Effect of p53 Status and STAT1 on Chemotherapy-Induced, Fas-Mediated Apoptosis in Colorectal Cancer

Cell fate regulation governed by p53: Friends or reversible foes in cancer therapy

Cancer is a leading cause of death worldwide. Targeted therapies aimed at key oncogenic driver mutations in combination with chemotherapy and radiotherapy as well as immunotherapy have benefited cancer patients considerably. Tumor protein p53 (TP53), a crucial tumor suppressor gene encoding p53, regulates numerous downstream genes and cellular phenotypes in response to various stressors. The affected genes are involved in diverse processes, including cell cycle arrest, DNA repair, cellular senescence, metabolic homeostasis, apoptosis, and autophagy. However, accumulating recent studies have continued to reveal novel and unexpected functions of p53 in governing the fate of tumors, for example, functions in ferroptosis, immunity, the tumor microenvironment and microbiome metabolism. Among the possibilities, the evolutionary plasticity of p53 is the most controversial, partially due to the dizzying array of biological functions that have been attributed to different regulatory mechanisms of p53 signaling. Nearly 40 years after its discovery, this key tumor suppressor remains somewhat enigmatic. The intricate and diverse functions of p53 in regulating cell fate during cancer treatment are only the tip of the iceberg with respect to its equally complicated structural biology, which has been painstakingly revealed. Additionally, TP53 mutation is one of the most significant genetic alterations in cancer, contributing to rapid cancer cell growth and tumor progression. Here, we summarized recent advances that implicate altered p53 in modulating the response to various cancer therapies, including chemotherapy, radiotherapy, and immunotherapy. Furthermore, we also discussed potential strategies for targeting p53 as a therapeutic option for cancer.

Mutant p53 in cancer: from molecular mechanism to therapeutic modulation

TP53, a crucial tumor suppressor gene, is the most commonly mutated gene in human cancers. Aside from losing its tumor suppressor function, mutant p53 (mutp53) often acquires inherent, novel oncogenic functions, which is termed "gain-of-function". Emerging evidence suggests that mutp53 is highly associated with advanced malignancies and poor prognosis, which makes it a target for development of novel cancer therapies. Herein, we provide a summary of our knowledge of the mutp53 types and mutp53 spectrum in cancers. The mechanisms of mutp53 accumulation and gain-of-function are also summarized. Furthermore, we discuss the gain-of-function of mutp53 in cancers: genetic instability, ferroptosis, microenvironment, and stemness. Importantly, the role of mutp53 in the clinic is also discussed, particularly with regard to chemotherapy and radiotherapy. Last, emphasis is given to emerging strategies on how to target mutp53 for tumor therapy. Thus, this review will contribute to better understanding of the significance of mutp53 as a target for therapeutic strategies.

JAK-STAT core cancer pathway: An integrative cancer interactome analysis

Through a comprehensive review and in silico analysis of reported data on STAT-linked diseases, we analysed the communication pathways and interactome of the seven STATs in major cancer categories and proposed rational targeting approaches for therapeutic intervention to disrupt critical pathways and addictions to hyperactive JAK/STAT in neoplastic states. Although all STATs follow a similar molecular activation pathway, STAT1, STAT2, STAT4 and STAT6 exert specific biological profiles associated with a more restricted pattern of activation by cytokines. STAT3 and STAT5A as well as STAT5B have pleiotropic roles in the body and can act as critical oncogenes that promote many processes involved in cancer development. STAT1, STAT3 and STAT5 also possess tumour suppressive action in certain mutational and cancer type context. Here, we demonstrated member-specific STAT activity in major cancer types. Through systems biology approaches, we found surprising roles for EGFR family members, sex steroid hormone receptor ESR1 interplay with oncogenic STAT function and proposed new drug targeting approaches of oncogenic STAT pathway addiction.

Therapeutic approaches targeting CD95L/CD95 signaling in cancer and autoimmune diseases

Cell death plays a pivotal role in the maintenance of tissue homeostasis. Key players in the controlled induction of cell death are the Death Receptors (DR). CD95 is a prototypic DR activated by its cognate ligand CD95L triggering programmed cell death. As a consequence, alterations in the CD95/CD95L pathway have been involved in several disease conditions ranging from autoimmune diseases to inflammation and cancer. CD95L-induced cell death has multiple roles in the immune response since it constitutes one of the mechanisms by which cytotoxic lymphocytes kill their targets, but it is also involved in the process of turning off the immune response. Furthermore, beyond the canonical pro-death signals, CD95L, which can be membrane-bound or soluble, also induces non-apoptotic signaling that contributes to its tumor-promoting and pro-inflammatory roles. The intent of this review is to describe the role of CD95/CD95L in the pathophysiology of cancers, autoimmune diseases and chronic inflammation and to discuss recently patented and emerging therapeutic strategies that exploit/block the CD95/CD95L system in these diseases.

A full-proteome, interaction-specific characterization of mutational hotspots across human cancers

Rapid accumulation of cancer genomic data has led to the identification of an increasing number of mutational hotspots with uncharacterized significance. Here we present a biologically informed computational framework that characterizes the functional relevance of all 1107 published mutational hotspots identified in approximately 25,000 tumor samples across 41 cancer types in the context of a human 3D interactome network, in which the interface of each interaction is mapped at residue resolution. Hotspots reside in network hub proteins and are enriched on protein interaction interfaces, suggesting that alteration of specific protein-protein interactions is critical for the oncogenicity of many hotspot mutations. Our framework enables, for the first time, systematic identification of specific protein interactions affected by hotspot mutations at the full proteome scale. Furthermore, by constructing a hotspot-affected network that connects all hotspot-affected interactions throughout the whole-human interactome, we uncover genome-wide relationships among hotspots and implicate novel cancer proteins that do not harbor hotspot mutations themselves. Moreover, applying our network-based framework to specific cancer types identifies clinically significant hotspots that can be used for prognosis and therapy targets. Overall, we show that our framework bridges the gap between the statistical significance of mutational hotspots and their biological and clinical significance in human cancers.

STAT1 Is Required for Decreasing Accumulation of Granulocytic Cells via IL-17 during Initial Steps of Colitis-Associated Cancer

Signal transducer and activator of transcription 1 (STAT1) acts as a tumor suppressor molecule in colitis-associated colorectal cancer (CAC), particularly during the very early stages, modulating immune responses and controlling mechanisms such as apoptosis and cell proliferation. Previously, using an experimental model of CAC, we reported increased intestinal cell proliferation and faster tumor development, which were consistent with more signs of disease and damage, and reduced survival in STAT1^-/- mice, compared with WT counterparts. However, the mechanisms through which STAT1 might prevent colorectal cancer progression preceded by chronic inflammation are still unclear. Here, we demonstrate that increased tumorigenicity related to STAT1 deficiency could be suppressed by IL-17 neutralization. The blockade of IL-17 in STAT1^-/- mice reduced the accumulation of CD11b+Ly6C^lowLy6G+ cells resembling granulocytic myeloid-derived suppressor cells (MDSCs) in both spleen and circulation. Additionally, IL-17 blockade reduced the recruitment of neutrophils into intestinal tissue, the expression and production of inflammatory cytokines, and the expression of intestinal STAT3. In addition, the anti-IL-17 treatment also reduced the expression of Arginase-1 and inducible nitric oxide synthase (iNOS) in the colon, both associated with the main suppressive activity of MDSCs. Thus, a lack of STAT1 signaling induces a significant change in the colonic microenvironment that supports inflammation and tumor formation. Anti-IL-17 treatment throughout the initial stages of CAC related to STAT1 deficiency abrogates the tumor formation possibly caused by myeloid cells.

TRIM29 Reverses Oxaliplatin Resistance of P53 Mutant Colon Cancer Cell

Background

Oxaliplatin is the first-choice chemotherapy method for patients with advanced colon cancer. However, its resistance leads to treatment failure for many patients. In our experiments, we aim to elucidate the associations among TRIM29 protein, mutant P53, and the resistance of colon cancer cells to oxaliplatin.

Methods

HCT116 and HT-29 cells were cultured and transfected with plasmids pIRES2-ZsGreen1-TRIM29-flag. Western blot and real-time qRT-PCR were utilized to examine the protein and mRNA expressions of TRIM29 and other related markers, respectively. MTT assay was utilized to determine the cell growth rate and generate the inhibition curve. Continuous culture in low-concentration oxaliplatin was conducted to construct oxaliplatin-resistant cell lines. The coimmunoprecipitation method and immunofluorescence detection were used to examine the interaction between TRIM29 and mutant P53 protein in HT29 cells.

Results

We successfully transfected pIRES2-ZsGreen1-TRIM29-flag into HCT116 and HT29 cells, which were utilized in the whole experiments. TRIM29 significantly increased the sensitivity of P53 mutant colon cancer cell HT29 to oxaliplatin. The oxaliplatin-resistant model of P53 mutant colon cancer cell HT29 was successfully constructed. TRIM29 physically bound with mutant P53 and retained it in the cytoplasm from the nucleus, which inhibited its transcription function of downstream genes such as MDR1. In addition, TRIM29 successfully reversed the resistance of HT29-OX resistant cell model to oxaliplatin.

Conclusion

In mutant P53 colon cancer cell HT29, TRIM29 greatly increased the sensitivity of HT29 to oxaliplatin and reverse oxaliplatin resistance. The underlying mechanism is TRIM29 may increase the sensitivity of HT29 to oxaliplatin by blocking the transcriptional function of mutant P53, which inhibits the transcription function of its downstream gene such as MDR1.

Fra-1 Inhibits Cell Growth and the Warburg Effect in Cervical Cancer Cells via STAT1 Regulation of the p53 Signaling Pathway

The oncogenesis of cervical cancer is a multi-factor and multi-step process, and major risk factors include oncogene activation with tumor suppressor gene inactivation, viral factors, and immune factors. For example, the human papillomavirus (HPV) has been linked to the occurrence of cervical cancer. At present, the pathogenesis of cervical cancer remains unclear. Fra-1 (Fos-related antigen 1, also known as FOSL1) is a member of the Fos family and an important nuclear transcription factor that regulates normal cell growth, differentiation, and apoptosis. In the present study, we found that Fra-1 inhibited the proliferation of cervical cancer cells while also promoting apoptosis and affecting cell cycle distribution. Moreover, Fra-1 up-regulated STAT1 expression and modulated p53 signal pathway activity in cervical cancer cells. Overexpression of Fra-1 inhibited cell senescence by altering sirtuin 1 (SIRT1) expression in HeLa cells, and Fra-1 overexpression restored mitochondrial disorder and suppressed metabolic reprogramming in HeLa cells. Silencing of STAT1 impaired the inhibitory effect of Fra-1 on cervical cancer cell growth, while knock-down of STAT1 reversed the effect on cell senescence and mitochondrial dysfunction caused by Fra-1 in HeLa cells. Silencing of STAT1 also recovered metabolic reprogramming in cervical cancer cells. In summary, our results show that Fra-1 inhibited cervical cancer cell growth and the Warburg effect via STAT1-mediated regulation of the p53 signaling pathway.

Irinotecan-Still an Important Player in Cancer Chemotherapy: A Comprehensive Overview

Irinotecan has been used in the treatment of various malignancies for many years. Still, the knowledge regarding this drug is expanding. The pharmacogenetics of the drug is the crucial component of response to irinotecan. Furthermore, new formulations of the drug are introduced in order to better deliver the drug and avoid potentially life-threatening side effects. Here, we give a comprehensive overview on irinotecan’s molecular mode of action, metabolism, pharmacogenetics, and toxicity. Moreover, this article features clinically used combinations of the drug with other anticancer agents and introduces novel formulations of drugs (e.g., liposomal formulations, dendrimers, and nanoparticles). It also outlines crucial mechanisms of tumor cells’ resistance to the active metabolite, ethyl-10-hydroxy-camptothecin (SN-38). We are sure that the article will constitute an important source of information for both new researchers in the field of irinotecan chemotherapy and professionals or clinicians who are interested in the topic.

Trichothecin Inhibits Cancer-Related Features in Colorectal Cancer Development by Targeting STAT3

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that contributes to cancer progression through multiple processes of cancer development, which makes it an attractive target for cancer therapy. The IL-6/STAT3 pathway is associated with an advanced stage in colorectal cancer patients. In this study, we identified trichothecin (TCN) as a novel STAT3 inhibitor. TCN was found to bind to the SH2 domain of STAT3 and inhibit STAT3 activation and dimerization, thereby blocking STAT3 nuclear translocation and transcriptional activity. TCN did not affect phosphorylation levels of STAT1. TCN significantly inhibited cell growth, arrested cell cycle at the G0/G1 phase, and induced apoptosis in HCT 116 cells. In addition, the capacities of colony formation, migration, and invasion of HCT 116 cells were impaired upon exposure to TCN with or without IL-6 stimulation. In addition, TCN treatment abolished the tube formation of HUVEC cells in vitro. Taken together, these results highlight that TCN inhibits various cancer-related features in colorectal cancer development in vitro by targeting STAT3, indicating that TCN is a promising STAT3 inhibitor that deserves further exploration in the future.

Overexpression of TP53 protein is associated with the lack of adjuvant chemotherapy benefit in patients with stage III colorectal cancer

TP53 mutations drive colorectal cancer development, with missense mutations frequently leading to accumulation of abnormal TP53 protein. TP53 alterations have been associated with poor prognosis and chemotherapy resistance, but data remain controversial. Here, we examined the predictive utility of TP53 overexpression in the context of current adjuvant treatment practice for patients with stage III colorectal cancer. A prospective cohort of 264 stage III patients was tested for association of TP53 expression with 5-year disease-free survival, grouped by adjuvant treatment. Findings were validated in an independent retrospective cohort of 274 stage III patients. Overexpression of TP53 protein (TP53+) was found in 53% and 52% of cases from the prospective and retrospective cohorts, respectively. Among patients receiving adjuvant chemotherapy, TP53+ status was associated with shorter disease-free survival (p ≤ 0.026 for both cohorts), while no difference in outcomes between TP53+ and TP53- cases was observed for patients treated with surgery alone. Considering patients with TP53- tumors, those receiving adjuvant treatment had better outcomes compared with those treated with surgery alone (p ≤ 0.018 for both cohorts), while no treatment benefit was apparent for patients with TP53+ tumors. Combined cohort-stratified analysis adjusted for clinicopathological variables and DNA mismatch repair status confirmed a significant interaction between TP53 expression and adjuvant treatment for disease-free survival (p_interaction = 0.030). For the combined cohort, the multivariate hazard ratio for TP53 overexpression among patients receiving adjuvant chemotherapy was 2.03 (95% confidence interval 1.41-2.95, p < 0.001), while the hazard ratio for adjuvant treatment among patients with TP53- tumors was 0.42 (95% confidence interval 0.24-0.71, p = 0.001). Findings were maintained irrespective of tumor location or when restricted to mismatch repair-proficient tumors. Our data suggest that adjuvant chemotherapy benefit in stage III colorectal cancer is restricted to cases with low-level TP53 protein expression. Identifying TP53+ tumors could highlight patients that may benefit from more aggressive treatment or follow-up.

Regulation of tNOX expression through the ROS-p53-POU3F2 axis contributes to cellular responses against oxaliplatin in human colon cancer cells

BACKGROUND

Oxaliplatin belongs to the platinum-based drug family and has shown promise in treating cancer by binding to DNA to induce cytotoxicity. However, individual patients show diverse therapeutic responses toward oxaliplatin due to yet-unknown underlying mechanisms. We recently established that oxaliplatin also exert its anti-cancer activity in gastric cancer cell lines by targeting tumor-associated NADH oxidase (tNOX), attenuate NAD⁺ generation and reduce NAD⁺-dependent sirtuin 1 (SIRT1) deacetylase activity, which in turn enhances p53 acetylation and apoptosis.

METHODS

In this study, differential cellular outcomes in response to oxaliplatin exposure of p53-wild-type versus p53-null HCT116 human colon cancer cells were examined. Cell growth profile was determined by cell impedance measurements and apoptosis was analyzed by flow cytometry. The engagement between oxaliplatin and tNOX protein was studied by cellular thermal shift assay. Furthermore, western blot analysis revealed that p53 was important in regulating tNOX expression in these cell lines.

RESULTS

In p53-wild-type cells, we found that oxaliplatin inhibited cell growth by inducing apoptosis and concurrently down-regulating tNOX at both the transcriptional and translational levels. In p53-null cells, in contrast, oxaliplatin moderately up-regulated tNOX expression and yielded no apoptosis and much less cytotoxicity. Further experiments revealed that in p53-wild-type cells, oxaliplatin enhanced ROS generation and p53 transcriptional activation, leading to down-regulation of the transcriptional factor, POU3F2, which enhances the expression of tNOX. Moreover, the addition of a ROS scavenger reversed the p53 activation, POU3F2 down-regulation, and apoptosis induced by oxaliplatin in p53-wild-type cells. In the p53-null line, on the other hand, oxaliplatin treatment triggered less ROS generation and no p53 protein, such that POU3F2 and tNOX were not down-regulated and oxaliplatin-mediated cytotoxicity was attenuated.

CONCLUSION

Our results show that oxaliplatin mediates differential cellular responses in colon cancer cells depending on their p53 status, and demonstrate that the ROS-p53 axis is important for regulating POU3F2 and its downstream target, tNOX. Notably, the depletion of tNOX sensitizes p53-null cells to both spontaneous and oxaliplatin-induced apoptosis. Our work thus clearly shows a scenario in which targeting of tNOX may be a potential strategy for cancer therapy in a p53-inactivated system.

A study on the correlation between STAT‑1 and mutant p53 expression in glioma

Glioma is the most common primary brain tumor in adults and the second most common malignant tumor in children. Aberrant expression of signal transducer and activator of transcription 1 (STAT‑1) and p53 are known to affect the occurrence and progression of malignant tumors. The aim of the present study was to investigate the expression of STAT‑1 and mutant p53 gene, as well as their correlation, in patients with glioma. The present study included 50 patients who underwent glioma resection at the First Affiliated Hospital of Inner Mongolia Medical University between December 2007 and December 2011, and 10 patients with acute cerebral contusion who underwent intracerebral hematoma removal at the same hospital between January 2013 and January 2014. The expression of STAT‑1 and mutant p53 protein in patients with different grades of glioma was assessed by immunohistochemistry. Spearman's correlation coefficient was employed to examine the correlation between STAT‑1 and the grade of glioma, and mutant p53 expression. The results demonstrated that the mean expression of STAT‑1 in glioma was significantly lower compared with normal brain tissue (P<0.05). However, there was no significant difference in the STAT‑1 positive expression rate between the two groups (χ2=1.38, P>0.05). The expression score (P<0.05) and positive expression rate (χ2=31.27, P<0.05) of mutant p53 in glioma was significantly higher compared with those in normal brain tissue. Statistical analysis revealed a negative correlation between STAT‑1 expression and the grade of glioma (r=‑0.767, P<0.05). In addition, mutant p53 expression was negatively correlated with STAT‑1 expression in glioma (r=‑0.876, P<0.05). The observed negative correlation between STAT‑1 and the pathological grade of glioma suggested an association between STAT‑1 and the occurrence and development of glioma, thus revealing the potential of STAT‑1 as a diagnostic biomarker and therapeutic target for glioma.

C-C motif chemokine 22 predicts postoperative prognosis and adjuvant chemotherapeutic benefits in patients with stage II/III gastric cancer

Immune molecules, which have been found to be important in tumor microenvironment, seem prospective in tumor therapy, but they are still not effective enough to use in clinical practice. C-C motif chemokine 22 (CCL22) exists in various malignancies and correlates with migration of regulatory T cells, but its clinical significance in gastric cancer is still unclear. In this study, a combined data set of 466 patients with gastric cancer after surgical resection, comprised of a discovery (n = 319) and a validation data set (n = 147), was enrolled. CCL22 expression was assessed by immunohistochemical staining and we evaluated prognostic values of CCL22 staining and clinical outcomes with use of Kaplan-Meier curve and Multivariate Cox regression analysis. Positive CCL22 expression predicted adverse overall survival independent of traditional pathological grade. Multivariate analysis defined CCL22 and TNM stage as two independent prognostic factors for overall survival. Besides, in patients with TNM stage II/III disease, the rate of overall survival was higher among patients with CCL22-positive tumors who were treated with 5-fluorouracil based adjuvant chemotherapy than that among those who were not (P = 0.012, P < 0.001 and P < 0.001, in discovery, validation and combined data set). But for these with CCL22-negative tumors, whether to undergo adjuvant chemotherapy showed no statistical significance (P = 0.595, P = 0.085 and P = 0.252, respectively). To conclude, CCL22 was identified as an independent adverse prognostic immunobiomarker for patients with gastric cancer after surgery, which is associated with tumor-infiltrating immunocytes and could be incorporated into TNM staging system to redefine a high-risk subgroup who were more likely to benefit from 5-fluorouracil based adjuvant chemotherapy.

Emerging roles of p53 and other tumour-suppressor genes in immune regulation

Tumour-suppressor genes are indispensable for the maintenance of genomic integrity. Recently, several of these genes, including those encoding p53, PTEN, RB1 and ARF, have been implicated in immune responses and inflammatory diseases. In particular, the p53 tumour- suppressor pathway is involved in crucial aspects of tumour immunology and in homeostatic regulation of immune responses. Other studies have identified roles for p53 in various cellular processes, including metabolism and stem cell maintenance. Here, we discuss the emerging roles of p53 and other tumour-suppressor genes in tumour immunology, as well as in additional immunological settings, such as virus infection. This relatively unexplored area could yield important insights into the homeostatic control of immune cells in health and disease and facilitate the development of more effective immunotherapies. Consequently, tumour-suppressor genes are emerging as potential guardians of immune integrity.

Peritoneal expression of Matrilysin helps identify early post-operative recurrence of colorectal cancer

Recurrence of colorectal cancer (CRC) following a potentially curative resection is a challenging clinical problem. Matrix metalloproteinase-7 (MMP-7) is over-expressed by CRC cells and supposed to play a major role in CRC cell diffusion and metastasis. MMP-7 RNA expression was assessed by real-time PCR using specific primers in peritoneal washing fluid obtained during surgical procedure. After surgery, patients underwent a regular follow up for assessing recurrence. transcripts for MMP-7 were detected in 31/57 samples (54%). Patients were followed-up (range 20-48 months) for recurrence prevention. Recurrence was diagnosed in 6 out of 55 patients (11%) and two patients eventually died because of this. Notably, all the six patients who had relapsed were positive for MMP-7. Sensitivity and specificity of the test were 100% and 49% respectively. Data from patients have also been corroborated by computational approaches. Public available coloncarcinoma datasets have been employed to confirm MMP7 clinical impact on the disease. Interestingly, MMP-7 expression appeared correlated to Tgfb-1, and correlation of the two factors represented a poor prognostic factor. This study proposes positivity of MMP-7 in peritoneal cavity as a novel biomarker for predicting disease recurrence in patients with CRC.

Upregulation of KPNβ1 in gastric cancer cell promotes tumor cell proliferation and predicts poor prognosis

KPNβ1, also known as importin β, P97, is reported as one of soluble transport factors that mediates transportion of proteins and RNAs between the nucleus and cytoplasm in cellular process. Recent studies show that KPNβ1 is a tumor gene which is highly expressed in several malignant tumors such as ovarian cancer, cervical tumor, neck cancer, and lung cancer via promoting cell proliferation or inhibiting cell apoptotic pathways. However, the the role of KPNβ1 in gastric cancer remains unclear. In this study, Western blot and immunohistochemistrical analyses showed that KPNβ1 was significantly upregulated in clinical gastric cancer specimens compared with adjacent noncancerous tissues. KPNβ1 was positively correlated with tumor grade, Ki-67, and predicted poor prognosis of gastric cancer. More importantly, through starvation-refeeding model, CCK8 assay, flow cytometry, colony formation assays, the vitro studies demonstrated that KPNβ1 promoted proliferation of gastric cancer cells, while KPNβ1 knockdown led to decreased cell proliferation and arrested cell cycle at G1 phase. Furthermore, our results also indicated that KPNβ1 expression could result in docetaxel resistance. And, KPNβ1 could interact with Stat1, contributed to its nucleus import in gastric cancer cells. These findings provided a novel promising therapeutic targets for clinical treatment against human gastric cancer.

Crude extract of Rheum palmatum L induced cell death in LS1034 human colon cancer cells acts through the caspase-dependent and -independent pathways

Crude extract of Rheum palmatum L (CERP) has been used to treat different diseases in the Chinese population for decades. In this study, we investigated the effects of CERP on LS1034 human colorectal cancer cells in vitro and also examined possible mechanisms of cell death. Flow cytometric assays were used to measure the percentage of viable cells, cell cycle distribution including the sub-G1 phase (apoptosis), the activities of caspase-8, -9, and -3, reactive oxygen species (ROS) and Ca(2+) levels, and mitochondrial membrane potential (ΔΨm). DNA damage, nuclei condensation, protein expression, and translocation were examined by Comet assay, 4'-6-diamidino-2-phenylindole (DAPI) staining, Western blotting, and confocal laser system microscope, respectively. CERP induced apoptosis as seen by DNA fragmentation and DAPI staining in a concentration- and time-dependent manner in cancer cells. CERP was associated with an increase in the Bax/Bcl-2 protein ratio and CERP promoted the activities of caspase-8, -9, and -3. Both ROS and Ca(2+) levels were increased by CERP but the compound decreased levels of ΔΨm in LS1034 cells. Laser confocal microscope also confirmed that CERP promoted the expressions of AIF, Endo G, cytochrome c, and GADD153 to induce apoptosis through mitochondrial-dependent pathway.

TP53 mutations in advanced colorectal cancer: the dark side of the moon

BACKGROUND

Evidence for TP53 mutations as biomarker in colorectal cancer (CRC) is conflicting.

METHODS

We assessed TP53 mutations in 51 patients with advanced CRC enrolled into a phase II, randomised trial of first-line tegafur-uracil (UFT)/leucovorin (LV) plus irinotecan (n = 23) versus UFT/LV plus oxaliplatin (n = 28).

RESULTS

Non-functional TP53 mutations were found in 35% of patients. The response rate was not significantly different according to TP53 status. Progression-free and overall survival were longer in patients with TP53 mutations compared to those with wild-type TP53 (9 vs. 6.5 months, p = 0.0504, and 39.2 vs. 19.6 months, p = 0.0055, respectively). On multivariable analysis, TP53 mutation was independently associated with a decreased risk of death (hazard ratio 0.329, 95% CI 0.159-0.679; p = 0.0026). Treatment arm did not interact with TP53 in influencing outcomes.

CONCLUSION

TP53 was not predictive of benefit from first-line irinotecan- or oxaliplatin-based chemotherapy. TP53 mutations may possibly be associated with a more indolent course of CRC after the diagnosis of metastatic disease.

Pharmacogenomic profiling and pathway analyses identify MAPK-dependent migration as an acute response to SN38 in p53 null and p53-mutant colorectal cancer cells

The topoisomerase I inhibitor irinotecan is used to treat advanced colorectal cancer and has been shown to have p53-independent anticancer activity. The aim of this study was to identify the p53-independent signaling mechanisms activated by irinotecan. Transcriptional profiling of isogenic HCT116 p53 wild-type and p53 null cells was carried out following treatment with the active metabolite of irinotecan, SN38. Unsupervised analysis methods showed that p53 status had a highly significant impact on gene expression changes in response to SN38. Pathway analysis indicated that pathways involved in cell motility [adherens junction, focal adhesion, mitogen-activated protein kinase (MAPK), and regulation of the actin cytoskeleton] were significantly activated in p53 null cells, but not p53 wild-type cells, following SN38 treatment. In functional assays, SN38 treatment increased the migratory potential of p53 null and p53-mutant colorectal cancer cell lines, but not p53 wild-type lines. Moreover, p53 null SN38-resistant cells were found to migrate at a faster rate than parental drug-sensitive p53 null cells, whereas p53 wild-type SN38-resistant cells failed to migrate. Notably, cotreatment with inhibitors of the MAPK pathway inhibited the increased migration observed following SN38 treatment in p53 null and p53-mutant cells. Thus, in the absence of wild-type p53, SN38 promotes migration of colorectal cancer cells, and inhibiting MAPK blocks this potentially prometastatic adaptive response to this anticancer drug.

Identification of an acetylation-dependant Ku70/FLIP complex that regulates FLIP expression and HDAC inhibitor-induced apoptosis

FLIP is a potential anti-cancer therapeutic target that inhibits apoptosis by blocking caspase 8 activation by death receptors. We report a novel interaction between FLIP and the DNA repair protein Ku70 that regulates FLIP protein stability by inhibiting its polyubiquitination. Furthermore, we found that the histone deacetylase (HDAC) inhibitor Vorinostat (SAHA) enhances the acetylation of Ku70, thereby disrupting the FLIP/Ku70 complex and triggering FLIP polyubiquitination and degradation by the proteasome. Using in vitro and in vivo colorectal cancer models, we further demonstrated that SAHA-induced apoptosis is dependant on FLIP downregulation and caspase 8 activation. In addition, an HDAC6-specific inhibitor Tubacin recapitulated the effects of SAHA, suggesting that HDAC6 is a key regulator of Ku70 acetylation and FLIP protein stability. Thus, HDAC inhibitors with anti-HDAC6 activity act as efficient post-transcriptional suppressors of FLIP expression and may, therefore, effectively act as 'FLIP inhibitors'.

CD95 signaling in colorectal cancer

CD95 and its ligand (CD95L) are widely expressed in colorectal tumors, but their role in shaping tumor behavior is unclear. CD95 activation on tumor cells can lead to apoptosis, while CD95L attracts neutrophils, suggesting a function in tumor suppression. However, CD95 can also promote tumorigenesis, at least in part by activating non-apoptotic signaling pathways that stimulate tumor cell proliferation, invasion and survival. In addition, CD95 signaling in stromal cells and tumor-infiltrating inflammatory cells has to be taken into account when addressing the function of CD95 and its ligand in colorectal tumor biology. We present a model in which the tumor-suppressing and tumor-promoting activities of CD95/CD95L together determine colorectal tumor behavior. We also discuss how these multiple activities are changing our view of CD95 and CD95L as potential therapeutic targets in the treatment of colorectal cancer. We conclude that locking CD95 in apoptosis-mode may be a more promising anti-cancer strategy than simply inhibiting or stimulating CD95.

Combination of ATP-competitive mammalian target of rapamycin inhibitors with standard chemotherapy for colorectal cancer

ATP-competitive mammalian target of rapamycin (mTOR) inhibitors are in early phase clinical trials. These novel targeted agents, including PP242, are mechanistically distinct from the allosteric, partial mTOR inhibitor, rapamycin. The goal of this study was to evaluate how PP242 best combines with standard chemotherapies for colorectal cancer (CRC), and which subsets of patients are most likely to benefit. The combination index for PP242 plus 5-fluorouracil, oxaliplatin, or irinotecan was determined in CRC cell lines with different mutational backgrounds. In KRAS mutant CRC cell lines, sensitivity to PP242 increases with co-mutation of PIK3CA. Mutation of p53 predicts resistance to chemotherapy, but not PP242. Efficacy of PP242 was comparable to that of standard chemotherapies over the dose range tested. Sensitivity or resistance to PP242 dictates relative synergy or antagonism, respectively, when PP242 is combined with 5-fluorouracil. The same trend exists for PP242 + oxaliplatin, but with a narrower dynamic range. Conversely potency of PP242 and the combination index for PP242 + irinotecan were unrelated, but synergy exists across all dose levels in PP242 and irinotecan sensitive, p53 wild-type cell lines. Overall, our in vitro analysis predicts that mutational status can be used to rank sensitivity to PP242 and standard chemotherapies. Single agent potency can in turn be used to predict the combination index in a drug-specific manner. Our data suggest a clinical trial to determine whether ATP-competitive mTOR inhibitors provide benefit in combination with standard chemotherapies for patients with PIK3CA mutant metastatic CRC, stratified by the presence or absence of KRAS co-mutation.

Delivery of intracellular-acting biologics in pro-apoptotic therapies

The recent elucidation of molecular regulators of apoptosis and their roles in cellular oncogenesis has motivated the development of biomacromolecular anticancer therapeutics that can activate intracellular apoptotic signaling pathways. Pharmaceutical scientists have employed a variety of classes of biologics toward this goal, including antisense oligodeoxynucleotides, small interfering RNA, proteins, antibodies, and peptides. However, stability in the in vivo environment, tumor-specific biodistribution, cell internalization, and localization to the intracellular microenvironment where the targeted molecule is localized pose significant challenges that limit the ability to directly apply intracellular-acting, pro-apoptotic biologics for therapeutic use. Thus, approaches to improve the pharmaceutical properties of therapeutic biomacromolecules are of great significance and have included chemically modifying the bioactive molecule itself or formulation with auxiliary compounds. Recently, promising advances in delivery of pro-apoptotic biomacromolecular agents have been made using tools such as peptide "stapling", cell penetrating peptides, fusogenic peptides, liposomes, nanoparticles, smart polymers, and synergistic combinations of these components. This review will discuss the molecular mediators of cellular apoptosis, the respective mechanisms by which these mediators are dysregulated in cellular oncogenesis, the history and development of both nucleic-acid and amino-acid based drugs, and techniques to achieve intracellular delivery of these biologics. Finally, recent applications where pro-apoptotic functionality has been achieved through delivery of intracellular-acting biomacromolecular drugs will be highlighted.

Epigenetics and chemoresistance in colorectal cancer: an opportunity for treatment tailoring and novel therapeutic strategies

Colorectal cancer is the second leading cause of cancer-related deaths in the world. Despite many therapeutic opportunities, prognosis remains dismal for patients with metastatic disease, and a significant portion of early-stage patients develop recurrence after chemotherapy. Epigenetic gene regulation is a major mechanism of cancer initiation and progression, through the inactivation of several tumor suppressor genes. Emerging evidence indicates that epigenetics may also play a key role in the development of chemoresistance. In the present review, we summarize epigenetic mechanisms triggering resistance to three commonly used agents in colorectal cancer: 5-fluorouracil, irinotecan and oxaliplatin. Those epigenetic biomarkers may help stratify colorectal cancer patients and develop a tailored therapeutic approach. In addition, epigenetic modifications are reversible through specific drugs: histone-deacetylase and DNA-methyl-transferase inhibitors. Preclinical studies suggest that these drugs may reverse chemoresistance in colorectal tumors. In conclusion, an epigenetic approach to colorectal cancer chemoresistance may pave the way to personalized treatment and to innovative therapeutic strategies.

Acquisition of p53 mutations in response to the non-genotoxic p53 activator Nutlin-3

Wild-type p53 is a stress-responsive tumor suppressor and potent growth inhibitor. Genotoxic stresses (e.g. ionizing and UV radiation or chemotherapeutic drug treatment) can activate p53, but also induce mutations in the P53 gene and thus select for p53-mutated cells. Nutlin-3a (Nutlin) is pre-clinical drug that activates p53 in a non-genotoxic fashion. Nutlin occupies the p53-binding pocket of MDM2, activating p53 by blocking the p53-MDM2 interaction. Because Nutlin neither binds p53 directly nor introduces DNA damage, we hypothesized Nutlin would not induce P53 mutations and therefore not select for p53-mutated cells. To test this, populations of SJSA-1 (p53 wild-type) cancer cells were expanded that survived repeated Nutlin exposures, and individual clones were isolated. Group 1 clones were resistant to Nutlin-induced apoptosis, but still underwent growth-arrest. Surprisingly, while some Group 1 clones retained wild-type p53, others acquired a heterozygous p53 mutation. Apoptosis resistance in Group 1 clones was associated with decreased PUMA induction and decreased caspase 3/7 activation. Group 2 clones were resistant to both apoptosis and growth-arrest induced by Nutlin. Group 2 clones had acquired mutations in the p53 DNA-binding domain and expressed only mutant p53s that were induced by Nutlin treatment, but were unable to bind the P21 and PUMA gene promoters, and unable to activate transcription. These results demonstrate that non-genotoxic p53 activation (e.g. by Nutlin treatment) can lead to the acquisition of somatic mutations in p53 and select for p53-mutated cells. These findings have implications for the potential clinical use of Nutlin and other small molecule MDM2 antagonists.

Camptothecin induces apoptosis of human retinoblastoma cells via activation of FOXO1

PURPOSE

The purpose of this study was to investigate the pro-apoptotic effect of camptothecin (CPT) on Y79 retinoblastoma cells and the role of Forkhead box, class O (FOXO1) in CPT-induced apoptosis.

METHODS

CPT-induced apoptosis was determined by flow cytometry with annexin V-FITC positive cells and Western blot of PARP expression, respectively. The expressions of FOXO1 were detected by Western blot. The transcriptional activity of FOXO1 was determined by luciferase reporter assay. siRNAs specifically inhibiting FOXO1 were used, and flow cytometry and Western blot were executed to test the role of FOXO1 in CPT-induced apoptosis.

RESULTS

CPT was extremely effective in inducing apoptosis of Y79 retinoblastoma cells. FOXO1 was highly expressed in Y79 cells. CPT not only elevated the FOXO1 dephosphorylation level but also promoted its transcriptional activity, suggesting that the activation of FOXO1 was, at least in part, triggered by CPT. The decreased annexin V positive cells and less PARP cleavage demonstrated that siRNAs-mediated inhibition of FOXO1 significantly abrogated CPT-induced apoptosis, indicating that FOXO1 plays an important role in CPT-induced apoptosis. Moreover, the expression of Bim was also elevated with the treatment of CPT, which is in accordance with the activation of FOXO1.

CONCLUSIONS

Our study provides the evidence that a high level of endogenous FOXO1 expression in retinoblastoma cells contributes, at least in part, to CPT-induced apoptosis, which may help broad application of CPT in retinoblastoma therapy in the future.

Prostate-derived factor--a novel inhibitor of drug-induced cell death in colon cancer cells

We investigated the role of the divergent transforming growth factor-beta superfamily member, prostate-derived factor (PDF), in regulating response to chemotherapies used in the treatment of colorectal cancer. A clear p53-dependent expression pattern of PDF was shown in a panel of colorectal cancer cell lines following acute exposure to oxaliplatin, 5-fluorouracil, and SN38. PDF gene silencing before chemotherapy treatment significantly sensitized cells expressing wild-type p53, but not p53-null or p53-mutant cells, to drug-induced apoptosis. Similarly, knockdown of PDF expression sensitized HCT116 drug-resistant daughter cell lines to their respective chemotherapies. Inducible PDF expression and treatment with recombinant PDF both significantly attenuated drug-induced apoptosis. Further analysis revealed that PDF activated the Akt but not the extracellular signal-regulated kinase 1/2 signaling pathway. Furthermore, cotreatment with the phosphatidylinositol 3-kinase inhibitor wortmannin abrogated PDF-mediated resistance to chemotherapy-induced apoptosis. Together, these data suggest that PDF may be a novel inhibitor of drug-induced cell death in colorectal cancer cells and that the mature secreted form of the protein activates the phosphatidylinositol 3-kinase/Akt pathway as an acute mechanism of chemoresistance.

Irinotecan therapy and molecular targets in colorectal cancer: a systemic review

Irinotecan is the second line chemotherapy for advanced stage colorectal cancer (CRC) after failure of first line chemotherapy with oxaliplatin and 5-fluorouracil. The aim of this review is to analyse the data on irinotecan as second line chemotherapy for advanced CRC and the potential roles of the molecular markers, p53 and vascular endothelial growth factor (VEGF) in the management of advanced CRC. Thus, the English literature from 1980 to 2008 concerning irinotecan, p53, VEGF and CRC was reviewed. On review, Phase II and III clinical trials showed that irinotecan improves pain-free survival, quality of life, 1-year survival, progression-free survival and overall survival in advanced CRC. p53 and VEGF were expressed in CRC and had a predictive power of aggressive clinical behaviour in CRC. Irinotecan sensitizes p53 wild type, mutant and null cells to Fas-mediated cell apoptosis in CRC cells. Wild type p53 cells were more sensitive to irinotecan than mutated p53. Irinotecan has an anti-VEGF effect inhibiting endothelial cell proliferation, increasing apoptosis and reducing microvascular density which is only limited by irinotecan toxicity levels. To conclude, irinotecan improves the patient's quality of life and the survival rates of patients with advanced CRC. p53 and VEGF status of the patients' tumour is likely to affect the responsiveness of CRC to irinotecan. It is recommended that studies of the expression of these molecular markers in relation to chemo-responsiveness of irinotecan should be carried out for better management of patients with advanced CRC.

TP53 mutations predict disease control in metastatic colorectal cancer treated with cetuximab-based chemotherapy

Recent studies have suggested that activation of the EGFR pathway leads to malignant transformation only if the p53 protein is inactivated. Therefore, we evaluated the impact of TP53 mutations on cetuximab-based chemotherapy (CT) sensitivity in combination with KRAS mutations that have been associated with cetuximab resistance. KRAS and TP53 status were assessed in tumours from 64 metastatic colorectal cancer patients treated with cetuximab-based CT and correlated to clinical response using the Fisher's exact test. Times to progression (TTPs) according to gene status were calculated using the Kaplan-Meier method and compared with log-rank test. TP53 mutations were found in 41 patients and were significantly associated with controlled disease (CD), as defined as complete response, partial response or stable disease (P=0.037) and higher TTP (20 vs 12 weeks, P=0.004). Remarkably, in the subgroup of 46 patients without KRAS mutation, but not in patients with KRAS mutation, TP53 mutations were also associated with CD (P=0.008) and higher TTP (24 vs 12 weeks, P=0.0007). This study suggests that TP53 mutations are predictive of cetuximab sensitivity, particularly in patients without KRAS mutation, and that TP53 genotyping could have a clinical interest to select patients who should benefit from cetuximab-based CT.

Ardipusilloside I induces apoptosis in human glioblastoma cells through a caspase-8-independent FasL/Fas-signaling pathway

Ardipusilloside I, a triterpenoid saponin isolated from Ardisia pusilla A. DC, suppresses the growth of a variety of cancer cells, and has certain immunomodulative properties. Herein, we investigated its effect on glioblastoma cell line U87MG cells and primary cultured human glioblastoma cells, and examined the underlying mechanism of action. Ardipusilloside I substantially decreased the number of viable cells of both cell lines in a time- and concentration-dependent manner, with a similar IC(50) of 4.05μM. Microscopy revealed apoptotic characteristics, including chromatin condensation and cell nucleus fragmentation, demonstrating that ardipusilloside I-induced apoptosis. Ardipusilloside I exposure also gradually increased the sub-G1 fraction (the apoptotic cell population) and an S phase-arrest of both glioblastoma cells. Furthermore, ardipusilloside I increased the expression of Fas and its ligand (FasL), and enhanced the activation of caspase-8 and caspase-3. Additionally, we observed a significant decreased apoptosis after the trigger effection of FasL was abolished by the neutralization antibody anti-FasL antibody and an unchanged apoptosis level when the activation of caspase-8 was interrupted by specific inhibitor z-IETD-fmk, which suggested that a casepase-8 independent FasL/Fas-signaling-mediated death receptor pathway is involved. These data suggested that ardipusilloside I could be developed as a chemotherapeutic agent for the management of gliomas.

Expression of HBX, an oncoprotein of hepatitis B virus, blocks reoviral oncolysis of hepatocellular carcinoma cells

Although reovirus has been used in tests as a potential cancer therapeutic agent against a variety of cancer cells, its application to hepatocellular carcinoma cells, in which the hepatitis B virus (HBV) X (HBX) protein of HBV plays a primary role, has not yet been explored. Here, we describe experiments in which we use reovirus to treat Chang liver carcinoma cells expressing either a vector only (Chang-vec) or a vector encoding HBX protein (Chang-HBX). Although Chang-vec cells readily support reoviral proliferation and undergo apoptosis, Chang-HBX cells are highly resistant to reoviral infection and virus-induced apoptosis, even though HBX protein induces activation of Ras and inactivation of PKR, which are normally thought to enhance reoviral oncolysis. The resistance of Chang-HBX cells to reovirus may instead be explained by HBX-induced downregulation of death receptor 5 and activation of Stat1. Phosphorylated Stat1 activates interferon (IFN)-stimulated regulatory element (ISRE)- and IFN-gamma-activated sequence (GAS)-mediated transcription, leading to the production of IFN-beta, whereas the reduced expression of Stat1 with its siRNA results in a decrease in IFN-beta production, by which Chang-HBX cells eventually succumb to reovirus infection. This result further indicates that HBX induces the establishment of an antiviral state through Stat1 activation. Thus, it appears that active Ras does not override the antiviral effect mediated by the activation of Stat1. Accordingly, we report that HBX, an oncoprotein of HBV, can prevent reoviral oncolysis of hepatocellular carcinoma. This suggests there may be limits to the practical application of reovirus in the treatment of human cancers already expressing other oncoviral proteins.

In vitro pharmacogenomic database and chemosensitivity predictive genes in gastric cancer

Gastric cancer is one of the most common cancers worldwide, and there are clinical caveats in predicting tumor response to chemotherapy. This study describes the construction of an in vitro pharmacogenomic database, and the selection of genes associated with chemosensitivity in gastric cancer cell lines. Gene expression and chemosensitivity databases were integrated using the Pearson correlation coefficient to give the GC-matrix. The 85 genes were selected that were commonly associated with chemosensitivity of the major anticancer drugs. We then focused on the genes that were highly correlated with each specific drug. Classification of cell lines based on the set of genes associated with each drug was consistent with the division into resistant or sensitive groups according to the chemosensitivity results. The GC-matrix of the gastric cancer cell line database was used to identify different sets of chemosensitivity-related genes for specific drugs or multiple drugs.

Altered gene expression in rat colonic adenocarcinomas induced in an azoxymethane plus 2-amino-1-methyl-6-phenylimidazo[4,5-b]- pyridine initiation-promotion model

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), the most abundant food-derived mutagenic/carcinogenic heterocyclic amine (HCA), has attracted particular attention as a probable human colon carcinogen. Some studies have shown that PhIP administered in the post-initiation phase is able to enhance rat colon carcinogenesis remarkably. To determine whether this genotoxicant leaves a DNA footprint in colon carcinogenesis, 6-week-old male F344 rats were first subcutaneously injected with azoxymethane (AOM) and then continuously treated with various doses (0-200 ppm) of PhIP added to their diet. Animals were killed at week 36 for histopathological examination, and colonic adenocarcinomas derived from animals receiving 0, 50 and 200 ppm PhIP were subjected to a novel three-dimensional (3D)-microarray and real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis. A total of five candidate genes were identified in adenocarcinomas following 200 ppm of PhIP and AOM initiation, with a dose-dependent increment. Among them, Stat1 (signal transducer and activator of transcription 1) and VEGFc (vascular endothelial growth factor c) demonstrated statistically significant upregulation by real-time RT-PCR. In addition, HSP90 (heat shock protein 90) and VEGFa showed a non-significant tendency to increase. In summary, overexpression of Stat1, VEGF and other genes could be involved in PhIP-enhanced colon tumorigenesis in the post-initiation phase.

NADPH oxidase promotes pancreatic cancer cell survival via inhibiting JAK2 dephosphorylation by tyrosine phosphatases

BACKGROUND & AIMS

Growth factors, such as insulin-like growth factor-1 (IGF-I), protect pancreatic cancer (PaCa) cells from death. We recently showed that reactive oxygen species (ROS) produced by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase Nox4 mediate the antiapoptotic effect of growth factors. Here, we examine the mechanisms of the antiapoptotic role of NADPH oxidase. We hypothesized that ROSs produced by NADPH oxidase inhibit key protein tyrosine phosphatases (PTPs) and thus sustain the activation of kinases mediating antiapoptotic pathways in PaCa cells.

METHODS

Transfections and pharmacologic inhibition were used to assess the effects of NADPH oxidase on Janus kinase 2 (JAK2) kinase, the low molecular weight-protein tyrosine phosphatase (LMW-PTP), and apoptosis.

RESULTS

We found that 1 target of ROSs is JAK2, an important antiapoptotic kinase in PaCa cells. Both serum-induced and IGF-I biphasic JAK2 phosphorylation, with a rapid (minutes) and transient first phase, and a slow and sustained (24-72 hours) second phase. Nox4 mediated the sustained phase of JAK2 phosphorylation, which was required for the antiapoptotic effects of IGF-I and serum. Transfection experiments identified the LMW-PTP as a negative regulator of sustained JAK2 phosphorylation. Growth factors inhibited LMW-PTP through its oxidation by NADPH oxidase. LMW-PTP colocalizes with Nox4 both in PaCa cells and in human pancreatic adenocarcinoma.

CONCLUSIONS

The results suggest a novel signaling pathway, in which NADPH oxidase activation results in inhibition of PTPs, such as LMW-PTP, leading, in turn, to enhanced and sustained phosphorylation of kinases, such as JAK2, and suppression of apoptosis. This pathway mediates the prosurvival effect of ROSs and suggests new targets for pancreatic cancer treatment.

Zinc induces ERK-dependent cell death through a specific Ras isoform

The effect of Zn on p53-independent cell death was examined in IIC9 embryonic fibroblasts. Despite the fact that these cells are p53-minus, Zn-mediated death occurs via an apoptotic mechanism. Death is facilitated by the presence of the Zn ionophore, pyrithione, indicating that intracellular Zn initiates the death response. Our investigations of the mechanism of Zn action demonstrate that Zn induces the death of IIC9 cells in a manner that is ERK-dependent. Expression of dn-(dominant negative)Ras attenuates ERK1/2 activation by Zn, and correspondingly reduces its cytotoxic effects. Raf-RBD pull-down experiments confirm that Zn treatment activates Ras and identified H-Ras as the specific isoform activated. This contrasts the activation of N-Ras that occurs when IIC9 cells are stimulated with thrombin. Thus, although the prolonged activation of the Ras/ERK pathway by Zn is similar to that seen when induced by mitogen, the distinguishing feature appears to be the isoform specificity of Ras activation.

Norcantharidin preferentially induces apoptosis in human leukemic Jurkat cells without affecting viability of normal blood mononuclear cells

Norcantharidin (NCTD) is known to have anti-cancer potentials. The aim of this study was to assess the apoptosis-inducing effect of NCTD on human leukemic Jurkat cells. We found that NCTD preferentially inhibited the growth of Jurkat cells in a dose- and time-dependent manner, but not the growth of normal blood mononuclear cells (MNC). Pretreatment with agonistic (CH-11) and antagonistic (ZB4) Fas antibodies on Jurkat cells showed that NCTD-induced apoptosis might not involve Fas-FasL signaling. Flow cytometric assay of Jurkat cells treated with NCTD showed a markedly increased sub-G1 DNA phase and cell cycle arrest at S phase. Western blot analysis of NCTD-treated cells showed increased expressions of cytochrome c, active caspase-9 and -3, and cleavage of poly(ADP-ribose) polymerase (PARP), but the expressions of Bcl-2, Bax and apoptosis-inducing factor were not increased. The transcription factor STAT1 was translocated from cytosol to nucleus. Pancaspase inhibitor z-VAD-FMK not only limited the level of sub-G1 phase, but also prevented the degradation of PARP in NCTD-treated cells. The NCTD-induced cell cycle arrest and apoptosis were mediated through the regulation of ataxia-telangiectasia mutated (ATM), rather than P63 protein. The conditioned medium produced from human MNC (NCTD-MNC-CM) increased the percentage of apoptotic cells and the expression of PARP cleavage in Jurkat cells. Protein array assay of NCTD-MNC-CM showed 32.4- and 6.2-folds increases in TNF-alpha and GM-CSF, respectively, and the expression of MCP-1, GRO, RANTES and IL-10 was decreased. We conclude that NCTD can induce apoptosis in human leukemic Jurkat cells via a caspase-dependent pathway without affecting the viability of normal MNC, and that the apoptosis-inducing effect of NCTD can also be achieved by soluble cytokines produced from peripheral MNC.

Low-Dose BBR3610 Toxicity in Colon Cancer Cells Is p53-Independent and Enhanced by Inhibition of Epidermal Growth Factor Receptor (ERBB1)-Phosphatidyl Inositol 3 Kinase Signaling

We have examined the mechanisms by which the multinuclear platinum chemotherapeutic BBR3610 kills human colon cancer cells. BBR3610 more efficiently killed HCT116, DLD1, SW480, and HT29 cells than BBR3464, cisplatin, or oxaliplatin. The amount of platinum uptake per cell and its incorporation into DNA were identical for BBR3464 and BBR3610. BBR3610 lethality (IC(75)) was unaltered comparing HCT116 wild-type and p53-/- cells, was reduced in p21-/- cells, and was enhanced in K-RAS D13 null cells. Small molecule or molecular inhibition of epidermal growth factor receptor (ERBB1) or phosphatidyl inositol 3 kinase (PI3K) enhanced BBR3610 toxicity in HCT116, DLD1, and SW480 cells. Small molecule or molecular inhibition of caspase 8 function abolished the toxicity of BBR3610 and of BBR3610 + ERBB1 inhibitor treatments, whereas inhibition of caspase 9 suppressed the ability of ERBB1 inhibitors to enhance BBR3610 lethality. Treatment with BBR3610 reduced AKT activity; the expression of dominant-negative AKT enhanced and expression of constitutively active AKT suppressed, respectively, the toxicity of BBR3610 and of BBR3610 + ERBB1 inhibitor treatments. Treatment with BBR3610 reduced expression of c-FLIP-s and MCL-1, levels that were maintained in cells expressing constitutively active AKT. Overexpression of c-FLIP-s or loss of BID function suppressed BBR3610 toxicity, whereas overexpression of XIAP or Bcl-xL suppressed the potentiation of cell killing by ERBB1 inhibitors. Collectively, our data argue that BBR3610 promotes cell killing via a caspase 8-dependent mechanism, which can be enhanced by ERBB1/PI3K inhibitors that promote additional BBR3610-dependent cell killing via activation of BAX and caspase 9.

Loss of ataxia telangiectasia mutated- and Rad3-related function potentiates the effects of chemotherapeutic drugs on cancer cell survival

The diverse responses of human cells to various forms of DNA damage are controlled by a complex network of signaling proteins. There has been considerable interest in the components of this signaling apparatus as potential targets for new forms of anticancer therapy. In this report, we examine the contributions of an upstream signaling molecule, the ataxia telangiectasia mutated- and Rad3-related (ATR) protein kinase, to the resistance of cancer cells to DNA-damaging agents that are commonly used as anticancer therapeutics. Loss of ATR function in knock-in cancer cells strikingly enhanced the effects of several of the most commonly used therapeutic compounds, impeding the progression of the cell cycle and reducing long-term cancer cell survival. Loss of ATR function potentiated the toxicity of alkylating agents most strikingly, antimetabolites moderately, and double-strand break-inducing agents to a lesser extent. These results suggest that specific inhibition of ATR activity will be a valid strategy to increase the effectiveness of currently used modes of therapy.

The role of spermidine/spermine N1-acetyltransferase in determining response to chemotherapeutic agents in colorectal cancer cells

Polyamines have been shown to play a role in the growth and survival of several solid tumors, including colorectal cancer. We identified the polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase (SSAT) as being one of the most highly inducible genes in two DNA microarray screens to identify novel determinants of response to chemotherapeutic agents in colorectal cancer. SSAT was shown to be inducible in response to 5-fluorouracil (5-FU) or oxaliplatin in parental and drug-resistant HCT116 cell lines. It was also shown that SSAT mRNA was up-regulated in response to 5-FU or oxaliplatin in a panel of six colorectal cancer cell lines. The polyamine analogue N(1),N(11)-diethylnorspermine (DENSpm) depletes polyamine pools and potently induces SSAT. We evaluated the effect of combining DENSpm with chemotherapeutic agents in HCT116 p53(+/+) cells and in HCT116 drug-resistant daughter cell lines. Western blot analyses showed that SSAT protein expression was dramatically enhanced when DENSpm was combined with oxaliplatin or 5-FU in HCT116 p53(+/+) cells. Using cell viability assays and flow cytometry, synergistic induction of cell death was observed following cotreatment of HCT116 p53(+/+) cells with DENSpm and each chemotherapeutic agent. Of note, this combined therapy increased the chemosensitivity of cells rendered resistant to each of these chemotherapeutic agents. Small interfering RNA-mediated down-regulation of SSAT resulted in loss of synergy between DENSpm and these agents. These results show that SSAT plays an important role in regulating cell death following combined cytotoxic drug and DENSpm treatment. Furthermore, DENSpm sensitizes both sensitive and resistant cells to chemotherapeutic agents. Taken together, these results suggest that SSAT may be an important target for therapeutic intervention in colorectal cancer.

Sensitization of p53-mutated epithelial ovarian cancer to CD95-mediated apoptosis is synergistically induced by cisplatin pretreatment

Epithelial ovarian carcinoma (EOC) remains a highly lethal malignancy. Despite the progress in surgical and therapeutic strategies, resistance to chemotherapy is still a major concern. Cytotoxic therapies mediate killing of cancer cells by activating the intrinsic mitochondrial apoptotic pathway, and p53 status is a key factor in determining the efficacy of apoptotic signaling. The extrinsic (CD95) death receptor-dependent signaling pathway also contributes to the efficacy of cancer therapy. We previously showed that EOC are generally resistant to CD95-dependent apoptosis. In p53 wild-type EOC tumors, CD95-mediated apoptosis is impaired at the receptor level by the long form of cellular FLICE-inhibitory protein, whereas this mechanism does not account for resistance in tumors with mutated p53 (p53mu). In the present study, we examined both intrinsic and death receptor-dependent apoptotic signaling in p53mu OVCAR3 EOC cell line, showing that these cells are less susceptible to cisplatin treatment as compared with p53 wild-type EOC cells and also resist CD95-mediated apoptosis due to inefficient formation of the death-inducing signaling complex and weak mitochondrial signal amplification. However, pretreatment of OVCAR3 cells with clinically relevant cisplatin concentrations significantly improved receptor-dependent apoptotic signaling by up-modulating CD95 receptor expression and increasing death-inducing signaling complex formation efficiency. The synergy of cisplatin pretreatment and CD95 triggering in inducing cell death was also shown in p53mu tumor cells derived from ascitic fluid of advanced-stage EOC patients. These findings support the effectiveness of a combined therapeutic treatment able to sensitize cancer cells to apoptosis even when p53 is functionally inactivated.

Inhibition of Fas expression by RNAi modulates 5-fluorouracil-induced apoptosis in HCT116 cells expressing wild-type p53

Drug resistance to 5-fluorouracil (5-FU) is still a major limitation to its clinical use. In addition, the clinical value of p53 as a predictive marker for 5-FU-based chemotherapy remains a matter of debate. Here, we used HCT116 human colorectal cancer cells expressing wild-type p53 and investigated whether inhibition of Fas expression by interference RNA modulates 5-FU-induced apoptosis. Cells were treated with 5-FU (1, 4 or 8 microM) for 8-48 h. Cell viability was evaluated by trypan blue dye exclusion. Apoptosis was assessed by changes in nuclear morphology and caspase activity. The interference RNA technology was used to silence Fas expression. Caspase activation, p53, Fas, cytochrome c, and Bcl-2 family protein expression was evaluated by immunoblotting. 5-FU was cytotoxic in HCT116 cells (p<0.001). Nuclear fragmentation and caspase-3, -8 and -9 activities were also markedly increased in HCT116 cells after 5-FU (p<0.001). In addition, wild-type p53 and Fas expression were 25- and 4-fold increased (p<0.05). Notably, when interference RNA was used to inhibit Fas, 5-FU-mediated nuclear fragmentation and caspase activity were markedly reduced in HCT116 cells. Finally, western blot analysis of mitochondrial extracts from HCT116 cells exposed to 5-FU showed a 6-fold increase in Bax, together with a 3-fold decrease in cytochrome c (p<0.001). In conclusion, 5-FU exerts its cytotoxic effects, in part, through a p53/Fas-dependent apoptotic pathway that involves Bax translocation and mitochondrial permeabilization.