A ginseng metabolite, compound K, induces autophagy and apoptosis via generation of reactive oxygen species and activation of JNK in human colon cancer cells

Compound K (20-O-(β-D-glucopyranosyl)-20(S)-protopanaxadiol) is an active metabolite of ginsenosides and induces apoptosis in various types of cancer cells. This study investigated the role of autophagy in compound K-induced cell death of human HCT-116 colon cancer cells. Compound K activated an autophagy pathway characterized by the accumulation of vesicles, the increased positive acridine orange-stained cells, the accumulation of LC3-II, and the elevation of autophagic flux. Whereas blockade of compound K-induced autophagy by 3-methyladenein and bafilomycin A1 significantly increased cell viability. In addition, compound K augmented the time-dependent expression of the autophagy-related proteins Atg5, Atg6, and Atg7. However, knockdown of Atg5, Atg6, and Atg7 markedly inhibited the detrimental impact of compound K on LC3-II accumulation and cell vitality. Compound K-provoked autophagy was also linked to the generation of intracellular reactive oxygen species (ROS); both of these processes were mitigated by the pre-treatment of cells with the antioxidant N-acetylcysteine. Moreover, compound K activated the c-Jun NH2-terminal kinase (JNK) signaling pathway, whereas downregulation of JNK by its specific inhibitor SP600125 or by small interfering RNA against JNK attenuated autophagy-mediated cell death in response to compound K. Compound K also provoked apoptosis, as evidenced by an increased number of apoptotic bodies and sub-G1 hypodiploid cells, enhanced activation of caspase-3 and caspase-9, and modulation of Bcl-2 and Bcl-2-associated X protein expression. Notably, compound K-stimulated autophagy as well as apoptosis was induced by disrupting the interaction between Atg6 and Bcl-2. Taken together, these results indicate that the induction of autophagy and apoptosis by compound K is mediated through ROS generation and JNK activation in human colon cancer cells.

The critical role of catalase in prooxidant and antioxidant function of p53

The tumor suppressor p53 is an important regulator of intracellular reactive oxygen species (ROS) levels, although downstream mediators of p53 remain to be elucidated. Here, we show that p53 and its downstream targets, p53-inducible ribonucleotide reductase (p53R2) and p53-inducible gene 3 (PIG3), physically and functionally interact with catalase for efficient regulation of intracellular ROS, depending on stress intensity. Under physiological conditions, the antioxidant functions of p53 are mediated by p53R2, which maintains increased catalase activity and thereby protects against endogenous ROS. After genotoxic stress, high levels of p53 and PIG3 cooperate to inhibit catalase activity, leading to a shift in the oxidant/antioxidant balance toward an oxidative status, which could augment apoptotic cell death. These results highlight the essential role of catalase in p53-mediated ROS regulation and suggest that the p53/p53R2-catalase and p53/PIG3-catalase pathways are critically involved in intracellular ROS regulation under physiological conditions and during the response to DNA damage, respectively.

Pathotypes and genetic relationship of worldwide collections of Elsinoë spp. causing scab diseases of citrus

Two scab diseases are recognized currently on citrus: citrus scab, caused by Elsinoë fawcettii, and sweet orange scab, caused by E. australis. Because the two species cannot be reliably distinguished by morphological or cultural characteristics, host range and molecular methods must be used to identify isolates. Four pathotypes of E. fawcettii and two of E. australis have been described to date based on host range. The host specificity and genetic relationships among 76 isolates from Argentina, Australia, Brazil, Korea, New Zealand, and the United States were investigated. Based on pathogenicity tests on eight differential hosts, 61 isolates were identified as E. fawcettii and 15 as E. australis. Of 61 isolates of E. fawcettii, 24 isolates were identified as the Florida broad host range (FBHR) pathotype, 7 as the Florida narrow host range (FNHR) pathotype, 10 as the Tryon's pathotype, and 3 as the "Lemon" pathotype. Two new pathotypes, the "Jingeul" and the satsuma, rough lemon, grape-fruit, clementine (SRGC), are described, and four isolates did not fit into any of the known pathotypes of E. fawcettii. Of the 15 isolates of E. australis from Argentina and Brazil, 9 belonged to the sweet orange pathotype and 6 from Korea to the natsudaidai pathotype. E. fawcettii and E. australis were clearly distinguishable among groups by random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) assays and the E. fawcettii group was divided into three subgroups, A-1, A-2, and A-3. The A-1 group was composed of the FBHR, FNHR, and SRGC pathotypes; some Lemon pathotypes; and the uncertain isolates. The A-2 subgroup included all of the Tryon's pathotype isolates and one of the three Lemon pathotype isolates and the A-3 group contained the Jingeul pathotype isolates. E. australis was differentiated into two groups: B-1, the natsudaidai pathotype isolates, and B-2, the sweet orange pathotype isolates. Isolates of E. fawcettii and E. australis were clearly distinguishable by sequence analysis of the internal transcribed spacer (ITS) region and the translation elongation factor 1 alpha (TEF) gene. There were also fixed nucleotide differences in the ITS and TEF genes that distinguished subgroups separated by RAPD-PCR within species. We confirmed two species of Elsinoë, two pathotypes of E. australis, and at least six pathotypes of E. fawcettii and described their distribution in the countries included in this study.

Development of PCR Assays for the Identification of Species and Pathotypes of Elsinoë Causing Scab on Citrus

Two scab pathogens of citrus, Elsinoë fawcettii and E. australis, cause citrus scab and sweet orange scab, respectively, and pathotypes of each species have been described. The two species cannot be readily distinguished by morphological or cultural characteristics and can be distinguished only by host range and the sequence of the internal transcribed spacer (ITS) region. In this study, random amplified polymorphic DNA (RAPD) assays clearly distinguished E. fawcettii and E. australis, and the sweet orange and natsudaidai pathotypes within E. australis also could be differentiated. We developed specific primer sets, Efaw-1 for E. fawcettii; Eaut-1, Eaut-2, Eaut-3, and Eaut-4 for E. australis; and EaNat-1 and EaNat-2 for the natsudaidai pathotype within E. australis using RAPD products unique to each species or pathotype. Other primer sets, Efaw-2 and Eaut-5, which were specific for E. fawcettii and E. australis, respectively, were designed from previously determined ITS sequences. The Efaw-1 and Efaw-2 primer sets successfully identified E. fawcettii isolates from Korea, Australia, and the United States (Florida) and the Eaut-1 to Eaut-5 primer sets identified both the sweet orange pathotype isolates of E. australis from Argentina and the natsudaidai pathotype isolates from Korea. The EaNat-1 and EaNat-2 primer sets were specific for isolates of the natsudaidai pathotype. The Efaw-1 and Efaw-2 primer sets successfully detected E. fawcettii from lesions on diseased leaves and fruit from Korea and primer pairs Eaut-1, Eaut-2, Eaut-3, Eaut-4, and Eaut-5 detected E. australis from lesions on sweet orange fruit from Brazil.

Apoptosis induction by 4beta-acetoxyscirpendiol from Paecilomyces tenuipes in human leukaemia cell lines

The carpophores of Paecilomyces tenuipes are known in the Orient for their strong antitumor activity. In continuation of our study on acetoxyscirpendiol (ASD, 4beta-acetoxyscirpene-3alpha,15-diol) as a cytotoxic component from this fungus, we report particularly on the mode of action of ASD in inducing apoptosis in human MOLT-4, THP-1 and Jurkat T cell leukaemia in vitro. The antiproliferative effects of ASD seem attributable to its induction of apoptosis in the cells, as it blocked the cell cycle, induced hypodiploidity and bound annexin V and also cleaved poly-(ADP-ribose) polymerase (PARP) in these cell lines. The 50% inhibitory concentrations (IC50) of ASD on MOLT-4, THP-1 and Jurkat T cells were found to be 60, 85 and 60 ng/ml, respectively. ASD arrested the cell cycle at the G1/S transition and showed hypodiploidity due to the accumulation of sub-G0 population. Annexin V binding was increased in the presence of ASD in the MOLT-4 cell line in a time-dependent manner. ASD and three of its derivatives also induced cleavage of PARP in both MOLT-4 and Jurkat T cell lines. From these data, it is suggested that ASD exerts its cytotoxic activity by inducing apoptosis in leukaemia cell lines in vitro.

Cytotoxic activities of acetoxyscirpenediol and ergosterol peroxide from Paecilomyces tenuipes

Paecilomyces tenuipes is one of the famous Chinese medicinal entomopathogenic fungi that parasites in the lavae of silkworm. Two cytotoxic components were isolated from methanolic extract of the carpophores of this fungus that was cultivated artificially. Spectral analyses of the cytotoxic components showed that they were known ergosterol peroxide (5alpha,8alpha-epidioxy-24(R)-methylcholesta-6,22-dien-3beta-ol) and acetoxyscirpenediol (4beta-acetoxyscirpene-3alpha,15-diol) that were isolated for the first time from this fungus. The 50% inhibitory concentrations (IC50) of ergosterol peroxide against human gastric tumor cell line (SNU-1), human hepatoma cell line (SNU-354), human colorectal tumor cell line (SNU-C4) and murine sarcoma-180 were 18.7, 158.2, 84.6 and 74.1 microM, respectively. The IC50 values of acetoxyscirpenediol against SNU-1, SNU-C4, SNU-354 and sarcoma-180 were 1.2,4.0, 2.2 and 1.9 microM, respectively. Cytotoxic activities of acetoxyscirpenediol were about 4.0-6.6 times stronger than those of cisplatin which is currently used clinically for cancer patients.

Leukemic cell line, KG-1 has a functional loss of hOGG1 enzyme due to a point mutation and 8-hydroxydeoxyguanosine can kill KG-1

We tested the cytotoxic action of 8-hydroxyguanine (8ohG) by observing the viability of several leukemic cell lines (KG-1, U937, Jurkat and K 562) in the presence of 8-hydroxydeoxyguanosine (8ohdG), a nucleoside of 8ohG. It was found that 8ohdG showed cytotoxic action only to KG-1 and that only KG-1 showed a homozygous arginine 209 to glutamine mutation in the hOGG1 gene with an almost negligible hOGG1 enzyme activity. Possibly, the selective cytotoxicity in 8ohdG to KG-1 may be due to its low capacity to cope with an increase in the 8ohG level in DNA resulting from the incorporation of 8ohdG present in the culture media. The mutational impairment of hOGG1 in KG-1 is the first report in leukemic cell lines. Using KG-1 with impaired hOGG1, we demonstrated cytotoxicity of 8ohdG probably due to its incorporation into cellular DNA. This new property of KG-1 may allow it to serve as an useful tool for studies of OGG1, oxidative DNA damage and the cytotoxic action of 8ohG. Oncogene (2000) 19, 4476 - 4479.

Modulation of the antiproliferative activity of anticancer drugs in hematopoietic tumor cell lines by the poly(ADP-ribose) polymerase inhibitor 6(5H)-phenanthridinone

Poly (ADP-ribose) polymerase (PARP) is involved in the cellular responses to genotoxic damage and its inhibition has been proposed as potentiating anticancer drug activity. Here, we evaluated the ability of the PARP inhibitor, 6(5H)-phenanthridinone, to modulate the antiproliferative activity of bleomycin, carmustin and doxorubicin in a murine (RDM4) and a human (U937) lymphoma cell lines. 6(5H)-phenanthridinone was shown to suppress PARP activity with the same potency in both cell lines. At 25 microM, this compound potentiated the activity of carmustin in RDM4 but not in U937 cells. In contrast, 6(5H)-phenanthridinone failed to affect the doxorubicin toxicity in murine lymphoma cells, whereas it prevented the cytotoxicity of this drug in the human cell line. Altogether, these findings indicated that 6(5H)-phenanthridinone modulates the cytotoxicity of anticancer agents differently according to the cell type and the drug. Therefore, this PARP inhibitor could be considered as the prototype of a new class of adjuncts in cancer chemotherapy.

An efficient stereoselective synthesis of [3S(1S,9S)]-3-[[[9-(benzoylamino) octahydro-6,10-dioxo-6H-pyridazino-(1,2-a)(1,2)-diazepin-1-yl]-carbonyl ]amino]-4-oxobutanoic acid, an interleukin converting enzyme (ICE) inhibitor

The title compound 1 is a potent interleukin-1beta-converting enzyme (ICE) inhibitor. Recently, an efficient chiral synthesis of compound 1 has been accomplished in our labs. The overall yield of this 18-step stereoselective synthesis was 9.8%.

Reduction of radiation-induced chromosome aberration and apoptosis by dithiothreitol

We have examined in vitro and in vivo radioprotective effects of a well-known thiol-containing compound, dithiothreitol (DTT). The treatment of both 0.5 and 1 mM of DTT significantly increased clonogenic survival of gamma-ray irradiated Chinese hamster (V79-4) cells. In order to investigate the possible radioprotective mechanism of DTT, we measured gamma-ray induced chromosome aberration by micronucleus assay. In the presence of 0.5 mM or 1 mM DTT, the frequencies of micronuclei were greatly reduced in all dose range examined (1.5-8 Gy). Slightly higher reduction in micronucleus formation was observed in 1 mM DTT-treated cells than in 0.5 mM DTT-treated cells. In addition, incubation with both 0.5 and 1 mM of DTT prior to gamma-ray irradiation reduced nucleosomal DNA fragmentation at about same extent, this result suggests that treatment of DTT at concentrations of 0.5 and 1 mM reduced radiation-induced apoptosis. In vivo experiments, we also observed that DTT treatment reduced the incidence of apoptotic cells in mouse small intestine crypts. In irradiated control group 4.4 +/- 0.5 apoptotic cells per crypt were observed. In DTT-administered and irradiated mice, only 2.1 +/- 0.4 apoptotic cells per crypt was observed. In vitro and in vivo data obtained in this study showed that DTT reduced radiation-induced damages and it seems that the possible radioprotective mechanisms of action of DTT are prevention of chromosome aberration.

Effect of 6(5H)-phenanthridinone, a poly (ADP-ribose)polymerase inhibitor, and ionizing radiation on the growth of cultured lymphoma cells

The ability of 6(5H)-phenanthridinone (Phen), a new potent poly(ADP-ribose)polymerase (PARP) inhibitor, to potentiate the effect of ionizing radiation on tumour cells was evaluated. RDM4 murine lymphoma cells were irradiated using a 60Co panoramic source and then examined for their growth, cell cycle distribution and apoptosis. Phen (100 microM) was found to inhibit more than 90% of the PARP activity in control and irradiated cells. Cell proliferation was assessed using Alamar Blue, a new fluorometric assay. Phen was found to sharply increase the radiation-induced inhibition of cell proliferation. Indeed, at 2.5 Gy the relative cell number of Phen-treated cells was 60% below control levels. At the same radiation dose, the G2M arrest was also significantly reinforced by the addition of Phen. Furthermore, this PARP inhibitor was shown to significantly increase the amount of DNA fragmentation as revealed by the DNA migration pattern in agarose gel electrophoresis. Comparable results were obtained with 3-aminobenzamide, another PARP inhibitor, but at concentrations 200-fold higher. Taken together, these results indicate the potential interest of Phen as a valuable pharmacological probe for investigating the role of PARP in cellular responses to radiation. They also suggest a possible use of Phen as an adjuvant in radiotherapy.

Cytotoxic properties of a phosphoglycoconjugated derivative of 7 beta-hydroxycholesterol upon normal and tumor cells in culture

The cytotoxic activity of a new hydrosoluble axysterol derivative, a phosphoric acid diester of 7 beta-hydroxycholesterol (7 beta-OHC, one of the most toxic oxysterol) and of galactose has been evaluated using cultured tumor cells of various origins, and compared with 7 beta-OHC. As its parent compound, XG-142 exhibits a significant cytotoxic activity against all the cell lines tested, but the IC50's were higher than those obtained with 7 beta-OHC. Moreover, the cytotoxicity was slower to appear than after a 7 beta-OHC treatment. Cell phase distribution was analysed, and revealed some differences between the two compounds. Both oxysterols induced apoptosis at micromolar concentrations, as evidenced by several methods including agarose gel electrophoresis of fragmented DNA and flow cytometry of propidium iodide labeled cells. Apoptosis was also obtained when 7 beta-OHC and XG-142 were combined at concentrations unable to induce this type of cell death when used separately. Upon normal murine spleen cells, XG-142 was found to be less toxic than 7 beta-OHC, and the capacity to respond to Con A stimulation was preserved. Therefore, XG-142 can be considered as a promising soluble analogue of 7 beta-OHC, and its application as anticancer agent should be considered.

The cytotoxicity of psoralidin from Psoralea corylifolia

A cytotoxic coumestan derivative, psoralidin (1), was isolated from the seed of Psoralea corylifolia. The IC50 values of 1 against SNU-1 and SNU-16 carcinoma cell lines were 53 and 203 micrograms/ml, respectively, indicating cytotoxic activity against stomach carcinoma cell lines.