Study On The Molecular Mechanism Of Hypothyroidism Induced By Tyrosine Kinase Inhibitors

Tyrosine kinase inhibitors(TKIs),as new targeted therapeutic drugs widely used to fight a variety of malignant tumor diseases,have improved the overall survival rate of many cancer patients through single drug use or combined with traditional radiotherapy and chemotherapy.With the wide application of TKIs,some adverse reactions caused by TKIs have been reported gradually.Although the adverse reactions caused by TKIs are easier to accept than those caused by chemotherapy drugs,they should not be ignored.Among them,hypothyroidism caused by TKIs has attracted much attention in clinic,and severe hypothyroidism affects the normal use of TKIs.However,the mechanism of hypothyroidism caused by TKIs currently proposed cannot explain the clinical phenomena such as better prognosis of tumor patients with thyroid dysfunction after the application of TKIs,and further evidence of various mechanisms is lacking at the molecular level.Objectives: the aims of the study were to determine whether TKIs could cause hypothyroidism through some in vivo and in vitro experiments,further explored the molecular mechanism of TKIs causing hypothyroidism.On this basis,the clinical significance of TKIs was discussed to provide a new idea for the clinical application of TKIs.Methods:1.Animal experiments in vivo:(1)C57 mice were divided into DMSO(control group),sunitinib group and sorafenib group by intragastric administration.After 40 days of the treatment,the mice were killed to separate thyroid tissue and pituitary gland;(2)The serum,pituitary gland and thyroid tissue of mice were used to detect thyroid function indexes by automatic biochemical analyzer,and the thyroid tissue was observed by real-time quantitative PCR and transmission electron microscopy to evaluate the changes of thyroid function in mice treated with TKIs;(3)Western blot and tissue immunofluorescence were used to determine the molecular expression of key genes in thyroid-related signaling pathways in mouse thyroid tissues,and qRT-PCR was further needed to determine the molecular transcription levels of the above genes,and to explore the relationship between hypothyroidism induced by TKIs and thyroid stimulating hormone receptor;(4)Western blot was used to determine the expressions of p-ERK,p-AKT and c-Myc in the thyroid of mice,and to explore whether the activities of MAPK/ERK and PI3K/ AKT signaling pathways and the expression of downstream gene c-Myc in mice treated with TKIs were affected to a certain extent;2.Cell experiment in vitro:(1)TKIs were used to treat thyroid cancer cell 8505 C.Western blot and qRT-PCR were used to detect the molecular expression of related genes in thyroid related signaling pathway;(2)TKIs were used to treat thyroid cancer cell 8505 C,and western blot was used to identify the expression of key genes and their downstream genes c-Myc in the two pathways of MAPK/ERK,PI3K/AKT;(3)Rescue experiment was used to explore the key role of c-Myc in the molecular mechanism of hypothyroidism induced by TKIs.Results:1.Compared with the control group,the thyroid function test results indicated that subclinical hypothyroidism occurred in all the drug addition groups,so TKIs treatment could cause the inhibition of thyroid function in mice;2.Through in vivo and in vitro experiments,it was found that TKIs caused hypothyroidism by down-regulating the expression of TSHR protein level,but the mRNA level of TSHR did not significantly change;3.In vivo and in vitro experiments showed that TKIs further regulated the down-regulation of c-Myc protein expression by inhibiting MAPK/ERK and PI3K/ AKT signaling pathways;4.Cell experiments in vitro showed that overexpression of c-Myc could reverse the down-regulation of TSHR protein expression induced by TKI.Conclusion:1.TKIs treatment could cause thyroid volume reduction and thyroid function inhibition in mice;2.The molecular mechanism of hypothyroidism induced by TKIs may be that TKIs inhibit the expression of TSHR through p-ERK/p-AKT—c-Myc signal axis,thus leading to thyroid dysfunction;3.TKIs have no significant effect on the expression of TSHR at the transcriptional level,and may have post-transcriptional inhibition on the expression of TSHR protein.