Intrinsic radiation resistance in human chondrosarcoma cells

https://doi.org/10.1016/j.bbrc.2006.05.158Get rights and content

Abstract

Human chondrosarcomas rarely respond to radiation treatment, limiting the options for eradication of these tumors. The basis of radiation resistance in chondrosarcomas remains obscure. In normal cells radiation induces DNA damage that leads to growth arrest or death. However, cells that lack cell cycle control mechanisms needed for these responses show intrinsic radiation resistance. In previous work, we identified immortalized human chondrosarcoma cell lines that lacked p16ink4a, one of the major tumor suppressor proteins that regulate the cell cycle. We hypothesized that the absence of p16ink4a contributes to the intrinsic radiation resistance of chondrosarcomas and that restoring p16ink4a expression would increase their radiation sensitivity. To test this we determined the effects of ectopic p16ink4a expression on chondrosarcoma cell resistance to low-dose γ-irradiation (1–5 Gy). p16ink4a expression significantly increased radiation sensitivity in clonogenic assays. Apoptosis did not increase significantly with radiation and was unaffected by p16ink4a transduction of chondrosarcoma cells, indicating that mitotic catastrophe, rather than programmed cell death, was the predominant radiation effect. These results support the hypothesis that p16ink4a plays a role in the radiation resistance of chondrosarcoma cell lines and suggests that restoring p16 expression will improve the radiation sensitivity of human chondrosarcomas.

Section snippets

Methods

Cell culture and viral transduction. Three chondrosarcoma cell lines were used in the present study. These were established from a grade II myxoid chondrosarcoma (CS-7), a grade I chondrosarcoma (CS-8), and a grade III chondrosarcoma (CS-9). Three normal chondrocyte cell strains were established from normal (non-osteoarthritic) femoral head cartilage (F), tibial plateau cartilage (TP), and distal femur chondrocytes (DF). All cell cultures were established as described [14]. In brief, cells from

Results

Western blot analyses show that the three chondrosarcoma cell lines used here were p16-deficient but expressed levels of p53, and pRb comparable to the levels found in normal chondrocyte strains (Fig. 1).

Clonogenic survival assays showed a strong, dose-dependent effect of γ-radiation on normal chondrocytes (Fig. 2). Survival in these cells was reduced to an average of 40% at 1 Gy, 21% at 2 Gy, 6% at 3 Gy, and to less than 0.8% at 5 Gy. Chondrosarcoma cell survival was significantly greater than

Discussion

In this study, we found that p16-deficient chondrosarcoma cells were intrinsically more radiation resistant than normal chondrocytes and that restoring p16 activity also restored radiation sensitivity. These results indicated that p16 loss could account for some of the intrinsic radioresistance of these cells. Comet assay data showed that radiation resistant, p16-deficient chondrosarcoma cells sustained levels of radiation-induced DNA damage comparable to the damage seen in p16ink4a-transduced

Uncited reference

[23].

Acknowledgments

This work was supported by the Ben Ling Chondrosarcoma Research Fund and the University of Iowa Department of Orthopaedics and Rehabilitation. The authors are grateful to Terese Nickol, Farshid Moussavi-Harami, and Gail Kurriger for expert technical assistance.

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