safely be discontinued in the long term. We aimed to assess whether imatinib can be discontinued without occurrence of molecular relapse in patients in complete molecular remission (CMR) while on imatinib. In our prospective, multicentre, non-randomised Stop Imatinib (STIM) study, imatinib treatment (of >2 years duration) was discontinued in patients with CML who were aged 18 years and older and in CMR (>5-log reduction in BCR-ABL and ABL levels and undetectable transcripts on quantitative RT-PCR). Patients who had undergone immunomodulatory treatment (apart from interferon α), treatment for other malignancies, or allogeneic haemopoietic stem-cell transplantation were not included. Patients were enrolled at 19 participating institutions in France. In this interim analysis, rate of relapse was assessed by use of RT-PCR for patients with at least 12 months of follow-up. Imatinib was reintroduced in patients who had molecular relapse. This study is registered with ClinicalTrials.gov, number NCT00478985. 100 patients were enrolled between July 9, 2007, and Dec 17, 2009. Median follow-up was 17 months (range 1-30), and 69 patients had at least 12 months follow-up (median 24 months, range 13-30). 42 (61%) of these 69 patients relapsed (40 before 6 months, one patient at month 7, and one at month 19). At 12 months, the probability of persistent CMR for these 69 patients was 41% (95% CI 29-52). All patients who relapsed responded to reintroduction of imatinib: 16 of the 42 patients who relapsed showed decreases in their BCR-ABL levels, and 26 achieved CMR that was sustained after imatinib rechallenge. Imatinib can be safely discontinued in patients with a CMR of at least 2 years duration. Imatinib discontinuation in this setting yields promising results for molecular relapse-free survival, raising the possibility that, at least in some patients, CML might be cured with tyrosine kinase inhibitors.

• Research highlights.

  Authors: Stéphanie Dulucq, François-Xavier Mahon

  Pharmacogenomics. 09/2010; 11(9):1201-3.

• Remission in CML: is DNA useful?

  Authors: François-Xavier Mahon

  Blood. 08/2010; 116(8):1192.

• A method to measure deferasirox in plasma using HPLC coupled with MS/MS detection and its potential application.

  Authors: Emmanuelle Chauzit, Stéphane Bouchet, Marguerite Micheau, François Xavier Mahon, Nicholas Moore, Karine Titier, Mathieu Molimard

  Therapeutic drug monitoring. 04/2010; 32(4):476-81.

  Iron overload resulting from transfusion dependency in some patients with chronic anaemia can be prevented by chelation. Deferasirox is an oral alternative to the well studied but inconvenientIron overload resulting from transfusion dependency in some patients with chronic anaemia can be prevented by chelation. Deferasirox is an oral alternative to the well studied but inconvenient deferroxamine therapy. The pharmacokinetic parameters of this new drug suggest potential interindividual variability and patients might benefit from pharmacologic drug monitoring. We developed an liquid chromatography coupled with tandem mass spectrometry (LC-MS-MS) method to quantify deferasirox in plasma. After protein precipitation, samples were injected onto an XTerra RP18 column with a gradient of acetonitrile and formiate buffer (4 mM, pH 3.0) with 5% methanol. Detection by electrospray ionization mass-spectrometry was performed using the multiple reaction monitoring mode. Sixty-three samples from patients treated with deferasirox were then analyzed to evaluate pharmacokinetic/pharmacodynamic relationships. Calibration curves were linear from 0.5 to 40 microg/mL. Interday and intraday precision were lower than 8.9% and 7.3%, respectively. Bias did not exceed 12.7%. Plasma iron overload did not interfere with analysis. Plasma drug concentrations of patients treated by deferasirox were compared with plasma ferritin, considered as a marker of treatment efficacy. No statistically significant correlation was observed, though higher ferritin concentrations (>1000 microg/L, n = 30) were observed in patients with lower mean deferasirox concentration (9.5 +/- 9.1 microg/mL). This simple method is suitable for routine monitoring of deferasirox concentrations in plasma as it requires very few steps and has a short runtime. It allows evaluation of patient compliance, drug-drug interactions, and further investigations of pharmacokinetic/pharmacodynamic relationships.

• Pharmacologic monitoring and determinants of intracytoplasmic drug levels.

  Authors: François-Xavier Mahon

  Best practice & research. Clinical haematology. 09/2009; 22(3):381-6.

  Imatinib (IM) is the gold standard for the treatment of chronic myeloid leukaemia (CML). However, there exists significant interpatient variability in plasma exposure for a given dose of the drug.Imatinib (IM) is the gold standard for the treatment of chronic myeloid leukaemia (CML). However, there exists significant interpatient variability in plasma exposure for a given dose of the drug. Several recent studies have revealed a correlation between imatinib trough plasma levels and clinical response, suggesting that measurement of plasma levels could be a useful tool to optimise IM dose. Despite this apparent link, many important questions on the use of IM blood level testing remain unanswered. We recommend IM dosing for patients (1) who are not responding to IM as well as expected, (2) who are suspected to be poorly compliant to their IM regimen, (3) who experience adverse events that are unusually severe for the prescribed dosage and (4) when a drug-drug interaction is suspected.

• Correlation between trough imatinib plasma concentration and clinical response in chronic myeloid leukemia.

  Authors: François-Xavier Mahon, Mathieu Molimard

  Leukemia research. 05/2009;

• The necrotic signal induced by mycophenolic acid overcomes apoptosis-resistance in tumor cells.

  Authors: Gwendaline Guidicelli, Benjamin Chaigne-Delalande, Marie-Sarah Dilhuydy, Benoît Pinson, Walid Mahfouf, Jean-Max Pasquet, François-Xavier Mahon, Philippe Pourquier, Jean-François Moreau, Patrick Legembre

  PLoS ONE. 02/2009; 4(5):e5493.

  BACKGROUND: The amount of inosine monophosphate dehydrogenase (IMPDH), a pivotal enzyme for the biosynthesis of the guanosine tri-phosphate (GTP), is frequently increased in tumor cells. TheBACKGROUND: The amount of inosine monophosphate dehydrogenase (IMPDH), a pivotal enzyme for the biosynthesis of the guanosine tri-phosphate (GTP), is frequently increased in tumor cells. The anti-viral agent ribavirin and the immunosuppressant mycophenolic acid (MPA) are potent inhibitors of IMPDH. We recently showed that IMPDH inhibition led to a necrotic signal requiring the activation of Cdc42. METHODOLOGY/PRINCIPAL FINDINGS: Herein, we strengthened the essential role played by this small GTPase in the necrotic signal by silencing Cdc42 and by the ectopic expression of a constitutive active mutant of Cdc42. Since resistance to apoptosis is an essential step for the tumorigenesis process, we next examined the effect of the MPA-mediated necrotic signal on different tumor cells demonstrating various mechanisms of resistance to apoptosis (Bcl2-, HSP70-, Lyn-, BCR-ABL-overexpressing cells). All tested cells remained sensitive to MPA-mediated necrotic signal. Furthermore, inhibition of IMPDH activity in Chronic Lymphocytic Leukemia cells was significantly more efficient at eliminating malignant cells than apoptotic inducers. CONCLUSIONS/SIGNIFICANCE: These findings indicate that necrosis and apoptosis are split signals that share few if any common hub of signaling. In addition, the necrotic signaling pathway induced by depletion of the cellular amount of GTP/GDP would be of great interest to eliminate apoptotic-resistant tumor cells.

• Evidence that Resistance to Nilotinib May Be Due to BCR-ABL, Pgp, or Src Kinase Overexpression.

  Authors: François-Xavier Mahon, Sandrine Hayette, Valérie Lagarde, Francis Belloc, Béatrice Turcq, Franck Nicolini, Coralie Belanger, Paul W Manley, Cédric Leroy, Gabriel Etienne, Serge Roche, Jean-Max Pasquet

  Cancer research. 01/2009; 68(23):9809-16.

  Targeting the tyrosine kinase activity of Bcr-Abl is an attractive therapeutic strategy in chronic myeloid leukemia (CML) and in Bcr-Abl-positive acute lymphoblastic leukemia. Whereas imatinib, aTargeting the tyrosine kinase activity of Bcr-Abl is an attractive therapeutic strategy in chronic myeloid leukemia (CML) and in Bcr-Abl-positive acute lymphoblastic leukemia. Whereas imatinib, a selective inhibitor of Bcr-Abl tyrosine kinase, is now used in frontline therapy for CML, second-generation inhibitors of Bcr-Abl tyrosine kinase such as nilotinib or dasatinib have been developed for the treatment of imatinib-resistant or imatinib-intolerant disease. In the current study, we generated nilotinib-resistant cell lines and investigated their mechanism of resistance. Overexpression of BCR-ABL and multidrug resistance gene (MDR-1) were found among the investigated mechanisms. We showed that nilotinib is a substrate of the multidrug resistance gene product, P-glycoprotein, using verapamil or PSC833 to block binding. Up-regulated expression of p53/56 Lyn kinase, both at the mRNA and protein level, was found in one of the resistant cell lines and Lyn silencing by small interfering RNA restored sensitivity to nilotinib. Moreover, failure of nilotinib treatment was accompanied by an increase of Lyn mRNA expression in patients with resistant CML. Two Src kinase inhibitors (PP1 and PP2) partially removed resistance but did not significantly inhibit Bcr-Abl tyrosine kinase activity. In contrast, dasatinib, a dual Bcr-Abl and Src kinase inhibitor, inhibited the phosphorylation of both BCR-ABL and Lyn, and induced apoptosis of the Bcr-Abl cell line overexpressing p53/56 Lyn. Such mechanisms of resistance are close to those observed in imatinib-resistant cell lines and emphasize the critical role of Lyn in nilotinib resistance. [Cancer Res 2008;68(23):9809-16].

• Triptolide cooperates with chemotherapy to induce apoptosis in acute myeloid leukemia cells.

  Authors: Arnaud Pigneux, François-Xavier Mahon, Maialene Uhalde, Marie Jeanneteau, Francis Lacombe, Noël Milpied, Josy Reiffers, Francis Belloc

  Experimental hematology. 11/2008;

  OBJECTIVE: Triptolide has shown antitumor activity in a broad range of solid tumors and on leukemic cells in vitro. MATERIALS AND METHODS: The THP1 cell line and primary acute myeloid leukemia (AML)OBJECTIVE: Triptolide has shown antitumor activity in a broad range of solid tumors and on leukemic cells in vitro. MATERIALS AND METHODS: The THP1 cell line and primary acute myeloid leukemia (AML) cells were cultured with triptolide alone or in association with AraC or idarubicin in increasing concentrations. Apoptosis was measured by flow cytometry using DiOC6(3) for the cell line and fluorescein isothiocyanateAnnexin-V and CD45 labeling for fresh blast cells. Protein expression was measured by Western blot. Cell cycle distribution of apoptotic cells was measured by flow cytometry. RESULTS: A synergistic effect was observed when triptolide was added to idarubicin or to AraC to induce apoptosis of THP-1 leukemic cells. The triptolide/AraC association was also investigated in vitro on primary blast cells from 25 AML patients. This combination induced significantly higher percentages of apoptosis vs treatment with each drug separately (p<0.005). The IkappaB and X-linked inhibitor of apoptosis protein contents, which were altered by triptolide in idarubicin-treated cells, were not modified in AraC-treated cells. The association of AraC with triptolide increased the number of cells blocked in the S phase and most underwent apoptosis. CONCLUSION: These results suggest that, by modifying the cell cycle kinetics, AraC sensitizes AML cells to apoptosis induced by low concentration triptolide. The in vitro proapoptotic effect of triptolide associated with the antiproliferative activity of AraC warrants further clinical investigation for treatment of AML patients, especially elderly patients for whom low-dose AraC treatment could be improved by the addition of triptolide.