Trough imatinib plasma levels are associated with both cytogenetic and molecular responses to standard-dose imatinib in chronic myeloid leukemia

Molecular Response to Imatinib and Its Correlation with mRNA Expression Levels of Imatinib Influx Transporter (OCT1) in Indian Chronic Myeloid Leukemia Patients

Background and objectives:

Imatinib mesylate is approved for the treatment of Chronic Myeloid Leukemia (CML). About 20% of patients with CML do not respond to treatment with Imatinib either initially or because of acquired resistance. In addition to mutated BCR-ABL1 kinase, the organic cation transporter1 (OCT1, encoded by SLC22A1) has been considered to contribute to Imatinib resistance in patients with chronic myeloid leukemia (CML). OCT1 has been reported to be the main influx transporter involved in Imatinib uptake into CML cells. To date, only a few studies have been reported on involvement of influx transporters in development of Imatinib resistance. Therefore this study was aimed to determine the expression level of Imatinib uptake transporter (OCT1) in CML patients and to correlate this level with molecular response.

Methods:

One hundred fifty eight patients on Imatinib were considered for gene expression analysis study for OCT1 gene. Total RNA was extracted from peripheral blood mononuclear cells. Complementary DNAs (cDNAs) were synthesized and Real Time Polymerase Chain Reaction (RQ-PCR) was performed.

Results:

High OCT1 expression was present in 81 (51.8%) patients and low OCT1 expression was in 77 (48.7%) patients. Low Sokal risk score group have a significantly high OCT1 expression (p=0.048). The rate of molecular response was higher in those with high OCT1 expression than in those with low OCT1 expression (p=0.05). Both event-free survival and median overall survival were significantly shorter in patients with low OCT1 expressions when compared to the patients with high OCT1 expression (p=0.03 and p=0.05).

Conclusions:

Our findings demonstrated that the mRNA expression level of OCT1 was significantly correlated with molecular response in CML patients. Based on these findings, present study believes that the pre-therapeutic higher expression of OCT1 may help to predict response to imatinib therapy in CML patients.

Simultaneous quantification of imatinib and its main metabolite N-demethyl-imatinib in human plasma by liquid chromatography-tandem mass spectrometry and its application to therapeutic drug monitoring in patients with gastrointestinal stromal tumor

The aim of this study was to improve and validate a more stable and less time-consuming method based on liquid chromatography and tandem mass spectrometry (LC- MS/MS) for the quantitative measurement of imatinib and its metabolite N-demethyl-imatinib (NDI) in human plasma. Separation of analytes was performed on a Waters XTerra RP₁₈ column (50 × 2.1 mm i.d., 3.5 μm) with a mobile phase consisting of methanol-acetonitrile-water (65:20:15, v/v/v) with 0.05% formic acid at a flow-rate of 0.2 mL/min. The Quattro MicroTM triple quadruple mass spectrometer was operated in the multiple-reaction-monitoring mode via positive electrospray ionization interface using the transitions m/z 494.0 → 394.0 for imatinib, m/z 479.6 → 394.0 for NDI and m/z 488.2 → 394.0 for IS. The method was linear over 0.01-10 μg/mL for imatinib and NDI. The intra- and inter-day precisions were all <15% in terms of relative standard deviation, and the accuracy was within ±15% in terms of relative error for both imatinib and NDI. The lower limit of quantification was identifiable and reproducible at 10 ng/mL. The method was sensitive, specific and less time-consuming and it was successfully applied in gastrointestinal stromal tumor patients treated with imatinib.

Imatinib-induced ophthalmological side-effects in GIST patients are associated with the variations of EGFR, SLC22A1, SLC22A5 and ABCB1

Imatinib-induced ophthalmological side-effects, including conjunctiva hemorrhage and periorbital oedema, although very common and still remain relatively little understood. The present study investigated the effects of genetic polymorphisms of drug targets and membrane transporters on these side effects. We found that the minor allele of EGFR rs10258429 and SLC22A1 rs683369 were significant risk determinants of conjunctival hemorrhage with OR of 7.061 (95%CI=1.791-27.837, P=0.005 for EGFR rs10258429 CT+TT vs CC), and 4.809 (95%CI=1.267-18.431, P=0.021 for SLC22A1 rs683369 GG+CG vs CC). The minor allele of SLC22A5 rs274558 and ABCB1 rs2235040 were protective factors to periorbital oedema with OR of 0.313 (95%CI=0.149-0.656, P=0.002 for SLC22A5 rs274558 AA+AG vs GG), and 0.253 (95%CI=0.079-0.805, P=0.020 for ABCB1 rs2235040 CT vs CC). These results indicated that variants in EGFR, SLC22A1, SLC22A5 and ABCB1 influenced the incidence of Imatinib-induced ophthalmological toxicities, and polymorphism analyses in associated genes might be beneficial to optimize Imatinib treatment.

Chronic Myeloid Leukemia in the Era of Tyrosine Kinase Inhibitors: An Evolving Paradigm of Molecularly Targeted Therapy

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm, characterized by the unrestrained expansion of pluripotent hematopoietic stem cells. CML was the first malignancy in which a unique chromosomal abnormality was identified and a pathophysiologic association was suggested. The hallmark of CML is a reciprocal chromosomal translocation between the long arms of chromosomes 9 and 22, t(9; 22)(q34; q11), creating a derivative 9q+ and a shortened 22q-. The latter, known as the Philadelphia (Ph) chromosome, harbors the breakpoint cluster region-abelson (BCR-ABL) fusion gene, encoding the constitutively active BCR-ABL tyrosine kinase that is necessary and sufficient for initiating CML. The successful implementation of tyrosine kinase inhibitors (TKIs) for the treatment of CML remains a flagship for molecularly targeted therapy in cancer. TKIs have changed the clinical course of CML; however, some patients nonetheless demonstrate primary or secondary resistance to such therapy and require an alternative therapeutic strategy. Therefore, the assessment of early response to treatment with TKIs has become an important tool in the clinical monitoring of CML patients. Although mutations in the BCR-ABL have proven to be the most prominent mechanism of resistance to TKIs, other mechanisms-either rendering the leukemic cells still dependent on BCR-ABL activity or supporting oncogenic properties of the leukemic cells independent of BCR-ABL signaling-have been identified. This article provides an overview of the current understanding of CML pathogenesis; recommendations for diagnostic tools, treatment strategies, and management guidelines; and highlights the BCR-ABL-dependent and -independent mechanisms that contribute to the development of resistance to TKIs.

Optimizing the dose in cancer patients treated with imatinib, sunitinib and pazopanib

AIM

Fixed dose oral tyrosine kinase inhibitors imatinib, sunitinib and pazopanib show a high interpatient variability in plasma exposure. A relationship between plasma exposure and treatment outcome has been established, which supports the rationale for dose optimization of these drugs. The aim of this study was to monitor how many patients reached adequate trough levels after therapeutic drug monitoring-based dose optimization in daily practice.

METHODS

A cohort study was performed in patients treated with imatinib, sunitinib or pazopanib of whom follow-up drug levels were measured between August 2012 and April 2016. Patients' characteristics were collected by reviewing electronic patient records. Drug levels were measured using high-performance liquid chromatography coupled with tandem mass spectrometry and trough levels were estimated using a predefined algorithm. Dose interventions were proposed based on trough levels.

RESULTS

In total, 396 trough levels were determined in 109 patients. Median sample frequency per patient was 3. During the first measurement only 38% of patients showed trough levels within the predefined target ranges despite standard dosing; 52% of the patients showed drug levels below and 10% above the target range. In 35 out of 41 patients (85%) dose interventions led to adequate trough levels. Eventually, 64% of the total cohort reached adequate trough levels.

CONCLUSIONS

Dose optimization proved an effective tool to reach adequate trough levels in patients treated with imatinib, sunitinib and pazopanib. The percentage of patients with adequate trough levels increased from 38 to 64%. Therapeutic drug monitoring may add to the improvement of efficacy and reduction of toxicity and costs of these treatments.

An activating mutation of GNB1 is associated with resistance to tyrosine kinase inhibitors in ETV6-ABL1-positive leukemia

Leukemias harboring the ETV6-ABL1 fusion represent a rare subset of hematological malignancies with unfavorable outcomes. The constitutively active chimeric Etv6-Abl1 tyrosine kinase can be specifically inhibited by tyrosine kinase inhibitors (TKIs). Although TKIs represent an important therapeutic tool, so far, the mechanism underlying the potential TKI resistance in ETV6-ABL1-positive malignancies has not been studied in detail. To address this issue, we established a TKI-resistant ETV6-ABL1-positive leukemic cell line through long-term exposure to imatinib. ETV6-ABL1-dependent mechanisms (including fusion gene/protein mutation, amplification, enhanced expression or phosphorylation) and increased TKI efflux were excluded as potential causes of resistance. We showed that TKI effectively inhibited the Etv6-Abl1 kinase activity in resistant cells, and using short hairpin RNA (shRNA)-mediated silencing, we confirmed that the resistant cells became independent from the ETV6-ABL1 oncogene. Through analysis of the genomic and proteomic profiles of resistant cells, we identified an acquired mutation in the GNB1 gene, K89M, as the most likely cause of the resistance. We showed that cells harboring mutated GNB1 were capable of restoring signaling through the phosphoinositide-3-kinase (PI3K)/Akt/mTOR and mitogen-activated protein kinase (MAPK) pathways, whose activation is inhibited by TKI. This alternative GNB1^K89M-mediated pro-survival signaling rendered ETV6-ABL1-positive leukemic cells resistant to TKI therapy. The mechanism of TKI resistance is independent of the targeted chimeric kinase and thus is potentially relevant not only to ETV6-ABL1-positive leukemias but also to a wider spectrum of malignancies treated by kinase inhibitors.

Field-assisted paper spray mass spectrometry for therapeutic drug monitoring: 1. the case of imatinib in plasma

The field-assisted paper spray (FAPS) - mass spectrometric method has been employed to quantify the imatinib (IMT) plasma levels in treated patients. The quantitative measurements have been performed on the collisionally generated fragment at m/z 394 of the protonated molecules of IMT and deuterated IMT (d₃ -IMT), used as internal standard. The FAPS-tandem mass spectrometry (MS/MS) method exhibits some limitations, because of the high number of operative parameters that need to be carefully controlled. For this aim, papers of different geometry, thickness, and porosity were tested. To obtain a more focalized and intense electrical field, a stainless steel needle was mounted axially and placed at 4 kV voltage. The variability observed in the measurements was ascribed either to the inter-individual variability (e.g. the concomitant presence of other compounds such as proteins, lipids, drugs and/or salts in the plasma of different patients) or to the uncontrollable variables in the instrumental set-up (e.g. sample deposition, changes in paper spray conditions). Furthermore, the manual sample deposition and solvent dripping strongly affects the measure reproducibility. Despite this, it is interesting to observe that, once applied in blind on 24 real plasma samples, FAPS-MS/MS led to results analogous to those obtained by the well-consolidated liquid chromatography-MS/MS, even if the mean coefficient of variation % (CV%) values of 20.4% and 2.6% were observed for the two methods, respectively. In conclusion, despite CV values are relatively high, it is worth noting that the FAPS-MS/MS method is much more straightforward, rapid and economical than the liquid chromatography-MS/MS one, and it appears therefore very promising for applications where a high precision is not always a required task, as e.g. in some cases of therapeutic drug monitoring. Copyright © 2017 John Wiley & Sons, Ltd.

An ultra-specific and sensitive sandwich ELISA for imatinib using two anti-imatinib antibodies

The development of an immunoassay for a low-molecular-weight drug first requires the identification of specific antibodies that do not cross-react with the drug's metabolites. If two antibodies can simultaneously recognize the entire structure of the drug, we can then utilize them to establish an ultra-specific sandwich ELISA, free from interference due to the metabolic products of the drug. This paper reports an ultra-specific and sensitive sandwich ELISA for determination of the tyrosine kinase inhibitor imatinib using two anti-imatinib antibodies. The anti-imatinib antibodies were obtained by two partial structures of imatinib as haptens (2-(5-amino-2-methylanilino)-4-(3-pyridyl)pyrimidine and 4-{(4-methyl-1-piperazinyl)-methyl}-benzoate). Under optimized conditions, this sandwich ELISA shows a linear detection range from 64 pg mL^-1 to 8 ng mL^-1, and a limit of detection of approximately 64 pg mL^-1 for 100-μL samples. The ELISA is specific to imatinib and while there was no cross-reactivity with the major metabolite N-desmethyl-imatinib, slight cross-reactivity was found with metabolite pyridine-N-oxide-imatinib. This assay demonstrated significantly lower cross-reactivity with metabolites than competitive ELISAs. Using this assay, drug levels were easily measured in rat blood after oral administration of imatinib via a single dose of 30 mg kg^-1 or 100 mg kg^-1. The levels in rat serum measured by this ELISA were comparable with those measured by HPLC, and there was a strong correlation between the values determined by the two methods (y = 0.983x + 0.081, R² = 0.948). Thus, we have successfully developed the first specific and sensitive sandwich ELISA for imatinib using two anti-imatinib antibodies. This sandwich ELISA will be a valuable tool for therapeutic drug monitoring and pharmacokinetic studies of imatinib.

Suppression of carboxylesterases by imatinib mediated by the down-regulation of pregnane X receptor

BACKGROUND AND PURPOSE

Imatinib mesylate (IM) is a first-line treatment for chronic myeloid leukaemia (CML) as a specific inhibitor of BCR-ABL tyrosine kinase. As IM is widely used in CML, in combination with other drugs, the effects of IM on drug-metabolizing enzymes (DMEs) are crucial to the design of rational drug administration. Carboxylesterases (CESs) are enzymes catalysing the hydrolytic biotransformation of several clinically useful drugs. Although IM is known to inhibit cytochromes P450 (CYPs), its effects on DMEs, and CESs in particular, are still largely undefined.

EXPERIMENTAL APPROACH

Hepatoma cell lines (HepG2 and Huh7) and primary mouse hepatocytes were used. mRNA and protein expression were evaluated by quantitative RT-PCR and Western blot analysis. Reporter luciferase activity was determined by transient co-transfection experiment. Pregnane X receptor (PXR) expression was regulated by overexpression and RNA interference. The activity of CESs was determined by enzymic and toxicological assays. Mice were treated with a range of doses of IM to analyse expression of CESs in mouse liver.

KEY RESULTS

The expression and activity of CESs were markedly repressed by IM, along with the down-regulation of PXR and inhibited expression and activity of CYP3A4 and P-gp.

CONCLUSIONS AND IMPLICATIONS

Down-regulation of PXR mediates IM-induced suppression of CESs. IM may inhibit expression of other genes targeted by PXR, thus inducing a wide range of potential drug-drug interactions during treatment of CML. The data deserve further elucidation including clinical trials.

The clinical relevance of imatinib plasma trough concentrations in chronic myeloid leukemia. A Belgian study

This retrospective multicenter study in patients with chronic myeloid leukemia in chronic phase was undertaken to confirm the clinical relevance of imatinib plasma concentrations monitoring in daily practice. Forty-one patients, with 47 imatinib plasma measurements, were analyzed during treatment with imatinib given at a fixed 400mg daily dose. A significant inverse relationship of imatinib concentration with the patients' weight was observed (Pearson's test: p=0.02, R²=0.1). More interestingly, patients with poor response (switched to another tyrosine kinase inhibitor because of imatinib failure, or because of disease progression after an initial response) displayed a significantly lower mean imatinib concentration as compared to patients maintained on imatinib (822ng/mL vs 1099ng/mL; Student's t-test, p=0.04). Failure or disease progression occurred more often in patients in the lowest quartile of imatinib concentrations compared to patients in the highest quartile (p=0.02, logrank test). No correlation could be established with other biological or clinical parameter, including complete cytogenic response and major molecular response.

IN CONCLUSION

in patients treated with imatinib at a fixed daily dose of 400mg, imatinib plasma concentrations decreased with increasing body weight and were lower in patients switched to another tyrosine kinase inhibitor due to imatinib failure. Systematic determination of imatinib plasma trough levels should be encouraged in such patients.

Trough concentration and ABCG2 polymorphism are better to predict imatinib response in chronic myeloid leukemia: a meta-analysis

AIM

The present study aimed to conduct a series of meta-analyses to investigate the influence of imatinib trough concentration (C₀), as well as ABCB1 and ABCG2 polymorphisms, on the clinical response in patients with chronic myeloid leukemia (CML).

METHODS

A literature search was conducted using the PubMed and Cochrane electronic databases to locate relevant papers from 2003 onward. Then, an initial meta-analysis of 14 studies involving 2184 patients was conducted to understand the effect of imatinib mesylate (IM) C₀ on clinical outcome in CML patients. Subsequently, a series of meta-analyses were performed, including up to 23 studies with 2577 patients, on the effect of genetic polymorphisms of ABCB1 and ABCG2 on the clinical response to IM.

RESULTS

Meta-analysis revealed that patients who achieved a major molecular response (MMR) have a significantly higher IM C₀ than those who failed to achieve an MMR. We also found that the patients who achieved a complete cytogenic response (CCyR) have a significantly higher IM C₀ than those who did not achieve a CCyR. However, no significant difference in IM C₀ was found between the complete molecular response and non-complete molecular response groups. Additional analysis showed that ABCG2 421 variant A allele was significantly associated with a higher rate of MMR and overall response, especially in Asian patients. Meta-analysis did not reveal a correlation between ABCB1 C3435T and C1236T polymorphisms with any clinical response to IM. However, the G2677T/A polymorphism could play a role in IM response in the recessive model.

CONCLUSION

This meta-analysis demonstrates that there was a significant correlation between the IM trough concentration and clinical responses, especially MMR and CCyR, in CML patients. Furthermore, we found that the probability of successful treatment was correlated with the ABCG2 C421A polymorphism, at least within the Asian population. We failed to determine an association between ABCB1 polymorphisms and IM response, although the G2677T/A polymorphism might be involved. However, further large-scale investigations using more sensitive genotyping methods would be required to confirm this.

In Vivo Cytochrome P450 3A Isoenzyme Activity and Pharmacokinetics of Imatinib in Relation to Therapeutic Outcome in Patients With Chronic Myeloid Leukemia

BACKGROUND

Cytochrome P450 3A (CYP3A) isoenzyme metabolic activity varies between individuals and is therefore a possible candidate of influence on the therapeutic outcome of the tyrosine kinase inhibitor imatinib in patients with chronic myeloid leukemia (CML). The aim of this study was to investigate the influence of CYP3A metabolic activity on the plasma concentration and outcome of imatinib in patients with CML.

METHODS

Forty-three patients with CML were phenotyped for CYP3A activity using quinine as a probe drug and evaluated for clinical response parameters. Plasma concentrations of imatinib and its main metabolite, CGP74588, were determined using liquid chromatography-mass spectrometry.

RESULTS

Patients with optimal response to imatinib after 12 months of therapy did not differ in CYP3A activity compared to nonoptimal responders (quinine metabolic ratio of 14.69 and 14.70, respectively; P = 0.966). Neither the imatinib plasma concentration nor the CGP74588/imatinib ratio was significantly associated with CYP3A activity.

CONCLUSIONS

The CYP3A activity does not influence imatinib plasma concentrations or the therapeutic outcome. These results indicate that although imatinib is metabolized by CYP3A enzymes, this activity is not the rate-limiting step in imatinib metabolism and excretion. Future studies should focus on other pharmacokinetic processes so as to identify the major contributor to patient variability in imatinib plasma concentrations.

Pharmaceutical Investigation for Individualized and Optimal Cancer Pharmacotherapy

After the year 2000, the treatment of cancer remarkably changed, including the development of outpatient cancer chemotherapy. Meanwhile, we have encountered many clinical problems related to cancer patient pharmacy services. To resolve these problems, I have tried to establish the individualized and optimal cancer pharmacotherapy utilizing the findings of basic research. In this review, three topics of my research will be introduced. 1) In 2005, information regarding the genetic polymorphism of UGT1A1*28 was described in the package insert of the drug irinotecan in the United States. At that time, however, there was little similar information for Japanese patients. Through clinical research, we demonstrated that UGT1A1*6 was a significant factor for neutropenia, as induced by irinotecan. 2) Tyrosine kinase inhibitors are mainly used at a fixed dose, but wide interpatient variability has been observed relative to their pharmacokinetics and/or pharmacodynamics. To overcome these variations, clinical and basic pharmacological research on erlotinib, sorafenib and sunitinib was carried out. Especially, in sunitinib therapy, we demonstrated that the breast cancer resistant protein in the intestine functions as a limiting factor for oral absorption, and that therapeutic drug monitoring could be helpful for avoiding severe toxicities, resulting in prolonged progression-free survival. 3) We quantitatively assessed side effect management by pharmacist intervention for outpatient chemotherapy. We calculated the improvement ratio between before and after pharmacist intervention, and found that 135 suggestions (50.8%) led to significant improvements, indicating that pharmacist intervention could be useful for attenuating the side effects of cancer chemotherapies.

Pharmacogenetics of drug transporters in modulating imatinib disposition and treatment outcomes in chronic myeloid leukemia & gastrointestinal stromal tumor patients

The use of imatinib in the treatment of BCR-ABL-positive chronic myeloid leukemia and gastrointestinal stromal tumors has significantly improved survival outcomes in patients afflicted by these malignancies. However, a substantial proportion of imatinib-treated patients still experience treatment failure. Suboptimal concentrations of imatinib have been postulated to contribute at least partially to the development of resistance against imatinib. Indeed, variations in the genes encoding drug transporters have been reported to markedly influence imatinib disposition and treatment outcomes in various populations. This review aims to consolidate and critically assess the studies conducted to date which have investigated the influence of pharmacogenetic variants in drug transporters on the disposition of imatinib and treatment outcomes in Asians and other populations.

High-performance Liquid Chromatographic Ultraviolet Detection of Nilotinib in Human Plasma from Patients with Chronic Myelogenous Leukemia, and Comparison with Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND

A method for determining nilotinib concentration in human plasma is proposed using high-performance liquid chromatography and ultraviolet detection.

MATERIALS & METHODS

Nilotinib and the internal standard dasatinib were separated using a mobile phase of 0.5% Na₂ PO₄ H₂ O (pH 2.5)-acetonitrile-methanol (55:25:20, v/v/v) on a Capcell Pak C18 MG II column (250 × 4.6 mm) at a flow rate of 1.0 ml/min, and ultraviolet measurement at 250 nm.

RESULTS

The calibration curve exhibited linearity over the nilotinib concentration range of 50-2,500 ng/ml at 250 nm, with relative standard deviations (n = 5) of 7.1%, 2.5%, and 2.9% for 250, 1,500, and 2,500 ng/ml, respectively. The detection limit for nilotinib was 5 ng/ml due to three blank determinations (ρ = 3).

CONCLUSION

This method was successfully applied to assaying nilotinib in human plasma samples from patients with chronic myelogenous leukemia. In addition, we compared the results with those measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) at BML, Inc. (a commercial laboratory). A strong correlation was observed between the nilotinib concentrations measured by our high-performance liquid chromatographic method and those obtained by LC/MS-MS (r² = 0.988, P < 0.01).

Making the diagnosis, the tools, and risk stratification: More than just BCR-ABL

The implementation of cytogenetic and molecular techniques into standard clinical practice has improved our ability to more accurately diagnose and monitor CML. Routine peripheral blood BCR-ABL transcript testing can help monitor response, predict outcome, and detect early resistance or poor adherence to TKI therapy. The widely-used Sokal, Hasford and EUTOS clinical risk stratification scores were developed in patients receiving chemotherapy, interferon and imatinib, respectively; their predictive ability in patients receiving next-generation tyrosine kinase inhibitors (TKIs) remains to be established. Newer more sensitive molecular techniques are being developed that may aid in the expanding emphasis on discontinuing therapy in patients with a deep and consistent molecular response.

Tyrosine kinase inhibitors in chronic myeloid leukaemia: which, when, for whom?

The therapeutic armamentarium for chronic myeloid leukaemia (CML) comprises mainly tyrosine kinase inhibitors (TKIs), with several agents available for frontline treatment, or for the treatment of disease resistance or intolerance to the first-choice or second-choice drug. The availability of different drugs is a major achievement, but means that choices must be made - which can be difficult and questionable at times. The most important end point considered in decision-making regarding treatment for any cancer is overall survival, but additional factors (such as age, prognostic category, safety, or the possibility of achieving treatment-free remission) should be considered when selecting an agent for frontline treatment. Regardless of the TKI selected for first-line treatment, guidelines that define the importance of reaching specific response indicators and procedures for vigilant follow-up monitoring are established to ensure timely implementation of second-line TKIs. Herein, we discuss the benefits and risks of the different TKIs available for the treatment of patients with CML, and how to decide when to employ these agents at different treatment settings.

Drug-drug interactions with imatinib: An observational study

Many patients treated with imatinib, used in cancer treatment, are using several other drugs that could interact with imatinib. Our aim was to study all the drug-drug interactions (DDIs) observed in patients treated with imatinib.We performed 2 observational studies, between the 1st January 2012 and the 31st August 2015 in the Midi-Pyrénées area (South Western France), using the French health insurance reimbursement database and then the French Pharmacovigilance Database (FPVD).A total of 544 patients received at least 1 reimbursement for imatinib. Among them, 486 (89.3%) had at least 1 drug that could potentially interact with imatinib. Paracetamol was the most frequent drug involved (77.4%). Proton pump inhibitors, dexamethasone and levothyroxine, were found in >10% of patients. In the FPVD, among a total of 25 reports of ADRs with imatinib recorded in the Midi-Pyrénées area, 10 (40%) had potential DDIs with imatinib. Imatinib was most frequently prescribed by hospital physicians and drugs interacting with imatinib, by general practitioners.Our study showed that at least 40% of the patients treated with imatinib were at risk of DDIs and that all prescribers must be cautious with DDIs in patients treated with imatinib. During imatinib treatment, we particularly recommend to limit the dose of paracetamol at 1300 mg per day, to avoid the use of dexamethasone, and to double the dose of levothyroxine.

Therapeutic drug monitoring and tyrosine kinase inhibitors

The therapeutic activity of drugs can be optimized by establishing an individualized dosage, based on the measurement of the drug concentration in the serum, particularly if the drugs are characterized by an inter-individual variation in pharmacokinetics that results in an under- or overexposure to treatment. In recent years, several tyrosine kinase inhibitors (TKIs) have been developed to block intracellular signaling pathways in tumor cells. These oral drugs are candidates for therapeutic drug monitoring (TDM) due to their high inter-individual variability for therapeutic and toxic effects. Following a literature search on PubMed, studies on TKIs and their pharmacokinetic characteristics, plasma quantification and inter-individual variability was studied. TDM is commonly used in various medical fields, including cardiology and psychiatry, but is not often applied in oncology. Plasma concentration monitoring has been thoroughly studied for imatinib, in order to evaluate the usefulness of TDM. The measurement of plasma concentration can be performed by various analytical techniques, with liquid chromatography-mass spectrometry being the reference method. This method is currently used to monitor the efficacy and tolerability of imatinib treatments. Although TDM is already being used for imatinib, additional studies are required in order to improve this practice with the inclusion of other TKIs.

ABCB1 1199G>A polymorphism (rs2229109) affects the transport of imatinib, nilotinib and dasatinib

AIM

ABCB1 (or P-glycoprotein) is implicated in the multidrug-resistance phenotype, including the resistance toward anticancer drugs such as tyrosine kinase inhibitors (TKIs). The purpose of this study was to evaluate in vitro the influence of the ABCB1 1199G>A SNP on ABCB1 transport activity toward selected TKIs (imatinib, nilotinib and dasatinib) that are currently used in chronic myelogenous leukemia.

MATERIAL & METHODS

Two different cell lines, HEK293 and K562, were stably transfected with ABCB1 1199G wild-type or ABCB1 1199A variant allele. The impact of this polymorphism on accumulation and antiproliferative effects of imatinib, nilotinib and dasatinib was evaluated.

RESULTS

In K562 models, the expression of Asn400 variant protein was associated with lower antiproliferative effects of imatinib, nilotinib and dasatinib compared with Ser400 wild-type protein. Moreover, in HEK293 cells, imatinib and nilotinib intracellular accumulation were lower in variant compared with wild-type models.

CONCLUSION

Imatinib, nilotinib and dasatinib are transported more efficiently by the ABCB1 variant (Asn400) compared with the wild-type (Ser400) protein. The impact of ABCB1 1199G>A SNP on TKI response should be further investigated in chronic myelogenous leukemia patients.

Extramedullary Involvement by Chronic Myelogeneous Leukemia in Five Patients With Unusual Clinicopathologic Features: A Review of the Effectiveness of Tyrosine Kinase Inhibitors

Chronic myelogeneous leukemia (CML) is associated with BCR-ABL1 fusion gene leading to an abnormal tyrosine kinase molecule. The accepted first-line treatment is imatinib mesylate (IM). CML uncommonly occurs in the extramedullary sites at initial presentation or relapse. Here we report five adult patients with CML who developed myeloid sarcoma (MS) while on treatment with IM. A retrospective medical chart analysis was performed to identify CML patients with MS who were diagnosed and treated at the University of Alabama at Birmingham. The age ranged between 21 and 36 years (median: 28.5) with a male to female ratio of 4:1. All of the patients were diagnosed with CML in chronic phase with initial treatment including IM. The median interval period between the initial diagnosis of CML and MS was 27 months (range 7 - 60 months). The sites of extramedullary involvement included lymph nodes (n = 2), central nervous system (n = 2) and hepatobiliary organs (n = 1). All patients were treated with either induction therapy or stem cell transplant (SCT) following the diagnosis of MS. The median survival was 16 months (range 1 - 72 months). The longest survival was observed in a patient who successfully received SCT therapy. IM is frequently used as the first therapeutic choice in new diagnosed CML; however, its penetration and effectiveness in extramedullary tissue is still unclear. The current report also supports the literature with less favorable prognosis of CML in younger individuals.

Therapeutic drug monitoring of imatinib, nilotinib, and dasatinib for patients with chronic myeloid leukemia

Imatinib, nilotinib, and dasatinib are tyrosine kinase inhibitors (TKIs) that have become first-line treatments for Philadelphia chromosome-positive chronic myeloid leukemia (CML). According to European LeukemiaNet recommendations, the clinical response of CML patients receiving TKI therapy should be evaluated after 3, 6, and 12 months. For patients not achieving a satisfactory response within 3 months, the mean plasma concentration for the three months of TKI administration must be considered. In TKI therapy for CML patients, therapeutic drug monitoring is a new strategy for dosage optimization to obtain a faster and more effective clinical response. The imatinib plasma trough concentration (C₀) should be set above 1000 ng/mL to obtain a response and below 3000 ng/mL to avoid serious adverse events such as neutropenia. For patients with a UGT1A1*6/*6, *6/*28, or *28/*28 genotype initially administered 300-400 mg/d, a target nilotinib C₀ of 500 ng/mL is recommended to prevent elevation of bilirubin levels, whereas for patients with the UGT1A1*1 allele initially administered 600 mg/d, a target nilotinib C₀ of 800 ng/mL is recommended. For dasatinib, it is recommended that a higher Cmax or C₂ (above 50 ng/mL) to obtain a clinical response and a lower C₀ (less than 2.5 ng/mL) to avoid pleural effusion be maintained by once daily administration of dasatinib. Although at present clinicians consider the next pharmacotherapy from clinical responses (efficacy/toxicity) obtained by a fixed dosage of TKI, the TKI dosage should be adjusted based on target plasma concentrations to maximize the efficacy and to minimize the incidence of adverse events.

An Automated Homogeneous Immunoassay for Quantitating Imatinib Concentrations in Plasma

BACKGROUND

Imatinib pharmacokinetic variability and the relationship of trough concentrations with clinical outcomes have been extensively reported. Although physical methods to quantitate imatinib exist, they are not widely available for routine use. An automated homogenous immunoassay for imatinib has been developed, facilitating routine imatinib testing.

METHODS

Imatinib-selective monoclonal antibodies, without substantial cross-reactivity to the N-desmethyl metabolite or N-desmethyl conjugates, were produced. The antibodies were conjugated to 200 nm particles to develop immunoassay reagents on the Beckman Coulter AU480 analyzer. These reagents were analytically validated using Clinical Laboratory Standards Institute protocols. Method comparison to liquid chromatography tandem mass spectrometry (LC-MS/MS) was conducted using 77 plasma samples collected from subjects receiving imatinib.

RESULTS

The assay requires 4 µL of sample without pretreatment. The nonlinear calibration curve ranges from 0 to 3000 ng/mL. With automated sample dilution, concentrations of up to 9000 ng/mL can be quantitated. The AU480 produces the first result in 10 minutes and up to 400 tests per hour. Repeatability ranged from 2.0% to 6.0% coefficient of variation, and within-laboratory reproducibility ranged from 2.9% to 7.4% coefficient of variation. Standard curve stability was 2 weeks and on-board reagent stability was 6 weeks. For clinical samples with imatinib concentrations from 438 to 2691 ng/mL, method comparison with LC-MS/MS gave a slope of 0.995 with a y-intercept of 24.3 and a correlation coefficient of 0.978.

CONCLUSIONS

The immunoassay is suitable for quantitating imatinib in human plasma, demonstrating good correlation with a physical method. Testing for optimal imatinib exposure can now be performed on routine clinical analyzers.

Molecular response to imatinib & its correlation with mRNA expression levels of imatinib influx & efflux transporters in patients with chronic myeloid leukaemia in chronic phase

Background & objectives:

Imatinib is the standard first-line treatment for chronic myeloid leukaemia (CML) patients. About 20 to 30 per cent patients develop resistance to imatinib and fail imatinib treatment. One of the mechanisms proposed is varying expression levels of the drug transporters. This study was aimed to determine the expression levels of imatinib transporter genes (OCT1, ABCB1, ABCG2) in CML patients and to correlate these levels with molecular response.

Methods:

Sixty three CML chronic phase patients who were on 400 mg/day imatinib for more than two years were considered for gene expression analysis study for OCT1, ABCB1 and ABCG2 genes. These were divided into responders and non-responders. The relative transcript expression levels of the three genes were compared between these two categories. The association between the expression values of these three genes was also determined.

Results:

No significant difference in the expression levels of OCT1, ABCB1 and ABCG2 was found between the two categories. The median transcript expression levels of OCT1, ABCB1 and ABCG2 genes in responders were 26.54, 10.78 and 0.64 versus 33.48, 7.09 and 0.53 in non-responders, respectively. A positive association was observed between the expression of the ABCB1 and ABCG2 transporter genes (r=0.407, P<0.05) while no association was observed between the expression of either of the ABC transporter genes with the OCT1 gene.

Interpretation & conclusions:

Our findings demonstrated that the mRNA expression levels of imatinib transporter genes were not correlated with molecular response in CML patients. Further studies need to be done on a large sample of CML patients to confirm these findings.

[Metastasized renal cell carcinoma. Measurement of plasma levels of the tyrosine kinase inhibitors sunitinib, sorafenib and pazopanib]

BACKGROUND

Several tyrosine kinase inhibitors (TKI) are used in the treatment of metastasized renal cell carcinoma (mRCC). This article presents a feasibility study for the measurement of plasma levels of sunitinib, sorafenib and pazopanib using liquid chromatography tandem mass spectrometry (LC-MS/MS).

METHODS

A total of 23 patients suffering from mRCC under treatment with sunitinib (n=16), sorafenib (n=3) and pazopanib (n=4) were included. Plasma samples (100 µl) were separated by liquid chromatographic analysis and the plasma levels of the TKIs determined by tandem mass spectrometry.

RESULTS

The plasma levels of sunitinib, sorafenib and pazopanib were measurable and the results reproducible. During storage of the plasma samples for 1 week at 4°C no significant decrease of the initial concentration was found. The highest plasma levels detected were 99 ng/ml for sunitinib, 9.8 µg/ml for sorafenib and 63 µg/ml for pazopanib. We could show variability in plasma levels according to changes in dosage of TKIs or during treatment-free intervals.

CONCLUSION

Measurement of TKI plasma levels using LC-MS/MS is feasible. Further clinical studies have to be conducted to examine if there are any threshold levels for the incidence of adverse events or response to treatment.

Association between the concentration of imatinib in bone marrow mononuclear cells, mutation status of ABCB1 and therapeutic response in patients with chronic myelogenous leukemia

Low concentrations of imatinib (IM) in bone marrow cells have been linked with poor prognosis in patients with chronic myeloid leukemia (CML), which may be caused by the emergence of ATP-binding cassette transporter B1 (ABCB1) mutations. The aim of present study was to investigate how clinical outcomes vary among patients with different single nucleotide polymorphisms (SNPs) of ABCB1. A total of 48 adult patients with CML and higher than median ABCB1 mRNA levels were selected for testing of ABCB1 SNPs. In 28 of the 48 patients, the IM concentration and expression levels of human organic cation transporter 1 (hOCT1) and ABCB1 in bone marrow mononuclear cells (BMMCs) were also tested. Correlations between treatment outcomes and IM concentration or the SNP status of ABCB1 were analyzed. Patients were classified by therapeutic response as major molecular response (MMR) (n=11), complete cytogenetic response (CCyR) (n=19) and non-CCyR (n=18) groups. It was found that the concentration of IM in BMMCs of the CCyR group was significant higher than that of the resistant groups (P=0.013). In addition, the IM concentration was positively correlated with the expression of hOCT1 mRNA (R=0.456, P=0.033), but negatively correlated with the expression of ABCB1 mRNA (R=-0.491, P=0.015). Furthermore, the mRNA expression level of ABCB1 was not associated with therapeutic response, but SNPs of the ABCB1 gene were associated with the response to IM. In conclusion, the concentration of IM in BMMCs may be regulated by the ABCB1 gene, and SNPs of the ABCB1 gene predict the therapeutic response to IM in patients with CML.

Pharmacodynamic Biomarker Development for PI3K Pathway Therapeutics

The phosphatidylinositol 3-kinase (PI3K) signaling pathway is integral to many essential cell processes, including cell growth, differentiation, proliferation, motility, and metabolism. Somatic mutations and genetic amplifications that result in activation of the pathway are frequently detected in cancer. This has led to the development of rationally designed therapeutics targeting key members of the pathway. Critical to the successful development of these drugs are pharmacodynamic biomarkers that aim to define the degree of target and pathway inhibition. In this review, we discuss the pharmacodynamic biomarkers that have been utilized in early-phase clinical trials of PI3K pathway inhibitors. We focus on the challenges related to development and interpretation of these assays, their optimal integration with pharmacokinetic and predictive biomarkers, and future strategies to ensure successful development of PI3K pathway inhibitors within a personalized medicine paradigm for cancer.

Relationship between imatinib trough concentration and outcomes in the treatment of advanced gastrointestinal stromal tumours in a real-life setting

BACKGROUND

Imatinib has dramatically improved the prognosis of advanced gastrointestinal stromal tumours (GISTs). Clinical trial data showed that patients with trough imatinib plasma concentrations (Cmin) below 1100 ng/ml (quartile 1) had shorter time to progression, but no threshold has been defined. The main objective of this study was to investigate in advanced GIST whether a Cmin threshold value associated with a longer progression-free survival (PFS) could be specified. This would be the first step leading to therapeutic drug monitoring of imatinib in GIST.

PATIENTS AND METHODS

Advanced GIST patients (n=96) treated with imatinib 400 mg/d (41 stomach, 34 small bowel, and 21 other primary site localisations) were prospectively included in this real-life setting study. Routine plasma level testing imatinib (Cmin) and clinical data of were recorded prospectively.

RESULTS

Small bowel localisation was associated with an increased relative risk of progression of 3.09 versus stomach localisation (p=0.0255). Mean Cmin (±standard deviation) was 868 (±536) ng/ml with 75% inter-individual and 26% intra-patient variability. A Cmin threshold of 760 ng/ml defined by log-rank test was associated with longer PFS for the whole population (p=0.0256) and for both stomach (p=0.043) and small bowel (p=0.049) localisations when analysed separately. Multivariate Cox regression analysis found that Cmin above 760 ng/ml was associated with 65% reduction risk of progression (p=0.0271) in the whole population independently of the anatomical localisation.

CONCLUSION

Concentration of imatinib significantly influences duration of tumour control treatment in GIST patients with a Cmin threshold of 760 ng/ml associated with prolonged PFS in real-life setting.

Routine therapeutic drug monitoring of tyrosine kinase inhibitors by HPLC-UV or LC-MS/MS methods

Analytical methods using high performance liquid chromatography coupled to ultraviolet detection (HPLC-UV) or liquid chromatography-tandem mass spectrometry (LC-MS/MS) have been reported for the quantification of oral tyrosine kinase inhibitors (TKIs) such as imatinib, nilotinib, and dasatinib in biological fluids. An LC-MS/MS method can simultaneously assay multiple TKIs and their metabolites with high sensitivity and selectivity for low plasma concentrations less than 1 ng/mL. For quantification of imatinib, nilotinib, and dasatinib, a limit of quantification (LOQ) of less than 10 ng/mL, 10 ng/mL, and 0.1 ng/mL, respectively, in the clinical setting is necessary. Because simpler and more cost-efficient methodology is desired for clinical analysis, plasma concentrations of imatinib and nilotinib (target trough concentrations of 1000 ng/mL and 800 ng/mL, respectively) could be assayed by an HPLC-UV method after comparison with results obtained from the standard LC-MS/MS method. However, in the quantification of dasatinib, the LC-MS/MS method that has high sensitivity and selectivity and is free from interference by endogenous impurities is superior to the HPLC-UV method. Highly precise analytical methods are needed for individualized treatment via dose adjustment of oral anticancer drugs, in particular those with low target plasma concentrations less than 10 ng/mL.