Clofarabine acts as radiosensitizer in vitro and in vivo by interfering with DNA damage response.
OBJECTIVE
Combination treatment with radiotherapy and chemotherapy has emerged as the dominant form of cancer adjuvant regimens in recent years. Clofarabine, a newly approved drug for pediatric leukemia, is a second-generation purine nucleoside analogue that can block DNA synthesis and inhibit DNA repair. Therefore, we hypothesized that clofarabine could work synergistically with radiotherapy to increase the tumor cell response.


METHODS
The effects of clofarabine on radiosensitivity have been established in several tumor cell lines in vitro and in vivo using colony-forming assays and tumor xenografts. The effect of clofarabine on the DNA damage response was also studied in vitro by measuring gamma-H2AX focus formation.


RESULTS
Clonogenic survival was significantly reduced in irradiated cells treated with clofarabine, demonstrating the strong radiosensitizing effect of clofarabine. Furthermore, clofarabine displayed a radiosensitizing effect that was greater than gemcitabine or 5-fluorouracil. We also found that low doses of clofarabine can prolong the presence of radiation-induced gamma-H2AX nuclear focus formation, and high doses of clofarabine can induce DNA double-strand breaks, suggesting that clofarabine can interfere with DNA damage response pathways. In addition, clofarabine-induced radiosensitization was also established in vivo using a colorectal cancer model, DLD-1, in athymic nude mice. When combined with fractionated radiotherapy, a moderate dose of clofarabine led to a significant increase in tumor growth inhibition.


CONCLUSIONS
Clofarabine acts as a powerful radiosensitizer both in vitro and in vivo by interfering with the DNA damage response.
Department of Biochemistry and Molecular Biology, Southern Research Institute, Birmingham, AL 35205, USA.
Mickael J
MJ
Cariveau
Murray
M
Stackhouse
Xiao-Li
XL
Cui
Kamal
K
Tiwari
William
W
Waud
John A
JA
Secrist
Bo
B
Xu
D000227:Adenine Nucleotides / Q000494:pharmacology*; D000818:Animals; D001087:Arabinonucleosides / Q000494:pharmacology*; D045744:Cell Line, Tumor; D000077866:Clofarabine; D004249:DNA Damage; D004260:DNA Repair / Q000187:drug effects*; D004273:DNA, Neoplasm / Q000187:drug effects / Q000528:radiation effects; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D011829:Radiation Dosage; D011836:Radiation Tolerance / Q000187:drug effects*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays
D000227:Adenine Nucleotides; D001087:Arabinonucleosides; D004273:DNA, Neoplasm; C468783:H2AX protein, human; D006657:Histones; D011838:Radiation-Sensitizing Agents; D000077866:Clofarabine