indication

For the treatment of pediatric and adult patients with acute T-cell lymphoblastic leukemia and T-cell lymphoblastic lymphoma whose disease has not responded to or has relapsed following treatment with at least two chemotherapy regimens.

pharmacology

Nelarabine is a prodrug of the cytotoxic deoxyguanosine analogue 9-ß-D-arabinofuranosylguanine (ara-G). Nelarabine is demethylated by adenosine deaminase (ADA) to ara-G. Ara-G is then transported into cells, where it undergoes three phosphorylation steps, resulting in the formation of ara-G triphosphate (ara-GTP). In the first phosphorylation step, ara-G is converted to ara-G monophosphate (ara-GMP). Ara-GMP is then monophosphorylated by deoxyguanosine kinase and deoxycytidine kinase to ara-G diphosphate, and then subsequently to the active ara-G triphosphate (ara-GTP). Ara-GTP is the one that exerts the pharmacological effect. Pre-clinical studies suggest that T-cells are particularly sensitive to nelarabine.

mechanism of action

Once nelarabine is metabolized into ara-GTP, the metabolite accumulates in leukemic blasts and incorporates into DNA to exert its S phase-specific cytotoxic effects, leading to the induction of fragmentation and apoptosis. Ara-GTP competes with endogenous deoxyGTP (dGTP) for incorporation into DNA. Once ara-GTP is incorporated at the 3' end of DNA, further DNA elongation is inhibited, which signals apoptosis and leads to cellular destruction. Additional cytotoxic activities may exist, but these are not fully understood.

toxicity

A single IV dose of 4,800 mg/m^2 was lethal in monkeys, and was associated with CNS signs including reduced/shallow respiration, reduced reflexes, and flaccid muscle tone. It is anticipated that overdosage would result in severe neurotoxicity (possibly including paralysis, coma), myelosuppression, and potentially death.

biotransformation

The principal route of metabolism for nelarabine is O-demethylation by adenosine deaminase to form ara-G, which undergoes hydrolysis to form guanine. In addition, some nelarabine is hydrolyzed to form methylguanine, which is O-demethylated to form guanine. Guanine is N-deaminated to form xanthine, which is further oxidized to yield uric acid. Ring opening of uric acid followed by further oxidation results in the formation of allantoin.

half life

Nelarabine and ara-G are rapidly eliminated from plasma with a half-life of approximately 30 minutes and 3 hours.

route of elimination

Excretion: Nelarabine and ara-G are partially eliminated by the kidneys.