¹⁸F-FDG PET As An Imaging Biomarker For The Response To FGFR

Rationale:Fibroblast Growth Factor Receptor(FGFR)is a highly promising therapeutic target for multiple type of tumors,which promoted the development of selective FGFR inhibitors.In recent years,three FGFRis have been approved for the treatment of FGFR2-fused cholangiocarcinoma or FGFR3-mutated bladder cancer.In addition,a small number of FGFRis are in phase Ⅱ/Ⅲ clinical.The overall clinical response FGFRi is far from satisfactory in cancer patients stratified by FGFR aberration,thus a novel biomarker to evaluate the therapeutic response to FGFRis is in urgent need.In previous studies,our team found that the changes of c-Myc in tumor after administration of inhibitors could indicate the efficacy of FGFRis.However,the detection of c-Myc is not easy due to the difficulty in obtaining tumor tissues in clinic,and it’s hard to monitoring in a dynamic manner.Hence a biomarker to evaluate the therapeutic response to FGFRis in a non-invasive and dynamic manner is greatly desired.Methods:Six FGFR-aberrant cancer cell lines were used,including four FGFRisensitive ones(NCI-H1581,NCI-H716,RT112 and Hep3B)and two FGFRi-resistant ones(primary for NCI-H2444 and acquired for NCI-H1581/AR).Cell viability and tumor xenograft growth analyses were performed to evaluate FGFRi sensitives,accompanied by corresponding 18F-fluorodeoxyglucose(18F-FDG)uptake assay.mTOR/PLCγ/MEK-ERK signaling blockade by specific inhibitors or siRNAs was applied to determine the regulation mechanism.Results:In this paper,proteomics technology was used to study the changes of proteins and pathways in sensitive cell lines after FGFR inhibition.We detected significant changed in proteins related to the glucose metabolism pathway in tumor cells after FGFR inhibition,thus speculated that the efficacy of the FGFRis could be monitored by targeting the tumor glucose metabolism.We then extended multiple FGFR dependent susceptible and resistant tumor cells and found that FGFR inhibitors reduced hexokinase 2(HK2)protein level and the level of 18F-FDG uptake in multiple FGFR-dependent susceptible tumor cells,which was not in the case with the resistant tumor cells.Therefore,we conducted a preliminary analysis of the mechanism of FGFR inhibition inhibiting tumor glucose metabolism.We found that FGFR inhibition reduced HK2 protein level by reducing HK2 transcription,and this effect was generated by inhibiting AKT-mTOR signaling pathway rather than through PLCγ,MEK-ERK and the important downstream effector c-Myc.Then we verified this effect in vivo and found that the uptake of 18F-FDG in FGFR-dependent tumor was significantly higher than the normal tissues.After FGFR inhibition,tumor’s 18F-FDG uptake level was decreased,and the protein level of HK2 and Ki67 in tumor were also decreased.However,the protein level of HK2 and Ki67 and the 18F-FDG uptake level were not affected in the resistant system.These results indicate the glucose uptake rate in the sensitive and drug-resistant system were different after FGFR inhibition,thus 18F-FDG PET could be used for non-invasive tumor monitoring with FGFR inhibitors.Conclusion:FGFR inhibitors reduce the level of glucose metabolism related kinase HK2 by inhibiting the AKT-mTOR pathway in the FGFR pathway.PET/CT imaging based on 18F-FDG can indirectly reflect the therapeutic effect of FGFR inhibitors,provide a visual and dynamic monitoring method for targeted FGFR therapy,and provide a new basis for the evaluation of the efficacy of individualized treatment with targeted drugs.