Uptake and metabolism of boronophenylalanine in human uveal melanoma cells in culture Relevance to boron neutron capture therapy of cancer cells.

The transport of boronophenylalanine (BPA) and its metabolic fate have been studied in a human uveal melanoma cell line isolated from a primary enucleated tumor. The boronated compound was rapidly incorporated into the cells reaching a peak of incorporation in two hours. This was followed by a trough between 10 and 24 hours and by an increase thereafter. The analogy with the amino acids phenylalanine (Phe) and tyrosine (Tyr) was studied in competition experiments incubating cultures of cell line MK-T, isolated in this laboratory, with [(3)H]-Phe and [(125)I]-Tyr, in the presence or absence of various concentrations of BPA, between 0 and 5 min. The presence of BPA severely reduced the uptake of both amino acids. The kinetics of the transport of [(3)H]-Phe and [(3)H]-Tyr in the presence of BPA, measured after 10 sec of incubation, showed that the boronated compound exerted a competitive inhibition on both transport systems. The intracellular metabolism of BPA was followed by measuring boron concentration (measured with Ionization Coupled Mass Spectrometry) in subcellular fractions and after membrane extraction by the detergent Triton X-100. The results showed that BPA remained in the supernatant and was not metabolized into macromolecules. These results and the relative absence of melanine in these cells, as observed by electron microscopy, suggest that BPA may be actively transported into melanoma cells but not metabolized. The results may have a relevance in studies on Boron Neutron Capture Therapy.