Fludarabine impairs the removal of oxaliplatin-induced DNA interstrand crosslinks in the mitochondrial DNA (mtDNA). CLL lymphocytes were incubated with 400 μM oxaliplatin in the absence or presence of 2.5 μM fludarabine for 5 hours when cells were washed into drug-free medium. DNA from cells allowed to repair for up to 8 hours was analyzed for ICLs remaining. (A) Representative ICL blot probed for the 16.5-kb mtDNA. (B) Quantitation of oxaliplatin ICLs remaining in the mtDNA as a function of repair time. Crosslinks remaining after repair in the absence (▪) or presence (•) of fludarabine were expressed as a percentage of initial ICL levels.