Development of New NanoAlbumin-based Radiotracers: Preclinical Evaluation Of [68Ga]Ga-DOTA-nanoHSA Conjugates for Lymphatic Imaging Applications.

Purpose: Sentinel lymph node (SLN) mapping is a critical procedure in the staging and treatment of cancers, such as breast cancer and melanoma. Current radiocolloids used in SLN localization, like [^99mTc]Tc-Sulfur Colloid, face limitations in imaging resolution and specificity. This study aims to evaluate the biodistribution of [⁶⁸Ga]Ga-DOTA-nanoHSA, a novel nanoparticle-based radiotracer, for SLN mapping using PET/CT imaging in both healthy and tumor-bearing murine models and compare results with [^99mTc]Tc-Sulfur Colloid as the current gold standard for lymph node staging in breast cancer. Additionally, the maximum tolerated dose and potential systemic toxicity of the carrier were assessed in humanized mice.

Methods: Nanoalbumin radiotracers were prepared by thermal denaturation of human serum albumin (HSA), followed by conjugation with 2,2',2″,2″'-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA) and labeling with gallium-68. The stability of [⁶⁸Ga]Ga-DOTA-nanoHSA was evaluated in the tracer formulations and in mouse serum. The novel radiotracers were administered subcutaneously and intratumorally in healthy and tumor-bearing mice, respectively, to evaluate SLN uptake via PET/CT imaging. Biodistribution was assessed in major organs, and the tracers' ability to accurately localize SLNs was compared to an existing standard. Toxicity was evaluated in humanized mice, where body weight, clinical scoring, and blood chemistry were monitored over a 14-days period. Mice received escalating doses of DOTA-nanoHSA to determine the maximum tolerated dose.

Results: [⁶⁸Ga]Ga-DOTA-nanoHSA tracers (30 nm and 70 nm) were reliably produced with high radiochemical purity (RCP > 90%). The stability of [⁶⁸Ga]Ga-DOTA-nanoHSA (30 nm) in the final formulations at pH 3.5 and 7.0 and in mouse serum was confirmed up to 4-6 h. [⁶⁸Ga]Ga-DOTA-nanoHSA (30 nm) demonstrated effective SLN localization in both healthy and tumor-bearing mice, with high uptake in SLNs and minimal off-target accumulation in non-lymphatic organs. DOTA-nanoHSA was well-tolerated in humanized mice, with no significant changes in body weight, clinical scores, or blood chemistry parameters, even at higher doses. No dose-dependent toxicity was observed.

Conclusion: [⁶⁸Ga]Ga-DOTA-nanoHSA (30 nm) demonstrated significant potential as a novel imaging agent for SLN mapping. Its favorable toxicity profile, combined with its effectiveness in SLN localization, suggests it could be a valuable alternative for SLN biopsy in clinical practice. Further studies are warranted to confirm these findings in human trials.