KRAS(D13) Promotes apoptosis of human colorectal tumor cells by ReovirusT3D and oxaliplatin but not by tumor necrosis factor-related apoptosis-inducing ligand

Modulation of Reoviral Cytolysis (II): Cellular Stemness

Oncolytic viruses (OVs) are an emerging cancer therapeutic that are intended to act by selectively targeting and lysing cancerous cells and by stimulating anti-tumour immune responses, while leaving normal cells mainly unaffected. Reovirus is a well-studied OV that is undergoing advanced clinical trials and has received FDA approval in selected circumstances. However, the mechanisms governing reoviral selectivity are not well characterised despite many years of effort, including those in our accompanying paper where we characterize pathways that do not consistently modulate reoviral cytolysis. We have earlier shown that reovirus is capable of infecting and lysing both certain types of cancer cells and also cancer stem cells, and here we demonstrate its ability to also infect and kill healthy pluripotent stem cells (PSCs). This led us to hypothesize that pathways responsible for stemness may constitute a novel route for the modulation of reoviral tropism. We find that reovirus is capable of killing both murine and human embryonic and induced pluripotent stem cells. Differentiation of PSCs alters the cells' reoviral-permissive state to a resistant one. In a breast cancer cell line that was resistant to reoviral oncolysis, induction of pluripotency programming rendered the cells permissive to cytolysis. Bioinformatic analysis indicates that expression of the Yamanaka pluripotency factors may be associated with regulating reoviral selectivity. Mechanistic insights from these studies will be useful for the advancement of reoviral oncolytic therapy.

Egress of non-enveloped enteric RNA viruses

A long-standing paradigm in virology was that non-enveloped viruses induce cell lysis to release progeny virions. However, emerging evidence indicates that some non-enveloped viruses exit cells without inducing cell lysis, while others engage both lytic and non-lytic egress mechanisms. Enteric viruses are transmitted via the faecal-oral route and are important causes of a wide range of human infections, both gastrointestinal and extra-intestinal. Virus cellular egress, when fully understood, may be a relevant target for antiviral therapies, which could minimize the public health impact of these infections. In this review, we outline lytic and non-lytic cell egress mechanisms of non-enveloped enteric RNA viruses belonging to five families: Picornaviridae, Reoviridae, Caliciviridae, Astroviridae and Hepeviridae. We discuss factors that contribute to egress mechanisms and the relevance of these mechanisms to virion stability, infectivity and transmission. Since most data were obtained in traditional two-dimensional cell cultures, we will further attempt to place them into the context of polarized cultures and in vivo pathogenesis. Throughout the review, we highlight numerous knowledge gaps to stimulate future research into the egress mechanisms of these highly prevalent but largely understudied viruses.

Molecular Tools for Metastatic Colorectal Cancer Characterization

In our recent publication [1], we have explored at the molecular level the consequences of reovirus administration to patients with KRAS mutated colorectal cancer (CRC). This was the first reported study where transcriptome assay was performed on KRAS mutated CRC patients receiving reovirus (pelareorep) therapy. Using peripheral mononuclear cells as a tumor surrogate, we have identified several hundred genes that were significantly altered in a transcriptome assay of patients receiving pelareorep serving as their own controls (pre and post reovirus administration) and compared to untreated controls [2]. We focused primarily on 884 immune related genes and published the data for genes with significance probability of 0.001 (1 in thousand for a perfect random occurrence). Samples were collected at 48 hours, day 8 and day 15 post reovirus administration and compared for dynamic gene expression alterations over time. Using PBMC we also performed flow cytometry, cytokine ELISA, immunohistochemistry, and determination of the expression level of CRC specific microRNA miR-29a-3p. Our data supports the therapeutic competence of reovirus and identifies the four major ways by which it exerts its antitumor effects.

Going (Reo)Viral: Factors Promoting Successful Reoviral Oncolytic Infection

Oncolytic viruses show intriguing potential as cancer therapeutic agents. These viruses are capable of selectively targeting and killing cancerous cells while leaving healthy cells largely unaffected. The use of oncolytic viruses for cancer treatments in selected circumstances has recently been approved by the Food and Drug Administration (FDA) of the US and work is progressing on engineering viral vectors for enhanced selectivity, efficacy and safety. However, a better fundamental understanding of tumour and viral biology is essential for the continued advancement of the oncolytic field. This knowledge will not only help to engineer more potent and effective viruses but may also contribute to the identification of biomarkers that can determine which patients will benefit most from this treatment. A mechanistic understanding of the overlapping activity of viral and standard chemotherapeutics will enable the development of better combinational approaches to improve patient outcomes. In this review, we will examine each of the factors that contribute to productive viral infections in cancerous cells versus healthy cells. Special attention will be paid to reovirus as it is a well-studied virus and the only wild-type virus to have received orphan drug designation by the FDA. Although considerable insight into reoviral biology exists, there remain numerous deficiencies in our understanding of the factors regulating its successful oncolytic infection. Here we will discuss what is known to regulate infection as well as speculate about potential new mechanisms that may enhance successful replication. A joint appreciation of both tumour and viral biology will drive innovation for the next generation of reoviral mediated oncolytic therapy.

Mutant KRAS promotes liver metastasis of colorectal cancer, in part, by upregulating the MEK-Sp1-DNMT1-miR-137-YB-1-IGF-IR signaling pathway

Although the role of insulin-like growth factor-I receptor (IGF-IR) in promoting colorectal liver metastasis is known, the mechanism by which IGF-IR is upregulated in colorectal cancer (CRC) is not defined. In this study, we obtained evidence that mutant KRAS transcriptionally activates IGF-IR gene expression through Y-box-binding protein (YB)-1 upregulation via a novel MEK-Sp1-DNMT1-miR-137 pathway in CRC cells. The mechanistic link between the tumor suppressive miR-137 and the translational regulation of YB-1 is intriguing because epigenetic silencing of miR-137 represents an early event in colorectal carcinogenesis due to promoter hypermethylation. This proposed signaling axis was further verified by the immunohistochemical evaluations of liver metastases from a cohort of 46 KRAS mutant CRC patients, which showed a significant correlation in the expression levels among Sp1, miR-137, YB-1, and IGF-1R. Moreover, suppression of the expression of YB-1 and IGF-IR via genetic knockdown or the pharmacological inhibition of MEK hampers KRAS-driven colorectal liver metastasis in our animal model studies. From a translational perspective, the identification of this KRAS-driven pathway might provide a mechanistic rationale for the use of a MEK inhibitor as an adjuvant, in combination with standard of care, to prevent the recurrence of colorectal liver metastasis in KRAS mutant CRC patients after receiving liver resection, which warrants further investigation.

Orthoreovirus outer-fiber proteins are substrates for SUMO-conjugating enzyme Ubc9

Reoviruses are potential anticancer agents due to their ability to induce cell death in tumor cells. Grass carp reovirus (GCRV) is one of the best characterized models on reovirus pathogenesis in vitro. However, there is little known about how SUMOylation affects reovirus pathogenesis. The SUMO conjugating enzyme 9 (Ubc9) determines the targets of SUMOylation. Here, the protein interactions between reovirus outer fiber proteins, specifically GCRV-104 VP55, and Ubc9 were probed using a yeast two-hybrid system. The N-terminal coiled-coil domain of VP55, containing a single lysine residue, was responsible for the interaction between VP55 and Ubc9 in yeast. In solid phase binding assays, a single amino acid mutation (K87R) prevented Ubc9 from binding to VP55. Overexpression of Ubc9 enhanced GCRV-104 infection efficiency, and knockdown of Ubc9 in CIK cells inhibited viral replication, which suggested that Ubc9 was a proviral factor. Furthermore, Ubc9 was shown to bind outer fiber proteins from type II GCRV, avian reovirus and mammalian reovirus in yeast. To our knowledge, this is the first study to show that Ubc9 binds to reovirus outer-fiber proteins and likely contributes to efficient orthoreovirus replication. These results suggest that SUMOylation modifications could be targeted to improve the therapeutic efficacy of oncolytic reovirus.

Oncogenic RAS-induced downregulation of ATG12 is required for survival of malignant intestinal epithelial cells

Activating mutations of RAS GTPase contribute to the progression of many cancers, including colorectal carcinoma. So far, attempts to develop treatments of mutant RAS-carrying cancers have been unsuccessful due to insufficient understanding of the salient mechanisms of RAS signaling. We found that RAS downregulates the protein ATG12 in colon cancer cells. ATG12 is a mediator of autophagy, a process of degradation and reutilization of cellular components. In addition, ATG12 can kill cells via autophagy-independent mechanisms. We established that RAS reduces ATG12 levels in cancer cells by accelerating its proteasomal degradation. We further observed that RAS-dependent ATG12 loss in these cells is mediated by protein kinases MAP2K/MEK and MAPK1/ERK2-MAPK3/ERK1, known effectors of RAS. We also demonstrated that the reversal of the effect of RAS on ATG12 achieved by the expression of exogenous ATG12 in cancer cells triggers both apoptotic and nonapoptotic signals and efficiently kills the cells. ATG12 is known to promote autophagy by forming covalent complexes with other autophagy mediators, such as ATG5. We found that the ability of ATG12 to kill oncogenic RAS-carrying malignant cells does not require covalent binding of ATG12 to other proteins. In summary, we have identified a novel mechanism by which oncogenic RAS promotes survival of malignant intestinal epithelial cells. This mechanism is driven by RAS-dependent loss of ATG12 in these cells.

PUMA and NF-kB Are Cell Signaling Predictors of Reovirus Oncolysis of Breast Cancer

BACKGROUND AND PURPOSE

Reovirus is a ubiquitous RNA virus that exploits aberrant signaling pathways for its replication. The oncolytic potential of reovirus against numerous cancers under pre-clinical/clinical conditions has been documented by us and others. Despite its proven clinical activity, the underlying mechanisms of reovirus oncolysis is still not well elucidated. If reovirus therapy is to be optimized for cancer, including breast cancer patients, it is imperative to understand the mechanisms of reovirus oncolysis, especially in treatment of resistant tumour.

EXPERIMENTAL APPROACH AND RESULTS

In the present study global gene expression profiling was utilized as a preliminary roadmap to tease-out pivotal molecules involved in reovirus induced apoptosis in breast cancer. Reovirus treated HTB133 and MCF7 breast cancer cells revealed transcriptional alteration of a defined subset of apoptotic genes and members of the nuclear factor-kappa B (NF-kB) family and p53 upregulated modulator of apoptosis (PUMA) were prominent. Since NF-kB can paradoxically suppress or promote apoptosis in cancer, the significance of NF-kB in reovirus oncolysis of breast cancer was investigated. Real time PCR analysis indicated a 2.9-4.3 fold increase in NF-kB p65 message levels following reovirus infection of MCF7 and HTB133, respectively. Nuclear translocation of NF-kB p65 protein was also dramatically augmented post reovirus treatment and correlated with enhanced DNA binding. Pharmacologic inhibition of NF-kB lead to oncolytic protection and significant down regulation of PUMA message levels. PUMA down regulation using siRNA suppressed reovirus oncolysis via significantly repressed apoptosis in p53 mutant HTB133 cells.

CONCLUSIONS

This study demonstrates for the first time that a prominent pathway of reovirus oncolysis of breast cancer is mediated through NF-kB and that PUMA upregulation is dependent on NF-kB activation. These findings represent potential therapeutic indicators of reovirus treatment in future clinical trials.

ERK mediated upregulation of death receptor 5 overcomes the lack of p53 functionality in the diaminothiazole DAT1 induced apoptosis in colon cancer models: efficiency of DAT1 in Ras-Raf mutated cells

Background

p53 is a tumour suppressor protein that plays a key role in many steps of apoptosis, and malfunctioning of this transcription factor leads to tumorigenesis. Prognosis of many tumours also depends upon the p53 status. Most of the clinically used anticancer compounds activate p53 dependent pathway of apoptosis and hence require p53 for their mechanism of action. Further, Ras/Raf/MEK/ERK axis is an important signaling pathway activated in many cancers. Dependence of diaminothiazoles, compounds that have gained importance recently due to their anticancer and anti angiogenic activities, were tested in cancer models with varying p53 or Ras/Raf mutational status.

Methods

In this study we have used p53 mutated and knock out colon cancer cells and xenograft tumours to study the role of p53 in apoptosis mediated by diaminothiazoles. Colon cancer cell lines with varying mutational status for Ras or Raf were also used. We have also examined the toxicity and in vivo efficacy of a lead diaminothiazole 4-Amino-5-benzoyl-2-(4-methoxy phenylamino)thiazole (DAT1) in colon cancer xenografts.

Results

We have found that DAT1 is active in both in vitro and in vivo models with nonfunctional p53. Earlier studies have shown that extrinsic pathway plays major role in DAT1 mediated apoptosis. In this study, we have found that DAT1 is causing p53 independent upregulation of the death receptor 5 by activating the Ras/Raf/MEK/ERK signaling pathway both in wild type and p53 suppressed colon cancer cells. These findings are also confirmed by the in vivo results. Further, DAT1 is more efficient to induce apoptosis in colon cancer cells with mutated Ras or Raf.

Conclusions

Minimal toxicity in both acute and subacute studies along with the in vitro and in vivo efficacy of DAT1 in cancers with both wild type and nonfunctional p53 place it as a highly beneficial candidate for cancer chemotherapy. Besides, efficiency in cancer cells with mutations in the Ras oncoprotein or its downstream kinase Raf raise interest in diaminothiazole class of compounds for further follow-up.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-016-0505-7) contains supplementary material, which is available to authorized users.

Oncolytic Viral Therapy Using Reovirus

Current mainstays in cancer treatment such as chemotherapy, radiation therapy, hormonal manipulation, and even targeted therapies such as Trastuzumab (herceptin) for breast cancer or Iressa (gefitinib) for non-small cell lung cancer among others are limited by lack of efficacy, cellular resistance, and toxicity. Dose escalation and combination therapies designed to overcome resistance and increase efficacy are limited by a narrow therapeutic index. Oncolytic viruses are one such group of new biological therapeutics that appears to have a wide spectrum of anticancer activity with minimal human toxicity. Since the malignant phenotype of tumors is the culmination of multiple mutations that occur in genes eventually leading to aberrant signaling pathways, oncolytic viruses either natural or engineered specifically target tumor cells taking advantage of this abnormal cellular signaling for their replication. Reovirus is one such naturally occurring double-stranded RNA virus that exploits altered signaling pathways (including Ras) in a myriad of cancers. The ability of reovirus to infect and lyse tumors under in vitro, in vivo, and ex vivo conditions has been well documented previously by us and others. The major mechanism of reovirus oncolysis of cancer cells has been shown to occur through apoptosis with autophagy taking place during this process in certain cancers. In addition, the synergistic antitumor effects of reovirus in combination with radiation or chemotherapy have also been demonstrated for reovirus resistant and moderately sensitive tumors. Recent progress in our understanding of viral immunology in the tumor microenvironment has diverted interest in exploring immunologic mechanisms to overcome resistance exhibited by chemotherapeutic drugs in cancer. Thus, currently several investigations are focusing on immune potentiating of reovirus for maximal tumor targeting. This chapter therefore has concentrated on immunologic cell death induction with reovirus as a novel approach to cancer therapy used under in vitro and in vivo conditions, as well as in a clinical setting. Reovirus phase I clinical trials have shown indications of efficacy, and several phase II/III trials are ongoing at present. Reovirus's extensive preclinical efficacy, replication competency, and low toxicity profile in humans have placed it as an attractive anticancer therapeutic for ongoing clinical testing that are highlighted in this chapter.

KRAS codon 12 and 13 mutations in relation to disease-free survival in BRAF-wild-type stage III colon cancers from an adjuvant chemotherapy trial (N0147 alliance)

PURPOSE

We examined the prognostic impact of specific KRAS mutations in patients with stage III colon adenocarcinoma receiving adjuvant FOLFOX alone or combined with cetuximab in a phase III trial (N0147). Analysis was restricted to BRAF-wild-type tumors, because BRAF mutation was associated with poor prognosis, and BRAF and KRAS mutations are mutually exclusive.

EXPERIMENTAL DESIGN

The seven most common KRAS mutations in codon 12 and codon 13 were examined in 2,478 BRAF-wild-type tumors. Because KRAS mutations in codon 12 (n = 779) or 13 (n = 220) were not predictive of adjuvant cetuximab benefit, study arms were pooled for analysis. Disease-free survival (DFS) was evaluated by HRs using Cox models.

RESULTS

KRAS mutations in codon 12 (multivariate HR, 1.52; 95% confidence interval, CI, 1.28-1.80; P < 0.0001) or codon 13 (multivariate HR, 1.36; 95% CI, 1.04-1.77; P = 0.0248) were significantly associated with shorter DFS compared with patients with wild-type KRAS/BRAF tumors, independent of covariates. KRAS codon 12 mutations were independently associated with proficient mismatch repair (P < 0.0001), proximal tumor site (P < 0.0001), low grade, age, and sex, whereas codon 13 mutations were associated with proximal site (P < 0.0001).

CONCLUSION

KRAS mutations in either codon 12 or 13 are associated with inferior survival in patients with resected stage III colon cancer. These data highlight the importance of accurate molecular characterization and the significant role of KRAS mutations in both codons in the progression of this malignancy in the adjuvant setting. Clin Cancer Res; 20(11); 3033-43. ©2014 AACR.

Shp2/MAPK signaling controls goblet/paneth cell fate decisions in the intestine

In the development of the mammalian intestine, Notch and Wnt/β-catenin signals control stem cell maintenance and their differentiation into absorptive and secretory cells. Mechanisms that regulate differentiation of progenitors into the three secretory lineages, goblet, paneth, or enteroendocrine cells, are not fully understood. Using conditional mutagenesis in mice, we observed that Shp2-mediated MAPK signaling determines the choice between paneth and goblet cell fates and also affects stem cells, which express the leucine-rich repeat-containing receptor 5 (Lgr5). Ablation of the tyrosine phosphatase Shp2 in the intestinal epithelium reduced MAPK signaling and led to a reduction of goblet cells while promoting paneth cell development. Conversely, conditional mitogen-activated protein kinase kinase 1 (Mek1) activation rescued the Shp2 phenotype, promoted goblet cell and inhibited paneth cell generation. The Shp2 mutation also expanded Lgr5+ stem cell niches, which could be restricted by activated Mek1 signaling. Changes of Lgr5+ stem cell quantities were accompanied by alterations of paneth cells, indicating that Shp2/MAPK signaling might affect stem cell niches directly or via paneth cells. Remarkably, inhibition of MAPK signaling in intestinal organoids and cultured cells changed the relative abundance of Tcf4 isoforms and by this, promoted Wnt/β-catenin activity. The data thus show that Shp2-mediated MAPK signaling controls the choice between goblet and paneth cell fates by regulating Wnt/β-catenin activity.

Heterogeneous reovirus susceptibility in human glioblastoma stem-like cell cultures

Glioblastoma (GB) is a devastating disease for which new treatment modalities are needed. Efficacious therapy requires the removal of stem-cell like cells, these cells drive tumor progression because of their ability to self-renew and differentiate. In glioblastoma, the GB stem-like cells (GSC) form a small population of tumor cells and possess high resistance to chemo and radiation therapies. To assess the sensitivity of GSC to reovirus-mediated cytolysis, a panel of GSC cultures was exposed to wild-type reovirus Type 3 Dearing (T3D) and its junction adhesion molecule-A (JAM-A)-independent mutant, jin-1. Several parameters were evaluated, including the fraction of cells expressing the JAM-A reovirus receptor, the fraction of cells synthesizing reovirus proteins, the number of infectious reovirus particles required to reduce cell viability, the amount of infectious progeny reovirus produced and the capacity of the reoviruses to infect the GSC in 3-dimensional (3D) tumor cell spheroids. Our data demonstrate a marked heterogeneity in the susceptibility of the cultures to reovirus-induced cytolysis. While in monolayer cultures the jin-1 reovirus was generally more cytolytic than the wild-type reovirus T3D, in the 3D GSC spheroids, these viruses were equally effective. Despite the variation in reovirus sensitivity between the different GSC cultures, our data support the use of reovirus as an oncolytic agent. It remains to be established whether the variation in the reovirus sensitivity correlates with a patient's response to reovirus therapy. Moreover, our data show that the expression of the JAM-A receptor is not a major determinant of reovirus sensitivity in 3D GSC cultures.

Lack of KRAS, NRAS, BRAF and TP53 mutations improves outcome of elderly metastatic colorectal cancer patients treated with cetuximab, oxaliplatin and UFT

There is conflicting evidence on the predictive role of KRAS status when cetuximab is added to oxaliplatin-based regimens. This study investigated the impact of KRAS, NRAS, BRAF, PI3KCA and TP53 status on outcome of elderly metastatic colorectal cancer patients enrolled in TEGAFOX-E (cetuximab, oxaliplatin and oral uracil/ftorafur--UFT) phase II study. Twenty-eight patients were enrolled and all were evaluable for safety and activity. Twenty-three specimens were analysed for KRAS, BRAF, NRAS, PI3KCA and TP53 mutational status by means of polymerase chain reaction and correlated with objective response, progression-free survival and overall survival. An evident increase of response rate was noted in KRAS/NRAS wild-type cases (70 versus 33%, P = 0.198). KRAS/NRAS wild-type status showed an independent association with a longer progression-free survival (44 versus 9 weeks, P = 0.009). Considering the combined assessment of BRAF, KRAS/NRAS and TP53, a trend towards an increase of response rate was noted in patients without mutations (83 versus 33%, P = 0.063). Moreover, patients with all wild-type genes had significantly longer progression-free survival than patients with any mutation (48 versus 10 weeks, P = 0.007). As a single biomarker, only KRAS/NRAS proteins maintained an independent value for outcome prediction. Patients with KRAS/NRAS, BRAF and TP53 wild-type tumours could derive the maximal benefits from treatment with cetuximab, oxaliplatin and UFT.

Oncolytic reovirus type 3 (Dearing) as a novel therapy in head and neck cancer

INTRODUCTION

Locally advanced head and neck cancer carries a poor prognosis, even with standard combination (surgery, radiotherapy, chemotherapy) treatment regimens. There is a pressing need for novel therapies with activity against this tumour type. Oncolytic reovirus type 3 (Dearing) is preferentially cytotoxic in tumour cells with an activated Ras signalling pathway and represents a promising novel therapy with relevance in head and neck cancer.

AREAS COVERED

In this review, we discuss the pre-clinical and clinical data that have underpinned the translational development of oncolytic reovirus thus far. In particular, we describe the iterative nature of the research programme through initial studies testing single-agent reovirus therapy and on to subsequent work in which reovirus has been combined with either radiotherapy or cytotoxic chemotherapy. We will trace the process by which oncolytic reovirus has reached Phase III evaluation in combination with carboplatin/paclitaxel in patients with platin-refractory, relapsed/metastatic head and neck cancer.

EXPERT OPINION

Reovirus is a self-amplifying, cancer-selective agent that offers huge potential advantages over standard chemotherapy, targeted small molecules or monoclonal antibodies. However, it is most likely that reovirus will show efficacy and be approved in combination with standard modalities (cytotoxic chemotherapy or radiotherapy) or other targeted agents, especially those that modulate signal transduction pathways. The next 5 years are critical for the development of oncolytic reovirus as an anti-cancer therapy and hinge on the ongoing Phase III trial in head and neck cancer and other Phase II programmes.

Synergistic effects of combined Wnt/KRAS inhibition in colorectal cancer cells

Activation of Wnt signalling due to inability to degrade β-catenin is found in >85% of colorectal cancers. Approximately half of colon cancers express a constitutively active KRAS protein. A significant fraction of patients show both abnormalities. We previously reported that simultaneous down-regulation of both β-catenin and KRAS was necessary to induce significant cell death and tumor growth inhibition of colorectal cancer cells. Although attractive, an RNAi-based therapeutic approach is still far from being employed in the clinical setting. Therefore, we sought to recapitulate our previous findings by the use of small-molecule inhibitors of β-catenin and KRAS. We show here that the β-catenin inhibitors PKF115-584 and pyrvinium pamoate block β-catenin-dependent transcriptional activity and synergize with the KRAS inhibitor S-trans, trans-farnesylthiosalicylic acid (FTS, salirasib) in colon cancer cells driven by Wnt and KRAS oncogenic signals, but not in cells carrying BRAF mutations. The combined use of these compounds was superior to the use of any drug alone in inducing cell growth arrest, cell death, MYC and survivin down-modulation, and inhibition of anchorage-independent growth. Expression analysis of selected cancer-relevant genes revealed down-regulation of CD44 as a common response to the combined treatments. These data provide a proof of principle for a combination therapeutic strategy in colorectal cancer.

Isolation of reovirus T3D mutants capable of infecting human tumor cells independent of junction adhesion molecule-A

Mammalian Reovirus is a double-stranded RNA virus with a distinctive preference to replicate in and lyse transformed cells. On that account, Reovirus type 3 Dearing (T3D) is clinically evaluated as oncolytic agent. The therapeutic efficacy of this approach depends in part on the accessibility of the reovirus receptor Junction Adhesion Molecule-A (JAM-A) on the target cells. Here, we describe the isolation and characterization of reovirus T3D mutants that can infect human tumor cells independent of JAM-A. The JAM-A-independent (jin) mutants were isolated on human U118MG glioblastoma cells, which do not express JAM-A. All jin mutants harbour mutations in the S1 segments close to the region that encodes the sialic acid-binding pocket in the shaft of the spike protein. In addition, two of the jin mutants encode spike proteins with a Q336R substitution in their head domain. The jin mutants can productively infect a wide range of cell lines that resist wt reovirus T3D infection, including chicken LMH cells, hamster CHO cells, murine endothelioma cells, human U2OS and STA-ET2.1 cells, but not primary human fibroblasts. The jin-mutants rely on the presence of sialic-acid residues on the cell surface for productive infection, as is evident from wheat germ agglutinin (WGA) inhibition experiments, and from the jin-reovirus resistance of CHO-Lec2 cells, which have a deficiency of sialic-acids on their glycoproteins. The jin mutants may be useful as oncolytic agents for use in tumors in which JAM-A is absent or inaccessible.

The effect of Zhangfei on the unfolded protein response and growth of cells derived from canine and human osteosarcomas

The objective of this study was to determine whether the protein Zhangfei could suppress the unfolded protein response (UPR) and growth of osteosarcoma cells. Dog (D-17) and a human (Saos-2) osteosarcoma cells were infected with adenovirus vectors expressing either Zhangfei or the control protein beta- galactosidase. We monitored cell growth as well as levels of UPR gene transcripts and proteins. We found that Zhangfei suppressed the growth of both D-17 and Saos-2 cells. Zhangfei-expressing D-17 cells displayed large vacuoles containing culture medium and expressed phosphatidylserine on their external surface suggesting that Zhangfei induced macropinocytosis and apoptosis in these cells. While Zhangfei inhibited the growth of both D-17 and Saos-2 cells, it inhibited thapsigargin-induced UPR, as detected by a decrease in transcripts for UPR genes, and HERP and GRP78 proteins, only in D-17 cells, suggesting that the ability of Zhangfei to suppress the UPR and tumour cells growth may not be linked.

Synthetic Lethality Induced by Loss of PKC δ and Mutated Ras

Synthetic lethal interaction between oncogenic Ha-ras and loss of PKC has been demonstrated. Recently, the authors reported that the concurrent knockdown of PKC α and β, via upregulating PKC δ, sensitizes cells with aberrant Ras signaling to apoptosis. As a continuation of the study, using shRNA, the authors demonstrate that loss of PKC δ causes a lethal reaction in NIH3T3/Hras or prostate cancer DU145 cells that overexpress JNK. In this apoptotic process, PKC α and β are upregulated and then associated with RACK1 (an adaptor for activated PKC) and JNK. Immunoblotting analysis shows that JNK is phosphorylated, accompanied with caspase 8 cleavage. The inhibition of JNK abrogates this apoptotic process triggered by PKC δ knockdown. Interestingly, without blocking PKC δ, the concurrent overexpression of wt- or CAT-PKC α and β is insufficient to induce apoptosis in the cells. Together with the authors' previous findings, the data suggest that PKC α/β and δ function oppositely to maintain a balance that supports cells expressing v-ras to survive and prevents them from being eliminated through oncogenic stress-induced apoptosis.

Stabilisation of p53 enhances reovirus-induced apoptosis and virus spread through p53-dependent NF-κB activation

Background:

Naturally oncolytic reovirus preferentially kills cancer cells, making it a promising cancer therapeutic. Mutations in tumour suppressor p53 are prevalent in cancers, yet the role of p53 in reovirus oncolysis is relatively unexplored.

Methods:

Human cancer cell lines were exposed to Nutlin-3a, reovirus or a combination of the two and cells were processed for reovirus titration, western blot, real-time PCR and apoptosis assay using Annexin V and 7-AAD staining. Confocal microscopy was used to determine translocation of the NF-κB p65 subunit.

Results:

We show that despite similar reovirus replication in p53^+/+ and p53^−/− cells, stabilisation of p53 by Nutlin-3a significantly enhanced reovirus-induced apoptosis and hence virus release and dissemination while having no direct effect on virus replication. Enhanced apoptosis by Nutlin-3a was not observed in p53^−/− or p53 knockdown cells; however, increased expression of Bax and p21 are required. Moreover, elevated NF-κB activation in reovirus-infected cells following Nutlin-3a treatment was necessary for enhanced reovirus-induced apoptosis, as synergistic cytotoxicity was overcome by specific NF-κB inhibitors.

Conclusion:

Nutlin-3a treatment enhances reovirus-induced apoptosis and virus spread through p53-dependent NF-κB activation, and combination of reovirus and Nutlin-3a might represent an improved therapy against cancers harbouring wild-type p53.

KRAS gene mutation in colorectal cancer is correlated with increased proliferation and spontaneous apoptosis

KRAS mutation occurs in 30% to 50% of colorectal cancers (CRCs) and has been suggested to be associated with proliferation and decreased apoptosis. In this study, we analyzed KRAS in 198 CRCs and compared the clinicopathologic variables between KRAS-mutated and wild-type CRCs. Also, a subset of 90 and 66 CRCs from this cohort underwent microsatellite instability testing and histomorphologic evaluation, and the frequency of microsatellite instability-high (MSI-H) and histomorphologic variables were compared between KRAS-mutated and wild-type CRCs. Clinicopathologic features (age, sex, and tumor site, depth, size, grade, and metastasis) were not different between KRAS-mutated and wild-type CRCs. Compared with wild-type KRAS CRCs, KRAS-mutated CRCs had a lower frequency of MSI-H (15% vs 42%; P = .015), a higher chance of having brisk mitosis (77% vs 43%, P = .022) and apoptosis (77% vs 28%; P = .00012), and a greater mean of mitotic figures (P = .0002) and apoptotic cells (P = .0008). KRAS mutation was associated with higher tumor cell turnover.

Oncogenic Ras promotes reovirus spread by suppressing IFN-beta production through negative regulation of RIG-I signaling

Reovirus is the first naturally occurring human virus reported to exploit activated Ras signaling in the host cell for infection, and is currently undergoing clinical trials as a cancer therapeutic. Recent evidence suggests that Ras transformation promotes three reoviral replication steps during the first round of infection: uncoating of the incoming virion, generation of progeny viruses with enhanced infectivity, and virus release through enhanced apoptosis. Whether oncogenic Ras also enhances reovirus spread in subsequent rounds of infection through other mechanisms has not been examined. Here, we show that compared with nontransformed cells, Ras-transformed cells are severely compromised not only in their response to IFN-beta, but also in the induction of IFN-beta mRNA following reovirus infection. Defects in both IFN-beta production and response allow for efficient virus spread in Ras-transformed cells. We show that the MEK/ERK pathway downstream of Ras is responsible for inhibiting IFN-beta expression by blocking signaling from the retinoic acid-inducible gene I (RIG-I) which recognizes viral RNAs. Overexpression of wild-type RIG-I restores INF-beta expression in reovirus-infected Ras-transformed cells. In vitro-synthesized viral mRNAs also invoke robust RIG-I-mediated IFN-beta production in transfected nontransformed cells, but not in Ras-transformed cells. Collectively, our data suggest that oncogenic Ras promotes virus spread by suppressing viral RNA-induced IFN-beta production through negative regulation of RIG-I signaling.

Oncogenic KRAS sensitises colorectal tumour cells to chemotherapy by p53-dependent induction of Noxa

Background:

Oxaliplatin and 5-fluorouracil (5-FU) currently form the backbone of conservative treatment in patients with metastatic colorectal cancer. Tumour responses to these agents are highly variable, but the underlying mechanisms are poorly understood. Our previous results have indicated that oncogenic KRAS in colorectal tumour cells sensitises these cells to chemotherapy.

Methods:

FACS analysis was used to determine cell-cycle distribution and the percentage of apoptotic and mitotic cells. A multiplexed RT–PCR assay was used to identify KRAS-controlled apoptosis regulators after exposure to 5-FU or oxaliplatin. Lentiviral expression of short-hairpin RNAs was used to suppress p53 or Noxa.

Results:

Oncogenic KRAS sensitised colorectal tumour cells to oxaliplatin and 5-FU in a p53-dependent manner and promoted p53 phosphorylation at Ser37 and Ser392, without affecting p53 stabilisation, p21 induction, or cell-cycle arrest. Chemotherapy-induced expression of the p53 target gene Noxa was selectively enhanced by oncogenic KRAS. Suppression of Noxa did not affect p21 induction or cell-cycle arrest, but reduced KRAS/p53-dependent apoptosis after exposure to chemotherapy in vitro and in tumour xenografts. Noxa suppression did not affect tumour growth per se, but strongly reduced the response of these tumours to chemotherapy.

Conclusion:

Oncogenic KRAS determines the cellular response to p53 activation by oxaliplatin or 5-FU, by facilitating apoptosis induction through Noxa.

Modification of mammalian reoviruses for use as oncolytic agents

The Reoviridae are a family of viruses with a non-enveloped icosahedral capsid and a segmented double-stranded RNA genome. Prototypes of the mammalian Orthoreoviruses have been isolated from human respiratory and enteric tracts and are not associated with human disease. One of these, human reovirus type 3 Dearing (T3D), usually serves as a model for the family. In the last decade the mammalian Orthoreoviruses, especially T3D, have been evaluated as oncolytic agents in experimental cancer therapy. This is based on the observation that reoviruses induce cell death and apoptosis in tumor cells, but not in healthy non-transformed cells. Several clinical trials have been initiated in Canada, the USA, and the UK, to study the feasibility and safety of this approach. Due to the segmented structure of their double-stranded RNA genomes genetic modification of Reoviridae has been notoriously difficult. Several techniques have been described recently that facilitate the genetic modification of reovirus genomes. The basis for reverse genetics of reovirus is the discovery in 1990 that reovirus RNA is infectious. Subsequently, it took ten years before a foreign gene was introduced into the reovirus genome. Here we review the methods for reovirus modification and their use for generating new reovirus-derived oncolytic agents.

Targeting cancer-initiating cells with oncolytic viruses

Recent studies in a variety of leukemias and solid tumors indicate that there is significant heterogeneity with respect to tumor-forming ability within a given population of tumor cells, suggesting that only a subpopulation of cells is responsible for tumorigenesis. These cells have been commonly referred to as cancer stem cells (CSCs) or cancer-initiating cells (CICs). CICs have been shown to be relatively resistant to conventional anticancer therapies and are thus thought to be responsible for disease relapse. As such, they represent a potentially critical therapeutic target. Oncolytic viruses are in clinical trials for cancer and kill cells through mechanisms different from conventional therapeutics. Because these viruses are not susceptible to the same pathways of drug or radiation resistance, it is important to learn whether CICs are susceptible to oncolytic virus infection. Here we review the available data regarding the ability of several different oncolytic virus types to target CICs for destruction.

Synthetic lethal interaction between oncogenic KRAS dependency and STK33 suppression in human cancer cells

An alternative to therapeutic targeting of oncogenes is to perform "synthetic lethality" screens for genes that are essential only in the context of specific cancer-causing mutations. We used high-throughput RNA interference (RNAi) to identify synthetic lethal interactions in cancer cells harboring mutant KRAS, the most commonly mutated human oncogene. We find that cells that are dependent on mutant KRAS exhibit sensitivity to suppression of the serine/threonine kinase STK33 irrespective of tissue origin, whereas STK33 is not required by KRAS-independent cells. STK33 promotes cancer cell viability in a kinase activity-dependent manner by regulating the suppression of mitochondrial apoptosis mediated through S6K1-induced inactivation of the death agonist BAD selectively in mutant KRAS-dependent cells. These observations identify STK33 as a target for treatment of mutant KRAS-driven cancers and demonstrate the potential of RNAi screens for discovering functional dependencies created by oncogenic mutations that may enable therapeutic intervention for cancers with "undruggable" genetic alterations.

Oncolytic viral therapy using reovirus

Current mainstays in cancer treatment such as chemotherapy, radiation therapy, hormonal manipulation, and even targeted therapies such as trastuzumab (Herceptin) for breast cancer or erlotinib (Tarceva) for non-small cell lung cancer are limited by lack of efficacy, cellular resistance, and toxicity. Dose escalation and combination therapies designed to overcome resistance and increase efficacy are limited by a narrow therapeutic index. Oncolytic viruses are one such group of new biological therapeutics that appears to have a wide spectrum of anticancer activity with minimal human toxicity. Because the malignant phenotype of tumours is the culmination of multiple mutations that occur in several genes eventually leading to aberrant signalling pathways, oncolytic viruses, either natural or engineered, specifically target tumour cells, taking advantage of this cellular deviant signalling for their replication. Reovirus is one such naturally occurring double-stranded RNA (dsRNA) virus that exploits altered Ras signalling pathways in a myriad of cancers. The ability of reovirus to infect and lyse tumours both solid and haematological, under in vitro, in vivo, and ex vivo conditions, is discussed in this chapter. The major mechanism of reovirus oncolysis of cancer cells has been shown to occur through apoptosis. In addition, the synergistic anti-tumour effects of reovirus in combination with radiation or chemotherapy has also been demonstrated for reovirus-resistant and moderately sensitive tumours. In most of the clinical trials undertaken to date, an anti-reovirus immune response has been seen likely circumventing efficacy. Investigation into the use of reovirus as an immune adjuvant is currently underway to try and re-direct this immune response to tumour. Reovirus phase I clinical trials have shown indications of efficacy and several phase I/II trials are ongoing at present. The extensive pre-clinical efficacy, replication competency, and low toxicity profile in humans has placed the reovirus as an attractive anti-cancer therapeutic for ongoing clinical testing.

A strategy for genetic modification of the spike-encoding segment of human reovirus T3D for reovirus targeting

Human Orthoreovirus Type 3 Dearing is not pathogenic to humans and has been evaluated clinically as an oncolytic agent. Its transduction efficiency and the tumor cell selectivity may be enhanced by incorporating ligands for alternative receptors. However, the genetic modification of reoviruses has been difficult, and genetic targeting of reoviruses has not been reported so far. Here we describe a technique for generating genetically targeted reoviruses. The propagation of wild-type reoviruses on cells expressing a modified sigma 1-encoding segment embedded in a conventional RNA polymerase II transcript leads to substitution of the wild-type genome segment by the modified version. This technique was used for generating reoviruses that are genetically targeted to an artificial receptor expressed on U118MG cells. These cells lack the junction adhesion molecule-1 and therefore resist infection by wild-type reoviruses. The targeted reoviruses were engineered to carry the ligand for this receptor at the C terminus of the sigma 1 spike protein. This demonstrates that the C terminus of the sigma 1 protein is a suitable locale for the insertion of oligopeptide ligands and that targeting of reoviruses is feasible. The genetically targeted viruses can be propagated using the modified U118MG cells as helper cells. This technique may be applicable for the improvement of human reoviruses as oncolytic agents.

Reovirus: viral therapy for cancer 'as nature intended'

Oncolytic viruses are tumour selective and able to lyse cancer cells after infection. Reovirus is an example of a wild-type oncolytic virus and is currently being investigated as a potential novel therapy for cancer. This overview gives a brief description of what is known about reovirus biology and summarises the preclinical data related to its oncolytic ability. The completed and ongoing clinical trials involving reovirus, both as a single agent and in combination with chemotherapy and radiotherapy, will be reviewed and their results discussed. Many of these clinical studies are being conducted by centres in the UK.

Transient infection of freshly isolated human colorectal tumor cells by reovirus T3D intermediate subviral particles

Reovirus T3D preferentially kills tumor cells expressing Ras oncogenes and has shown great promise as an anticancer agent in various preclinical tumor models. Here, we investigated whether reovirus can infect and kill tumor cell cultures and tissue fragments isolated from resected human colorectal tumors, and whether this was affected by the presence of endogenous oncogenic KRAS. Tissue fragments and single-cell populations isolated from human colorectal tumor biopsies were infected with reovirus virions or with intermediate subviral particles (ISVPs). Reovirus virions were capable of infecting neither single-cell tumor cell populations nor small fragments of intact viable tumor tissue. However, infection of tumor cells with ISVPs resulted in transient viral protein synthesis, irrespective of the presence of oncogenic KRAS, but this did not lead to the production of infectious virus particles, and tumor cell viability was largely unaffected. ISVPs failed to infect intact tissue fragments. Thermolysin treatment of tumor tissue liberated single cells from the tissue and allowed infection with ISVPs, but this did not result in the production of infectious virus particles. Immunohistochemistry on tissue microarrays showed that junction adhesion molecule 1, the major cellular reovirus receptor, was improperly localized in the cytoplasm of colorectal tumor cells and was expressed at very low levels in liver metastases. This may contribute to the observed resistance of tumor cells to reovirus T3D virions. We conclude that infection of human colorectal tumor cells by reovirus T3D requires processing of virions to ISVPs, but that oncolysis is prevented by a tumor cell response that aborts viral protein synthesis and the generation of infectious viral particles, irrespective of KRAS mutation status.

Ras transformation mediates reovirus oncolysis by enhancing virus uncoating, particle infectivity, and apoptosis-dependent release

Reovirus, a potential cancer therapy, replicates more efficiently in Ras-transformed cells than in non-transformed cells. It was presumed that increased translation was the mechanistic basis of reovirus oncolysis. Analyses of each step of the reovirus life cycle now show that cellular processes deregulated by Ras transformation promote not one but three viral replication steps. First, in Ras-transformed cells, proteolytic disassembly (uncoating) of the incoming virions, required for onset of infection, occurs more efficiently. Consequently, threefold more Ras-transformed cells become productively infected with reovirus than non-transformed cells, which accounts for the observed increase of reovirus proteins in Ras-transformed cells. Second, Ras transformation increases the infectious-to-noninfectious virus particle ratio, as virions purified from Ras-transformed cells are fourfold more infectious than those purified from non-transformed cells. Progeny assembled in non- and Ras-transformed cells appear similar by electron microscopy and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis, suggesting that Ras transformation introduces a subtle change necessary for virus infectivity. Finally, reovirus release, mediated by caspase-induced apoptosis, is ninefold more efficient in Ras-transformed cells. The combined effects of enhanced virus uncoating, infectivity, and release result in >100-fold differences in virus titers within one round of replication. Our analysis reveals previously unrecognized mechanisms by which Ras transformation mediates selective viral oncolysis.