title: Curcumin and its cyclohexanone analogue inhibited human Equilibrative nucleoside transporter 1 (ENT1) in pancreatic cancer cells.
abstract: Our group investigated combining the phytochemical curcumin and gemcitabine in a liposome, to improve gemcitabine's activity against pancreatic tumours. While optimising the curcumin: gemcitabine ratio for co-encapsulation, we found that increasing curcumin concentrations relative to gemcitabine resulted in antagonistic interactions. As curcumin is a promiscuous transporter inhibitor; we suspected that increased resistance occurred via inhibition of Equilibrative nucleoside transporter 1 (ENT1)-mediated gemcitabine uptake. To test our hypothesis, we determined whether curcumin and a related analogue, 2,6-bis((3-methoxy-4-hydroxyphenyl)methylene)-cyclohexanone (or A13), inhibited ENT1-mediated accumulation of [3H]uridine and [3H]gemcitabine into pancreatic cancer cells. We then confirmed the inhibition of gemcitabine accumulation by investigating whether curcumin/A13 could increase gemcitabine resistance in growth inhibition assays. We found that curcumin and A13 concentration-dependently inhibited the ENT1-mediated accumulation of both uridine and gemcitabine in MIA PaCa-2 and PANC-1 cells. We also found that non-toxic concentrations of curcumin and A13 significantly increased the resistance of both cell lines to gemcitabine. Increased resistance only occurred when curcumin/A13 was co-incubated with gemcitabine, and not with sequential exposure (i.e., curcumin first, followed by gemcitabine, or vice versa). We also found that the curcumin analogue (3E,5E)-3,5-bis[(2-fluorophenyl)methylene]-4-piperidinone (or EF24) did not inhibit gemcitabine accumulation, making it more suitable in combinations than curcumin/A13. From these results, we concluded that curcumin and A13 are inhibitors of the ENT1 transporter, but only at high concentrations (2-20µM). Curcumin is unlikely to inhibit gemcitabine uptake in tumours but may interfere with the oral absorption of ENT1 substrates due to high gut concentrations readily achievable from over-the-counter tablets/capsules.
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
authors.forename: Jezrael L
authors.initials: JL
authors.lastname: Revalde
authors.affiliation: School of Interprofessional Health Studies, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand. Electronic address: yali@aut.ac.nz.
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
authors.forename: Tharaka S
authors.initials: TS
authors.lastname: Wijeratne
authors.affiliation: School of Interprofessional Health Studies, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand.
authors.forename: Piyush
authors.initials: P
authors.lastname: Bugde
authors.affiliation: Department of Chemistry, University of Otago, Dunedin, New Zealand.
authors.forename: Bill C
authors.initials: BC
authors.lastname: Hawkins
authors.affiliation: Department of Pharmacology and Toxicology, University of Otago, Dunedin, New Zealand.
authors.forename: Rhonda J
authors.initials: RJ
authors.lastname: Rosengren
authors.affiliation: Department of Pharmacology and Clinical Pharmacology, Faculty of Medical and Health Sciences, University of Auckland, Auckland, New Zealand.
authors.forename: James W
authors.initials: JW
authors.lastname: Paxton
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003474:Curcumin / Q000737:chemistry* / Q000494:pharmacology*; D003512:Cyclohexanones / Q000737:chemistry*; D003841:Deoxycytidine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D004347:Drug Interactions; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D033721:Equilibrative Nucleoside Transporter 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006801:Humans; D010190:Pancreatic Neoplasms / Q000473:pathology*; D014529:Uridine / Q000378:metabolism; D000093542:Gemcitabine
chemical_list: D000970:Antineoplastic Agents; D003512:Cyclohexanones; D033721:Equilibrative Nucleoside Transporter 1; D003841:Deoxycytidine; C036468:cyclohexanone; D003474:Curcumin; D014529:Uridine; D000093542:Gemcitabine
keywords: A13 (PubChem CID: 1550234); Curcumin; Curcumin (PubChem CID: 969516); Curcumin analogues; Dipyridamole (PubChem CID: 3108); EF24; EF24 (PubChem CID: 77895890); ENT1; Gemcitabine; Gemcitabine (PubChem CID: 60750); Nitrobenzylthioinosine (PubChem CID: 65407); Pancreatic cancer