Changes in imatinib plasma trough level during long-term treatment of patients with advanced gastrointestinal stromal tumors: correlation between changes in covariates and imatinib exposure

Changes in imatinib plasma trough level during long-term treatment in patients with intermediate- or high-risk gastrointestinal stromal tumors: Relationship between covariates and imatinib plasma trough level

Background

Imatinib is the first-line adjuvant treatment for gastrointestinal stromal tumors (GISTs). Considering that some studies have suggested that imatinib (IM) plasma trough levels (C_min) change with time, the aim of this study is to assess the changes in IM C_min in patients with GIST in a long-term study and to elucidate the relationships between clinicopathological features and IM C_min.

Methods

In 204 patients with intermediate- or high-risk GIST who were taking IM, IM C_min was analyzed. Patient data were grouped according to the duration of medication (A: 1-3 months, B: 4-6 months, C: 7-9 months, D: 10-12 months, E: ≤12 months, F: 12<-≤36 months, G: >36 months). The correlation between IM C_min at different time stages and clinicopathological characteristics was assessed.

Results

Statistically significant differences were observed between Groups A, C, and D (P = 0.049 and 0.01, respectively). In Group E, IM C_min correlated with sex (P = 0.049) and age (P = 0.029) and negatively correlated with body weight, height, and body surface area (P = 0.007, 0.002, and 0.001, respectively). In Groups F and G, IM C_min was significantly higher in non-gastric operation patients than in patients with gastrectomy (P = 0.002, 0.036) and was significantly higher in patients with the primary sites of others than in the stomach (P < 0.001, = 0.012). In addition, IM C_min was much higher in patients with mutation sites other than KIT exon 11 in Group F (P = 0.011).

Conclusion

This is the first study of IM C_min during the long-term treatment of patients with intermediate- or high-risk GIST. IM C_min was the highest for the first 3 months and then declined, and long-term administration of IM showed a relatively stable plasma trough level. The IM C_min correlated with different clinical characteristics at different durations of medication. This meant that future "trough level-clinicopathological characteristics" analyses should be time-point-specific. We also need to formulate time-specific medication monitoring plans in clinical practice to study disease progression caused by the occurrence of drug resistance.

Determination of the absolute bioavailability of oral imatinib using a stable isotopically labeled intravenous imatinib-d8 microdose

PURPOSE

The aim of this study was to ascertain whether the absolute bioavailability of oral imatinib (Glivec®) during steady state plasma pharmacokinetics in cancer patients could be determined through a concomitant intravenous administration of a single 100 μg microdose of deuterium labeled imatinib (imatinib-d8). Secondly, the usefulness of liquid chromatography-tandem mass spectrometry (LC-MS/MS) was investigated for simultaneous analysis of orally and intravenously administered imatinib.

METHODS

Included patients were on a stable daily dose of 400 mg oral imatinib prior to study participation. On day 1, patients received a 100 μg intravenous imatinib-d8 microdose 2.5 h after intake of the oral dose. Plasma samples were collected for 48 h. Imatinib and imatinib-d8 concentrations were simultaneously quantified using a validated LC-MS/MS assay. The absolute bioavailability was calculated by comparing the dose-normalized exposure with unlabeled and stable isotopically labeled imatinib in plasma.

RESULTS

A total of six patients were enrolled. All patients had a history of gastrointestinal stromal tumors (GIST). The median absolute bioavailability of oral imatinib at steady state was 76% (range 44-106%). Imatinib and imatinib-d8 plasma concentrations were quantified in all collected plasma samples, with no samples below the limit of quantification for imatinib-d8.

CONCLUSION

The absolute bioavailability of imatinib was successfully estimated at steady state plasma pharmacokinetics using the stable isotopically labeled microdose trial design. This study exhibits the use of a stable isotopically labeled intravenous microdose to determine the absolute bioavailability of an oral anticancer agent in patients with LC-MS/MS as the analytical tool.

Imatinib, sunitinib and pazopanib: From flat-fixed dosing towards a pharmacokinetically guided personalized dose

Tyrosine kinase inhibitors (TKIs) are anti‐cancer drugs that target tyrosine kinases, enzymes that are involved in multiple cellular processes. Currently, multiple oral TKIs have been introduced in the treatment of solid tumours, all administered in a fixed dose, although large interpatient pharmacokinetic (PK) variability is described. For imatinib, sunitinib and pazopanib exposure‐treatment outcome (efficacy and toxicity) relationships have been established and therapeutic windows have been defined, therefore dose optimization based on the measured blood concentration, called therapeutic drug monitoring (TDM), can be valuable in increasing efficacy and reducing the toxicity of these drugs.

In this review, an overview of the current knowledge on TDM guided individualized dosing of imatinib, sunitinib and pazopanib for the treatment of solid tumours is presented. We summarize preclinical and clinical data that have defined thresholds for efficacy and toxicity. Furthermore, PK models and factors that influence the PK of these drugs which partly explain the interpatient PK variability are summarized. Finally, pharmacological interventions that have been performed to optimize plasma concentrations are described. Based on current literature, we advise which methods should be used to optimize exposure to imatinib, sunitinib and pazopanib.

Blood neutrophil-to-lymphocyte ratio is associated with prognosis in advanced gastrointestinal stromal tumors treated with imatinib

INTRODUCTION

Neutrophil-to-lymphocyte ratio (NLR) was shown to be prognostic in several solid malignancies. There are limited data about predictive/prognostic value of NLR during targeted therapy of patients with advanced gastrointestinal stromal tumors (GIST). The aim of this study was to asses a clinical value of this ratio in patients with advanced GIST.

METHODS

Between 2001 and 2016, 385 patients with metastatic/unresectable GIST treated initially with imatinib were included in the analysis. In all patients, the NLR was assessed at the baseline, after 3 months of treatment, and upon disease progression (or last observation). The cutoff values for NLR were set at 2.7 and 5.4. Kaplan-Meier survival probability estimation with log-rank test and Cox proportional hazards model were used for analysis.

RESULTS

Median progression-free survival (PFS) on imatinib treatment was 44.8 months, 5-year rate 43%; median overall survival (OS) 87.2 months, 10-year rate 36.3%. NLR >2.7 at baseline was significantly associated with poorer OS and PFS: median OS was 89.3 months (95% confidence interval [CI] 80.2-115) for NLR ratio ≤2.7 vs 59.4 months (95% CI 48.6-82) for NLR >2.7 (p < .001); median PFS was 59.4 vs 32.7 (p < .001), respectively. In multivariate model adjusted for mitotic index and driver mutation in the tumor (KIT exon 11 mutation versus other), NLR ratio was proven to be statistically significant (hazard ratio 1.09; 95% CI 1.01-1.19; p = .030). Among patients with disease progression, NLR >2.7 assessed at the third month of treatment was linked with significantly shorter median time to progression (7.5 vs 19 months).

CONCLUSIONS

Our results demonstrate the usefulness of NLR as a prognostic and predictive marker as well as a marker for treatment monitoring in patients with advanced GIST treated with imatinib.

Prospective Analysis in GIST Patients on the Role of Alpha-1 Acid Glycoprotein in Imatinib Exposure

Background

For imatinib, a relationship between systemic exposure and clinical outcome has been suggested. Importantly, imatinib concentrations are not stable and decrease over time, for which several mechanisms have been suggested. In this study, we investigated if a decrease in alpha-1 acid glycoprotein (AGP) is the main cause of the lowering in imatinib exposure over time.

Methods

We prospectively measured imatinib trough concentration (C_min) values in 28 patients with gastrointestinal stromal tumours, at 1, 3 and 12 months after the start of imatinib treatment. At the same time points, AGP levels were measured.

Results

Overall, imatinib C_min and AGP levels were correlated (r² = 0.656; P < 0.001). However, AGP levels did not fluctuate significantly over time, nor did the change in AGP levels correlate with the change in the imatinib C_min.

Conclusion

We showed that systemic AGP levels are not likely to be a key player in the decrease in systemic imatinib exposure over time. As long as intra-individual changes in imatinib exposure remain unexplained, researchers should standardize the sampling times for imatinib in order to be able to assess the clinical applicability of therapeutic drug monitoring.

Imatinib Pharmacokinetics in a Large Observational Cohort of Gastrointestinal Stromal Tumour Patients

BACKGROUND

Low trough imatinib concentration (C _min) values have been associated with poor clinical outcomes in gastrointestinal stromal tumour (GIST) patients. This study describes the pharmacokinetics of imatinib in a large cohort of GIST patients in routine clinical care.

METHODS

An observational study was performed in imatinib-treated GIST patients. Patient and tumour characteristics were derived from the Dutch GIST Registry and medical records. Imatinib concentrations were measured by liquid chromatography with tandem mass spectrometry. The analyses included the occurrence of a low imatinib C _min (<1000 µg/L), the change in the C _min over time and the correlation between exposure and response.

RESULTS

In total, 421 plasma samples were available from 108 GIST patients. Most patients (79.6 %) received an imatinib dose of 400 mg. The inter- and intrapatient variabilities in C _min were 54 and 23 %, respectively. In the first steady-state sample, 44.4 % of patients presented with C _min values <1000 µg/L; 32.4 % of patients had values <1000 µg/L in >75 % of their samples. Only 33.3 % of patients had C _min values ≥1000 µg/L in all measured samples. No decrease in C _min over time was found (P > 0.05). Fifty-seven (91.9 %) of 62 palliative-treated patients had a tumour response (median C _min 1271 µg/L). Five palliative patients (8.1 %) did not respond (median C _min 920 µg/L). Given the limited number of non-responders in this cohort, no statistically significant association with clinical benefit could be demonstrated.

CONCLUSION

In routine clinical care, one third of GIST patients are systematically underexposed with a fixed dose of imatinib. Prospective clinical studies are needed to investigate the value of C _min-guided imatinib dosing in GIST patients.

A lower dosage of imatinib in patients with gastrointestinal stromal tumors with toxicity of the treatment

This study investigated the efficiency and safety of imatinib in the lower dose (300 mg/d) in patients with gastrointestinal stromal tumor (GIST) who cannot tolerate imatinib in the standard dose (400 mg/d).Steady-state imatinib trough concentration (Cmin) values in 18 patients with GIST who were taking 300 mg/d or 400 mg/d imatinib were measured. The clinical features, toxicity data, and follow-up data were collected.Around 18 patients with GIST were investigated in which 9 patients received 300 mg/d imatinib. The mean imatinib Cmin value of the 18 patients was 1841 ng/mL (1018-3897 ng/mL). The difference between the patients treated with 400 mg/d (n=9) and those treated with 300 mg/d (n = 9), which have imatinib Cmin values of 2122±1003 ng/mL and 1559±478 ng/mL, respectively, was not significant (P = 0.148). In total, 12 of the 18 patients had complete resection of the primary tumor, 8 of whom received postoperative imatinib 300 mg/d. After the average follow-up of 15.4 months, no recurrence was documented. Of the 6 patients with unresected GIST, 1 received imatinib 300 mg/d for 13 months. The tumor size of this patient continued to decrease. In contrast to patients treated with imatinib 400 mg/d, patients treated with imatinib 300 mg/d notably exhibited lesser drug-related side effects.Patients with GIST who exhibited intolerance to the standard dose of imatinib (400 mg/d), a lower dose of 300 mg/d could provide not only sufficient plasma Cmin and good disease control but also the alleviation of the side effects.

Variability in bioavailability of small molecular tyrosine kinase inhibitors

Small molecular tyrosine kinase inhibitors (smTKIs) are in the centre of the very quickly expanding area of personalized chemotherapy and oral applicability thereof. The number of drugs in this class is rapidly growing, with twenty current approvals by both the European Medicines Agency (EMA) and the Food and Drug Administration (FDA). The drugs are, however, generally characterized by a poor oral, and thus variable, bioavailability. This results in significant variation in plasma levels and exposure. The cause is a complex interplay of factors, including poor aqueous solubility, issued permeability, membrane transport and enzymatic metabolism. Additionally, food and drug-drug interactions can play a significant role. The issues related with an impaired bioavailability generally receive little attention. To the best of our knowledge, this article is the first to provide an overview of the factors that determine the bioavailability of the smTKIs.

Controversies in the management of gastrointestinal stromal tumors

Major advances in the medical treatment of gastrointestinal tumors (GISTs) have improved survival for both patients with advanced disease and those diagnosed with high-risk primary tumors. The Consensus approaches to best practice management of gastrointestinal stromal tumors, published in this journal in 2008, provided guidance for the management of GIST to both clinicians and regulatory authorities. Since then, clinical trials have demonstrated the benefit of adjuvant imatinib in high-risk patients, and mature data from advanced GIST studies suggest that a small but significant proportion of patients with advanced disease can achieve long-term benefit with ongoing imatinib treatment. Other evolving management strategies include the controversial use of palliative or debulking surgery to improve outcomes in advanced GIST and the development of promising new multikinase inhibitors, such as regorafenib, which has established benefit in the third-line setting. This review provides an update of recent developments in GIST management and discusses new controversies that these advances have generated.

What are the current outcomes of advanced gastrointestinal stromal tumors: who are the long-term survivors treated initially with imatinib?

The introduction of imatinib to clinical practice revolutionized therapy of advanced gastrointestinal stromal tumors (GIST), but its long-term results have been only just collected. We have attempted to identify factors related to the long-term survival. We have analyzed the data of 430 inoperable/metastatic/recurrent GIST patients treated with imatinib in reference centers, assessed the factors influencing the long-term overall survival (OS), and compared the outcomes in three periods of initiation of imatinib therapy during one decade (2001–2003, 2004–2006, 2007–2010). During analyzed time periods, we have found decrease in median largest tumor size at the start of imatinib therapy: 90.5 mm (2001–2003) versus 74 mm (2004–2006) versus 58 mm (2007–2010) (p = 0.002). Median progression-free survival (PFS) on 1st line imatinib was 37.5 months, without differences in PFS between three groups. Median OS was 5.8 years, 8-year OS rate was 43 %, and no difference in OS was demonstrated for patients treated in analyzed time periods. Independent good prognostic factors for longer OS were as follows: surgery of residual disease, initial WHO performance status 0/1, normal baseline albumin level, and the presence of exon 11 KIT mutations. Current median OS in advanced GIST reaches 6 years. The long-term survivors were characterized by smaller maximal tumors at imatinib start, better blood tests results, better performance status, and the surgical removal of residual disease. The latter might reduce the impact of tumor size and equalize the long-term results of therapy during last decade from introduction of imatinib. After introduction of subsequent lines of therapy (as sunitinib), the effect of primary mutational status on the long-term OS is also less visible.

A long-term prospective population pharmacokinetic study on imatinib plasma concentrations in GIST patients

PURPOSE

Imatinib minimal (trough) plasma concentrations after one month of treatment have shown a significant association with clinical benefit in patients with gastrointestinal stromal tumors (GIST). Considering that a retrospective pharmacokinetic analysis has also suggested that imatinib clearance increases over time in patients with soft tissue sarcoma and GIST, the primary aim of this study was to assess systemic exposure to imatinib at multiple time points in a long-term prospective population pharmacokinetic study. As imatinib is mainly metabolized in the liver, our secondary aim was to elucidate the potential effects of the volume of liver metastases on exposure to imatinib.

EXPERIMENTAL DESIGN

Full pharmacokinetic blood sampling was conducted in 50 patients with GIST on the first day of imatinib treatment, and after one, six, and 12 months. In addition, on day 14, and monthly during imatinib treatment, trough samples were taken. Pharmacokinetic analysis was conducted using a compartmental model. Volume of liver metastases was assessed by computed tomographic (CT) imaging.

RESULTS

After 90 days of treatment, a significant decrease in imatinib systemic exposure of 29.3% compared with baseline was observed (P < 0.01). For every 100 cm(3) increase of metastatic volume, a predicted decrease of 3.8% in imatinib clearance was observed.

CONCLUSIONS

This is the first prospective pharmacokinetic study in patients with GIST, showing a significant decrease of approximately 30% in imatinib exposure after long-term treatment. This means that future "trough level - clinical benefit" analyses should be time point specific. GIST liver involvement, however, has a marginal effect on imatinib clearance.