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Nelarabine


ACCESSION NB: DB01280


TYPE: small molecule


GROUP: approved


DESCRIPTION:
Nelarabine is a chemotherapy drug used in T-cell acute lymphoblastic leukemia. Nelarabine is a purine nucleoside analog converted to its corresponding arabinosylguanine nucleotide triphosphate (araGTP), resulting in inhibition of DNA synthesis and cytotoxicity.

VOLUME OF DISTRIBUTION: Not Available

CATEGORIES:
Antineoplastic Agents

ABSORPTION: Not Available

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.

PHARMACODYNAMICS:
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.

PROTEIN BINDING:
Nelarabine and ara-G are not substantially bound to human plasma proteins (<25%) in vitro, and binding is independent of nelarabine or ara-G concentrations up to 600 mM.

METABOLISM:
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. Enzyme Metabolite Reaction Km Vmax Adenosine deaminase arabinofuranosylguanine demethylation Deoxycytidine kinase ara-G diphosphate phosphorylation Deoxyguanosine kinase, mitochondrial ara-G diphosphate phosphorylation

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.

AFECTED ORGANISMS:
Humans and other mammals