[The sodium-iodide symporter. Pathophysiologic, diagnostic and therapeutic significance]

Tumor suppressor protein p53 exerts negative transcriptional regulation on human sodium iodide symporter gene expression in breast cancer

PURPOSE

Aberrant expression of human sodium iodide symporter (NIS) in breast cancer (BC) is well documented but the transcription factors (TF) regulating its aberrant expression is poorly known. We identify the presence of three p53 binding sites on the human NIS promoter sequence by conducting genome-wide TF analysis, and further investigate their regulatory role.

METHODS

The differences in transcription and translation were measured by real-time PCR, luciferase reporter assay, site-directed mutagenesis, in vivo optical imaging, and chromatin immunoprecipitation. The relation of NIS and p53 in clinical samples was judged by TCGA data analysis and immunohistochemistry.

RESULTS

Overexpression of wild-type p53 as a transgene or pharmacological activation by doxorubicin drug treatment shows significant suppression of NIS transcription in multiple BC cell types which also results in lowered NIS protein content and cellular iodide intake. NIS repression by activated p53 is further confirmed by non-invasive bioluminescence imaging in live cell and orthotropic tumor model. Abrogation of p53-binding sites by directional mutagenesis confirms reversal of transcriptional activity in wild-type p53-positive BC cells. We also observe direct binding of p53 to these sites on the human NIS promoter. Importantly, TCGA data analysis of NIS and p53 co-expression registers an inverse relationship between the two candidates.

CONCLUSION

Our data for the first time highlight the role of p53 as a negative regulator of functional NIS expression in BC, where the latter is a potential targeted radioiodine therapy candidate. Thus, the study provides an important insight into prospective clinical application of this approach that may significantly impact the patient with mutant versus wild-type p53 profile.

Radioprotection of thyroid cells mediated by methimazole

PURPOSE

The radioprotective effect of antithyroid drugs on radioiodine treatment is a controversial issue. However, it is of clinical relevance whether antithyroid medication has to be interrupted for therapy and when antithyroid medication can be continued after radioiodine treatment. We investigated DNA damage caused by internal or external radiation using thyroid cells (sodium iodine symporter [NIS] positive).

MATERIALS AND METHODS

Adherent thyroid cells were irradiated following incubation with the mediators methimazole and perchlorate using either X-ray tube or Re-188-perrhenate. DNA damage was quantified by OTM (Olive's tail moment) of the alkaline comet assay.

RESULTS

Following external irradiation of 15 Gy OTM was 4.3 ± 4.2 compared to 0.5 ± 1.4 in controls. DNA damage was reduced by methimazole to 70%. Incubation with Re-188 showed effects depending on presence of the mediators. Non-irradiated controls had a mean OTM < 1, internal irradiation increased OTM to 25.5 ± 9.1 in cells without mediators. OTM decreased to 60% after pre-incubation with methimazole and to 15% with perchlorate. Re-188 uptake was modified by both perchlorate and, to a lesser extent, methimazole.

CONCLUSIONS

Methimazole was shown to have a radioprotective effect not only by its scavenger capacity but also by interaction with NIS. Perchlorate acted by competitive inhibition of NIS mediated Re-188 uptake.

Serum anti - TPO levels in benign and malignant breast tumors

Breast cancer is a hormone dependent neoplasm. Conflicting results regarding the clinical correlation between breast cancer and thyroid diseases have been reported. The objective of this study was to determine the association of anti - TPO levels in patients having complaints of a lump in breast. Serum samples and Fine needle aspiration cytology (FNAC) samples were collected from 31 female patients with a lump in breast between the age group of 20-75 years. 31 age matched normal healthy controls were also examined for the same parameters. Serum samples were analyzed for its anti - TPO levels. FNAC reports confirmed patients as having duct cell carcinoma. They had raised serum anti - TPO levels compared to controls. FNAC results of others (n=26) were reported as fibroadenoma whose anti - TPO levels were less than the controls.