Research Article: Cudraflavone C Induces Tumor-Specific Apoptosis in Colorectal Cancer Cells through Inhibition of the Phosphoinositide 3-Kinase (PI3K)-AKT Pathway

Date Published: January 20, 2017

Publisher: Public Library of Science

Author(s): Hsien-Chuen Soo, Felicia Fei-Lei Chung, Kuan-Hon Lim, Veronica Alicia Yap, Tracey D. Bradshaw, Ling-Wei Hii, Si-Hoey Tan, Sze-Jia See, Yuen-Fen Tan, Chee-Onn Leong, Chun-Wai Mai, Javier S Castresana.

http://doi.org/10.1371/journal.pone.0170551

Abstract

Cudraflavone C (Cud C) is a naturally-occurring flavonol with reported anti-proliferative activities. However, the mechanisms by which Cud C induced cytotoxicity have yet to be fully elucidated. Here, we investigated the effects of Cud C on cell proliferation, caspase activation andapoptosis induction in colorectal cancer cells (CRC). We show that Cud C inhibits cell proliferation in KM12, Caco-2, HT29, HCC2998, HCT116 and SW48 CRC but not in the non-transformed colorectal epithelial cells, CCD CoN 841. Cud C induces tumor-selective apoptosis via mitochondrial depolarization and activation of the intrinsic caspase pathway. Gene expression profiling by microarray analyses revealed that tumor suppressor genes EGR1, HUWE1 and SMG1 were significantly up-regulated while oncogenes such as MYB1, CCNB1 and GPX2 were down-regulated following treatment with Cud C. Further analyses using Connectivity Map revealed that Cud C induced a gene signature highly similar to that of protein synthesis inhibitors and phosphoinositide 3-kinase (PI3K)-AKT inhibitors, suggesting that Cud C might inhibit PI3K-AKT signaling. A luminescent cell free PI3K lipid kinase assay revealed that Cud C significantly inhibited p110β/p85α PI3K activity, followed by p120γ, p110δ/p85α, and p110α/p85α PI3K activities. The inhibition by Cud C on p110β/p85α PI3K activity was comparable to LY-294002, a known PI3K inhibitor. Cud C also inhibited phosphorylation of AKT independent of NFκB activity in CRC cells, while ectopic expression of myristoylated AKT completely abrogated the anti-proliferative effects, and apoptosis induced by Cud C in CRC. These findings demonstrate that Cud C induces tumor-selective cytotoxicity by targeting the PI3K-AKT pathway. These findings provide novel insights into the mechanism of action of Cud C, and indicate that Cud C further development of Cud C derivatives as potential therapeutic agents is warranted.

Partial Text

Colorectal cancer (CRC) is the third most common type of cancer and is one of the leading causes of cancer-related mortality worldwide, resulting in approximately 700,000 deaths every year [1, 2]. Despite aggressive screening and public health promotion, the global burden of CRC is anticipated to rise by 60% by 2030 [3]. Furthermore, despite recent advancements in targeted therapeutics, the 5-year survival rates remain low, particularly in patients diagnosed with advanced disease [4]. Thus, discovery of novel chemotherapeutic agents is imperative.

Cudraflavone is a prenylflavone originally isolated from the root of Cudrania tricuspidata (Carr.) Bur. (Moraceae) [19]. Interestingly, Cudrania tricuspidata (Carr.) Bur is applied as a folk remedy in Korea [57], and has demonstrated anti-inflammatory activities [58]. To date, a total of 3 analogs of Cud have been isolated, including Cud A, B and C [19, 59]. Cud A has been shown to inhibit melanin production through suppression of tyrosinase [60] and potentially evokes antidepressant activities via inhibition of brain monoamine oxidase [61]. Similarly, Cud B also inhibited melanin production [62] and brain monoamine oxidase [61]. In addition, Cud B inhibited cancer cells growth and induced mitochondrial-dependent apoptosis in human oral cancer cells through regulation of MAPK, NFκB, and SIRT1 signaling [18]. While several benefits of Cud C have been reported recently, such as inhibition of melanin production [13], inhibition of pancreatic lipases [14], and HSV activation [15], few studies have been conducted to evaluate its anti-proliferative activities [16, 17]. Virtually nothing is known regarding the mechanism underlying the antitumor activities of Cud C.

Our study demonstrates that Cud C is a PI3K-AKT inhibitor with selective anti-tumor activities against CRC cells. These results imply that Cud C offers tremendous potential for further development as a therapeutic agent for CRC.

 

Source:

http://doi.org/10.1371/journal.pone.0170551