Differential induction of apoptosis on human lymphoblastic leukemia Nalm-6 and Molt-4 cells by various antitumor drugs

Immunogenic Cell Death: A Step Ahead of Autophagy in Cancer Therapy

Immunogenic cell death (ICD) plays a major role in providing long lasting protective antitumor immunity by the chronic exposure of damage associated molecular patterns (DAMPs) in the tumor microenvironment (TME). DAMPs are essential for attracting immunogenic cells to the TME, maturation of DCs, and proper presentation of tumor antigens to the T cells so they can kill more cancer cells. Thus for the proper release of DAMPs, a controlled mechanism of cell death is necessary. Drug induced tumor cell killing occurs by apoptosis, wherein autophagy may act as a shield protecting the tumor cells and sometimes providing multi-drug resistance to chemotherapeutics. However, autophagy is required for the release of ATP as it remains one of the key DAMPs for the induction of ICD. In this review, we discuss the intricate balance between autophagy and apoptosis and the various strategies that we can apply to make these immunologically silent processes immunogenic. There are several steps of autophagy and apoptosis that can be regulated to generate an immune response. The genes involved in the processes can be regulated by drugs or inhibitors to amplify the effects of ICD and therefore serve as potential therapeutic targets.

The cardioprotective effects of L-carnitine on rat cardiac injury, apoptosis, and oxidative stress caused by amethopterin

Amethopterin is used as a chemotherapeutic agent, and its antioxidant activity is used to treat many cancer types. This study aimed to study the ameliorating effect of L-carnitine against amethopterin-induced cardiac injury and oxidative stress in male rats. Sixty male albino rats were equally divided into six groups; the first and second groups were the control and L-carnitine groups, respectively, while the third group was treated with amethopterin rat group; the fourth and fifth groups were co-treated and post-treated with amethopterin rat with L-carnitine, respectively, and the sixth group was self-treated with amethopterin rat group. Cholesterol, triglycerides, low-density lipoprotein (LDL), glutathione, and total protein levels in amethopterin group showed a significant decrease when compared with control group, while high-density lipoprotein (HDL), glutamic oxaloacetic transaminase (GOT), malondialdehyde (MDA), catalase, and nitric oxide (NO) levels in amethopterin group showed a significant increase when compared with control group. Cholesterol, triglycerides, LDL, GOT, MDA, and catalase levels in the self-treated group showed a significant increase when compared with amethopterin group, while glutathione, total protein, and NO levels in the self-treated group showed significant decrease when compared with amethopterin group. Many of abnormalities as moderate hydrophobic changes of myofibrillar structure with striations, myocardial atrophy, cytoplasmic vacuoles, edema, and leukocyte infiltration were detected in cardiac tissues in amethopterin rat group. A significant increase of the apoptotic protein p53 and CD68 immunoreactivity, despite a significant decrease in the antiapoptotic Bcl-2 proteins after amethopterin injection when compared with control group, was observed. Treatment (co and post) with L-carnitine improved the biochemical, histopathological, and immunohistochemical alterations in the heart treated with amethopterin.

Effects of pentoxifylline and alpha lipoic acid on methotrexate-induced damage in liver and kidney of rats

The aim of the current study was to investigate the probable protective effects of Pentoxifylline (PTX) and Alpha Lipoic Acid (ALA), which display anti-oxidative efficacy against hepatotoxicity and nephrotoxicity, those being the major side effects of Methotrexate (MTX). Rats were divided into four groups: a control group; MTX (20mg/kg/day) group; MTX+PTX (20mg/kg/day+50mg/kg/day) group; and an MTX+ALA (20mg/kg/day+100mg/kg/day) group. At the end of the experiment, biochemical, histochemical and immunohistochemical analyses were performed on liver and kidney tissues of rats. We determined Glutathione Peroxidase (GSH-Px), Superoxide Dismutase (SOD), Catalase (CAT), Malondialdehyde (MDA), Nitric Oxide (NO) and Xanthine Oxidase (XO) levels in the liver and kidney. Moreover, Gamma Glutamyl Transferase (GGT), Direct Bilirubin (DBil), Blood Urea Nitrogen (BUN), and urea levels were measured in the serum. The histochemical evaluation revealed a significant decrease in MTX caused damage in the PTX- and ALA-treated groups (especially in ALA group). On the other hand, the immune staining of iNOS and TNF-α were observed most densely in the MTX group, while the density decreased in the PTX- and ALA-administered groups. We determined increased GGT, BUN, urea and levels of CAT, MDA, NO, and XO values in both groups, while GSH-Px (an increase in liver tissue) and DBil levels were decreased in the group that received MTX. However, we determined decreased SOD levels in liver tissue. In the PTX and ALA groups, the levels of GGT, BUN and urea as well as the levels of CAT, MDA, NO and XO decreased (SOD increased in the liver tissue), and the levels of GSH-Px and DBil increased. In conclusion, it can be stated that, although ALA is more effective in preventing the toxic effects of MTX on the liver and kidney, PTX also has a preventive effect. As a result, we can readily suggest that ALA and PTX can have protective effects by decreasing MDA, NO, BUN and urea values as antioxidants against MTX-induced damage in liver and kidney of rats.

Role of base-excision repair in the treatment of childhood acute lymphoblastic leukaemia with 6-mercaptopurine and high doses of methotrexate

Methotrexate (MTX) and 6-mercaptopurine (6MP) are the most commonly used drugs in the therapy of childhood acute lymphoblastic leukaemia (ALL). The main genotoxic effect of MTX resulting from inhibition of thymidylate synthase is mis-incorporation of uracil into DNA, which is considered essential for the effectiveness of the Protocol M in ALL IC BFM 2002/EURO LB 2002 regimens. In this study, we investigated the level of basal and induced DNA damage as well as the effectiveness of DNA repair in lymphocytes of children with ALL at four time-points during therapy with MTX and 6MP. To assess DNA damage and the efficacy of DNA repair we used the modified alkaline comet assay with uracil DNA glycosylase (Udg) and endonuclease III (EndoIII). In addition, we examined the induction of apoptosis in the lymphocytes of the patients during treatment. Finally, we compared the activity of base-excision repair (BER), involved in removal of both uracil and oxidized bases from DNA in lymphocytes of children with ALL and lymphocytes of healthy children. BER efficiency was estimated in an in vitro assay with cellular extracts and plasmid substrates of heteroduplex DNA with an AP-site. Our results indicate that there is a significant decrease in the efficacy of DNA repair associated with an increased level of uracil in DNA and induction of apoptosis during therapy. Moreover, it was found that the BER capacity was decreased in the lymphocytes of ALL patients in contrast to that in lymphocytes of healthy children. Thus, we suggest that an impairment of the BER pathway may play a role in the pathogenesis and therapy of childhood ALL.

Sequential cytotoxicity: a theory examined using a series of 3,5-bis(benzylidene)-1-diethylphosphono-4-oxopiperidines and related phosphonic acids

The concept of sequential cytotoxicity, which states that successive chemical attacks on cellular constituents can be more deleterious to neoplasms than normal cells, was evaluated using a series of 3,5-bis(benzylidene)-1-diethylphosphono-4-oxopiperidines 1 and related phosphonic acids 2, which were screened against a panel of malignant and normal cell lines. The compounds proved to be not only potent cytotoxins (71% of the CC(50) figures are submicromolar) but to display greater cytotoxicity to the neoplastic cells. QSAR revealed that both cytotoxic potencies and selective toxicity were increased by a rise in the electron-withdrawing properties and a decrease in the hydrophobicity of the aryl substituents. Utilisation of the PL10 concept and evaluation of druglike properties revealed 1c as the lead tumour-specific cytotoxin. This molecule activated caspase-3 in HL-60 cells but not in the HSC-2 cell line. While 1c caused internucleosomal DNA fragmentation in HL-60 cells, it did not elicit this effect in either HSC-2 and HSC-4 cells. Clearly 1c exerts its cytotoxic potencies by different mechanisms and such pleiotropy is likely the principal reason for the remarkable display of preferential toxicity towards malignant cells of the compounds in series 1 and 2.

Protective effect of beta-carotene on methotrexate-induced oxidative liver damage

In this study, the authors aimed to investigate the role of oxidative stress on the hepatic damage caused by methotrexate (MTX) and the possible protective effects of beta-carotene against this damage. The rats were divided into four groups as control, MTX (20 mg/kg ip), beta-carotene (10 mg/kg/day ip) + MTX, and beta-carotene. Histopathologic alterations were evaluated for defining the liver damage. The tissue, malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GP-x) contents and serum aspartate aminotransferase (AST) and alanine aminotranferase (ALT) activities were also examined. Histopathologic damage for each group score findings have been determined as control: 0.66 +/- 0.33; MTX: 7.0 +/- 0.68; beta-carotene + MTX: 3.3 +/- 0.42; and beta-carotene: 0.5 +/- 0.3. In the MTX-treated group, MDA, AST, and ALT values were increased, while SOD and GP-x values were decreased compared with the control group. In the beta-carotene + MTX-treated group, AST and ALT values significantly decreased, while all other parameters were similar to the control group. This study shows that beta-carotene has a protective effect on MTX-induced oxidative hepatic damage. Consequently, it seems that an antioxidant agents like beta-carotene may be useful in decreasing the side effects of chemotherapy.

Role of ursodeoxycholic acid in prevention of methotrexate-induced liver toxicity

AIM

Methotrexate (MTX)-induced hepatotoxicity restricts the clinical use of this immunosuppressive drug. In this study, our aim was to research the role of oxidative stress in the hepatic toxicity of MTX and the protective effect of ursodeoxycholic acid (UDCA) in this setting.

METHODS

Wistar type rats (n = 32) were divided into four groups; group-1 as the MTX + UDCA, group-2 as the MTX, group-3 as the UDCA, group-4 as the saline-receiving groups. The MTX + UDCA and MTX groups of rats received 50 mg/kg of UDCA administered orally; whilst physiological saline was administered orally to the MTX and saline groups and continued for the next 6 days. On the second day of the study, the MTX + UDCA and MTX groups had a single intraperitoneal dose of MTX of 20 mg/kg. The UDCA and saline groups also received similar volumes of physiological saline intraperitoneally. On the sixth day, serum samples were collected and analyzed for ALT, alkaline phosphatase (ALP) and gamma glutamyl transpeptidase (GGT) and homogenated liver tissues were examined for reactive oxygen metabolites (ROM); luminol, lucigenin, lipid peroxygenation product malondialdehyde (MDA) and glutathione (GSH) levels.

RESULTS

In the MTX group, serum ALT, ALP, GGT and tissue ROM levels were higher and GSH level was lower. On the histopathological examination, hepatocellular necrosis was clearly more evident in the MTX group than the MTX + UDCA group.

CONCLUSIONS

UDCA treatment protects against MTX-induced liver toxicity. Histopathologically hepatocyte necrosis can be prevented by UDCA treatment, indicating clearly the hepatoprotective effect of this agent on MTX-induced liver injury.

1-Aryl-2-dimethylaminomethyl-2-propen-1-one hydrochlorides and related adducts: A quest for selective cytotoxicity for malignant cells

The primary objective of this study was to discover one or more clusters of compounds which are not equitoxic but display cytoselectivity toward different malignant cells. Furthermore a most important consideration is that such molecules should also display greater cytotoxic potencies to tumors than normal tissues. Two series of compounds are described which meet these criteria, namely the 1-aryl-2-dimethylaminomethyl-2-propen-1-one hydrochlorides 1a-e and 1-aryl-3-dimethylamino-2-hydroxymethyl-1-propanone hydrochlorides 2a-e. A number of these compounds possess marked cytotoxic potencies (IC(50) and CC(50) values within the 10(-6) and 10(-7) molar range) which are greater than these of the reference drug melphalan. Statistical analyses demonstrated that cytotoxic potencies are influenced by the size of the aryl substituents in series 1 and to some extent by the electronic properties of the aryl groups in series 2. The mode of action of a representative compound 1e in HL-60 cells included inducing apoptosis and activation of caspases -3, -8, and -9.

3-(3,4,5-Trimethoxyphenyl)-1-oxo-2-propene: A novel pharmacophore displaying potent multidrug resistance reversal and selective cytotoxicity

This study revealed that various alicyclic and acyclic compounds containing the 3-(3,4,5-trimethoxyphenyl)-2-propenoyl group displayed potent MDR reversal properties. In particular, a concentration of 4 microg/ml of 2,5-bis(3,4,5-trimethoxyphenylmethylene)cyclopentanone was 31 times more potent than verapamil as a MDR revertant. In general, they were selectively toxic to malignant rather than normal cells. Two representative compounds induced apoptosis in human HL-60 cells and markedly activated caspase-3.

Induction of caspase-3 activated DNase mediated apoptosis by hexane fraction of Tinospora cordifolia in EAT cells

Tinospora cordifolia (Guduchi) has been used for centuries for treating various ailments including cancer in Ayurvedic system of medicine. In this study, we report the mechanism of cell death exhibited by the hexane extract fraction of T. cordifolia (TcHf) against Ehrlich ascites tumor (EAT) in mice. Treatment of EAT bearing animals with TcHf resulted in growth inhibition and induction of apoptosis in a dose-dependent manner. TcHf induced the formation of apoptotic bodies, nuclear condensation, typical DNA ladder, activation of caspase-3, decreased cell number and ascites volume. We examined TcHf for its effect on proliferation and cell cycle progression in EAT cells. The results showed that TcHf inhibited the proliferation of EAT cells by blocking cell cycle progression in the G1 phase. In Western blot analysis, apoptosis in the EAT cells was associated with the constitutive expression of caspase activated DNase (CAD) in both nucleus and cytoplasm after TcHf treatment. Further more the expression of pro-apoptotic gene, Bax, was increased and the expression of anti-apoptotic gene, Bcl-2, was decreased in a time dependent manner by TcHf treatment. All results indicate that the hexane fraction of T. cordifolia is capable of inducing apoptosis in EAT cells in vivo.

The BCL2 major breakpoint region (mbr) regulates gene expression

BCL2 expression is finely tuned by a variety of environmental and endogenous stimuli and regulated at both transcriptional and post-transcriptional levels. Our previous investigations demonstrated that the BCL2 major breakpoint region (mbr) in the 3'-UTR upregulates reporter gene expression, which implies that this region possessed intrinsic regulatory function. However, the effect of the mbr on BCL2 expression, and the underlying regulatory mechanisms, remain to be elucidated. To assess the direct effect of the mbr on the transcriptional activity of the BCL2 gene, we employed targeted homologous recombination to establish a mbr(+)/mbr(-) heterozygous Nalm-6 cell line and then compared the transcriptional activity and apoptotic effect on transcription between the wild type and targeted alleles. We found that deletion of the mbr significantly decreased the transcriptional activity of the corresponding allele in the mbr(+)/mbr(-) cell. The BCL2 allele deleted of the mbr had a slower response to apoptotic stimuli than did the wild type allele. The regulatory function of the mbr was mediated through SATB1. Overexpression of SATB1 increased BCL2 expression, while knockdown of SATB1 with RNAi decreased BCL2 expression. Our results clearly indicated that the mbr could positively regulate BCL2 gene expression and this regulatory function was closely related to SATB1.

Design, synthesis and cytotoxic properties of novel 1-[4-(2-alkylaminoethoxy)phenylcarbonyl]-3,5-bis(arylidene)-4-piperidones and related compounds

The 3,5-bis(arylidene)-4-piperidones 1 contain the 1,5-diaryl-3-oxo-1,4-pentadienyl pharmacophore which is considered to interact at a complementary binding site in susceptible neoplasms. The hypothesis was formulated that the presence of an acyl group attached to the piperidyl nitrogen atom in series 1 may interact with an additional binding site thereby enhancing cytotoxic potencies. This concept led to the synthesis of various N-acyl-3,5-bis(arylidene)-4-piperidones 3-7 many of which displayed significant cytotoxicity towards a variety of cancer cell lines. A comparison of the potencies between the compounds in series 1 and the related nonquaternary analogues 3-6 revealed that in approximately half of the comparisons made, the N-acyl analogues had increased potencies.

Cytotoxic 5-aryl-1-(4-nitrophenyl)-3-oxo-1,4-pentadienes mounted on alicyclic scaffolds

The 5-aryl-1-(4-nitrophenyl)-3-oxo-1,4-pentadienyl pharmacophore was incorporated into four series of compounds 1-4. Compounds 1a-g comprised a cluster of 3-arylidene-1-(4-nitrophenylmethylene)-2-oxo-3,4-dihydro-1H-naphthalenes while the analogues 2a-g consisted of a group of 6-arylidene-2-(4-nitrophenylmethylene)cyclohexanones. Three other compounds prepared in this study were 1-(4-nitrophenylmethylene)-3-(3,4,5-trimethoxyphenylmethylene)-2-oxo-2,3-dihydro-1H-indene 3a as well as two 5-arylidene-2-(4-nitrophenylmethylene)cyclopentanones 4a,b. The compounds were evaluated against human Molt 4/C8 and CEM T-lymphocytes as well as murine L1210 cells. In general, the compounds in series 1 displayed marked cytotoxicity having IC50 values in the 1-5 microM range while the related cyclohexyl analogues in series 2 were slightly less potent (IC50 figures were mainly 5-10 microM). The relative locations of two aryl rings present in all four series were considered to contribute significantly to bioactivity and may have accounted for the virtual absence of cytotoxic properties in series 3 and 4. Most of the compounds were administered intraperitoneally to mice using doses up to and including 300 mg/kg. No mortalities were noted. The inhibiting effect of most of the compounds towards Helicobacter pylori is noteworthy. The modes of action of representative compounds include the induction of apoptosis while some compounds weakly inhibited tubulin polymerisation and human N-myristoyltransferase.

The activities of purine-catabolizing enzymes and the level of nitric oxide in rat kidneys subjected to methotrexate: Protective effect of caffeic acid phenethyl ester

The aim of this experimental study was to investigate the possible role of nitric oxide (NO) levels, and activities of adenosine deaminase (ADA) and xanthine oxidase (XO) in the pathogenesis of methotrexate-induced nephrotoxicity, and was the effect of caffeic acid phenethyl ester (CAPE), the potent free radical scavenger, in decreasing the toxicity. A total of 19 adult male rats were divided into three experimental groups, as follows: control group, MTX-treated group, and MTX+CAPE treated group. MTX were administered intraperitoneally (i.p.) with 20 mg/kg for single dose. CAPE was administered i.p. with a dose of 10 micromol//kg once daily for 7 days. The injection of MTX induced a significant increase in the activities of ADA and XO, and NO levels in renal tissue of rats (p < 0.0001). Co-treatment with CAPE caused a significantly decrease activities of ADA and XO, and the levels of NO in renal tissue (p < 0.0001). The results of this study revealed that NO, XO and ADA may play an important role in the pathogenesis of MTX-induced oxidative renal damage. CAPE may have protective potential in this process and it will become a promising drug in the prevention of this undesired side effect of MTX.

Mechanism of mahanine-induced apoptosis in human leukemia cells (HL-60)

Mahanine, a carbazole alkaloid occurs in the edible part of Micromelum minutum, Murraya koenigii and related species has been found to induce apoptosis in human myeloid cancer cell (HL-60). Concentration of 10 microM mahanine caused a complete inhibition of cell proliferation and the induction of apoptosis in a time dependent manner. Mahanine-induced cell death was characterized with the changes in nuclear morphology, DNA fragmentation, activation of caspase like activities, poly(ADP-ribose) polymerase cleavage, release of cytochrome c into cytosol and stimulation of reactive oxygen species generation. The cell death was completely prevented by a pancaspase inhibitor benzyloxycarbonyl-L-aspart-1-yl-[(2,6-dichlorobenzoyl)oxy]methane (Z-Asp-CH(2)-DCB). Mahanine activated various caspases such as caspase-3, -6, -8 and -9 (like) activities but not caspase-1 like activity. More than 70% cell survival was observed in the presence of a caspase-3 inhibitor. In addition, co-treatment of cyclosporin A markedly increased the survival of mahanine-treated HL-60 cells. Flow cytometric analysis revealed that mahanine decreased the mitochondrial membrane potential of intact cells, and disrupted cell cycle progression by increasing the number of cells in sub-diploid region, concomitantly with the decrease of cells in diploid phases, particularly at late hours of apoptosis. The overall results suggest that mahanine down regulates cell survival factors by activation of caspase-3 through mitochondrial dependent pathway, and disrupts cell cycle progression.

Treatment-specific changes in gene expression discriminate in vivo drug response in human leukemia cells

To elucidate the genomics of cellular responses to cancer treatment, we analyzed the expression of over 9,600 human genes in acute lymphoblastic leukemia cells before and after in vivo treatment with methotrexate and mercaptopurine given alone or in combination. Based on changes in gene expression, we identified 124 genes that accurately discriminated among the four treatments. Discriminating genes included those involved in apoptosis, mismatch repair, cell cycle control and stress response. Only 14% of genes that changed when these medications were given as single agents also changed when they were given together. These data indicate that lymphoid leukemia cells of different molecular subtypes share common pathways of genomic response to the same treatment, that changes in gene expression are treatment-specific and that gene expression can illuminate differences in cellular response to drug combinations versus single agents.

A new bis-indole, KARs, induces selective M arrest with specific spindle aberration in neuroblastoma cell line SH-SY5Y

KARs, new semisynthetic antitumor bis-indole derivatives, were found to be inhibitors of tubulin polymerization with lower toxicity than vinblastine or vincristine, used in chemotherapy. Here, we compare the effect of KARs with those of vinblastine and vincristine on cell viability, cell proliferation, and cell cycle in neuroblastoma cell line (SH-SY5Y). At concentrations of the different compounds equivalent in causing 50% of inhibition of cell growth, KARs induced a complete arrest in the G2/M phase, whereas vinblastine and vincristine induced a partial arrest in both G0/G1 and G2/M. Moreover, a combination of KAR-2 and W13 (an anticalmodulin drug) qualitatively caused a similar arrest in both G0/G1 and G2/M than vinblastine. Levels of cyclin A and B1 were higher in KARs-treated cells than in vinblastine- or vincristine-treated cells. Cdc2 activity was much higher in KAR-2 than in vinblastine-treated cells, indicating a stronger mitotic arrest. The effect of KAR2 and vinblastine on microtubules network was analyzed by immunostaining with anti-tubulin antibody. Results indicated that KAR-2-induces the formation of aberrant mitotic spindles, with not apparent effect on interphase microtubules, whereas vinblastine partially destroyed interphase microtubules coexisting with normal and aberrant mitotic spindles.

Different effects of methotrexate on DNA mismatch repair proficient and deficient cells

Antifolates exert their antiproliferative activity through the inhibition of dihydrofolate reductase and, as a consequence, of thymidylate synthesis, thereby inducing nucleotide misincorporation and impairment of DNA synthesis. We investigated the processes involved in the repair of antifolate-induced damage and their relationship with cell death. Since misincorporated bases may be removed by DNA mismatch repair (MMR), the study was carried out on the MMR-proficient human cell lines HeLa and HCT116+chr3, and, in parallel, on the MMR-deficient cell lines HeLa cell-clone12, defective in the protein hPMS2, and HCT116, with an inactive hMLH1. After treatment with methotrexate (MTX), we observed that DNA repair synthesis occurs independently of the cellular MMR function. Clear signs of apoptosis such as nuclear shrinkage, chromatin condensation and degradation, DNA laddering, and poly (ADP-ribose) polymerase (PARP) proteolysis, were visible in both MMR(+) and MMR(-) cells. Remarkably, cell viability was lower and the apoptotic process was triggered more efficiently in the MMR-competent cells.

A conformational and structure-activity relationship study of cytotoxic 3,5-bis(arylidene)-4-piperidones and related N-acryloyl analogues

A series of 3,5-bis(arylidene)-4-piperidones 1 and related N-acryloyl analogues 2 were prepared as candidate cytotoxic agents with a view to discerning those structural features which contributed to bioactivity. A number of the compounds were markedly cytotoxic toward murine P388 and L1210 leukemic cells and also to human Molt 4/C8 and CEM neoplasms. Approximately 40% of the IC50 values generated were lower than the figures obtained for melphalan. In virtually all cases, the N-acyl compounds were significantly more bioactive than the analogues 1. In general, structure-activity relationships revealed that the cytotoxicity of series 1 was correlated positively with the size of the aryl substituents, while in series 2, a -sigma relationship was established. In particular, various angles and interatomic distances were obtained by molecular modeling, and the presence of an acryloyl group on the piperidyl nitrogen atom in series 2 affected the relative locations of the two aryl rings. This observation, along with some differences in distances between various atoms in series 1 and 2, may have contributed to the disparity in cytotoxicity between 1 and 2. The results obtained by X-ray crystallography of representative compounds were mainly in accordance with the observations noted by molecular modeling. Selected compounds interfered with the biosynthesis of DNA, RNA, and protein in murine L1210 cells, while others were shown to cause apoptosis in the human Jurkat leukemic cell line. This study has revealed the potential of these molecules for development as cytotoxic and anticancer agents.

Cytotoxic 2,6-bis(arylidene)cyclohexanones and related compounds

A number of 2-arylidenecyclohexanones 1, 2, 6-bis(arylidene)cyclohexanones 2 and related Mannich bases 3-5 were prepared. Various torsion angles as well as atomic charges on olefinic carbon atoms were determined by molecular modelling on all compounds. These molecules showed cytotoxicity towards murine P388 and L1210 cells as well as to human Molt 4/C8 and CEM T-lymphocytes. The average cytotoxicity of the dienones 2 was more than three times greater than was found with the monoarylidene analogues 1, and, in general, were slightly more cytotoxic than the Mannich bases 3-5. A number of the compounds displayed potency towards a panel of human tumour cell lines and most of the representative compounds in series 2-5 were selectively toxic to colon cancers and leukaemic cells.

Sequential cytotoxicity: a theory evaluated using novel 2-[4-(3-aryl-2-propenoyloxy)phenylmethylene]cyclohexanones and related compounds

Five series of novel compounds were synthesized in order to evaluate the theory of sequential cytotoxicity which seeks to exploit the view that various cancer cells are particularly susceptible to successive attacks by cytotoxic agents. The compounds prepared were various 2-[4-(3-aryl-2-propenoyloxy)phenylmethylene]cyclohexanone s 1 and the related Mannich bases 2. In addition the analogues 3-5 lacking an olefinic bond in the ester group were also synthesized, which were predicted to be less cytotoxic than the compounds of series 1 and 2. The atomic charges at the potential sites for interaction with cellular constituents were determined by molecular modeling calculations. The biodata obtained from murine and human neoplastic cells revealed that the predictions made regarding the viability of the theory were fulfilled in approximately two-thirds of the cases indicating that further investigation of this hypothesis is warranted. In addition, the significant potencies of some of the Mannich bases toward human tumor cell lines, in particular coupled to their selective toxicity toward human leukemic and colon cancer cells, confirms their usefulness in serving as lead molecules for further development. A preliminary investigation into the mode of action of representative compounds revealed their ability to induce apoptosis and inhibit the biosyntheses of ribonucleic acid and proteins.

Relative level of expression of Bax and Bcl-XL determines the cellular fate of apoptosis/necrosis induced by the overexpression of Bax

The Bax protein plays a critical role in the apoptosis of cancers induced by radiotherapy or chemotherapy, which induce both apoptosis and necrosis. We transduced various glioblastoma cells with the Bax gene via an adenoviral vector and found that A-172 cells led to necrotic cell death, while U251 cells apoptotic cell death, even though a similar level of Bax protein was introduced. A-172 cells displayed a much higher constitutive expression of the Bcl-XL protein compared with that of U251 cells. Upon simultaneous overexpression of the Bcl-XL and Bax proteins in the U251 cells, Bax-induced apoptosis of U251 cells was suppressed and an increase in the number of necrotic cells was seen. Moreover, induction of a higher amount of Bax protein in A-172 cells increased the percentage of apoptotic cells. In conclusion, if a cancerous cell expresses a high enough amount of Bax to undergo death, apoptosis will be induced. If a cancerous cell expresses a level of Bcl-XL which prevents Bax-induced apoptosis, the overexpression of Bax leads to necrotic cell death.

Inducers of cytochrome P450 2E1 enhance methotrexate-induced hepatocytoxicity

OBJECTIVES

To study the effect of cytochrome P450 2E1-inducers on methotrexate (MTX)-induced cytotoxicity in human hepatocytes, and investigate the role of silymarin in preventing this toxicity.

DESIGN AND METHODS

Cells were exposed to MTX in the presence of either ethanol (EtOH) or acetaminophen (APAP), or either combined with silymarin (S). Apoptosis and necrosis were measured by analyzing 6000 cells/sample using transmission electron microscopy, while cytokine release and apoptosis were quantitated by ELISA. Cytokine expression was measured by RT-PCR. Gluthatione (GSH) content was determined in cytosolic (c) and mitochondrial (m) fractions.

RESULTS

MTX+EtOH and MTX+APAP increased MTX cytotoxicity 2.9-fold and 1.9-fold, respectively. S abolished this toxicity. MTX + EtOH increased the release of IL 6, IL 8 and TNF alpha by 1.0, 1.2, and 1.1 times, respectively. Cytokine expression was upregulated versus control for IL 6 (22%), IL 8 (38%), and TNF alpha (29%). Addition of 0.5 mmol/L S downregulated TNF alpha expression and reduced cytokine release. TNF alpha increased cytotoxicity by 22%, while anti-TNFalpha antibody eradicated it. MTX+EtOH depleted 45% mGSH (0 < 0.001) while S replenished it to 87% (p < 0.001), when both were compared to control levels.

CONCLUSIONS

Cytochrome P450 2E1-inducers contribute to increase oxidative stress in MTX-exposed cells by increasing TNF alpha and depleting both cGSH and mGSH. This enhances MTX-cytotoxicity and promotes apoptosis.

Oxythiamine and dehydroepiandrosterone induce a G1 phase cycle arrest in Ehrlich's tumor cells through inhibition of the pentose cycle

Transketolase (TK) reactions play a crucial role in tumor cell nucleic acid ribose synthesis utilizing glucose carbons, yet, current cancer treatments do not target this central pathway. Experimentally, a dramatic decrease in tumor cell proliferation after the administration of the TK inhibitor oxythiamine (OT) was observed in several in vitro and in vivo tumor models. Here, we demonstrate that pentose cycle (PC) inhibitors, OT and dehydroepiandrosterone (DHEA), efficiently regulate the cell cycle and tumor proliferation processes. Increasing doses of OT or DHEA were administered by daily intraperitoneal injections to Ehrlich's ascites tumor hosting mice for 4 days. The tumor cell number and their cycle phase distribution profile were determined by DNA flow histograms. Tumors showed a dose dependent increase in their G0-G1 cell populations after both OT and DHEA treatment and a simultaneous decrease in cells advancing to the S and G2-M cell cycle phases. This effect of PC inhibitors was significant, OT was more effective than DHEA, both drugs acted synergistically in combination and no signs of direct cell or host toxicity were observed. Direct inhibition of PC reactions causes a G1 cell cycle arrest similar to that of 2-deoxyglucose treatment. However, no interference with cell energy production and cell toxicity is observed. PC inhibitors, specifically ones targeting TK, introduce a new target site for the development of future cancer therapies to inhibit glucose utilizing pathways selectively for nucleic acid production.

Conformational and quantitative structure-activity relationship study of cytotoxic 2-arylidenebenzocycloalkanones

Various 2-arylideneindanones 1, 2-arylidenetetralones 2, and 2-arylidenebenzosuberones 3 were synthesized with the aim of determining the relative orientations of the two aryl rings which favored cytotoxicity. Molecular modeling of the unsubstituted compound in each series revealed differences in the spatial arrangements of the two aryl rings, and evaluation of these compounds against P388, L1210, Molt 4/C8, and CEM cells as well as a panel of human tumor cell lines indicated that in general the order of cytotoxicity was 3 > 2 > 1. In particular 2-(4-methoxyphenylmethylene)-1-benzosuberone (3k) had the greatest cytotoxicity, possessing 11 times the potency of the reference drug melphalan when all five screens were considered. Series 3 was considered in further detail. First, excision of the aryl ring fused to the cycloheptanone moiety in series 3 led to some 2-arylidene-1-cycloheptanones 4 which had approximately one-third of the bioactivity of the analogues 3. Second, in some screens cytotoxicity was correlated negatively with the sigma values and positively with the MR constants of the substituents in the arylidene aryl ring of 3. Third, X-ray crystallography of five representative compounds (3i,k-n) revealed differences in the locations of the aryl rings which may have contributed to the variations in cytotoxicity. Finally three members of series 3 inhibited RNA and protein syntheses and induced apoptosis in human Jurkat T cells. This study has revealed that 2-arylidene-1-benzosuberones are a group of useful cytotoxic agents, and in particular 3k serves as a prototypic molecule for subsequent structural modifications.

Caspase proteases mediate apoptosis induced by anticancer agent preactivated MC540 in human tumor cell lines

The molecular events involved in tumor cell death induced by novel photoproducts of merocyanine 540 (pMC540) are poorly understood. Using HL60 leukemia and M14 melanoma cell lines we investigated the role of the apoptotic pathway in pMC540-mediated cell death. Tumor cells exposed to pMC540 showed cell size shrinkage and an increase in the sub-diploid DNA content. A loss of membrane phospholipid asymmetry associated with apoptosis was induced by pMC540 in both tumor cell lines as evidenced by the externalization of phosphatidylserine. A dose-dependent increase in caspase-3 protease activity suppressed by the tetrapeptide inhibitor DEVD-CHO was observed in both cell lines. Western blot analysis of poly (ADP-ribose) polymerase, a caspase substrate, showed the classical cleavage pattern (116 to 89 kDa) associated with apoptosis in pMC540-treated cell lysates. Furthermore, caspase inhibition blocked the externalization of membrane PS, indicating that the loss of membrane phospholipid asymmetry is a downstream event of caspase activation. These findings demonstrate that tumor cell death induced by pMC540 is mediated by caspase proteases.