Analysis of leukotriene B4 metabolism in human promyelocytic HL-60 cells

The medicinal chemistry of stable synthetic leukotriene B3 and B4 analogues

Leukotriene B3 and B4 are part of an important class of signaling molecules – the leukotrienes, implicated in the inflammation process. Their pro-inflammatory effects have been widely recognized for almost three decades but it is only recently that their benefit in host defense has begun to be acknowledged. Their use as therapeutic agents is, unfortunately, limited by rapid metabolism. However, over the past 25 years, a number of stable leukotriene B3 and B4 analogues have been produced. In this review, we examine their medicinal chemistry and biological evaluation.

Expression and induction of CYP4F subfamily in human leukocytes and HL60 cells

We investigated the expression of the CYP4F subfamily in human leukocytes and HL60 cells. Enzymatic activity assay, immunocytochemical staining, and reverse transcription-polymerase chain reaction (RT-PCR) analysis of human leukocytes showed that polymorphonuclear leukocytes (PMNs) expressed CYP4F3B and CYP4F12 in addition to CYP4F3. Transcription start site of CYP4F3B mRNA in the leukocytes was identical to that of CYP4F3 mRNA. The HL60 cells, which were differentiated into PMN-like shapes by treatment with all-trans-retinoic acid (RA), also expressed CYP4F3, CYP4F3B and CYP4F12. CYP4F3 was expressed in one third of the peripheral monocytes, which omega-hydroxylated leukotriene B(4) (LTB(4)) at a rate 11 times lower than that of PMN. The cells that were differentiated into a form similar to monocytes/macrophages in shape by treatment with 12-myristate 13-acetate expressed mRNA for CYP4F3 and CYP4F3B. Promoter analysis of the CYP4F3 gene demonstrated that a region (-174/-90) of this gene was important for its promoter activity in the HL60 cells. This is the first report on the distribution of different CYP4F isoforms in leukocytes and their induction in HL60 cells.

Synthesis of 10,11-dihydroleukotriene B(4) metabolites via a nickel-catalyzed coupling reaction of cis-bromides and trans-alkenyl borates

Synthesis of 10,11-dihydro-, 10,11,14,15-tetrahydro-, and 10, 11-dihydro-12-oxoleukotriene B(4) compounds (2, 4, 5) was accomplished stereoselectively by using the nickel-catalyzed coupling reaction illustrated in Scheme 1. The C(1)-C(7) fragments, TBS ether 10a for 2 and 4 and ethyoxyethyl (EE) ether 10b for 5, were prepared in enantiomerically pure forms (>99% ee) by a modified literature procedure (ref 11a). On the other hand, boronate esters 11a and 11b, which correspond to the C(8)-C(20) parts of 2 and 4, respectively, were synthesized from (R)-epichlorohydrin (18) of 99% ee. Briefly, 18 was converted into acetylenes 24 and 32 through epoxide ring-opening with LiC triple bond CC(5)H(11)/BF(3).OEt(2) or C(7)H(15)MgBr/CuCN. Hydroboration of these acetylenes with (+)-(Ipc)(2)BH followed by reaction with MeCHO afforded the corresponding diethyl boronates, which upon ligand exchange with Me(2)C(CH(2)OH)(2) furnished boronate esters 11a and 11b in 75% and 77% yields, respectively. In a similar manner, racemic boronate ester rac-11a, an intermediate for synthesis of 5, was prepared from racemic epichlorohydrin. For synthesis of 2, borate 25 was generated from 11a (1.5 equiv) and MeLi (1.6 equiv). Without isolation, 25 was submitted to reaction with 10a (1 equiv) in the presence of a Ni(0) species at room temperature overnight to afford 26, which upon treatment with TBAF furnished 2 in 64% yield from 10a. Similarly, 11b and 10a furnished 4 in good yield. To synthesize 5, rac-11a and EE ether 10b were joined by the coupling reaction to produce 39, which was transformed into 40 by desilylation with TBAF. After hydrolysis of 40, oxidation with PDC followed by deprotection of the EE group furnished 5 in 36% yield from 40. In addition, 2 was converted into amide 3 in 92% yield.

Altered leukotriene B4 levels by HL-60 cells after monocytic/macrophage differentiation

The differentiation of HL-60 human promyelocytic leukaemia cells into specific monocytic or granulocytic lineage cells depending of the inductor agent is accompanied by selective regulation of several key enzymes involved in the synthesis of eicosanoids. In this communication we have investigated the changes in arachidonic acid metabolic profiles during phorbol 12-myristate 13-acetate (PMA)-induced monocytic differentiation of HL-60 cells. Our results show that HL-60 cells have spontaneous capacity to synthesize large amounts of LTB4, but PMA-differentiated cells lose the ability to release LTB4. Significant differences are found between HL-60 cells and PMA-treated cells in basal conditions and under ionophore stimulation. The addition of LTB4 at the time of PMA differentiation did not have effects on cell proliferation, but nordihydroguaiaretic acid (NDGA), a potent 5-lipoxygenase inhibitor, also inhibited HL-60 cell proliferation and did not have any effect on PMA-differentiated cell proliferation.

12(R)-methyl-leukotriene B3: a stable leukotriene B analogue toward the reductase metabolism

Biological potencies of 12(R)-methyl-LTB3 [12(R)-Me-LTB3] and 12(S)-Me-LTB3 and their stability toward reductase metabolism are described. 12(R)- and 12(S)-Me-LTB3 of more than 95% chemical purity were synthesized highly stereoselectively via the palladium catalyzed coupling reaction of the vinylborane derived from the enzyme 1 and Sia2BH with the iodide 2 of R and S configuration. To assess biological activity of 12-Me-LTB3, cytosolic free calcium ([Ca2+]i) rise in rat PMNLs and binding affinity to the LTB4 receptors were compared with those of natural LTB4. The potency of 12(R)-Me-LTB3 was found to be almost equal to LTB4, while, by complete contrast, 12(S) isomer showed very low activity of 1/200-1/400. These results indicate that the C(12) hydroxyl group of R configuration is essential to elicit the biological activity and that [Ca2+]i rise elicited by 12-Me-LTB3 is mediated through interaction with the LTB4 receptors. Stability of 12(R)-Me-LTB3 toward the reductase metabolism was evaluated by using rat PMNLs. Thus, rat PMNLs were incubated at 37 degrees C with 12(R)-Me-LTB3 and LTB4, respectively. The amount of 12(R)-Me-LTB3 was almost unchanged up to 30 min under these conditions, though LTB4 was rapidly consumed in a time-dependent manner, thus strongly indicating that 12(R)-Me-LTB3 is not metabolized via the reductase pathway.