br Introduction br Colorectal cancer CRC is the third
Colorectal cancer (CRC) is the third most common type of cancer in the world . In 2012, approximately 1.36 million new cases were diagnosed with CRC, out of which 694,000 deaths were reported . Although CRC is more common in developed countries, mortality rate is higher in developing countries [1,2]. Modern lifestyle has been asso-ciated with higher rates of obesity, diabetes, ageing, consumption of alcohol and cigarettes, and also lack of physical activity, all of which can contribute to increased risk of CRC [3–5]. It is predicted that the incidence of CRC will be increased by 90% in 2030 . The current management of colon cancer such as surgery, radiotherapy and che-motherapy have considerable side eﬀects including cytotoxicity in other organs such as heart, kidney, bladder, lung and the nervous system. As an example, 5-fluorouracil (5-FU), which is commonly used to treat diﬀerent types of colon cancer, is associated with a wide range
of adverse eﬀects, such as cardiovascular toxicity, diarrhea, dehydra-tion, abdominal pain, nausea, stomatitis and hand-foot syndrome [36–40]. Taking all these into consideration, there is an urgent need for new chemotherapeutic agents to combat CRC with minimal toxicity to normal tissue and possess a more favorable therapeutic window.
Apoptosis induction is an important target for cancer treatment. Apoptosis is a programmed cell death in which proteolytic enzymes called caspases play an important role in this event. Activation of cas-pase cascades is usually initiated by either intracellular or extracellular signals through activation of apoptosis stimulators. The release of cy-tochrome C from the mitochondria activates caspase 9, while fas-as-sociated protein with death domain (FADD) cleaves pro-caspase 8 to the active form leading to cell death [7–10]. It is to be noted that this event is usually regulated by anti-apoptotic proteins such as Bcl-2 and in-hibitors of apoptosis protein (IAP) family [11–14]. Ideally, an agent that is able to promote cancer Tunicamycin to undergo apoptosis could be
E-mail addresses: [email protected] (Z. Mohamed), [email protected] (A. Sinniah), [email protected] (Z.A. Ibrahim), [email protected] (M.A. Alshawsh).
selected as a promising candidate to combat cancer.
In the last few decades, research has focused on various flavonoid compounds, which had demonstrated potential pharmacological prop-erties. These compounds have shown beneficial health eﬀects against various diseases including cancer [15,16]. The compound 8-pre-nylnaringenin (8-PN) is a prenylflavonoid found in diﬀerent natural sources such as, hops (Humulus lupulus) and beer. The flowers from hops are used in beer making, which provide the bitter flavor and pungent aroma of beer . It has been shown that hops extract has anti-pro-liferative properties against some colon cancer cells such as HT-29 and SW620. Moreover, the anti-proliferative eﬀects of hops extract are due to the xanthohumol and isoxanthohumol and are enriched in hops. Same as 8-PN, xanthohumol and isoxanthohumol are other members of prenylflavonoid . Despite various studies that had been carried out on diﬀerent flavonoids, studies assessing the anticancer properties of 8-PN is still very limited.
Increasing evidence suggests that 8-PN can trigger MAP kinase pathway and induce apoptosis in MCF-7 breast cancer cells . Ad-ditionally, a study by Pepper et al.  have also demonstrated that 8-PN inhibited angiogenesis in bovine microvascular endothelial (BME) and endothelial cells from the bovine thoracic aorta (BAE) cells at a concentration of 3–10 μM . Another study reported that 8-PN de-monstrated a biphasic action on MCF-7 breast cancer cells; whereby the compound induced cell proliferation at 10−8–10−6 M concentration, but on the other hand apoptosis was observed to happen at 10−5 M concentration . Furthermore, 8-PN acts as a potent inhibitor of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and may be used as a chemopreventive compound against colon and liver cancer [21–23]. In addition, 8-PN inhibits cell viability of colorectal Caco-2 cells at con-centration of 40–50 μM and Caco-2 cells were arrested in G0/G1 phase . Despite these evidences, the eﬀect of 8-PN against some important colorectal cell lines such as HCT-116 has not yet been investigated. Therefore, this study was designed to assess the pro-apoptotic proper-ties of 8-PN against HCT-116 colon cancer cells using in vitro assays and to identify the possible apoptotic pathway using caspase cascade and annexin V assay.