9-Norbornyl-6-chloropurine Is a Novel Antileukemic Compound Interacting with Cellular GSH

Aim: 6-Chloropurines substituted at position 9 with bicyclic skeletons represent promising chemotherapeutic agents. We explored the metabolism and membrane transport of 9-norbornyl-6-chloropurine (NCP) aiming to understand its mechanism of action. Materials and Methods: The metabolism of NCP was studied in vitro in whole cells (CCRF-CEM), cellular extracts, subcellular fractions and purified enzymes. Transport experiments were conducted in Caco-2 cell monolayers. Results: Three metabolites were identified, a glutathione conjugate (NCP-GS), NCP- cysteinylglycine and NCP-cysteine. Both glutathione-S- transferase inhibition and glutathione (GSH) depletion prevented metabolite formation and increased the cytotoxicity of NCP. Transepithelial transport (Caco-2) indicated good permeability, with P app (12.6±0.3) ×10 -5 cm/s. Importantly, the drug induced glutathione depletion in treated cells and affected the activity of several GSH- dependent enzymes. Conclusion: The novel nucleoside analog NCP represents a promising orally available antileukemic agent, acting through lowering of GSH levels in tumor cells. 6-Chloropurines substituted at position 9 with variously modified bicyclic skeletons represent analogs of carbocyclic nucleosides, where the bicyclic part mimics the sugar moiety. Many of these compounds, previously synthesized in our laboratories, have been reported as efficient antivirals against Coxsackieviruses (Picornaviridae) (1, 2). These (+)ssRNA