CLINICAL PHARMACOLOGY
Mechanism of Action
Vandetanib is a tyrosine kinase inhibitor. In vitro studies have shown that vandetanib inhibits the activity of tyrosine kinases including members of the epidermal growth factor receptor (EGFR) family, vascular endothelial cell growth factor (VEGF) receptors, rearranged during transfection (RET), protein tyrosine kinase 6 (BRK), TIE2, members of the EPH receptors kinase family, and members of the Src family of tyrosine kinases. Vandetanib inhibits endothelial cell migration, proliferation, survival and new blood vessel formation in in vitro models of angiogenesis. Vandetanib inhibits EGFR-dependent cell survival in vitro. In addition, vandetanib inhibits epidermal growth factor (EGF)-stimulated receptor tyrosine kinase phosphorylation in tumor cells and endothelial cells and VEGF-stimulated tyrosine kinase phosphorylation in endothelial cells.
In vivo vandetanib administration reduced tumor cell-induced angiogenesis, tumor vessel permeability, and inhibited tumor growth and metastasis in mouse models of cancer.
There is no evidence of a relationship between RET mutations and efficacy with vandetanib.
Pharmacokinetics
A population pharmacokinetic analysis of vandetanib was conducted in 231 patients with MTC following oral administration of 300 mg daily doses. The pharmacokinetics of vandetanib at the 300 mg dose in MTC patients are characterized by a mean clearance of approximately 13.2 L/h, a mean volume of distribution of approximately 7450 L, and a median plasma half-life of 19 days.
Absorption
Following oral administration of vandetanib, absorption is slow with peak plasma concentrations typically achieved at a median of 6 hours, range 4-10 hours, after dosing. Vandetanib accumulates approximately 8-fold on multiple dosing with steady state achieved from approximately 3 months.
Exposure to vandetanib is unaffected by food.
Distribution
Vandetanib binds to human serum albumin and α1-acid-glycoprotein with in vitro protein binding being approximately 90%. In ex vivo plasma samples from colorectal cancer patients at steady state exposure after 300 mg once daily, the mean percentage protein binding was 93.7% (range 92.2 to 95.7%).
Metabolism
Following oral dosing of 14C-vandetanib, unchanged vandentanib and metabolites vandetanib N-oxide and N-desmethyl vandetanib were detected in plasma, urine and feces. A glucuronide conjugate was seen as a minor metabolite in excreta only. N-desmethyl-vandetanib is primarily produced by CYP3A4 and vandetanib-N-oxide by flavin–containing monooxygenase enzymes FMO1 and FMO3. N-desmethyl-vandetanib and vandetanib-N-oxide circulate at concentrations of approximately 7-17.1% and 1.4-2.2%, respectively, of those of vandetanib.
Excretion
Within a 21-day collection period after a single dose of 14C-vandetanib, approximately 69% was recovered with 44% in feces and 25% in urine. Excretion of the dose was slow and further excretion beyond 21 days would be expected based on the plasma half-life.
Vandetanib was not a substrate of hOCT2 expressed in HEK293 cells. Vandetanib inhibits the uptake of the selective OCT2 marker substrate 14C-creatinine by HEK-OCT2 cells, with a mean IC50 of approximately 2.1 μg/mL. This is higher than vandetanib plasma concentrations (approximately 0.81 μg/mL) observed after multiple dosing at 300 mg. Inhibition of renal excretion of creatinine by vandetanib provides an explanation for increases in plasma creatinine seen in human subjects receiving vandetanib.
Special Populations
Effects of Age and Gender
In a population pharmacokinetic evaluation in cancer patients, no relationship was apparent between oral clearance and patient age or gender.
Ethnicity
Based on a cross-study comparison in a limited number of patients, Japanese (N=3) and Chinese (N=7) patients had on average exposures that were higher than Caucasian (N=7) patients receiving the same dose.
Pediatric
The pharmacokinetics of vandetanib have not been evaluated in pediatric patients.
QT Prolongation
In 231 medullary thyroid cancer patients randomized to receive vandetanib 300 mg once daily in the phase 3 clinical trial, vandetanib was associated with sustained plasma concentration-dependent QT prolongation. Based on the exposure-response relationship, the mean (90% CI) QTcF change from baseline (ΔQTcF) was 35 (33-36) ms for the 300-mg dose. The ΔQTcF remained above 30 ms for the duration of the trial (up to 2 years). In addition, 36% of patients experienced greater than 60 ms increase in ΔQTcF and 4.3% of patients had QTcF greater than 500 ms. Cases of Torsades de pointes and sudden death have been reported [see Warnings and Precautions (5.1, 5.11)].
NONCLINICAL TOXICOLOGY
Carcinogenesis, Mutagenesis, Impairment of Fertility
Carcinogenicity studies have not been conducted with vandetanib.
Vandetanib was not mutagenic in vitro in the bacterial reverse mutation (Ames) assay and was not clastogenic in both the in vitro cytogenetic assay using human lymphocytes or in the in vivo rat micronucleus assay.
Based on nonclinical findings, male and female fertility may be impaired by treatment with vandetanib. In a fertility study in male rats, vandetanib had no effect on copulation or fertility rate when undosed females were mated with males administered 1, 5, or 20 mg/kg/day of vandetanib (approximately 0.03, 0.22, or 0.40 times, respectively, the AUC in patients with cancer at the recommended human dose of 300 mg/day). There was a slight decrease in the number of live embryos at 20 mg/kg/day and an increase in preimplantation loss at >5 mg/kg/day. In a female fertility study, there was a trend towards increased estrus cycle irregularity, a slight reduction in pregnancy incidence and an increase in implantation loss. In a repeat-dose toxicity study in rats, there was a decrease in the number of corpora lutea in the ovaries of rats administered 75 mg/kg/day vandetanib (approximately 1.8 times the AUC in patients with cancer at the recommended human dose) for 1 month.
Animal Pharmacology and/or Toxicology
In an animal model of wound-healing, mice dosed with vandetanib had reduced skin-breaking strength compared with controls. This suggests that vandetanib slows but does not prevent wound healing. The appropriate interval between discontinuation of vandetanib and subsequent elective surgery required to avoid the risks of impaired wound healing has not been determined.
Nodular masses were observed in a 6-month toxicology study in rats during treatment with ≥5 mg/kg/day vandetanib (approximately 0.22 or 0.40 times, respectively, the AUC in patients with cancer at the recommended human dose of 300 mg/day). Masses were palpable during clinical assessments as early as week 13, were observed in multiple organs, and were associated with hemorrhagic or inflammatory findings.
|
