Cladribine

Cladribine is a purine nucleoside analog. It must first be phosphorylated intracellularly by deoxycytidine kinase to form cladribine monophosphate, and is then further phosphorylated by other kinases into cladribine triphosphate. During DNA synthesis, cladribine triphosphate can be incorporated into DNA, interfering with DNA synthesis and repair and causing the accumulation of DNA damage and strand breaks, which promotes apoptosis. Because lymphocytes express particularly high levels of deoxycytidine kinase, cladribine causes extensive apoptosis of both T and B lymphocytes.