Imatinib Levels Research Articles

Long-term efficacy of imatinib in a practical setting is correlated with imatinib trough concentration that is influenced by body size: a report by the Nagasaki CML Study Group

Imatinib has dramatically improved long-term survival of chronic myelogenous leukemia (CML) patients. To analyze its efficacy in a practical setting, we registered most of CML patients in Nagasaki Prefecture of Japan. Of these, 73 patients received imatinib as an initial therapy. The overall survival rate of these patients was 88.7% at 6 years, and the cumulative complete cytogenetic response rate was 82.5% at 18 months. These results are comparable with the data of other reports including the IRIS study; however, the administered imatinib dose was smaller in our study than that in other reports. To address these discrepancies, we measured the trough concentration of imatinib among 35 patients. Although 39% of the patients were administered less than 400 mg/day, the trough level was comparable to those of previous reports. The trough level of imatinib showed a significant relationship with its efficacy, and was clearly related to dose of imatinib administrated and dose of imatinib divided by body surface area (BSA). Considering the smaller BSA of Japanese patients as compared to those of foreign origin, the results suggest that a lower dose of imatinib could maintain enough trough level and provided excellent results for the treatment of CML in our registry.

Drug monitoring of imatinib levels in patients undergoing therapy for chronic myeloid leukaemia: comparing plasma levels of responders and non-responders

Imatinib mesylate is used as first line therapy in the treatment of chronic myeloid leukaemia. This study was designed to study the correlation of plasma levels of imatinib with response to the therapy. A total of 40 chronic myeloid leukaemia patients in the chronic phase of the disease were recruited and placed into two groups of 20 patients: imatinib responders and imatinib non-responders, respectively. Each blood sample was taken 24 h after and immediately prior to taking a 400 mg oral dose of imatinib. Drug levels were detected by high-performance liquid chromatography. The mean plasma imatinib levels in the imatinib non-responders were significantly lower than those in the imatinib responders (0.70 vs. 2.34 microM, respectively; p = 0.002). Plasma levels of imatinib were correlated with response to the therapy, so routine monitoring of the therapeutic levels of the drug should be carried out specifically in treatment-resistant cases for determining dose escalation.

Imatinib Trough Plasma Concentration and Its Correlation with Clinical Response in Chronic Phase and Accelerated Phase of CML

Introduction: Imatinib mesylate trough plasma level is suggested to be one of the determinants of clinical efficacy in the treatment of patients with CML. Maintaining an imatinib trough level at or higher than 1000 ng/mL is suggested to be important for achieving optimal response.Aim: Evaluation of clinical relevance of monitoring imatinib trough plasma level.Material: Forty-seven imatinib treated CML patients (23 male/24 female, mean age 50±15.8 (SD) years) were included. Fifty one blood samples for pharmacokinetic analysis were taken. Patients treated with 400 mg of imatinib were in the first chronic phase. Patients treated with 600 mg of imatinib were in the first chronic phase resistant to imatinib 400 mg (loss of cytogenetic response) or accelerated phase at diagnosis. Mean imatinib treatment duration was 20 months (range 0.75–84 months). Blood samples were collected at 24 hours (most within ±3 hours) after the last dose of imatinib (steady state trough level).Results: Mean trough imatinib plasma levels (Cmin) in patients treated with 400 mg and with 600 mg were 1102±574 (SD) ng/mL (females 1091ng/mL, males 1118 ng/mL) and 1337±577 (SD) ng/mL (females 1498 ng/mL, males 1287 ng/mL) respectively. In patients treated with 400 mg of imatinib optimal response was achieved in 82.8% (N=29) with Cmin=1153 ng/mL (range 370 –2524). Suboptimal response was achieved in 2.8% (N=1) of patients with Cmin=820 ng/mL. Resistance was showed in 14% (N=5) with Cmin=865 ng/mL (range 10–2436). In patients achieving CCyR and MMR Cmin was 731.4 ng/mL and 1305 ng/mL respectively. In patients treated with 600 mg of imatinib optimal response was achieved in 58.8% (N=10) with Cmin=1358 ng/mL (range 790–2133). Suboptimal response was achieved in 11.7% (N=2) of patients with Cmin=1347 ng/mL (range 1302–1392). Resistance was found in 17.6% (N=3) with Cmin=1007 ng/mL (range 250–2085). There was no correlation between Cmin and age, body mass or body surface area.Discussion: Imatinib is the drug of choice for most patients with chronic and accelerated phase of CML. The mechanisms of resistance to imatinib are being investigated and the issue of non-compliance is considered. The data presented confirms the opinion that mean imatinib trough plasma level results should be analyzed together with other clinical data. In previous papers the importance of imatinib concentration monitoring in compliance evaluation was emphasized. The analysis presented suggests moreover considerable value of imatinib serum level monitoring in early diagnosis of resistance to treatment when analyzed together with fluctuations of the transcript level. High serum imatinib levels in resistant patients provide other than noncompliance mechanisms of resistance. Isolated cases when CMR is achieved and imatinib level is significantly below desirable value (581 and 383 ng/mL) remain remarkable. Imatinib serum level monitoring may appear particularly useful in monitoring of response in slow responders, when CCR and MMR is achieved beyond 12 months and 18 months of treatment respectively.Conclusions: The data presented confirms the importance of monitoring imatinib trough plasma level as an adequate evaluation of treatment efficacy and allows taking optimal therapeutical decisions when considered together with cytogenetic and molecular assessments.

CML Patients with Low OCT-1 Activity Achieve Better Molecular Responses on High Dose Imatinib Than on Standard Dose. Those with High OCT-1 Activity Have Excellent Responses on Either Dose: A TOPS Correlative Study

We have previously demonstrated in CML patients enrolled to the Australian TIDEL trial, (600mg imatinib upfront in newly diagnosed patients) that patients with high OCT-1 activity, measured in patient blood mononuclear cells prior to imatinib start, achieve a superior molecular response, compared to those with low OCT-1 activity 1. Furthermore, the impact of low OCT-1 activity could be partially overcome with increased imatinib dose. We now prospectively test the predictive value of OCT-1 activity on the achievement of a major molecular response (<0.1 BCR-ABL IS) by 12 months, in CML patients enrolled to the TOPS trial (randomised 400 vs 800 mg imatinib). A subset of 131 TOPS2 patients had OCT-1 activity measured prior to the start of therapy, as part of the Global Novartis Correlative Science Studies. 41 had high OCT-1 activity (>7.2ng/200,000 cells) as defined in our original study. Patients with high OCT-1 activity had a markedly superior rate of MMR, on either standard or high dose imatinib (table 1). Significantly, a greater proportion of patients with low OCT-1 activity achieved MMR on the high dose arm compared to those on standard dose. This finding was not evident in the high OCT-1 activity group.The % of patients achieving MMR by 12 months (n)TotalLow OCT-1 ActivityHigh OCT-1 Activityp- valueTotal48% (90)90% (41)<0.001400mg59% (34)24% (17)94% (17)<0.001800mg62% (97)53% (73)87% (24)0.044p-value0.270.0120.64Table 1: The % of patients achieving MMR based on OCT-1 activity and Randomised dose.The median OCT-1 activity for those patients achieving a MMR (n=80) was 6.05ng/200,000 cells compared to 3.9 for those patients failing to achieve MMR (n=51:p=0.003). Of the 131 patients, trough imatinib levels were available on 61. A greater proportion of patients with a trough imatinib plasma level of >1000ng/ml 3 (n=50) at 1 month achieved MMR (88%) compared to those with plasma levels of <1000ng/ml (n=11:45%: p=0.032). Importantly, OCT-1 activity is not significantly different comparing those patients with trough levels >1000ng/ml (5.6ng/200,000 cells) at 1 month to those with lower trough levels (7.3ng/200,000 cells: p=0.117). This indicates that OCT-1 activity is not providing a surrogate marker of imatinib PK. Dividing the imatinib PK data into quartiles, there is no significant difference in the % of patients achieving MMR based on trough imatinib levels, in patients with high OCT-1 activity. In contrast significantly fewer patients with low OCT-1 activity and low trough levels achieve MMR by 12 months. (Table 2)The % of patients achieving MMR by 12 months (n)Imatinib PK (ng/ml)TotalLow OCT-1 ActivityHigh OCT-1 ActivityP valueQuartile 1 <160047% (15)12% (8)86% (7)0.013Quartile 2 >1600 <250080% (15)67% (6)89% (9)0.469Quartile 3 >2500 <350080% (15)77% (13)100% (2)0.654Quartile 4 >350075% (16)60% (10)91% (6)0.559Table 2: The percentage of patients achieving MMR based on quartile analysis of imatinib PK at day 29In the Australian cohort of 60 patients where detailed molecular response data is available the median molecular response in the 4 subgroups at 12 months shows a significant difference between the 400 mg group with low and high OCT-1 activity (Median BCR-ABL 0.2% IS v 0.02% IS p=0.03) but no difference in the 800 mg groups (low OCT-1 activity v high Median BCR-ABL 0.05% IS v 0.03% IS p=0.139). These analyses support our original proposal that OCT-1 activity defined at diagnosis has a major impact on molecular response and raises the possibility of patient-specific dosing. Patients with low OCT-1 activity are likely to achieve superior molecular responses if they receive imatinib at doses greater than 400 mg, whereas we could not find evidence of a molecular benefit to high dose imatinib for patients with high OCT-1 activity. The clinical value of monitoring trough imatinib drug levels remains to be clearly defined but it is likely to be greatly enhanced if it assessed in the context of the patient's OCT-1 activity.

Imatinib (IM) Pharmacokinetic (PK) Exposure and Its Correlation with Clinical Outcome in Patients with Chronic-Phase Chronic Myeloid Leukemia (CML-CP) for 400 Mg and 800 Mg Daily Doses (Tyrosine Kinase Dose Optimization Study [TOPS

Background: Correlation between IM plasma level and clinical response has been previously reported [Larson et al., Picard et al.]. TOPS is an open-label, randomized, multicenter Phase III study investigating whether 800 mg of IM (400 mg twice daily) results in an improved efficacy compared with 400 mg daily IM in newly diagnosed, previously untreated CML-CP. This analysis reports IM trough plasma levels (Cmin) at both doses and their correlation with clinical response and safety parameters.Methods: IM PK trough samples were collected at time 0 (predose), and following 1, 6, 9, and 12 month treatment for both 400 mg/day (mg/d) and 800 mg/d arms. Plasma concentrations of IM and CGP74588 (major metabolite) were determined by a validated LC/MS/MS (liquid chromatography and tandem mass spectrometry) method. Correlation of IM exposure with clinical response (major molecular response [MMR] rates and time to first MMR) was assessed by grouping patients into quartiles based on their measured IM Cmin levels in month 1. For correlation with frequency of adverse events [AEs], an average Cmin (aCmin) over 12 months corrected for dose intensity was used for the analysis. Correlations were assessed for the entire evaluable population and for each dose group separately.Results: IM PK exposure was proportional to dose and stable over time. For the 400 mg/d dose (n=78–87), the median IM Cmin values at month 1, 6, 9, and 12 were 1190, 1060, 1210, and 1295 ng/mL, respectively; and for the 800 mg/d dose (n=148–167) the corresponding Cmin values for each month were 2720, 2340, 2170, and 2150 ng/mL, respectively. The intra-patient variability (CV%) was low and similar between the 400 mg/d and 800 mg/d doses, 25% and 27%, respectively. The inter-patient variability (CV%) was 38% for 400 mg/d and 58% for 800 mg/d. Despite this inter-patient variability there was a strong correlation between IM Cmin at month 1 (Table 1) and time to MMR or MMR at 3, 6, 9 and 12 months.Table 1: MMR rates over 12 months based on month 1 IM Cmin quartiles for evaluable patients with PK dataMMR Rate* (%)Relative benefit (Fishers Exact Test p-value)Month of treatment (No. of evaluable patients)IM Cmin Q1 <1165 ng/mLIM Cmin Q2-Q3 1165–3180 ng/mLIM Cmin Q4 >3180 ng/mLQ2-Q3 vs Q1Q4 vs Q1Month 3 (218)0/54 (0%)15/108 (14%)10/56 (18%)NA (0.0027)NA (0.0013)Month 6 (208)8/51 (16%)38/103 (37%)22/54 (41%)2.35 (0.0084)2.60 (0.0052)Month 9 (212)21/57 (37%)60/103 (58%)29/52 (56%)1.58 (0.013)1.51 (0.0561)Month 12(214)21/56 (38%)62/107 (58%)30/51 (59%)1.55 (0.0142)1.57 (0.0338)*No. of patients achieving MMR/total number of patients evaluable at each visitBased on the evaluable population at month 12, patients with higher Cmin at month 1 (>1165 ng/mL, Q2-Q4) achieved MMR faster than patients with lower Cmin (<1165 ng/mL, Q1) (P=0.0149). The MMR rate at 12 months was 58% for Q2-Q4 group and 38% for Q1 group (P=0.0263). In the 400 mg/d group, the MMR rate at month 12 was 24% for patients with Cmin below 851 ng/mL (Q1 for 400 mg/d), compared to 56% for patients with Cmin above 851 ng/mL (Q2-Q4; P=0.0207). In the 800 mg/d arm, the overall MMR at 12 month was 50%, and no significant differences were observed between different Cmin quartiles, although it should be noted that the majority of patients (88%) at this high dose level achieved a Cmin above 1165 ng/mL as compared with 52% for the 400 mg/d group. Using aCmin over 12 months as a rough estimate of exposure including dose changes, a slightly higher incidence of all grade AEs for the most frequently reported AEs such as rash, diarrhea, fatigue, and all cause edema, was observed in patients in the highest quartile but no significant differences in the frequency of grade 3/4 AEs were observed.Conclusion: In TOPS, IM plasma trough level was proportional to dose and stable over time despite a high inter-patient variability which may have been attributable to dose changes. Patients with a IM Cmin in the lowest quartile showed a lower MMR rate at 12 months, whereas patients in the highest aCmin quartile showed a higher frequency of all grades of some AEs. The TOPS trial confirms previous observations that IM Cmin of approximately <1000 ng/mL are associated with poorer outcomes. Monitoring IM levels can provide an added benefit to CML patients on IM to achieve the best clinical outcomes.

The M351T BCR-ABL Kinase Mutation Is Uncommon in Asian Patients with Imatinib-Resistant Chronic Myeloid Leukemia: Possible Relationship with Imatinib Plasma Levels.

To date, more than 50 BCR-ABL kinase domain mutations have been described in patients with imatinib-resistant (IM-R) chronic myeloid leukemia (CML) and 66% of these reported cases have mutations occurring at seven amino acid substitutions (G250, Y253, E255, T315, M351, F359 and H396) (Apperley JF. Lancet Oncol. 2007; 8:1018–29). These data have been derived from a predominantly Caucasian population and the pattern of mutations among Asian patients has not been well characterized. In this study, direct sequencing of the BCR-ABL kinase domain was performed in 94 IM-R CML patients of different Asian ethnicities (52% Chinese, 19% Malay, 18% Indian and 11% of other Asian ethnic origins). The median age at diagnosis of CML was 43 years with 90% diagnosed in the chronic phase (CP), 3% in the accelerated phase (AP) and 7% in blast crisis (BC). At diagnosis, 16% had a low Sokal score, 29% an intermediate score and 54% a high score. At the time of mutation analysis, the median duration of disease was 35 months (1–192) and 56% were in CP, 16% in AP and 28% in BC. The median dose of imatinib (IM) was 600 mg OD and the median duration of treatment was 24 months (1–80). Primary IM resistance occurred in 64% and 36% had acquired resistance. The incidence of mutations detected is listed in the table below. A total of 46 BCR-ABL kinase domain mutations were detected in 42 patients. Three patients had more than 1 mutation. Compared to the reported incidence of mutations in the Caucasian population, the distribution of mutations in our study cohort was fairly similar with 55% of the mutations occurring at six amino acid substitutions (G250, Y253, E255, T315, F359 and H396). A significant difference is the absence of M351T mutation which accounts for approximately 10% of mutations detected in the Western population (p=0.017, Fisher's exact test). This mutation has a low level IM-insensitivity (cellular proliferation IC50 = 880 nM) and is thought to be associated with a loss of function and may be selected on drug exposure (Griswold IJ. Mol Cell Biol. 2006; 26:6082–93). A possible hypothesis for the absence of the M351T mutation in our population is that, at the same doses of IM, plasma IM levels in Asian patients are higher than that of Caucasian patients, thus resulting in the suppression of this low level IM-insensitive mutation but not of the high level IM-insensitive mutations. Pharmacokinetic analysis in a separate cohort of 27 patients treated with IM 400 mg OD in our institution revealed a mean steady-state plasma trough level of 2782 ng/ml. This level is higher than the level of 979 ng/ml reported in patients from the IRIS trial which enrolled a predominantly Caucasian population (Larson RA. Blood 2008; 111:4022–28). Our study suggests that the incidence of certain BCR-ABL kinase domain mutations may vary in different ethnic origins and that this variation may be related to different pharmacokinetic profiles. This observation may have important implications for planning and monitoring the ideal therapeutic IM dose for CML patients from different ethnicities.Mutationn%Approx reported incidence (%) (Apperley, 2007)T240A12Not reportedM244V244L248V122G250E3710 (incl G250A)Q252H242 (incl Q252R)Y253F/H71511E255K/V61311 (incl E255D/R)T277A12Not reportedE279K24<1L298V12<1T315I4914F317L243 (incl F317C/V)M351T0010E355A/G243 (incl E355K)F359C/V376 (incl F359L)H396R245 (incl H396P)S438C24<1E453K241 (incl E453V)E459K371 (incl E459L)

Influence of Enzyme-Inducing Antiepileptic Drugs on Trough Level of Imatinib in Glioblastoma Patients

Background:Imatinib mesylate is used in combination with hydroxyurea (HU) in ongoing clinical phase II studies in recurrent glioblastoma multiforme (GBM). CYP3A4 enzyme-inducing antiepileptic drugs (EIAEDs) like carbamazepine, phenytoin, and oxcarbazepine - as well as non-EIAEDs like valproic acid, levetiracetam, and lamotrigine - are frequently used in patients with GBM. Since CYP3A4 is the major isozyme involved in the metabolism of imatinib, we investigated the influence of EIAEDs on imatinib pharmacokinetics (pk).Methods:GBM patients received 600 mg imatinib p.o./o.d. in combination with 1.0 g HU p.o./o.d..together with either EIAEDs, non-EIAEDs, or no antiepileptic drug (non-AEDs) comedication. Trough plasma levels of imatinib and its active main metabolite N-desmethyl-imatinib (CGP74588) were determined biweekly in these patients, total 543 samples being collected from 224 patients (up to 6 times / patient). All three groups were compared to each other and with historical pharmacokinetic data obtained from patients with chronic myeloid leukemia (CML).Results:Mean imatinib trough levels in patients not receiving AEDs ( 1404 ng/ml, CV 64%) and on non-EIAEDs (1374 ng/ml, CV 46%) were comparable with mean imatinib trough levels of the historical control group of CML patients (1400 ng/ml, CV 50%). Mean trough levels of imatinib were reduced up to 2.9-fold (477 ng/ml, CV 70%) in patients treated with EIAEDs. Only slight, but although significant differences were observed in the mean trough level of the metabolite CGP74588 between EIAED-, non-EIAED and no-AED patients, 240 ng/ml (CV 57%) , 351 ng/ml (CV 34%) and 356 ng/ml (CV 52%), respectively. The corresponding mean level for CML patients was 300 ng/ml (CV 50%).Conclusion:Significant decreases of imatinib and CGP74588 trough levels were observed for patients receiving EIAEDs. The EIAED-induced reduction in trough imatinib levels can be avoided by switching to non-EIAEDs comedication or compensated by administering higher imatinib doses. In addition these data demonstrate that there is no significant difference in the pharmacokinetics of imatinib between patients with glioblastoma and CML.

Cytogenetic and molecular responses to standard-dose imatinib in chronic myeloid leukemia are correlated with Sokal risk scores and duration of therapy but not trough imatinib plasma levels

Cytogenetic and molecular responses to standard-dose imatinib (IM) were correlated with trough IM plasma levels for 78 patients with chronic myeloid leukemia (CML) after a minimum of 12 months of IM therapy. The mean trough IM plasma level was 1065 ng/ml (range, 203–2910). There was no correlation of mean plasma trough IM levels and complete cytogenetic response (CCR) at 1 year (CCR 1010 ng/ml vs no CCR 1175 ng/ml P = .29) or major molecular response (MMR) (MMR1067 ng/ml vs no MMR 1063 ng/ml P = .74) after a median of 1298 days of IM therapy. CCR and MMR did correlate with Sokal risk scores with the odds of achieving CCR or MMR for a low risk vs high risk score of 10.8 (95% CI 2.2–53.5) and 6.4 (95% CI 1.4–29.4), respectively. Furthermore, a longer duration of IM therapy also was associated with a greater likelihood of achieving MMR ( P = .02).

Identifying the early-onset cases of breast and colorectal cancers most likely to carry a germline mutation in a ‘high-risk’ cancer predisposition gene

Polymorphisms in genes coding for imatinib transporters and metabolizing enzymes may affect imatinib pharmacokinetics and clinical response. Aim of this study was to assess the influence of polymorphisms in MDR1 and CYP3A5 genes on imatinib trough levels, cytogenetic and molecular response in patients with CML. Newly diagnosed patients with chronic-phase CML started on imatinib therapy were enrolled and followed up prospectively for 24 months. The following single nucleotide polymorphisms were genotyped; C1236T, C3435T, G2677T/A in MDR1 gene and A6986G in CYP3A5 gene. Genotyping was done using PCR-RFLP method and validated by direct gene sequencing. Trough levels of imatinib were measured using LC–MS/MS. Cytogenetic response was assessed by conventional bone-marrow cytogenetics. Molecular response was assessed by qRTPCR using international scale. A total of 173 patients were included, out of which 71 patients were imatinib responders, while 102 were non-responders. Marked inter-individual variability in trough levels of imatinib was seen. Patients with GG genotype for CYP3A5-A6986G (P = 0.016) and TT genotype for MDR1-C3435T (P = 0.013) polymorphisms had significantly higher trough levels of imatinib. Patients with AA genotype for CYP3A5-A6986G [RR = 1.448, 95% CI (1.126, 1.860), P = 0.029] and CC genotype for MDR1-C1236T [RR = 1.397, 95% CI (1.066, 1.831), P = 0.06] & MDR1-C3435T [RR = 1.508, 95% CI (1.186, 1.917), P = 0.018] polymorphisms were at high risk for failure of imatinib therapy. Patients with CGC haplotype for MDR1 polymorphisms had significantly lower imatinib trough levels and were at a higher risk of imatinib failure [RR = 1.547, 95% CI (1.324, 1.808), P < 0.001]. GG vs. non-GG genotype for CYP3A5-A6986G [adjusted OR: 0.246; 95% CI (0.116, 0.519); P < 0.001] and TT vs. non-TT genotype for MDR1-C1236T [adjusted OR: 0.270; 95% CI (0.110, 0.659); P = 0.004] & MDR1-C3435T [adjusted OR: 0.289; 95% CI (0.135, 0.615); P = 0.001] polymorphisms were independent factors predicting imatinib response in multivariate analysis. To conclude, MDR1 and CYP3A5 genetic polymorphisms significantly influence plasma trough levels and therapeutic response of imatinib in patients with CML. Genotyping of these polymorphisms could be of value to individualize the therapy and optimize the clinical outcomes.

Trough imatinib plasma levels in patients treated for advanced gastrointestinal stromal tumors evidence of large interpatient variations under treatment with standard doses

10564 Background: Large interpatient variations of trough imatinib level have been reported in patients with CML given imatinib 400- 600 mg/d; moreover, the 24h residual plasma level of imatinib was found correlated with imatinib efficacy. Methods: Trough plasma levels of imatinib were determined by high performance liquid chromatography-tandem mass spectrometry in patients with advanced GIST, seen at IB 24h (imatinib 400 mg/d) or 12h (imatinib 400 mg bid) after the last dose intake. Results: From March 2007 to October 2007, 31 dosages were performed in 24 patients. Imatinib dose was 400 mg/d (median duration 26 months), for 24 determinations, and 800 mg/d for 7 (dose increased for tumor progression in 6). There were 11 female and 13 male patients and the median age was 66 years (range: 45–90); treatment was for liver (6), peritoneal 7) metastasis or both (8); 3 patients had inoperable primaries. Mean and median trough plasma levels were 799 and 450ng/ml (range: 188–3,321) for a prescribed dose of 400 mg/d and 1,778 and 715 ng/ml (range 374–3,349) for 800 mg/d. Five patients are still responders for 5 years or more and 4/5 had imatinib levels >1000 ng/ml. The inter-patient variability was in contrast to low intra- patient variability, except in one patient whose compliance was corrected. Among 4 patients with very low levels (3 with <250 ng/ml at 400 mg/d, and 1 at 374 ng/ml at 800 mg/d), poor compliance to treatment could be suspected in 3 patients; 3 of those patients were imatinib responders. In this series, no relationship between imatinib trough plasma levels and drug interaction was found. Conclusions: In this preliminary study, large inter-patient variations of imatinib trough plasma levels were found. Very low levels suggest a bad compliance to treatment. High trough imatinib levels were found in long-term responders to imatinib. It remains to be determined whether a threshold that is correlated with optimal drug efficacy exists. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Novartis Novartis

Imatinib pharmacokinetics (PK) and its correlation with clinical response in patients with unresectable/metastatic gastrointestinal stromal tumor (GIST)

4523 Background: In the phase II study B2222, 147 pts with unresectable/metastatic GIST were randomized 1:1 to receive imatinib (IM) at 400 vs 600 mg daily. The estimated survival rate at 60 months was 47.6%. We report the PK of IM and the correlation of IM levels with clinical response. Methods: The IM plasma levels were analyzed in a subset of pts (n=73) for whom PK data on day 1 of treatment or at steady state (Day 29) was available (n=34 and 39 for 400 and 600 mg/day, respectively). IM PK was evaluated using a population PK approach. A correlation between IM plasma exposure and clinical outcome was explored by grouping pts into quartiles according to IM trough levels at steady state (Cmin). The clinical outcome parameters evaluated include overall objective responses (OOR=CR+PR), time to progression (TTP), and KIT mutation status. Results: Clinical response tended to correlate with IM trough exposure. OOR was achieved by 8 of 18 (44%) pts in Q1 (Cmin <1,110 ng/mL) compared with 24 of 36 (67%) and 14 of 19 (74%) in Q2-Q3 (≥1,110 - <2,040 ng/mL), and Q4 (≥2,040 ng/mL), respectively (p=0.060 for Q1 vs Q2-Q4). The median TTP was 11.3 months for pts in Q1 and over 30 months for Q2-Q4 (p=0.0029). In pts with GIST with exon 11 KIT mutation (n=39), the OOR was 55.6% for Q1 vs 93.3% for Q2-Q4 (p=0.006). The IM plasma AUC, peak concentration, and Cmin were highly correlated, with IM Cmin having the best correlation with response. Conclusions: Exposure to adequate drug levels of IM appears to correlate with clinical benefit; pts with the lowest IM levels show the lowest OOR and shortest TTP. These results suggest that monitoring IM exposure may be important for optimal clinical outcome. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Novartis Infinity, MedImmune, Novartis, Pfizer Novartis MedImmune, Novartis, Pfizer Infinity, Novartis, Pfizer Infinity, Novartis, Pfizer

Current and emerging tests for the laboratory monitoring of chronic myeloid leukaemia and related disorders

Chronic myeloid leukaemia (CML) is a molecularly defined disease. The BCR-ABL fusion occurs in all cases of classical CML and leukaemic cells express a constitutively activated BCR-ABL tyrosine kinase. Other fusion oncogenes involving tyrosine kinases, including ABL and PDGFRA/B, have been identified, and are associated with leukaemic syndromes that may resemble CML. The discovery and treatment of these related disorders has been facilitated by our detailed understanding of CML. Imatinib mesylate has significantly improved the outcome of patients with CML, but there remains a significant minority of chronic phase CML patients for whom the response to treatment with standard dose imatinib is suboptimal. Cytogenetic and molecular monitoring of the response to treatment provides important prognostic information. Achievement of a major molecular response (MMR) in chronic phase patients treated de novo with imatinib confers near 100% freedom from progression to advanced phase, and MMR is now an important goal of therapy. Standardisation of BCR-ABL molecular monitoring is under way and should enable the accurate and reproducible identification of MMR in laboratories around the world. Point mutations in the kinase domain of BCR-ABL are the most common cause of acquired resistance to imatinib treatment. The susceptibility of a mutation to imatinib, nilotinib, or dasatinib may help to guide changes in therapy in a patient with resistance. In addition to these established methods of monitoring, there are new tests in development that may assist in determining prognosis and optimising therapy. Among patients receiving the same dose of imatinib, the plasma level of imatinib shows considerable inter-patient variation, and there is emerging evidence that higher levels may be associated with improved response to treatment. The intracellular concentration of imatinib also shows considerable variation, most likely related to differences in influx and efflux transport mechanisms. We discuss how these established and emerging assays might be used to optimise the treatment of CML patients.

Imatinib metabolite profiling in parallel to imatinib quantification in plasma of treated patients using liquid chromatography–mass spectrometry

Besides affecting the systemic bioavailability of the parent drug, drug metabolizing enzymes (DMEs) may produce bioactive and/or toxic metabolites of clinical interest. We have investigated the capability to analyze simultaneously the parent drug and newly identified metabolites in patients' plasma by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The anticancer drug, imatinib, was chosen as a model drug because it has opened a new area in cancer therapy and is given orally and chronically. In addition, resistance and rare but sometimes severe side effects have been reported with this therapy. The quantification of imatinib and the profiling of its metabolites in plasma were established following three steps: (1) set-up of a generic sample extraction and LC-MS/MS conditions, (2) metabolite identification by LC-MS/MS using either in vitro incubations performed with human liver microsomes (HLMs) or patient plasma samples, (3) the simultaneous determination of plasma levels of imatinib and 14 metabolites in the plasma samples of 38 patients. Partial or cross method validation has been done and revealed that precise determinations of metabolite levels can be performed whereas pure standards are not available. Preliminary results indicate that the disposition of imatinib and its metabolites is related to interindividual variables and that outlier metabolite profiles can be revealed. This article underscores that, in addition to usual therapeutic drug monitoring (TDM), LC-MS/MS methods can simultaneously record a complete drug metabolic profile enabling various correlation studies of clinical interest.

Pharmacologic markers and predictors of responses to imatinib therapy in patients with chronic myeloid leukemia

Clinical resistance to imatinib often occurs in the absence of a mutation in the BCR-ABL kinase domain. Imatinib is transported out of cells by the efflux transporter ABCB1 (MDR1, whose product is p-glycoprotein). By contrast, the influx transporter, human organic cation transporter 1 (hOCT1) (also known as SLC22A1), transports imatinib into cells. Recent studies have identified that patients with low expression or activity of hOCT1 have a lower probability of achieving a cytogenetic or molecular remission. Prospective studies are currently investigating whether early trends in transporter expression can be used to guide treatment decisions. Plasma imatinib levels are higher in patients responding well to treatment, and may be useful in patients with suboptimal response or dubious compliance. Uptake of the second generation tyrosine kinase inhibitors, dasatinib and nilotinib, is less dependent upon hOCT1. These two drugs may therefore achieve adequate intracellular concentrations even in patients with low hOCT1 expression.

Constitutive Overexpression of P-glycoprotein, Rather than Breast Cancer Resistance Protein or Organic Cation Transporter 1, Contributes to Acquisition of Imatinib-Resistance in K562 Cells

The purpose of this study was to investigate the contribution of drug transporters in acquired imatinib-resistance. Specifically, we focused on the efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), and an influx transporter, organic cation transporter 1 (OCT1). We established imatinib-resistant K562 cells (K562/IM). Real-time PCR or Western blot analyses were performed to examine the mRNA or protein levels. Alamar blue method was used in the cytotoxicity assay. The transport activities and intracellular imatinib levels were measured by flow cytometry and HPLC, respectively. K562/IM displayed a 47-fold increase in resistance to imatinib over the parent K562 cells. Both P-gp and BCRP were overexpressed in K562/IM relative to K562. Furthermore, the intracellular imatinib level was markedly reduced in K562/IM. Interestingly, cyclosporin A, a P-gp inhibitor, but not fumitremorgin C, a BCRP inhibitor, restored both imatinib-sensitivity and the intracellular imatinib level. By contrast, no significant difference in the expression and function of OCT1 was observed between K562/IM and K562. P-gp, rather than BCRP or OCT1, is partially responsible for the development of imatinib-resistance due to constitutive and functional overexpression, leading to reduced intracellular accumulation of imatinib in K562/IM.

New strategies in controlling drug resistance.

Chronic myeloid leukemia (CML) is most often caused by the translocation of chromosomes 9 and 22 to create the fusion protein, BCR-ABL. This constitutively active tyrosine kinase promotes cell division and blocks apoptosis, leading to unregulated growth of hematopoietic stem cells. Imatinib is a small molecule that binds to BCR-ABL at the site in which adenosine triphosphate (ATP) binds and blocks BCR-ABL function by blocking its ability to use ATP. As a front-line therapy, imatinib has been tremendously successful, with 80% to 90% of patients with chronic phase (CP) CML remaining progression free for more than 5 years. Increasingly, however, imatinib-resistant clones are appearing that allow the disease to progress. dealing with the rise of these resistant clones has presented an important challenge to health care providers. To review the mechanisms by which CML becomes resistant to imatinib and to discuss the new therapeutic alternatives to imatinib and when they should be considered. Managed care weighs advances and associated costs to determine the introduction of imatinib has indefinitely lengthened the survival time of patients with CML, transforming this into a chronic disease condition. However, care must be taken to avoid the appearance of imatinib- resistant clones. resistance can manifest through 1 of several mechanisms, including increased plasma protein binding, increased drug efflux, the appearance of BCR-ABL mutants that have low affinity for imatinib, the appearance of BCR-ABL independent proliferation signals, and the amplification of the BCR-ABL gene. Subtherapeutic dosing is highly likely to result in the selection of a resistant clone; thus, it is of paramount importance to ensure the imatinib dose is sufficient. Measurements of plasma levels of imatinib are proving to be predictive of outcomes, suggesting that the monitoring of imatinib levels will be an important and necessary aspect of monitoring disease. Several clinical trials have shown that high-dose imatinib provides greater and faster response rates. This also may lead to better long-term blockade of disease progression. waiting until disease progression begins appears to lead to greater resistance to high-dose imatinib and should be avoided. dasatinib is a next-generation kinase inhibitor that binds to both SrC and to multiple conformations of BCR-ABL. It is capable of blocking several BCR-ABL mutants that are resistant to imatinib. Clinical trials have shown dasatinib is effective in maintaining patients in CP and can return a percentage of patients with advanced CML to CP. economic analysis indicates that the cost-efficacy ratio for imatinib is approximately $40,000 per year and compares favorably with the costs of accepted procedures, such as dialysis. data have shown that tyrosine kinases also have better mortality rates than allogeneic bone marrow transplant for the first 8 years and appear to also be more cost-effective than transplantation for this time frame. New clinical data are beginning to supply us with effective dosing and monitoring parameters for imatinib and dasatinib treatment of CML. economic analysis indicates that these therapies are acceptable in cost and effective in providing good quality of life to patients.

To assess the response and toxicity of imatinib mesylate and low-dose cytarabine in imatinib non-responder chronic myeloid leukemia, chronic phase (CML-CP) patients: A pilot study

17507 Background: To overcome primary imatinib mesylate (Gleevec ) resistance, we used a combination of imatinib mesylate and low dose cytarabine to treat patients of CML-CP. Methods: Between January 2005 and July 2006, 30 patients (median age 34 years, range 20 to 57 years, M:F ratio 5:1) were enrolled. 2/30 patients had primary hematological and 28/30 had primary cytogenetic resistance. 7 patients had been pretreated with interferon alpha. Treatment consisted of imatinib 400mg daily and cytarabine 10mg subcutaneous daily for 10 days every month. Median of 5 cycles (range 3–6) was administered. Patients were monitored on outpatient basis with weekly blood counts. Bone marrow cytogenetics was done 3 monthly to assess cytogenetic response (CGR). Toxicity was recorded as per NCI CTC (version 2). Primary end points were response and toxicity at the end of 6 cycles. We measured plasma imatinib levels by HPLC in 20 of these patients (J Chromatography B 2004;84:431–34) and compared the levels with 20 patients who were imatinib responders. Results: 11/30 (37%) patients obtained major CGR including complete CGR in 6/30 (20%). None of the patients with primary hematological resistance responded. Grade 3/4 hematological and non hematological toxicities were seen in 3.33% (n=1) and6.66% (n=2) patients respectively. 8/30 (27%) patients discontinued treatment due to reversible cardiac arrest (n=1), hepatitis (n=1), progression to BC/AP (n=2), grade 4 thrombocytopenia (n=1), loss of CHR (n=2), and consent withdrawl (n=1). The mean plasma imatinib levels in non responders were significantly lower, compared to imatinib responders (0.70 micro moles vs 2.34 micro moles, p=0.002). Conclusions: Present study confirms the activity of low dose cytarabine and imatinib in patients having primary cytogenetic resistance. The reasons for low plasma imatinib levels among non responders and methods to circumvent so as to achieve higher plasma levels of imatinib needs further study. No significant financial relationships to disclose.

Biochemical evidence of tumor response and measurable levels of the drug in glioblastoma tissue from patients treated with imatinib

2023 Background: Glioblastoma multiforme (GBM) carries a grave prognosis. There are phase I-II studies indicating that imatinib is active in GBM in pre-treated patients. To better understand the molecular basis of imatinib’s activity in this disease we performed a pharmacodynamic neoadjuvant study with imatinib in GBM. Methods: Patients underwent CT guided biopsy of their brain tumors. If diagnosed with GBM they were immediately treated with 7 days of imatinib 400mg po BID followed by either definitive surgery or, if that was not feasible, followed by re-biopsy. Corticosteroid dose was stable during this period and valproic acid was the only anti-epileptic drug allowed in order to avoid pharmacokinetic interaction with imatinib. Treatment after recovery was as per usual institutional policy. Pre and post treatment tissue specimens were analyzed by immunohistochemistry, proteomic technology and molecular biological methods. Pharmacokinetic studies were also performed. Results: Twenty patients were enrolled in 2 institutions with a median age of 64, of which 14 were male and 6 female. PS was 0 in 2, 1 in 9 and 2 in 9. Seventeen patients had pure GBM, 2 had mixed GBM with astrocytoma and one had anaplastic astrocytoma. Eighteen patients had stable disease on pre and post treatment MRI, one had progressed and one was not evaluable. Median survival was 6.2 months (1.1–18mo). Intact imatinib was quantified in the post treatment tissue specimens and correlations were made with serum imatinib levels per patient. No correlation was seen. Tissue specimens were analyzed by in situ MALDI mass spectroscopy and differential protein expression profiles were detected, when pre and post treatment specimens were compared. The identification of candidate proteins is ongoing. In 11 patients with evaluable, high-quality, matched pre and post imatinib biopsies, 4 had biochemical evidence of tumor response (decreased AKT or MAPK, or increased p27). In addition, 2 patients showed high-level EGFR activation, and one patient had high-level PDGFR activation. Conclusions: Treatment of GBM patients with imatinib results in measurable levels of the drug in the tumor. Potential indicators of biochemical response in a subset of patients were identified. No significant financial relationships to disclose.

Correlation of Pharmacokinetic Data with Cytogenetic and Molecular Response in Newly Diagnosed Patients with Chronic Myeloid Leukemia in Chronic Phase (CML-CP) Treated with Imatinib - An Analysis of IRIS Study Data.

A total of 551 pts with newly diagnosed CML-CP received imatinib (IM) 400 mg orally once daily as part of the IRIS study (O'Brien et al, NEJM 2003). We now summarize the correlation of clinical responses with the steady-state trough plasma concentrations (Cmin) of IM and its major active metabolite CGP74588. Cmin is a reflection of IM clearance and metabolism in CML pts. Trough PK samples (24 hrs post dose) were obtained in IM pts at Day 1 and steady state (Day 29). The plasma concentrations of IM and CGP74588 were determined by liquid chromatography/mass spectrometry. Estimated rates of complete cytogenetic response (CCyR - 0% Ph+) and major molecular response (MMR - ≥ 3 log reduction in BCR-ABL/BCR ratio from a standardized baseline value for untreated pts) were given for the lower and upper quartiles (below Q1=25th percentile, above Q3=75th percentile) and the inter-quartile range of PK trough levels. After 4 weeks of IM at 400 mg, the overall mean (±SD, CV%) steady-state trough levels (Cmin) for IM and CGP74588 (n=351 pts) were 979 (±530, 54.1%) and 242 (±106, 43.6%) ng/mL, respectively. Median (Q1–Q3, min-max) values (in ng/mL) were 879 (647–1170, 153–3910) for IM and 223 (169–291, 50–841) for CGP74588. Times to CCyR and MMR within CCyR pts were significantly different between the three groups of IM plasma exposure (low/intermediate/high; p<0.025). The same was observed for CGP74588, since the parent drug and metabolite levels were highly correlated (0.77, Spearman correlation coefficient). Overall, Cmin of IM was statistically significantly higher in pts who achieved CCyR (1009±544 ng/mL vs. 812±409 ng/mL, p=0.0116). The estimated MMR rate among all pts was significantly lower in pts with low IM levels: only an estimated 59%x43%=25% of all pts with IM levels <647 ng/mL achieved a MMR at 1 year (yr), compared to 40% of all other pts. By 4 yrs an estimated 53% achieved MMR despite low steady state Cmin levels compared with 80% for pts with high Cmin (and 72% for pts within inter-quartile range).CCyR and MMR rates [95% CI] within 1, 2, and 4 yrs by categories of IM trough plasma concentrations measured on Day 29IM trough level< 647 ng/mL (Q1) N = 87647–1170 ng/mL N = 178> 1170 ng/mL (Q3) N = 86CCyR (%)− 1 yr59 [48, 70]71 [64, 78]73 [63, 83]− 2 yrs73 [63, 83]80 [73, 86]84 [75, 92]− 4 yrs81 [71, 91]87 [81, 93]89 [82, 96]MMR (%) in pts with CCyR− 1 yr43 [28, 59]56 [47, 66]55 [41, 68]− 2 yrs63 [49, 78]78 [69, 86]86 [76, 96]− 4 yrs65 [50, 80]83 [75, 91]90 [81, 100]The trough plasma level following the 1st dose also showed a correlation with CCyR and MMR responses, but appeared to be less predictive than the trough level at steady state. Although all CML-CP pts had received 400 mg qd IM, CCyR and MMR rates at 1 to 4 yrs were depending on their IM trough level (24 hrs after the last dose) after 4 weeks of IM. Similar results were observed for the major active metabolite of IM. These results suggest that achieving and maintaining an adequate plasma concentration of IM is important for a good clinical response, and that therapeutic drug monitoring could be done by measuring trough levels at steady state conditions.

Therapeutic Drug Monitoring of Imatinib and Impact on Clinical Decision Making.

OBJECTIVES: Imatinib (IM) has demonstrated durable clinical efficacy in the majority of chronic myeloid leukemia (CML) patients. Optimal response may be influenced by multiple innate and external factors, some of which may be controlled by monitoring plasma concentrations of the drug. This abstract reports 6 cases where analyzing plasma IM trough concentrations (Cmin) in patients treated with three commonly used IM doses (400, 600, and 800 mg daily) influenced clinical decision making.METHODS: IM trough blood samples were collected at a time before that day's IM dosing. Plasma concentrations of IM were determined by a validated LC/MS/MS method.RESULTS: In large population studies of CML patients enrolled in Phase I, II, and III clinical trials, the mean Cmin levels of IM at 400 mg qd, 600 mg qd, and 400 mg bid doses were: 981 (±543, 55%, n=394), 1572 (±1032, 66%, n=14), and 3479 (±1264, 36%, n=14) ng/mL, respectively. Large inter-patient variability was shown at all three doses. Of the 6 cases detailed in the table below, 4 (ID 1, 3, 4, and 5) had dose reduction due to tolerability concerns with subsequent improvement of symptoms following dose adjustment. One patient (ID 2) had a dose increase because of a poor qRT-PCR response. Another (ID 6) had a dose increase due to low plasma IM exposure resulting from drug-drug interaction with phenytoin, a known inducer of CYP3A4 (the major metabolizing isozyme for IM). After dose adjustment, all six patients showed good clinical response to IM treatment. The new mean Cmin value in these patients was 2000 (±471) ng/mL, representing a 24% coefficient of variability.CONCLUSIONS: Although the data is limited, IM drug monitoring proved useful in managing tolerability, lack of efficacy, adherence or potential drug interactions that modulate imatinib drug concentrations. More prospective studies are needed to demonstrate the value of IM drug monitoring in routine clinical practice.Patient IDAge, SexCML StageIM Daily Dose1st Cmin (ng/mL)Reason for Dose ChangeNew Dosing RegimenNew Cmin (ng/mL)154, fCP200 mg bid, Jan 033048, Sep 05transfusion-dependent, anemia, Sep 05300 mg, Oct 052130, Jan 0629, fCP300 mg, Jan 05not doneqRT-PCR 0.016, Jan 06400 mg, Jan 062341, Jul 06313, fCP300 mg bid, May 05; 700 mg, Aug 05; 600 mg, Sep 051966, Feb 06nausea, fatigue, arthralgias, myalgia, ongoing400 mg, Mar 061222, May 06467, fCP400 mg, Feb 05not donemyelosuppression, Mar 05200 mg, Mar 051928, May 06553, fCP400 mg, Apr 03; 600 mg, May 03; 800 mg, Jul 04not doneinflammatory pulmonary reaction with shortness of breath; dose held, Mar 05400 mg, Oct 052378, May 06673, mCP350 mg, on phenytoin, Apr 9935, Jun 99stopped phenytoin, Jul 99500 mg, Jul 99not done; qRT-PCR negative, Jul 06CP, chronic phase1