Carboranyl oligonucleotides. 3. Biochemical properties of oligonucleotides containing 5-(o-carboranyl-1-yl)-2'-deoxyuridine.

Boronated oligonucleotides are potential candidates for boron neutron capture therapy, antisense technology, and as tools in molecular biology. The biological properties of dodecathymidylic acids containing one or more 5-(o-carboran-1-yl)-2'-deoxyuridine residues at different locations within the oligonucleotide chain were studied. 5-(o-Carboran-1-yl)-2'-deoxyuridine containing oligonucleotides manifested marked increased lipophilicity and resistance to 3'- or 5'-phosphodiesterases compared to the corresponding unmodified oligomer. They were substrates for T4 polynucleotide kinase and primers for Escherichia coli polymerase I and human immunodeficiency virus type 1 reverse transcriptase but not for human DNA polymerase alpha and beta. They also formed heteroduplexes that were substrates for E. coli RNase H, an essential property for antisense technology. These studies indicate that the carboranyl-containing oligonucleotides have desirable properties that need to be exploited further in the design of novel biopharmaceuticals.

Pharmacokinetics of 5-carboranyl-2'-deoxyuridine in rats.

The pharmacokinetics of 5-carboranyl-2'-deoxyuridine (CDU) after intravenous administration of 25 mg/kg was investigated in rats. The uptake of CDU into brain was also examined. Concentrations of CDU in plasma, urine, and brain were measured by reverse phase HPLC. Plasma concentrations of CDU declined in a biexponential fashion with a terminal half-life of 1.26 +/- 0.28 h. The plasma protein binding of CDU was linear and the average fraction bound to plasma proteins was 0.95 +/- 0.02. The total clearance of CDU was 0.69 +/- 0.20 L/h/kg whereas clearance of unbound drug was much greater (15.33 +/- 4.44 L/h/kg). Thus, the total clearance of the drug is limited, in part, by the high degree of plasma protein binding, resulting in a moderate total clearance. No unchanged CDU was detected in urine. Furthermore, there was no trace of CDU glucuronide in urine samples. The steady-state volume of distribution of CDU was 0.70 +/- 0.23 L/kg. The brain:total plasma CDU concentration ratios determined in two rats were 0.47 and 0.36, while the brain:unbound plasma CDU concentration ratios were 10.26 and 7.87. The results of this study suggest that it is possible to achieve significant levels of CDU in brain. The high degree of plasma protein binding restricted extensive distribution of this lipophilic compound. The results of this study suggest further investigations of CDU as a neutron sensitizer for boron neutron capture therapy (BNCT) are warranted.

Cellular pharmacology and biological activity of 5-carboranyl-2'-deoxyuridine.

PURPOSE: The intracellular uptake and metabolism of 5-carboranyl-2'-deoxyuridine was investigated in primary human lymphocytes and in a T lymphoblastoid cell line using unlabeled and tritium labeled compound. The cytotoxicity and antiviral activity of the compound and stability to enzyme degradation was determined. METHODS AND MATERIALS: A novel method for radiolabeling the 5-carboranyl moiety of pyrimidine nucleosides was developed. Cells were exposed to unlabeled and tritium labeled 5-carboranyl-2'-deoxyuridine and the intracellular uptake and egress of the compound determined by high pressure liquid chromatography. The viability and growth of normal and malignant cells, including human and rat gliomas, in the presence of the compound was determined. RESULTS: Substantial levels of 5-carboranyl-2'-deoxyuridine-5'-monophosphate are formed intracellularly and this major metabolite can be detected in cells 48 h after removal of the parent compound from the medium. No significant phosphorylation to the 5'-diphosphate or triphosphate of 5-carboranyl-2'-deoxyuridine was detected. Furthermore, radiolabeled 5-carboranyl-2'-deoxyuridine was not incorporated into deoxyribonucleic acid. 5-carboranyl-2'-deoxyuridine was essentially nontoxic to human lymphocytes as well as human or rat glioma cells, and had no marked effect in human lymphocytes acutely infected with human immunodeficiency virus type 1. CONCLUSION: The results demonstrate for the first time that 5-carboranyl-2'-deoxyuridine is phosphorylated intracellularly and suggest that it should be considered for further studies as a potential sensitizer for boron neutron capture therapy.