PT  - JOURNAL ARTICLE
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
TI  - Cellular influx, efflux, and anabolism of 3-carboranyl thymidine analogs: Potential boron delivery agents for neutron capture therapy.
AID  - 10.1124/jpet.113.207464
DP  - 2013 Jan 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - jpet.113.207464
4099  - http://jpet.aspetjournals.org/content/early/2013/09/04/jpet.113.207464.short
4100  - http://jpet.aspetjournals.org/content/early/2013/09/04/jpet.113.207464.full
AB  - 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. 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 (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 3CTA (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 3CTAs.