Abstract
Apoptosis induction and micronuclei formation were compared following cytotoxic treatments in two rat glioma differing in p53 integrity. In vitro, micronuclei emergence but not apoptosis was linked to the p53 mutated status. In vivo, micronuclei assays were more sensitive to evaluate DNA damage induced by chemotherapy in a p53-mutated solid tumour.
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Main
Most anticancer agents exert their action by triggering apoptosis (Mow et al, 2001). The product of the tumour-suppressor gene p53 is a key mediator in this process (Soussi, 2000). In normal cells, wild-type p53 either arrests cell proliferation until the genetic damage is repaired or forces the cell to commit apoptosis (Cadwell and Zambetti, 2001). In cancer cells, where p53 alleles are often mutated, decrease in apoptosis can be compensated by the process of mitotic catastrophe, a form of cell death resulting from abnormal mitosis and leading to the formation of cells with multiple micronuclei (MN) (Roninson et al, 2001). This study aimed to compare induction of apoptosis and MN formation after chemo- or radiotherapy, in vitro in two rat glioma cell lines differing in p53 integrity, the 9L expressing a mutated p53 gene and the C6 the wild-type gene, and in vivo on established 9L solid tumours.
Materials and methods
Animals and cell lines
All experiments on Fischer 344 rats have been carried out with local ethical committee approval and met the standards required by the UKCCCR guidelines (Workman et al, 1998). The 9L gliosarcoma cell line and the C6 glioblastoma cell line were maintained in complete medium, RPMI 1640 supplemented with 10% fœtal calf serum, 1% L-glutamine, 1% sodium pyruvate, 1% nonessential amino acids, 100 IU ml−1 penicillin and 100 μg ml−1 streptomycin.
In vitro and in vivo radio- or chemotherapy
For in vitro treatments, 9L and C6 cells were γ-irradiated (80 Gy, 137Cs irradiator) or treated for 2 h with chemotherapeutic drugs and recultured during 24 or 72 h for apoptosis tests or 4 h for MN assays. For in vivo treatments, tumour-bearing rats (105 9L s.c. at day 0) received i.p. injections of cisplatin (1 mg kg−1), or were irradiated locally at the tumour site (20 Gy) at days 4, 11 and 18 and were killed the day after. The tumours were then dissected and prepared distinctly for apoptosis or MN assays.
Apoptosis assays
Analysis of caspase 3 activity
Caspase-3 activation was measured in vitro by the cleavage of a specific fluorogenic substrate (Ac-DEVD-AMC, BD Biosciences, Erembodegem, Belgium). Briefly, 24 or 72 h after treatment, cells were lysed and incubated first in protease buffer and then for 2 h at 37°C with Ac-DEVD-AMC substrate (1 mg ml−1). The enzyme-catalysed release of fluorescent AMC was measured, by referring to a standard curve, with a fluorimeter, at 380 nm excitation and 440 nm emission wavelengths.
Measurement of phosphatidylserine translocation using AnnexinV–FITC
Phosphatidylserine outer translocation on treated cells was detected by flow cytometry (BD FACScan and CellQuest software) using AnnexinV–FITC binding (1 μg ml−1) (BD Biosciences) and PI (2 μg ml−1) counterstaining.
TUNEL assay
Treated tumours excised from rats were directly cryo-preserved in OCT, cut into 10-μm-thick sections and kept at −20°C. Paraformaldehyde 4% fixed tissue sections were permeabilised in PBS–Triton X-100 1% solution and incubated for 1 h at 37°C with TdT enzyme (In Situ Cell Death Detection, Roche Molecular Biochemicals, Brussels, Belgium) able to add fluorescein-conjugated nucleotides to the free 3′ ends of DNA fragments generated in apoptotic cells. Slides were analysed under fluorescence microscopy.
Micronucleus assay
Micronuclei (MN) are detected in cells that have completed nuclear division following a method developed by Fenech (2000) that identifies such cells by their binucleate (BN) appearance after blocking cytokinesis with cytochalasin-B. Briefly, in vitro treated 9L or C6 cells were incubated with cytochalasin-B (3 μg ml−1) for 24 h. Ex vivo resected treated 9L tumours were first dissociated in DNAse/collagenase solution and recultured before cytochalasin-B was added. After a hypotonic shock in 0.075 M KCl, cells were stained with Hoechst 33342 (2 μg ml−1) and examined with a fluorescence microscope, under UV light. BN cells with MN were counted within two independent experiments involving at least triplicates of 500 cells.
Statistics
Statistical analysis was done using the unpaired t-test.
Results and discussion
We have investigated and compared in vitro apoptosis induction and MN formation in p53 mutated 9L or p53 wild-type C6 cells treated either by irradiation or by chemotherapeutic agents (chosen according to their opposite efficacies on tumour cell viability, data not shown). Apoptosis was quantified by relevant tests addressing different stages of the process: measure of caspase-3 activity (Figure 1A and C) and externalisation of phosphatidylserines (AnnexinV–FITC/PI assay) (Figure 1B and D). Results show, in general, similar induction of apoptosis in 9L or C6 cells. Irradiation and mitomycin C at 3 μg ml−1 were the best inducers in both the cell lines and cisplatin at 3 μg ml−1 quite less effective. Our results are in agreement with the model in which p53 ‘senses’ DNA damage through direct interaction withDNA-damage sites, and then triggers downstream events leading to apoptosis if the damages are not repaired (Bennett, 1999). Especially, in C6 cells expressing the wild-type p53 protein, hardly any apoptosis was observed after 24 h, increasing with drug concentration and with time. In 9L cells expressing a mutated form of p53, alternative p53-independent pathways of apoptosis could be active, implicating proteins such as p73 (Catani et al, 2002).
On the other hand, MN assays were more discriminatory to detect DNA damage in relation to the p53 status of the tumour cells. Indeed, emergence of BN cells with MN was quite high in 9L cells with a mutated p53 gene (Figure 1E) and quite low in C6 cells expressing the wild-type p53 (Figure 1F). Cisplatin at 10 μg ml−1 and γ-irradiation provoked even such damage in 9L cells that four, five or six MN were often detected per cell, which is unusual (data not shown). On the contrary, in C6 cells, more than three MN per cell were observed rarely (data not shown). The emergence of MN is attributed to the ability of cytotoxic agents to provoke DNA strand breaks either directly as for irradiation or indirectly as the results of drug insertion into the DNA helix (Brabec, 2002). Our data fit with previous observations showing the importance of wild-type p53 protein expression in the balance between cell cycle arrest/DNA repair and apoptosis induction (Ferreira et al, 1999). Indeed, very few MN were detectable in C6 cells. On the contrary, in p53-mutated 9L cells, there is less growth arrest or DNA repair and therefore a higher emergence of MN, as described for head and neck carcinoma cells transfected with a mutant p53 (Masunaga et al, 2002).
In vivo induction of apoptosis in established 9L tumours was assessed after local tumour irradiation (20 Gy) or systemic injection of a nontoxic dose of cisplatin (1 mg kg−1) (Burger et al, 2002). Data from TUNEL assays (Figure 2A–C) and from anti-active caspase-3 immunostaining (data not shown) revealed the presence of apoptotic cells only after irradiation but not after cisplatin treatment. However, by the MN assay, DNA damages were detected in the same in vivo treated 9L tumours also after chemotherapy. Indeed, as shown in Figure 2D, similar emergence of total BN cells with MN was observed for both treatments, even if the number of BN cells bearing ⩾3 MN per cell was increased in the case of γ-irradiation (Figure 2E). This result contrasts with the conclusion of apoptosis tests. However, due to the in vivo clearance of apoptotic cells by macrophages, there was no means to quantify the time-dependent accumulation of apoptotic cells (Savill and Fadok, 2000).
The MN assay is generally used to determine the in vivo genotoxicity of carcinogens in normal cells like human hymphocytes (Gonzalez Borroto et al, 2001; Migliore et al, 2002). Only a few recent publications reported MN formation in cell lines derived from tumours (Truter et al, 2002). We have thus successfully applied this technique on a solid tumour, to evaluate its in vivo sensitivity to chemotherapy, assessing the real effect of the drug on the tumour mass rather than a systemic toxicity. Correlating apoptosis induction and MN formation could help to set up new promising strategies of immunotherapy, combining dendritic cell vaccination with radio- or chemotherapy as producing sources of tumour antigens.
Change history
16 November 2011
This paper was modified 12 months after initial publication to switch to Creative Commons licence terms, as noted at publication
References
Bennett MR (1999) Mechanisms of p53-induced apoptosis. Biochem Pharmacol 58: 1089–1095, doi:10.1016/S0006-2952(99)00153-7
Brabec V (2002) DNA modifications by antitumor platinum and ruthenium compounds: their recognition and repair. Prog Nucleic Acid Res Mol Biol 71: 1–68
Burger KN, Staffhorst RW, de Vijlder HC, Velinova MJ, Bomans PH, Frederik PM, de Kruijff B (2002) Nanocapsules: lipid-coated aggregates of cisplatin with high cytotoxicity. Nat Med 8: 81–84, doi:10.1038/nm0102-81
Cadwell C, Zambetti GP (2001) The effects of wild-type p53 tumor suppressor activity and mutant p53 gain-of-function on cell growth. Gene 277: 15–30, doi:10.1016/S0378-1119(01)00696-5
Catani MV, Costanzo A, Savini I, Levrero M, de L, V, Wang JY, Melino G, Avigliano L (2002) Ascorbate up-regulates MLH1 (Mut L homologue-1) and p73: implications for the cellular response to DNA damage. Biochem J 364: 441–447
Fenech M (2000) The in vitro micronucleus technique. Mutat Res 455: 81–95, doi:10.1016/S0027-5107(00)00065-8
Ferreira CG, Tolis C, Giaccone G (1999) p53 and chemosensitivity. Ann Oncol 10: 1011–1021
Gonzalez Borroto JI, Creus A, Marcos R (2001) Genotoxic evaluation of the furylethylene derivative 2-furyl-1-nitroethene in cultured human lymphocytes. Mutat Res 497: 177–184, doi:10.1016/S1383-5718(01)00262-5
Masunaga S, Ono K, Takahashi A, Ohnishi T, Kinashi Y, Takagaki M (2002) Radiobiological characteristics of solid tumours depending on the p53 status of the tumour cells, with emphasis on the response of intratumour quiescent cells. Eur J Cancer 38: 718–727, doi:10.1016/S0959-8049(01)00430-0
Migliore L, Frenzilli G, Nesti C, Fortaner S, Sabbioni E (2002) Cytogenetic and oxidative damage induced in human lymphocytes by platinum, rhodium and palladium compounds. Mutagenesis 17: 411–417
Mow BM, Blajeski AL, Chandra J, Kaufmann SH (2001) Apoptosis and the response to anticancer therapy. Curr Opin Oncol 13: 453–462
Roninson IB, Broude EV, Chang BD (2001) If not apoptosis, then what? Treatment-induced senescence and mitotic catastrophe in tumor cells. Drug Resist Updat 4: 303–313, doi:10.1054/drup.2001.0213
Savill J, Fadok V (2000) Corpse clearance defines the meaning of cell death. Nature 407: 784–788
Soussi T (2000) The p53 tumor suppressor gene: from molecular biology to clinical investigation. Ann NY Acad Sci 910: 121–137
Truter EJ, Santos AS, Els WJ (2002) Correlation between cell survival, clonogenic activity and micronuclei induction in DMBA-OC-1R cells treated with immunospecific albumin microspheres containing cisplatin and 5-fluorouracil. Cell Biol Int 26: 505–516, doi:10.1006/cbir.2002.0886
Workman P, Twentyman P, Balkwill F, Balmain A, Chaplin D, Double J, Embleton J, Newell D, Raymond R, Stables J, Stephens T, Wallace J (1998) United Kingdom Co-ordinating Committee on Cancer Research (UKCCCR) guidelines for the welfare of animals in experimental neoplasia (second edition). Br J Cancer 77: 1–10
Acknowledgements
G Driessens is fellow of the Fonds pour la Formation à la Recherche dans l'Industrie et dans l'Agriculture. We thank Bernard Van Gansbeke for providing us the chemotherapeutic molecules. This work was supported by the Belgian State, Prime Minister's office, Service for Science, Technology, and Culture, the Fonds National de la Recherche Scientifique, the Fonds de la Recherche Scientifique Médicale, the Actions de Recherche Concertées of the Communauté Française de Belgique and Télévie.
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Driessens, G., Harsan, L., Robaye, B. et al. Micronuclei to detect in vivo chemotherapy damage in a p53 mutated solid tumour. Br J Cancer 89, 727–729 (2003). https://doi.org/10.1038/sj.bjc.6601163
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DOI: https://doi.org/10.1038/sj.bjc.6601163
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