Advantages of 99mTc-3PRGD2 SPECT over CT in the preoperative assessment of lymph node metastasis in patients with esophageal cancer

99mTc-3PRGD2 SPECT/CT Imaging for Diagnosing Lymph Node Metastasis of Primary Malignant Lung Tumors

OBJECTIVE

To evaluate 99mtechnetium-three polyethylene glycol spacers-arginine-glycine-aspartic acid (99mTc-3PRGD2) single-photon emission computed tomography (SPECT)/computed tomography (CT) imaging for diagnosing lymph node metastasis of primary malignant lung neoplasms.

MATERIALS AND METHODS

We prospectively enrolled 26 patients with primary malignant lung tumors who underwent 99mTc-3PRGD2 SPECT/CT and 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET)/CT imaging. Both imaging methods were analyzed in qualitative (visual dichotomous and 5-point grades for lymph nodes and lung tumors, respectively) and semi-quantitative (maximum tissue-to-background radioactive count) manners for the lymph nodes and lung tumors. The performance of the differentiation of lymph nodes with and without metastasis was determined at the per-lymph node station and per-patient levels using histopathological results as the reference standard.

RESULTS

Total 42 stations had metastatic lymph nodes and 136 stations had benign lymph nodes. The differences between metastatic and benign lymph nodes in the visual qualitative and semiquantitative analyses of 99mTc-3PRGD2 SPECT/CT and 18F-FDG PET/CT were statistically significant (all P < 0.001). The area under the receiver operating characteristic curve (AUC) in the semi-quantitative analysis of 99mTc-3PRGD2 SPECT/CT was 0.908 (95% confidence interval [CI], 0.851-0.966), and the sensitivity, specificity, positive predictive value, and negative predictive value were 0.86 (36/42), 0.88 (120/136), 0.69 (36/52), and 0.95 (120/126), respectively. Among the 26 patients (including two patients each with two lung tumors), 15 had pathologically confirmed lymph node metastasis. The difference between primary lung lesions in patients with and without lymph node metastasis was statistically significant only in the semi-quantitative analysis of 99mTc-3PRGD2 SPECT/CT (P = 0.007), with an AUC of 0.807 (95% CI, 0.641-0.974).

CONCLUSION

99mTc-3PRGD2 SPECT/CT imaging may notably perform in the direct diagnosis of lymph node metastasis of primary malignant lung tumors and indirectly predict the presence of lymph node metastasis through uptake in the primary lesions.

Advances in Clinical Oncology Research on 99mTc-3PRGD2 SPECT Imaging

The integrin alpha(α)v beta(β)3 receptor is ubiquitous in malignant tumors and has a certain level of specificity for tumors. Technetium-99m hydrazinonicotinamide-dimeric cyclic arginyl-glycyl-aspartic acid peptide with three polyethylene glycol spacers (99mTc-3PRGD2) can bind specifically to the integrin αvβ3 receptor with high selectivity and strong affinity. Thus, it can specifically mark tumors and regions with angiogenesis for tumor detection and be used in single-photon emission computed tomography (SPECT) imaging. This modality has good application value for diagnosing and treating tumor lesions, such as those in the lung, breast, esophagus, head, and neck. This review provides an overview of the current clinical research progress of 99mTc-3PRGD2 SPECT imaging for tumor lesions, including for the diagnosis and differential diagnosis of tumors in different body parts, evaluation of related metastases, and evaluation of efficacy. In addition, the future clinical application prospects and possibilities of 99mTc-3PRGD2 SPECT imaging are further discussed.

An Integrin Alpha 6-Targeted Radiotracer with Improved Receptor Binding Affinity and Tumor Uptake

In this study, we reported a ^99mTc-labeled integrin α₆-targeted peptide as the molecular imaging probe for tumor imaging by single-photon emission computed tomography (SPECT). We found that replacing Cys-Cys cyclized RWY peptide (sequence: cCRWYDENAC) with lactam-bridged cyclic cKiE peptide (sequence: cKRWYDENAisoE) did not sacrifice the integrin α₆-binding affinity and specificity of cKiE radiotracer. To further improve the radiotracer's tumor targeting capability, the dimerized cKiE peptide (termed cKiE2) was designed, and the corresponding radiotracer ^99mTc-cKiE2 was evaluated for tumor uptake and in vivo pharmacokinetics properties in tumor models. We found that cKiE2 showed higher binding affinity to integrin α₆ than did monomeric RWY or cKiE peptide. The biodistribution results showed that the tumor uptake of ^99mTc-cKiE2 was twice higher than that of ^99mTc-RWY (3.20 ± 0.12 vs 1.26 ± 0.06 %ID/g, P < 0.001) at 0.5 h postinjection. The tumor to nontargeting tissue ratios were also enhanced in most normal organs. Specificity of ^99mTc-cKiE2 for integrin α₆ was demonstrated by competitive blocking of tumor uptake with excess cold peptide (3.20 ± 0.24 to 1.38 ± 0.23 %ID/g, P < 0.001). The integrin α₆-positive tumors were clearly visualized by ^99mTc-cKiE2/SPECT with low background except with a relatively high kidney uptake. The tumor uptake of ^99mTc-cKiE2 correlates well with the tumor integrin α₆ expression levels in a linear fashion (R² = 0.9623). We also compared ^99mTc-cKiE2 with an integrin α_vβ₃-targeted radiotracer ^99mTc-3PRGD₂ in the orthotopic hepatocellular carcinoma tumor models. We found that the orthotopic tumor was clearly visualized with ^99mTc-cKiE2. ^99mTc-3PRGD₂ imaging did not show tumor contours in situ as clearly as ^99mTc-cKiE2. The tumor-to-liver ratios of ^99mTc-cKiE2 and ^99mTc-3PRGD₂ were 2.20 ± 0.17 and 0.85 ± 0.20. In conclusion, ^99mTc-cKiE2 is an improved SPECT radiotracer for imaging integrin α₆-positive tumors and has great potential for further clinical application.