Background

Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor derived from the parafollicular C-cells of the thyroid gland. In patients with distant metastases, only targeted therapy can prolong survival. Mutations in the gene encoding the Rearranged during Transfection (RET) tyrosine kinase, play a vital role in the development MTCs. Tyrosine kinase inhibitors (TKIs) block tyrosine kinases such as RET and thereby inhibit tumor proliferation. With the increasing availability of TKIs, it has become a challenge to determine the best treatment option for each individual patient. This study therefore aims to set up an in vitro MTC organoid model to study its potential for drug screening.

Methods

Single cells were isolated from surgically obtained MTC biopsies, suspended in Matrigel, and plated in a tissue culture plate with growth medium. To study the self-renewal potential of putative MTC stem cells, the organoids formed after three weeks were dissociated and replated (passaging). To check MTC origin, MTC-specific proteins, were characterized by immunofluorescent (IF) staining in MTC tissue and organoids. To determine the functionality of the organoids, hormone levels (calcitonin and CEA) were measured in the medium. To investigate cytotoxicity, MTC-organoids were exposed to various TKIs, and hormone excretion levels were determined.

Results

Nine MTC biopsies were processed and cultured to organoids. Six cultures were used to determine organoid formation efficiency (OFE), with a maximum OFE of 6.3% in passage 1 (p1), 5.9% in p2, and 9.4% in p3. IF staining showed expression of MTC-specific markers in both tissue and organoids. Hormone measurement in organoid medium showed MTC-specific production of calcitonin and CEA, which was reduced when the organoids were exposed to TKIs.

Conclusion

MTC organoids can be successfully cultured in vitro and show MTC-specific protein expression and hormone production. In addition, they respond to TKIs, and have the potential to be used as a prediction model in the future warranting further studies.