Cat's Whiskers Tea (Orthosiphon Stamineus) Extract Inhibits Growth of Colon Tumor in Nude Mice and Angiogenesis in Endothelial Cells via Suppressing VEGFR Phosphorylation

Abstract

Cat's whiskers (Orthosiphon stamineus) is commonly used as Java tea to treat kidney stones including a variety of angiogenesis-dependent diseases such as tumorous edema, rheumatism, diabetic blindness, and obesity. In the present study, antitumor potential of standardized 50% ethanol extract of O. stamineus leaves (EOS) was evaluated against colorectal tumor in athymic mice and antiangiogenic efficacy of EOS was investigated in human umbilical vein endothelial cells (HUVEC). EOS at 100 mg/kg caused 47.62 ± 6.4% suppression in tumor growth, while at 200 mg/kg it caused 83.39 ± 4.1% tumor regression. Tumor histology revealed significant reduction in extent of vascularization. Enzyme-linked immunosorbent assay showed EOS (200 mg/kg) significantly reduced the vascular endothelial growth factor (VEGF) level in vitro (211 ± 0.26 pg/ml cell lysate) as well as in vivo (90.9 ± 2 pg/g tissue homogenate) when compared to the control (378 ± 5 and 135.5 ± 4 pg, respectively). However, EOS was found to be noncytotoxic to colon cancer and endothelial cells. In vitro, EOS significantly inhibited the migration and tube formation of human umbilical vein endothelial cells (HUVECs). EOS suppressed VEGF-induced phosphorylation of VEGF receptor-2 in HUVECs. High performance liquid chromatography (HPLC) analysis of EOS showed high rosmarinic acid contents, whereas phytochemical analysis revealed high protein and phenolic contents. These results demonstrated that the antitumor activity of EOS may be due to its VEGF-targeted antiangiogenicity.

ACKNOWLEDGMENTS

We gratefully acknowledge the financial support of the Universiti Sains Malaysia, under grant number 1001/PPSK/8120243, RU, and Malaysian Ministry of Higher Education, grant number FRGS: 203/PFARMASI/671196. The authors are also thankful to the MAKNA Research Grant No. 304/PFARMASI/650547/M122. We also acknowledge scientific contributions from Christopher Parish and his group, Cancer and Vascular Biology Centre, John Curtin School of Medical Research, Australian National University, in aiding us to establish the angiogenesis assay system.