Imatinib Levels Research Articles

Selective Escalation of Imatinib Therapy and Early Switching to Nilotinib In De Novo Chronic Phase CML Patients: Interim Results From the TIDEL-II Trial

AbstractAbstract 209 Background:Although the majority of chronic phase (CP) Philadelphia positive (Ph+) chronic myelogenous leukemia (CML) patients (pts) achieve good disease control with imatinib, some pts demonstrate suboptimal responses. Early dose escalation or switching to nilotinib, a more potent BCR-ABL kinase inhibitor, as soon as suboptimal molecular response is recognised may improve response and disease outcome. Aim:To optimise clinical and molecular outcomes in Ph+ CML using imatinib (IM) as frontline therapy with selective IM dose escalation based on pharmacokinetic (PK) results and switching to nilotinib (NIL) in case of suboptimal response, or IM-intolerance. Method:TIDEL-II is a multicentre, single arm prospective ALLG trial in de novo CP-CML pts with 2 separate sequential cohorts. In Cohort I, pts are treated with IM 600mg/d up-front, aiming for BCR-ABL RQ-PCR target values of ≤ 10%, 1%, and 0.1% IS (major molecular response, MMR) at 3, 6, and 12 months respectively. Pts who do not reach these treatment targets are classified as suboptimal responders. Dose escalation to 800mg/d or maximal tolerated dose occurs if trough IM level is <1000ng/mL at day 22, or for suboptimal response. A switch to NIL (400mg bid) is triggered if molecular targets are still not met 3 months after IM escalation, or for loss or response, or for IM intolerance (Grade III/IV or persistent Grade II non-haematological toxicity). Results:105 pts were assessed with median follow up of 18.9 months (range: 9–33) in cohort I. For pts with a minimum of 12 months follow up (n=80), complete cytogenetic response (CCR), MMR and complete molecular response (CMR)# rates at 12 months were 92%, 66% and 11% respectively. BCR-ABL levels at 3 months were predictive of MMR at 12 months, but not for CMR due to small pt numbers (Table 1). For pts who failed to achieve BCR-ABL of ≤10% at 3 months, the 12 month MMR rate was 25% (vs 5% in TIDEL-I where pts were also started on IM 600mg/d and suboptimal responders were dose escalated to IM 800mg/d). Of the 105 pts, 16 pts dose escalated IM due to a day 22 IM blood level <1000ng/mL, after which 2/16 switched to NIL (1 suboptimal, 1 intolerant); all achieved CCR. Twelve pts dose escalated for suboptimal response, 7 subsequently switched to NIL for again failing treatment targets. In all, 21/105 pts (20%) switched to NIL: 7 for suboptimal response and 14 for intolerance. The median time to switching and the median pre-switch prescribed IM dose were 468 days & 800mg/d for the suboptimal group; and 183 days & 600mg/d for the intolerant group respectively. Of these, 20/21 achieved or remained in CCR. At the time of switching to NIL, 19/21 pts were not in MMR. With a median follow-up of 295 days post switch to NIL, 9/12 intolerant pts (75%) achieved MMR, whereas 1/7 suboptimal IM responders (14%) achieved MMR (median follow up after switching: 286 days). Only 7/105 pts (7%) discontinued treatment: 4 for non-compliance, 1 pt with a T315I mutation and 2 pts with blast crisis (BC). Progression to BC was associated with detectable mutations: 1 pt with 4 different mutations including T315I and 1 pt with H396P mutation. The progression rate to AP/BC was 2%. The overall mutation rate was 5/105 (5%). The 2 pts who progressed and the pt who discontinued when a T315I mutation was detected were among the 28 pts with BCR-ABL values >1.0% at 3 months. In contrast, no resistant mutations were detected or transformations occurred in the 49 pts with BCR-ABL values ≤1.0% at 3 months. Conclusion: A strategy of selective intensification of BCR-ABL inhibitor therapy based on molecular response and PK values resulted in a 66% MMR rate by 12 months. Despite a minority of pts (20%) requiring a switch to NIL, this has enhanced the rate of MMR by 12 months when compared to IM intensification alone as seen in TIDEL-I where the rate of MMR and CMR by 12 months was 47% and 9% respectively. The IM intolerant pts demonstrated excellent response rates after switching to NIL. To date, the results from TIDEL-II compare favourably with other frontline strategies with regards to response and transformation rates. Disclosures:Yeung:Novartis Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding. Osborn:Novartis Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding. White:Novartis Pharmaceuticals: Research Funding; Bristol Myers Squibb: Research Funding. Branford:Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Research Funding. Slader:Novartis Pharmaceuticals: Employment, Equity Ownership. Ross:Novartis Pharmaceuticals: Honoraria, Research Funding. Mills:Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees. Hughes:Novartis: Honoraria, Research Funding, Speakers Bureau; Bristol-Meyers Squibb: Honoraria, Research Funding; Ariad: Honoraria.

In Contrast to Imatinib, Dasatinib Intracellular Concentration In CML-CD34+ Progenitors Is Not Significantly Different Than That Observed In CD34- Mature Cells.

AbstractAbstract 1205Long term follow up of imatinib (IM) clinical studies and in vitro studies suggest that tyrosine kinase inhibitors (TKI) do not eradicate leukemic stem cells. Refractoriness of leukemic stem cells is postulated to be due to inadequate Bcr-Abl kinase inhibition which in turn could be due to low intracellular uptake and retention (IUR) of TKI. We have previously demonstrated that IM cellular uptake is predominantly mediated by the organic cation transporter protein (OCT-1) and patients with low OCT-1 activity have suboptimal response as compared to patients with high OCT-1 activity. More recently Engler et al (Leukemia 2010) demonstrated that IM IUR is significantly lower in CML-CD34+ cells compared to CD34- cells. This could be due to low expression and activity of the OCT-1 protein and/or high expression of ABCB1 and/or ABCG2 (Jiang et al Leukemia 2007). Although dasatinib is clinically available there are no published data assessing dasatinib IUR in CML-CD34+ progenitors. We and others have previously demonstrated that dasatinib cellular uptake is predominantly OCT-1 independent and dasatinib is a substrate of ABCB1 and ABCG2. We hypothesized that dasatinib IUR would be lower in CML-CD34+ cells compared to CD34- cells. In this study we compare dasatinib and IM IUR; and OCT-1 and ABCB1 mRNA expression in CML-CD34+ and CD34- cells of newly diagnosed CML-CP patients. CD34+ and CD34- cells were incubated with 14C-dasatinib (100 nM and 1 μM) or 14C-IM (2 μM) for 2h and IUR was assessed as described previously (Hiwase et al Clin Cancer Res. 2008). As shown previously, the OCT-1 expression and activity was lower in CML-CD34+ cells, and resulted in lower IM IUR in CML-CD34+ cells compared to CML-CD34- cells (15±5 vs. 27±5; p=0.04; Fig 1A and C). However at a therapeutically achievable concentration (100 nM dasatinib) and at higher concentration (1 μM dasatinib), there was no significant difference in dasatinib IUR in CML-CD34+ and CD34- cells (Fig 1B). Low OCT-1 expression and activity in CML-CD34+ cells did not influence the dasatinib IUR; further confirming that dasatinib cellular influx is predominantly OCT-1 independent. Despite higher ABCB1 mRNA expression in CML-CD34+ cells, the dasatinib IUR was not lower in CML-CD34+ cells compared to CD34- cells. High ABCB1 mRNA expression may not necessarily translate into high ABCB1 activity. To this end, we assessed the effect of PSC-833, an ABCB1 inhibitor, on dasatinib IUR and dasatinib mediated Bcr-Abl kinase inhibition in CML-CD34+ cells. The baseline p-Crkl, a surrogate marker of Bcr-Abl kinase activity, was significantly higher in CML-CD34+ compared to CML-CD34- cells (67±5% vs. 55±8%; p=0.002; n=9). PSC-833 neither increased dasatinib IUR, nor enhanced dasatinib mediated Bcr-Abl kinase inhibition in CML-CD34+ cells (% p-Crkl at 10 nM dasatinib: 20±6 vs. 27±10). Similarly, Ko143, an ABCG2 inhibitor, did not significantly change dasatinib IUR or Bcr-Abl kinase inhibition (% p-Crkl at 10 nM dasatinib: 21±3 vs. 27±10). In summary, although dasatinib is an ABCB1 and ABCG2 substrate, ABCB1 and ABCG2 inhibitors neither increase dasatinib IUR, nor enhance dasatinib mediated Bcr-Abl kinase inhibition in CML-CD34+ cells. This data suggest that dasatinib IUR in CML-CD34+ cells is not influenced by ABCB1 and ABCG2. Hatziieremia et al (Exp. Hematology, 2009) reported that ABCB1 activity is low in CML-CD34+ cells and suggested that it did not influence IM level in CML-CD34+ cells. We further demonstrated that 100 nM dasatinib inhibited ≥95% Bcr-Abl kinase activity in CML-CD34+ and CD34- cells.In summary our data demonstrates that in contrast to IM, the intracellular concentration of dasatinib is equivalent in mature and immature CML cell compartments which may contribute to better targeting of early CML progenitors with dasatinib. [Display omitted] Disclosures:White:Novartis: Honoraria, Research Funding; BMS: Research Funding. Hughes:Novartis: Honoraria, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding.

Practical Considerations for Monitoring Patients With Chronic Myeloid Leukemia

Current routine monitoring strategies for chronic myeloid leukemia (CML) incorporate hematologic, cytogenetic, and molecular analysis. BCR-ABL1 kinase domain mutation analysis is an important assessment in specific circumstances. The recommendations for when and how frequently to undertake these assessments have recently been updated. However, response assessment is not always straightforward and access to some analytical tools may not be available. Pharmacokinetic assessment of imatinib levels may correlate with clinical response and could help in assessing issues of suboptimal response, excessive toxicity, or noncompliance. Here we provide practical considerations for monitoring response, offer suggestions for alternative assessments in case of failure or limited access of analyses, and consider future monitoring tools.

Uptake of synthetic Low Density Lipoprotein by leukemic stem cells — a potential stem cell targeted drug delivery strategy

Chronic Myeloid Leukemia (CML) stem/progenitor cells, which over-express Bcr-Abl, respond to imatinib by a reversible block in proliferation without significant apoptosis. As a result, patients are unlikely to be cured owing to the persistence of leukemic quiescent stem cells (QSC) capable of initiating relapse. Previously, we have reported that intracellular levels of imatinib in primary primitive CML cells (CD34 +38 lo/−), are significantly lower than in CML progenitor cells (total CD34 +) and leukemic cell lines. The aim of this study was to determine if potentially sub-therapeutic intracellular drug concentrations in persistent leukemic QSC may be overcome by targeted drug delivery using synthetic Low Density Lipoprotein (sLDL) particles. As a first step towards this goal, however, the extent of uptake of sLDL by leukemic cell lines and CML patient stem/progenitor cells was investigated. Results with non-drug loaded particles have shown an increased and preferential uptake of sLDL by Bcr-Abl positive cell lines in comparison to Bcr-Abl negative. Furthermore, CML CD34 + and primitive CD34 +38 lo/− cells accumulated significantly higher levels of sLDL when compared with non-CML CD34 + cells. Thus, drug-loading the sLDL nanoparticles could potentially enhance intracellular drug concentrations in primitive CML cells and thus aid their eradication.

Relationship of serum imatinib trough level and response in CML patients: Long term follow-up

One hundred and three patients with Philadelphia chromosome or BCR-ABL positive chronic myeloid leukemia (CML) in chronic phase who were on oral imatinib were included in this study. The study aimed to assess the relationship between imatinib trough serum levels and clinical outcome (as determined by molecular response) in Jordanian CML patients who have been on imatinib therapy for at least 12 months. The mean trough imatinib serum level in the group with complete molecular response (CMR) was 2891±856ng/ml, the group with major molecular response (MMR) was 2337±434ng/ml, the group with complete cytogenetic response (CCyR) was 1817±563ng/ml, and the group without CCyR was 1723±673ng/ml. A receiver operating characteristic (ROC) curve was constructed after dividing patient sample into two groups, those with MMR or better and those without MMR, in order to estimate a threshold for imatinib level that correlates with a favorable response (the former group), and analysis yielded a value of 2158ng/ml.

Personalized cancer therapy for gastrointestinal stromal tumor: synergizing tumor genotyping with imatinib plasma levels

Imatinib has exceptional activity in controlling gastrointestinal stromal tumor (GIST) due to inhibition of the constitutively active conformation of KIT and platelet-derived growth factor-alpha (PDGFRA), which is commonly seen in this tumor. This review explores the current available data on the correlation between imatinib plasma levels, response to treatment, and the mutational status of KIT and PDGFRA. A recent retrospective analysis demonstrated a relationship between imatinib plasma levels and progression-free survival in patients with advanced GIST. Plasma imatinib levels were notably unrelated to the daily administered dose of imatinib in this small series. Prior phase III trials have demonstrated that dose escalation of imatinib may lead to increased disease control in a subset of patients with advanced GIST who progress on standard dose imatinib. Moreover, patients with GIST carrying an exon 9 mutation may benefit from higher doses of imatinib. Current available data suggest a possible correlation between imatinib plasma level and progression-free survival in patients with advanced GIST. A prospective trial is underway to evaluate whether modification of imatinib dose to achieve a target imatinib plasma level will impact patient outcome when compared with standard imatinib dosing (www.clinicaltrials.gov, NCT01031628).

Trough plasma concentration of imatinib reflects BCR–ABL kinase inhibitory activity and clinical response in chronic‐phase chronic myeloid leukemia: A report from the BINGO study

Pharmacokinetic (PK) factors have been suggested to be involved in the unfavorable clinical responses of chronic myeloid leukemia (CML) patients treated with imatinib. The purpose of this study was to clarify prognostic implications of PK factors in CML patients treated with imatinib. The plasma trough (C(min)) level of imatinib and serum α(1)-acid glycoprotein (AGP) level were measured on two different days in 65 CML patients treated with imatinib for more than 12 months. We further examined whether the C(min) level of imatinib actually reflects inhibitory activity against BCR-ABL kinase using the plasma inhibitory activity (PIA) assay. Since the differences of five patients were statistically rejected by the Smirnov-Grubbs' test, we excluded them for further analysis. The C(min) level was strongly associated with the achievement of MMR at the 12th month, and ROC analysis demonstrated C(min) levels and their discrimination potential for major molecular response (MMR) with the best sensitivity (63.2%) and specificity (68.2%) at a C(min) threshold of 974 ng/mL. The α(1)-Acid glycoprotein (AGP) level was within the normal range in 57 of 60 patients, indicating little impact of AGP on our study. There was a weak correlation between PIA against phospho (P)-BCR-ABL and the C(min) level of imatinib (r(2) = 0.2501, P = 0.0007), and patient plasma containing >974 ng/mL imatinib sufficiently inhibited P-BCR-ABL. These results collectively indicated that maintaining ∼1000 ng/mL of C(min) was clinically and biologically important for the optimal response in CML patients treated with imatinib. A prospective intervention study is required to establish PK-based management in CML patients treated with imatinib.

Abstract 3538: An atomic absorption spectroscopy assay (AASA) as a surrogate method to measure imatinib (IM) uptake via the organic cation transporter 1 (OCT1)

Abstract Background. In chronic myeloid leukaemia (CML) 15 to 30% of patients (pts) treated with the ABL specific tyrosine kinase inhibitor IM may develop resistance. In these pts clonal evolution, amplification of the BCR-ABL gene or kinase domain mutations have been identified as underlying mechanisms. Additionally, pharmacokinetic alterations leading to reduced intracellular imatinib levels may also exist. IM is transported into the cell via the OCT1. The activity of this transporter could play a pivotal role for the intracellular IM concentration. Until now, uptake efficacy of IM is primarily measured by using radioactive labelled IM. Due to the limitations of these methods, we tried to establish alternative methods to measure the activity of OCT1 using cellular OCT1 dependent oxaliplatin (OX) uptake as a surrogate. Materials &amp; Methods. To quantitatively analyse OX uptake in human cell lines an AASA was established. Conversely, radioactive IM uptake was measured by scintillation analysis. We compared the uptake of OX and IM in different human cell lines, including JURKAT, Molt-4, K-562, KU-812, Lama-87, KCL-22 and OCI-AML-2. Ten different transport inhibitors were used to block IM or OX uptake, respectively. Furthermore, we investigated the expression levels of different influx (OCT1, OCT2, OCT3) and efflux transporters (ABCB1, ABCC1, ABCG2) in those cell lines. Results. IM and OX both were taken up linearly into cells within a range from 0,4 to 2 µM (IM) or 1 to 10 µM (OX). 150 mM verapamil and 100 µM prazosin could effectively inhibit cellular uptake of both drugs (21%±8% and 27%±8%). However, a differential uptake pattern between OX and IM was observed in relation to the different cell lines. In contrast, we could show that 15 µM citalopram inhibited the transport of 5 µM OX in a similar type as the uptake of 1-2 µM IM into all cell lines tested yet (1,14±0,15*). In this regard citalopram may be most useful for further studies on OCT1 activity. Using real-time PCR, an adequate expression of OCT1 mRNA could be detected in all cell lines tested, albeit the levels differed significantly from 150 to 27.000 fold less than in the internal control (ß-actin). However, the mRNA expression level of OCT1 does not seem to be a predictor for IM or OX uptake. The expression pattern of the efflux transporters showed no significant distribution, too. Conclusions. Here, we demonstrate the feasibility and accuracy of AASA testing of oxaliplatin as a surrogate marker for IM uptake via OCT1. As this methodology is secure, fast and sensitive, this approach may substitute conventional testing of OCT1 activity by radio labelled IM. On a clinical level, this procedure could be helpful as a clinical tool to test IM pharmacokinetics in CML patients. However, patient sample derived data will be needed to further evaluate this approach. * 1 would stand for 100% equality of uptake of imatinib or oxaliplatin Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3538.

Imatinib plasma levels: correlation with clinical benefit in GIST patients

Imatinib plasma levels: correlation with clinical benefit in GIST patients

Integrating pharmacogenetics and therapeutic drug monitoring: optimal dosing of imatinib as a case-example

To illustrate the interface of pharmacogenetics and therapeutic drug monitoring and to estimate target blood level for imatinib in the treatment of chronic myelogenous leukemia A literature review to provide the evidence and necessary data to support the case for the interface, and quantitative analysis of the data to estimate the target blood level for imatinib using receiver operating curve (ROC; signal detection theory) analysis. One study estimated the optimum target level of imatinib in chronic myelogenous leukaemia as 1002 ng/mL (1.70 microM) through ROC analysis. Using individual-patient level data reported in another study and the same methodology, we estimated the target level as 0.95 microM. This is consistent with the results of other observational studies where dose-response was not the primary research objective. The available evidence suggests considerable inter-individual variability in dose-blood level response. In addition to the pharmacogenetics of metabolic enzymes and transporters, genetic mutations in genes participating in the signalling pathways may also account for the wide inter-individual variability in dose-blood level and dose-clinical response relationships. A single-dose regimen for all pharmacogenetically eligible patients is not the optimum strategy for prescribing imatinib to patients with chronic myelogenous leukaemia. We suggest that therapeutic drug monitoring aimed at ensuring a trough target level of 1 microM would reduce the incidence of pseudo-resistance and hence personalize treatment and optimise response to imatinib. Persistent resistance can then be probed further for other causes.

Imatinib Blood Level Testing – Current Perspectives and Key Questions

Imatinib is the gold standard for the treatment of chronic myeloid leukaemia. Several recent studies have revealed a correlation between imatinib trough plasma levels and clinical response, suggesting that measurement of plasma levels can be a useful tool for optimising imatinib dose. However, a number of important questions on the use of imatinib blood level testing (BLT) remain unanswered. These questions were discussed at a European expert meeting held in Bordeaux, France, under the auspices of the European Treatment and Outcome Study (EUTOS) for chronic myeloid leukaemia. The key views were that: imatinib blood level measured between days seven and 29 of treatment could be a prognostic indicator and an important baseline for evaluating subsequent measurements; an imatinib trough plasma threshold for optimal response of 1,000ng/ml has been proposed but needs further validation; there is insufficient evidence to define any relationship between imatinib plasma levels and adverse events; and, although it is not yet possible to define and validate a comprehensive algorithm for the application of BLT in clinical practice, a working model has been developed. Pan-European collaboration, data pooling and initiation of a prospective clinical trial would be important steps in addressing current uncertainties.

Early Dose-Escalation in Chronic Myeloid Leukaemia Patients with Low Plasma Imatinib Levels Leads to Equivalent BCR-ABL Values and Drug Levels at 6 Months to Those with Optimal Drug Levels: First Analysis From the TIDEL II Trial of De-Novo Patients Treated with 600mg Imatinib.

Abstract 1131Poster Board I-153 AimLow trough plasma imatinib levels have been associated with a poorer response to treatment in chronic myeloid leukaemia (CML) in chronic phase. We hypothesised that dose-escalation in patients with low day 22 trough levels could improve outcomes. In this interim analysis, we compared the BCR-ABL levels for patients who were dose escalated due to initial suboptimal imatinib levels to those with optimal imatinib levels. We also determined whether dose escalation leads to an increase in plasma imatinib levels. MethodImatinib trough and peak levels were measured in 74 chronic phase CML patients enrolled to the Australasian Leukaemia and Lymphoma Group TIDEL II study at day 8, day 22, and 3 and 6 months after commencing imatinib 600 mg. Patients with a day 22 imatinib trough level of <1000 ng/ml were dose escalated to 800 mg daily where tolerated. BCR-ABL levels were measured at 1, 2, 3 and 6 months using RQ-PCR and values were reported on the international reporting scale (IS). ResultsThe median follow-up was 36 weeks, with 64 of 74 patients having 3 month data and 50 having 6 month data. At day 22, 11 (15%) patients had an imatinib trough level <1000 ng/ml, with 7 of these able to dose-escalate to 800 mg. The other 4 subjects with a low imatinib trough level were either unable to tolerate dose-escalation or were already on a dose <600 mg. At 3 and 6 months, the mean (±SD) imatinib trough level in those who had been dose escalated to 800 mg due to a day 22 trough level of <1000 ng/ml was no longer significantly different from those with a day 22 trough level of ≥1000 ng/ml (1710 ±392 vs 1760 ±949 ng/ml at 3 months, p=0.74; 1642 ±566 vs 1535 ±755 ng/ml at 6 months, p=0.75). At 2 months, the patients who were dose escalated had a significantly higher median BCR-ABL% IS level compared with those with optimal imatinib levels at day 22 (17.5% vs 6.4%, p=0.02). By 3 and 6 months this difference in BCR-ABL level had diminished and was no longer significantly different (7.3% vs 1.9% at 3 months, p=0.06; 2.1% vs 2.7% at 6 months, p=0.66). ConclusionThis data suggests that selective dose-escalation based on Day 22 imatinib trough levels of <1000 ng/ml may result in subsequent plasma concentrations equivalent to patients with day 22 levels of >1000 ng/ml and equivalent BCR-ABL reductions. Whether this strategy can ameliorate the adverse prognostic impact of low plasma imatinib concentrations on standard dose will be the subject of ongoing study. DisclosuresWhite:Novartis and Britol-Myers Squibb: Research Funding. Branford:Novartis Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Bristol-Myers Squibb: Honoraria, Research Funding. Slader:Novartis Pharmaceuticals Australia: Employment, Equity Ownership. Hughes:Bristol Meyers Squibb: Advisor, Honoraria, Research Funding; Novartis: Advisor, Honoraria, Research Funding.

Imatinib and Nilotinib Intracytoplasmic Determination Levels.

Abstract 2750Poster Board II-726 IntroductionCellular uptake of imatinib is known to be mediated by Oct-1 but efflux by MDR1. In the cell, metabolism, particularly by CYP3A4, produces metabolites that could be carried by other transporters such as MRP2. Nilotinib seems to suffer less from the influence from such transporters. The aim of this study was to determine the impact of cellular exchange on the intracellular concentrations of imatinib, nilotinib or both in vitro but also among patients in order to improve the therapeutic drug monitoring of these medicines. MethodsIn vitro studies used the chronic myeloid leukemia cell line K562 overexpressing MDR1 (K562mdr) and wild-type K562 cells (K562wt). To investigate cellular uptake and the intra/extracellular concentration relationship, these were incubated with imatinib or nilotinib for 2h in the presence or absence of transporter inhibitors (verapamil, PSC833). Cells were precipitated by acetonitrile (with internal standards) and analysis was performed using HPLC-tandem mass spectrometry (Waters Acquity-TQD). The intracellular concentration of peripheral blood mononuclear cells (PBMC) of patients treated by these drugs was also investigated. ResultsIn K562wt, the presence of verapamil, an inhibitor of both Oct-1 and MDR1, reduced imatinib intracellular concentration compared to the steady-state untreated K652wt, but the presence of PSC833, a specific inhibitor of MDR1, had little effect on the level of imatinib. K562mdr, that had lower steady-state imatinib cellular concentration than K562wt, recovered higher levels with verapamil but PSC833 allowed the greatest concentrations. Experiments investigating nilotinib found no difference between cell lines with or without inhibitors. Finally, the presence of both imatinib and nilotinib seemed to modify the steady-state concentration found individually.Intracellular imatinib concentration was correlated with that found in the culture medium (extracellular), but the gradient was different for each conditions for both K562wt and K562mdr, with or without inhibitors. At every concentration tested, we found the same differences in levels than in the kinetic study. Saturation was observed with imatinib, especially for untreated K562wt indicating probable involvement of active transport.Investigation of nilotinib under the same conditions did not show any difference in the gradient of each conditions and the relationship was more linear.The raw intracellular concentrations of PBMC obtained from patients (n=30) were very variable, especially for the imatinib. Correction by plasma concentration indicates individual patient's capacity for intracellular incorporation and a trend was found with response to the treatment. ConclusionContrary to imatinib, nilotinib did not seem to be under influence of MDR1, nor of OCT1. The intracellular concentration appears as a good way to investigate pharmacokinetic resistance and could be an additional help for the management of the treatment, especially for imatinib. Disclosures:Mahon:Amgen: Honoraria; Novartis Pharma: Consultancy, Honoraria, Research Funding; Alexion: Consultancy, Honoraria.

Effects of Reduced Dose of Imatinib to Korean Chrionic Myeloid Leukemia in Chronic Phase.

Abstract 4290 BackgroundSome patients of CML in chronic phase receive reduced doses of imatinib due to some adverse effects. Recently, the efficacy of reduced dose of imatinib for the patients with small BSA was reported by our group and Japanese group, recently. This study was tried to verify the hypothesis of which BSA of CML patients might be an important factor to predict the effect of reduced dose imatinib. MethodFifty-six patients having record of BSA from the Korea University Medical Center who were treated with imatinib were retrospectively analyzed. ResultAll of the patients started the imatinib therapy with 400mg/day dose. 20 patients (35.7%) among them were reduced dose to 300mg and 4 of them were further reduced to 200mg/day. The main reasons for dose reduction were severe neutropenia or thrombocytopenia (grade 3 or 4) (89.4%). Following the dose reduction, the rate of toxicity was reduced and treatment was resumed and the dose was gradually increased until 9 patients tolerated a maintenance dose of 400mg/day and remainder had been taken the reduced dose. The cumulative CCR at 12 months was similar in both group (P = 0.89, 70.0% in reduced dose vs 72.7% in standard dose). The mean imatinib dose/BSA was significantly lower in patients receiving the reduced dose compared with those receiving the standard dose (P < 0.001)(183.4 ± 26.9 vs 230.5 ± 21.4), although the mean BSA didn't show the difference according to reduction of dose (P = 0.079)(1.62 ± 0.20 vs 1.75 ± 0.13). After median follow-up period of 37.3 months (6.0-76.1 months), 15 patients (75.0%) have sustained CCR in patients receiving reduced dose of imatinib. ConclusionFrom this study, we could find that the reduced dose of imatinib in CML patients might assure the relatively satisfactory response with low intolerable adverse effects. But we could not verify that BSA was the main factor to predict the effect of reduced dose of imatinib. So, further studies including though level of imatinib will be needed to clarify the effect of reduced dose of imatinib. Disclosures:No relevant conflicts of interest to declare.

Imatinib Meslylate Plasma Levels Predict Compliance in Patients with Chronic Myelogenous Leukemia.

Abstract 4274 INTRODUCTIONImatinib mesylate, an inhibitor of the BCR-ABL fusion protein, serves as the current standard of care in the treatment of chronic myeloid leukemia (CML). Since its introduction, significant improvements have been seen in both the course and prognosis of CML. Although imatinib is highly effective in treating CML, recent studies have demonstrated that approximately 30% of patients discontinue imatinib for at least 30 days during their first year of therapy. Clinically, treatment non-adherence is a common reason patients experience suboptimal outcomes and it has therefore become important to establish methods to predict compliance. Based on the association of treatment response with adherence, plasma imatinib levels can be used to predict compliance. METHODSA retrospective analysis was conducted on 19 CML patients (female 5, male 14; median age= 45.3) who received imatinib treatment at LAC+USC Medical Center. Patient charts, laboratory reports and physical examination reports were assessed and plasma concentrations were measured: 1) using liquid chromatography and 2) tandem mass spectrometry. A comparison was then made between Imatinib levels and CCyR. Compliance with imatinib therapy was assessed by chart review and patient history. RESULT: Nineteen patients were analyzed in this study: 1(5%), 17 (90%), and 1 (5%) were treated with 300, 400 and 600 mg imatinib daily, respectively. Fifteen (79%) were Hispanic, 4(21%) were previously treated with interferon, most patients (95%) were in chronic phase when they were diagnosed except one who was in accelerated phase. The median duration of imatinib therapy at the time of plasma imatinib testing was 37 months. The mean and SDs of trough plasma imatinib level was 1362 ng/ml and789 ng/ml, respectively. We found that the imatinib trough concentration was higher in our analysis compared to those reported in the IRIS study and the French group studies, 969 ng/ml and 1058 ng/ml respectively. The patients were divided into two groups (Q1–Q2) based on their imatinib trough level. The average of trough level of the first group (Q1) was 780 ng/ml (±230) (n=9), and that of the second group (Q2) was 1885 ng/ml (±746) (n=10). In total 67% (6 out of 9) of the patients in the first group (Q1) and 20% (2 out of 10) of patients in the second group (Q2) had poor compliance, demonstrating a significantly better compliance in the Q2 (P=0.0001). In terms of their response rate to treatment, Of the 17 patients, a total of 11 achieved a CCyR at 18 months (65%): 63% (5 out of 8) in Q1; 67% (6 out of 9) in Q2. There was no significant correlation between plasma imatinib level and response rate. However, there was a significant correlation between the compliance and the response rate. 80% (8 out of 10) of patients who were adherent to the treatment had CCyR at 18 months, compared to only 43% (3 out of 7) of patients who had CCyR at 18 months in the non-adherent group. (P value=0.0001). Conclusions: Non-adherence to imatinib therapy is common in CML patients and is associated with suboptimal response. Non-compliance should be considered as a possible reason for a patient's poor response to imatinib, prior to considering the patient as imatinib-resistant. Plasma imatinib level can be used as one of the tools to predict compliance. By examining patients' plasma imatinib level, it was shown that high imatinib plasma levels point to a higher likelihood of compliance, and low levels predict a lower likelihood of compliance. Disclosures:Gorospe:Novartis: Honoraria, Speakers Bureau. Yang:Novartis: Honoraria, Research Funding.

Determination of imatinib plasma levels in patients with chronic myeloid leukemia by high performance liquid chromatography–ultraviolet detection and liquid chromatography–tandem mass spectrometry: Methods’ comparison

The aims of this study were to validate and compare HPLC and LCMSMS analytical methods and their applicability for the quantitation of imatinib in human plasma. A total of 50 patients with chronic myeloid leukemia (CML) in chronic phase (CP) receiving 400 mg/day imatinib were enrolled in the study. Drug levels were determined by HPLC–UV and LCMSMS. HPLC intra-day accuracy ranged from 100.51 to 103.19%. LCMSMS accuracy ranged from 89.72 to 106.29%. The correlation coefficient between both methods was r 2 = 0.96. HPLC can be used for imatinib levels’ determinations in patients accurately and precisely.

Cyclosporin A sensitises Bcr-Abl positive cells to imatinib mesylate independently of P-glycoprotein expression

The effect of cyclosporin A (CsA) on imatinib treated Bcr-Abl positive K562 cells was studied. Similarly to other authors we found that imatinib induced apoptosis and erythroid differentiation in K562 cells. While its low concentrations induced predominantly erythroid differentiation, higher concentrations induced apoptosis. We found that CsA significantly potentiated cytotoxic effects of imatinib. A detailed analysis revealed that CsA shifted the balance between differentiation and apoptosis in favour of apoptosis. Our findings indicated that the observed effect of CsA was mediated neither through inhibition of ERK1/2 (extracellular signal-regulated kinases 1/2), nor through inhibition of p38 MAPK. We further observed that CsA might sensitise cells to apoptosis due to a changed cellular redox status as combined treatment of cells with imatinib and CsA resulted in a dramatic decrease of the ratio between reduced (GSH) and oxidised (GSSG) glutathione GSH/GSSG and in a significant suppression of thioredoxin reductase enzymatic activity. Our results indicated that K562 cells did not express detectable level of P-glycoprotein (P-gp). In addition, CsA did not affect significantly the intracellular level of imatinib. Therefore we excluded the possibility that CsA increased sensitivity of cells to imatinib by the inhibition of P-gp-mediated drug efflux or by another mechanism involving modulation of intracellular drug concentration.

Mean cell volume can be an early predictor for the cytogenetic response of chronic myeloid leukemia patients treated with imatinib?

Imatinib-induced macrocytic anemia was known to result from c-kit inhibition in chronic myeloid leukemia (CML). However, recent studies showed that the prevalence of anemia is increased with high trough imatinib level and increased doses of imatinib influence decreased proliferation of burst forming units-erythroids (BFU-Es). The aim of this study was to evaluate the continuously increased mean cell volume (MCV) level's correlation with cytogenetic response and the favorable outcome in early chronic phase (CP)–CML patients.Clinical importance of MCV level was evaluated to correlate with cytogenetic response and compared with Sokal score, a known excellent prognostic parameter of cytogenetic response (CCR) in 84 early CP–CML patients.The patients with early and continuously increased MCV level irrespective of anemia achieved higher CCR after 12 months of imatinib therapy than patients with non-CCR (p=0.011). When the value was compared with low Sokal score, elevated MCV was independent predictor of CCR (RR=12.925, p=0.002 vs. RR=35.445, p<0.001). Furthermore, the patients with early and continuously increased MCV level had a higher probability of maintaining CCR than non-increased level (p=0.019). Increased MCV level was surrogate marker of achievement and durability to CCR for early CP–CML patients in the present study.

Relationship between an effective dose of imatinib, body surface area, and trough drug levels in patients with chronic myeloid leukemia

The standard dose of imatinib for the treatment of chronic-phase chronic myeloid leukemia (CML) is 400 mg/day. Some patients receive reduced doses of imatinib because of serious adverse effects. Recently, the effective plasma threshold for trough imatinib levels was demonstrated to be 1,002 ng/mL. In this study, we evaluated the association of an imatinib dose with trough plasma concentrations and clinical outcomes in 31 patients with chronic-phase CML who were treated at Kumamoto University Hospital. Twenty-seven patients were optimally treated with various doses of imatinib. The mean (+/-SD) trough plasma concentrations of imatinib were 1.40 +/- 0.57 microg/mL in 13 patients receiving 400 mg/day and 1.15 +/- 0.44 microg/mL in 9 patients receiving 300 mg/day as an effective dose. Mean trough levels of the two groups were not significantly different and exceeded the effective plasma threshold. Body surface area (BSA) was significantly smaller in patients receiving the reduced dose compared with those receiving the standard dose (p = 0.001). The effective imatinib dose was associated with age and gender as well as BSA. A reduced dose of 300 mg/day of imatinib may be sufficient for the treatment of CML patients with smaller body size, particularly when intolerability arises.

Clinical Strategies to Achieve an Early and Successful Response to Tyrosine Kinase Inhibitor Therapy

Imatinib is the standard of care for previously untreated chronic myeloid leukemia (CML), with high response rates that lead to improved event-free and overall survival compared with interferon alfa. Imatinib dose is one important factor affecting response, and early clinical studies showed promising molecular response rates with high-dose therapy. Large, randomized trials are now ongoing to test this potential benefit and establish whether a starting dose of 800 mg/d improves long-term clinical outcomes compared with the current standard dose of 400 mg/d. Low plasma imatinib levels are associated with a decreased chance of response. The importance of imatinib dosing and plasma levels is likely due to their impact on intracellular concentrations of the drug. Cellular influx of imatinib is mediated by the OCT-1 protein, and patients with low OCT-1 activity may benefit from dose-intensive therapy. For nonresponding or slowly responding patients, dose escalation to 600 to 800 mg/d may lead to durable responses in patients with primary or secondary resistance. Regular monitoring of response is crucial to maximize therapeutic success, and improved understanding of the factors affecting response will guide future clinical strategies.