Non-caspase-mediated apoptosis contributes to the potent cytotoxicity of the enediyne antibiotic lidamycin toward human tumor cells

EZH2 mediates lidamycin-induced cellular senescence through regulating p21 expression in human colon cancer cells

Lidamycin (LDM) is a novel member of the enediyne antibiotics identified in China with potent antitumor activity. However, it remains unclear whether LDM has potential molecular targets that may affect its antitumor activity. Enhancer of zeste homolog 2 (EZH2) functions as a histone lysine methyltransferase and mediates trimethylation on histone 3 lysine 27 (H3K27me3). High EZH2 level is found to be positively correlated with the aggressiveness, metastasis and poor prognosis of cancer. Here, we aim to study the role of EZH2 in LDM-induced senescence, as well as in the cytotoxicity of LDM in human colon cancer cells. LDM is found to be relatively more potent in inhibiting the colon cancer cells harboring high EZH2 level and induces irreversible cellular senescence at IC50 dose range, as evidenced by senescence-associated β-galactosidase staining, cell cycle arrest and molecular changes of senescence regulators including p21 in HCT116 and SW620 cells. More importantly, LDM is found to markedly inhibit EZH2 expression at both protein and mRNA levels upon the induction of p21 and cellular senescence. LDM also selectively inhibits EZH2 expression as compared with other histone lysine methyltransferases. Knockdown of p21 with siRNAs abolishes LDM-induced senescence, whereas EZH2 knockdown markedly increases p21 expression and causes senescent phenotype. Enrichment of both EZH2 and H3K27me3 levels in the p21 promoter region is reduced by LDM. Moreover, EZH2 overexpression reduces cellular senescence, p21 expression and DNA damage response upon LDM exposure. LDM also demonstrates potent antitumor efficacy in xenografted animal models. Collectively, our work provides first demonstration that EZH2 may mediate, at least partially, the senescence-inducing effects of LDM by regulating p21 expression and DNA damage effect. Thus, EZH2 may serve as a potential target and biomarker to indicate the clinical efficacy of the potent enediyne antitumor drug.

Factor VII light chain-targeted lidamycin shows intensified therapeutic efficacy for liver cancer

The overexpression of tissue factor (TF) observed in numerous cancer cells and clinical samples of human cancers makes TF an ideal target for cancer therapy. The purpose of this study is to develop a TF-targeting energized fusion protein hlFVII-LDP-AE, which is composed of a human Factor VII light chain (hlFVII) as the targeting domain conjugated to the cytotoxic antibiotic lidamycin (LDM, LDP-AE) as the effector domain. The potential efficacy of hlFVII-LDP-AE for cancer therapy was tested in vitro by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and colony formation assays and in vivo with a BALB/c nude mouse xenograft model of human liver cancer line HepG2. The inhibitory concentration (IC(50)) value of hlFVII-LDP-AE varied from 0.15 to 0.64 nM for the various human tumor lines. hlFVII-LDP-AE showed a tumor growth inhibition rate of 90.6% at the dose of 0.6 mg/kg in in vivo animal experiments. The mechanism through which hlFVII-LDP-AE inhibits tumor growth also was determined by Hoechst 33342 staining and Tdt-mediated dUTP nick-end labeling (TUNEL) assay. hlFVII-LDP-AE causes tumor cell death through inducing chromatin condensation and cleavage of genomic DNA. These findings suggest that the hlFVII-LDP-AE protocol is efficacious and tolerated in the mouse model of human liver cancer HepG2 and has clinical applicability for treating cancer patients.

Synthesis and anticancer activity of 13-membered cyclic enediynes

We herein describe the synthesis of 15 novel 13-membered cyclic enediyne derivatives using simple and straightforward approach. Representative examples were screened for their anticancer activities on 60 different human tumor cell lines representing various histologies viz. leukemia, melanoma, and cancers of lung, colon, kidney, ovary, breast, prostate, and central nervous system. The enediyne derivatives with halogen substitutions, especially fluorides were found to be active against most of the cell lines. The initial results indicates marginal to good inhibition for the growth of tumor cells for several cell lines, which shows the potential of these class of compound towards anticancer application.

Role of prosurvival molecules in the action of lidamycin toward human tumor cells

OBJECTIVE

Lidamycin, an enediyne antibiotic, leads to apoptosis and mitotic cell death of human tumor cells at high and low concentrations. The reason why tumor cells have distinct responses to lidamycin remains elusive. This study was to elucidate if cellular prosurvival molecules are involved in these responses.

METHODS

Cleavage of chromatin and DNA was observed by chromatin condensation and agarose gel electrophoresis. Accumulation of rhodamine 123 in lidamycin-treated cells was assayed by flow cytometry. Cell multinucleation was detected by staining with Hoechst 33342. Western blot and senescence-associated beta-galactosidase (SA-beta-gal) staining were used to analyze protein expression and senescence-like phenotype, respectively.

RESULTS

SIRT1 deacetylase remained unchanged in 0.5 nmol/L lidamycin whereas cleavage occurred when apoptosis was induced by lidamycin. Increased FOXO3a, SOD-1 and SOD-2 expression and transient phosphorylation of ERK were detected after exposure of human hepatoma BEL-7402 cells to 0.5 nmol/L lidamycin. High expressions of SIRT1 and Akt were found in colon carcinoma HCT116 p53 knock-out cells exposed to lidamycin. Degradation of PARP and p53 by lidamycin as a substitute for SIRT1 and Akt was confirmed with caspase inhibitor Q-VD-OPh and proteasome inhibitor MG132. Resistance to lidamycin-induced DNA cleavage was observed in breast cancer doxorubicin-resistant MCF-7 cells. This was not induced by P-glycoprotein as no accumulation of rhodamine 123 was detected in the resistant cells following exposure to lidamycin. In contrast to sensitive MCF-7 cells, a lower multinucleation rate for the resistant cells was measured following exposure to equal concentrations of lidamycin.

CONCLUSIONS

Cellular prosurvival molecules, such as SIRT1, Akt, SOD-1, SOD-2 and other unknown factors can influence the action of lidamycin on human tumor cells.

Syntheses and antibacterial activity of phendioxy substituted cyclic enediynes

Syntheses and antibacterial activity of 13-membered 1,3-phendioxy substituted cyclic enediynes are reported. The compounds were screened against gram-positive and gram-negative strains and some of the compounds exhibit potent antibacterial activity.

Analysis of mechanisms contributing to AraC-mediated chemoresistance and re-establishment of drug sensitivity by the novel heterodinucleoside phosphate 5-FdUrd-araC

Chemoresistance is a biological response of cells to survive toxic stress. During cancer treatment the development of chemoresistance is a major problem. The mechanisms how cells become insensitive, and which downstream pathways are affected are not completely understood. Since it has not been well analysed which and how many regulative disorders are subsummised under the term "chemoresistance", we examined and measured arabinosylcytosine (AraC)-mediated desensitation of two mechanisms relevant for tissue homeostasis, cell cycle inhibition and apoptosis induction. MCF-7 cells harbouring ectopic mutated p53 were suitable for this investigation because they activated these mechanisms subsequently and became insensitive to AraC with regard to cell cycle inhibition and apoptosis induction. The major causal mechanism of acquired resistance against AraC was most likely through the inhibition of the first step of AraC phosphorylation within the cell, which is rate limiting for its activation. With regard to cell cycle inhibition AraC-resistant cells were also resistant against 5-fluorodeoxyuridine (5-FdUrd), but fully responsive to 5-FdUrd-induced apoptosis, evidencing that cell cycle and apoptosis are independent of each other. Apoptosis correlated with AIF-activation and was independent of Caspase 7, whereas cell cycle inhibition correlated with cyclinD1 expression but not with induction of p21 or p27. The phosphate conjugated 5-FdUrd-araC heterodimer (5-Fluoro-2'-desoxyuridylyl-(3'-->5')-Arabinocytidine), which is a prodrug of AraC-monophosphate, reactivated AIF and down-regulated cyclin D1 in AraC-resistant cells and circumvented resistance to apoptosis and to cell cycle inhibition. Also, cells which were resistant to 5-FdUrd or doxorubicin were sensitive to 5-FdUrd-araC. This investigation demonstrates that chemoresistance affects apoptosis induction and cell cycle inhibition independently and that detailed knowledge about the affected downstream pathways would enable the design of targeted intervention with small molecules to restore chemosensitivity.

2,3-Dihydroxybenzoic acid attenuates kanamycin-induced volume reduction in mouse utricular type I hair cells

The aminoglycoside kanamycin is a commonly used antibiotic, but unfortunately it is oto- and nephrotoxic in large doses. The negative effects are thought to be due to the formation of free radicals which is why strong antioxidants and iron chelators like 2,3-dihydroxybenzoic acid (DHB) are of great interest. This study estimates cellular quantitative changes in the utricular macula of mice following systemic treatment with kanamycin alone or in combination with DHB. The animals were injected with either saline, kanamycin or kanamycin + DHB for 15 days and perfusion fixed three weeks after last injection. Total volume of the utricle, as well as total number of hair and supporting cells, were estimated on light microscopic sections. Total volume and mean volume of hair cell types I and II and supporting cells were estimated on digital transmission electron micrographs. Total volume of the utricular macula, hair cell type I and supporting cells decreased significantly in animals injected with kanamycin but not in animals co-treated with DHB. Hair and supporting cell numbers remained unchanged in all three groups. In conclusion, the kanamycin-induced volume reduction of type I hair cells was attenuated by DHB.

Vitamin K analog (compound 5) induces apoptosis in human hepatocellular carcinoma independent of the caspase pathway

A systemic vitamin K analog, compound 5 (Cpd 5), possesses the ability to inhibit cell growth of tumor cells. Therefore, we investigated the effect of Cpd 5 in human hepatocellular carcinoma (HCC) cell lines and evaluated its role in apoptosis. Human HCC cell lines were cultured and treated with Cpd 5. Apoptosis was assessed using DAPI staining and Annexin-V membrane staining. The expression of caspases, XIAP and Bcl-xL was also investigated. Cpd 5 decreased cell viability in a dose-dependent manner in two HCC cells (HLE and SK-Hep1) containing mutant p53, but not in the HepG2 cell line, which contained wild-type p53. Cpd 5-treated HLE and SK-Hep1 cells showed typical apoptotic features, nuclear condensation and nuclear fragmentation upon DAPI staining. Positive membranous staining for Annexin-V was also seen in these cells. Both caspase-8 and caspase-3 activities were up-regulated slightly. Pro-caspase-8 protein levels decreased slightly in both cells. Although the expression of Bcl-xL was not influenced by Cpd 5, that of XIAP decreased in HLE cells. However, the pan-caspase inhibitor, zVAD, could not significantly prevent Cpd 5-induced apoptosis and Cpd 5 could not augment TRAIL-induced apoptosis. These results demonstrate that Cpd 5 induced apoptosis in human HCC cell lines, mainly independently of caspase activities. This may contribute to its highly potent cytotoxicity toward HCC cells.

Tissue distribution and excretion of 125I-lidamycin in mice and rats

AIM: To investigate the tissue distribution, urinary and fecal excretions of ¹²⁵I-lidamycin (¹²⁵I-C-1027) in mice and its biliary excretion in rats.

METHODS: The total radioactivity assay (RA method) and the radioactivity assay after precipitation with 200 mL/L trichloroacetic acid (TCA-RA method) were used to dete-rmine the tissue distribution, and the urinary and fecal excretions of ¹²⁵I-C-1027 in mice and its biliary excretion in rats.

RESULTS: Tissue concentrations reached the peak at the fifth minute after administration of ¹²⁵I-C-1027 to mice. The highest concentration was in kidney, and the lowest in brain at all test-time points. The organs of the concentr-ations of ¹²⁵I-C-1027 from high to low were kidney, lung, liver, stomach, spleen, uterus, ovary, intestine, muscle, heart, testis, fat, and brain in mice. The accumulative excretion amounts of 0-24 h, and 0-96 h after administration of ¹²⁵I-C-1027 were 68.36 and 71.64% in urine, and 2.60 and 3.21% in feces of mice, respectively, and the accumulative excretion amount of 0-24 h was 3.57% in bile in rats.

CONCLUSION: Our results reflect the characteristics of the tissue distribution, urinary and fecal excretions of ¹²⁵I-C-1027 in mice and the biliary excretion of ¹²⁵I-C-1027 and its metabolites in rats, and indicate that ¹²⁵I-C-1027 and its metabolites are mainly distributed in kidney, and excreted in urine.

Pharmacokinetics of C-1027 in mice as determined by TCA-RA method

AIM

To validate a radioactivity assay, the TCA-RA method, for the measurement of C-1027 in serum and to evaluate its application in determination of pharmacokinetics of C-1027 in mice.

METHODS

(125)I-C-1027 was prepared by the Iodogen method and separated by HPLC. The radioactivity assay was established and used to determine (125)I-C-1027 in mice at doses of 10, 50 and 100 microg/kg after precipitation with 20% trichloroacetic acid (TCA-RA method). Several pharmacokinetic parameters were determined after intravenous injection of (125)I-C-1027 to mice.

RESULTS

After intravenous injection of (125)I-C-1027 to mice, at doses of 10, 50 and 100 microg/kg; the apparent distribution volumes (V(d)) were 0.26, 0.31 and 0.33 L/kg; the biological half-lives (T(1/2)) were 3.10, 3.40 and 3.90 h; the areas under curve (AUC) were 18.41, 103.69 and 202.74 ng/h/mL; the elimination rate constants (K) were 1.04, 1.26 and 0.58/h; and the total body clearance (Cl) were 0.54, 0.48 and 0.49 L/kg/h, respectively.

CONCLUSION

TCA-RA is a sensitive, reliable and suitable method for the determination of (125)I-C-1027 in mouse serum.

Chemosensitization of bladder cancer cell lines by human telomerase reverse transcriptase antisense treatment

PURPOSE

Responses of transitional cell carcinoma of the bladder (TCC) to commonly used chemotherapy agents such as mitomycin C (MMC), cisplatin and gemcitabine are often disappointing. Since human telomerase reverse transcriptase (hTERT) is tumor specifically expressed and contributes to the immortality and malignancy of the majority of tumors, it is regarded as a suitable antitumor target. We investigated whether combinations of hTERT antisense (AS)-oligonucleotides (ODNs) with common chemotherapy (CT) schedules may improve drug mediated antitumor effects.

MATERIALS AND METHODS

Initial screening for enhancement of the inhibitory effects of MMC, cisplatin and gemcitabine on viability by treatment with the 2 hTERT AS-ODNs ASt2206 and ASt2331 was performed in 4 TCC cell lines prior to CT. Apoptosis was assessed by annexin V staining and detection of activated caspase-3 using Western blot analysis. Nonsense (NS)-ODN served as a control in all experiments.

RESULTS

All cell lines responded to the anticancer agents tested. Treatment with AS plus CT resulted in a significantly stronger inhibition of viability than the NS plus CT control in the majority of combinations, indicating an AS specific enhancement effect. For example, ASt2331 plus MMC decreased viability to 17% in contrast to NS plus MMC (58%) in EJ28 cells. All ASt2331 plus CT combinations specifically increased the rate of apoptosis 1.3 to 3.0-fold compared with NS plus CT. Apoptosis induction was associated with caspase 3 activation.

CONCLUSIONS

Enhancement of cytotoxic drug effects on the growth of TCC cells by hTERT AS-ODNs presented herein allows a dose decrease in chemotherapy and confirms the suitability of hTERT as a target in a specific therapy approach.

Sterile 20 Kinase Phosphorylates Histone H2B at Serine 10 during Hydrogen Peroxide-Induced Apoptosis in S. cerevisiae

Apoptosis is a highly coordinated cell suicide mechanism in vertebrates. Phosphorylation of serine 14 of histone H2B, catalyzed by Mst1 kinase, has been linked to chromatin compaction during apoptosis. We extend these results to unicellular eukaryotes by demonstrating that H2B is specifically phosphorylated at serine 10 (S10) in a hydrogen peroxide-induced cell death pathway in S. cerevisiae. H2B S10A mutants are resistant to cell death elicited by H(2)O(2) while H2B S10E phospho-site mimics promote cell death and induce the "constitutive" formation of condensed chromatin. Ste20 kinase, a yeast homolog of mammalian Mst1 kinase, translocates into the nucleus in a caspase-independent fashion and directly phosphorylates H2B at S10. Conservation of targeted H2B phosphorylation and the enzyme system responsible for the process point to an ancient mechanism of chromatin remodeling that likely plays an important role in governing cellular homeostasis in a wide range of organisms.

Mitotic cell death in BEL-7402 cells induced by enediyne antibiotic lidamycin is associated with centrosome overduplication

AIM: Mitotic cell death has been focused on in tumor therapy. However, the precise mechanisms underlying it remain unclear. We have reported previously that enediyne antibiotic lidamycin induces mitotic cell death at low concentrations in human epithelial tumor cells. The aim of this study was to investigate the possible link between centrosome dynamics and lidamycin-induced mitotic cell death in human hepatoma BEL-7402 cells.

METHODS: Growth curve was established by MTT assay. Cell multinucleation was detected by staining with Hoechst 33342. Flow cytometry was used to analyze cell cycle. Aberrant centrosomes were detected by indirect immunofluorescence. Western blot and senescence-associated β-galactosidase (SA-β-gal) staining were used to analyze protein expression and senescence-like phenotype, respectively.

RESULTS: Exposure of BEL-7402 cells to a low concentration of lidamycin resulted in an increase in cells containing multiple centrosomes in association with the appearance of mitotic cell death and activation of SA-β-gal in some cells, accompanied by the changes of protein expression for the regulation of proliferation and apoptosis. The mitochondrial signaling pathway, one of the major apoptotic pathways, was not activated during mitotic cell death. The aberrant centrosomes contributed to the multipolar mitotic spindles formation, which might lead to an unbalanced division of chromosomes and mitotic cell death characterized by the manifestation of multi- or micronucleated giant cells. Cell cycle analysis revealed that the lidamycin treatment provoked the retardation at G2/M phase, which might be involved in the centrosome overduplication.

CONCLUSION: Mitotic cell death and senescence can be induced by treatment of BEL-7402 cells with a low concentration of lidamycin. Centrosome dysregulation may play a critical role in mitotic failure and ultimate cell death following exposure to intermediate dose of lidamycin.

Different DNA lesions trigger distinct cell death responses in HCT116 colon carcinoma cells

The pleiotrophic cellular response to DNA damage includes activation of cell cycle checkpoints, induction of DNA repair pathways, and initiation of programmed cell death among others. The fate of cells with damaged DNA depends on the coordination of these different responses. The clinical efficacy of genotoxic therapies is influenced by cell fate and thus by how the DNA damage response is coordinated. While a great deal has been learned about how different DNA lesions activate distinct cell cycle checkpoints and DNA repair pathways, less is known about whether the type of DNA lesion influences the qualitative and quantitative nature of the cell death response. To address this question, HCT116 colon carcinoma cells have been treated with equally cytotoxic doses of the antitumor DNA alkylating agents adozelesin or bizelesin or the DNA strand scission agent C-1027. The relative contribution of cell cycle arrest and cell death to measured cytotoxicity varied among the three drugs. Apoptotic cell death accounts for most C-1027 cytotoxicity while cell cycle arrest and cell death both contribute to the cytotoxicity of the alkylating agents. Each of the drugs induces a distinct but overlapping pattern of caspase activation. In addition, the cell death response to these drugs is differentially dependent on p53 and p21. These observations suggest that the type of DNA lesion influences not only the relative extent of apoptotic cell death at a given cytotoxic dose but also the qualitative nature of that response.