Enhanced antitumor therapy by inhibition of p21waf1 in human malignant mesothelioma

Inhibition of p21 activates Akt kinase to trigger ROS-induced autophagy and impacts on tumor growth rate

Owing to its ability to induce cellular senescence, inhibit PCNA, and arrest cell division cycle by negatively regulating CDKs as well as being a primary target of p53, p21 is traditionally considered a tumor suppressor. Nonetheless, several reports in recent years demonstrated its pro-oncogenic activities such as apoptosis inhibition by cytosolic p21, stimulation of cell motility, and promoting assembly of cyclin D-CDK4/6 complex. These opposing effects of p21 on cell proliferation, supported by the observations of its inconsistent expression in human cancers, led to the emergence of the concept of "antagonistic duality" of p21 in cancer progression. Here we demonstrate that p21 negatively regulates basal autophagy at physiological concentration. Akt activation, upon p21 attenuation, driven ROS accumulation appears to be the major underlying mechanism in p21-mediated modulation of autophagy. We also find p21, as a physiological inhibitor of autophagy, to have oncogenic activity during early events of tumor development while its inhibition favors survival and growth of cancer cells in the established tumor. Our data, thereby, reveal the potential role of autophagy in antagonistic functional duality of p21 in cancer.

Melatonin and (-)-Epigallocatechin-3-Gallate: Partners in Fighting Cancer

We have demonstrated previously that melatonin attenuates hepatotoxicity triggered by high doses of (−)-epigallocatechin-3-gallate (EGCG) in mice. The current work investigated the influence of melatonin on the oncostatic activity of EGCG in two cancer cell lines, wherein melatonin induced an opposite response of p21. In human tongue cancer TCA8113 cells, melatonin-induced p21 and EGCG-mediated formation of quinoproteins were positively associated with the oncostatic effects of melatonin and EGCG. Melatonin-stimulated an increase in p21 which was correlated with a pronounced nuclear translocation of thioredoxin 1 and thioredoxin reductase 1, both of which are known to induce p21 via promoting p53 trans-activation. Melatonin did not influence the EGCG-mediated increase of quinoprotein formation nor did EGCG impair melatonin-induced p21 up-regulation. Co-treatment with both agents enhanced the cell-killing effect as well as the inhibitory activities against cell migration and colony formation. It is known that p21 also plays a powerful anti-apoptotic role in some cancer cells and confers these cells with a survival advantage, making it a target for therapeutic suppression. In human hepatocellular carcinoma HepG2 cells, melatonin suppressed p21 along with the induction of pro-survival proteins, PI3K and COX-2. However, EGCG prevented against melatonin-induced PI3K and COX-2, and melatonin probably sensitized HepG2 cells to EGCG cytotoxicity via down-regulating p21, Moreover, COX-2 and HO-1 were significantly reduced only by the co-treatment, and melatonin aided EGCG to achieve an increased inhibition on Bcl2 and NFκB. These events occurring in the co-treatment collectively resulted in an enhanced cytotoxicity. In addition, the co-treatment also enhanced the inhibitory activities against cell migration and colony formation. Overall, the results gathered from these two cancer cell lines with a divergent p21 response to melatonin show that the various oncostatic activities of melatonin and EGCG together are more robust than each agent alone, suggesting that they may be useful partners in fighting cancer.

Synergistic anti-tumor effect of bullfrog sialic acid-binding lectin and pemetrexed in malignant mesothelioma

Malignant mesothelioma is an aggressive cancer with limited therapeutic options. Sialic acid-binding lectin isolated from Rana catesbeiana oocytes (cSBL) is a multifunctional protein with anti-cancer activity. The effects of pemetrexed, cisplatin, and cSBL were evaluated in mesothelioma and normal mesothelial cell lines. We evaluated cytotoxicity, apoptosis, caspase-3 cleavage and activation, cell proliferation, cell cycle arrest, and levels of cell cycle proteins in H28 cells treated with pemetrexed, cisplatin, and cSBL alone or in combination. Treatment with cSBL alone was cytotoxic to mesothelioma cells. The anti-cancer effect of cSBL was observed in a broader range of cell lines and exhibited greater cancer cell selectivity than pemetrexed or cisplatin. Combination treatment with pemetrexed + cSBL resulted in greater dose-dependent cytotoxicity than pemetrexed + cisplatin, the standard of care in mesothelioma. The synergistic effect of pemetrexed + cSBL was mediated by the cytostatic effect of pemetrexed and the cytotoxic effect of cSBL. It thus appears that cSBL has therapeutic potential for the treatment of mesothelioma.

Testis specific Y-like 5: gene expression, methylation and implications for drug sensitivity in prostate carcinoma

BACKGROUND

TSPYL5, a putative tumor suppressor gene, belongs to the nucleosome assembly protein family. The chromosomal location of the TSPYL5 gene is 8Q22.1, and its exact role in prostate cancer etiology remains unclear. Further TSPYL5 gene and protein expression in prostate carcinoma cells and diseased tissues including its susceptibility for epigenetic silencing is unknown. Also, not known is the variation in TSPYL5 protein expression with regards to progression of prostatic carcinoma and its possible role in drug sensitivity.

METHODS

TSPYL5, DNMT-1 and DNMT-B gene expression in DU145, LNCaP and RWPE-1 cells and prostate tumor tissues was analyzed by qRT-PCR and RT-PCR. Demethylation experiments were done by treating DU145 and LNCaP cells with 5-aza-2'-deoxycytidine in vitro. Methylation analysis of TSPYL5 gene was performed by methylation specific PCR and pyrosequencing. TSPYL5 protein expression in benign and diseased prostate tumor tissues was performed by immunohistochemistry and in the cells by Western blotting.

RESULTS

TSPYL5 was differentially expressed in non-tumorigenic prostate epithelial cells (RWPE-1), androgen independent (DU145), dependent (LNCaP) prostate carcinoma cells and tissues. Methylation-specific PCR and pyrosequencing analysis identified an inverse relationship between DNA methylation and expression leading to the silencing of TSPYL5 gene. Treatment of prostate carcinoma cells in which TSPYL5 was absent or low (DU145 and LNCaP) with the demethylating agent 5-aza-2'-deoxycytidine upregulated its expression in these cells. Immunohistochemical studies clearly identified TSPYL5 protein in benign tissue and in tumors with Gleason score (GS) of 6 and 7. TSPYL5 protein levels were very low in tumors of GS ≥ 8. TSPYL5 overexpression in LNCaP cells increased the cell sensitivity to chemotherapy drugs such as docetaxel and paclitaxel, as measured by the cellular viability. Furthermore, the cells also exhibited reduced CDKN1A expression with only marginal reduction in pAKT.

CONCLUSIONS

Decrease in TSPYL5 protein in advanced tumors might possibly function as an indicator of prostate tumor progression. Its absence due to methylation-induced silencing can lead to reduced drug sensitivity in prostate carcinoma.

CGK733-induced LC3 II formation is positively associated with the expression of cyclin-dependent kinase inhibitor p21Waf1/Cip1 through modulation of the AMPK and PERK/CHOP signaling pathways

Microtubule-associated protein 1A/1B-light chain 3 (LC3)-II is essential for autophagosome formation and is widely used to monitor autophagic activity. We show that CGK733 induces LC3 II and LC3-puncta accumulation, which are not involved in the activation of autophagy. The treatment of CGK733 did not alter the autophagic flux and was unrelated to p62 degradation. Treatment with CGK733 activated the AMP-activated protein kinase (AMPK) and protein kinase RNA-like endoplasmic reticulum kinase/CCAAT-enhancer-binding protein homologous protein (PERK/CHOP) pathways and elevated the expression of p21Waf1/Cip1. Inhibition of both AMPK and PERK/CHOP pathways by siRNA or chemical inhibitor could block CGK733-induced p21Waf1/Cip1 expression as well as caspase-3 cleavage. Knockdown of LC3 B (but not LC3 A) abolished CGK733-triggered LC3 II accumulation and consequently diminished AMPK and PERK/CHOP activity as well as p21Waf1/Cip1 expression. Our results demonstrate that CGK733-triggered LC3 II formation is an initial event upstream of the AMPK and PERK/CHOP pathways, both of which control p21Waf1/Cip1 expression.

Iron depletion enhances the effect of sorafenib in hepatocarcinoma

ABSTACT Human hepatocellular carcinoma (HCC) is known to have a poor prognosis. Sorafenib, a molecular targeted drug, is most commonly used for HCC treatment. However, its effect on HCC is limited in clinical use and therefore new strategies regarding sorafenib treatment are required. Iron overload is known to be associated with progression of chronic hepatitis and increased risk of HCC. We previously reported that iron depletion inhibited cancer cell proliferation and conversely induced angiogenesis. Indeed iron depletion therapy including iron chelator needs to be combined with anti-angiogenic drug for its anti-cancer effect. Since sorafenib has an anti-angiogenic effect by its inhibitory targeting VEGFR, we hypothesized that sorafenib could complement the anti-cancer effect of iron depletion. We retrospectively analyzed the relationship between the efficacy of sorafenib and serum iron-related markers in clinical HCC patients. In clinical cases, overall survival was prolonged in total iron binding capacity (TIBC) high- and ferritin low-patients. This result suggested that the low iron-pooled patients, who could have a potential of more angiogenic properties in/around HCC tumors, could be adequate for sorafenib treatment. We determined the effect of sorafenib (Nexavar®) and/or deferasirox (EXJADE®) on cancer cell viability, and on cell signaling of human hepatocarcinoma HepG2 and HLE cells. Both iron depletion by deferasirox and sorafenib revealed insufficient cytotoxic effect by each monotherapy, however, on the basis of increased angiogenesis by iron depletion, the addition of deferasirox enhanced anti-proliferative effect of sorafenib. Deferasirox was confirmed to increase vascular endothelial growth factor (VEGF) secretion into cellular supernatants by ELISA analysis. In in vivo study sorafenib combined with deferasirox also enhanced sorafenib-induced apoptosis. These results suggested that sorafenib combined with deferasirox could be a novel combination chemotherapy for HCC.

p21(WAF1) modulates drug-induced apoptosis and cell cycle arrest in B-cell precursor acute lymphoblastic leukemia

p21(WAF1) is a well-characterized mediator of cell cycle arrest and may also modulate chemotherapy-induced cell death. The role of p21(WAF1) in drug-induced cell cycle arrest and apoptosis of acute lymphoblastic leukemia (ALL) cells was investigated using p53-functional patient-derived xenografts (PDXs), in which p21(WAF1) was epigenetically silenced in T-cell ALL (T-ALL), but not in B-cell precursor (BCP)-ALL PDXs. Upon exposure to diverse cytotoxic drugs, T-ALL PDX cells exhibited markedly increased caspase-3/7 activity and phosphatidylserine (PS) externalization on the plasma membrane compared with BCP-ALL cells. Despite dramatic differences in apoptotic characteristics between T-ALL and BCP-ALL PDXs, both ALL subtypes exhibited similar cell death kinetics and were equally sensitive to p53-inducing drugs in vitro, although T-ALL PDXs were significantly more sensitive to the histone deacetylase inhibitor vorinostat. Transient siRNA suppression of p21(WAF1) in the BCP-ALL 697 cell line resulted in a moderate depletion of the cell fraction in G1 phase and marked increase in PS externalization following exposure to etoposide. Furthermore, stable lentiviral p21(WAF1) silencing in the BCP-ALL Nalm-6 cell line accelerated PS externalization and cell death following exposure to etoposide and vorinostat, supporting previous findings. Finally, the Sp1 inhibitor, terameprocol, inhibited p21(WAF1) expression in Nalm-6 cells exposed to vorinostat and also partially augmented vorinostat-induced cell death. Taken together, these findings demonstrate that p21(WAF1) regulates the early stages of drug-induced apoptosis in ALL cells and significantly modulates their sensitivity to vorinostat.

Telomere Dysfunction, Chromosomal Instability and Cancer

Telomeres form protective caps at the ends of linear chromosomes to prevent nucleolytic degradation, end-to-end fusion, irregular recombination, and chromosomal instability. Telomeres are composed of repetitive DNA sequences (TTAGGG)n in humans, that are bound by specialized telomere binding proteins. Telomeres lose capping function in response to telomere shortening, which occurs during each division of cells that lack telomerase activity-the enzyme that can synthesize telomeres de novo. Telomeres have a dual role in cancer: telomere shortening can lead to induction of chromosomal instability and to the initiation of tumors, however, initiated tumors need to reactivate telomerase in order to stabilize chromosomes and to gain immortal growth capacity. In this review, we summarize current knowledge on the role of telomeres in the maintenance of chromosomal stability and carcinogenesis.

ShRNA-mediated Bmi-1 silencing sensitizes multiple myeloma cells to bortezomib

The introduction of bortezomib has resulted in a paradigm shift in the treatment of multiple myeloma (MM) and has contributed to the improved survival of patients with MM. Inevitably, resistance to therapy develops, and thus the clinical efficacy of bortezomib is hampered by drug resistance. The oncogene B-cell‑specific Moloney murine leukemia virus insertion site‑1 (Bmi-1) has been implicated in the pathogenesis of various human malignancies. Furthermore, RNA interference (RNAi)‑mediated Bmi-1 silencing has been shown to sensitize tumor cells to chemotherapy and radiation. The role of Bmi-1 in influencing the response to bortezomib therapy has not been investigated to date. In the present study, Bmi-1 was silenced in two MM cell lines (U266 and RPMI8226) using short hairpin RNA (shRNA) targeting Bmi-1 (shBmi-1). A cell counting kit-8 (CCK-8) assay was performed to analyze cell proliferation and evaluate the 50% inhibitory concentration (IC50) values of bortezomib. Cell cycle progression and apoptosis were analyzed by flow cytometry (FCM), and the mRNA and protein expression of associated genes (Bmi-1, p14, p21, Bcl-2 and Bax) was quantified by RT-qPCR and western blot analysis, respectively. The IC50 values significantly decreased in the cells transfected with shBmi-1 (p<0.05). The depletion of Bmi-1 sensitized the MM cells to bortezomib, which increased the G1 phase duration and enhanced bortezomib‑induced apoptosis (p<0.05). The expression of p21 and Bax (apoptosis inducer) was upregulated, whereas that of the anti-apoptotic protein, Bcl-2, was downregulated in the Bmi-1‑silenced cells (p<0.05). The depletion of Bmi-1 enhanced the sensitivity of MM cells to bortezomib by inhibiting cell proliferation and inducing cell cycle arrest and apoptosis. Our data suggest that Bmi-1 may serve as an important novel therapeutic target in MM.

Aberrant expression of p53, p21, cyclin D1, and Bcl2 and their clinicopathological correlation in ampullary adenocarcinoma

Previous studies on the molecular alterations in ampullary adenocarcinoma (AA) are limited, and little is known about their clinical implications. The objective of this study is to examine the expression of p53, p21, cyclin D1, and Bcl2 and their clinical significance in patients with AA. Tissue microarrays were constructed using archival tissue from 92 patients with AA who underwent pancreaticoduodenectomy at our institution. Each tumor was sampled in triplicate with a 1.0-mm punch from representative areas. The expression of p53, p21, cyclin D1, and Bcl2 was evaluated by immunohistochemistry, and the staining results were correlated with clinicopathological features and survival. Among 92 cases studied, overexpression of p53, p21, cyclin D1, and Bcl2 was observed in 58.7%, 39.2%, 71.7%, and 5.4% of tumors, respectively. Patients whose tumor showed high level of cyclin D1 expression had higher risk of disease recurrence (P = .02) and worse recurrence-free and overall survivals after pancreaticoduodenectomy than did those with no or low cyclin D1 expression (P = .027 and P = .02, respectively). In multivariate analysis, cyclin D1 expression was an independent prognostic factor for both recurrence-free and overall survival (P < .05). However, there was no significant correlation between p53, p21, or Bcl2 expression and survival (P > .05). Our study showed that p53, p21, and cyclin D1, but not Bcl2, are frequently overexpressed in AAs. Cyclin D1 overexpression is associated with increased risk of disease recurrence and worse survival in patients with AA after resection.

Pharmacological targeting of p53 through RITA is an effective antitumoral strategy for malignant pleural mesothelioma

Malignant mesothelioma, a very aggressive tumor associated to asbestos exposure, is expected to increase in incidence, and unfortunately, no curative modality exists. Reactivation of p53 is a new attractive antitumoral strategy. p53 is rarely mutated in mesothelioma, but it is inactivated in most tumors by the lack of p14(ARF). Here, we evaluated the feasibility of this approach in pleural mesothelioma by testing RITA and nutlin-3, two molecules able to restore p53 function through a different mechanism, on a panel of mesothelioma cell lines representing the epithelioid (NCI-H28, NCI-H2452, IST-MES 2), biphasic (MSTO-211H), and sarcomatoid (NCI-H2052) histotypes compared with the normal mesothelial HMC-hTERT. RITA triggered robust caspase-dependent apoptosis specifically in epithelioid and biphasic mesothelioma cell lines, both through wild-type and mutant p53, concomitant to p21 downregulation. Conversely, nutlin-3 induced a p21-dependent growth arrest, rather than apoptosis, and was slightly toxic on HMC-hTERT.   Interestingly, we identified a previously undetected point mutation of p53 (p.Arg249Ser) in IST-MES 2, and showed that RITA is also able to reactivate this p53 mutant protein and its apoptotic function. RITA reduced tumor growth in a MSTO-211H-derived xenograft model of mesothelioma and synergized with cisplatin, which is the mainstay of treatment for this tumor. Our data indicate that reactivation of p53 and concomitant p21 downregulation effectively induce cell death in mesothelioma, a tumor characterized by a high intrinsic resistance to apoptosis. Altogether, our findings provide the preclinical framework supporting the use of p53-reactivating agents alone, or in combination regimens, to improve the outcome of patients with mesothelioma.

Disulfiram targets cancer stem-like cells and reverses resistance and cross-resistance in acquired paclitaxel-resistant triple-negative breast cancer cells

Background:

Triple-negative breast cancer (TNBC) has significantly worse prognosis. Acquired chemoresistance remains the major cause of therapeutic failure of TNBC. In clinic, the relapsed TNBC is commonly pan-resistant to various drugs with completely different resistant mechanisms. Investigation of the mechanisms and development of new drugs to target pan-chemoresistance will potentially improve the therapeutic outcomes of TNBC patients.

Methods:

In this study, 1-(4,5-Dimethylthiazol-2-yl)-3,5-diphenylformazan (MTT), combination index (CI)–isobologram, western blot, ALDEFLUOR analysis, clonogenic assay and immunocytochemistry were used.

Results:

The chemoresistant MDA-MB-231_PAC10 cells are highly cross-resistant to paclitaxel (PAC), cisplatin (CDDP), docetaxel and doxorubicin. The MDA-MB-231_PAC10 cells are quiescent with significantly longer doubling time (64.9 vs 31.7 h). This may be caused by high expression of p21^Waf1. The MDA-MB-231_PAC10 cells express high aldehyde dehydrogenase (ALDH) activity and a panel of embryonic stem cell-related proteins, for example, Oct4, Sox2, Nanog and nuclealisation of HIF2α and NF-κBp65. We have previously reported that disulfiram (DS), an antialcoholism drug, targets cancer stem cells (CSCs) and enhances cytotoxicity of anticancer drugs. Disulfiram abolished CSC characters and completely reversed PAC and CDDP resistance in MDA-MB-231_PAC10 cells.

Conclusion:

Cancer stem cells may be responsible for acquired pan-chemoresistance. As a drug used in clinic, DS may be repurposed as a CSC inhibitor to reverse the acquired pan-chemoresistance.

EVI1 inhibits apoptosis induced by antileukemic drugs via upregulation of CDKN1A/p21/WAF in human myeloid cells

Overexpression of ecotropic viral integration site 1 (EVI1) is associated with aggressive disease in acute myeloid leukemia (AML). Despite of its clinical importance, little is known about the mechanism through which EVI1 confers resistance to antileukemic drugs. Here, we show that a human myeloid cell line constitutively overexpressing EVI1 after infection with a retroviral vector (U937_EVI1) was partially resistant to etoposide and daunorubicin as compared to empty vector infected control cells (U937_vec). Similarly, inducible expression of EVI1 in HL-60 cells decreased their sensitivity to daunorubicin. Gene expression microarray analyses of U937_EVI1 and U937_vec cells cultured in the absence or presence of etoposide showed that 77 and 419 genes were regulated by EVI1 and etoposide, respectively. Notably, mRNA levels of 26 of these genes were altered by both stimuli, indicating that EVI1 regulated genes were strongly enriched among etoposide regulated genes and vice versa. One of the genes that were induced by both EVI1 and etoposide was CDKN1A/p21/WAF, which in addition to its function as a cell cycle regulator plays an important role in conferring chemotherapy resistance in various tumor types. Indeed, overexpression of CDKN1A in U937 cells mimicked the phenotype of EVI1 overexpression, similarly conferring partial resistance to antileukemic drugs.

Glutathione S-transferase P1-1 as a target for mesothelioma treatment

Malignant pleural mesothelioma is a poorly responsive tumor known to overexpress the phase II detoxification enzyme glutathione-S-transferase, which catalyzes the conjugation between glutathione and platinum(II)-containing drugs. Therefore, we evaluated the effect of the strong glutathione S-transferase inhibitor NBDHEX on human mesothelioma cell lines (MSTO-211H, MPP89, MM-B1 and Mero 48a) featuring the most common mesothelioma phenotypes: epithelioid and biphasic. Even though a different response to NBDHEX was observed, the molecule was very effective on all cell lines tested, triggering a sustained activation of both JNK and p38, followed by caspase activation and apoptosis. NBDHEX also caused severe oxidative stress in the MPP89 cells and, to a lesser extent, in the MMB1 cells, while it did not cause a significant redox imbalance in the other cell lines. The efficacy of the drug was found to be comparable or even higher than that of cisplatin. Moreover, it showed synergistic or additive effects when used in combination with cisplatin. In conclusion, NBDHEX was effective on mesothelioma cell lines, with IC(50) values in the low micromolar range (IC(50) between 1 and 4 μM). These findings indicate that NBDHEX, alone or in combination with cisplatin, is a promising new strategy for treating this rare and aggressive malignancy.

Tumour suppressor genes in chemotherapeutic drug response

Since cancer is one of the leading causes of death worldwide, there is an urgent need to find better treatments. Currently, the use of chemotherapeutics remains the predominant option for cancer therapy. However, one of the major obstacles for successful cancer therapy using these chemotherapeutics is that patients often do not respond or eventually develop resistance after initial treatment. Therefore identification of genes involved in chemotherapeutic response is critical for predicting tumour response and treating drug-resistant cancer patients. A group of genes commonly lost or inactivated are tumour suppressor genes, which can promote the initiation and progression of cancer through regulation of various biological processes such as cell proliferation, cell death and cell migration/invasion. Recently, mounting evidence suggests that these tumour suppressor genes also play a very important role in the response of cancers to a variety of chemotherapeutic drugs. In the present review, we will provide a comprehensive overview on how major tumour suppressor genes [Rb (retinoblastoma), p53 family, cyclin-dependent kinase inhibitors, BRCA1 (breast-cancer susceptibility gene 1), PTEN (phosphatase and tensin homologue deleted on chromosome 10), Hippo pathway, etc.] are involved in chemotherapeutic drug response and discuss their applications in predicting the clinical outcome of chemotherapy for cancer patients. We also propose that tumour suppressor genes are critical chemotherapeutic targets for the successful treatment of drug-resistant cancer patients in future applications.

Cellular senescence and cancer chemotherapy resistance

Innate or acquired resistance to cancer therapeutics remains an important area of biomedical investigation that has clear ramifications for improving cancer specific death rates. Importantly, clues to key resistance mechanisms may lie in the well-orchestrated and highly conserved cellular and systemic responses to injury and stress. Many anti-neoplastic therapies typically rely on DNA damage, which engages potent DNA damage response signaling pathways that culminate in apoptosis or growth arrest at checkpoints to allow for damage repair. However, an alternative cellular response, senescence, can also be initiated when challenged with these internal/external pressures and in ideal situations acts as a self-protecting mechanism. Senescence-induction therapies are an attractive concept in that they represent a normal, highly conserved and commonly invoked tumor-suppressing response to overwhelming genotoxic stress or oncogene activation. Yet, such approaches should ensure that senescence by-pass or senescence re-emergence does not occur, as emergent cells appear to have highly drug resistant phenotypes. Further, cell non-autonomous senescence responses may contribute to therapy-resistance in certain circumstances. Here we provide an overview of mechanisms by which cellular senescence plausibly contributes to therapy resistance and concepts by which senescence responses can be influenced to improve cancer treatment outcomes.

Sorafenib attenuates p21 in kidney cancer cells and augments cell death in combination with DNA-damaging chemotherapy

There are few effective therapeutic options for metastatic renal cell carcinoma (RCC). Conventional chemotherapeutic agents are ineffective since these tumors are unusually resistant to DNA damage, likely due to an exuberant DNA repair response. Sorafenib, as one of the few available effective therapeutic options for metastatic RCC, has been shown to inhibit cell proliferation by inhibition of tyrosine kinases. We have recently shown that sorafenib inhibits soluble epoxide hydrolase, which catalyzes metabolism of the anti-inflammatory epoxyeicosatrienoic acids. Given previous work demonstrating the anti-apoptotic role of p21 in RCC as a potential mechanism for its drug resistance, we asked whether sorafenib signals through this pathway. We now show that sorafenib markedly decreases p21 levels in several RCC and hepatocellular carcinoma cells. Neither the MEK inhibitor PD98059 nor the sEH inhibitor t-AUCB, which represent known sorafenib-targeted signaling pathways, alter p21 levels, demonstrating that the p21 inhibitory effect of sorafenib is independent of these signaling cascades. In cells treated with doxorubicin to augment p21, sorafenib markedly decreases this protein, and the combinations of paclitaxel or doxorubicin with sorafenib show additive cytotoxicity as a function of the VHL status of the cells, suggesting that lower doses of each agent could be used in the clinical setting. In summary, we show a novel signaling pathway by which sorafenib exerts its salutary effects in RCC; future work will focus on the use of these drug combinations in the context of conventional therapeutics, and novel compounds and protocols targeting p21 in conjunction with sorafenib should be pursued.

p53-independent epigenetic repression of the p21(WAF1) gene in T-cell acute lymphoblastic leukemia

The p53 protein is a primary mediator of cellular apoptosis and growth arrest after exposure to DNA-damaging agents. Previous work has shown that the majority of childhood acute lymphoblastic leukemia (ALL) cases express a wild type p53 gene, although the functionality of the p53 pathway has rarely been validated. In the present study, the integrity of the p53 pathway was investigated in a panel of ALL cell lines and xenografts established from direct patient explants in immune-deficient mice. A focused real-time quantitative reverse transcription PCR array of known p53-regulated genes identified p21(WAF1) (CDKN1A) as the highest ranked gene to be differentially expressed between B-cell precursor (BCP)-ALL and T-ALL xenografts following exposure to the DNA-damaging drug etoposide. Lack of p21(WAF1) induction was observed in six of seven T-ALL xenograft lines, as well as primary T-ALL cells following irradiation exposure, despite an otherwise functional p53 response. Repression of p21(WAF1) in T-ALL cells was associated with decreased acetylated H3K9 localized at its promoter compared with BCP-ALL cells, together with increased CpG methylation within the first exon and intron. Although the histone deacetylase inhibitor vorinostat failed to induce p21(WAF1) in T-ALL samples, the combination of vorinostat and the demethylating agent decitabine reactivated expression of the silenced p21(WAF1) gene in the Molt-4 T-ALL cell line. Considering the known anti-apoptotic function of p21(WAF1), our findings have significant implications for the responses of T- versus BCP-ALL cells to chemotherapeutic drugs that induce p21(WAF1).

p21(WAF1/CIP1) upregulation through the stress granule-associated protein CUGBP1 confers resistance to bortezomib-mediated apoptosis

Background

p21^WAF1/CIP1 is a well known cyclin-dependent kinase inhibitor induced by various stress stimuli. Depending on the stress applied, p21 upregulation can either promote apoptosis or prevent against apoptotic injury. The stress-mediated induction of p21 involves not only its transcriptional activation but also its posttranscriptional regulation, mainly through stabilization of p21 mRNA levels. We have previously reported that the proteasome inhibitor MG132 induces the stabilization of p21 mRNA, which correlates with the formation of cytoplasmic RNA stress granules. The mechanism underlying p21 mRNA stabilization, however, remains unknown.

Methodology/Principal Findings

We identified the stress granules component CUGBP1 as a factor required for p21 mRNA stabilization following treatment with bortezomib ( =  PS-341/Velcade). This peptide boronate inhibitor of the 26S proteasome is very efficient for the treatment of myelomas and other hematological tumors. However, solid tumors are sometimes refractory to bortezomib treatment. We found that depleting CUGBP1 in cancer cells prevents bortezomib-mediated p21 upregulation. FISH experiments combined to mRNA stability assays show that this effect is largely due to a mistargeting of p21 mRNA in stress granules leading to its degradation. Altering the expression of p21 itself, either by depleting CUGBP1 or p21, promotes bortezomib-mediated apoptosis.

Conclusions/Significance

We propose that one key mechanism by which apoptosis is inhibited upon treatment with chemotherapeutic drugs might involve upregulation of the p21 protein through CUGBP1.

Advances in the biology of malignant pleural mesothelioma

Malignant pleural mesothelioma is a highly aggressive cancer with a very poor prognosis. Although the mechanism of carcinogenesis is not fully understood, approximately 80% of malignant pleural mesothelioma can be attributed to asbestos fiber exposure. This disease is largely unresponsive to conventional chemotherapy or radiotherapy, and most patients die within 10-17 months of their first symptoms. Currently, malignant pleural mesothelioma therapy is guided by clinical stage and patient characteristics rather than by the histological or molecular features of the tumor. Several molecular pathways involved in malignant pleural mesothelioma have been identified; these include cell cycle regulation, apoptosis, growth factor pathways, and angiogenesis. Unfortunately, several agents targeting these processes, including erlotinib, gefitinib, and imatinib, have proven ineffective in clinical trials. A greater understanding of the molecular pathways involved in malignant pleural mesothelioma is needed to develop better diagnostics, therapeutics, and preventative measures. Moreover, understanding the biological basis of mesothelioma progression may facilitate personalized treatment approaches, and early identification of poor prognostic indicators may help reduce the heterogeneity of the clinical response. This paper reviews advances in the molecular biology of malignant pleural mesothelioma in terms of pathogenesis, the major molecular pathways and the associated therapeutic strategies, and the roles of biomarkers.

Induction of senescence markers after neo-adjuvant chemotherapy of malignant pleural mesothelioma and association with clinical outcome: an exploratory analysis

The aim of this study was to assess the induction of senescence markers versus apoptosis pathways in malignant pleural mesothelioma (MPM) tumour samples before and after neo-adjuvant platinum-based chemotherapy and to investigate their relationship with clinical outcome. Specific senescence pathways were assessed by quantifying the expression of p21 and plasminogen activator inhibitor-1 (PAI-1) for the p21-p53 pathway, IGFBP7 for the IGF pathway and ALDH1A3 for the IFN pathway. p21 and PAI-1 expression were also assessed by immunohistochemistry. In addition, beta-galactosidase activity staining at pH 6.0 was performed. Apoptosis was determined by TUNEL assay. Clinical outcome was assessed by modified RECIST criteria, progression-free and overall survival. In a training set (n=9 patients) paired comparison demonstrated a significant increase in p21 (p<0.05), PAI-1 (p<0.01) and apoptosis (p<0.01) after neo-adjuvant chemotherapy. The patients with the highest increase in PAI-1 had stable disease, whilst patients with little change in senescence markers accompanied by a high increase in apoptosis had an objective response after chemotherapy. The hypothesis that stable disease might be associated with an increase in senescence markers was confirmed in a tissue microarray (n=26 patients) using p21 and PAI-1 immunohistochemistry as readouts. For patients where survival and time to progression data were available, increased PAI-1 levels were significantly associated with a worst outcome. Our results demonstrate induction of senescence markers by neo-adjuvant chemotherapy in a proportion of patients with MPM and its potential association with a poor outcome.

An orthotopic implantation mouse model of human malignant pleural mesothelioma for in vivo photon counting analysis and evaluation of the effect of S-1 therapy

Human malignant pleural mesothelioma (HMPM) is an aggressive neoplasm that is highly resistant to conventional therapies. We established 3 HMPM cell lines (TCC-MESO-1, TCC-MESO-2 and TCC-MESO-3) from Japanese patients; the first 2 from the primary and metastatic tumors of a patient with the epithelioid type of HMPM, and the third from a patient with biphasic characteristics of the tumor (epithelioid and sarcomatous phenotypes). The 3 cell lines resembled the original HMPMs in their morphological and biological features, including the genetic alterations such as lack of p16 expression and mutation of p53. Their tumorigenicity was determined in SCID mice by orthotopic implantation (20-46%). The tumorigenicity of the HMPM cell lines, which was relatively low, was enhanced by repeated subcultures and orthotopic implantations, and 3 competent tumorigenic sublines were produced (Me1Tu, Me2Tu and Me3Tu sublines from the TCC-MESO-1, TCC-MESO-2 and TCC-MESO-3 cell lines, respectively). The resultant HMPM sublines efficiently generated tumors in the SCID mice (100%) following orthotopic implantation. SCID mice implanted with the competent sublines, into one of which the luciferase gene was introduced, displayed quantitative fluctuation of the bioluminescence for the tumor volume in vivo. Oral administration of S-1, an anticancer agent, suppressed the proliferation of the luciferase gene-expressing Me1Tu subline in the mouse models in vivo, with a treated-to-control ratio of the mean tumor volume of 0.2. The orthotopic implantation mouse model proved to be useful for quantitative evaluation of the efficacy of novel anticancer drugs and also for studying the biology of HMPMs in vivo.

Sorafenib inhibits ERK1/2 and MCL-1(L) phosphorylation levels resulting in caspase-independent cell death in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive, rapidly progressive malignancy without effective therapy. We evaluate sorafenib efficacy and impact on the cellular pro-survival machinery in vitro, efficacy of sorafenib as monotherapy and in combination with the naturally occurring death receptor agonist, TRAIL using human MPM cell lines, MSTO-211H, M30, REN, H28, H2052 and H2452. In vitro studies of the six MPM lines demonstrated single agent sensitivity to the multikinase inhibitor sorafenib and resistance to TRAIL. H28 and H2452 demonstrated augmented apoptosis with the addition of TRAIL to sorafenib in vitro. Treated cell lines demonstrated sorafenib-induced rapid dephosphorylation of AKT followed shortly by near complete dephosphorylation of the constitutively phosphorylated ERK1/2. Sorafenib therapy also decreased phosphorylation of B-Raf and mTOR in several cell lines. Within 3 h of sorafenib treatment, a number of known pro-survival molecules were dephosphorylated and/or downregulated in expression including MCL-1(L), c-FLIP(L), survivin and cIAP(1). These changes and eventual cell death did not elicit significant caspase-3 activation or PARP cleavage and pretreatment with the pan-caspase inhibitor, Z-VAD-FMK, did not block sorafenib efficacy but did block the effect of TRAIL monotherapy. Pre-treatment with Z-VAD-FMK did not block the synergistic effect of TRAIL and sorafenib in H28. In summary, single agent treatment with sorafenib results in widespread inhibition of the pro-survival machinery in vitro leading to cell death via a primarily caspase-independent mechanism. Combining sorafenib therapy with TRAIL, may be useful in order to provide a more efficient death signal and this synergistic effect appears to be caspase-independent. Pilot in vivo data demonstrates promising evidence of therapeutic efficacy in human tumor bearing xenograft nu/nu mice. We document single agent activity of sorafenib against MPM, unravel novel effects of sorafenib on anti-apoptotic signaling mediators, and suggest the combination of sorafenib plus TRAIL as possible therapy for clinical testing in MPM.

Update in neoplastic lung diseases and mesothelioma

CONTEXT

Lung cancer is a common disease frequently seen by the surgical pathologist. Although secondary to improvements in screening and radiologic techniques and aggressive resection of small pulmonary nodules, the diagnosis of preneoplastic lesions is increasing in frequency and importance. Consequently, a greater understanding of their role in the development of lung carcinoma is needed for optimal patient care. Two lesions often encountered as small pulmonary nodules are bronchioloalveolar carcinoma and adenocarcinoma, which can be challenging to distinguish. Recently, updates to the TNM classification of non-small cell lung carcinoma have been reported that directly impact prognosis and treatment algorithms. Identification of new molecular targets in pleural mesothelioma and in preneoplastic lesions may lead to improved therapeutic strategies.

OBJECTIVE

To present recent advances in our understanding of neoplastic lung diseases and mesothelioma and to describe how these advances relate to the current practice of pulmonary pathology.

DATA SOURCES

Published literature from PubMed (National Library of Medicine) and primary material from the authors' institution.

CONCLUSIONS

It is important for the surgical pathologist to understand current diagnostic classifications of non-small cell lung cancer and to be aware of the range of preneoplastic lesions, as well as the features useful for distinguishing bronchioloalveolar carcinoma from adenocarcinoma in small pulmonary nodules. Although pleural mesothelioma has distinct features, it can also overlap histologically with adenocarcinoma, and immunohistochemistry can greatly aid in accurate diagnosis. New therapies targeting molecular markers in both non-small cell lung cancer and mesothelioma rely on accurate histopathologic diagnosis of these entities.

p21(WAF1/CIP1) and cancer: a shifting paradigm?

The cyclin-dependent kinase inhibitor p21(WAF1/CIP1) is a key mediator of p53-dependent cell cycle arrest and may play the role of a tumor suppressor in cancer. However, it has been shown that p21 may also act as an oncogene, because it inhibits apoptosis and may promote cell proliferation in some tumors. These data point out to "antagonistic duality" of p21, because it possesses anticancer and procancer properties at the same time. New data suggest that more and more proteins also may play contradictory roles in cancer thus challenging current paradigm of established oncogenes and tumor suppressors. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.

The plexin-A1 receptor activates vascular endothelial growth factor-receptor 2 and nuclear factor-kappaB to mediate survival and anchorage-independent growth of malignant mesothelioma cells

The semaphorins and their receptors, the neuropilins and the plexins, are constituents of a complex regulatory system that controls axonal guidance. Moreover, many types of tumor cells express various members of semaphorins and receptors, but the biological activities within tumor mass and the signal transduction mechanism(s) they use are largely unknown. Here, we show that in asbestos-related malignant pleural mesothelioma (MPM), Semaphorin-6D (Sema6D) and its receptor plexin-A1 are frequently expressed and trigger a prosurvival program that promotes anchorage-independent growth of MPM cells. Interestingly, the same response is also controlled by the tyrosine kinase receptors of vascular endothelial growth factor (VEGF) through a nuclear factor-kappaB (NF-kappaB)-dependent pathway. We found that in MPM cells, plexin-A1 and VEGF-receptor 2 (VEGF-R2) are associated in a complex. Moreover, the presence of Sema6D promotes the tyrosine phosphorylation of VEGF-R2 in a plexin-A1-dependent manner. This is necessary for basal and Sema6D-induced NF-kappaB transcriptional activity, and NF-kappaB mediates tumor cell survival. Expression of Sema6D and plexin-A1 is induced by asbestos fibers and overexpression of plexin-A1 in nonmalignant mesothelial cells inhibits cell death after asbestos exposure. This work identifies a new biological function of semaphorins in cancer cells and suggests the involvement of an undescribed survival pathway during MPM tumorigenesis.