Synthesis of 99mTc-EC-AMT as an imaging probe for amino acid transporter systems in breast cancer

Radiolabeling and Biological Evaluation of Novel 99mTc-Nitrido and 99mTc-Oxo Complexes with 4-Methoxy-L-Phenylalanine Dithiocarbamate for Tumor Imaging

To develop novel radiolabeled amino acid tumor imaging agents, 4-methoxy-L-phenylalanine dithiocarbamate (MOPADTC) was synthesized successfully, and two kinds of 99mTc-labeled complexes ([99mTc]TcN-MOPADTC and [99mTc]TcO-MOPADTC) with high radiochemical purities (RCP > 95%) were obtained. The in vitro stability and partition coefficient were determined, and the results show that both of these complexes have good in vitro stability; [99mTc]TcO-MOPADTC is hydrophilic, while [99mTc]TcN-MOPADTC is slightly lipophilic. The biodistribution of [99mTc]TcN-MOPADTC and [99mTc]TcO-MOPADTC in mice bearing S180 tumors shows that the tumor uptake and tumor/muscle ratio of [99mTc]TcO-MOPADTC were higher than the tumor uptake and tumor/muscle ratio of [99mTc]TcN-MOPADTC. In addition, the tumor retention of [99mTc]TcO-MOPADTC is better than the tumor retention of [99mTc]TcN-MOPADTC. A competitive inhibition assay was performed, and the results indicate that [99mTc]TcO-MOPADTC may enter cells primarily via the L-alanine/L-serine/L-cysteine (ASC) system. Single-photon emission computed tomography (SPECT) imaging of [99mTc]TcO-MOPADTC shows obvious accumulation in tumor sites, suggesting that [99mTc]TcO-MOPADTC is a novel potential tumor-imaging agent.

Preparation and assessment of a new radiotracer technetium-99m-6-hydrazinonicotinic acid-tyrosine as a targeting agent in tumor detecting through single photon emission tomography

The goal of investigation was to bring up an impressive way to synthesize technetium-99 m-6-hydrazinonicotinic acid-tyrosine (^99mTc-HYNIC-Tyr), a newfound radiotracer, and to assess the capacity of being as a tumor scintigraphy agent. The conjugate was prepared by solid phase method using tritely chloride resin. The precursor HYNIC-Tyr was labeled with ^99mTc which was accomplished at 100 °C through the coligands tricine and EDDA. Furthermore, the serum albumin binding, cellular attachment, organs uptake and tumor accumulation were measured. C6 glioma cells were used for cellular and tumor uptake studies. ^99mTc-HYNIC-Tyr was prepared with labeling yield of >99% (n = 3). Radiotracer showed stability in serum proteins in incubates temperature. Specific cellular attachment of radiotracer was noticeable in C6 glioma cells with dissociation constant in nano molar range (21.03 ± 1.54 nM). The amount of uptake in C6 rat glioma xenograft was 2.61 ± 0.12 percent of injection dose per gram after 30 min. In whole-body scintigraphy, C6 glioma tumor was easy to be traced and interpreted at 1 h after administration of radiotracer. Our data suggest that ^99mTc-HYNIC-Tyr, a new radiotracer based on amino acid, efficiently differentiates the tumor cells and goes into them. Our results indicate that this radiotracer has excellent capacity to detect tumor cells in rat and to be included as a radiopharmaceutical for detecting cancer tumors.

Development of (99m)Tc-EC-tyrosine for early detection of breast cancer tumor response to the anticancer drug melphalan

RATIONALE AND OBJECTIVES

Radiolabeled tyrosine analogues that have been successfully used in tumor imaging accumulate in tumor cells via an upregulated L-type amino acid transporter system. The anticancer drug melphalan is an L-type amino acid transporter substrate. Therefore, radiolabeled tyrosine analogues may have great potential in evaluating treatment responses to melphalan. In this study, a (99m)Tc-labeled tyrosine analogue, (99m)Tc tyrosine using N,N'-ethylene-di-L-cysteine (EC) as a chelator, was developed and its potential for noninvasively assessing tumors' early response to melphalan determined.

MATERIALS AND METHODS

EC-tyrosine was synthesized in a three-step procedure and labeled with (99m)Tc. To assess cellular uptake kinetics, the percentage uptake of (99m)Tc-EC-tyrosine in the rat breast cancer cell line 13762 was measured. Planar imaging was performed in rats with 13762 cell-derived tumors. To determine the transport mechanisms of (99m)Tc-EC-tyrosine, a competitive inhibition study using L-tyrosine as an inhibitor was performed in vitro and in vivo. To assess tumors' response to melphalan, tumor-bearing rats were treated with different doses of melphalan, and planar imaging was performed 0 and 3 days after treatment. Immunohistochemical analyses were conducted to determine expressions of L-type amino acid transporter 1 and cellular proliferation marker Ki-67.

RESULTS

L-tyrosine significantly inhibited (99m)Tc-EC-tyrosine uptake in vitro and in vivo. Tumor volume decreased in a dose-dependent manner with melphalan, and tumor/muscle ratios of (99m)Tc-EC-tyrosine were significantly reduced in treated groups. Immunohistochemical data indicated that about 70% of tumor cells in the melphalan-treated groups underwent apoptosis, and the changes in tumor/muscle ratios reflected the decreased percentage of viable cells in treated tumors.

CONCLUSIONS

These findings suggest that (99m)Tc-EC-tyrosine has great potential for monitoring tumor response to melphalan in breast tumor-bearing rats.

Development of tyrosine-based radiotracer 99mTc-N4-Tyrosine for breast cancer imaging

The purpose of this study was to develop an efficient way to synthesize ^99mTc-O-[3-(1,4,8,11-tetraazabicyclohexadecane)-propyl]-tyrosine (^99mTc-N4-Tyrosine), a novel amino acid-based radiotracer, and evaluate its potential in breast cancer gamma imaging. Precursor N4-Tyrosine was synthesized using a 5-step procedure, and its total synthesis yield was 38%. It was successfully labeled with ^99mTc with high radiochemical purity (>95%). Cellular uptake of ^99mTc-N4-Tyrosine was much higher than that of ^99mTc-N4 and the clinical gold standard ¹⁸F-2-deoxy-2-fluoro-glucose (¹⁸F-FDG) in rat breast tumor cells in vitro. Tissue uptake and dosimetry estimation in normal rats revealed that ^99mTc-N4-Tyrosine could be safely administered to humans. Evaluation in breast tumor-bearing rats showed that although ^99mTc-N4-Tyrosine appeared to be inferior to ¹⁸F-FDG in distinguishing breast tumor tissue from chemical-induced inflammatory tissue, it had high tumor-to-muscle uptake ratios and could detect breast tumors clearly by planar scintigraphic imaging. ^99mTc-N4-Tyrosine could thus be a useful radiotracer for use in breast tumor diagnostic imaging.