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1360    I. J. Radiation Oncology • Biology • Physics

Table 1. Radiosensitivity paramcters (SF_?, a, and fi) calculalcd using the linear-quadratic model in KB and KB3 ccii lincs cxposed to dcxamethasone (DEX, 10^_oM, 24 h) or TNFa (2.5

ng/mL, 10 min)

		Celi lines
	KB		KB3
	Control	DEX	Control	TNFa
sf2*	0.799*	0.758	0.480	0.632
a	0.052	0.114	0.064	0.054
fi	0.030	0.012	0.151	0.087

* Surviving fraction at 2 Gy. ^y Mean valucs of thrcc independent expcriments. Notę: Standard deviations were less than 15%.

Volumc 51, Numbcr 5, 2001

pathway. A similar observation has been dcscribed al-ready in Hodgkin’s lymphoma cells, which were pro-tected from irradiation without a dccreasc in NF-kB activity in the prescncc of DEX (28).

This study demonstrates that the constitutive NF-kB level influences the intrinsic radiosensitivity of the KB and KB3 celi lines. Morcovcr, if our work does not formally involve anti-apoptotic activities of NF-kB in resistance to radiotherapy, it certainly indicates that this transcription factor plays a central role in basal intrinsic radiosensitivity and could protect cells against apoptosis, probably by controlling the expression of apoptosis inhibitors. Modulation of this basal level could be recommended bcforc ionizing radiation ex-posure to inerease radiotherapy response.

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