6-Mercaptopurine transport by equilibrative nucleoside transporters in conditionally immortalized rat syncytiotrophoblast cell lines TR-TBTs

• Published in: Journal of pharmaceutical sciences Vol. 100; no. 9; p. 3773
• Main Authors: Lee, Na-young, Sai, Yoshimichi, Nakashima, Emi, Ohtsuki, Sumio, Kang, Young-sook
• Format: Journal Article
• Language: English
• Published: United States 01-09-2011
• Subjects: Animals; Antimetabolites, Antineoplastic - pharmacokinetics; Base Sequence; Carrier Proteins - metabolism; Cell Line, Transformed; DNA Primers; Mercaptopurine - pharmacokinetics; Rats; Trophoblasts - cytology; Trophoblasts - metabolism
• ISSN: 1520-6017
• DOI: 10.1002/jps.22631

Recently, more women were provided with 6-mercaptopurine (6-MP) during pregnancy. Therefore, we attempted to clarify the transport mechanisms of 6-MP through blood-placenta barrier using rat conditionally immortalized syncytiotrophoblast cell lines (TR-TBTs). The uptake of 6-MP was time- and ATP dependent, but sodium independent in TR-TBTs. 6-MP was eliminated over 50% from the cells within 30 min. The uptake of 6-MP was saturable with Michaelis-Menten constant values of 198 μM and 250 μM in TR-TBT 18d-1 and TR-TBT 18d-2, respectively. 6-Thioguanine, azathioprine, and hypoxantine, structural analogues of 6-MP, strongly inhibited [(14) C]6-MP uptake. Equilibrative nucleoside transporter (ENT) inhibitors, adenosine and uridine, significantly inhibited [(14) C]6-MP uptake. However, several organic anions and cations had no effect on [(14) C]6-MP uptake in TR-TBTs. These results suggest that sodium-independent transporters, ENTs, may be involved in 6-MP uptake at the placenta. In addition, multidrug resistance protein (MRP) inhibitors, methotrexate, probenecid, cefmetazole, and sulfinpyrazone, significantly increased the accumulation of [(14) C]6-MP in the cells. It is indicated that 6-MP may be eliminated across the blood-placental barrier via MRPs. TR-TBTs expressed mRNA of ENT1, ENT2, MRP4, and MRP5. These findings are important for the therapy of acute lymphoblastic leukemia and autoimmune diseases of pregnant women, and should be useful data in elucidating teratogenicity of 6-MP during pregnancy.