Experimental And Clinical Study On The Uptake Mechanism Of¹⁸F-FDG And¹⁸F-FLT In Lung Cancer Microenvironment

PartⅠ:Experimental Study on the Uptake Mechanism of ¹⁸F-FDG and ¹⁸F-FLT in Lung Cancer MicroenvironmentObjective:¹⁸F-FDG or ¹⁸F-FLT PET/CT imaging has become an important clinical tool in the evaluation of malignancy treatment.However,it is still unclear which of ¹⁸F-FDG and ¹⁸F-FLT imaging distribution characteristics.This study intends to identify the abnormal uptake of ¹⁸F-FDG and ¹⁸F-FLT in malignant lung tumors,to relate to the specific components of the tumor microenvironment,and to investigate the characteristics of radioactive distribution of ’8F-FDG and ’8F-FLT in the lung cancer microenvironment.Methods:20 BALB/c mice(6 weeks old,¹⁸-22 g),were divided into group A and B with 10 mice in each group.All tumor-bearing mice were implanted subcutaneously with A549（right hind leg）and HTB177（left hind leg）cell lines.Group A:10 tumor-bearing mice in Group A were divided into two groups,’8F-FDG group and ¹⁸F-FLT group with 5 mice in each group.The radioactivity distributions of ¹⁸F-FDG and ¹⁸F-FLT in tumors were studied by autoradiographys which was compared with histological studies such as pimonidazole for hypoxia and bromodeoxyuridine（Brdu）for proliferation.Group B:10 tumor-bearing mice in Group B were divided into B1 group and B2 group with 5 mice in each group.In the B1 group,the first PET scan was performed 1 h after ¹⁸F-FLT injection.¹⁸F-FDG was injected immediately after the first PET scan,and afterl hour,the second PET scan was performed.B2 group was injected with Brdu and ¹⁸F-FLT at the same time.The first PET scan was performed 1 hour later.After 14 hours,the same tumor-bearing mice were injected with ¹⁸F-FDG and pimonidazole at the same time.A second PET scan was performed 1 hour later.Animals were sacrificed after two sets of PET imaging and the results were compared with DAR and histology.Results:Results from Group A:（1）Complex tumor microenvironment in NSCLC:H&E staining in HTB177 subcutaneously implanted tumors revealed a complex tumor microenvironment.According to oxygenation status and cell proliferation,cancer cells are further divided into two subcategories:Cancer cells close to functional blood vessels（positive for Hoechst 33342）were negative for pimonidazole but positive for Brdu.Positive expression indicates that the cells have good oxygenation and proliferation capabilities;The tumor cells,which were approximately 150μm away from functional blood vessels or close to the necrotic area,were positive for pimonidazole but negative for Brdu,indicating that these cancer cells were hypoxic and had less proliferation.（2）In the hypoxic region,the uptake ratio（8.27）of the mixture of both ¹⁸F-FLT and ¹⁸F-FDG relative to the necrotic area was not significantly different from that（6.92）of ¹⁸F-FDG alone,but higher than ¹⁸F-FLT（1.54）,P<0.01;In the proliferative region,the uptake ratio（3.42）of the mixture of both ¹⁸F-FLT and ¹⁸F-FDG relative to the necrotic area was not significantly different from that（3.16）of ¹⁸F-FLT alone,but higher than ¹⁸F-FDG（1.87）,P<0.01.Results from Group B:（1）PET imaging of ¹⁸F-FDG,¹⁸F-FLT and mixed-injected in tumor-bearing mice revealed intratumoral radioactivity distributions of ¹⁸F-FDG,¹⁸F-FLT,and a combination of both in HTB177 tumors.Superimposed imaging of immunohistochemical staining:Pimonidazole and Brdu were injected at 14-hour intervals and their imaging results showed a mutually exclusive pattern.（2）Different tracer distribution patterns were shown in PET images of 5 bearing A549 and HTB177 tumor mice after separate or simultaneous injection of tracers,suggesting that the hypoxia or proliferation of the tumor was stable during the 14-hour interval.Compared with PET scan 2,PET scan 1 had significantly enhanced radioactivity uptake compared to ¹⁸F-FLT images.Conclusions:There was a mismatch between the radioactivity distribution of ¹⁸F-FLT and ¹⁸F-FDG in malignant cells.¹⁸F-FDG mainly concentrated in the hypoxic region,while ¹⁸F-FLT mainly concentrated in the proliferative region.The combined application of ¹⁸F-FLT+¹⁸F-FDG can completely display the absolute survival volume of malignant tumors compared with single tracer PET imaging,and can more accurately display the total survival tumor tissue,which will be a powerful imaging strategy for tumor efficacy assessment.Part Ⅱ:Clinical Study on the Uptake Mechanism of ¹⁸F-FDG and ¹⁸F-FLT in Lung Cancer MicroenvironmentObjective:In preclinical studies,it was found that the radioactive distribution of ¹⁸F-FLT and ¹⁸F-FDG in tumors was inconsistent.¹⁸F-FLT was mainly distributed in areas where proliferating cells were active,while ¹⁸F-FDG was mainly concentrated in areas where hypoxic tumor cells were active.Based on preclinical studies,the radioactivity distribution characteristics of ¹⁸F-FLT and ¹⁸F-FDG in tumors of lung cancer patients will be studied.Methods:Ninety-five patients with isolated lung lesions,who visited Inner Mongolia Medical University Affiliated Hospital from October 2014 to December 2016,were enrolled.Among them,69 were males and 26 were females.All the enrolled patients were confirmed by pathological results,benign benign ones.Patients in both groups received ¹⁸F-FDG and ¹⁸F-FLT PET/CT scan within 3 days.Image analysis method:Three nuclear in 31 cases,malignant in 64 cases.Patients were divided into 64 lung cancer patients and 31 medicine doctors compose a reading team to analyze each image.The reading team visually scored the radioactivity uptake of ¹⁸F-FDG and ¹⁸F-FLT within each field of view of each image,to evaluate ¹⁸F-FDG diagnosis alone,¹⁸F-FLT diagnosis alone,¹⁸F-FDG combined with ¹⁸F-FLT diagnosis for each image,and to evaluate whether SUVmax regions,where ¹⁸F-FLT and ¹⁸F-FDG imaging agents concentrated,were consistent.The 4 diagnostic indicators were compared with the corresponding pathological results and statistical analysis was performed.Results:（1）In the lung cancer group,47 cases（79%）were inconsistent in the SUVmax area of ¹⁸F-FLT and ¹⁸F-FDG imaging agents.17 cases,accounting for 21%of the lung cancer group,were consistent in the SUVmax area of both imaging agents.In the benign group,12 cases（39%）were inconsistent in the SUVmax area of ¹⁸F-FLT and ¹⁸F-FDG imaging agents.19 cases,accounting for 61%of the benign group,were consistent in the SUVmax area of both imaging agents.There was a statistically significant difference in SUVmax area of ¹⁸F-FLT and ¹⁸F-FDG imaging agents in the benign and lung cancer groups（P<0.05）.（2）In the comparison of ¹⁸F-FLT and ¹⁸F-FDG imaging agent concentration SUVmax region with pathological results,the diagnostic specificity（67.742%）,sensitivity（78.125%）,coincidence rate（78.947%）,positive predictive value（84.375%）,and negative predictive value（67.742%）of pulmonary benign nodules were analyzed,evaluation results of which were higher than that of ¹⁸F-FDG diagnosis alone,¹⁸F-FLT diagnosis alone,and ¹⁸F-FDG combined with the ¹⁸F-FLT diagnosis.This indicator,whether SUVmax area of ¹⁸F-FLT and ¹⁸F-FDG imaging agent concentration were consistent or not,showed a clear advantage in the sensitivity,specificity,coincidence rate,positive predictive value,and negative predictive value of lung cancer diagnosis.Conclusions:The inconsistent image characteristics of ¹⁸F-FLT and ¹⁸F-FDG imaging agents in the concentrated SUVmax region are common features of lung cancer patients.The mismatch of intratumoral radioactivity distribution SUVmax between ¹⁸F-FDG and ¹⁸F-FLT reflected heterogeneity of cancer cells,hypoxia(increased ¹⁸F-FDG uptake)and high proliferation(¹⁸F-FLT uptake),which can be used as one of the characteristic indicators for the diagnosis of lung cancer.