Development and evaluation of 68Ga-D75CM-NODAGA: A 68Ga-Labeled multimodal imaging tracer for sentinel lymph node detection

Introduction: Sentinel lymph node biopsy (SLNB) is a critical component of tumor management, serving as a key determinant in cancer staging and guiding treatment strategies.¹ The selective targeting of sentinel lymph nodes (SLNs) is pivotal for accurate disease assessment, providing clinicians with vital information. The development of diagnostic radiopharmaceuticals for the precise localization of the Sentinel Lymph Node (SLN), the hypothetical first lymph node to receive lymph and metastatic cells from the primary site of the tumor, is actively explored to identify affected tissues that require surgical removal. The metastatic pathway of some cancers usually follows a course that begins from the nearby lymph nodes. Therefore, if the first draining lymph node, the SLN, is negative in tumor metastasis, the presence of cancerous cells in all other lymph nodes is highly improbable. Thus, SLNB gradually replaces extensive lymph node removal in patients with cancer, offering more accurate diagnosis and reducing unnecessary lymphadenectomy. This study endeavors to develop and rigorously evaluate the potential clinical utility of D75CM-NODAGA, a novel 68Ga-labeled imaging tracer, in the context of SLNB. By seamlessly integrating state-of-the-art radioimaging techniques with the precision of microPET/MRI, we aspire to enhance SLN visualization to an unprecedented level and to provide invaluable insights that can further inform and refine therapeutic strategies for patients with cancer.

Methods: The mannosylated compound D75CM was synthesized, followed by the coupling with the succinimidyl ester of NODAGA. Specifically, a reaction of a 75 KD dextran with allyl bromide yielded the intermediate allyl dextran with about 40% coupling. The addition of cysteine to allyl dextran resulted in the dextran-S-cysteine derivative D75C. This compound was mannosylated (approx. 65%) by coupling to the in situ activated cyanomethyltetraacetyl-1-thio-D-mannopyranoside. Subsequently, the reaction of the succinimidyl ester of NODAGA with free amine groups resulted in the formation of the final compound. Purification of the compound has been performed by ultrafiltration. Labeling was achieved by adding 0.5 mL ⁶⁸GaCl₃ to a 100 μL solution of the NODAGA mannosylated dextran and incubating at 40 ^oC for 20 min. Quality control and stability studies have been performed by radio-TLC and radio-HPLC. The biological evaluation was performed by biodistribution and imaging studies in Swiss albino mice after subcutaneous injection in the footpad.

Results: The preliminary biological testing of the ⁶⁸Ga complex showed high accumulation in the popliteal lymph node (4.09 % ID) and fast injection site clearance (40.61 %/ID) at 120 min p.i. This data are comparable with our previous data (Pirmettis I., et al., Papasavva A., et al.) indicating that the attachment of NODAGA chelator did not alter its biodistribution. Furthermore, a dynamic imaging study using microPET/MRI (enabling simultaneous PET and MRI acquisition; Bruker USA) confirmed the rapid elimination rate from the injection site.

Conclusions: In the current study, a new PET tracer for SLN was developed. The new D75CM-NODAGA labeled compounds did reveal attractive biological features as a novel PET imaging agent for SLND with ⁶⁸Ga, justifying further investigations in both the pre-clinical and clinical setting.

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