Mechanism of Action

Vandetanib is a 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. In addition, the N-desmethyl metabolite of the drug, representing 7 to 17.1% of vandetanib exposure, has similar inhibitory activity to the parent compound for VEGF receptors (KDR and Flt-1) and EGFR. 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 CAPRELSA.

Pharmacokinetics

A population pharmacokinetic analysis of CAPRELSA was conducted in 231 patients with MTC following oral administration of 300 mg daily doses. The pharmacokinetics of CAPRELSA 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 CAPRELSA, 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 vandetanib 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 CAPRELSA have not been evaluated in pediatric patients.

QT Prolongation

In 231 medullary thyroid cancer patients randomized to receive CAPRELSA 300 mg once daily in the phase 3 clinical trial, CAPRELSA 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 BOXED WARNING and WARNINGS AND PRECAUTIONS].

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 CAPRELSA slows but does not prevent wound healing. The appropriate interval between discontinuation of CAPRELSA 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.

Clinical Studies

A double-blind, placebo-controlled study randomized patients with unresectable locally advanced or metastatic medullary thyroid cancer to CAPRELSA 300 mg (n=231) versus Placebo (n=100).

The primary objective was demonstration of improvement in progression-free survival (PFS) with CAPRELSA compared to placebo. Other endpoints included evaluation of overall survival and overall objective response rate (ORR). Centralized, independent blinded review of the imaging data was used in the assessment of PFS and ORR. Upon objective disease progression based on the investigator's assessment, patients were discontinued from blinded study treatment and given the option to receive open-label CAPRELSA. Nineteen percent (44/231) of the patients initially randomized to CAPRELSA opted to receive open-label CAPRELSA after disease progression, and 58% (58/100) of the patients initially randomized to placebo opted to receive open-label CAPRELSA after disease progression.

The result of the PFS analysis, based on the central review RECIST assessment, showed a statistically significant improvement in PFS for patients randomized to CAPRELSA (Hazard Ratio = 0.35; 95% Confidence Interval (CI) = 0.24-0.53; p < 0.0001). Analyses in the subgroups of patients who were symptomatic or had progressed within 6 months prior to their enrollment showed similar PFS results (HR = 0.31 95% CI: 0.19, 0.53 for symptomatic patients; HR = 0.41 95% CI: 0.25, 0.66 for patients who had progressed within 6 months prior to enrollment).

At the time of the primary analysis of PFS, 15% of the patients had died and there was no significant difference in overall survival between the two treatment groups. The overall objective response rate (ORR) for patients randomized to CAPRELSA was 44% compared to 1% for patients randomized to placebo. All objective responses were partial responses.

Figure 1: Progression Free Survival

Table 3: Summary of key efficacy findings

Last reviewed on RxList: 10/18/2012
This monograph has been modified to include the generic and brand name in many instances.