A NEW EPIDERMAL GROWTH FACTOR RECEPTOR INHIBITOR IN COLON CANCER CELLS

Members of the EGFR family of receptor tyrosine kinases, which includes EGFR, ErbB-2/HER-2, Erb-B-3/HER-3, and ErbB-4/HER-4, collectively referred to as EGFRs, serve as critical mediators of the cellular communication network regulating complex biological processes such as growth, differentiation, motility, or death. Since deregulated signalling by EGFRs is frequently noted in a variety of human cancers, interference with growth factor receptor activation and/or with intracellular growth factor-activated signal transduction pathways represents a promising strategy for the development of novel and selective anticancer therapies. Small molecule inhibitors of EGFR, such as gefitinib (Iressa) and erlotinib (Tarceva; OSI-774), monoclonal antibodies to EGFR (cetuximab/IMC-C225/Erbitux), and HER-2 (trastuzumab/Herceptin) are being utilized as anti-cancer therapeutics. In this respect, shikonin is a naturally occurring naphtoquinone isolated from the roots of many traditional medicinal plants, that has been demonstrated to have great antitumor potential by inhibiting cell growth in various cancer cell lines [1], inducing apoptosis in leukemia HL-60 cells [2] and inhibiting epidermal growth factor receptor signalling in human epidermoid carcinoma cells [3]. Moreover a shikonin derivative, -hydroxyisovalerylshikonin (-HIVS) exerts a strong, non-ATP-competitive inhibition of EGFR kinase activity, suggesting that both it and the parent compound may bind to the peptide binding site [3,4]. This feature of -HIVS is very useful for the inhibition of PTK activity in vivo, because -HIVS does not need to compete with ATP at intracellular millimolar concentrations. Encouraged by these findings and aware that shikonin, because of its poor solubility, has little potential as an anticancer drug candidate, we have designed and synthesized a library of naphtoquinone derivatives in order to obtain effective compounds endowed with more “drug-like” properties. In this study we have tested the anti-tumour activity ant the efficacy of FR18, the first compound of this class, as a novel EGFR inhibitor, by using the HT29 colon adenocarcinoma cell model and by comparing its potency with an anti-EGFR-blocking monoclonal antibody. The results presented in this work have shown that the EGFR-blocking antibody induced growth arrest in G0/G1, while FR18 determined an increase of cells in the G2/M phase and apoptotic cell death. At the EGFR level, FR18 treatment determined a dramatic reduction of the ligand-receptor interaction as confirmed by coimmunoprecipitation experiments and spectral confocale microscopy. In conclusion our data suggest that FR18 selectively induces apoptosis in HT29 cancer cells by interfering with EGFR receptor signalling. BIBLIOGRAFIA 1. Guo XP, Zhang XY, Zhang SD [Clinical trial on the effects of shikonin mixture on later stage lung cancer]. Zhong Xi Yi Jie He Za Zhi 1991, 11:598-599. 2. Yoon Y, Kim YO, Lim NY, Jeon WK, Sung HJ. Shikonin, an ingredient of Lithospermum erythrorhizon induced apoptosis in HL60 human premyelocytic leukemia cell line. Planta Med 1999, 65:532-535. 3. Singh F, Gao D, Lebwohl MG, Wei H. Shikonin modulates cell proliferation by inhibiting epidermal growth factor receptor signaling in human epidermoid carcinoma cells. Cancer Lett 2003, 200:115-121. 4. Nakaya K, Miyasaka T. A shikonin derivative, beta-hydroxyisovalerylshikonin, is an ATP-non-competitive inhibitor of protein tyrosine kinases. Anticancer Drugs 2003, 14:683-693.