Effect of p53 status in radioimmunotherapy Auger

Objectives In the present study, we investigated the role of the protein p53 in the cellular response to 125I- monoclonal antibodies (mAbs) localized at the cell surface or within cytoplasm.

Methods Two form of a carcinoma colic cell line HCT 116 proficient or deficient in p53 were used. They were treated either with internalizing or non-internalizing ¹²⁵I-mAbs. Survival was assessed by standard clonogenic assay and dosimetry was investigated using the MIRD cellular approach. For this purpose, uptake of radioactivity per cell was measured and S-factors for 125I were calculated for cell surface and cytoplasm localization. DNA damage was assessed by the alkaline comet technique and by the micronucleus assay. The level of the protein p53 and p21 were determined by a western blotting approach.

Results We showed that the toxicity due to 125I decays was greater with non-internalizing rather than with internalizing 125I-mAb. This effect was observed in a similar way for the p53 (+/+) and p53 (-/-) HCT 116 cells. We showed that in p53(+/+) and p53 (-/-) cells, DNA damage, as revealed by the micronucleus assay, were produced. These results indicate that although nuclear DNA damage are produced under both types of 125I localization, the strongest toxicity associated to non-internalizing 125I-mAbs is not mediated by p53.

Conclusions We confirmed that non-internalizing ¹²⁵I-mAbs are more cytotoxic than internalizing 125I-mAbs. We showed that this membrane sensitivity to Auger electrons is not mediated by p53. Ongoing experiments are assessing the role of ceramide and p38, as mediators of apoptosis.