Elsevier

Leukemia Research

Volume 23, Issue 1, January 1999, Pages 43-50
Leukemia Research

Boswellic acid acetate induces differentiation and apoptosis in leukemia cell lines

https://doi.org/10.1016/S0145-2126(98)00096-4Get rights and content

Abstract

Boswellic acid acetate (BC-4), a compound isolated from the herb Boswellia carterii Birdw., can induce differentiation and apoptosis of leukemia cells. Based on cell morphology and NBT reduction, BC-4 induced monocytic differentiation of myeloid leukemia HL-60, U937 and ML-1 cells at a dose under 12.5 μg/ml (24.2 μM). BC-4 was a potent inducer, with 90% of the cells showing morphologic changes and 80–90% of the cells showing NBT reduction. Specific and non-specific esterase were also increased by BC-4. Based on benzidine staining assay, BC-4 failed to induce erythroid leukemia DS-19 and K562 cells differentiation. In contrast to its selective differentiation effect, BC-4 strongly inhibited growth of all cell lines tested. The growth inhibition effect was dose- and time-dependent. In HL-60 cells, 20 μg/ml (38.8 μM) of BC-4 decreased viable cell number by 60% at 24 h, whereas at 3 days there was virtually no viable cells. Morphologic and DNA fragmentation analysis proved that BC-4 induced cell apoptosis. The dual apoptotic and differentiation effects of BC-4 suggest that it may be a powerful agent in the treatment of leukemia.

Introduction

Based on a differentiation-inducer screening in HL-60 cells, Boswellic acid acetate (BC-4) was identified as a potent differentiation inducer [1]. Boswellic acid acetate (Fig. 1) which exists in two isoforms, α-Boswellic acid acetate (BC-4-I) and β-Boswellic acid acetate (BC-4-II), is one of several active principles isolated from Boswellia carterii Birdw. with a pentacyclic triterpene structure. Boswellic acid derivatives have been reported to inhibit topoisomerases [2]and 5-lipoxygenase (5-LO) 3, 4. 5-LO is expressed mainly in hematopoietic cells [5]and catalyzes two reactions in the biosynthetic pathway leading to the formation of leukotrienes from arachidonic acid [6]. 5-LO mRNA expression has been found in a number of different types of cultured tumor cells and 5-LO inhibitors (e.g. caffeic acid and BW755c) inhibit leukemia and solid tumor cell growth in vitro 7, 8, 9, 10, 11. DNA topoisomerases are ubiquitous enzymes involved in essential nuclear functions, such as DNA replication, transcription and recombination [12]. Topoisomerases are targets of some antitumor drugs [13]. It is known that topoisomerase I and II inhibitors like camptothecin and Vp16 induce leukemia cell differentiation 14, 15and apoptosis 16, 17. The inhibitory effects of BC-4 on 5-LO and topoisomerases suggest that BC-4 will have a chemotherapeutic effect on cancer. In this paper, we compared the growth inhibition and differentiation induction of BC-4 in myelocytic leukemia and erythroleukemia cell lines, and found that BC-4 specifically induced myelocytic leukemia cell differentiation at low concentration, and at high concentration inhibited the growth of all leukemia cell lines tested.

Section snippets

Chemicals

Boswellic acid acetate was purified from Boswellia carterii Birdw. Briefly, extudative resin from Boswellia caterii Birdw. was exhaustively extracted with 70% aqueous acetone in a percolator to yield a crude extract. The crude extract was treated with methylene chloride, and the methylene chloride soluble fraction was concentrated. This crude mixture was chromatographed over silica gel by using increasing amounts of acetone in methylene chloride as eluent. A crude mixture of α- and β-Boswellic

Differentiation effects of BC-4 in leukemia cells

Differentiation effects of BC-4 were studied in three myeloid leukemia cell lines and the results were shown in Table 1. BC-4 showed differentiation-inducing effects in all three cell lines. Treatment with 12.5 μg/ml BC-4 caused 70–90% of the cells to obtain NBT reduction and more than 90% of the cells to show monocytic morphologic maturation with increased cytoplasm and polygonal nuclei (Table 2, Fig. 2). Phase microscopy examination showed that BC-4 treated ML-1 cells grew as aggregates (Fig.

Discussion

Boswellia carterii Birdw. is a herb in traditional Chinese medicine which has been used for activating blood circulation and relieving pain. The present study shows that BC-4, one of the isolated principles from Boswellia carterii Birdw., has antileukemia effects with characteristic of inducing differentiation and apoptosis.

The differentiation-inducing effect of BC-4 is cell-specific. Thus, ML-1 and U937 which can be induced to differentiate along a monocytic pathway in response to a variety of

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