IN-VITRO AND IN-VIVO EVALUATION OF CARBORANYL URIDINES AS BORON DELIVERY AGENTS FOR NEUTRON-CAPTURE THERAPY

Tire purpose of the present study was to evaluate 2' and 5'O- (o-carbo ran-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 MDCK hu man glioma, B16 melanoma, SP2/0 myeloma and MDCK fibroblasts. All tumo r and non-tumor cell lines had high uptake of CBU-2' (46-75 ppm), indi cating that uptake was izot selective for neoplastic cells and was ind ependent of cell proliferation. In vitro persistence studies showed hi gh 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 w ere cultured in the presence of 3 metabolic inhibitors (rotenone, dipy ridamole and NBMPR 4-nitrobenzyl)thio]-9-beta-D-ribofuranosylpurine}) and none of these blocked the cellular uptake of CBU-2' suggesting tha t uptake was neither energy nor nucleoside transport dependent. In viv o studies in F98 glioma bearing rats showed that CBU-2' in tumor attai ned concentrations of 8.0 +/- 2.1 mu g B/g tissue, which was 13x great er than that in normal brain of the ipsilateral and contralateral cere bral hemispheres (0.6 +/- 0.2 mu g B/g). The B levels, however, were s till lower that the minimum 20-35 mu g 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 tumo rs. 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 upta ke of H-3-thymidine, and the survival of F98 glioma cells using a clon ogenic assay, which suggests that these compounds should be further ev aluated as potential cytoreductive chemotherapeutic agents.