B. Djordjevic et al., INCREASING RADIOSENSITIVITY IN THE COURSE OF FRACTIONATED X-IRRADIATION - THE EFFECT OF CONTACT WITH DEAD AND DYING CELLS, Radiation research, 150(3), 1998, pp. 275-282
Citations number
26
Categorie Soggetti
Biology Miscellaneous","Radiology,Nuclear Medicine & Medical Imaging
We have measured survival after successive 2-Gy doses of X rays in HeL
a cells and 1-Gy doses in cells of the nonimmortalized human fibroblas
t cell line AG15-22 under conditions where any effect of cell prolifer
ation during multifraction X irradiation has been factored out. When H
eLa cells in parallel series of (pseudo)hybrid spheroids (i.e. in aggl
omerates consisting of a mixture of supralethally irradiated HeLa feed
er and viable HeLa cells) were exposed to n daily radiation doses and
then trypsinized and exposed to the last dose, the surviving fraction
at 2 Gy (SF2) declined exponentially from 0.55 +/- 0.01 to 0.31 +/- 0.
01 after the fifth fraction. In monolayer HeLa cell cultures, the decl
ine in SF2 was smaller but significant and was not influenced by the p
resence of feeder cells. Pure spheroids, composed entirely of viable H
eLa cells, showed the same decline in SF2 as did monolayer cells. The
cumulative;effect curve (i.e. the product of SF2 values) was linear-qu
adratic with the quadratic term increasing in the order monolayer, pur
e spheroids, pseudohybrid spheroids. SF2(n) and D-0Eff (deduced from t
he initial SF2) severely underestimated cumulative radiosensitivity. T
his cumulative effect is clearly associated with the proximity of leth
ally irradiated cells and might be explained by differential populatio
n shifts in the course of the multifraction regimen. Similarly, AG15-2
2 cells irradiated with daily 1-Gy doses of X rays showed a larger inc
rease in radiosensitivity when in hybrid spheroids than when in pure s
pheroids. However, for the AG15-22 cells, SF1 was twofold lower for th
e former than for the latter condition and remained constant for both
conditions rather than decreasing with increasing fraction number. Thi
s large radiosensitizing effect remains unexplained. (C) 1998 by Radia
tion Research Society.