Green tea compounds inhibit tyrosine phosphorylation of PDGF β‐receptor and transformation of A172 human glioblastoma

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Abstract
The effect of the green tea compounds 2‐(3,4‐dihydroxyphenyl)‐3,4‐dihydro‐2H‐1‐benzopyran‐3,5,7‐triol (catechin), epicathechin (EC), epigallocathechin‐3 gallate (EGCG), epicathechin‐3 gallate (ECG) and catechin‐3 gallate (CG) on the tyrosine phosphorylation of PDGF β‐receptor (PDGF‐Rβ) and on the anchorage‐independent growth of A172 glioblastoma cells in semisolid agar has been investigated. Treatment of A172 glioblastoma with 50 μM CG, ECG, EGCG and 25 μM Tyrphostin 1296 resulted in an 82±17%, 77±21%, 75±8% and 55±11%, respectively (mean±S.D., n=3) inhibition of the PDGF‐BB‐induced tyrosine phosphorylation of PDGF‐Rβ. The PDGF‐Rβ downstream intracellular transduction pathway including tyrosine phosphorylation of phospholipase C‐γ1 (PLC‐γ1) and phosphatidylinositol 3′‐kinase (PI 3′‐K) was also inhibited. Spheroid formation was completely inhibited by 50 μM ECG, CG, EGCG and by 25 μM Tyrphostin 1296. We conclude that catechins of the green tea possessing the gallate group in their chemical structure act as anticancer agents probably partly via their ability to suppress the tyrosine kinase activity of the PDGF‐Rβ.