Similar T/N ratio between 18F-FBPA diagnostic and BPA therapeutic dosages for boron neutron capture therapy in orthotropic tongue cancer model

Assessing the effectiveness of fluorinated and α-methylated 3-boronophenylalanine for improved tumor-specific boron delivery in boron neutron capture therapy

A [10B]boron agent and a nuclear imaging probe for pharmacokinetic estimation form the fundamental pair in successful boron neutron capture therapy (BNCT). However, 4-[10B]borono-l-phenylalanine (BPA), used in clinical BNCT, has undesirable water solubility and tumor selectivity. Therefore, we synthesized fluorinated and α-methylated 3-borono-l-phenylalanine (3BPA) derivatives to realize improved water solubility, tumor targetability, and biodistribution. All 3BPA derivatives exhibited over 10 times higher water solubility than BPA. Treatment with α-methylated 3BPA derivatives resulted in decreased cell uptake via l-type amino acid transporter (LAT) 2 while maintaining LAT1 recognition, thereby significantly improving LAT1/LAT2 selectivity. Biodistribution studies showed that fluorinated α-methyl 3BPA derivatives exhibited reduced boron accumulation in nontarget tissues, including muscle, skin, and plasma. Consequently, these derivatives demonstrated significantly improved tumor-to-normal tissue ratios compared to 3BPA and BPA. Overall, fluorinated α-methyl 3BPA derivatives with the corresponding radiofluorinated compounds hold potential as promising agents for future BNCT/PET theranostics.

Correlation between L-amino acid transporter 1 expression and 4-borono-2-18 F-fluoro-phenylalanine accumulation in humans

BACKGROUND

The correlation between L-type amino acid transporter 1 (LAT1) expression and 4-borono-2-18 F-fluoro-phenylalanine (18 F-FBPA) accumulation in humans remains unclear. This study aimed to investigate the correlation between LAT1 expression in tumor tissues and 18 F-FBPA accumulation in patients with head and neck cancer who participated in a clinical trial of 18 F-FBPA positron emission tomography (PET).

METHODS

Altogether, 28 patients with head and neck cancer who participated in a clinical trial of 18 F-FBPA PET at our institution between March 2012 and January 2018 were included. Correlations between standardized uptake values (SUVs); the maximum SUV (SUVmax ), the mean SUV within a 1 cm3 sphere centered at a single point, that is, the SUVmax (SUVpeak ), the minimum SUV (SUVmin ), and the intensity of LAT1 expression (maximum and minimum LAT1 expressions) were investigated.

RESULTS

Weak correlations were identified between SUVmax and LAT1 maximum score, SUVmin and LAT1 maximum score, and SUVmin and LAT1 minimum score (ρ = 0.427, 0.362, and 0.330, respectively). SUVmax and LAT1 minimum score, SUVpeak and LAT1 maximum score, and SUVpeak and LAT1 minimum score demonstrated moderate correlations (ρ = 0.535, 0.556, and 0.661, respectively). Boron neutron capture therapy (BNCT) was performed in 2 of the 4 patients with discrepancies between 18 F-FBPA accumulation and intensity of LAT1 expression, and the intensity of LAT1 expression was a better predictor of treatment response.

CONCLUSION

18 F-FBPA accumulation and the intensity of LAT1 expression demonstrated a moderate correlation; however, LAT1 expression may be a better predictor of treatment response of BNCT in patients with discrepancies.

EGFR-Targeted Cellular Delivery of Therapeutic Nucleic Acids Mediated by Boron Clusters

New boron carriers with high boron content and targeted cancer-cell delivery are considered the first choice for boron neutron capture therapy (BNCT) for cancer treatment. Previously, we have shown that composites of antisense oligonucleotide and boron clusters are functional nanoparticles for the downregulation of expression of epidermal growth factor receptor (EGFR) and can be loaded into EGFR-overexpressing cancer cells without a transfection factor. In this study, we hypothesize that free cellular uptake is mediated by binding and activation of the EGFR by boron clusters. Proteomic analysis of proteins pulled-down from various EGFR-overexpressing cancer cells using short oligonucleotide probes, conjugated to 1,2-dicarba-closo-dodecaborane (1,2-DCDDB, [C₂B₁₀H₁₂]) and [(3,3'-Iron-1,2,1',2'-dicarbollide)^-] (FESAN, [Fe(C₂B₉H₁₁)₂]^-), evidenced that boron cage binds to EGFR subdomains. Moreover, inductively coupled plasma mass spectrometry (ICP MS) and fluorescence microscopy analyses confirmed that FESANs-highly decorated B-ASOs were efficiently delivered and internalized by EGFR-overexpressing cells. Antisense reduction of EGFR in A431 and U87-MG cells resulted in decreased boron accumulation compared to control cells, indicating that cellular uptake of B-ASOs is related to EGFR-dependent internalization. The data obtained suggest that EGFR-mediated cellular uptake of B-ASO represents a novel strategy for cellular delivery of therapeutic nucleic acids (and possibly other medicines) conjugated to boron clusters.