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. 2012 Apr 23:7:62.
doi: 10.1186/1748-717X-7-62.

The combination of olaparib and camptothecin for effective radiosensitization

Katsutoshi Miura  1 , Koh-ichi Sakata, Masanori Someya, Yoshihisa Matsumoto, Hideki Matsumoto, Akihisa Takahashi, Masato Hareyama
Affiliations

The combination of olaparib and camptothecin for effective radiosensitization

Katsutoshi Miura et al. Radiat Oncol. .

Abstract

Background: Poly (ADP-ribose) polymerase-1 (PARP-1) is a key enzyme involved in the repair of radiation-induced single-strand DNA breaks. PARP inhibitors such as olaparib (KU-0059436, AZD-2281) enhance tumor sensitivity to radiation and to topoisomerase I inhibitors like camptothecin (CPT). Olaparib is an orally bioavailable inhibitor of PARP-1 and PARP-2 that has been tested in multiple clinical trials. The purpose of this study was to investigate the characteristics of the sensitizing effect of olaparib for radiation and CPT in order to support clinical application of this agent.

Methods: DLD-1 cells (a human colorectal cancer cell line) and H1299 cells (a non-small cell lung cancer cell line) with differences of p53 gene status were used. The survival of these cells was determined by clonogenic assay after treatment with drugs and X-ray irradiation. The γH2AX focus formation assay was performed to examine the influence of olaparib on induction and repair of double-stranded DNA breaks after exposure to radiation or CPT.

Results: A radiosensitizing effect of olaparib was seen even at 0.01 μM. Its radiosensitizing effect after exposure for 2 h was similar to that after 24 h. H1299 cells with depletion or mutation of p53 were more radioresistant than H1299 cells with wild-type p53. However, similar enhancement of radiosensitization by olaparib was observed with all of the tested cell lines regardless of the p53 status. Olaparib also sensitized cells to CPT. This sensitizing effect was seen at low concentrations of olaparib such as 0.01 μM, and its sensitizing effect was the same at both 0.01 μM and 1 μM. The combination of olaparib and CPT had a stronger radiosensitizing effect. The results of the γH2AX focus assay corresponded with the clonogenic assay findings.

Conclusion: Olaparib enhanced sensitivity to radiation and CPT at low concentrations and after relatively short exposure times such as 2 h. The radiosensitizing effect of olaprib was not dependent on the p53 status of tumor cells. These characteristics could be advantageous for clinical radiotherapy since tumor cells may be exposed to low concentrations of olaparib and/or may have different levels of p53 mutation. The combination of olaparib and CPT had a stronger radiosensitizing effect, indicating that combining a PARP inihibitor with a topoiomerase I inhibitor could be promising for clinical radiosensitization.

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Figures

Figure 1
Figure 1
a. The relationship between concentrations of olaparib and radiosensitizing effects. DLD-1 cells were treated with various concentrations of olaparib for 1 h before radiation and 24 h after radiation. b. The relationship between exposure time (1 h or 24 h) of olaparib and radiosensitizing effects. DLD-1 cells were treated with 1 μM of olaparib for 1 h before radiation and 1 h or 23 h after radiation. c. Clonogenic cell survival assay of H1299 cells with various status of p53 gene. m143, m175, and m248 were made with transfection of mutated p53 gene into codon 143, 175, 248 of H1299 cells, respectively. “Control”: treated with radiation alone; “Olaparib (+)”:treated with radiation and olaparib. Cells were treated with 1 μM of olaparib for 1 h before radiation and 2 h after radiation.
Figure 2
Figure 2
a. The effect of olaparib on CPT toxicity. DLD-1 cells were treated with 1 μM of olaparib and various cocentrations of CPT for 6 h. Values shown are the mean ± standard error of the mean. b. The relationship between concentrations of olaparib and sensitizing effects to CPT in DLD-1 cells. Cells were treated with 0.01 μM of CPT and various concentrations of olaparib for 6 h. Values shown are the mean ± standard error of the mean.
Figure 3
Figure 3
a. Cell survivals with radiation combined with olaparib and/or CPT. DLD-1 cells were treated with 0.1 or 1 μM of olaparib and/or 0.01 μM of CPT for 4 h before irradiation and for 2 h after radiation. b. Radiosensitization with olaparib and/or CPT. Figure 3b was made by modifying Figure 3a. The survival fraction of CPT at 0 Gy in Figure 3a was corrected to 1.
Figure 4
Figure 4
γH2AX foci at 24 hours after irradiation and cell cycle distribution. DLD-1 cells were treated with 4 Gy of radiation and/or 1 μM of olaparib for 8 h and/or 10nM of CPT for 6 h. (a) Foci of γH2AX and Rad51 in DLD-1 cells treated with various combinations of olaparib, CPT, or irradiation (IR). DAPI(4',6-diamidino-2-phenylindole) was used to stain nucleus. Ola(+): with olaparib. IR(−): without irradiation. (b) Results of cells that were positive for Rad51 foci. (c) Results of cells that were negative for Rad51 foci. (d) Cell cycle distributions.
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References

    1. Hall EJ. In: Radiobiology for the radiologist, ed. 6. Hall EJ, Giaccia AM, editor. Lippincott Williams & Wilkins, Philadelphia; 2006. DNA strand breaks and chromosomal aberrations; pp. 16–29.
    1. Saleh-Gohari N, Bryant HE, Schultz N, Parker KM, Cassel T, Helleday T. Spontaneous homologous recombination is induced by collapsed replication forks that are caused by ebdogenous DNA single-strand breaks. Mol Cell Biol. 2005;25(16):7158–7169. doi: 10.1128/MCB.25.16.7158-7169.2005. - DOI - PMC - PubMed
    1. Caldecott KW. Protein-protein inetractions during mammalian DNA single-strand break repair. Biochem Soc Trans. 2003;31:247–251. - PubMed
    1. Chalmers AJ. The potential role and application of PARP inhibitors in cancer treatment. Brit Med Bull. 2009;89:23–40. - PubMed
    1. Dungey FA, Loser DA, Chalmers AJ. Replication-dependent radiosensitization of human glioma cells by inhibition of poly (ADP-ribose) polymerase: mechanisms and therapeutic potential. Int J Radiat Oncol Biol Phys. 2008;72(4):1188–1197. doi: 10.1016/j.ijrobp.2008.07.031. - DOI - PubMed

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