Patient-Derived Medullary Thyroid Cancer Organoids; a Model for Patient-tailored Drug and PET-Tracer Screening

BackgroundMedullary thyroid carcinoma (MTC) is a neuroendocrine tumor derived from the parafollicular C-cells of the thyroid gland. PET imaging, with various PET tracers, is performed when distant metastatic disease is suspected. After the recognition of progressive disease on imaging, targeted therapy may be initiated to prolong survival. Mutations in the gene encoding the REarranged during Transfection (RET) tyrosine kinase play a key role in the development of MTC. It seems that tyrosine kinase inhibitors (TKIs) inhibit tumor proliferation, but it remains challenging to determine the best patient specific treatment option. Here, we aim to set up an in vitro MTC organoid model to study its potential for patient-tailored drug-screening and uptake of PET tracers. MethodsDispersed cells obtained from surgical MTC biopsies were suspended in Matrigel with defined medium allowing MTC organoid formation. To study putative MTC stem cells, the self-renewal potential of organoids was tested by dissociation to single cells and re-plating. To check MTC origin, MTC-specific gene expression and proteins were characterized by qPCR and immunofluorescent (IF) staining. To investigate cytotoxicity, MTC-organoids (MTOs) were exposed to various TKIs after which hormone (calcitonin and CEA) excretion levels were determined. Lastly, we evaluated cell-specific uptake of clinically used Positron Emission Tomography (PET) tracers. ResultsNine MTC biopsies were processed and cultured as MTOs. Eight MTO lines were used to determine organoid formation efficiency (OFE), which yielded a maximum OFE of 6.3% in passage 1 (p1), 5.9% in p2, and 9.4% in p3, indicating the presence of putative stem cells. IF staining showed expression of MTC-specific markers in both tissue and MTOs showing tissue resemblance. Tumor marker measurements in MTO medium showed MTC-specific production of calcitonin and CEA with changed concentrations after exposure to TKIs. Exposure to PET tracers showed significant uptake in the MTOs. ConclusionMTC organoids can be successfully cultured and resemble the tissue of origin in gene expression, protein expression and functionality. In addition, MTOs can take up PET tracers, and have the potential to be used as a prediction model for TKI treatment in the future.