From bench to clinic with apoptosis-based therapeutic agents

Maspin suppresses survival of lung cancer cells through modulation of Akt pathway

PURPOSE

Maspin is a tumor suppressor protein that has been reported to stimulate the cell death of cancer and inhibit the metastasis of cancer. The present study aimed to explore the survival pathway by which maspin modulates the resistance of human lung cancer cells to chemotherapeutic drugs, and the consequences of maspin gene therapy in an animal model.

MATERIALS AND METHODS

NCI-H157 and A549 cells were transfected with either a mock vector (pCMVTaq4C), maspin (pCMV-maspin), siControl or siMaspin. RT-PCR and Western blot analysis were performed to study the expressions of survival proteins in lung cancer. cDNA microarray analysis was carried out to compare the maspin-modulated gene expression between the xenograft tumors derived from the lung cancer cells that were stably transfected with pCMVTaq4C or pCMV-maspin. Maspin gene therapy was performed by intra-tumoral injections of pCMVTaq4C or pCMV-maspin into the pre-established subcutaneous tumors in nude mice.

RESULTS

Maspin significantly decreased the survival to doxorubicin and etoposide, whereas did not affect the survival to cisplatin in the NCI-H157 cells. Interestingly, transfection with a maspin plasmid resulted in a significant reduction of the phosphorylation of Akt in the NCI-H157 cells, whereas knockdown of maspin increased the phosphorylation of Akt in the A549 cells. Microarray analysis of the xenograft tumors revealed a specific gene expression profile, demonstrating that maspin is associated with the differential expressions of PTEN and IGF2R. Direct transfer of pCMV-maspin into the tumor significantly retarded the tumor growth in the animal experiments (p=0.0048).

CONCLUSION

Lung cancer cells lacking maspin could be resistant to chemotherapeutic drugs such as doxorubicin or etoposide, at least in part by maintaining Akt phosphorylation.

Design and Synthesis of Potential New Apoptosis Agents: Hybrid Compounds Containing Perillyl Alcohol and New Constrained Retinoids

Novel retinoids 1-3 containing perillyl alcohol were synthesized through the addition of perillyl alcohol to the activated carboxylic acids (retinoids) promoted by DCC (N, N'-Dicylohexyl cabodiimide). A set of structurally and functionally diverse perillyl alcohol derivatives of retinoids were obtained in good yields (78-82%). Biological evaluation of these novel hybrid compounds (containing retinoids and perillyl alcohol) is currently underway in our laboratory.

Expression of caspase and apoptotic signal pathway induced by sulfur dioxide

Sulfur dioxide (SO(2)) is a common air pollutant that is released in low concentrations into the atmosphere and in higher concentrations in some work places. In the present study, male Wistar rats were housed in exposure chambers and treated with 14.00 +/- 1.01, 28.00 +/- 1.77, and 56.00 +/- 3.44 mg/m(3) SO(2) for 7 days (6 hr/day), while control rats were exposed to filtered air under the same conditions. The mRNA and protein levels of caspase-3, caspase-8, and caspase-9 were analyzed using a real-time reverse transcription-polymerase chain reaction (real-time RT-PCR) assay and an immunohistochemistry method. Activities of caspases were detected using colorimetric and fluorescent assays. Chromatin degradation and cell morphological changes were investigated by TUNEL assay and H&E staining in livers and lungs, respectively. The results showed that mRNA levels, protein levels and activities of caspase-3, caspase-8, and caspase-9 were increased in a dose-dependent manner in livers and lungs of rats after SO(2) inhalation. In addition, livers were infiltrated with lymphocytes, congestion and inflammation occurred in lungs, and eosinophil cells and apoptotic cells increased in both livers and lungs after SO(2) inhalation. These results suggest that SO(2) exposure increases the expression and activity of both initiator and and effector caspases, and may induce apoptosis in liver and lung of rats through both death receptor and mitochondrial pathways.

Induction of apoptosis in human leukaemia HL-60 cells by furanone-coumarins from Murraya siamensis

To identify potential anti-tumour agents, we screened five furanone-coumarins isolated from Murraya siamensis Craib (Rutaceae) for their ability to inhibit the growth of human leukaemia HL-60 cells. Among the furanone-coumarins tested, murrayacoumarin B (compound 2) showed significant cytotoxicity against HL-60 cells. Fluorescence microscopy with Hoechst 33342 staining revealed that the percentage of apoptotic cells with fragmented nuclei and condensed chromatin increased in a time-dependent manner after treatment with murrayacoumarin B. Interestingly, this furanone-coumarin induced the loss of the mitochondrial membrane potential. In addition, treatment with murrayacoumarin B stimulated the activities of caspase-9 and caspase-3, and caspase-9 and caspase-3 inhibitors suppressed the apoptosis induced by murrayacoumarin B. These results suggest that murrayacoumarin B induced apoptosis in HL-60 cells through activation of the caspase-9/caspase-3 pathway triggered by mitochondrial dysfunction.

Validation of SAG/RBX2/ROC2 E3 ubiquitin ligase as an anticancer and radiosensitizing target

PURPOSE

Sensitive to apoptosis gene (SAG; also known as RBX2 or ROC2) was originally cloned as a redox-inducible antioxidant protein and was later characterized as a RING component of SCF E3 ubiquitin ligases. SAG overexpression inhibits apoptosis induced by many stimuli both in vitro and in vivo. SAG mRNA was overexpressed in human lung tumor tissues with a correlation to poor patient survival. To investigate whether SAG serves as an anticancer target, we determined the effect of SAG silencing on cell proliferation, survival, and radiosensitivity.

EXPERIMENTAL DESIGN

SAG protein expression in human tumors was evaluated by immunohistochemical staining using tumor tissue arrays. SAG expression in cancer cells was knocked down by siRNA silencing. The anticancer effects of SAG silencing were evaluated by in vitro assays for cell growth and survival and by an in vivo orthotopic xenograft tumor model. Radiosensitization by SAG silencing of human cancer cells was determined by clonogenic survival assay. Apoptosis induction was evaluated by fluorescence-activated cell sorting analysis, caspase-3 activation assay, and Western blotting of apoptosis-associated proteins.

RESULTS

SAG was overexpressed in multiple human tumor tissues compared with their normal counterparts. SAG silencing selectively inhibited cancer cell proliferation, suppressed in vivo tumor growth, and sensitized radiation-resistant cancer cells to radiation. Mechanistically, SAG silencing induced apoptosis with accumulation of NOXA, whereas SAG overexpression reduced NOXA levels and shortened NOXA protein half-life.

CONCLUSIONS

The findings showed that SAG E3 ubiquitin ligase plays an essential role in cancer cell proliferation and tumor growth and may serve as a promising anticancer and radiosensitizing target.

Design of small-molecule Smac mimetics as IAP antagonists

Smac/DIABLO, discovered in 2000 as a protein released from mitochondria into the cytosol in response to apoptotic stimuli, functions as an endogenous antagonist of X-linked inhibitor of apoptosis protein (XIAP) and several other IAP proteins through direct binding. The interaction between Smac and IAPs involves the AVPI tetrapeptide binding motif on the N-terminus of Smac and a well-defined groove on the surface of these IAP proteins, providing an ideal site for the design of small-molecule Smac mimetics. Potent and cell-permeable small-molecule Smac mimetics have provided powerful pharmacological tools for study of the regulation of apoptosis by IAP proteins, and several such compounds are now in early clinical trials as new anticancer agents.

Expression of livin in gastric cancer and induction of apoptosis in SGC-7901 cells by shRNA-mediated silencing of livin gene

BACKGROUND

Because of increased resistance to apoptosis in tumor cells, inhibition of specific anti-apoptotic factors may provide a rational approach for the development of novel therapeutic strategies. Livin, a novel inhibitor of apoptosis protein family, has been found to be expressed in various malignancies and is suggested to have poorly prognostic significance. However, no data are available concerning the significance of livin in gastric cancer. In this study, we detected the expression of livin in human gastric carcinoma and investigated the apoptotic susceptibility of SGC - 7901 cell by shRNA-mediated silencing of the livin gene.

METHODS

The mRNA and protein expression of livin were analyzed by RT-PCR and western blot assay. The relationship between livin expression and clinical pathologic parameters was investigated. The small interfering RNA eukaryotic expression vector specific to livin was constructed by gene recombination, and the nucleic acid was sequenced. Then it was transfected into SGC-7901 cells by Lipofectamin 2000. RT-PCR and Western blot assay were used to validate gene-silencing efficiency of livin in SGC-7901 cells. Stable clones were obtained by G418 screening. The cell apoptosis was assessed by flow cytometry (FCM). Cell growth state and 50 % inhibition concentration (IC50) of 5-FU and cisplatin was determined by MTT method.

RESULTS

The expression of livin mRNA and protein were detected in 19 of 40 gastric carcinoma cases (47.5%) and SGC-7901 cells. No expression of livin was detected in tumor adjacent tissues and benign gastric lesion. The positive correlation was found between livin expression and poor differentiation of tumors as well as lymph node metastases (P<0.05). Four small interfering RNA eukaryotic expression vector specific to livin were constructed by gene recombination. And one of them can efficiently decrease the expression of livin, the inhibition of the gene was not less than 70% (P<0.01). The recombinated plasmids were extracted and transfected gastric cancer cells. The stable clones were obtained by G418 screening, and were amplified and cultured. When livin gene was silenced, the reproductive activity of the gastric cancer cells was significantly lower than the control groups(P<0.05). The study also showed that IC50 of 5-Fu and cisplatin on gastric cancer cells treated by shRNA was decreased and the cells were more susceptible to proapoptotic stimuli (5-Fu and cisplatin) (P<0.01).

CONCLUSIONS

Livin is overexpressed in gastric carcinoma with a relationship to tumor differentiation and lymph node metastases, which is suggested to be one of the molecular prognostic factors for some cases of gastric cancer. ShRNA can inhibit livin expression in SGC-7901 cells and induce cell apoptosis. Livin may serve as a new target for apoptosis-inducing therapy of gastric cancer.

Clematis montana lectin, a novel mannose-binding lectin from traditional Chinese medicine with antiviral and apoptosis-inducing activities

A novel mannose-binding lectin (designated CML) was isolated from Clematis montana Buch.-Ham stem (Ranunculaceae) using ion exchange and gel filtration chromatographies on DEAE-Sepharose and Sephacryl S-100. The purified C. montana lectin was a homodimer of 11,968.9 Da subunits as determined by gel filtration and MS. The hemagglutinating activity of CML was inhibited by branched oligomannosides. The N-terminal 15-amino acid sequence of CML, DNVKYSGQVKNTGSA, has not been reported for other lectins. Also, the peptide mass fingerprinting assay confirmed that there is no match result of similar plant lectins for CML, indicating CML may be a novel plant lectin. CML showed marked antiviral activity against various viruses in cell culture. Subsequently, CML was also found to exhibit remarkable inhibitory effect on L929, HeLa, MCF7 and HepG2 cells. Furthermore, CML specially induced L929 cell apoptosis in dose-dependent manner as evidenced by MTT, fluorescent microscopy, LDH activity-based cytotoxicity assays and DNA ladder. Moreover, due to both caspase inhibitors and Western blot analyses, caspase was also found to play the important role in the potential apoptotic mechanism of CML. When the carbohydrate-binding site was fully inhibited by sugars, cytotoxicity was abruptly decreased and apoptotic phenomenon in L929 cells was not observed, suggesting a significant correlation between mannose-binding-specific activity and the antineoplastic mechanism.

Regulation of HSP70 on activating macrophages using PDT-induced apoptotic cells

Although anti-tumor immunological responses have been mainly associated with necrosis, apoptosis-associated immune responses have been recently suggested as well. In this study, we investigated anti-tumor immune responses and regulatory mechanisms of HSP70 using apoptotic cells induced by photodynamic therapy (PDT). The relationships between HSP70 release, HSP70 translocation and macrophage responses were studied using confocal fluorescence microscopy, FACS and ELISA. Macrophages incubated with apoptotic cells as well as necrotic tumor cells showed a high level of TNFalpha secretion. Apoptotic cells but not the apoptotic cell supernatants induced TNFalpha secretion. During both necrosis and apoptosis processes, the TNFalpha production was diminished drastically when HSP70 or TLR-2 was inhibited. After the PDT treatment, cytoplasmic HSP70 was released from the necrotic cells, while HSP70 rapidly translocated to the surface of the apoptotic cells. Furthermore, the TNFalpha secretion and the tumor cytotoxicity of splenocytes from mice immunized with apoptotic cells appeared similar to that of splenocytes immunized with necrotic cells. Our in vitro and in vivo results show that apoptosis can potentially have higher impact in inducing immunological responses, hence clarifying the immunological regulatory mechanisms of HSP70 under cell apoptosis and necrosis induced by PDT treatment. These findings could lead to an optimal PDT treatment based on immunological responses.

Molecular cloning and bioinformatics analysis of a novel spliced variant of survivin from human breast cancer cells

Survivin gene and its two alternatively spliced variants, survivin-2 B and survivin- Delta Ex3 gene were cloned from human breast cancer cell lines B-cap37 firstly. A new gene designated as survivin-image (SI) was cloned from above cell lines, which has not been reported yet to clone from any cell lines. It was found that the novel gene 507 bp comprises partial survivin gene (345 bp), partial image gene (155 bp) of eye cancer and other insertion of 7 bp by analyzing with a series of recent bioinformatics software at the level of nucleotide and protein deduced. Predicted 3-D structures of the new molecule showed greatly similar to that of survivin in N-terminal containing BIR by homology modeling. These results suggested SI gene (GenBank accession No.AY830084) might be a novel alternatively spliced isoforms of the survivin gene involved in other functional significances related to tumorigenesis.

KLF6-SV1 is a novel antiapoptotic protein that targets the BH3-only protein NOXA for degradation and whose inhibition extends survival in an ovarian cancer model

Defects in apoptosis are not only a hallmark of cancer initiation and progression but can also underlie the development of chemoresistance. How the tightly regulated cascade of protein-protein interactions between members of three competing protein families regulating the apoptotic cascade is subverted in tumor cells is incompletely understood. Here, we show that KLF6-SV1, whose overexpression is associated with poor survival in several different cancers and is an alternatively spliced isoform of the Krüppel-like tumor suppressor KLF6, is a critical prosurvival/antiapoptotic protein. KLF6-SV1 binds the proapoptotic BH3-only protein NOXA, which results in their mutual HDM2-dependent degradation. In turn, this increases the intracellular concentration of the prosurvival binding partner of NOXA, Mcl-1, and effectively blocks apoptosis. In an ovarian cancer model, systemically delivered small interfering RNA against KLF6-SV1 induces spontaneous apoptosis of tumor cells, decreases tumor burden, and restores cisplatin sensitivity in vivo. Moreover, i.p. delivery of siKLF6-SV1 RNA halts ovarian tumor progression and improves median and overall survival (progression-free for >15 months; P < 0.0002) in mice in a dose-dependent manner. Thus, KLF6-SV1 represents a novel regulator of protein interactions in the apoptotic cascade and a therapeutically targetable control point.

A combination of micronutrients is beneficial in reducing the incidence of prostate cancer and increasing survival in the Lady transgenic model

We have previously shown that administration of a combination of micronutrients (selenium, vitamin E, and lycopene) inhibits prostate cancer (PCa) development in the Lady transgenic model. In the present study, we examine timing of initiation of micronutrients, and the effect of micronutrient combinations, on PCa development in Lady transgenic model. Transgenic males were randomized to either a control diet; control diet supplemented with human equivalent doses of vitamin E, selenium, and lycopene (E+S+L); or control diet supplemented with vitamin E and selenium (E+S). In separate experiments, the combination of E+S+L was initiated at varying time points (4, 8, 20, and 36 weeks of age). A combination of E+S+L resulted in a significant reduction in PCa and liver metastasis when intervention was commenced within 8 weeks of age (P < 0.0001). Immunohistochemical analysis revealed a strong correlation between disease-free state with up-regulation of the prognostic marker p27(Kip1) (P < 0.0001) and decreased expression of proliferating cell nuclear antigen and significantly increased apoptotic index (P < 0.0001). On the contrary, a combination of E+S was not effectual in preventing PCa, with a high proportion (84.6%) of animals developing PCa and a small proportion (11.5%) developing high-grade PIN. Early commencement of micronutrients (E+S+L) is beneficial in reducing PCa. Lycopene is an essential component of the combination and effective (when used with E+S) for PCa prevention. These observations provide support for their chemopreventive effect and some clues about their mechanism of action. These key findings will be complementary to the outcome from the Selenium and Vitamin E Chemoprevention Trial.

Design, synthesis, and evaluation of potent, nonpeptidic mimetics of second mitochondria-derived activator of caspases

A series of new Smac mimetics have been designed, synthesized, and evaluated. The most potent compound 10 binds to XIAP, cIAP-1, and cIAP-2 BIR3 proteins with K(i) of 3.9, 0.37, and 0.25 nM, respectively. Compound 10 antagonizes XIAP in a cell-free functional assay and induces rapid cIAP-1 degradation in cancer cells. Compound 10 inhibits cell growth in the MDA-MB-231 cancer cell line with an IC(50) of 8.9 nM.

Mechanism of hepatoprotection in proestrus female rats following trauma-hemorrhage: heme oxygenase-1-derived normalization of hepatic inflammatory responses

Hepatic damage occurs in males and ovariectomized (OVX), not in proestrus (PE), females following trauma-hemorrhage (T-H). The mechanism responsible for hepatoprotection remains unknown. We hypothesized protection in PE is a result of enhanced heme oxygenase-1 (HO-1)-derived down-regulation of liver inflammatory responses. PE and OVX rats underwent T-H (midline laparotomy, 60% blood loss). PE rats received vehicle (Veh; saline), HO-1 inhibitor chromium mesoporphyrin IX chloride (CrMP; 2.5 mg/kg), zinc protoporphyrin IX (ZnPP; 25 mg/kg), or Akt/PI-3K inhibitor Wortmannin (Wort; 1 mg/kg) 30 min prior to resuscitation or sham operation i.p. OVX rats received Veh or 17beta-estradiol (E2; 1 mg/kg) 30 min before hemorrhage. Rats were killed 2 h thereafter. Following T-H, left ventricular performance was maintained in PE and E2 OVX rats but was depressed in OVX and CrMP-, ZnPP-, and Wort-treated PE rats; liver damage was not evident in PE rats, and CrMP, ZnPP, and Wort abrogated protection; liver HO-1, p38 MAPK, Akt/PI3K, and Bcl-2 expression increased in PE and E2 OVX rats, which was abrogated by CrMP, ZnPP, and Wort, and liver ICAM-1, caspase-3, phospho-IkappaB-alpha, and NF-kappaB expression increased in OVX and CrMP-, ZnPP-, and Wort-PE rats; liver myeloperoxidase, NF-kappaB DNA-binding activity, TNF-alpha, IL-6, plasma proinflammatory cytokines, and cytokine-induced neutrophil chemoattractants increased in OVX and CrMP-, ZnPP-, and Wort-PE rats; and plasma estradiol levels and hepatic estrogen receptor-alpha and -beta expression decreased in OVX but were unaltered by CrMP, ZnPP, and Wort. Thus, enhanced HO-1 in PE and E2 OVX females modulates inflammatory responses and protects liver following T-H.

Involvement of FLIP in 2-methoxyestradiol-induced tumor regression in transgenic adenocarcinoma of mouse prostate model

PURPOSE

The purpose of this study is to investigate whether Fas-associated death domain interleukin-1 converting enzyme like inhibitory protein (FLIP) inhibition is a therapeutic target associated with 2-methoxyestradiol (2-ME2)-mediated tumor regression.

EXPERIMENTAL DESIGN

Expression and levels of FLIP were analyzed using (a) real-time PCR and immunoblot analysis in androgen-independent PC-3 cells treated with the newly formulated 2-ME2 and (b) immunohistochemistry in different Gleason pattern human prostate tumors. Transient transfections and chromatin immunoprecipitation (ChIP) assays were used to identify the transcription factors that regulate FLIP. Involvement of FLIP in 2-ME2-induced tumor regression was evaluated in transgenic adenocarcinoma mouse prostate (TRAMP) mice.

RESULTS

High Gleason pattern (5+5) human prostate tumors exhibit significant increase in FLIP compared with low Gleason pattern 3+3 (P=or<0.04). 2-ME2 reduced the levels and promoter activity of FLIP (P=0.001) in PC-3 cells. Transient expression assays show sequences between -503/+242 being sufficient for 2-ME2-induced inhibition of FLIP promoter activity. Cotransfection experiments show that overexpression of Sp1 activated, whereas Sp3 inhibited, Sp1 transactivation of FLIP promoter activity (P=0.0001). 2-ME2 treatment reduced binding of Sp1 to the FLIP promoter as evidenced by ChIP. Further, levels of FLIP associated with Fas or FADD decreased, whereas cleavage of caspase-8, levels of Bid, and apoptosis increased in response to 2-ME2 treatment in PC-3 cells. Administration of 2-ME2 regressed established prostate tumors in TRAMP mice that were associated with reduced expression of FLIP and Sp1.

CONCLUSION

Targeting Sp1-mediated FLIP signaling pathway may provide a novel approach for prostate cancer management.

[Cellular mechanisms of tumor response: clinical demands]

Diseases caused by cancer have become more common due to an increase in life-expectation, but the probability of reaching an old age with or without a tumor disease is still increasing. According to the statistics of the German Cancer register, at present more than half of cancer patients survive for at least 5 years after cancer has been diagnosed. Many tumors can be cured using innovative neoadjuvant and adjuvant therapy regimes, but the options for palliative therapy have also been improved. This leads to an increasing importance of the evaluation of the tumor response using imaging techniques. Classically, tumor response is measured by imaging using the RECIST (response evaluation criteria in solid tumors) criteria, which define the changes in size of the tumor during therapy. However, there is increasingly more evidence that RECIST as the only measure of tumor response, does not document tumor response for all tumor entities and especially not for many medications known as targeted therapy. This article gives a review of the principles and mode of effect of various therapy regimes as well as the clinical demands on imaging techniques.

Identification of ADP-ribosylation factor 4 as a suppressor of N-(4-hydroxyphenyl)retinamide-induced cell death

Yeast-based functional screening for inhibitors of Bcl-2-associated X protein (Bax)-induced cell death in yeast identified ADP-ribosylation factor 4 (ARF4) as a novel anti-apoptotic gene in human glioblastoma-derived U373MG cells. Yeast or U373MG cells that overexpressed ARF4 exhibited reduced reactive oxygen species (ROS) generation in response to Bax or N-(4-hydroxyphenyl)retinamide (4-HPR), respectively, which suggests that ROS play a role in the inhibition of cell death by ARF4. The 4-HPR-mediated phosphorylation of c-JUN N-terminal kinase, p38, and extracellular signal-regulated kinase was markedly suppressed in U373MG cells that stably expressed ARF4. Stable ARF4 transfectants were also refractory to 4-HPR-induced mitochondrial translocation of Bax, release of mitochondrial cytochrome c, and activation of caspase-3. Our results suggest that ARF4 participates in the regulation of glioblastoma apoptosis through the inhibition of stress-mediated apoptotic signals.

Structure-based design, synthesis, evaluation, and crystallographic studies of conformationally constrained Smac mimetics as inhibitors of the X-linked inhibitor of apoptosis protein (XIAP)

Small molecules designed to mimic the binding of Smac protein to X-linked inhibitor of apoptosis protein (XIAP) are being pursued as a promising new class of anticancer drugs. Herein, we report the design, synthesis, and comprehensive structure-activity relationship studies of a series of conformationally constrained bicyclic Smac mimetics. Our studies led to the discovery of a number of highly potent and cell-permeable Smac mimetics and yielded important new insights into their structure-activity relationship for their binding to XIAP and for their activity in inhibition of cancer cell growth. Determination of the crystal structure of one potent Smac mimetic, compound 21, in complex with XIAP BIR3 provides the structural basis for its high-affinity binding to XIAP and for the design of highly potent Smac mimetics.

Design of small-molecule peptidic and nonpeptidic Smac mimetics

Smac/DIABLO is a protein released from mitochondria into the cytosol in response to apoptotic stimuli. Smac promotes apoptosis at least in part through antagonizing inhibitor of apoptosis proteins (IAPs), including XIAP, cIAP-1, and cIAP-2. Smac interacts with these IAPs via its N-terminal AVPI binding motif. There has been an enormous interest in academic laboratories and pharmaceutical companies in the design of small-molecule Smac mimetics as potential anticancer agents. This task is particularly challenging because it involves targeting protein-protein interactions. Nevertheless, intense research has now generated potent, specific, cell-permeable small-molecule peptidomimetics and nonpeptidic mimetics. To date, two types of Smac mimetics have been reported, namely, monovalent and bivalent Smac mimetics. The monovalent compounds are designed to mimic the binding of a single AVPI binding motif to IAP proteins, whereas the bivalent compounds contain two AVPI binding motif mimetics tethered together through a linker. Studies from several groups have clearly demonstrated that both monovalent and bivalent Smac mimetics not only enhance the antitumor activity of other anticancer agents but also can induce apoptosis as single agents in a subset of human cancer cell lines in vitro and are capable of achieving tumor regression in animal models of human cancer. In general, bivalent Smac mimetics are 100-1000 times more potent than their corresponding monovalent Smac mimetics in induction of apoptosis in tumor cells. However, properly designed monovalent Smac mimetics can achieve oral bioavailability and may have major advantages over bivalent Smac mimetics as potential drug candidates. In-depth insights on the molecular mechanism of action of Smac mimetics have been provided by several independent studies. It was shown that Smac mimetics induce apoptosis in tumor cells by targeting cIAP-1/-2 for the rapid degradation of these proteins, which leads to activation of nuclear factor kappaB (NF-kappaB) and production and secretion of tumor necrosis factor alpha (TNFalpha). TNFalpha promotes formation of a receptor-interacting serine-threonine kinase 1 (RIPK1)-dependent caspase-8-activating complex, leading to activation of caspase-8 and -3/-7 and ultimately to apoptosis. For the most efficient apoptosis induction, Smac mimetics also need to remove the inhibition of XIAP to caspase-3/-7. Hence, Smac mimetics induce apoptosis in tumor cells by targeting not only cIAP-1/-2 but also XIAP. The employment of potent, cell-permeable, small-molecule Smac mimetics has yielded important insights into the regulation of apoptosis by IAP proteins. To date, at least one Smac mimetic has been advanced into clinical development. Several other Smac mimetics are in an advanced preclinical development stage and are expected to enter human clinical testing for the treatment of cancer in the near future.

HO-1 activation can attenuate cardiomyocytic apoptosis via inhibition of NF-kappaB and AP-1 translocation following cardiac global ischemia and reperfusion

BACKGROUND

NF-kappaB and AP-1 play important roles in regulation of inflammatory responses that lead to cardiomyocytic injury following cardiopulmonary bypass (CPB) and cardiac global ischemia and reperfusion. It has been reported that heme oxygenase-1 (HO-1) can block those responses. Our aim was to determine whether HO-1 activation could decrease myocardial ischemia-reperfusion injury with cardioplegia during CPB and attenuate apoptosis of cardiomyocytes.

MATERIALS AND METHODS

Rabbits (10 in each group) were randomized to receive either bypass only (Group 1), CPB plus intravenous normal saline (Group 2), hemin (HO-1 inducer; Group 3), SnPP (HO-1 inhibitor; Group 4), or hemin + SnPP (Group 5) 2 d before CPB. In all groups except Group 1, cold (4 degrees C) antegrade intermittent crystalloid cardioplegia was delivered every 20 min for a total of 60 min of cardiac arrest, after CPB was established. Rabbits were weaned from CPB and reperfused for 4 h. Blood was sampled at various time points. The reperfused hearts were harvested for Western blotting and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) experiments.

RESULTS

The postoperative elevation of serum levels of IL-10, IL-6, and TNF-alpha were significantly decreased in Group 3, but HO-1 inhibitor abolished this effect (Group 4). Moreover in Group 3, the number of apoptotic cardiomyocytes, level of apoptosis-related activated fragments of caspase-3 and Akt, and level of nuclear NF-kappaB and AP-1 translocation were significantly decreased.

CONCLUSIONS

HO-1 activation can dampen the surge of inflammation-related cytokines during CPB and decrease the occurrence of cardiomyocytic apoptosis via inhibition of NF-kappaB and AP-1 translocation.

Isoquinoline-1,3,4-trione derivatives inactivate caspase-3 by generation of reactive oxygen species

Caspase-3 is an attractive therapeutic target for treatment of diseases involving disregulated apoptosis. We report here the mechanism of caspase-3 inactivation by isoquinoline-1,3,4-trione derivatives. Kinetic analysis indicates the compounds can irreversibly inactivate caspase-3 in a 1,4-dithiothreitol (DTT)- and oxygen-dependent manner, implying that a redox cycle might take place in the inactivation process. Reactive oxygen species detection experiments using a chemical indicator, together with electron spin resonance measurement, suggest that ROS can be generated by reaction of isoquinoline-1,3,4-trione derivatives with DTT. Oxygen-free radical scavenger catalase and superoxide dismutase eliciting the inactivation of caspase-3 by the inhibitors confirm that ROS mediates the inactivation process. Crystal structures of caspase-3 in complexes with isoquinoline-1,3,4-trione derivatives show that the catalytic cysteine is oxidized to sulfonic acid (-SO(3)H) and isoquinoline-1,3,4-trione derivatives are bound at the dimer interface of caspase-3. Further mutagenesis study shows that the binding of the inhibitors with caspase-3 appears to be nonspecific. Isoquinoline-1,3,4-trione derivative-catalyzed caspase-3 inactivation could also be observed when DTT is substituted with dihydrolipoic acid, which exists widely in cells and might play an important role in the in vivo inactivation process in which the inhibitors inactivate caspase-3 in cells and then prevent the cells from apoptosis. These results provide valuable information for further development of small molecular inhibitors against caspase-3 or other oxidation-sensitive proteins.

ABT-737 induces expression of the death receptor 5 and sensitizes human cancer cells to TRAIL-induced apoptosis

Because Bcl-2 family members inhibit the ability of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) to induce apoptosis, we investigated whether ABT-737, a small molecule Bcl-2 inhibitor, enhances TRAIL killing. We demonstrate that a combination of ABT-737 and TRAIL induced significant cell death in multiple cancer types, including renal, prostate, and lung cancers, although each agent individually had little activity in these tumor cells. All of these cell lines expressed the Mcl-1 protein that is known to block the activity of ABT-737 and TRAIL but did not block the synergy between these agents. However, Bax-deficient cell lines, including DU145 and HCT116 cells and those cell lines expressing low levels of TRAIL receptor, were resistant to apoptosis induced by these agents. To understand how ABT-737 functions to markedly increase TRAIL sensitivity, the levels of specific death-inducing signaling complex components were evaluated. Treatment with ABT-737 did not change the levels of c-FLIP, FADD, and caspase-8 but up-regulated the levels of the TRAIL receptor DR5. DR5 up-regulation induced by ABT-737 treatment occurred through a transcriptional mechanism, and mutagenesis studies demonstrated that the NF-kappaB site found in the DR5 promoter was essential for the ability of ABT-737 to increase the levels of this mRNA. Using luciferase reporter plasmids, ABT-737 was shown to stimulate NF-kappaB activity. Together, these results demonstrate that the ability of ABT-737 and TRAIL to induce apoptosis is mediated through activation of both the extrinsic and intrinsic pathways. Combinations of ABT-737 and TRAIL can be exploited therapeutically where antiapoptotic Bcl-2 family members drive tumor cell resistance to current anticancer therapies.

Identifying breast cancer druggable oncogenic alterations: lessons learned and future targeted options

Although the introduction of novel therapies and drug combinations has improved the prognosis of metastatic breast cancer, this disease remains incurable. It is therefore important to develop additional novel therapeutic strategies and agents. Increased understanding of the biology and the molecular alterations present in breast cancer is facilitating the design of targeted therapies directed to oncogenic proteins. Here, we review the signaling pathways and proteins that participate in breast cancer proliferation and survival, with special emphasis in those that are druggable. We will also comment on how the knowledge on the basic pathogenetic processes is translated into drug development strategies that are reaching the breast cancer clinic.

Myrtucommulone from Myrtus communis induces apoptosis in cancer cells via the mitochondrial pathway involving caspase-9

Myrtucommulone (MC) is a unique, nonprenylated acylphloroglucinol contained in the leaves of myrtle (Myrtus communis). Here, we addressed the potential of MC to induce apoptosis of cancer cells. MC potently induced cell death of different cancer cell lines (EC(50) 3-8 microM) with characteristics of apoptosis, visualized by the activation of caspase-3, -8 and -9, cleavage of poly(ADP-ribose)polymerase (PARP), release of nucleosomes into the cytosol, and DNA fragmentation. MC was much less cytotoxic for non-transformed human peripheral blood mononuclear cells (PBMC) or foreskin fibroblasts (EC(50) cell death = 20-50 microM), and MC up to 30 microM hardly caused processing of PARP, caspase-3, -8 and -9 in human PBMC. MC-induced apoptosis was mediated by the intrinsic rather than the extrinsic death pathway. Thus, MC caused loss of the mitochondrial membrane potential in MM6 cells and evoked release of cytochrome c from mitochondria. Interestingly, Jurkat cells deficient in caspase-9 were resistant to MC-induced cell death and no processing of PARP or caspase-8 was evident. In cell lines deficient in either CD95 (Fas, APO-1) signalling, FADD or caspase-8, MC was still able to potently induce cell death and PARP cleavage. Conclusively, MC induces apoptosis in cancer cell lines, with marginal cytotoxicity for non-transformed cells, via the mitochondrial cytochrome c/Apaf-1/caspase-9 pathway.

Targeting the extrinsic apoptosis pathway in cancer

Mutational inactivation of the p53 tumor-suppressor gene, which regulates apoptosis mainly via the cell-intrinsic pathway, reduces the sensitivity of many cancers to conventional treatments. Targeting the cell-extrinsic pathway, which triggers p53-independent apoptosis, offers a unique therapeutic strategy to induce apoptosis in cancer cells. This article focuses on two proapoptotic receptor agonists, recombinant human Apo2-ligand/TNF-related apoptosis-inducing ligand (rhApo2L/TRAIL) and Apomab, which activate death receptor (DR) 4 and/or DR5, thus stimulating the cell-extrinsic pathway. These agents are under investigation for the treatment of solid tumor and hematologic malignancies. Preclinical data indicate that both molecules cause significant regression or growth inhibition of malignant tumors without significant toxicity. Initial data on rhApo2L/TRAIL and Apomab from phase 1 safety trials also confirm that these agents are suitable for further clinical investigation.

Cysteine cathepsins trigger caspase-dependent cell death through cleavage of bid and antiapoptotic Bcl-2 homologues

As a model for defining the role of lysosomal cathepsins in apoptosis, we characterized the action of the lysosomotropic agent LeuLeuOMe using distinct cellular models. LeuLeuOMe induces lysosomal membrane permeabilization, resulting in release of lysosomal cathepsins that cleave the proapoptotic Bcl-2 family member Bid and degrade the antiapoptotic member Bcl-2, Bcl-xL, or Mcl-1. The papain-like cysteine protease inhibitor E-64d largely prevented apoptosis, Bid cleavage, and Bcl-2/Bcl-xL/Mcl-1 degradation. The pancaspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(OMe)fluoromethyl ketone failed to prevent Bid cleavage and degradation of anti-apoptotic Bcl-2 homologues but substantially decreased cell death, suggesting that cathepsin-mediated apoptosis in these cellular models mostly follows a caspase-dependent pathway. Moreover, in vitro experiments showed that one or more of the cysteine cathepsins B, L, S, K, and H could cleave Bcl-2, Bcl-xL, Mcl-1, Bak, and BimEL, whereas no Bax cleavage was observed. On the basis of inhibitor studies, we demonstrate that lysosomal disruption triggered by LeuLeuOMe occurs before mitochondrial damage. We propose that degradation of anti-apoptotic Bcl-2 family members by lysosomal cathepsins synergizes with cathepsin-mediated activation of Bid to trigger a mitochondrial pathway to apoptosis. Moreover, XIAP (X-chromosome-linked inhibitor of apoptosis) was also found to be a target of cysteine cathepsins, suggesting that cathepsins can mediate caspase-dependent apoptosis also downstream of mitochondria.

Antrodia camphorata inhibits proliferation of human breast cancer cells in vitro and in vivo

Antrodia camphorata (A. camphorata) has been shown to induce apoptosis in cultured human breast cancer cells (MDA-MB-231). In this study, we report the effectiveness of the fermented culture broth of A. camphorata in terms of tumor regression as determined using both in vitro cell culture and in vivo athymic nude mice models of breast cancer. We found that the A. camphorata treatment decreased the proliferation of MDA-MB-231 cells by arresting progression through the G1 phase of the cell cycle. This cell cycle blockade was associated with reductions in cyclin D1, cyclin E, CDK4, cyclin A, and proliferating cell nuclear antigen (PCNA), and increased CDK inhibitor p27/KIP and p21/WAF1 in a dose and time-dependent manner. Furthermore, the A. camphorata treatment was effective in delaying tumor incidence in the nude mice inoculated with MDA-MB-231 cells as well as reducing the tumor burden when compared to controls. A. camphorata treatment also inhibited proliferation (cyclin D1 and PCNA) and induced apoptosis (Bcl-2 and TUNEL) when the tumor tissue sections were examined histologically and immunohistochemically. These results suggest that the A. camphorata treatment induced cell cycle arrest and apoptosis of human breast cancer cells both in vitro and in vivo.

Abundant anti-apoptotic BCL-2 is a molecular target in leukaemias with t(4;11) translocation

Chemotherapy resistance from imbalanced apoptosis regulation may contribute to poor outcome in leukaemias with t(4;11). Anti-apoptotic BCL-2 expression and target modulation were characterized in cell lines with t(4;11) and BCL-2 expression was examined in MLL and non-MLL infant/paediatric leukaemia cases by Western blot analysis and/or real-time polymerase chain reaction. Cytotoxicity of Genasensetrade mark (Oblimersen Sodium, G3139) alone or combined with cytotoxic drugs was assessed by MTT [(3-4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assays of the cell lines, applying pharmacostatistical response surface modelling of drug interactions. Apoptosis and cell cycle were evaluated by flow cytometry in RS4:11 cells. Primary leukaemias and cell lines with t(4;11) expressed abundant BCL2 mRNA and protein. Variable, sometimes substantial BCL2 mRNA was detected in other leukaemia subtypes. G3139 reduced BCL2 mRNA and protein in RS4:11 cells. The most sensitive cell line to single-agent G3139 was RS4:11. Low G3139 concentrations sensitized RS4:11 and MV4-11 cells to select anti-leukaemia cytotoxic drugs. In RS4:11 cells, combining G3139 with doxorubicin (ADR) increased active caspase 3 and TUNEL staining compared to ADR alone, indicating greater apoptosis, and G3139 increased S-phase progression. The abundant BCL-2 affords a molecular target in leukaemias with t(4;11). G3139 exhibits preclinical activity and synergy with select cytotoxic agents in RS4:11 and MV4-11 cells, and these effects occur through apoptosis.

Therapeutic efficacy of Ac-DMQD-CHO, a caspase 3 inhibitor, for rat spinal cord injury

We investigated the therapeutic efficacy of Ac-DMQD-CHO, a caspase-3 inhibitor, and functional recovery in spinal cord injury in a rat model. Thirty rats were randomized into three groups of 10 each. In groups 2 and 3, spinal cord trauma was produced in the thoracic region. Group 3 rats were treated with Ac-DMQD-CHO. Treatment responses were evaluated based on histopathological and TUNEL staining findings at 24 h and 5 days post-injury. Neurologic performance was assessed during and following treatment. Twenty-four hours after injury, light microscopy examination revealed diffuse hemorrhagic necrosis, edema, vascular thrombi, and polymorphonuclear leukocyte infiltration in group 2 and 3 rats, but cavitation and demyelinization were less prominent in group 3. At this time point, treatment of the rats with Ac-DMQD-CHO significantly reduced the number of apoptotic cells. Traumatic injury to the spinal cord causes apoptosis and administration of Ac-DMQD-CHO decreases apoptosis and improves functional outcome.

Structure-based discovery of a novel non-peptidic small molecular inhibitor of caspase-3

Ac-DNLD-CHO is a novel caspase-3 specific peptide inhibitor that was rationally designed by our computational strategy. The specificity was shown to be due to the specific interaction of NLD moiety with the active site of caspase-3 on the basis of docking mode and site-directed mutagenesis analyses. Here, we computationally screened non-peptidic small molecular inhibitors of caspase-3 from our chemical library using a reliable pharmacophore derived from the specific binding mode of NLD. Through in vitro enzyme assay of the screened candidate compounds, we discovered a novel caspase-3 specific small molecular inhibitor, CS4566, which has a unique scaffold structure. The binding mode of CS4566 to caspase-3 mimics that of NLD, especially LD moiety. This represents a promising lead compound for creating non-peptidic pharmaceuticals for caspase-mediated diseases, such as neurodegenerative disorders.