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Both Antiangiogenesis- and Angiogenesis-Independent Effects Are Responsible for Hepatocellular Carcinoma Growth Arrest by Tyrosine Kinase Inhibitor PTK787/ZK222584

Centre for the Study of Liver Disease and Department of Surgery, The University of Hong Kong, Pokfulam, Hong Kong, China

Requests for reprints: Ronnie T. Poon, Department of Surgery, The University of Hong Kong, Queen Mary Hospital, 102 Pokfulam Road, Hong Kong, China. Phone: 852-28553641; Fax: 852-28175475; E-mail: poontp{at}hkucc.hku.hk.

Vascular endothelial growth factor (VEGF) plays an important role in tumor angiogenesis of hepatocellular carcinoma. Inhibition of VEGF receptors could theoretically reduce angiogenesis and tumor growth in hepatocellular carcinoma, but this remains to be proven with an experimental study. This study examined the angiogenesis-dependent and angiogenesis-independent activities of PTK787/ZK222584 (PTK787), a tyrosine kinase inhibitor of VEGF receptors, in nude mice bearing human hepatocellular carcinoma xenografts. The in vitro effects of PTK787 on proliferation, apoptosis, and cell cycle distribution in human hepatocellular carcinoma cell lines were also studied. Oral administration of PTK787 resulted in a significant reduction in tumor volume and microvessel formation of hepatocellular carcinoma xenografts in nude mice. PTK787 inhibited tumor cell proliferation in a dose-dependent manner and also induced tumor cells to undergo apoptosis both in vivo and in vitro. The proapoptotic response was associated with down-regulation of Bcl-2 and Bcl-x_L expression and induction of cleavage of caspase-3. In addition, PTK787 induced growth arrest in hepatocellular carcinoma cells, which was associated with G₁ arrest and partial G₂-M block. This effect correlated with an increase in p21^{WAF1/ CIP1} (p21) and p27^KIP1 (p27) protein expression. In conclusion, this study showed that PTK787 is a potent inhibitor of tumor growth in hepatocellular carcinoma by both antiangiogenic effect and direct effects on tumor cell proliferation and apoptosis. Our data suggest that blockage of VEGF receptors may provide an effective therapeutic approach for human hepatocellular carcinoma.

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