TY - JOUR T1 - Cellular Influx, Efflux, and Anabolism of 3-Carboranyl Thymidine Analogs: Potential Boron Delivery Agents for Neutron Capture Therapy JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 388 LP - 397 DO - 10.1124/jpet.113.207464 VL - 347 IS - 2 AU - Elena Sjuvarsson AU - Vijaya L. Damaraju AU - Delores Mowles AU - Michael B. Sawyer AU - Rohit Tiwari AU - Hitesh K. Agarwal AU - Ahmed Khalil AU - Sherifa Hasabelnaby AU - Ayman Goudah AU - Robin J. Nakkula AU - Rolf F. Barth AU - Carol E. Cass AU - Staffan Eriksson AU - Werner Tjarks Y1 - 2013/11/01 UR - http://jpet.aspetjournals.org/content/347/2/388.abstract N2 - 3-[5-{2-(2,3-Dihydroxyprop-1-yl)-o-carboran-1-yl}pentan-1-yl]thymidine (N5-2OH) is a first generation 3-carboranyl thymidine analog (3CTA) that has been intensively studied as a boron-10 (10B) delivery agent for neutron capture therapy (NCT). N5-2OH is an excellent substrate of thymidine kinase 1 and its favorable biodistribution profile in rodents led to successful preclinical NCT of rats bearing intracerebral RG2 glioma. The present study explored cellular influx and efflux mechanisms of N5-2OH, as well as its intracellular anabolism beyond the monophosphate level. N5-2OH entered cultured human CCRF-CEM cells via passive diffusion, whereas the multidrug resistance-associated protein 4 appeared to be a major mediator of N5-2OH monophosphate efflux. N5-2OH was effectively monophosphorylated in cultured murine L929 [thymidine kinase 1 (TK1+)] cells whereas formation of N5-2OH monophosphate was markedly lower in L929 (TK1–) cell variants. Further metabolism to the di- and triphosphate forms was not observed in any of the cell lines. Regardless of monophosphorylation, parental N5-2OH was the major intracellular component in both TK1+ and TK1– cells. Phosphate transfer experiments with enzyme preparations showed that N5-2OH monophosphate, as well as the monophosphate of a second 3-carboranyl thymidine analog [3-[5-(o-carboran-1-yl)pentan-1-yl]thymidine (N5)], were not substrates of thymidine monophosphate kinase. Surprisingly, N5-diphosphate was phosphorylated by nucleoside diphosphate kinase although N5-triphosphate apparently was not a substrate of DNA polymerase. Our results provide valuable information on the cellular metabolism and pharmacokinetic profile of 3-carboranyl thymidine analogs. ER -