Comparative Evaluation of Using NOTA and DOTA Derivatives as Bifunctional Chelating Agents in the Preparation of 68Ga-Labeled Porphyrin: Impact on Pharmacokinetics and Tumor Uptake in a Mouse Model

Effectiveness of [67Cu]Cu-trastuzumab as a theranostic against HER2-positive breast cancer

PURPOSE

To evaluate the imaging and therapeutic properties (theranostic) of 67Cu-labeled anti-human epidermal growth factor receptor II (HER2) monoclonal antibody trastuzumab against HER2-positive breast cancer (BC).

METHODS

We conjugated trastuzumab with p-SCN-Bn-NOTA, 3p-C-NETA-NCS, or p-SCN-Bn-DOTA, and radiolabeled with [67Cu]CuCl2. Immunoconjugate internalization was evaluated in BT-474, JIMT-1 and MCF-7 BC cells. In vitro stability was studied in human serum (HS) and Phosphate Buffered Saline (PBS). Flow cytometry, radioligand binding and immunoreactive fraction assays were carried out. ImmunoSPECT imaging of [67Cu]Cu-NOTA-trastuzumab was done in mice bearing BT-474, JIMT-1 and MCF-7 xenografts. Pharmacokinetic was studied in healthy Balb/c mice while dosimetry was done in both healthy Balb/c and in athymic nude mice bearing JIMT-1 xenograft. The therapeutic effectiveness of [67Cu]Cu-NOTA-trastuzumab was evaluated in mice bearing BT-474 and JIMT-1 xenografts after a single intravenous (i.v.) injection of ~ 16.8 MBq.

RESULTS

Pure immunoconjugates and radioimmunoconjugates (> 95%) were obtained. Internalization was HER2 density-dependent with highest internalization observed with NOTA-trastuzumab. After 5 days, in vitro stabilities were 97 ± 1.7%, 31 ± 6.2%, and 28 ± 4% in HS, and 79 ± 3.5%, 94 ± 1.2%, and 86 ± 2.3% in PBS for [67Cu]Cu-NOTA-trastuzumab, [67Cu]Cu-3p-C-NETA-trastuzumab and [67Cu]Cu-DOTA-trastuzumab, respectively. [67Cu]Cu-NOTA-trastuzumab was chosen for further evaluation. BT-474 flow cytometry showed low KD, 8.2 ± 0.2 nM for trastuzumab vs 26.5 ± 1.6 nM for NOTA-trastuzumab. There were 2.9 NOTA molecules per trastuzumab molecule. Radioligand binding assay showed a low KD of 2.1 ± 0.4 nM and immunoreactive fraction of 69.3 ± 0.9. Highest uptake of [67Cu]Cu-NOTA-trastuzumab was observed in JIMT-1 (33.9 ± 5.5% IA/g) and BT-474 (33.1 ± 10.6% IA/g) xenograft at 120 h post injection (p.i.). Effectiveness of the radioimmunoconjugate was also expressed as percent tumor growth inhibition (%TGI). [67Cu]Cu-NOTA-trastuzumab was more effective than trastuzumab against BT-474 xenografts (78% vs 54% TGI after 28 days), and JIMT-1 xenografts (90% vs 23% TGI after 19 days). Mean survival of [67Cu]Cu-NOTA-trastuzumab, trastuzumab and saline treated groups were > 90, 77 and 72 days for BT-474 xenografts, while that of JIMT-1 were 78, 24, and 20 days, respectively.

CONCLUSION

[67Cu]Cu-NOTA-trastuzumab is a promising theranostic agent against HER2-positive BC.

Noninvasive Classification of Human Triple Negative Breast Cancer by PET Imaging with GRP78-Targeted Molecular Probe [68Ga]DOTA-VAP

PURPOSE

There is currently no effective noninvasive method for accurate molecular typing of triple negative breast cancer (TNBC) except needle biopsy. Glucoregulated Protein 78 (GRP78) is overexpressed in TNBC cells and tumors which closely related to the invasion, metastasis, and drug resistance of cancer. Meanwhile, it has been verified that VAP peptide bind specifically to GRP78 in vitro and in vivo. In this study, we constructed a GRP78-targeted molecular probe Ga-68-radiolabeled DOTA-VAP conjugate ([⁶⁸Ga]DOTA-VAP) based on VAP peptide, and evaluated its potential to distinguish TNBC from non-TNBC tumors.

PROCEDURES

DOTA-VAP was synthesized and then radiolabeled with Ga-68 to obtain [⁶⁸Ga]DOTA-VAP. The expression of GRP78 in TNBC MDA-MB-231 and non-TNBC MCF-7 cells was validated by Western Blot, and cell binding or uptake experiments with both [⁶⁸Ga]DOTA-VAP and 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) were also performed. Biodistribution analysis and positron emission tomography (PET) imaging of [⁶⁸Ga]DOTA-VAP were carried out in subcutaneous MDA-MB-231 and MCF-7 human breast cancer tumor models with [¹⁸F]FDG PET imaging as comparison.

RESULTS

[⁶⁸Ga]DOTA-VAP was prepared with high radiochemical purity which showed excellent stability in vitro. The MDA-MB-231 tumors were clearly visualized by [⁶⁸Ga]DOTA-VAP PET imaging with a low background, except for the relatively high liver uptake. Cells and tumors of MDA-MB-231 could be distinguished from MCF-7 by [⁶⁸Ga]DOTA-VAP instead of [¹⁸F]FDG. Biodistribution results were consistent with the imaging results. The blocking study with excess cold peptide showed significantly reduced tumor uptake, which indicated the specificity of [⁶⁸Ga]DOTA-VAP targeting MDA-MB-231 tumors in vivo.

CONCLUSIONS

GRP78-targeted PET imaging with [⁶⁸Ga]DOTA-VAP provided an effective approach for the noninvasive accurate classification of TNBC from other breast cancer subtypes comparing with [¹⁸F]FDG. GRP78 may be a potential target for the diagnosis and treatment of TNBC. For clinical transformation, efforts should be made to overcome deficiencies of [⁶⁸Ga]DOTA-VAP such as relative high uptake in normal tissues.

Metalloporphyrins in Medicine: From History to Recent Trends

The history of metalloporphyrins dates back more than 200 years ago. Metalloporphyrins are excellent catalysts, capable of forming supramolecular systems, participate in oxygen photosynthesis, transport, and used as contrast agents or superoxide dismutase mimetics. Today, metalloporphyrins represent complexes of conjugated π-electron system and metals from the entire periodic system. However, the effect of these compounds on living systems has not been fully understood, and researchers are exploring the properties of metalloporphyrins thereby extending their further application. This review provides an overview of the variety of metalloporphyrins that are currently used in different medicine fields and how metalloporphyrins became the subject of scientists' interest. Currently, metalloporphyrins utilization has expanded significantly, which gave us an opprotunuty to summarize recent progress in metalloporphyrins derivatives and prospects of their application in the treatment and diagnosis of different diseases.

Comparative evaluation of 68Ga-labelled TATEs: the impact of chelators on imaging

Background

⁶⁸Ga-labelled peptides targeting somatostatin receptor 2 (SSTR2) have demonstrated encouraging results in managing patients with neuroendocrine tumours (NETs). In addition to metal chelation, bifunctional chelators have also been found to impact imaging outcomes due to their differences in stability, charge, hydrophilicity, etc. In the present work, a comparative pharmacokinetic evaluation and imaging characteristics were performed between ⁶⁸Ga-labelled somatostatin analogues (TATE) using NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) and DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) as bifunctional chelating agents (BFCAs).

Results

Both ⁶⁸Ga-NOTA-TATE and ⁶⁸Ga-DOTA-TATE were obtained with high radiochemical purity. ⁶⁸Ga-NOTA-TATE demonstrated higher in vitro stability (≥ 99%) than ⁶⁸Ga-DOTA-TATE (≥ 95%) after 3 h of incubation. The water solubilities (partition coefficients, − 1.76 ± 0.06 vs. − 2.72 ± 0.16) and plasma protein binding rates (12.12% vs. 30.6%) were lower for ⁶⁸Ga-NOTA-TATE than for ⁶⁸Ga-DOTA-TATE. Differential pharmacokinetics and comparable tumour affinities (within 1 h) were observed in AR42J tumour-bearing mice. Healthy volunteer imaging studies showed comparable distribution patterns of these two imaging agents. However, the maximum standardized uptake values (SUVmax) of the two tracers varied in each organ. The two PET agents demonstrated almost identical SUVmax values in the kidneys. ⁶⁸Ga-NOTA-TATE did have a lower SUVmax in most other organs compared with ⁶⁸Ga-DOTA-TATE, including the liver (4.2 vs. 10.1), potentially due to the lower protein binding rate.

Conclusion

⁶⁸Ga-NOTA-TATE and ⁶⁸Ga-DOTA-TATE demonstrated comparable tumour uptake in an AR42J mouse model. An initial clinical study revealed that ⁶⁸Ga-NOTA-TATE may have reduced background uptake in the major organs such as the liver. Although the subject numbers were limited, further investigation of ⁶⁸Ga-NOTA-TATE is warranted for detecting SSTR2-positive neuroendocrine tumours.

Synthesis of novel technetium-99m tricarbonyl-HBED-CC complexes and structural prediction in solution by density functional theory calculation

HBED-CC (N,N'-bis[2-hydroxy-5-(carboxyethyl)benzyl]ethylene diamine-N,N'-diacetic acid, L₁ ) is a common bifunctional chelating agent in preparation of ⁶⁸Ga-radiopharmaceuticals. Due to its high stability constant for the Ga³⁺ complex (logK_GaL = 38.5) and its acyclic structure, it is well known for a rapid and efficient radiolabelling at ambient temperature with Gallium-68 and its high in vivo stability. [^99mTc][Tc(CO)₃(H₂O)₃]⁺ is an excellent precursor for radiolabelling of biomolecules. The aim of this study was to develop a novel preparation method of ^99mTc-HBED-CC complexes. In this study, HBED-CC-NI (2,2'-(ethane-1,2-diylbis((2-hydroxy-5-(3-((2-(2-nitro-1H-imidazol-1-yl)ethyl)amino)-3-oxopropyl)benzyl)-azanediyl))-diacetic acid, L₂ ), a derivative of HBED-CC, was designed and synthesized. Both L₁ and L₂ were radiolabelled by [^99mTc][Tc(CO)₃(H₂O)₃]⁺ successfully for the first time. In order to explore the coordination mode of metal and chelates, non-radioactive Re(CO)₃ L₁ and Re(CO)₃ L₂ were synthesized and characterized spectroscopically. Tc(CO)₃ L₁ and Tc(CO)₃ L₂ in solution were calculated by density functional theory and were analysed with radio-HPLC chromatograms. It showed that [^99mTc]Tc(CO)₃ L₂ forms two stable diastereomers in solution, which is similar to those of [⁶⁸Ga]Ga-HBED-CC complexes. Natural bond orbital analysis through the natural population charges revealed a charge transfer between [^99mTc][Tc(CO)₃]⁺ and L₁ or L₂ . The experimental results showed that tricarbonyl technetium might form stable complex with HBED-CC derivatives, which is useful for the future application of using HBED-CC as a bifunctional chelating agent in developing new ^99mTc-radiopharmaceuticals as diagnostic imaging agents.

Synthesis and evaluation of 64Cu-radiolabeled NOTA-cetuximab (64Cu-NOTA-C225) for immuno-PET imaging of EGFR expression

Objective

Epidermal growth factor receptor (EGFR) is overexpressed in a wide variety of solid tumors, serving as a well-characterized target for cancer imaging or therapy. In this study, we aimed to design and synthesize a radiotracer, ⁶⁴Cu-NOTA-C225, targeting EGFR for tumor positron emission tomography (PET) imaging.

Methods

Cetuximab (C225) was conjugated to a bifunctional chelator, p-isothiocyanatobenzyl-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), and further radiolabeled with copper-64 for PET imaging. ⁶⁴Cu-NOTA-IgG and Cy5.5-C225 were also synthesized as control probes. A431 and A549 mouse models were established for micro-PET and/or near-infrared fluorescence (NIRF) imaging.

Results

⁶⁴Cu-NOTA-C225 exhibited stability in vivo and in vitro up to 24 h and 50 h post-injection, respectively. A431 tumors with average standard uptake values (SUVs) of 5.61±0.69, 6.68±1.14, 7.80±1.51 at 6, 18 and 36 h post-injection, respectively, which were significantly higher than that of moderate EGFR expressing tumors (A549), with SUVs of 0.89±0.16, 4.70±0.81, 2.01±0.50 at 6, 18 and 36 h post-injection, respectively. The expression levels of A431 and A549 were confirmed by western blotting. Additionally, the tracer uptake in A431 tumors can be blocked by unlabeled cetuximab, suggesting that tracer uptake by tumors was receptor-mediated. Furthermore, NIRF imaging using Cy5.5-C225 showed that the fluorescence intensity in tumors increased with time, with a maximal intensity of 8.17E+10 (p/s/cm²/sr)/(μW/cm²) at 48 h post-injection, which is consistent with the paradigm from micro-PET imaging in A431 tumor-bearing mice.

Conclusions

The ⁶⁴Cu-NOTA-C225 PET imaging may be able to specifically and sensitively differentiate tumor models with different EGFR expression levels. It offers potentials as a PET radiotracer for imaging of tracer EGFR-positive tumors.

Selective radiolabelling with 68Ga under mild conditions: a route towards a porphyrin PET/PDT theranostic agent

A theranostic conjugate for use as a positron emission tomography (PET) radiotracer and as a photosensitiser for photodynamic therapy (PDT) has been synthesised. A water-soluble porphyrin was coupled with the bifunctional chelate, H4Dpaa.ga. This conjugate is capable of rapid 68Ga complexation under physiological conditions; with 93% and 80% radiochemical yields achieved, at pH 4.5 and pH 7.4 respectively, in 15 min at 25 °C. Photocytotoxicity was evaluated on HT-29 cells and showed the conjugate was capable of >50% cell death at 50 μM upon irradiation with light, while causing minimal toxicity in the absence of light (>95% cell survival).

Development of 64Cu-NOTA-Trastuzumab for HER2 Targeting: A Radiopharmaceutical with Improved Pharmacokinetics for Human Studies

The purpose of this study was to develop ⁶⁴Cu-labeled trastuzumab with improved pharmacokinetics for human epidermal growth factor receptor 2 (HER2). Methods: Trastuzumab was conjugated with SCN-Bn-NOTA and radiolabeled with ⁶⁴Cu. Serum stability and immunoreactivity of ⁶⁴Cu-NOTA-trastuzumab were tested. Small-animal PET imaging and biodistribution studies were performed in a HER2-positive breast cancer xenograft model (BT-474). The internal dosimetry for experimental animals was determined using the image-based approach with the Monte Carlo N-particle code. Results: ⁶⁴Cu-NOTA-trastuzumab was prepared with high radiolabeling yield and radiochemical purity (>98%) and showed high stability in serum and good immunoreactivity. Uptake of ⁶⁴Cu-NOTA-trastuzumab was highest at 48 h after injection as determined by PET imaging and biodistribution results in BT-474 tumors. The blood radioactivity concentrations of ⁶⁴Cu-NOTA-trastuzumab decreased biexponentially with time in both mice with and mice without BT-474 tumor xenografts. The calculated absorbed dose of ⁶⁴Cu-NOTA-trastuzumab was 0.048 mGy/MBq for the heart, 0.079 mGy/MBq for the liver, and 0.047 mGy/MBq for the spleen. Conclusion: ⁶⁴Cu-NOTA-trastuzumab was effectively targeted to the HER2-expressing tumor in vitro and in vivo, and it exhibited a relatively low absorbed dose due to a short residence time. Therefore, ⁶⁴Cu-NOTA-trastuzumab could be applied to select the right patients and right timing for HER2 therapy, to monitor the treatment response after HER2-targeted therapy, and to detect distal or metastatic spread.