Does Trans-Stimulation of L-Tyrosine Lead to an Increase in Boron Uptake in Head and Neck Squamous Cell Carcinoma Cells?

(1) Background: For advanced head and neck squamous cell carcinoma (HNSCC), boron neutron capture therapy (BNCT) is a potential therapeutic option, but high concentrations of boron within HNSCC are necessary. Therefore, this in vitro pilot study examined the uptake and concentration of boron in HNSCC cells using the trans-stimulation effect of L-tyrosine when compared to non-stimulated samples. (2) Methods: Two HNSCC cell lines were incubated with L-tyrosine for up to two hours, followed by incubation with three L-para-boronophenylalanine (BPA) concentrations (5, 20, 50 ppm) at eight incubation times (1–4.5 h in half-hour steps). Subsequently, cellular boron uptake was measured via inductively coupled plasma mass spectrometry. (3) Results: No differences between laryngeal and oral SCC cells were seen; therefore, data were pooled. In total, boron uptake was not significantly increased in trans-stimulated samples when compared to the control group (all p > 0.05). Nevertheless, with trans-stimulation, higher BPA concentrations resulted in higher intracellular boron concentrations (5 < 20 < 50 ppm; all: p < 0.05), whereas these differences were less distinct in the non-trans-stimulated group. (4) Conclusions: The effect of trans-stimulation for up to two hours seems to be less relevant for HNSCC, though trans-stimulated HNSCC cells seem to have a more distinct BPA-dose-dependent cellular boron uptake that might be addressed in further research.