Info
Background:
Hepatocellular carcinoma (HCC) is a leading cause of cancer mortality, with most patients diagnosed at unresectable stages, highlighting the need for alternative therapies. Transarterial embolization (TAE) is widely used for liver tumors but is often limited by incomplete tumor necrosis. Boron neutron capture therapy (BNCT) is a targeted radiotherapy that relies on selective boron accumulation, where neutron irradiation induces high linear energy transfer (LET) particles for localized tumor cell killing while sparing normal tissues. Despite its potential, BNCT is limited by rapid clearance and insufficient tumor retention of conventional boron agents.
Hypothesis/Objective:
Compared with conventional small-molecule boron compounds, TAE agents can be selectively retained within hepatocellular carcinoma due to its characteristic tumor vasculature. However, studies on boron-containing microspheres remain limited. Therefore, this study aims to develop gluconic acid-functionalized chitosan microspheres as a theranostic platform for synergistic embolization and sustained boron delivery via pH-sensitive linkages. In addition, these materials are designed to be biodegradable, thereby enhancing the biosafety of the microspheres.
Methods:
Chitosan microspheres were prepared via emulsification followed by ionic crosslinking with sodium tripolyphosphate to form stable particles. Surface functionalization was achieved through EDC/NHS-mediated conjugation of gluconic acid, introducing cis-diol groups. Boric acid was subsequently loaded onto the microspheres via reversible boronate ester formation. For imaging purposes, the microspheres were further conjugated with a DOTA chelator and radiolabeled with ⁶⁸Ga for PET/MR tracking. An orthotopic hepatoma model was established by implanting N1S1-F5 cells into the liver of Sprague-Dawley (SD) rats. Following hepatic arterial administration, PET/MR imaging was performed to evaluate microsphere distribution over time, allowing determination of the optimal irradiation window. Biodistribution studies were conducted to quantify boron levels in tumor and normal tissues, and histological analysis was performed to confirm embolization effects. BNCT-induced tumor growth inhibition and body weight changes were longitudinally monitored to evaluate therapeutic efficacy and safety.
Results:
The boron-containing chitosan microspheres (Borosan) exhibited a spherical morphology with an average particle size of 31.6 ± 3.8 μm. The non-decay-corrected radiochemical yield of 68Ga-Borosan was 32% ± 11%, with stability maintained for at least 2 h. In PET imaging of orthotopic hepatoma-bearing rats, the microspheres predominantly localized within the liver and tumor following embolization, demonstrating sustained retention up to 2 h. Ex vivo imaging confirmed their distribution along the hepatic vasculature, reaching both normal liver lobes and tumor tissues. Biodistribution studies showed tumor uptake of 24.7 ± 17.9 and 38.9 ± 20.0 %ID/g at 30 and 60 min post-injection, respectively, while liver retention ranged from 3.1 to 5.7 %ID/g. The corresponding tumor-to-liver ratios were 5.6 and 8.8 at 30 and 60 min, respectively. ICP-MS analysis revealed that boron concentrations in hepatoma reached 165 ± 69 ppm at 30 min post-injection. Therapeutically, Borosan-mediated BNCT demonstrated potential for tumor remission. No significant changes in body weight or severe liver dysfunction were observed throughout the study, indicating a favorable safety profile.
Conclusion:
This study demonstrated Borosan enables effective tumor-targeted embolization, high and sustained tumor boron accumulation, and favorable tumor-to-liver contrast in an orthotopic hepatoma model. The achieved boron levels were sufficient for BNCT, resulting in observable tumor suppression without significant systemic toxicity or liver dysfunction. Collectively, these findings support Borosan as a promising biodegradable theranostic platform for combined embolization and sustained boron delivery in BNCT applications.
Author
WanChi Chan
National Yang Ming Chiao Tung University