Cytotoxicity of boron containing dipeptide analogs

Novel boron-containing compound, halogenated boroxine, induces selective cytotoxicity through apoptosis triggering in UT-7 leukemia

Apoptosis induction is a promising approach in targeting tumor cells. As halogenated boroxine (HB) shows antitumor activity, but its mechanism of action in hematological tumors remains unclear, in this study, we aimed to analyze apoptosis triggering in normal and UT-7 leukemia cells by HB. Methods for assessing cell viability and cytotoxicity, apoptosis detection, relative expression of 84 apoptosis-associated genes and BCL-2, and functional analysis were applied. Pronounced HB activities in inhibition of cell viability, cytotoxicity, and apoptosis induction with measurable differences between tumor and normal cells were found. HB modulated the expression of 21 genes, predominantly downregulated the antiapoptotic genes in leukemia. The functional association revealed HB's impact on inhibition of NF-κB signaling pathway. BCL-2 expression decreasing was found only in UT-7 leukemia. This study identified HB as an apoptosis inducer affecting leukemia but not normal cells considering mechanisms of selective activity that may be a great advantage of HB applications.

Syntheses of the first amine-dicarboxyboranes and their bis(methylester) and bis(N-ethylamide) derivatives

Amine-bis(N-ethylcarbamoyl)boranes [A.BH(CONHEt)(2), 3; A = trimethylamine (Me(3)N, a), quinuclidine (Q, b), pyridine (py, f), 4-picoline (pic, g)] have been prepared after deprotonation of [amine-bis(C-hydroxy-N-ethylimidate)hydroboron(2+)] cations (2), which were formed by the hydrolysis of [amine-bis(ethylnitrilium)hydroboron(2+)]tetrafluoroborates (1). Numerous representatives of 3 [A = diethylamine (Et(2)NH, c), piperidine (pip, d), pyrrolidine (pyrr, e), 4-aminopyridine (4-NH(2)-py, h), 4-(dimethylamino)pyridine (DMAP, i), imidazole (Him, j), 1-methylimidazole (Mim, k)] have been prepared by base exchange reactions from 3a. 3a-e are extremely stable in aqueous media, either acidic or alkaline, probably because of the considerable steric hindrance of possible reaction centers. However, they were transformed into amine-dicarboxyboranes [A.BH(COOH)(2), 4a-e] in acidic medium under vigorous conditions (100-130 degrees C). This transformation was accompanied by significant decomposition, probably owing to the protonation on the N atom, resulting in the rupture of the B-N bond. As an exception, 4b, where N atom in a rigid bicycle is not prone to attacks, could be isolated in very good yield. On the other hand, amine-bis(N-ethylcarbamoyl)boranes containing amines with sp(2)-hybridized N atoms (3f-k) undergo complete decomposition under similar conditions probably because of the increased hydridic character of the hydrogen adjacent to boron. Base exchange reactions starting from 4b resulted in the ammonium salts of 4c-e, h, i of composition [A.BH(COOH)(COO(-))][AH(+)], which in turn could be transformed into the diacids 4, except 4h, by protonation. As salt formation indicates, the 4 compounds are stronger acids as univalent acids than the corresponding A.BH(2)(COOH) complexes. 4a-e, i were readily esterified into amine-bis(methoxycarbonyl)boranes (5a-e, i) in methanol, employing a catalytic amount of HBr. 5a-e, i are stable in alkaline medium but are readily hydrolyzed in acidic medium. Hydrolysis of [amine-bis(C-methoxy-N-ethylimidate)hydroboron(2+)] cations did not give the corresponding bisesters 5 in alkaline, neutral, or acidic medium.

In vivo and in vitro effects of boron and boronated compounds

Boron is ubiquitously present in soils and water. Associated with pectin it is essential for vascular plants as a component of cell walls, and it stabilizes cell membranes. It is required for the growth of pollen tubes and is involved in membrane transport, stimulating H(+)-pumping ATPase activity and K+ uptake. However, a high boron concentration in the soils is toxic to plants and some boronated derivatives are used as herbicides. An absolute requirement for boron has not been definitively demonstrated in animals and humans. However, experiments with boron supplementation or deprivation show that boron is involved in calcium and bone metabolism, and its effects are more marked when other nutrients (cholecalciferol, magnesium) are deficient. Boron supplementation increases the serum concentration of 17 beta-estradiol and testosterone but boron excess has toxic effects on reproductive function. Boron may be involved in cerebral function via its effects on the transport across membranes. It affects the synthesis of the extracellular matrix and is beneficial in wound healing. Usual dietary boron consumption in humans is 1-2 mg/day for adults. As boron has been shown to have biological activity, research into the chemistry of boronated compounds has increased. Boronated compounds have been shown to be potent anti-osteoporotic, anti-inflammatory, hypolipemic, anti-coagulant and anti-neoplastic agents both in vitro and in vivo in animals.