Albumin nanoparticle electrostatically loaded with highly anionic Gd-thiacalixarene complex for MRI-guided neutron capture therapy

Abstract

As a neutron capture therapy (NCT) agent, 157Gd garners significant attention due to the largest neutron capture cross section, emission of γ rays and Auger electrons, and facilitation of magnetic resonance imaging-guided NCT. Owing to its high kinetic stability, 1H relaxivity, and facile conjugation to albumin via electrostatic interactions, the negatively charged Gd3TCAS2 complex {TCAS = thiacalix[4]arene-p-tetrasulfonate (TCAS)} was incorporated into albumin nanoparticles (ANPs) in various configurations, including shell, core, and core-shell types, contingent on the positioning of Gd3TCAS2 within the ANP. The characteristics of the ANPs optimized with respect to loading capacity (LC) were explored, all of which demonstrated particle sizes suitable for passive delivery. The LC of Gd3TCAS2 per ANP increased in the following order: shell (1.1 %) < core (1.4 %) < core-shell (8.1 %). The leakage of Gd3TCAS2 after 7 d of storage was approximately 2 % for all ANPs, indicating stable Gd3TCAS2 loading. The 1H relaxivity (e.g., core-shell: r1 = 10.7 mM–1s–1) surpassed that of the Gd3TCAS2 complex alone (3.15 mM–1s–1). The luminescence emanating from Tb in MCF-7 cells co-cultured with Tb3TCAS2-loaded ANPs corroborated this cellular uptake. Gd uptake into MCF-7 cells via Gd3TCAS2-loaded ANPs was most pronounced for core-shell ANP at 1.33 ± 0.06 nmol/106 cells. The cytotoxicity of Gd3TCAS2-loaded ANPs was mitigated compared to free Gd3TCAS2 (CC50 = 52 µM), with shell and core-shell ANPs demonstrating nearly 100 % cell survival even at 50 µM. Cell viability post thermal neutron irradiation revealed the highest NCT efficacy for free Gd3TCAS2, attributed to its elevated cellular uptake (15.71 ± 0.57 nmol/106 cells). Core-shell ANP also exhibited a notable reduction in cell viability relative to the control, validating their potential as a promising GdNCT agent.