ANTI-CANCER ACTION OF β-LAPACHONE A COMPONENT OF THE HERB PAU D’ARCO
Dr. Evangelos Kontargyris, Bsc, Biomedical Sciences, PhD,
Doctor of the Medical School of the University of Ioannina
Pau d’arco is an herb, well known in South America, which is made from the inner bark of the Tabebuia tree and contains the active substances naphthoquinones, which are derivatives of benzoic acid. A naphthoquinone, called β-lapachone, has been found in in vitro studies in cancer cells to have potent anti-cancer properties through certain cytotoxic mechanisms associated with molecular biology and also through possible biochemical pathways.
Pau d’arco is a popular herb that is available in tea bags, capsules and powder from health food stores. Also known are lapacho, ipe roxo and taheebo. The herb is made from the inner bark of a large tree of various kinds, with pink, purple or yellow flowers, which grows in Brazil and Argentina and is called Tabebuia. In South America, pau d’arco is used to treat cancer as well as the flu, fever, malaria, infections, syphilis, gonorrhea and at least one type of lupus. In addition to its action against bacteria, fungi and the symptoms of inflammation, it is also used as a diuretic and hemostatic. 1, 2
It has been found that in pau d’arco there are various active substances called naphthoquinones which are merely derivatives of benzoic acid and interact synergistically in anti-cancer therapy.1, 2 Indeed, a recent study in breast cancer cells Liquid extract of pau d ‘arco from the inner bark of the tree from the species Tabebuia avellandae 3 (Figure 1) causes reduced growth and induction of apoptosis in these cells. Specifically, the cytotoxic effects of pau d’arco resulted in the interruption of the cell cycle in the “S” phase where DNA replication takes place and the chromatin is concentrated (Figure 2), which is characteristic of death from apoptosis in cells. that’s all. 4
Figure 1. Flowers from the tree Tabebuia avellanedae. 3
Figure 2. Morphology of breast cancer cells “MCF-7” in Transmission Electron Microscopy. (A) Cells without topau d ‘arco (control) (B) Cells after 1.5 mg / ml pau d’ arco for 24 hours. The peripheral condensation and fragmentation of the nuclear chromatin of the apoptotic cell are clearly visible. 4
A series of in vitro laboratory studies performed on cells of various types of cancer have shown that a naphthoquinone called β-lapachone (Figure 3), which is contained in the pau d ‘arco from the tree Tabebuia avellandae, has strong anti-cancer properties. These studies reveal some mechanisms of molecular biology and some possible biochemical pathways through which the cytotoxic effect of β-lapachone is exerted on cells and therefore its anticancer activity is explained in detail.
Figure 3. The chemical structure of β-lapachone.5
A first reported study was performed on cultured human prostate cancer cells “PC-3” and showed in principle that β-lapachone greatly reduced the growth of these cells by inducing death from apoptosis and inhibited the cell cycle process in phase “G1” (Figure 4). In the “G1” phase of the cell cycle, cells under normal survival conditions increase in size and prepare for the synthesis (replication) of DNA. Β-lapachone has also been shown to affect the cell cycle through two biochemical pathways: The first pathway involves a significant reduction in phosphorylation of the retinoblastoma protein (pRB), which in turn leads to the inhibition of controlling the transition from phase “G1” to phase “S”. According to the second pathway, the expression of the p21 protein and its binding to the cyclin-dependent kinase “cyclin / Cdk2” increases. This binding results in a reduction in kinase activity.6
Figure 4. PC-3 prostate cancer cells, Wright stained under a light microscope at x 200 magnification. 3 and 6 μM β-lapachone were administered for 6 hours. 6
In addition, another study in a different series of prostate cancer cells (DU145) again showed that β-lapachone causes growth inhibition and induces apoptosis in these cells (Figure 5). Apoptosis has been shown to be primarily due to increased expression of Bax pre-apoptotic protein and decreased Bcl-2 anti-apoptotic protein. It was also found that β-lapachone reduced mRNA levels and protein expression of cyclooxygenase “COX-2”, an enzyme that affects the formation of prostaglandins which play a role in many bodily functions including inflammation. Finally, β-lapachone is reported to inhibit the telomerase activity of an enzyme that works by maintaining and repairing telomere lengths, ie the terminal ends of chromosomes. In particular, telomerase adds repetitive small pieces of DNA to the ends of chromosomes to prevent the destruction and loss of genetic material during cell division. 7, 8
Figure 5. Prostate cancer cells “DU145” in the light microscope at x 200 magnification. The cells were incubated with different concentrations of β-lapachone (from 1 to 5 μM, for 48 hours) and the morphological changes due to the induction of apoptosis by β- lapachone as the doses increased, it is obvious.7
In other cancers, research has shown that β-lapachone induces growth inhibition and apoptosis in human colon cancer cells
(Figure 6).
Apoptotic cell death is due to a decrease in the expression of Bcl-2 and also to the inhibition of “nuclear factor κB” (NF-κB), a protein complex that controls many biological processes in cells including apoptosis.9 Also β-lapach has been found to inhibit the growth and induce apoptosis of human lung cancer cells. These effects are due to decreased expression of Bcl-2, c-myc oncogene, human telomerase RNA and increased Bax expression.10 It is also known that β-lapachone causes growth retardation and apoptotic cell death. liver cancer primarily by decreasing the expression of Bcl-2 and also the anti-apoptotic protein Bcl-XL, as well as by decreasing the expression of Bax(Figure 7).
The same study revealed that apoptosis is not induced through the so-called extrinsic apoptotic pathway, in which the “Fas death receptor” (Fasreceptor) and the binding molecule for Fas (Fas ligand or FasL) play a key role. Therefore, considering that the proteases caspase-9 (caspase-9) and caspase-3 (caspase-3) are activated, it is concluded that the induction of apoptosis in these cells by β-lapachone occurs through the so-called endogenous or mitochondrial apoptotic intrinsic apoptotic pathway) .11 Another study has found that β-lapachone reduces cell viability by inducing apoptosis in human bladder cancer cells also through the mitochondrial pathway. This is because β-lapachone decreases Bcl-2 expression, increases Bax expression, activates caspases-3 and -9, and inhibits Fas and FasL receptor levels in these cells.12 Finally, a recent research has shown that β-lapachone induces direct apoptotic toxicity in human leukemia cells by activating caspase-3 and loss of telomerase activity attributed to the down-regulation of reverse transcriptase .13
Figure 6. Colon cancer cells “HCT-116” under a light microscope at x 200 magnification. Cells were incubated with various concentrations of β-lapachone (1 to 5 μM for 24 hours) and morphological changes due to induction of apoptosis by β-lapachone as the doses increased, it is obvious. 9
Figure 7. HepG2 liver cancer cells stained with DAPI (linked to cell DNA) on a x 400 fluorescence microscope. Cells were incubated with various β-lapachone concentrations from 1 to 5 μM for 48 hours. In cells that did not receive β-lapachone (control) the structural features of the nucleus are intact, while those in which β-lapachone was administered underwent chromatin concentration as the doses increased. 11
In addition to its cytotoxic effect on various cancers, β-lapachone has also been found to have anti-metastatic and anti-invasive properties. In particular, a study in liver cancer cells showed that β-lapachone increases the expression of the early growth response gene-1 (Egr-1), the protein thrombospondin 1 or TSP-1. and calcium-dependent E-cadherin. The tumor suppressor gene Egr-1 regulates the expression of various genes involved in the metastasis of cancerous tumors, including the thrombospondin 1 gene, which in turn inhibits neovascularization, limiting tumor growth. Neovascularization is the growth of blood vessels in cancerous tumors and under normal and healthy conditions does not occur. Finally, E-cadherin is an intercellular adhesion molecule, it is expressed specifically in the cell membrane of epithelial cells and it has been found that during the infiltration and metastasis of various cancerous tumors, the expression of this protein is reduced.14
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