Anticancer Drug Discovery of New Tegafur-Derivatives for Colorectal Cancer Therapy

Colorectal cancer (CRC) incidence rate has been ranked 1st place for six years in Taiwan and the second leading cause of cancer deaths in both men and women in the United States. The survival rate is highly dependent upon stage of CRC when it is first diagnosed. There will be a 90% 5-year survival rate for cancers detected at the localized stage but extremely low (10%) 5-year survival rate for patients with metastatic CRC. 5-fluorouracil (5-FU) or its prodrug, tegafur, is included in standard combination therapy (regimen) for the pre- and postoperative treatment of patients with CRC. Although current oral administration UFT (combination of tegafur, and uracil at a biomodulator in a 1:4 ratio)-based chemoradiotherapy is effective and improved survival rate in patients, different studies of combination with adjuvant agents and tegafur are carried out in patients with newly diagnosed or recurrent disease. Based on previous clinical experience, further improvements in patient outcomes (eg., reduced the rate of recurrence) may result from the combination of UFT with targeted agents. Therefore, we hypothesize that if multifunctional prodrug, through introducing different moieties to parent structure (Tegafur), will lead to an significant augmentation in its potency via triggering different molecular signaling events in tumor cells? Recently, HDAC6 has been shown as an attractive target for the treatment of cancer due to low toxicity. Inhibition of HDAC6 resulted in decreased cell motility and growth inhibition. In this project, our goal is planning to evaluate and characterize dual (or multiple)-functional of tegafur-derivatives by incorporating functional groups for HDAC6 enzyme inhibition to tegafur in CRC cells. Our preliminary data showed that one potential compound, MPT0G321, displays selective HDAC6 inhibitory effect by in vitro HDAC enzyme assay and showing upregulation of acetylated-α tubulin without affecting acetylated-Histone H3 levels in HCT116 cells. MPT0G321 also inhibits cell proliferation and induces apoptotic cell death by activation of caspase-3,-8,-9, and PARP in CRC HCT116 cells. Further, our results show exposure to MPT0G321 induces activation of Chk2, accumulation of p53, and reduces the protein expression level of Rad51. Those findings suggest MPT0G321 may affect DNA repair and also trigger DNA damage response (DDR) in cells. The underlying mechanism of the compound needs further investigation. This will also allow us to understand the role of HDAC6 in CRC and how important of optimization of different mechanistic compounds for new generation of drug development. Three aims are proposed to achieve this goal: Aim 1: (a) identify if the antitumor activity is attributed to 5-FU or functional groups for HDAC6 enzyme inhibition and (b) our colleagues will synthesize more tegafur-derivatives with modified structures to be tested for anti-tumor activities against CRC cells by drug screening. We will perform Structure–Activity Relationships (SAR) to study effects of Tegafur and its derivatives on viability of cancer cell. Aim 2: (a) find the most potential compound after evaluating newly synthesized tegafur-derivatives and (b) study detailed mechanism of actions of the potential compounds to identify and characterize the drug-induced signaling transduction to prevent or treat metastasis and drug resistance in CRC. Aim 3: (a) evaluate the combination strategy of tegafur-derivatives and clinical therapeutic drugs and (b) establish in vivo xenograft tumor model with CRC cells to study monotherapy of tegafur-derivatives and combinational treatment of tegafur-derivatives and clinical therapeutic agents. By executing these specific aims, we expect to find out a promising multi-functional tegafur-derivative that will be greatly beneficial to patients with CRC through monotherapy or combination therapy.