title: In vitro and in vivo evaluation of carboranyl uridines as boron delivery agents for neutron capture therapy.
abstract: The purpose of the present study was to evaluate 2' and 5'-O-(o-carboran-1-ylmethyl)uridine (CBU-2' and CBU-5') as delivery agents for Boron Neutron Capture Therapy (BNCT) of brain tumors. The in vitro cellular uptake, persistence, subcellular distribution and cytotoxicity, and in vivo biodistribution of CBU-2' have been studied as follows. Cellular uptake studies were carried out with the F98 rat glioma, U-87 MG human glioma, B16 melanoma, SP2/0 myeloma and MDCK fibroblasts. All tumor and non-tumor cell lines had high uptake of CBU-2' (46-75 ppm), indicating that uptake was not selective for neoplastic cells and was independent of cell proliferation. In vitro persistence studies showed high cellular retention of CBU-2' compared to sodium borocaptate (BSH), when cells were transferred from boron-containing to boron-free medium and cultured for an additional 24-48 hours. Subcellular fractionation revealed 75.6% of the recoverable boron was cell membrane associated, 15.6% was in the cytosol, and 8.8% was in the nuclear fraction, but no boron was detectable in the RNA and DNA fractions. F98 glioma cells were cultured in the presence of 3 metabolic inhibitors (rotenone, dipyridamole and NBMPR ¿6-[(4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine¿) and none of these blocked the cellular uptake of CBU-2' suggesting that uptake was neither energy nor nucleoside transport dependent. In vivo studies in F98 glioma bearing rats showed that CBU-2' in tumor attained concentrations of 8.0 +/- 2.1 micrograms B/g tissue, which was 13 x greater than that in normal brain of the ipsilateral and contralateral cerebral hemispheres (0.6 +/- 0.2 microgram B/g). The B levels, however, were still lower than the minimum 20-35 microgram B/g, which are required for in vivo BNCT. In summary, our in vitro and in vivo data indicate that CBU-2' was not sufficiently selective for in vivo targeting of brain tumors. However, CBU-2' and CBU-5' were highly toxic for F98 glioma cells in vitro (IC50 = 3 - 13 x 10(-5) M), as determined by measuring the uptake of 3H-thymidine, and the survival of F98 glioma cells using a clonogenic assay, which suggests that these compounds should be further evaluated as potential cytoreductive chemotherapeutic agents.
authors.affiliation: Department of Pathology, Ohio State University, Columbus 43210, USA.
authors.forename: L
authors.initials: L
authors.lastname: Liu
authors.forename: R F
authors.initials: RF
authors.lastname: Barth
authors.forename: W
authors.initials: W
authors.lastname: Tjarks
authors.forename: A H
authors.initials: AH
authors.lastname: Soloway
authors.forename: A K
authors.initials: AK
authors.lastname: Anisuzzaman
mesh_terms: D000818:Animals; D001896:Boron Compounds / Q000493:pharmacokinetics* / Q000494:pharmacology*; D016754:Boron Neutron Capture Therapy / Q000379:methods*; D004176:Dipyridamole / Q000494:pharmacology; D004285:Dogs; D005069:Evaluation Studies as Topic; D005347:Fibroblasts / Q000378:metabolism / Q000528:radiation effects; D005910:Glioma / Q000378:metabolism / Q000532:radiotherapy; D006801:Humans; D008546:Melanoma, Experimental / Q000378:metabolism / Q000532:radiotherapy; D009101:Multiple Myeloma / Q000378:metabolism / Q000532:radiotherapy; D009369:Neoplasms / Q000378:metabolism* / Q000532:radiotherapy*; D051381:Rats; D011916:Rats, Inbred F344; D012402:Rotenone / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism; D013868:Thioinosine / Q000031:analogs & derivatives / Q000494:pharmacology; D013936:Thymidine / Q000493:pharmacokinetics; D014018:Tissue Distribution; D014316:Tritium; D014407:Tumor Cells, Cultured; D014529:Uridine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology
chemical_list: C099168:5'-O-(o-carboran-1-ylmethyl)uridine; D001896:Boron Compounds; D012402:Rotenone; D014316:Tritium; C076220:2'-O-(carboran-1-ylmethyl)uridine; D013868:Thioinosine; D004176:Dipyridamole; C001789:4-nitrobenzylthioinosine; D013936:Thymidine; D014529:Uridine