Deguelin inhibits the growth of colon cancer cells through the induction of apoptosis and cell cycle arrest G. Murillo a , G. I. Salti a , J. W. Kosmeder II b , J. M. Pezzuto b , R. G. Mehta a, * a Department of Surgical Oncology, College of Medicine, University of Illinois at Chicago, IL 60613, USA b Program of Collaborative Research in the Pharmaceutical Sciences, Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois at Chicago, IL 60612, USA Received 4 December 2001; received in revised form 12 March 2002; accepted 12 June 2002 Abstract As previously demonstrated, deguelin [(7aS, BaS)-13, 13a-dihydro-9,10-dimethoxy-3,3-dimethyl-3H-bis[1]benzo-pyrano[3,4-b: 6 0 ,5 0 -e]pyran-7(7aH)-one mediates anti-proliferative properties in a variety of cell types. In the present study, deguelin was found to suppress the growth of HT-29 colon cancer cells with an IC 50 of 4.32  10 8 M. The cells were arrested in the G1-S-phase of the cycle. Investigations of G1/S regulatory proteins by Western blot analyses showed an upregulation of p27, and decreased expression levels of cyclin E and CDK4. Furthermore, by 24 h, exposure to deguelin resulted in an increase in the hypophosphorylated form of Rb. Since hypophosphorylated pRb binds to and inactivates E2F1, additional studies were performed and downregulation of E2F1 was observed after 24 h of treatment with deguelin. These results are consistent with the observation that deguelin arrested cells in the G1-S- phase. In addition, based on ethidium bromide/acridine orange staining, detection of digoxigenin-labelled genomic 3 0 -OH DNA ends, and DNA laddering, it was found that deguelin exerts its growth inhibitory effects via the induction of apoptosis. Based on these data, the potential of deguelin to serve as a cancer chemotherapeutic agent for colon cancer may be suggested. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Deguelin; Cell cycle; Apoptosis; Colon cancer; HT-29; G1 arrest 1. Introduction During the past 20 years, the identification of novel cancer preventive agents has received considerable attention [1–3]. The mechanism of action of a chemo- preventive agent is often related to the stage of carcino- genesis at which it is active [4]. For example, antioxidants are often anti-initiators, whereas inhibitors of ornithine decarboxylase (ODC), agents that obstruct cell differentiation or induce programmed cell death, are generally anti-promoters. Chemotherapeutic agents, on the other hand, are used for established tumours that are aggressively progressing. The major difference between chemopreventive and chemotherapeutic agents is that chemopreventive agents are generally non-toxic, whereas chemotherapeutic agents are highly cytotoxic with narrow therapeutic ranges. Thus, there appears to be an ill-defined discrimination between the chemo- preventive and chemotherapeutic effects of a com- pound, especially if the compound is active during the later stages of carcinogenesis. Under these circum- stances, chemopreventive agents acting during the pro- gression stage of carcinogenesis can be considered as potential chemotherapeutic agents. Since chemopreven- tive agents, by definition, must be non-toxic, these agents may serve as safer alternatives. Accordingly, a variety of chemopreventive agents have been considered as potential adjuvant chemotherapeutic agents [5]. These include retinoids, cyclooxygenase (COX) inhibitors, ODC inhibitors, flavonoids, triterpenes, and others [6]. Deguelin, a rotenoid, was identified as a potential chemopreventive agent from Mundulea sericea within the Leguminosae family (Fig. 1). This was accomplished during the process of activity-guided fractionation in an effort to identify novel chemopreventive agents [7]. Deguelin is a potent inhibitor of ODC activity with an IC 50 of 0.7 ng/ml in cultured mouse 308 cells, and has 0959-8049/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0959-8049(02)00192-2 European Journal of Cancer 38 (2002) 2446–2454 www.ejconline.com * Corresponding author. Tel. +1-312-413-1156; fax: 1-312-996-9365. E-mail address: raju@uic.edu (R.G. Mehta).