Abstract 2030: Fisetin, a dietary flavonoid for the prevention and treatment of PIK3CA-mutant colorectal cancer

Abstract

Abstract Colorectal cancer (CRC) is one of the most frequent and deadliest cancers worldwide with patients often diagnosed in advanced stages of the disease. Approximately 15-20% of advanced colorectal cancers harbor activating mutations in PIK3CA, which has been identified as an important oncogene in multiple cancers. Therefore, modeling the effects of this type of mutation in the mammalian colon is significant. Fisetin is a naturally occurring flavonoid in strawberry, apple, persimmon, grape, onion and cucumber. 5-Fluorouracil (5-FU) is the most used chemotherapeutic agent in CRC; however, it has serious side-effects. Therefore, augmentation of the 5-FU therapeutic effect could lead to lower effective doses and subsequently fewer side effects. We conducted in-vitro and in-vivo studies to determine the effect of fisetin, 5-FU and their combination on PI3K/AKT/mTOR signaling in PIK3CA-mutant colon cancer cells (HCT116 and HT-29), PIK3CA wild-type colon cancer cells (SW480), and newly developed mouse models. We found that there was more pronounced decrease in cell-viability and number of colonies in PIK3CA-mutant colon cancer cells than PIK3CA wild-type colon cancer cells. Apoptotic genes and proteins are promising targets for cancer treatment as they provide several theoretical basis to influence pathways causing greater tumor cell death. We observed an increase in the protein expression of Bax and decrease in Bcl2 on treatment with combination of fisetin and 5-FU than either agent alone. The full size PARP (116 KD) protein was also cleaved to yield an 85 KD fragment after treatment of cells with fisetin, 5-FU and their combination. Apoptotic effects of fisetin and 5-FU combination were also confirmed by flow cytometry in PIK3CA-mutant colon cancer cells. The PI3K/AKT pathway is frequently activated in CRC leading to tumorigenesis and the resistance to chemotherapy. Treatment of PIK3CA-mutant colon cancer cells with fisetin and 5-FU caused decrease in the expression of (i) PI3K (p85 and p110), (ii) phosphorylation of Akt (Ser473 and Thr308), (iii), phosphorylation of mTOR, its target proteins, and constituents of mTOR signaling complex. Treatment with fisetin and 5-FU also led to an increase in the phosphorylation of AMPKα. Next, we performed studies to investigate the effect of the treatment of combination of fisetin and 5-FU on colorectal tumorigenesis in FC13K1ApcMin/+ mice. These animals form tumors in the distal small intestine and colon that have lost APC activity and express constitutively active PI3K as often occurs in humans. Interestingly, the effect of fisetin was much stronger than that of 5-FU and comparable to the fisetin and 5-FU combination. Both fisetin only and combination treatment groups had significantly lower incidence relative to the control group. We suggest that fisetin could be used as a preventive agent as well as an adjuvant with 5-FU for the treatment of PIK3CA-mutant CRC. Citation Format: Naghma Khan, Farah Jajeh, Devon Miller, Rachel Van Doorn, Richard B. Halberg, Hasan Mukhtar. Fisetin, a dietary flavonoid for the prevention and treatment of PIK3CA-mutant colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2030. doi:10.1158/1538-7445.AM2017-2030