p53-dependent radiobiological responses to internalised indium-111 in human cells.
BACKGROUND
The p53 tumour suppressor protein plays a pivotal role in the response of mammalian cells to DNA damage. It regulates cell cycle progression, apoptosis and DNA repair mechanisms and is therefore likely to influence response to targeted radionuclide therapy. This study investigated the role of p53 in the cellular response to the Auger-emitting radionuclide indium-111.


METHODS
Two stable clones of a HT1080 fibrosarcoma cell line, differing only in p53 status due to RNAi-mediated knockdown of p53 expression, were incubated for 1 h with [¹¹¹In]-oxinate (0-10 MBq/ml). Radiopharmaceutical uptake into HT1080 cells was measured in situ using a non-contact phosphorimager method. Cellular sensitivity and DNA damage were measured by, respectively, clonogenic survival analysis and the single cell gel electrophoresis (Comet) assay.


RESULTS
Mean uptake of [¹¹¹In]-oxinate in HT1080 cells was unaffected by p53 status, reaching a maximum of 9Bq/cell. [¹¹¹In]-oxinate-induced cytotoxicity was also identical in both clones, as measured by IC50 (0.68 MBq/ml). However the formation of DNA damage, measured immediately after treatment with [¹¹¹In]-oxinate, was found to be up to 2.5-fold higher in the p53-deficient HT1080 clone.


CONCLUSIONS
The increased DNA damage induced in p53-deficient HT1080 cells suggests an early deficiency in the repair of DNA damage during the treatment period. However, the similarity in cellular sensitivity, irrespective of p53 status, suggests that reduced p53 leads to a concomitant reduction in p53-dependent cytotoxicity despite the persistence of DNA damage. The results may provide insight into how tumours that differ in p53 status respond to therapeutic radionuclides.
School of Biosciences, University of Kent, Canterbury, CT2 7NJ Kent, UK.
Amanda J
AJ
Weeks
Philip J
PJ
Blower
Daniel R
DR
Lloyd
D001692:Biological Transport; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000528:radiation effects; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair / Q000528:radiation effects; D015972:Gene Expression Regulation, Neoplastic / Q000528:radiation effects; D006801:Humans; D007205:Indium Radioisotopes / Q000378:metabolism* / Q000627:therapeutic use; D011853:Radiobiology; D019275:Radiopharmaceuticals / Q000378:metabolism* / Q000627:therapeutic use; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
D050759:Cyclin-Dependent Kinase Inhibitor p21; D007205:Indium Radioisotopes; D019275:Radiopharmaceuticals; D016159:Tumor Suppressor Protein p53