3048 - Quercetin, A Natural Flavonoid Compound, Sensitizes Pancreatic Ductal Adenocarcinoma to Radiation Therapy
Presenter(s)
V. Gandhi1, T. Laufer2, and A. C. Mueller3; 1UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA, 2Department of Radiation Oncology, Sidney Kimmel Medical College of Thomas Jefferson University, Philadelphia, PA, 3Department of Radiation Oncology, UPMC Hillman Cancer Center, University of Pittsburgh, Philadelpha, PA
Purpose/Objective(s): Pancreatic ductal adenocarcinoma (PDAC) is one of the most treatment resistant cancers, with incidence to morbidity ratio almost 1. Radiotherapy (RT) is one of the major treatment modalities for PDAC but its proximity to radiosensitive gastrointestinal organs makes it difficult to deliver effective doses of radiation. One strategy to increase the efficacy of RT is combination with radiosensitizing drugs, to selectively increase the sensitivity of tumor cell killing by RT. Here, we investigated Quercetin, a nutraceutical flavonoid compound with proposed impacts on DNA repair, free radical scavenging, cell cycle progression and cellular metabolism for its effect with RT in PDAC.
Materials/Methods: We utilized 4 different PDAC cell lines from mouse (PK5L1940) and human (AsPC-1, BxPC-3 and PANC-1) in vitro, and syngeneic (PK5L1940) tumor bearing C57BL/6 mice in vivo. We performed clonogenic assays, treating with quercetin (25 µM) overnight followed by increasing doses of RT. We then examined the effect of quercetin and RT on cell cycle progression by propidium iodide FACS. We determined the impact of quercetin and/or RT on DNA damage repair kinetics by ?-H2AX western blot in a time dependent manner. To test the effect of quercetin in vivo, C56BL/6 mice were injected subcutaneously with 5 X 105 cells and tumors allowed to grow for 7 days. Mice were treated with vehicle, Quercetin (100 mg/kg of body weight for 7 days), 16 Gy RT (day 10) + Vehicle, or 16 Gy RT + Quercetin. Tumor size was measured twice a week and mice were euthanized when tumor volume reached 2000 mm3. Experiment was terminated when average tumor volume of RT + vehicle treated group reached 2000 mm3.
Results: Quercetin sensitized the different PDAC cells lines with dose modification factor (DMF) at D50 (Dose required to kill 50% of cell population) of 0.53, 0.07,0.45 and 0.58 in PK5L1940, AsPC-1, PANC-1 and BXPC-3, respectively. Quercetin alone arrested cells in S-phase, while RT arrested cells in G2/M phase. Quercetin + RT significantly increased the S-phase population. ?-H2AX levels were also significantly higher with combination treatment as compared to RT treated cells at respective tie points. in vivo, while quercetin and RT individually did not significantly decrease or delayed tumor growth, the combination of quercetin and RT significantly delayed tumor growth at all time points. On the day of experiment termination when all other treatment groups have reached average tumor volume of 2000 mm3, the average tumor volume of the combination group was 1127 mm3.
Conclusion: Quercetin sensitizes various mouse and human PDAC cells for RT in vitro as well as mouse PDAC tumors in vivo. Quercetin arrests cells in S-phase and significantly increases the persistence of RT induced ?-H2AX levels suggesting the direct or indirect interference of quercetin in DNA-damage repair.