Mechanisms of anti-cancer action and pharmacology of clofarabine

Clofarabine, a next-generation deoxyadenosine analogue, was developed on the basis of experience with cladribine and fludarabine in order to achieve higher efficacy and avoid extramedullary toxicity. During the past decade this is the only drug granted approval for treatment of pediatric acute leukemia. Recent clinical studies have established the efficacy of clofarabine in treating malignancies with a poor prognosis, such as adult, elderly, and relapsed pediatric leukemia. The mechanisms of its anti-cancer activity involve a combination of direct inhibition of DNA synthesis and ribonucleotide reductase and induction of apoptosis. Due to this broad cytotoxicity, this drug is effective against various subtypes of leukemia and is currently being tested as an oral formulation and for combination therapy of both leukemias and solid tumors. In this review we summarize current knowledge pertaining to the molecular mechanisms of action and pharmacological properties of clofarabine, as well as clinical experiences with this drug with the purpose of facilitating the evaluation of its efficacy and the development of future therapies.

Clofarabine's mechanism of action. Upon entering the cell, clofarabine is phosphorylated stepwise by deoxycytidine kinase (dCK), monophosphate kinase (MPkinase), and diphosphate kinase (DPkinase) to its triphosphate active form (clofarabineTP). ClofarabineTP acts as an inhibitor of DNA polymerase-α (DMA pol α) and -ɛ (DNA pol ɛ) by competing with the natural substrate dATP. When incorporated into DNA clofarabine leads to DNA damage, which signals activation or apoptotic pathways. It can further inhibit ribonucleotide reductase (RR), causing dNTP pool reduction and thus reinforcing its own incorporation into DNA. By directly affecting the mitochondrial transmembrane potential, clofarabine releases cytochrome c and apoptosis-inducing factor (AIF).Figure optionsDownload as PowerPoint slide