Chendil D, Oakes R, Alcock RA, Patel N, Mayhew C, Mohiuddin M, Gallicchio VS, Ahmed MM. Low dose fractionated radiation enhances the radiosensitization effect of paclitaxel in colorectal tumor cells with mutant p53.
Cancer 2000;
89:1893-900. [PMID:
11064345 DOI:
10.1002/1097-0142(20001101)89:9<1893::aid-cncr4>3.3.co;2-2]
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Abstract
BACKGROUND
The current study was undertaken to investigate the influence of wild-type or mutant p53 status on the radiosensitizing effect of paclitaxel in colorectal tumor cell lines.
METHODS
HCT-116 (contains wild-type p53) and HT-29 (contains mutant p53) established from moderately differentiated colorectal carcinomas were used in this study. Colony-forming assay was performed after exposure to either different radiation doses (0.5-6 gray [Gy]) or paclitaxel (1-10 nM) or in combination. Induction of p53 and p21(waf1/cip1) by these treatments were determined by immunocytochemistry and Western blot analysis.
RESULTS
Radiation caused an increase in nuclear p53 and p21(waf1/cip1) proteins in HCT-116 cells, indicating that p53 functionally induced p21(waf1/cip1). However, induction of nuclear p53 and p21(waf1/cip1) protein was not evident in HT-29 cells, suggesting that p53 was not functional in these cells. Survival data showed that the HCT-116 cells (survival fraction of exponentially growing cells that were irradiated at the clinically relevant dose of 2 Gy [SF(2)] = 0.383; dose required to reduce the fraction of cells to 37% [D(0)] = 223 centigray [cGy]) were significantly sensitive to ionizing radiation (P < 0.008) when compared with the HT-29 cells (SF(2) = 0.614; D(0) = 351 cGy). Paclitaxel caused a higher degree of clonogenic inhibition in HCT-116 (D(0) = 0.7 nM) than HT-29 (D(0) = 1.11 nM) cells (P < 0.06). When paclitaxel and radiation were combined, an enhanced radiosensitizing effect (P < 0.05) was observed in HCT-116 cells (SF(2) = 0.138; D(0) = 103 cGy), whereas in HT-29 cells no significant radiosensitization of paclitaxel was observed (SF(2) = 0.608; D(0) = 306 cGy). However, pretreatment with paclitaxel followed by multifractionated low dose radiation (0.5- or 1-Gy fractions for a total dose of 2 Gy) significantly enhanced the radiosensitizing effect in both HCT-116 and HT-29 cells.
CONCLUSIONS
The results of the current study suggested that multifractionated radiation given at very low doses after exposure of cells to paclitaxel conferred a potent radiation sensitizing effect irrespective of p53 status.
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