Abstract
To support a phase III randomized trial of the multi-targeted tyrosine kinase inhibitor cabozantinib in neuroendocrine tumors, we developed a high-performance liquid chromatography mass spectrometry method to quantitate cabozantinib in 50 μL of human plasma. After acetonitrile protein precipitation, chromatographic separation was achieved with a Phenomenex synergy polar reverse phase (4 μm, 2 × 50 mm) column and a gradient of 0.1% formic acid in acetonitrile and 0.1% formic acid in water over a 5-min run time. Detection was performed on a Quattromicro quadrupole mass spectrometer with electrospray, positive-mode ionization. The assay was linear over the concentration range 50–5000 ng/mL and proved to be accurate (103.4–105.4%) and precise (<5.0%CV). Hemolysis (10% RBC) and use of heparin as anticoagulant did not impact quantitation. Recovery from plasma varied between 103.0–107.7% and matrix effect was −47.5 to −41.3%. Plasma freeze–thaw stability (97.7–104.9%), stability for 3 months at −80°C (103.4–111.4%), and stability for 4 h at room temperature (100.1–104.9%) were all acceptable. Incurred sample reanalysis of (N = 64) passed: 100% samples within 20% difference, −0.7% median difference and 1.1% median absolute difference. External validation showed a bias of less than 1.1%. This assay will help further define the clinical pharmacokinetics of cabozantinib.
Introduction
Cabozantinib-S-malate is a multi-targeted tyrosine kinase receptor inhibitor used in the treatment of medullary thyroid cancer and renal cell carcinoma (1, 2). While cabozantinib pharmacokinetics is similar in healthy volunteers and patients with renal cell carcinoma, glioblastoma multiforme, castration-resistant prostate cancer and hepatocellular carcinoma, patients with medullary thyroid carcinoma have an approximately 93% higher apparent oral clearance, resulting in half the steady-state concentrations (3, 4). It is, therefore, important to elucidate the pharmacokinetics of cabozantinib in additional types of cancer where it is being evaluated for its efficacy. To support the use of cabozantinib in a Phase III clinical trial for advanced neuroendocrine tumors (A021602, ClinicalTrials.gov Identifier: NCT03375320), we developed and validated an LC–MS/MS assay to quantitate cabozantinib in human plasma. While some assays for cabozantinib have been reported, to our knowledge, this is the first assay validated to FDA guidance, addressing performance in hemolyzed blood, and incorporating both incurred sample reanalysis and external validation.
Experimental
Chemicals and reagents
Cabozantinib-S-malate (99.6% purity) was purchased from LC Laboratories, (Woburn, MA, USA), and [D4]-cabozantinib (98.9% purity) was purchased from ALSACHIM (Illkirch Graffenstaden, France), see Supplementary Figure 1. Acetonitrile (HPLC grade), water (HPLC grade) and dimethyl sulfoxide (DMSO) were purchased from Fisher Scientific (Fairlawn, NJ, USA). Formic acid was purchased from Sigma-Aldrich (St. Louis, MO, USA). Control EDTA human plasma was purchased from Lampire Biological Laboratories (Pipersville, PA, USA). Nitrogen for mass spectrometric applications was provided by a Nitrogen Generator (Parker Balston, Haverhill, MA, USA).
Chromatography
The LC system consisted of an Agilent (Palo Alto, CA, USA) 1100 autosampler and 1100 binary pump, a Phenomenex (Torrance, CA USA) Synergi Polar-RP 80 Å (4 μm, 50 × 2 mm) column, and a gradient mobile phase. Mobile phase solvent A was 0.1% (v/v) formic acid in acetonitrile, and mobile phase solvent B was 0.1% (v/v) formic acid in water. The initial mobile phase composition was 45% solvent A pumped at 0.4 mL/min. The percentage of A was increased to 90% over 1.5 min. and held at 90% A from 2 to 3 min. Between 3.1 and 5.0 min, the percentage of solvent A was decreased back to 45%, while increasing the flow rate to 0.8 mL/min, resulting in a total run time of 5 min.
Mass spectrometry
Mass spectrometric detection was carried out using a Waters (Milford, MA, USA) Quatt romicro triple-stage, benchtop quadrupole mass spectrometer with electrospray ionization in positive multiple reaction monitoring (MRM) mode. The settings of the mass spectrometer for all analytes were as follows: capillary voltage 4.0 kV; cone voltage 60.0 V; collision voltage 35 V. The source temperature was set at 120°C; the desolvation was set at temperature 450°C, and the cone and desolvation gas flows were 60 and 550 L/h, respectively. Quadrupoles 1 and 3 each had low mass and high mass resolution set at 12.0. The dwell time was 0.2 s, and the interscan delay was 0.1 s. The MRM m/z transitions monitored were: 502.0 > 323.0 for cabozantinib and 506.0 > 323.0 for [D4]-cabozantinib. The basic LC system and mass spectrometer approach and operation with 1/y2 weighted linear regression have been reported previously (5).
Preparation of calibration standards and quality control samples
Stock solutions of cabozantinib were prepared by weighing cabozantinib-S-malate salt and adding DMSO to a final concentration of 1 mg/mL cabozantinib free base. Stock solutions of internal standard [D4]-cabozantinib were prepared at 5 mg/mL in DMSO. The 5 mg/mL [D4]-cabozantinib stock was diluted in acetonitrile to obtain a working solution of 0.1 mg/mL. All stocks were stored at −80°C. On the day of assay, [D4]-cabozantinib was diluted in acetonitrile to acquire a 0.002 mg/mL solution. The 1 mg/mL of cabozantinib was serially diluted (in 10-fold steps) in acetonitrile to obtain the lower calibration working solutions. In a final step, these calibration working solutions were diluted in human plasma to produce the following cabozantinib concentrations: 50, 100, 200, 500, 1000, 2000, 5000 ng/mL. For each calibration series, zero and blank samples were also prepared from control plasma. Quality control (QC) solutions were prepared and stored at −80°C. These solutions were diluted in human plasma to produce the following QC samples of either: Lower Limit of Quantitation (LLOQ) 50 ng/mL, QC Low (QCL) 75 ng/mL; QC Mid (QCM) 750 ng/mL and QC High (QCH) 4000 ng/mL. Stock solutions were verified by duplicate independent preparation from powder. The final concentration of acetonitrile was 5% or less for each calibration point and QC level.
Sample preparation
A volume of 50 μL of the standard, QC, or unknown plasma sample was pipetted into a microfuge tube and 10 μL of internal standard at 2 μg/mL was added to each tube. Next, 200 μL of acetonitrile was added followed by vortexing for 30 s on a Vortex Genie-2 set at 10 (Model G-560 Scientific Industries, Bohemia, NY, USA). Samples were centrifuged at 17 200 × g at room temperature for 10 min. The supernatants were transferred to autosampler vials, followed by injection of 5 μL into the LC–MS/MS system.
Validation procedures
Validation procedures addressed the elements of the FDA Guidance for Industry-Bioanalytical Method Validation (6), including accuracy and precision, selectivity, extraction recovery and matrix effect, and stability. Additional items included the impact of hemolysis, heparin as alternative anticoagulant and dilutional integrity up to 50 000 μg/mL.
Calibration curve and LLOQ
Calibration standards and blanks were prepared (see section Preparation of calibration standards and quality control samples and Sample preparation) and analyzed in triplicate (and in three independent runs) to establish the calibration range with acceptable accuracy and precision, as previously described (5).
Accuracy and precision
The accuracy and precision of the assay were determined by analyzing samples at the LLOQ, QCL, QCM and QCH concentrations (N = 6 per run, three independent runs), as previously described (5, 7).
Selectivity and specificity
Six individual batches of control, drug-free human plasma were processed and analyzed according to the described procedure (see Sections Chromatography, Mass spectrometry, Preparation of calibration standards and quality control samples and Sample preparation). Responses of analytes at the LLOQ concentrations were compared with the response of the blank plasma samples.
Carry-over was assessed by injecting plasma samples with 50 000 ng/mL cabozantinib, followed by serial plasma blank injections.
Extraction recovery and matrix effect
We determined the extraction recoveries and matrix effects from plasma, as previously described (5).
Stability
Long-term stability experiments were performed by comparing with freshly prepared stock solution made from powder. In addition, the stabilities of in stock solution at room temperature for 6 h were determined in replicates of three. All stability testing in plasma was performed in replicates of four or more at the QCL, QCM and QCH concentrations. The stability in plasma at −80°C was determined by assaying samples before and after storage. The effect of three freeze/thaw cycles analyte concentrations on plasma was evaluated by assaying samples after they had been frozen (−80°C) and thawed on three separate days and comparing the results with those of freshly prepared samples. The stabilities in plasma during sample preparation were evaluated by assaying samples before and after 4 h of storage at room temperature. To evaluate the autosampler stability in reconstituted samples in the autosampler, we re-injected QC samples and calibration curves approximately 96 h after the first injection and compared the concentrations derived from the second injection with those derived from the first injection. The results of the second runs were expressed as a percentage of their respective values in the first runs.
Optional items
Impact of hemolysis was assessed by adding 10% (v/v) pre-hemolyzed whole blood to blanks, LLOQ and QCH samples (N = 4).
Heparinized plasma was evaluated as an alternative anticoagulated matrix to the standard EDTA plasma by analyzing EDTA plasma QCL, QCM and QCH samples (N = 4) against a heparin plasma triplicate standard curve. Selectivity of heparinized plasma was calculated by comparing response of analyte at LLOQ to that of blank plasma samples.
Dilutional integrity was shown by preparing plasma samples (N = 5) at 50 000 μg/mL and analysis after 10-fold dilution (to 5000 μg/mL) with control plasma.
Application of the assay
To document the applicability of the assay to clinical situations, we determined the concentration of cabozantinib in plasma samples from patients enrolled in the ongoing Phase III double-blind study of 60 mg of oral cabozantinib vs placebo (Alliance for Clinical Trials in Oncology study A021602, ClinicalTrials.gov Identifier: NCT03375320).
Incurred sample reanalysis and external validation
Upon completion of the validation, incurred sample reanalysis utilizing the identical assay was performed on plasma samples from an ongoing clinical trial (see section Application of the assay). ISR was done on plasma samples that had values above LLOQ.
Blinded QCs were prepared by the Analytical Pharmacology Core for the Johns Hopkins Kimmel Cancer Center.
Results and discussion
Development
Mass spectrometry
Both cabozantinib and IS were infused separately into the mass spectrometer with mobile phase containing either 50% methanol and 50% water with 0.1% formic acid or 50% acetonitrile and 50% water with 0.1% formic acid. There was no remarkable difference in the ionization effects between the chosen organic solvents. Acetonitrile was chosen as the organic solvent due to its greater ability to precipitate proteins and create a cleaner final matrix for our desired dilute and shoot sample preparation. Optimized mass spectrometric parameters are listed in Mass spectrometry section, and postulated fragmentation is shown in Supplementary Figure 2.
In case extra assurance is desired by means of a qualifier ion, MRM m/z transition 502.0 > 391.3 may be monitored. This transition has an intensity of 30% of the quantifier transition m/z 502.0 > 323.0, with a suggested tolerance of ±25% (8). The accuracy and precision performance of a triplicate calibration curve with QC samples was not negatively impacted by addition of the qualifier transition (accuracy at QCL, QCM and QCH, N = 6 each was 100.4, 100.3 and 100.6%), and the mean relative ion intensity across these 18 QC samples was 31.0% (range 29.9–31.5%).
Extraction and sample preparation
To expedite sample preparation, we chose to pursue a method of dilute-and-shoot sample preparation. This process used a 1:4 ratio of sample to acetonitrile (v/v) and demonstrated the ability to obtain our desired sensitivity of the 50 ng/mL LLOQ, which would be sufficient to characterize cabozantinib pharmacokinetics at common dosages.
Chromatography
We evaluated the following three columns: Synergi Polar RP 80 Å (50 × 2.0 mm, 4 μm), Synergi Hydro RP 80 Å (50 × 2.0 mm, 4 μm), and Luna phenylhexyl (50 × 2.0 mm, 3 μm). All of the columns tested displayed adequate peak shape for cabozantinib, however, the Polar RP column exhibited longer retention time than both the Hydro RP and the phenylhexyl columns. Furthermore, the phenylhexyl column produced back pressure much greater than the other columns resulting in longer overall run time due to the wash-out and re-equilibrium time needs at lower flow rate. The Polar RP column allowed for adequate retention with a higher percentage of starting acetonitrile in the gradient, facilitating the dilute and shoot sample preparation.
N-oxide metabolite
After validating the assay, we obtained cabozantinib N-oxide (Toronto Research Chemicals, Ontario, Canada), a CYP3A4 mediated metabolite, reported to occur at approximately 15% of parent cabozantinib concentrations (9). The mean cross-talk of 5000 ng/mL cabozantinib N-oxide into cabozantinib was 0.38%. When cabozantinib N-oxide was added to plasma at 5000 ng/mL and left at room temperature for 4 h, the average concentration of cabozantinib N-oxide measured as cabozantinib was 0.855 ng/mL, which is negligible (<1.7%) relative to the LLOQ of 50 ng/mL.
Validation of the assay
Chromatography
The retention times were for both cabozantinib and [D4]-cabozantinib was 1.5 min. This corresponds to a capacity factory of 1.06 with a void time of 0.7 min. Representative chromatograms of compound (blank and LLOQ), and internal standard in plasma are displayed in Figure 1.
Figure 1.
Representative chromatograms of: (A) cabozantinib (m/z 502.0 > 323.0; 1.5 min) added to control plasma at the LLOQ concentration of 50 ng/mL (top trace with an offset of 100 counts) and control human plasma (bottom trace); (B) [D4]-cabozantinib internal standard (m/z 506.0 > 323.0; 1.5 min) added to control plasma at a concentration at 2 μg/mL (top trace with an offset of 500 counts) and control human plasma (bottom trace); (C) patient sample (top trace cabozantinib, bottom trace internal standard).
Calibration curve and LLOQ
The selected assay range of 50–5000 ng/mL fulfilled the FDA criteria (6) for the LLOQ concentration and the calibration curve. Accuracies and precisions at the different concentrations from triplicate calibration curves on three separate days are reported in Supplementary Table I. Representative calibration curves and corresponding correlation and regression coefficient are shown in Supplementary Figure 3.
Accuracy and precision
The range of QC based accuracies was 103.4–105.4%. The intra- and inter-assay precisions for the tested concentrations (LLOQ, QCL, QCM, QCH) were all within the defined acceptance criteria (Table I) (6).
Table I.
Assay Performance Data for the Quantitation of LLOQ, QCL, QCM and QCH of Cabozantinib in Human Plasma
| Concentration (ng/mL) | Accuracy (%) | Intra-assay precision (CV %) | Inter-assay precision (CV %) |
|---|---|---|---|
| 50 (LLOQ) | 105.3 | 3.2 | 2.0 |
| 75 (QCL) | 105.4 | 3.3 | 1.4 |
| 750 (QCM) | 103.4 | 3.3 | 4.5 |
| 4000 (QCH) | 104.8 | 2.2 | 4.8 |
N = 18; 6-fold results, each in three separate runs, for each concentration. LLOQ, Lower Limit of Quantitation; QCL, QC Low; QCM, QC Mid; QCH, QC High
Selectivity and specificity
Chromatograms of six individual control plasma samples contained no co-eluting peaks >20% of the analyte areas at the LLOQ concentration (interference <2.2%).
The mean cross-talk of 10 × ULOQ of cabozantinib into IS was 0.004% which amounts to 2 ng/mL. The mean cross-talk of 5000 ng/mL IS into cabozantinib was 0.12%.
Carry-over was 0.025%.
Extraction recovery and matrix effect
The recoveries of cabozantinib ranged from 103.0% to 107.7% (CV 10% to 30%). Cabozantinib matrix effect ranged from −47.5 to −41.2% (CV 9.8–25%) (Supplementary Table II). Although the extraction and matrix effect displayed some variability, this was adequately corrected for by the internal standard used, as is evident from the appropriate accuracies across the concentration ranges (Table I and Supplementary Table I).
Stability
The stability of stock solutions at room temperature for 6 h were 99.9% (Supplementary Table III). Stability in stock solution for 5 months at −80°C was 93.4%. The stability after 3 freeze thaw cycles (−80°C to RT) was between 97.7 and 104.9%. Long-term stability in plasma at −80°C for 3 months was adequate with recoveries between 103.4 and 111.4%. The concentrations derived for plasma extracts at the quality control concentrations, when reconstituted and kept in the autosampler for 96 h, were 96.5 to 97.2% of the initial concentrations (CV 1.0–3.8%). Importantly, the reinjection run passed the requirements of any run set by the FDA (6).
Optional items
Presence of hemolysis did not result in extra peaks in blank plasma, and also did not impact quantitation with an accuracy of 98.6–100.5% (CV 3.9–8.4%).
Heparinized plasma was free of interference, and when used to quantitate EDTA plasma QC samples resulted in adequate performance with an accuracy of 103.7–109.8% (CV 2.2–3.6%).
Dilutional integrity was confirmed with 105.7% accuracy (CV 4.2%).
Application of the assay
As seen in Figure 2, the assay was capable of quantitating cabozantinib in plasma of patients dosed with cabozantinib. There appears to be some variability in trough levels both between and within patients, which will be further characterized in the ongoing phase III trial.
Figure 2.
Sequential plasma trough concentrations of cabozantinib in five patients after 60 mg oral cabozantinib once daily during each 28-day treatment cycle.
Incurred sample reanalysis and external validation
Incurred sample reanalysis of 64 samples yielded the following results: 0% samples with a difference larger than 20%, −0.7% median difference, 1.1% median absolute difference. These results were within the defined acceptance criteria of 67% of results having a difference within ±20% (6).
Blinded QCs (six levels total) prepared by an external laboratory were analyzed in replicates of 4. Results were precise with less than 1.1%CV. One of the blinded QCs was correctly identified as below LLOQ, while the other five were quantitated with a bias less than 1.1%.
Conclusion
We developed and validated an analytical method for the quantitation of cabozantinib in human plasma following the most recent FDA guidance (6), addressing performance in hemolyzed blood, and incorporating both incurred sample reanalysis and external validation, thereby distinguishing it from previously reported assays (Supplementary Table IV). Our analytical method is being used to characterize the exposure-response relationship in a phase III trial of advanced neuroendocrine tumors.
Supplementary Material
Contributor Information
Reyna Jones, Cancer Therapeutics Program, UPMC Hillman Cancer Center, 5115 Centre Ave, Pittsburgh, PA 15232 , USA.
Julianne Holleran, Cancer Therapeutics Program, UPMC Hillman Cancer Center, 5115 Centre Ave, Pittsburgh, PA 15232 , USA.
Robert A Parise, Cancer Therapeutics Program, UPMC Hillman Cancer Center, 5115 Centre Ave, Pittsburgh, PA 15232 , USA.
Michelle A Rudek, Department of Oncology and Medicine, Johns Hopkins University School of Medicine and Johns Hopkins Sidney Kimmel Cancer Center, 1800 Orleans St, Baltimore, MD 21287, USA.
Jennifer Chan, Dana Farber/Partners CancerCare, Dana-Farber Cancer Institute 450 Brookline Ave. Boston, MA 02215-5450, USA.
Yujia Wen, Alliance for Clinical Trials in Oncology, 125 S. Wacker Drive, Suite 1600, Chicago, IL 60606 , USA.
Joga Gobburu, Center for Translational Medicine, University of Maryland, 20 North Pine Street Baltimore, Maryland 21201 , USA.
Lionel D Lewis, Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, The Geisel School of Medicine at Dartmouth, 1 Medical Center Dr, Lebanon, NH 03766, USA.
Jan H Beumer, Cancer Therapeutics Program, UPMC Hillman Cancer Center, 5115 Centre Ave, Pittsburgh, PA 15232 , USA; Division of Hematology-Oncology, Department of Medicine, University of Pittsburgh School of Medicine, 5115 Centre Ave, Pittsburgh, PA 15232, USA; Department of Pharmaceutical Sciences, University of Pittsburgh, School of Pharmacy, 3501 Terrace St Pittsburgh, PA 15261, USA.
Funding
This work was supported by the National Cancer Institute at the National Institutes of Health under grant numbers [U10CA180821, U10CA180882, and U24CA196171 to the Alliance for Clinical Trials in Oncology, UG1CA233184, UG1CA233196, UG1CA233323, P30CA47904 to the UPMC Hillman Cancer Center Cancer Pharmacokinetics and Pharmacodynamics Facility (CPPF), R50CA211241, and P30CA006973 to the Analytical Pharmacology Core of the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins]. The content of this manuscript is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute.
ClinicalTrials.gov Identifier: NCT03375320.
References
- 1. Viola, D., Cappagli, V., Elisei, R.; Cabozantinib (XL184) for the treatment of locally advanced or metastatic progressive medullary thyroid cancer; Future Oncology, (2013); 9(8): 1083–1092. [DOI] [PubMed] [Google Scholar]
- 2. Singh, H., Brave, M., Beaver, J.A., Cheng, J., Tang, S., Zahalka, E. et al. ; U.S. Food and Drug Administration approval: Cabozantinib for the treatment of advanced renal cell carcinoma; Clinical Cancer Research, (2017); 23(2): 330–335. [DOI] [PubMed] [Google Scholar]
- 3. Nguyen, L., Chapel, S., Tran, B.D., Lacy, S.; Updated population pharmacokinetic model of cabozantinib integrating various cancer types including hepatocellular carcinoma; Journal of Clinical Pharmacology, (2019); 59: 1551–1561. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4. Lacy, S., Yang, B., Nielsen, J., Miles, D., Nguyen, L., Hutmacher, M.; A population pharmacokinetic model of cabozantinib in healthy volunteers and patients with various cancer types; Cancer Chemotherapy and Pharmacology, (2018); 81(6): 1071–1082. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5. Kim, K.P., Parise, R.A., Holleran, J.L., Lewis, L.D., Appleman, L., van Erp, N. et al. ; Simultaneous quantitation of abiraterone, enzalutamide, N-desmethyl enzalutamide, and bicalutamide in human plasma by LC-MS/MS; Journal of Pharmaceutical and Biomedical Analysis, (2017); 138: 197–205. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6. U.S. Department of Health and Human Services Food and Drug Administration ; Guidance for Industry-Bioanalytical Method Validation. 10903 New Hampshire Avenue, Silver Spring, MD 20993: U.S.Department of Health and Human Services; Food and Drug Administration; Center for Drug Evaluation and Research (CDER); Center for Veterinary Medicine (CVM), (2018). [Google Scholar]
- 7. Rosing, H., Man, W.Y., Doyle, E., Bult, A., Beijnen, J.H.; Bioanalytical liquid chromatographic method validation. A review of current practices and procedures; Journal of Liquid Chromatography & Related Technologies, (2000); 23(3): 329–354. [Google Scholar]
- 8. Commission Decision (2002/657/EC) of 12 August 2002 Implementing Council Directive 96/23/EC ; Concerning the performance of analytical methods and the interpretation of results, Brussels, Belgium: The Commission of the European Communities, (2002), pp. 8–36. [Google Scholar]
- 9. Nguyen, L., Holland, J., Miles, D., Engel, C., Benrimoh, N., O'Reilly, T. et al. ; Pharmacokinetic (PK) drug interaction studies of cabozantinib: Effect of CYP3A inducer rifampin and inhibitor ketoconazole on cabozantinib plasma PK and effect of cabozantinib on CYP2C8 probe substrate rosiglitazone plasma PK; Journal of Clinical Pharmacology, (2015); 55(9): 1012–1023. [DOI] [PubMed] [Google Scholar]
- 10. Krens, S.D., Meulen, E., Jansman, F.G.A., Burger, D.M., Erp, N.P.; Quantification of cobimetinib, cabozantinib, dabrafenib, niraparib, olaparib, vemurafenib, regorafenib and its metabolite regorafenib M2 in human plasma by UPLC–MS/MS; Biomedical Chromatography, (2020); 34(3): e4758. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 11. Jolibois, J., Schmitt, A., Royer, B.; A simple and fast LC-MS/MS method for the routine measurement of cabozantinib, olaparib, palbociclib, pazopanib, sorafenib, sunitinib and its main active metabolite in human plasma; Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences, (2019); 1132: 121844. [DOI] [PubMed] [Google Scholar]
- 12. Ren, L.J., Wu, H.J., Sun, L.H., Xu, X., Mo, L.Y., Zhang, L. et al. ; A sensitive LC-MS/MS method for simultaneous determination of cabozantinib and its metabolite cabozantinib N-oxide in rat plasma and its application in a pharmacokinetic study; Biomedical Chromatography, (2018); 32(7): e4227. [DOI] [PubMed] [Google Scholar]
- 13. Abdelhameed, A.S., Attwa, M.W., Kadi, A.A.; An LC-MS/MS method for rapid and sensitive high-throughput simultaneous determination of various protein kinase inhibitors in human plasma; Biomedical Chromatography, (2017); 31(2): e3793. [DOI] [PubMed] [Google Scholar]
- 14. Su, Q., Li, J., Ji, X., Li, J., Zhou, T., Lu, W. et al. ; An LC-MS/MS method for the quantitation of cabozantinib in rat plasma: Application to a pharmacokinetic study; Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences, (2015); 985: 119–123. [DOI] [PubMed] [Google Scholar]
- 15. Wang, X., Wang, S., Lin, F., Zhang, Q., Chen, H.L., Wang, X. et al. ; Pharmacokinetics and tissue distribution model of cabozantinib in rat determined by UPLC-MS/MS; Journal of Chromatography. B, Analytical Technologies in the Biomedical and Life Sciences, (2015); 983-984: 125–131. [DOI] [PubMed] [Google Scholar]
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