Anticancer Drug Etoposide Research Articles

Inhibition of etoposide-induced apoptosis with peptide aldehyde inhibitors of proteasome.

Recent investigations have indicated the involvement of proteasome in programmed cell death. The present studies show that although peptide aldehyde inhibitors of proteasome are by themselves weak inducers of apoptosis, they inhibit the apoptotic effect of the anticancer drug etoposide in rat thymocytes. Acetyl-Leu-Leu-norvalinal (LLnV-al) and other related peptide aldehydes inhibited the increase in caspase activity and DNA fragmentation that followed treatment with etoposide and their effect was related to their potency as proteasome inhibitors. To inhibit etoposide-induced apoptosis, LLnV-al must be present within 3 h of treatment with etoposide, in the same way as the inhibitor of protein synthesis cycloheximide must be. Etoposide caused a rapid accumulation of p53 protein that was not inhibited by LLnV-al, which was also a strong inducer of p53. Peptide aldehydes were also weak activators of caspase activity, suggesting that the same mechanism, i.e. the blocking of proteasome function, both triggers apoptosis and inhibits the effect of etoposide. These results are consistent with a model in which proteasome is selectively involved in the pathway used by etoposide to induce cell suicide.

Granzyme Release and Caspase Activation in Activated Human T-Lymphocytes

Recently it has been reported that caspase-3 activation occurs in stimulated T-lymphocytes without associated apoptosis (Miossec, C., Dutilleul, V., Fassy, F., and Diu-Hercend, A. (1997) J. Biol. Chem. 272, 13459-13462). To explore this phenomenon, human peripheral blood lymphocytes (PBLs) were stimulated with mitogenic lectins or anti-CD3 antibody, and the proteolytic processing of different caspases and caspase substrates was analyzed by immunoblotting. Proteolytic processing of caspases-3 and -7 and the caspase substrates poly(ADP-ribose) polymerase, GDP dissociation inhibitor, and PKCdelta was observed when PBLs were activated in vitro, and lysates were prepared using RIPA buffer which contains 1% Nonidet P-40, 0.5% deoxycholate, and 0.1% SDS. In contrast, when a lysis buffer containing 2% SDS was used, the caspases remained in their zymogen pro-forms, and no proteolytic processing of caspase substrates was detected. Moreover, in experiments using intact cells and a cell-permeable fluorigenic caspase substrate, no caspase activity was observed in activated T-cells, whereas it was clearly detected when PBLs were treated with the apoptosis-inducing anticancer drug etoposide. Since the granzyme B is a direct activator of caspase-3 and its expression is induced following T-cell activation, we tested the effects of anti-GraB, an engineered serpin that specifically inhibits GraB. When the activated T-lymphocytes were lysed in RIPA buffer containing anti-GraB, no proteolytic processing or activation of caspase-3 was observed, strongly suggesting that release of GraB or similar proteases from their storage sites in cytotoxic granules during the lysis procedure is responsible for caspase activation. These findings demonstrate that T-cells do not process caspases upon activation and caution about the method of cell lysis used when studying granzyme-expressing cells.

Discovery of podophyllotoxins

This review deals with the historical discovery of particularly important lignan derivatives used in cancer chemotherapy. From isolation of the naturally occurring podophyllotoxin, an inhibitor of microtubule assembly, to hemisynthesis of the clinically important anticancer drugs etoposide and tenoposide, it will be demonstrated how the activities and the ability of this class of compounds to inhibit topoisomerase II were discovered by different research teams. By virtue of these discoveries, new hemisynthetic derivatives, with different mechanisms of action, are bringing improvements in the ability to treat cancer.

In VitroPropagation ofPodophyllum peltatum

The lignan podophyllotoxin, occurring in Podophyllum emodi Wall, ex Royale and Podophyllum peltatum. L., is the starting compound for the semi-synthesis of the anticancer drugs etoposide and teniposide. In this study, we evaluate development of an in vitro propagation protocol to rapidly produce high yielding Podophyllum peltatum plants. Rhizome tips were inoculated on MS medium supplied with 4.4 microM N(6)-benzyladenine and 0.025% (w/v) activated charcoal. These explants formed terminal buds, similar to the ones found in nature. These buds were sources of in vitro bud cultures. These bud cultures were classified as: apical, axillary, and adventitious and the effects of various N(6)-benzyladenine concentrations on the three types of bud cultures were evaluated through bud, leaf, and root inductions. Cultures of axillary and adventitious buds were more proliferous for bud induction. Podophyllotoxin contents of in vitro rooted bud and plantlet cultures were similar to the content found in the wild. Plantlets and buds were acclimatized under controlled environment conditions.

The anti-cancer drug etoposide can induce caspase-8 processing and apoptosis in the absence of CD95 receptor-ligand interaction.

Caspase-8 (FLICE) can associate with and be activated by CD95 (APO-1/Fas), an apoptosis-inducing member of the Tumour Necrosis Factor receptor family. We find that, in Jurkat T cells, the DNA damaging anti-cancer drug etoposide induces apoptosis and, surprisingly, processing of caspase-8. Therefore, we have investigated whether etoposide involves CD95 receptor activation. We find that etoposide does not induce CD95 ligand expression at the mRNA level. In addition, blocking of CD95 receptor function with a specific antibody does not inhibit etoposide-induced apoptosis. Apparently, in Jurkat cells, etoposide can induce caspase-8 processing and apoptosis in a CD95-independent fashion. Likewise, we find that thymocytes from the CD95-deficient lpr/lpr mouse strain readily undergo apoptosis in response to etoposide. Moreover, since inhibition of the secretory pathway with brefeldin A does not inhibit etoposide-induced apoptosis, we exclude the requirement for a newly synthesized receptor ligand to induce the apoptotic pathway. We conclude that, at least in certain cell types, etoposide does not require CD95 receptor function to induce caspase-8 processing and apoptosis.

Prognostic factors in patients with pleural mesothelioma: the European Organization for Research and Treatment of Cancer experience.

Identification of prognostic factors in patients with malignant pleural mesothelioma based on prospectively collected international data. From October 1984 to October 1993, 204 eligible adult patients with malignant pleural mesothelioma were entered into five consecutive prospective European Organization for Research and Treatment of Cancer (EORTC) phase II clinical trials designed to assess the efficacy of various anticancer drugs (mitoxantrone, epidoxorubicin, etoposide, and paclitaxel). The Cox model was used to assess 13 factors related to biology and disease history with respect to survival. The median survival duration was 12.6 months from diagnosis and 8.4 months from trial entry. In the multivariate analysis, poor prognosis was associated with a poor performance status, a high WBC count, a probable/possible histologic diagnosis of mesothelioma, male gender, and having sarcomatous tissue as the histologic subtype. Taking these five factors into consideration, patients were classified into two groups: a good-prognosis group (1-year survival rate, 40%; 95% confidence interval [CI], 30% to 50%) and a poor-prognosis group (1-year survival, 12%; 95% CI, 4% to 20%). These results may help to design new clinical trials in pleural mesothelioma by selecting more homogenous groups of patients.

Determination of the cytotoxic catechol metabolite of etoposide (3′O-demethyletoposide) in human plasma by high-performance liquid chromatography

The anticancer drug etoposide undergoes O-demethylation in humans. The formed catechol metabolite exhibits significant cytotoxic activity. A simple, rapid, selective, and sensitive reversed-phase high-performance liquid chromatography assay was developed for the measurement of etoposide catechol in plasma of tumour patients. The metabolite was quantified using electrochemical detection. Ascorbic acid was added to each sample to prevent oxidation of etoposide catechol during sample preparation. Linear responses were obtained between 40 ng/ml and 1.25 μg/ml with correlation coefficients exceeding 0.991. The detection limit was 10 ng/ml. Recovery, within-day precision, between-day precision and accuracy were satisfactory. The method has been applied to characterize the concentration–time profile of etoposide catechol in plasma of tumour patients following administration of high-dose etoposide.

Treatment of the P815 murine mastocytoma with cisplatin or etoposide up-regulates cell-surface Fas (CD95) expression and increases sensitivity to anti-Fas antibody-mediated cytotoxicity and to lysis by anti-CD3-activated killer-T cells.

We have investigated the effect of pre-treatment with the anti-cancer drugs cisplatin and etoposide on the susceptibility of P815 murine mastocytoma cells to lysis by murine spleen-derived anti-CD3-activated killer-T (AK-T) cells. A 20 hr pre-treatment with cisplatin (0.2-2 microg/ml) or etoposide (0.01-1 microg/ml) rendered P815 cells significantly more sensitive to AK-T cell-mediated lysis in a 4 hr 51Cr-release assay than untreated control tumor cells. At lower concentrations, pre-treatment with cisplatin or etoposide had no direct cytotoxic effects on P815 tumor cells, as measured by the MTT assay. AK-T cell-mediated killing of P815 tumor cells pre-treated with 2 microg/ml cisplatin or 1 microg/ml etoposide was only partially inhibitable by the Ca2+ chelator EGTA, suggesting that the Ca2+-independent Fas (CD95)/Fas ligand cytolytic pathway of AK-T cells contributes to cytotoxicity. In comparison to untreated control P815 cells, 2 microg/ml cisplatin- or 1 microg/ml etoposide-treated P815 cells exhibited increased expression of Fas mRNA and cell-surface Fas, which correlated with increased sensitivity to lysis by AK-T cells. In addition, pre-treatment with cisplatin or etoposide caused P815 tumor cells to become sensitive to the cytotoxic effects of anti-Fas antibody in a 4 hr 51Cr-release assay. Taken together, our results demonstrate that short-term exposure to concentrations of cisplatin and etoposide in the low cytotoxic range and below up-regulates Fas expression by P815 tumor cells, thereby facilitating cytotoxicity mediated through the Fas/Fas ligand cytolytic pathway.

Listeriolysin O potentiates immunotoxin and bleomycin cytotoxicity.

Antitumor immunotoxins were formed by covalently attaching the ribosome-inactivating protein ricin A chain (RA) to the antitumor antibodies BR96 and L6. In vitro cytotoxicity assays established that BR96-RA was cytotoxic to H2987 human lung adenocarcinoma cells (IC50 = 6 nM), while L6-RA exhibited very low levels of cytotoxic activity (18% cell kill at 67 nM). The virulence factor from the intracellular pathogen Listeria monocytogenes, listeriolysin O (LLO), was able to potentiate the cytotoxicity of BR96-RA and L6-RA by 120- and > 1340-fold, respectively, resulting in IC50 values of approximately 50 pM. LLO also potentiated the cytotoxicity of the peptide anticancer drug bleomycin by a factor of > 2500 but had no effect on the cytotoxic activities of the anticancer drugs cytarabine and etoposide phosphate. In addition, LLO did not potentiate the cytotoxic activity of unconjugated ricin A chain or L6-RA on H2987 cells that were saturated with L6 prior to conjugate treatment. These results are attributed to LLO-induced alteration of the intracellular trafficking of molecules that are incorporated into acidic vesicles.

Increased sensitivity to anticancer drugs and decreased inflammatory response in mice lacking the multidrug resistance-associated protein.

The multidrug resistance-associated protein (MRP) mediates the cellular excretion of many drugs, glutathione S-conjugates (GS-X) of lipophilic xenobiotics and endogenous cysteinyl leukotrienes. Increased MRP levels in tumor cells can cause multidrug resistance (MDR) by decreasing the intracellular drug concentration. The physiological role or roles of MRP remain ill-defined, however. We have generated MRP-deficient mice by using embryonic stem cell technology. Mice homozygous for the mrp mutant allele, mrp-/-, are viable and fertile, but their response to an inflammatory stimulus is impaired. We attribute this defect to a decreased secretion of leukotriene C4 (LTC4) from leukotriene-synthesizing cells. Moreover, the mrp-/- mice are hypersensitive to the anticancer drug etoposide. The phenotype of mrp-/- mice is consistent with a role for MRP as the main LTC4-exporter in leukotriene-synthesizing cells, and as an important drug exporter in drug-sensitive cells. Our results suggest that this ubiquitous GS-X pump is dispensable in mice, making treatment of MDR with MRP-specific reversal agents potentially feasible.

Oncogenic transformation potentiates apoptosis, S-phase arrest and stress-kinase activation by etoposide.

The exact mechanisms for the selective toxicity of chemotherapeutic drugs against tumor cells are not fully understood. We designed a series of experiments to test the possibility that the positive proliferative signal initiated by oncogenes might change the sensitivity for apoptosis induction by the anticancer drug etoposide (VP16), an inhibitor of topoisomerase II (Topo II). Treatment with VP16 induced significantly increased apoptosis in NIH3T3 cells transformed by oncogenic src, ras or raf, compared with the normal 3T3 cells. Apopototic changes involved nuclear DNA fragmentation, morphological alterations and decreased viability. Furthermore it was shown that stress-activated protein kinase (SAPK) was activated much more strongly in all three transformed lines compared to untransformed cells by VP16 treatment, while slight activation of extracellular signal-regulated kinase (ERK1) was observed in all four cell lines. In addition, the transformed cells displayed arrest in mid-S-phase following the treatment, whereas NIH3T3 cells were primarily arrested in late S and G2/M phase. Finally, the cyclin-dependent kinase inhibitor p21 WAF1 was induced in all four cell lines, although induction of p53 was not detected in any of these cell lines. Taken together our results demonstrated that oncogenic transformation can sensitize the cells to apoptosis induction, stress kinase activation and cell cycle arrest in response to VP16 treatment. These results may have important implications for understanding the selective toxicity of anti-cancer drugs in tumor cells.

Induction of in vitro nuclear apoptosis activity coincides with the production of 50 kDa cytosolic protein.

Human monocytic leukemia U937 cells undergo apoptosis when cells are treated with the anticancer drug etoposide. To study the mechanism of drug-induced apoptosis, we used an in vitro apoptosis system with cytosol from etoposide-treated U937 cells. The cytosol from apoptotic U937 cells showed activity to induce morphologic changes and oligonucleosomal DNA fragmentation in isolated nuclei in vitro; both are typical features of apoptosis. We generated monoclonal antibodies to the proteins in the etoposide-treated U937 cytosol. We found that a 50 kDa protein, recognized by SN-1 monoclonal antibody, appeared in the cytosol of U937 cells, in accordance with its cell-free apoptosis activity. Z-Asp, an inhibitor of interleukin-1beta converting enzyme (ICE) family proteases, inhibited the appearance of the 50 kDa protein and the emergence of the cell-free apoptosis activity in the etoposide-treated U937 cytosol. These results indicate that the 50 kDa protein is produced by the activation of ICE family protease during apoptosis and suggest some roles of the protein in the development of apoptosis.

Azatoxin is a mechanistic hybrid of the topoisomerase II-targeted anticancer drugs etoposide and ellipticine.

One approach to broadening the diversity of topoisomerase II-targeted anticancer agents is to generate novel compounds by combining structural elements of drugs known to stimulate enzyme-mediated DNA cleavage. The first agent to emerge from such a rational drug design is azatoxin, a hybrid drug that fuses chemical structures from etoposide and ellipticine. Since these drugs differ significantly in their structural and mechanistic attributes, azatoxin may preferentially retain the functional properties of one of these two drugs, behave as a hybrid molecule, or act as a novel pharmacophore. Therefore, the properties of azatoxin were characterized to determine relationships between its mechanism of action and those of its parent compounds. Azatoxin, like etoposide, binds to DNA in a nonintercalative fashion. However, similar to ellipticine, the drug has no effect on enzyme-mediated DNA religation and apparently stimulates scission primarily by enhancing cleavage complex formation. Depending on the species of topoisomerase II examined, the cleavage potency of azatoxin resembles that of either of its chemical parents. Furthermore, out of 43 DNA cleavage sites analyzed, approximately 90% of those induced by azatoxin are shared with either etoposide, ellipticine, or both drugs. Finally, competition studies indicate that azatoxin interacts with topoisomerase II in the enzyme domain utilized by etoposide and ellipticine. Taken together, these results strongly suggest that azatoxin is a mechanistic hybrid of its parent compounds and shares functional properties with both drugs.

Expression of multidrug-resistance-associated protein (MRP) and chemosensitivity in human gastric cancer.

Evidence has accumulated that, in addition to the MDR1 gene-coded P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP) also mediates the multidrug resistance (MDR) of various human tumors. In the case of gastric cancer, there is little or no involvement of P-glycoprotein, and the mechanisms of MDR remain to be understood. To search for a possible relationship between expression of MRP and sensitivity to anti-cancer agents in gastric cancer, 4 gastric cancer cell lines, 43 human gastric carcinomas and 17 adjacent normal gastric tissue samples were analyzed. Expression of MRP mRNA was evaluated using reverse transcription PCR (RT-PCR) and Southern hybridization. Sensitivity of the test samples to the anti-cancer drugs cisplatin (CDDP), doxorubicin (DXR) and etoposide (VP-16) was examined using the MTT¿3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl [2H]-tetrazolium bromide¿ assay. Immunohistochemical staining with the use of the MRP antibody (MRPr1) was done to confirm the findings regarding the expression of mRNA levels. The MRP expression evaluated with RT-PCR and Southern hybridization as well as with immunohistochemical staining revealed that 23 of 43 gastric-cancer tissues (53.5%), 15 of 17 normal gastric tissues (88%) and 3 of 4 gastric-cancer cell lines (75%) were positive. The MTT assay showed that DXR was significantly more sensitive (p < 0.01) in gastric carcinoma tissues lacking MRP expression than in those with positive expression. The same tendency was seen with the other agents used. Of the cell lines, one which showed no MRP expression also had a higher sensitivity to CDDP, DXR and VP-16 than the other positive cases. These results show that MRP expression is involved in MDR of human gastric cancer and is inversely related to the chemosensitivity of tumor cells against some anticancer drugs.

Modulation of Multidrug Resistance by SDZ PSC 833 in Leukemic and Solid‐tumor‐bearing Mouse Models

P‐Glycoprotein inhibitors, including the nonimmunosuppressive cyclosporin D analog SDZ PSC 833 (PSC 833), have been developed to circumvent multidrug resistance. In the present study, the potential of PSC 833 in reversing multidrug resistance was evaluated in various systemic treatment models with leukemic and solid‐tumor‐bearing mice. Having a relatively wide therapeutic window of daily p.o. doses from 12.5 to 75 mg/kg, PSC 833 significantly improved the antileukemic activity of the anticancer drugs adriamycin (ADM), vincristine (VCR) and etoposide (VP‐16) given i.p. or i.v. against i.p.‐inoculated vincristine‐resistant P388 tumor (P388/VCR). PSC 833 in combination with i.p.‐injected anticancer drugs in optimal schedule and dosage induced apparent cures in some leukemic mice, whereas no cures were obtained with the cyclosporin A/anticancer drug combinations. PSC 833 combined with i.v.‐injected anticancer drugs was highly active, but not curative, against P388/VCR and parental P388 tumors (maximum T/C>175%). PSC 833 in combination with intravenous treatment with ADM showed prominent anti‐solid‐tumor activity against s.c.‐inoculated colon adenocarcinoma 26 and human colorectal adenocarcinoma HCT‐15. Against colon adenocarcinoma 26, the PSC 833/ADM combinations induced cure in two or three of six mice. PSC 833/ADM combinations significantly inhibited the growth of the tumor with maximum percent inhibitions of 83 and 73% in the early and advanced stages of the HCT‐15 tumor models, respectively. The present study demonstrated that PSC 833 is highly active in potentiating the antitumor activity of systemically administered ADM, VCR and VP‐16 against four murine and human tumors with a relatively wide therapeutic window of daily p.o. dose range of 12.5–100 mg/kg.

Alterations of nuclear p53 protein and proliferating cell nuclear antigen during anticancer drug-induced apoptosis of human hepatoma cells: a flow cytometric analysis

Anticancer drugs etoposide and mitomycin C caused apoptosis in human hepatoma cells. Flow cytometry disclosed that both nuclear level of p53 protein and the number of p53 protein-positive nuclei increased preceding the apoptosis. In contrast, the number of proliferating cell nuclear antigen (PCNA)-positive nuclei decreased in those cells cultured with anticancer drugs. Two-color flow cytometric patterns of p53 protein- and PCNA-positive nuclei were different in the control cells and in those treated with etoposide and mitomycin C. These findings suggest that cell cycle regulatory proteins play important roles in anticancer drug-induced apoptosis in human hepatoma cells.

Stability and compatibility of a mixture of the anti-cancer drugs etoposide, cytarabine and daunorubicine for infusion

We evaluated (i) the stability of a mixture of the three anti-cancer agents used for the treatment of leukemia, namely etoposide, cytarabine and daunorubicine, in 5% glucose, and (ii) its compatibility towards various materials during an infusion protocol as performed for therapeutic purposes in hospital practice. Etoposide and cytarabine were assayed by high-performance liquid chromatography with a C18 type column and UV detection. Daunorubicine was assayed by visible spectrophotometry. The stability study showed all three anti-cancer drugs to be stable in 5% glucose solution, both alone and mixed. Best conservation was obtained by keeping bottles containing the mixture in the dark at room temperature. During the infusion protocol used in clinical practice, etoposide, cytarabine and daunorubicine were stable and compatible with the various materials present in the infusion sets and extension tubing (polyvinyl chloride, polyethylene) and catheters (silicone). Observed variations in concentration did not exceed 10% of initial concentrations of each drug, though we would advocate changing infusion sets and extension tubing daily.

Apoptosis and nuclear levels of p53 protein and proliferating cell nuclear antigen in human hepatoma cells cultured with tumor promoters.

Anticancer drugs etoposide and mitomycin C increased nuclear p53 protein and decreased proliferating cell nuclear antigen (PCNA) of PLC/PRF/5 human hepatoma cells. These changes were followed by DNA fragmentation and apoptosis. Teleocidin antagonized both apoptosis and alterations of nuclear p53 protein and PCNA induced by these anticancer drugs. In contrast, thapsigargin antagonized only drug-induced nuclear accumulation of p53 protein. Therefore, the inhibition of apoptosis appears not to be the common mechanism of tumor promotion. Both tumor promoters suppressed the increase in nuclear p53 protein, suggesting that an inadequate DNA repair due to the reduced nuclear accumulation of p53 protein might be playing important role in enhancing carcinogenesis.

The solubilization of lipophilic derivatives of podophyllotoxins in sub-micron sized lipid emulsions and their cytotoxic activity against cancer cells in culture

Sub-micron sized lipid emulsions with lipophilic drugs entrapped in the oil core are a novel drug carrier system with many potential applications. In this study, lipophilic derivatives of the anticancer drugs etoposide and teniposide, with an unsaturated fatty acid esterified to the phenolic 4'-hydroxyl, were solubilized in lipid emulsions. The emulsion droplets formed (particle diameter 104 nm) showed good physical stability and no leakage of entrapped drug. The fatty acid derivatives were chemically stable in the lipid emulsion preparations in both buffer and serum-containing medium. The cytotoxic activity of the drug emulsions was assessed in vitro against K562 and T-47D cancer cells and compared to the effect of the parent drugs under the same conditions. The linoleic acid derivative of etoposide showed very much the same cytotoxic activity as the parent drug while the oleic acid derivative of teniposide demonstrated a very low activity against K562 cells and only modest activity against T-47D cells. These fatty acid derivatives of the highly potent anticancer agents etoposide and teniposide represent a valuable addition to the supply of drugs suitable for incorporation into drug delivery emulsions.

Cloning mammalian genes by expression selection of genetic suppressor elements: association of kinesin with drug resistance and cell immortalization.

We describe a general strategy for cloning mammalian genes whose downregulation results in a selectable phenotype. This strategy is based on expression selection of genetic suppressor elements (GSEs), cDNA fragments encoding either specific peptides that act as dominant inhibitors of protein function or antisense RNA segments that efficiently inhibit gene expression. Since GSEs counteract the gene from which they are derived, they can be used as dominant selectable markers for the phenotype associated with downregulation of the corresponding gene. A retroviral library containing random fragments of normalized (uniform abundance) cDNA expressed in mouse NIH 3T3 cells was used to select for GSEs inducing resistance to the anticancer drug etoposide. Three GSEs were isolated, two of which are derived from unknown genes and the third encodes antisense RNA for the heavy chain of a motor protein kinesin. The kinesin-derived GSE induces resistance to several DNA-damaging drugs and immortalizes senescent mouse embryo fibroblasts, indicating that kinesin is involved in the mechanisms of drug sensitivity and in vitro senescence. Expression of the human kinesin heavy-chain gene was decreased in four of four etoposide-resistant HeLa cell lines, derived by conventional drug selection, indicating that downregulation of kinesin represents a natural mechanism of drug resistance in mammalian cells.