In vitro activity: Vandetanib also inhibits VEGFR3 and EGFR with IC50 of 110 nM and 500 nM, respectively. Vandetanib is not sensitive to PDGFRβ, Flt1, Tie-2 and FGFR1 with IC50 of 1.1-3.6 μM, while almost has no activity against MEK, CDK2, c-Kit, erbB2, FAK, PDK1, Akt and IGF-1R with IC50 above 10 μM. Vandetanib inhibits VEGF-, EGF- and bFGF-stimulated HUVEC proliferation with IC50 of 60 nM, 170 nM and 800 nM, with no effect on basal endothelial cell growth. Vandetanib inhibits tumor cell growth with IC50 of 2.7 μM (A549) to 13.5 μM (Calu-6). Vandetanib displays an inhibitory effect on the basal ABCG2-ATPase. Parental and ABCG2-expressing A431 cells showed similar sensitivities toward Vandetanib. Exposure to EGFR inhibitors decreases pEGFR levels in A431 cells, with Vandetanib displaying only a moderate effect. Vandetanib displays a slight but measurable effect, whereas gefitinib, pelitinib and neratinib completely inhibit ABCG2-mediated efflux of mitoxantrone from A431/ABCG2 cells, similarly to the specific ABCG2 inhibitor Ko143. Vandetanib inhibits both PC3wt and PC3R cell lines with similar IC50 of 13.3 μM and 11.5 μM, respectively. Vandetanib suppresses phosphorylation of VEGFR2 in HUVEC and EGFR in hepatoma cells and inhibits cell proliferation. Vandetanib causes an accumulation of cells in the G0-G1 phases in GEO and OVCAR-3 cells and increases apoptosis in OVCAR-3, ZR-75-1, MCF-10A ras, and GEO cells. Vandetanib causes a dose-dependent inhibition of EGFR phosphorylation in mouse NIH-EGFR fibroblasts and human MCF-10A ras breast cancer cells, two cell lines that overexpress the human EGFR. Vandetanib treatment results in a dose-dependent inhibition of soft agar growth in seven human cell lines (breast, colon, gastric, and ovarian) with functional EGFR but lacking VEGFR2.

Kinase Assay: Vandetanib is incubated with enzyme, 10 mM MnCl2, and 2 μM ATP in 96-well plates coated with a poly(Glu, Ala, Tyr) 6:3:1 random copolymer substrate. Phosphorylated tyrosine is then detected by sequential incubation with a mouse IgG anti-phosphotyrosine 4G10 antibody, a horseradish peroxidase-linked sheep antimouse immunoglobulin antibody, and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid). This methodology is adapted to examine selectivity versus tyrosine kinases associated with EGFR, PDGFRβ, Tie-2, FGFR1, c-kit, erbB2, IGF-1R, and FAK. All enzyme assays (tyrosine or serine-threonine) used appropriate ATP concentrations at or just below the respective Km (0.2–14 μM). Selectivity versus serine-threonine kinases (CDK2, AKT, and PDK1) is examined using a relevant scintillation proximity-assay (SPA) in 96-well plates. CDK2 assays contained 10 mM MnCl2, 4.5 μM ATP, 0.15 μCi of [γ-33 P]ATP/reaction, 50 mM HEPES (pH 7.5), 1 mM DTT, 0.1 mM sodium orthovanadate, 0.1 mM sodium fluoride, 10 mM sodium glycerophosphate, 1 mg/mL BSA fraction V, and a retinoblastoma substrate (part of the retinoblastoma gene, 792–928, expressed in a glutathione S-transferase expression system; 0.22 μM final concentration). Reactions are allowed to proceed at room temperature for 60 minutes before quenching for 2 hours with 150 μL of a solution containing EDTA (62 mM final concentration), 3 μg of a rabbit immunoglobulin anti-glutathione S-transferase antibody and protein A SPA-polyvinyltoluene beads (0.8 mg/reaction). Plates are then sealed, centrifuged (1200× g for 5 minutes), and counted on a Microplate scintillation counter for 30 seconds.

Cell Assay: Tumor cells (Calu-6, PC-3, MDA-MA-231, SKOV-3, SW620, A549, A431, B16-F10(AP3) and Lewis Lung cells) are plated in their respective media at predetermined densities that are known to enable logarithmic cell growth during the period of assay (PC-3, 500 cells/well; all others, 1000 cells/well). Plates are incubated for 24 hours (37 °C with CO2) before the addition of Vandetanib (0.1–100 μM) or vehicle (0.1% DMSO in medium). Plates are reincubated for an additional 72 hours before assessing cell proliferation by [3 H]thymidine incorporation by a beta counter.