Nelarabine is a prodrug of arabinosylguanine nucleotide triphosphate (araGTP), a type of purine nucleoside analog, which causes inhibition of DNA synthesis and cytotoxicity. Pre-clinical studies suggest that T-cells are particularly sensitive to nelarabine. In October 2005, it was approved by the FDA for acute lymphoblastic leukemia and T-cell lymphoblastic lymphoma that has not responded to or has relapsed following treatment with at least two chemotherapy regimens. It was later approved in the European Union in October 2005. Complete responses have been achieved with this medication.