Clofarabine is metabolized intracellularly to the active 5'-monophosphate metabolite by deoxycytidine kinase and 5'-triphosphate metabolite by mono- and di-phospho-kinases. This metabolite inhibits DNA synthesis through an inhibitory action on ribonucleotide reductase, and by terminating DNA chain elongation and inhibiting repair through competitive inhibition of DNA polymerases. This leads to the depletion of the intracellular deoxynucleotide triphosphate pool and the self-potentiation of clofarabine triphosphate incorporation into DNA, thereby intensifying the effectiveness of DNA synthesis inhibition. The affinity of clofarabine triphosphate for these enzymes is similar to or greater than that of deoxyadenosine triphosphate. In preclinical models, clofarabine has demonstrated the ability to inhibit DNA repair by incorporation into the DNA chain during the repair process. Clofarabine 5'-triphosphate also disrupts the integrity of mitochondrial membrane, leading to the release of the pro-apoptotic mitochondrial proteins, cytochrome C and apoptosis-inducing factor, leading to programmed cell death.
Clofarabine is a purine nucleoside antimetabolite that differs from other puring nucleoside analogs by the presence of a chlorine in the purine ring and a flourine in the ribose moiety. Clofarabine seems to interfere with the growth of cancer cells, which are eventually destroyed. Since the growth of normal body cells may also be affected by clofarabine, other effects also occur. Clofarabine prevents cells from making DNA and RNA by interfering with the synthesis of nucleic acids, thus stopping the growth of cancer cells.
Clofarabine is sequentially metabolized intracellularly to the 5ê-monophosphate metabolite by deoxycytidine kinase and mono- and di-phosphokinases to the active 5ê-triphosphate metabolite. Clofarabine has high affinity for the activating phosphorylating enzyme, deoxycytidine kinase, equal to or greater than that of the natural substrate, deoxycytidine.
There were no known overdoses of clofarabine. The highest daily dose administered to a human to date (on a mg/m2 basis) has been 70 mg/m2/day _ 5 days (2 pediatric ALL patients). The toxicities included in these 2 patients included grade 4 hyperbilirubinemia, grade 2 and 3 vomiting, and grade 3 maculopapular rash.
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