Effect of exogenous human sodium iodide symporter expression on growth of MATLyLu cells

A whole-body dual-modality radionuclide optical strategy for preclinical imaging of metastasis and heterogeneous treatment response in different microenvironments

Imaging spontaneous cancer cell metastasis or heterogeneous tumor responses to drug treatment in vivo is difficult to achieve. The goal was to develop a new highly sensitive and reliable preclinical longitudinal in vivo imaging model for this purpose, thereby facilitating discovery and validation of anticancer therapies or molecular imaging agents.

METHODS

The strategy is based on breast cancer cells stably expressing the human sodium iodide symporter (NIS) fused to a red fluorescent protein, thereby permitting radionuclide and fluorescence imaging. Using whole-body nano-SPECT/CT with (99m)TcO4(-), we followed primary tumor growth and spontaneous metastasis in the presence or absence of etoposide treatment. NIS imaging was used to classify organs as small as individual lymph nodes (LNs) to be positive or negative for metastasis, and results were confirmed by confocal fluorescence microscopy. Etoposide treatment efficacy was proven by ex vivo anticaspase 3 staining and fluorescence microscopy.

RESULTS

In this preclinical model, we found that the NIS imaging strategy outperformed state-of-the-art (18)F-FDG imaging in its ability to detect small tumors (18.5-fold-better tumor-to-blood ratio) and metastases (LN, 3.6-fold) because of improved contrast in organs close to metastatic sites (12- and 8.5-fold-lower standardized uptake value in the heart and kidney, respectively). We applied the model to assess the treatment response to the neoadjuvant etoposide and found a consistent and reliable improvement in spontaneous metastasis detection. Importantly, we also found that tumor cells in different microenvironments responded in a heterogeneous manner to etoposide treatment, which could be determined only by the NIS-based strategy and not by (18)F-FDG imaging.

CONCLUSION

We developed a new strategy for preclinical longitudinal in vivo cancer cell tracking with greater sensitivity and reliability than (18)F-FDG PET and applied it to track spontaneous and distant metastasis in the presence or absence of genotoxic stress therapy. Importantly, the model provides sufficient sensitivity and dynamic range to permit the reliable assessment of heterogeneous treatment responses in various microenvironments.

Morphological and histometric parameters of the thyroid gland in slaughter cattle

The study presents an evaluation of morphological and histometric parameters of the thyroid gland of slaughtered cattle (29 cows, 10 bulls, 7 heifers and 4 calves). The thyroid gland of bulls contained 34.7% of large follicles while their content in cows and heifers was 32.6% and only 19.2%, respectively. The average follicle length was 162.0±19.8 μm in bulls, 153.5±24.8 μm in cows and 122.4±10.1 μm in heifers. The highest thyreocytes were found in heifers and bulls (9.45±1.17 and 9.42±1.50 μm, respectively) and the lowest in cows (8.46±2.13 μm). A positive relationship was determined between the iodine content of the thyroid gland and the percentage of large follicles (r = 0.55) while the relationship between iodine content and thyreocyte height was negative (r = -0.21). In the thyroid gland of older cows medium and large follicles with low cubic to flat thyreocytes were dominant. Some follicles contained necrotic thyreocytes and the cytoplasm contained lipofuscin. The results suggest the influence of an increased iodine content in the thyroid gland on follicle size and thyreocyte height.

Sodium iodide symporter and the radioiodine treatment of thyroid carcinoma

Since the specific accumulation of iodide in thyroid was found in 1915, radioiodine has been widely applied to diagnose and treat thyroid cancer. Iodide uptake occurs across the membrane of the thyroid follicular cells and cancer cells through an active transporter process mediated by the sodium iodide symporter (NIS). The NIS coding genes were cloned and identified from rat and human in 1996. Evaluation of the NIS gene and protein expression is critical in the management of thyroid cancer, and several approaches have been tried to increase NIS levels. Identification of the NIS gene has provided a means of expanding its role in the radionuclide gene therapy of nonthyroidal cancers as well as thyroid cancer. In this article, we explain the relationship between NIS expression and the treatment of thyroid carcinoma with I-131, and we include a review of the results of our experimental and clinical trials.

Efficacy of 99mTc pertechnetate and 131I radioisotope therapy in sodium/iodide symporter (NIS)-expressing neuroendocrine tumors in vivo

PURPOSE

There is growing interest in the human sodium/iodide symporter (NIS) gene both as a molecular imaging reporter gene and as a therapeutic gene. Here, we show the feasibility of radioisotope therapy of neuroendocrine tumors. As a separate application of NIS gene transfer, we image NIS-expressing tumors with pinhole SPECT in living subjects.

METHODS

Biodistribution studies and in vivo therapy experiments were performed in nude mice carrying stably NIS-expressing neuroendocrine tumor xenografts following i.v. injection of (131)I and (99m)Tc pertechnetate. To show the usefulness of NIS as an imaging reporter gene, (99m)Tc pertechnetate uptake was imaged in vivo using a clinical gamma camera in combination with a custom-made single pinhole collimator, followed by SPECT/small animal MRI data coregistration.

RESULTS

NIS-expressing neuroendocrine tumors strongly accumulated (131)I and (99m)Tc pertechnetate, as did thyroid, stomach, and salivary gland. The volume of NIS-expressing neuroendocrine tumors decreased significantly after therapeutic administration of (131)I or (99m)Tc pertechnetate, whereas control tumors continued to grow. NIS-mediated uptake of (99m)Tc pertechnetate could be imaged in vivo at high resolution with a clinical gamma camera equipped with a custom-made single pinhole collimator. High-resolution functional and morphologic information could be combined in a single three-dimensional data set by coregistration of SPECT and small animal MRI data. Lastly, we demonstrated a therapeutic effect of (99m)Tc pertechnetate on NIS-expressing neuroendocrine tumors in cell culture and, for the first time, in vivo, thought to be due to emitted Auger and conversion electrons.

CONCLUSIONS

NIS-expressing neuroendocrine tumors efficiently concentrate radioisotopes, allowing for in vivo high-resolution small animal SPECT imaging as well as rendering possible successful radioisotope therapy of neuroendocrine tumors.

Imaging of metastatic pulmonary tumors following NIS gene transfer using single photon emission computed tomography

The Na+/I- symporter (NIS) is a membrane glycoprotein that facilitates the uptake of iodine into thyroid follicular cells. Recently, we and others have demonstrated the feasibility of imaging subcutaneous xenografts expressing exogenous NIS, suggesting that NIS may serve as an imaging reporter gene to monitor vector delivery and therapeutic gene expression. In this study, we established NIS-expressing pulmonary tumors in nude mice to investigate the minimal tumor size required for in vivo detection of pulmonary tumors by single photon emission computed tomography (SPECT) with pinhole collimation. In order to define the anatomic location of NIS-expressing tumor nodules detectable by SPECT, we performed simultaneous, dual-isotope imaging. We injected 1 mCi 99mTc-MAA via tail vein to image pulmonary perfusion and injected 1 mCi Na125I intraperitoneally to image NIS-expressing tumors. Fused images showed that 99mTc-MAA perfusion defects correlated with NIS-mediated 125I uptake. Post-mortem analysis revealed that tumors 3 mm in diameter could be detected by SPECT with pinhole collimation. These studies demonstrate the feasibility of SPECT to detect pulmonary tumors expressing exogenous NIS in mice.