| The morbidity and mortality of lung cancer in China was significantly increased in recent years. The survival rate of patients with lung cancer is closely related to whether the disease can be diagnosed early and promptly, which is also of vital importance on therapeutic effects, especially for solitary pulmonary nodule (SPN). 18F-FDG PET/CT imaging were widely used for the diagnosis, differential diagnosis and staging workup of patients with lung cancer. Amounts of reports on the literatures and clinical data verified the high sensitivity and specificity of 18F-FDG PET/CT imaging. However, certain false-positive and false-negative cases often occur in 18F-FDG PET/CT imaging. The false-negative cases mainly appeared in some kind of lesions with low metabolism and well differentiation. The most common one is bronchioloalveolar carcinoma, which become a big problem for nuclear medicine doctors at present.Objective: In this study, SPECT imaging and bio-distribution in BALB/C nude mice bearing NCI-H358 human bronchioloalveolar carcinoma were performed, using the tracers 99mTc-RGD-4CK, 99mTc-N(NOET)2, 99mTc-MIBI and 18F-FDG with different imaging mechanism. The ratios of tumor to non-tumor with these four tracers were compared to evaluate the most sensitive one in diagnosing the well-differentiated lung cancer. We hope the result can be a help to lower the false-negative rate in 18F-FDG imaging.Methods: NCI-H358 was cultured in RPMI-1640 supplemented with 15% fetal bovine serum and incubated at 37°C in 5% CO2-95% air. Adherent tumor cells were harvested from 80%-90% subconfluent cultures by a brief exposure to 0.25% trypsin and 0.02% EDTA. After resuspension, centrifugation and dilution, 1×107(200μl) cell inoculum was subcutaneously injected into the right axilla of each nude mouse. Observation and measurement were performed every other day until the longest diameter of tumor came up to 0.7-1.0cm.The mice with no significant differences in weight and tumor size were chosen and divided them randomly into a, b, c, d four groups. 18F-FDG, 99mTc-MIBI, 99mTc-N(NOET)2 and 99mTc-RGD-4CK was injected(7.4MBq-200μl)in a tail vein of ,respectively,5 each group conscious and restrained nude mice.120 minutes following tracer injection, the animals were anaesthetized using an intraperitoneal injection of chloral hydrate (10%wt/vol-5ml/kg) and placed under the pin-hole collimator of single photon emission computed tomography (SPECT) and a 300k-counts whole-body planar image acquisition was performed. After the acquisition the blood was obtained from retrobulbar venous plexus and then the animals were euthanized by cervical dislocation and samples from the heart, liver, spleen, lung, kidney, stomach, small intestine, skeletal muscle and tumor were obtained. Organs were quickly rinsed and activities of the tracers were assessed using a gamma-well counter. All tissue counts were corrected for background and decay during the time of counting. Tissue activities of the tracers were expressed as percent of the injected dose per gram of wet weight (%ID/g).Tumor samples of each group were fixed into 4% paraformaldehyde, embedded with paraffin wax and resected into 5μm section. Routine HE staining and immuno- chemical staining were performed to evaluate the expression of pulmonary surfactant- associated protein A (SP-A) and proliferating cell nuclear antigen (PCNA).Results:1 Formation and characterization of tumorsTwenty xenotransplantation models for human non-small cell lung cancer in BALB/C nude mice were all successfully established. The tumor formation rate was 100%.Macroscopic observation: The mass of tumor were fleshpink, nodular, smooth-faced and section-offwhite. Haematoxylin Eosin staining revealed that the tumor cells were homogeneous with adenoid arrangement, large and hyperchromatic nuclei with obvious atypia, which matched the characteristic of malignant tumor. The tumor exhibited cytoplasmic and plasma membrane pulmonary surfactant- associated protein A (SP-A) immunoreactivity, but had a low expression of PCNA.2 SPECT imaging results:The tracer FDG accumulated obviously on chest of nude mice and partially overlaid the tumor implanted in axilla, leading to an indistinct outline of tumor body. Tumors in group c and d were readily detected with 99mTc-N(NOET)2 and 99mTc-RGD-4CK, whereas the administration of 99mTc-MIBI did not allow tumor visualization. Results from planar image semi-quantification showed that tumor to contralateral muscle activity ratios (T/NT) of four tracers were statistically different from each other in NCI-H358-bearing mice (F=131.996,p=0.000<0.01).The highest T/NT ratio was group d(3.40±0.27), while the lowest one was group b(0.99±0.16).3 Bio-distribution results:Statistical differences were observed in the uptake of four tracers in nude mice bearing NCI-H358 (F=147.882, p=0.000<0.01). Consistant with the imaging results, tumor to contralateral muscle activity ratios (T/NT) of 99mTc-RGD-4CK (3.43±0.36) was significantly higher than the other three tracers. And the lowest one was also 99mTc-MIBI (0.44±0.08). Different from the imaging results,the T/NT ratios of 18F-FDG(2.32±0.14)and 99mTc-N(NOET)(22.59±0.53) had no significant differences(p=0.635>0.05).Conclusion:1 The uptake of 99mTc-N(NOET)2 in NCI-H358 tumor was higher than 99mTc-MIBI and had no significant differences with 18F-FDG.2 NCI-H358 tumor showed higher uptake of 99mTc-RGD-4CK than 18F-FDG. It suggest that when diagnosing the well-differentiated lung cancer such as bronchioloalveolar carcinoma, the tracer 99mTc-RGD-4CK may be more sensitive than 18F-FDG, which appears as a promising tracer of tumor imaging.
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