The 10 boron neutron-capture therapy (BNCT) is an emerging antitumoral method that shows increasing biomedical interest. BNCT is based on the selective accumulation of the 10 boron isotope within the tumor, which is then irradiated with low-energy thermal neutrons, generating nuclear fission that produces 7 lithium, 4 helium, and γ rays. Simple catechol-borate esters have been rather overlooked as precursors of melanin biosynthesis, and therefore, a proof-of-concept approach for using dopamine-borate (DABO) as a suitable boron-containing candidate for potential BNCT is presented here. DABO can spontaneously oxidize and autopolymerize in vitro, giving a soluble, eumelaninlike brown-black poly-DABO product. Melanotic melanoma cell cultures treated with 1 mM DABO for 24 and 48 h were viable and showed no signs of damage or cell death. The stability and possible trans-esterification of DABO is shortly discussed. Chemical calculations and quantitative structure-activity relationships (QSAR) analysis of DABO and the BNCT agent BPA indicated that they should be cell permeant and accumulate within lysosomes and melanosomes. Molecular modeling allows visualization of both the DABO precursor and the structure of a borate derivative of the proposed catechol-porphycene model for eumelanin, showing interesting features from molecular orbital calculations. The main difference between DABO and other agents, such as BPA, is that it is not a boronic acid nor a boron cluster. This simple catechol-borate ester (protected from oxidation and blackening) could be administrated to living cells and organisms, in which biosynthesis of boron-melanin in melanoma melanocytes can lead to improved BNCT.
Diaryl-furanones are specific analytical reagents for the biochemical detection of primary amines by fluorescence techniques. Well-known reagents are fluorescamine (Fluram) and 2-methoxy-2,4-diphenyl-3(2H)-furanone (MDPF), yielding fluorescent products with λem at 480–490 nm. Although the reaction products claim to be pyrrolinones, recent studies show that they are really 3-oxopyrrole (pyrrolone) derivatives. Both reagents have been used for the cytochemical demonstration of primary amines. In this work, we have applied the fluorescent products of MDPF with amines (n-butylamine, BA; glucosamine, GA; and spermine, Sp), which showed interesting fluorescence reactions with chromatin DNA. 2,4-diphenyl-3-oxopyrrole products (diPOPy) can be easily synthesized according to well-known procedures, by mixing solutions of MDPF in acetone with water at pH 9 containing the amino compounds. DiPOPy derivatives of BA, GA, and Sp were used for spectroscopic, microscopic, and molecular modeling studies, showing a bright and selective blue–green fluorescence on DNA substrates, mainly chromatin, kinetoplast DNA, and stretched chromatin fibers. The cationic diPOPy fluorophore is planar, with a high partial positive charge in the N atom, and suitable for intercalative binding to DNA. A mechanism of fluorescamine fluorescence due to an inner-salt isomeric form is proposed, and an astonishing correlation between adenine–thymine-rich centromeric heterochromatin in mouse metaphase chromosomes after reaction of the fluorescamine reagent with protein amino groups is also discussed.
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