Herbal formula Huang Qin Ge Gen Tang enhances 5-fluorouracil antitumor activity through modulation of the E2F1/TS pathway

Background: 5-Fluorouracil (5-FU) remains the most widely used agent to treat colorectal cancer (CRC). However, its clinical efficacy is currently limited by the development of drug resistance. Traditional Chinese Herbal Medicine (TCM) has been shown to enhance the efficacy of standard anticancer agents. However, there are only a limited number of well-controlled preclinical and clinical studies documenting the potential benefit of TCM. Herein, we screened a series of TCM formulas in in vitro and in vivo animal models to identify biologically active formulas that were effective against CRC. Methods: Cell proliferation and clonogenic assays, cell cycle analysis, immunoblot analysis and qRT-PCR were performed to investigate the mechanism(s) of action of the most active formula Huang-Qin-Ge-Gen-Tang (HQGGT) on growth of human CRC cells. In vivo animal models were used to document the antitumor activity of HQGGT alone and HQGGT in combination with 5-FU. Results: We identified HQGGT, which suppressed the in vivo growth of human colon cancer HT-29 xenografts without associated toxicities. HQGGT displayed anti-proliferative activity against a wide range of CRC cell lines. This growth suppression correlated with induction of apoptosis. HQGGT enhanced the cytotoxicity of 5-FU against human 5-FU-resistant cells (H630R1) and mouse colon cancer cells (MC38). Our studies showed that the mechanism of action of this synergism was the result of suppression of thymidylate synthase (TS) expression by HQGGT. We analyzed different batches of HQGGT and observed consistent chemical fingerprints and biological activity. Finally, we show that orally administered HQGGT significantly enhanced the antitumor effect of 5-FU in mice bearing MC38 xenografts. Conclusions: These findings provide support for the potential role of HQGGT as a novel modulator of fluoropyrimidine chemotherapy in the treatment of CRC.