Abstract: AimTo study the antitumor mechanism of 3-substituted aryl oxindole (PH II-7) and determine its effects on cell cycle distribution of tumor cells. MethodsThe cell cycle distributions were determined with FACS. The cell cycle regulation-related proteins of K562 lysates were analyzed with Western Blot. The inhibition of PH II-7 on DNA synthesis of tumor cells were estimated though ³H-thymidine incorporation and the tyrosine kinase activity of EGFR of A431 lysates was measured with ELISA. ResultsPH II-7 effected cell cycle distribution of several tumor cells, including multidrug resistant tumor cell lines, and accumulation of cells in the G₀-G₁ stages was observed. The cell cycle regulation-related proteins CDK2, Rb and c-myc were inhibited by PH II-7 in a dose dependent manner, whereas the expression of CyclinE was increased after exposure to PH II-7. Furthermore, PH II-7 2.0 mg·L^-1 was shown to inhibit the incorporation of ³H-thymidine into DNA, and 21.89％-41.29% of the PTK activity of EGFR in A431 lysates was inhibited by PH II-7 2-8 mg·L^-1 in a dose-dependant manner. ConclusionPH II-7, a new anti-tumor agent, blocks the transition of cell cycle of tumor cells from G₁ to S phase by inhibition CDK2.