BIODISTRIBUTION OF A TECHNETIUM-99M RADIOLABELED PEPTIDE DERIVED FROM LAMININ-111 IN A BREAST CANCER MODEL

Introduction/Justification

Breast cancer is a significant public health concern, ranking as the second most common tumor type among women. According to the World Health Organization (WHO), more than 14 million people develop breast cancer annually, with this number projected to rise to over 21 million by 2030. Studies have shown that biologically active peptides derived from laminin-111 can regulate gene expression in breast cancer-derived cells, among which the YIGSR peptide is of particular interest. Peptides designed to inhibit intracellular signaling pathways fall within the realm of molecular targeted therapies, which commonly focus on receptors overexpressed in tumors.

Objectives

This study aimed to evaluate the biological behavior of the HYIGSR peptide, a laminin-111 derivative, radiolabeled with technetium-99m ([99mTc]Tc(CO)3), in a biodistribution assay using both control and breast cancer model mice.

Materials and Methods

The HYIGSR peptide was radiolabeled using the tricarbonyl method, which enabled labeling at the histidine residue with the organometallic aqua-ion [99mTc(H2O)3(CO)3]+, abbreviated as [99mTc]Tc(CO)3. The reaction was carried out by reducing [99mTc]TcO4- under 1 atm of CO for 30 min at 70°C, followed by incubation with approximately 148 MBq of [99mTc]Tc(CO)3 for 30 min at 85°C. The radiochemical purity of [99mTc]Tc(CO)3-HYIGSR was assessed using TLC-SG strips with 0.9% NaCl as the eluent. A breast cancer animal model was established by inoculating female Balb/c nude mice with 1 × 10⁷ MDA-MB-231 breast cancer cells. After 30 days, in vivo (molecular imaging) and ex vivo biodistribution studies were performed. The radiolabeled peptide was intravenously administered to both healthy and tumor-bearing female Balb/c nude mice, and ex vivo biodistribution analysis was conducted at 1 and 3 h post-injection. Molecular imaging of healthy mice was acquired via planar scintigraphy using a single-hole collimator on a Discovery VH clinical gamma camera, with an acquisition time of 5 min and a geometric magnification of 9 × . All animal experiments adhered to local ethical guidelines for animal research (Protocol number: CEUA – HIAE 6015-24).

Results

The radiolabeling process using [99mTc]Tc(CO)3 was successfully standardized, yielding [99mTc]Tc(CO)3-HYIGSR with a radiochemical purity of 95.53 ± 1.19% (n = 5). Ex vivo biodistribution analysis in female Balb/c nude mice (n = 4) demonstrated rapid blood clearance over time, with increased uptake in the kidneys. Minimal accumulation of the radiolabeled peptide was observed in the heart, spleen, lungs, and muscle, with the percentage of the injected dose per gram (%ID/g) remaining below 5%. However, high uptake was observed in the liver, stomach, intestine, and thyroid. In tumor-bearing mice, tumor uptake was measured at 0.58 ± 0.25 %ID/g, with a tumor-to-muscle ratio of 1.54 ± 0.14. Preliminary molecular imaging in the healthy group confirmed in vivo biodistribution findings consistent with ex vivo data.

Conclusion

These findings suggest that while the [99mTc]Tc(CO)3-HYIGSR complex demonstrated efficient radiolabeling, further modifications may be necessary to enhance its tumor-targeting capabilities and improve its overall diagnostic potential.