肿瘤细胞TRAIL耐受与其受体的关系

肿瘤坏死因子相关凋亡诱导配体(TRAIL)能与含有死亡域的死亡受体DR4、DR5相结合,诱导多种肿瘤细胞发生凋亡而对正常细胞无明显毒性.但肿瘤细胞对TRAIL的耐受限制了其广泛应用于临床.受体与配体的结合是凋亡信号启动的起始及关键环节,因此肿瘤细胞发生TRAIL耐受的机制与受体的表达、定位、分布、功能等密切相关.联合其...     

Targeting pro-apoptotic trail receptors sensitizes HeLa cervical cancer cells to irradiation-induced apoptosis

PURPOSE: To investigate the potential of irradiation in combination with drugs targeting the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death receptor (DR)4 and DR5 and their mechanism of action in a cervical cancer cell line. METHODS AND MATERIALS: Recombinant human TRAIL (rhTRAIL) and the agonistic antibodies against DR4 and DR5 were added to irradiated HeLa cells. The effect was evaluated with apoptosis and cytotoxicity assays and at the protein level. Membrane receptor expression was measured with flow cytometry. Small-interfering RNA against p53, DR4, and DR5 was used to investigate their function on the combined effect. RESULTS: rhTRAIL and the agonistic DR4 and DR5 antibodies strongly enhanced 10-Gy-induced apoptosis. This extra effect was 22%, 23%, and 29% for rhTRAIL, DR4, and DR5, respectively. Irradiation increased p53 expression and increased the membrane expression of DR5 and DR4. p53 suppression, as well as small-interfering RNA against DR5, resulted in a significant downregulation of DR5 membrane expression but did not affect apoptosis induced by irradiation and rhTRAIL. After small-interfering RNA against DR4, rhTRAIL-induced apoptosis and the additive effect of irradiation on rhTRAIL-induced apoptosis were abrogated, implicating an important role for DR4 in apoptosis induced through irradiation in combination with rhTRAIL. CONCLUSION: Irradiation-induced apoptosis is strongly enhanced by targeting the pro-apoptotic TRAIL receptors DR4 or DR5. Irradiation results in a p53-dependent increase in DR5 membrane expression. The sensitizing effect of rhTRAIL on irradiation in the HeLa cell line is, however especially mediated through the DR4 receptor.     

Modulation of TRAIL resistance in colon carcinoma cells: Different contributions of DR4 and DR5

Background  

rhTRAIL is a therapeutic agent, derived from the TRAIL cytokine, which induces apoptosis in cancer cells by activating the membrane death receptors 4 and 5 (DR4 and DR5). Here, we investigated each receptor's contribution to rhTRAIL sensitivity and rhTRAIL resistance. We assessed whether agonistic DR4 or DR5 antibodies could be used to circumvent rhTRAIL resistance, alone or in combination with various chemotherapies.     

Expression of TRAIL and TRAIL death receptors in stage III non-small cell lung cancer tumors.

PURPOSE: Several in vitro studies have shown that non-small cell lung cancer (NSCLC) cell lines are sensitive to apoptosis induction by the recombinant human (rh) tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) death ligand, indicating that rhTRAIL might become an attractive molecule for treatment of NSCLCs. To investigate the therapeutic potential of rhTRAIL, the expression of TRAIL and its apoptosis-inducing receptors DR4 and DR5 was evaluated in tumors of stage III NSCLC patients. EXPERIMENTAL DESIGN: Before treatment, tumor biopsies from locally advanced NSCLC patients were obtained by bronchoscopy. DR4, DR5, and TRAIL expression were determined immunohistochemically in 87 tumors. Patients were randomized for treatment with 60 Gy radiotherapy with or without carboplatin as radiosensitizer. RESULTS: DR4, DR5, and TRAIL were expressed in 99%, 82%, and 91% of the tumors, respectively. Seventeen percent of the samples expressed only DR4 and no DR5. In NSCLCs with squamous cell differentiation, a typical staining pattern for DR4 and DR5 was observed. Cells from the basal layer were strongly positive, and the more mature cells were less positive or negative. An inverse staining pattern was observed for TRAIL. Poorly differentiated areas showed strong staining intensity for DR4, DR5, and TRAIL. DR5-positive staining was associated with increased risk of death (odds ratio, 5.76; 95% confidence interval, 1.04-31.93; P = 0.045). CONCLUSIONS: The majority of the locally irresectable stage III NSCLCs expressed at least one of the two death receptors for TRAIL. Therefore, these death receptors may provide a target for the use of rhTRAIL as a new adjunct in the treatment of stage III NSCLC.     

Proteasome inhibitor MG132 sensitizes HPV-positive human cervical cancer cells to rhTRAIL-induced apoptosis

In cervical carcinogenesis, the p53 tumor suppressor pathway is disrupted by HPV (human papilloma virus) E6 oncogene expression. E6 targets p53 for rapid proteasome-mediated degradation. We therefore investigated whether proteasome inhibition by MG132 could restore wild-type p53 levels and sensitize HPV-positive cervical cancer cell lines to apoptotic stimuli such as rhTRAIL (recombinant human TNF-related apoptosis inducing ligand). In a panel of cervical cancer cell lines, CaSki was highly, HeLa intermediate and SiHa not sensitive to rhTRAIL-induced apoptosis. MG132 strongly sensitized HeLa and SiHa to rhTRAIL-induced apoptosis in a caspase-dependent and time-dependent manner. MG132 massively induced TRAIL receptor DR4 and DR5 membrane expression in HeLa, whereas in SiHa only DR5 membrane expression was upregulated from almost undetectable to high levels. Antagonistic DR4 antibody partially inhibited apoptosis induction by rhTRAIL and MG132 in HeLa but had no effect on apoptosis in SiHa. Inhibition of E6-mediated p53 proteasomal degradation by MG132 resulted in elevated levels of active p53 as demonstrated by p53 small interfering RNA (siRNA) sensitive p21 upregulation. Although p53 siRNA partially inhibited MG132-induced DR5 upregulation in HeLa and SiHa, no effect on rhTRAIL-induced apoptosis was observed. MG132 plus rhTRAIL enhanced caspase 8 and caspase 3 activation and concomitant cleavage of X-linked inhibitor of apoptosis (XIAP), particularly in HeLa. In addition, caspase 9 activation was only observed in HeLa. Downregulation of XIAP using siRNA in combination with rhTRAIL induced high levels of apoptosis in HeLa, whereas MG132 had to be added to the combination of XIAP siRNA plus rhTRAIL to induce apoptosis in SiHa. In conclusion, proteasome inhibition sensitized HPV-positive cervical cancer cell lines to rhTRAIL independent of p53. Our results indicate that not only DR4 and DR5 upregulation but also XIAP inactivation contribute to rhTRAIL sensitization by MG132 in cervical cancer cell lines. Combining proteasome inhibitors with rhTRAIL may be therapeutically useful in cervical cancer treatment.     

Differential activation of JNK1 isoforms by TRAIL receptors modulate apoptosis of colon cancer cell lines

Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis on binding to its receptors, death receptor 4 and 5 (DR4, DR5). TRAIL can also activate c-Jun N-terminal kinase (JNK) through the adaptor molecules, TNF receptor-associated factor 2 (TRAF2) and receptor-interacting protein (RIP). The role of JNK in TRAIL-induced tumour cell apoptosis is unclear. In this study, we demonstrate that JNK is activated by TRAIL in colon cancer cells. Inhibition of JNK with L-JNKI reduced rhTRAIL-induced cell death but enhanced cell death induced by selective activation of DR4 or DR5. This difference was unrelated to receptor internalisation or differential activation of c-Jun, but activation of different JNK isoforms. Our data demonstrate that JNK1, but not JNK2 is activated by rhTRAIL in the examined colon cancer cell lines. Although rhTRAIL activated both the long and short isoforms of JNK1, selective activation of DR4 or DR5 led to predominant activation of the short JNK1 isoforms (JNK1α1 and/or JNK1β1). Knockdown of JNK1α1 by shRNA enhanced apoptosis induced by TRAIL, agonistic DR4 or DR5 antibodies. On the other hand, knockdown of the long JNK1 isoforms (JNK1α2 and JNK1β2) had the opposite effect; it reduced TRAIL-induced cell death. These data indicate that the short JNK1 isoforms transmit an antiapoptotic signal, whereas the long isoforms (JNK1α2 or JNK1β2) act in a proapoptotic manner.     

TRAIL delivered by mesenchymal stromal/stem cells counteracts tumor development in orthotopic Ewing sarcoma models

Ewing sarcoma (EWS) is the second most frequent pediatric malignant bone tumor. EWS patients have not seen any major therapeutic progress in the last 30 years, in particular in the case of metastatic disease, which requires new therapeutic strategies. The pro‐apoptotic cytokine TNF‐Related Apoptosis Inducing Ligand (TRAIL) can selectively kill tumor cells while sparing normal cells, making it a promising therapeutic tool in several types of cancer. However, certain EWS cell lines appear resistant to recombinant human (rh) TRAIL‐induced apoptosis. We therefore hypothesized that a TRAIL presentation at the surface of the carrier cells might overcome this resistance and trigger apoptosis. For this purpose, human adipose mesenchymal stromal/stem cells (MSC) transfected in a stable manner to express full‐length human TRAIL were co‐cultured with several human EWS cell lines, inducing apoptosis by cell‐to‐cell contact even in cell lines initially resistant to rhTRAIL or AMG655, an antibody agonist to the death receptor, DR5. In vivo, TRAIL delivered by MSCs was able to counteract tumor progression in two orthotopic models of Ewing sarcoma, associated with caspase activation, indicating that a cell‐based delivery of a potent apoptosis‐inducing factor could be relevant in EWS.     

Inhibition of IGF-1R-dependent PI3K activation sensitizes colon cancer cells specifically to DR5-mediated apoptosis but not to rhTRAIL

Background

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) initiates apoptosis in tumor cells upon binding to its cognate agonistic receptors, death receptors 4 and 5 (DR4 and DR5). The activity of the insulin-like growth factor 1 (IGF-1) survival pathway is often increased in cancer, influencing both cell proliferation and apoptosis. We hypothesized that inhibiting the IGF-1 receptor (IGF-1R) using NVP-AEW541, a small molecular weight tyrosine kinase inhibitor of the IGF-1R, could increase death receptor (DR)-mediated apoptosis in colon cancer cells.

Methods

The analyses were performed by caspase assay, flow cytometry, Western blotting, immunoprecipitation and fluorescent microscopy.

Results

Preincubation with NVP-AEW541 surprisingly decreased apoptosis induced by recombinant human TRAIL (rhTRAIL) or an agonistic DR4 antibody while sensitivity to an agonistic DR5 antibody was increased. NVP-AEW541 could inhibit IGF-1-induced activation of the phosphatidylinositol 3-kinase (PI3K) pathway. The effects of the PI3K inhibitor LY294002 on TRAIL-induced apoptosis were similar to those of NVP-AEW541, further supporting a role for IGF-1R-mediated activation of PI3K. We show that PI3K inhibition enhances DR5-mediated caspase 8 processing but also lowers DR4 membrane expression and DR4-mediated caspase 8 processing. Inhibition of PI3K reduced rhTRAIL sensitivity independently of the cell line preference for either DR4- or DR5-mediated apoptosis signaling.

Conclusions

Our study indicates that individual effects on DR4 and DR5 apoptosis signaling should be taken into consideration when combining DR-ligands with PI3K inhibition.     

H-Ras regulation of TRAIL death receptor mediated apoptosis

TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis through the death receptors (DRs) 4 and/or 5 expressed on the cell surface. Multiple clinical trials are underway to evaluate the antitumor activity of recombinant human TRAIL and agonistic antibodies to DR4 or DR5. However, their therapeutic potential is limited by the high frequency of cancer resistance. Here we provide evidence demonstrating the role of H-Ras in TRAIL receptor mediated apoptosis. By analyzing the genome wide mRNA expression data of the NCI60 cancer cell lines, we found that H-Ras expression was consistently upregulated in TRAIL-resistant cell lines. By contrast, no correlation was found between TRAIL sensitivity and K-Ras expression levels or their mutational profiles. Notably, H-Ras upregulation associated with a surface deficiency of TRAIL death receptors. Selective inhibition of H-Ras activity in TRAIL-resistant cells restored the surface expression of both DR4 and DR5 without changing their total protein levels. The resulting cells became highly susceptible to both TRAIL and agonistic DR5 antibody, whereas K-Ras inhibition had little or no effect on TRAIL-induced apoptosis, indicating H-Ras plays a distinct role in the regulation of TRAIL death receptors. Further studies are warranted to determine the therapeutic potential of H-Ras-specific inhibitors in combination with TRAIL receptor agonists.     

Proteasome inhibitor sensitizes oral squamous cell carcinoma cells to TRAIL-mediated apoptosis

Oral squamous cell carcinoma (OSCC) cells are relatively resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis during culture. We investigated the role of a proteaosome inhibitor in the survival and apoptosis of these cells. We found that the proteasome inhibitor MG132 markedly accelerated TRAIL-mediated apoptosis in OSCC cell lines HSC-2 and HSC-3. Addition of TRAIL to MG132-treated cells resulted in Bid cleavage. Furthermore, the inhibitors of caspase-3, caspase-8 and caspase-9 reduced the accelerative effect of MG132 on TRAIL-mediated apoptosis. These results suggest that the pro-apoptotic effect of a proteasome inhibitor on TRAIL-mediated apoptosis may contribute to both extrinsic and intrinsic pathways. MG132 enhanced the expression of the TRAIL receptors DR4 and DR5, and neutralization of DR5 receptors showed a marked reduction of TRAIL-mediated apoptosis, whereas that of DR4 was a partial reduction. MG132 also markedly reduced cellular FLICE-inhibitory protein (c-FLIP), cellular inhibitor of apoptosis protein-1 (cIAP-1), X-linked IAP (XIAP) and survivin. Therefore, MG132 provides partial regulation of TRAIL-mediated apoptosis in OSCC cells via modulation of DR5, c-FLIP, cIAP-1, XIAP and survivin. The proteasome inhibitor MG132 may therefore represent a novel strategy for overcoming resistance to TRAIL-mediated apoptosis in OSCC cells.     

Cisplatin down-regulation of cellular Fas-associated death domain-like interleukin-1beta-converting enzyme-like inhibitory proteins to restore tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis in human melanoma cells.

PURPOSE: Many melanoma cell lines and primary cultures are resistant to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. In this study, we investigated the molecular mechanisms that control melanoma cell resistance and searched for chemotherapeutic drugs that could overcome the TRAIL resistance in melanoma cells. EXPERIMENTAL DESIGN: We examined 21 melanoma cell lines and 3 primary melanoma cultures for their sensitivity to TRAIL-induced apoptosis, and then tested cisplatin, chemptothecin, and etoposide for their synergistic effects on TRAIL sensitivity in resistant melanoma cells. RESULTS: Of 21 melanoma cell lines, 11 showed various degrees of sensitivity to TRAIL-induced apoptosis through caspase-8-initiated cleavage of caspase-3 and DNA fragmentation factor 45. The remaining cell lines and primary cultures were resistant to TRAIL, but cisplatin, chemptothecin, and etoposide sensitized the resistant cell lines and primary cultures to TRAIL-induced apoptosis, which also occurred through the caspase-8-initiated caspase cascade. Of the two TRAIL death receptors (DR4 and DR5), melanoma cells primarily expressed DR5 on cell surface. Cisplatin treatment had no effects on cell surface DR5 expression or intracellular expression of Fas-associated death domain and caspase-8. Instead, cisplatin treatment down-regulated intracellular expression of the short form of cellular Fas-associated death domain-like interleukin-1beta-converting enzyme-like inhibitory protein (c-FLIP) and inhibited phosphorylation of the long form of c-FLIP. CONCLUSIONS: The results presented here indicate that cisplatin inhibits c-FLIP protein expression and phosphorylation to restore TRAIL-induced caspase-8-initiated apoptosis in melanoma cells, thus providing a new combined therapeutic strategy for melanomas.     

Thyroid carcinoma cells are resistant to FAS-mediated apoptosis but sensitive to tumor necrosis factor-related apoptosis-inducing ligand

Fas (APO-1/CD95) is a transmembrane protein of the tumor necrosis factor (TNF)/nerve growth factor receptor superfamily that induces apoptosis in susceptible normal and neoplastic cells upon cross-linking by its ligand (FasL). TNF-related apoptosis-inducing ligand (TRAIL) is a more recently identified member of the TNF superfamily that has been shown to selectively kill neoplastic cells by engaging two cell-surface receptors, DR4 and DR5. Two additional TRAIL receptors (DcR1 and DcR2) do not transmit an apoptotic signal and have been proposed to confer protection from TRAIL-induced apoptosis. We addressed the expression of Fas, DR4, and DR5 in thyroid carcinoma cell lines and in 31 thyroid carcinoma specimens by Western blot analysis and immunohistochemistry, respectively, and tested the sensitivity of thyroid carcinoma cell lines to Fas- and TRAIL-induced apoptosis. Fas was found to be expressed in most thyroid carcinoma cell lines and tissue specimens. Although cross-linking of Fas did not induce apoptosis in thyroid carcinoma cell lines, Fas-mediated apoptosis did occur in the presence of the protein synthesis inhibitor cycloheximide, suggesting the presence of a short-lived inhibitor of the Fas pathway in these cells. Cross-linking of Fas failed to induce recruitment and activation of caspase 8, whereas transfection of a constitutively active caspase 8 construct effectively killed the SW579 papillary carcinoma cell line, arguing that the action of the putative inhibitor occurs upstream of caspase 8. By contrast, recombinant TRAIL induced apoptosis in 10 of 12 thyroid carcinoma cell lines tested, by activating caspase-10 at the receptor level and triggering a caspase-mediated apoptotic cascade. Resistance to TRAIL did not correlate with DcR1 or DcR2 protein expression and was overcome by protein synthesis inhibition in 50% of the resistant cell lines. One medullary carcinoma cell line was resistant to Fas-and TRAIL-induced apoptosis, even in the presence of cycloheximide, and to transfection of constitutively active caspase-8, suggesting a different regulation of the apoptotic pathway. Our observations indicate that TRAIL effectively kills carcinomas that originate from the follicular epithelium of the thyroid gland, by inducing caspase-mediated apoptosis, and may provide a potentially potent therapeutic reagent against thyroid cancer.     

Nutlin-3 preferentially sensitises wild-type p53-expressing cancer cells to DR5-selective TRAIL over rhTRAIL

Background:

Tumour cell-selective activation of apoptosis by recombinant human TNF-related apoptosis-inducing ligand (rhTRAIL) is enhanced through co-activation of p53 by chemotherapeutic drugs. The novel anticancer agent nutlin-3 provides a promising alternative for p53 activation by disrupting the interaction between p53 and its negative feedback regulator MDM2.

Methods:

We examined whether nutlin-3 enhances apoptosis induction by rhTRAIL and the DR5-selective TRAIL variant D269H/E195R in wild-type p53-expressing ovarian, colon and lung cancer cell lines and in an ex vivo model of human ovarian cancer.

Results:

Nutlin-3 enhanced p53, p21, MDM2 and DR5 surface expression. Although nutlin-3 did not induce apoptosis, it preferentially enhanced D269H/E195R-induced apoptosis over rhTRAIL. Combination treatment potentiated the cleavage of caspases 8, 9, 3 and PARP. P53 and MDM2 siRNA experiments showed that this enhanced apoptotic effect was mediated by wild-type p53. Indeed, nutlin-3 did not enhance rhTRAIL-induced apoptosis in OVCAR-3 cells harbouring mutant p53. Addition of the chemotherapeutic drug cisplatin to the combination further increased p53 and DR5 levels and rhTRAIL- and D269H/E195R-induced apoptosis. As a proof of concept, we show that the combination of D269H/E195R, nutlin-3 and cisplatin induced massive apoptosis in ex vivo tissue slices of primary human ovarian cancers.

Conclusion:

Nutlin-3 is a potent enhancer of D269H/E195R-induced apoptosis in wild-type p53-expressing cancer cells. Addition of DNA-damaging agents such as cisplatin further enhances DR5-mediated apoptosis.     

The clinical trail of TRAIL

The naturally occurring tumour necrosis factor related apoptosis-inducing ligand (TRAIL) induces apoptosis through two death receptors, death receptor 4 (DR4) and death receptor 5 (DR5), that are expressed on the cell membrane. Binding of the ligand to the death receptors leads to activation of the extrinsic apoptosis pathway. Chemotherapy on the other hand stimulates the intrinsic apoptosis pathway via activation of p53 in response to cellular damage. Many cancer cells have mutations in p53 causing resistance to chemotherapy-induced apoptosis. Concomitant signalling through the extrinsic pathway may overcome this resistance. Moreover, enthusiasm for TRAIL as an anticancer agent is based on the demonstration of rhTRAIL-induced selective cell death in tumour cells and not in normal cells. In this review, we provide an overview of the TRAIL pathway, the physiological role of TRAIL and the factors regulating TRAIL sensitivity. We also discuss the clinical development of novel agents, i.e. rhTRAIL and agonistic antibodies, that activate the death receptors.     

Ewing's sarcoma family tumors are sensitive to tumor necrosis factor-related apoptosis-inducing ligand and express death receptor 4 and death receptor 5

In this study, we investigated the sensitivity of Ewing's sarcoma family tumors (ESFTs) of children and adolescents to the tumor necrosis factor-related apoptosis-inducing Ligand (TRAIL). TRAIL binds to death receptors (DRs) DR4, DR5, DcR1, and DcR2. Either DR4 or DR5 can induce apoptosis, whereas DcR1 and DcR2 are considered inhibitory receptors. Nine of 10 ESFT cell lines, including several that were Fas resistant, underwent apoptosis with TRAIL through activation of caspase-10, capase-8 (FLICE), caspase-3, and caspase-9. In contrast to the Fas signaling pathway, caspase-10, but not caspase-8 or the Fas-associated death domain-containing molecule, was recruited to the TRAIL receptor-associated signaling complex. We found that 9 of 10 ESFT cell lines expressed both DR4 and DR5 by Western blotting, whereas the TRAIL-resistant line expressed only DR4. However, DR4 was absent from the cell surface in the resistant and two additional lines (three of five tested lines), suggesting that it may have been nonfunctional. On the contrary, DR5 was located on the cell surface in all four sensitive lines tested, being absent only from the cell surface of the resistant line that was also DR5-negative by Western blotting. In agreement with these findings, the resistance of the line was overcome by restoration of DR5 levels by transfection. Levels of DcR1 and DcR2 or levels of the FLICE-inhibitory protein (FLIP) did not correlate with TRAIL resistance, and protein synthesis inhibition did not sensitize the TRAIL-resistant line to TRAIL. Because these data suggested that sensitivity of ESFTs to TRAIL was mainly based on the presence of DR4/DR5, we investigated the presence of these receptors in 32 ESFT tissue sections by immunohistochemistry. We found that 23 of 32 tumor tissues (72%) expressed both receptors, 8 of 32 (25%) expressed one receptor only, and 1 was negative for both. Our finding of wide expression of DR4/DR5 in ESFT in vivo, in combination with their high sensitivity to TRAIL in vitro and the reported lack of toxicity of TRAIL in mice and monkeys, suggests that TRAIL may be a novel effective agent in the treatment of ESFTs.     

Effects and expression of TRAIL and its apoptosis-promoting receptors in human pancreatic cancer

Pancreatic cancer cells are usually resistant to apoptosis mediated by tumor necrosis factor (TNF)-alpha or FasL, and their toxicity towards normal cells hampers their application for therapeutic use. TNF-related apoptosis-inducing ligand (TRAIL), a novel member of the TNF family, triggers apoptosis in a variety of malignant cells, but exhibits less cytotoxicity in normal cells. To investigate the therapeutic potential of TRAIL, we analyzed the expression of TRAIL and its apoptosis-inducing receptors (DR4 and DR5) in the normal and cancerous human pancreas, and the sensitivity of pancreatic cancer cells to TRAIL cytotoxicity. TRAIL, DR4 and DR5 mRNA levels were concomitantly increased in pancreatic cancers compared with normal controls (P<0.01), and there were positive correlations between the expression levels of TRAIL and DR4, TRAIL and DR5 and between DR4 and DR5 mRNA (r=0.85, r=0.87, r=0.91; P<0.01). Immunostaining revealed the presence of the corresponding proteins frequently within the same cancer cells. In five pancreatic cancer cell lines, TRAIL, DR4 and DR5 mRNA expression was detectable at various levels. However, independent of the presence of DR4 and DR5, TRAIL cytotoxicity assays revealed that pancreatic cancer cells showed a significantly lower sensitivity (LD(50)>85 ng/ml) to TRAIL treatment than Jurkat T lymphoma cells (LD(50)=7.2 ng/ml). These findings show that pancreatic cancers are insensitive towards TRAIL-mediated apoptosis despite expression of TRAIL and its receptors, suggesting the presence of mediators which inhibit the TRAIL cell-death-inducing pathway in pancreatic cancer cells.     

A robust ex vivo model for evaluation of induction of apoptosis by rhTRAIL in combination with proteasome inhibitor MG132 in human premalignant cervical explants

Development of medical therapies for high-grade cervical intraepithelial neoplasia (CIN II/III) is hampered by the lack of CIN II/III cell lines. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis upon binding to its receptors DR4 or DR5. Proteasome inhibition by MG132 sensitized cervical cancer cell lines to recombinant human (rh)TRAIL. In our study, we aimed to develop an ex vivo model for CIN II/III and to investigate the apoptosis-inducing effect of rhTRAIL and/or MG132 in cervical explants from CIN II/III patients. A short-term ex vivo culture system was optimized for cervical biopsies, in which explants from normal cervix and CIN II/III lesions were exposed to either rhTRAIL (1 microg/ml), MG132 (5 microM) or the combination and compared to untreated explants for apoptosis induction. Normal cervix (n = 90) and CIN II/III (n = 24) explants could be reproducibly put in culture and kept viable for up to 7 days using a transwell membrane system. CIN II/III explants (n = 5) were highly sensitive to rhTRAIL plus MG132 (mean % apoptosis: 91 +/- 5) compared to normal cervix (n = 10) treated with rhTRAIL plus MG132 (mean % apoptosis: 24 +/- 10, p < 0.0001), while monotherapy with either rhTRAIL, MG132 or medium resulted in a mean % apoptosis <10 in both CIN II/III and normal cervix. Our ex vivo model system allows preclinical evaluation of (topical) medical therapies for CIN II/III. A strong synergistic apoptosis-inducing effect of the combination of rhTRAIL and MG132, especially in CIN II/III lesions indicates that rhTRAIL combined with proteasome inhibitors deserves exploration as medical treatment for CIN II/III.     

Drug-induced caspase 8 upregulation sensitises cisplatin-resistant ovarian carcinoma cells to rhTRAIL-induced apoptosis

Background:

Drug resistance is a major problem in ovarian cancer. Triggering apoptosis using death ligands such as tumour necrosis factor-related apoptosis inducing ligand (TRAIL) might overcome chemoresistance.

Methods:

We investigated whether acquired cisplatin resistance affects sensitivity to recombinant human (rh) TRAIL alone or in combination with cisplatin in an ovarian cancer cell line model consisting of A2780 and its cisplatin-resistant subline CP70.

Results:

Combining cisplatin and rhTRAIL strongly enhanced apoptosis in both cell lines. CP70 expressed less caspase 8 protein, whereas mRNA levels were similar compared with A2780. Pre-exposure of particularly CP70 to cisplatin resulted in strongly elevated caspase 8 protein and mRNA levels. Caspase 8 mRNA turnover and protein stability in the presence or absence of cisplatin did not differ between both cell lines. Cisplatin-induced caspase 8 protein levels were essential for the rhTRAIL-sensitising effect as demonstrated using caspase 8 small-interfering RNA (siRNA) and caspase-8 overexpressing constructs. Cellular FLICE-inhibitory protein (c-FLIP) and p53 siRNA experiments showed that neither an altered caspase 8/c-FLIP ratio nor a p53-dependent increase in DR5 membrane expression following cisplatin were involved in rhTRAIL sensitisation.

Conclusion:

Cisplatin enhances rhTRAIL-induced apoptosis in cisplatin-resistant ovarian cancer cells, and induction of caspase 8 protein expression is the key factor of rhTRAIL sensitisation.     

重组人TRAIL蛋白联合顺铂对人卵巢癌细胞生长及凋亡的影响

背景与目的：研究发现肿瘤坏死因子的相关凋亡诱导配体(tumor necrosis factor-related apoptosis inducing ligand,TRAIL)可以增强化疗药物对肿瘤细胞的杀伤作用。本研究旨在探讨TRAIL与顺铂联合应用对体外培养的卵巢癌细胞SKOV3和OVCAR3生长凋亡的影响及可能的诱导机制。方法：利用MTT法和流式细胞仪检测在顺铂和重组人TRAIL蛋白共同作用下,SKOV3和OVCAR3细胞的增殖抑制效应及细胞凋亡程度;并应用实时荧光定量聚合酶链反应(real-time fluorescent quantitative polymerase chain reaction,RTFQ-PCR)检测药物处理后TRAIL死亡受体DR4、DR5的mRNA表达水平;同时用蛋白[质]印迹法(Western blot)检测DR4、DR5的蛋白表达水平。结果：SKOV3和OVCAR3细胞均对TRAIL蛋白敏感,随着TRAIL蛋白浓度的升高,细胞的生长抑制率可达64%;而TRAIL与顺铂联合用药对两种细胞的抑制率均达到92%以上,对细胞的增殖抑制呈现高效协同作用,与单独用药组比较差异有统计学意义(P<0.05);TRAIL和顺铂联合组两种细胞凋亡率分别为(31.50±0.79)%和(36.60±1.31)%,显著高于单独用药组;RTFQ-PCR和Western blot检测结果显示,SKOV3和OVCAR3细胞在TRAIL与顺铂联合用药后,死亡受体DR4、DR5表达水平均显著上调。结论：在体外,TRAIL与化疗药物顺铂联用能明显抑制卵巢癌细胞增殖,诱导肿瘤细胞凋亡。TRAIL能明显增强顺铂对卵巢癌细胞的敏感性,其诱导机制可能与死亡受体DR4、DR5表达水平上调有关。     

The promise of cancer therapeutics targeting the TNF-related apoptosis-inducing ligand and TRAIL receptor pathway

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily and has been shown to induce apoptosis in cancer cells but not normal cells. TRAIL triggers apoptosis through binding to its receptors DR4 and KILLER/DR5. Chemo or radiotherapy induces apoptosis through activation of p53 in response to cellular damage, whereas TRAIL induces apoptosis independent of p53. Mutations or deletions of p53 occurred in more than half of human tumors confer resistance to chemo-radiotherapy. Treatment of TRAIL-resistant tumors with agents targeting death receptors, intrinsic Bcl-2 family members, inhibitor of apoptosis proteins or PI3K/Akt pathway restores the sensitivity to TRAIL-induced apoptosis. Combination of rhTRAIL or the agonist antibody for TRAIL receptor with conventional chemotherapeutic agents results in enhanced efficacy in preventing tumor progression and metastasis. Therefore, the rational design of TRAIL-based therapy combining with other modality that either synergizes to apoptosis induction or overcomes the resistance represents a challenging strategy to achieve the systemic tumor targeting and augment the antitumor activity of cancer therapeutics.