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Synthesis and Evaluation of 99mTc-Labeled Folate-Tripeptide Conjugate as a Folate Receptor-Targeted Imaging Agent in a Tumor-Bearing Mouse Model

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Abstract

Purpose

The folate receptor (FR) is an attractive molecular target since it is overexpressed in a variety of human tumors. The purpose of the present study was to synthesize and evaluate the feasibility of a novel 99mTc-ECG-EDA (Glu-Cys-Gly-ethylenediamine)-folate as an FR-positive tumor imaging agent in a mouse tumor model.

Materials and Methods

ECG-EDA-folate was synthesized using solid phase peptide synthesis (SPPS) and radiolabeled with 99mTc using tripeptide ECG as a chelator. FR-positive KB cells were inoculated in athymic nude mice. Following injection of 99mTc-ECG-EDA-folate, serial scintigraphy and micro-SPECT/CT imaging were performed at various time points with and without pre-administration of excess free folate. Mean count densities (MCD) for regions of interest drawn on KB tumors and major normal organs at each time point were measured, and uptake ratios of tumor to normal organs were calculated.

Results

ECG-EDA-folate was labeled with 99mTc with high radiolabeling efficiency and stability (>96 %). FR-positive tumors were clearly visualized on both scintigraphy and micro-SPECT/CT images and the tumor uptake of 99mTc-ECG-EDA-folate was markedly suppressed with faint visualization of tumors by pre-administration of excess free folate on serial planar scintigraphy, indicating FR-specific binding of the agent. Furthermore, semiquantitative analysis of MCD data showed again that both tumor MCD and tumor-to-normal organ ratios decreased considerably by pre-administration of excess free folate, supporting FR-specific tumor uptake. Tumor-to-normal organ ratios approximately increased with time after injection until 4 h.

Conclusion

The present study demonstrated that 99mTc-ECG-EDA-folate can bind specifically to FR with clear visualization of FR-positive tumors in a mouse tumor model.

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Acknowledgments

This study was supported by Wonkwang University in 2013.

Conflict of Interest

Myoung Hyoun Kim, Woo Hyoung Kim, Chang Guhn Kim, and Dae-Weung Kim declare that they have no conflict of interest.

Ethical Standard

All procedures performed in this study involving animals were approved by the animal ethics committee in our university and were in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.

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Authors and Affiliations

  1. Department of Nuclear Medicine, Wonkwang University School of Medicine, Iksan, Korea

    Myoung Hyoun Kim, Chang Guhn Kim & Dae-Weung Kim

  2. Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea

    Woo Hyoung Kim

  3. Institute of Wonkwang Medical Science, Iksan, Korea

    Chang Guhn Kim & Dae-Weung Kim

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  1. Myoung Hyoun Kim
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  2. Woo Hyoung Kim
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Correspondence to Chang Guhn Kim.

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Manuscript has not been published before or is not under consideration for publication anywhere else and has been approved by all co-authors.

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Kim, M.H., Kim, W.H., Kim, C.G. et al. Synthesis and Evaluation of 99mTc-Labeled Folate-Tripeptide Conjugate as a Folate Receptor-Targeted Imaging Agent in a Tumor-Bearing Mouse Model. Nucl Med Mol Imaging 49, 200–207 (2015). https://doi.org/10.1007/s13139-015-0336-2

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  • DOI: https://doi.org/10.1007/s13139-015-0336-2

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