In vitro Evaluation immunmodulatorischer Therapien zur Behandlung des anaplastischen Schilddrüsenkarzinoms

Anaplastic thyroid carcinoma (ATC) is one of the most aggressive and deadliest malignancies because of its high metastatic potential and the lack of effective therapy. Therefore, it is strongly needed to identify targeted and multimodal effective therapies based on its aberrant molecular background. In the present study the cell viability of ATC cells was investigated after the treatment with the PD-L1 inhibitor atezolizumab, the HDACi panobinostat and the TKI Sorafenib. Furthermore, RT qPCR and Western Blot were used to modulation of the transcripts and proteins related to the autophagic genes UVRAG, SQSTM1, TFEB, BECN1, MAP1LC3B, PRKAA1_1 and PRKAA 2_1. Finally, the protein level of PD-L1 was analysed. The established ATC cell line C643 and three PDTTs were used as ATC model for this study. Thyroid follicular epithelial immortalized cells Nthy-ori 3-1 were used as control. The viability of C643 spheroids was detected by the use of the Real Time GloTM kit. Panobinostat caused a significant reduction of cell viability at 10 nM concentration. The treatment with 500 ng/ml of atezolizumab und 1 µM of sorafenib showed only a slight reduction of cell viability. Interestingly, the combination of 500 ng/ml of atezolizumab with 10 nM of panobinostat or 1 µM of sorafenib showed a synergic effect; especially the combination of atezolizumab and panobinostat caused a significant reduction of cell viability. Besides, the treatment with panobinostat alone and in combination with atezolizumab caused a darkening of the spheroid and a complete loss of its structure. Furthermore, the solo administration of atezolizumab, panobinostat and sorafenib caused an over-expression of most of the autophagy transcripts, while the combination of atezolizumab with panobinostat or sorafenib caused a significant change in the expression of two autophagy transcripts. However, the solo administration with panobinostat caused a significant down-regulation of the protein level of nearly all autophagy markers, which confirmed a strong ongoing autophagy process leading to cell death. Interestingly, after treatment with the combination of atezolizumab and panobinostat a higher protein level of the autophagy proteins could be detected, compared to the solo administration with panobinostat. These results indicate an inhibitory effect on autophagy process exerted by atezolizumab. Nonetheless, the combination of atezolizumab and panobinostat led to a significant reduction of cell viability. These findings indicated that the combination with panobinostat resulted effective by overcoming the inhibitory effect exerted by atezolizumab on autophagy process, which caused a reduction of cell proliferation and finally decay. However, similar findings could not be observed after administration with atezolizumab and sorafenib or after the combination of the two compounds, therefore a reduction of cell viability is not caused by an induction of autophagy process. Another important finding was the potential upregulation of PD-L1 after treatment with panobinostat and sorafenib, supporting the possibility to sensitize ATC cells to a therapy with the PD-L1 inhibitor atezolizumab. The results made in this study show the high potential of using combined treatment. The combination of the PD-L1 inhibitor atezolizumab and the HDACi panobinostat could be an effective therapeutic concept for patients affected by ATC. Further investigations are needed to verify the role of PD-L1 and autophagy in vivo.