Phytomedicine 106 (2022) 154406 Available online 20 August 2022 0944-7113/© 2022 Elsevier GmbH. All rights reserved. Original Article Isoliquiritigenin inhibits pancreatic cancer progression through blockade of p38 MAPK-regulated autophagy Zhu Zhang a, b, c, 1 , Wen-qing Chen a, b, 1 , Shi-qing Zhang d, 1 , Jing-xuan Bai a , Bin Liu e , Ken Kin-Lam Yung b, c, * , Joshua Ka-Shun Ko a, f, ** a Teaching and Research Division, School of Chinese Medicine, Hong Kong Baptist University, Hong Kong SAR, China b Department of Biology, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong SAR, China c Golden Meditech Centre for NeuroRegeneration Sciences, Hong Kong Baptist University, Hong Kong SAR, China d JNU-HKUST Joint Laboratory for Neuroscience and Innovative Drug Research, College of Pharmacy, Jinan University, Guangzhou, China e Department of Traditional Chinese Medicine, Institute of Integration of Traditional and Western Medicine of Guangzhou Medical University, The Second Affliated Hospital of Guangzhou Medical University, Guangzhou Medical University, Guangzhou, China f Centre for Cancer and Infammation Research, School of Chinese Medicine, Hong Kong Baptist University, 7 Baptist University Road, Kowloon Tong, Hong Kong SAR, China A R T I C L E INFO Keywords: Isoliquiritigenin Pancreatic cancer Apoptosis Autophagy p38 MAPK ABSTRACT Background: Pancreatic cancer has been characterized by poor prognosis, early metastasis and dissatisfactory treatment outcome. The high basal level of autophagy in tumor cells leads to chemoresistance and tumor pro- gression. Thus, it is imminent to explore novel effective chemotherapeutic adjuvants to increase patients’ sur- vival rate. Isoliquiritigenin (ISL) is a bioactive favonoid obtained from the Traditional Chinese herbal medicine Glycyrrhiza glabra, and it possesses a broad range of pharmacological effects. In this study, the anti-cancer effect of ISL in pancreatic cancer treatment and the underlying mechanism are investigated. Methods: MTT assay, colony formation and EdU analysis were performed to explore the growth inhibition of ISL on pancreatic cancer cells. Apoptosis were analyzed using TUNEL and fow cytometry. The formations of autophagosomes were analyzed by immunofuorescence microscopy and transmission electron microscopy. RFP- GFP-LC3B probe was applied to detect the autophagy fux. To assess the structural interaction of ISL with p38 protein, molecular docking assays were performed. The molecular mechanism was elucidated by using western immunoblotting. Subsequently, the inhibition of ISL on tumor growth was determined in vivo using pancreatic tumor mice model. Results: ISL inhibited pancreatic cancer cell growth and induced apoptosis, both in vitro and in vivo. ISL caused accumulation of autophagosome through blockade of late stage autophagic fux. Moreover, autophagy inducer rapamycin enhanced ISL-evoked cell growth inhibition and promoted apoptosis, while inhibition of autopha- gosome formation by siAtg5 attenuated ISL-induced apoptosis. It is remarkable that ISL synergistically sensitized the cytotoxic effect of gemcitabine and 5-fuorouracil on pancreatic cancer cells as both drugs induced auto- phagy. Molecular docking analysis has indicated that ISL acted by direct targeting of p38 MAPK, which was confrmed by ISL-induced phosphorylation of p38. The autophagy fux induced by p38 inhibitor SB203580 was blocked by ISL, with further increasing toxicity of ISL in pancreatic cancer cells. Abbreviations: ATCC, American type culture collection; BSA, bovine serum albumin; CDI, Co-effcient of drug interaction; CQ, chloroquine; DAPI, 4 ′ ,6-diamidino- 2-phenylindole; DMSO, dimethyl sulfoxide; DMEM, dulbecco’s modifed eagle’s medium; EdU, 5-ethynyl-2 ′ -deoxyuridine; FBS, fetal bovine serum; FITC, annexin V- fuorescein isothiocyanate; GEM, gemcitabine; HCQ, hydroxychloroquine; IF, immunofuorescence; IHC, immunohistochemical; ISL, isoliquiritigenin; MD, molecular dynamics; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide; PDAC, pancreatic ductal adenocarcinoma; PFA, paraformaldehyde; PI, propidium iodide; Rap, rapamycin; RMSD, root-mean-square deviation; ROS, reactive oxygen species; SD, standard deviation; TEM, transmission electron microscopy; TUNEL, terminal deoxynucleotidyl transferase dUTP Nick-end labeling; YASARA, yet another scientifc artifcial reality application; 5-FU, 5-fuorouracil. * Corresponding author at: Department of Biology, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong SAR, China. ** Corresponding author at: Centre for Cancer and Infammation Research, School of Chinese Medicine, Hong Kong Baptist University, 7 Baptist University Road, Kowloon Tong, Hong Kong SAR, China. E-mail addresses: kklyung@hkbu.edu.hk (K.K.-L. Yung), jksko@hkbu.edu.hk (J.K.-S. Ko). 1 These authors contributed equally to this work. Contents lists available at ScienceDirect Phytomedicine journal homepage: www.elsevier.com/locate/phymed https://doi.org/10.1016/j.phymed.2022.154406 Received 8 April 2022; Received in revised form 22 July 2022; Accepted 17 August 2022