Inhibition of 6-Mercaptopurine-Resistant Cancer Cells in Culture by Bis(Thioinosine)-5′,-5‴-Phosphate

Pronucleotides: toward the in vivo delivery of antiviral and anticancer nucleotides

To overcome the many hurdles preventing the use of antiviral and anticancer nucleosides as therapeutics, the development of a prodrug methodology (i.e., pronucleotide) for the in vivo delivery of nucleotides has been proposed as a solution. The ideal pronucleotide should be non-toxic, stable in plasma and blood, capable of being i. v. and/or orally dosed, and intracellularly convertible to the corresponding nucleotide. Although this goal has yet to be achieved, many clever and imaginative pronucleotide approaches have been developed, which are likely to be important pharmacological tools. This review will discuss the major advances and future directions of the emerging field of antiviral and anticancer pronucleotide design and development.

THE METABOLISM OF 9-ARABINOSYL-6-MERCAPTOPURINE IN NORMAL AND NEOPLASTIC TISSUES

Arabinosyl-6-mercaptopurine (ara-6-MP) was found to increase the survival time of mice bearing 6-mercaptopurine (6-MP)-sensitive or 6-MP-resistant tumors. Studies with the radiosulfur-labeled drug in mice showed that the drug was rapidly cleared from the blood, distributed throughout the tissues, and relatively rapidly excreted in the urine. Arabinosyl-6-mercaptopurine was neither cleaved to 6-mercaptopurine by the Ehrlich ascites tumor nor converted to nucleotide to any appreciable extent under the conditions studied. Arabinosyl-6-mercaptopurine at a dosage level of 300 mg/kg produced a minimal inhibition of orotic acid-6-C14incorporation into the DNA cytosine of the Ehrlich ascites tumor. No effect on the incorporation of glycine-2-C14into acid-soluble or nucleic acid purines of the Ehrlich ascites tumor was noted at this dosage level. No toxicity has been observed with the doses of ara-6-MP studied (300 mg/kg).