CUG2, a novel oncogene confers reoviral replication through Ras and p38 signaling pathway

The heterogeneous sensitivity of pediatric brain tumors to different oncolytic viruses is predicted by unique gene expression profiles

Despite decades of research, the prognosis of high-grade pediatric brain tumors (PBTs) remains dismal; however, recent cases of favorable clinical responses were documented in clinical trials using oncolytic viruses (OVs). In the current study, we employed four different species of OVs: adenovirus Delta24-RGD, herpes simplex virus rQNestin34.5v1, reovirus R124, and the non-virulent Newcastle disease virus rNDV-F0-GFP against three entities of PBTs (high-grade gliomas, atypical teratoid/rhabdoid tumors, and ependymomas) to determine their in vitro efficacy. These four OVs were screened on 14 patient-derived PBT cell cultures and the degree of oncolysis was assessed using an ATP-based assay. Subsequently, the observed viral efficacies were correlated to whole transcriptome data and Gene Ontology analysis was performed. Although no significant tumor type-specific OV efficacy was observed, the analysis revealed the intrinsic biological processes that associated with OV efficacy. The predictive power of the identified expression profiles was further validated in vitro by screening additional PBTs. In summary, our results demonstrate OV susceptibility of multiple patient-derived PBT entities and the ability to predict in vitro responses to OVs using unique expression profiles. Such profiles may hold promise for future OV preselection with effective oncolytic potency in a specific tumor, therewith potentially improving OV responses.

Centromere protein N promotes lung adenocarcinoma progression by activating PI3K/AKT signaling pathway

BACKGROUND

As an important member of centromere family, centromere associated protein N (CENPN) was abnormally expressed in varied malignant tumors.

OBJECTIVE

This paper aimed to analyze the expression and related mechanism of CENPN in lung adenocarcinoma (LUAD).

METHODS

The expression of CENPN in LUAD was analyzed by Gene Expression Profiling Interactive Analysis (GEPIA) database. The mRNA expression, protein expression, cell viability, cell invasion, cell apoptosis, cell stem like characteristics were detected by RT-PCR, western blot, CCK8 assay, transwell assay, flow cytometry and spheroidization assay, respectively. Finally, the pathological changes of xenograft were estimated by H&E staining, and the expression of proteins was detected by immunohistochemistry.

RESULTS

GEPIA analysis showed that the CENPN expression in LUAD was significantly higher than that in normal lung tissue, which was negatively correlated with the prognosis. These results were consistent with our clinical data. Besides, CENPN was highly expressed in LUAD cell lines. In addition, the upregulation of CENPN amplified the cell viability, stemness and invasive ability in PC9 cells. However, the knockdown of CENPN inhibited the cell activity, stemness, invasive ability with increased cell apoptosis in A549. Furthermore, CENPN could positively regulate the phosphorylation of PI3K and AKT. The PI3K inhibitor, 740Y-P, could reverse the effect of CENPN silencing on the expression of Ki-67, cleaved caspase 3, OCT4, and snail 1. Finally, the downregulation of CENPN restrained the growth of xenograft and inactivated the PI3K/AKT pathway.

CONCLUSION

CENPN was abnormally overexpressed in LUAD, and promoted tumor progression of LUAD by affecting PI3K/AKT pathway.

Overexpression of Cancer Upregulated Gene 2 (CUG2) Decreases Spry2 Through c-Cbl, Leading to Activation of EGFR and β-Catenin Signaling

Purpose

The mechanism by which cancer upregulated gene 2 (CUG2) overexpression induces cancer stem cell-like phenotypes is not fully understood. Because the increased activity and expression of epidermal growth factor receptor (EGFR) kinase have been reported in A549 cancer cells overexpressing CUG2 (A549-CUG2) compared with control cells (A549-Vec), the Sprouty2 (Spry2) protein has gained attention as the downstream molecule of EGFR signaling. Therefore, we aim to identify the role of Spry2 in CUG2-overexpressing lung cancer cells.

Materials and Methods

Spry2 expression levels were examined in A549-CUG2 and A549-Vec cells by Western blotting and qRT-PCR. Cell migration, invasion, and sphere formation were examined after Spry2 suppression and overexpression. EGFR-Stat1 and Akt-ERK protein phosphorylation levels were detected via immunoblotting. NEK2 kinase and β-catenin reporter assay were performed for downstream of Spry2 signaling.

Results

Although A549-CUG2 cells showed lower levels of the Spry2 protein than A549-Vec cells, no difference in levels of Spry2 transcript was observed between both cells via qRT-PCR. Furthermore, MG132 treatment enhanced the protein levels and ubiquitination of Spry2, suggesting that Spry2 protein expression can be regulated via the ubiquitin-proteasome pathway. The enforced expression of c-Cbl, known as the binding partner of Spry2, decreased the Spry2 protein levels, whereas its knockdown oppositely increased them. Epithelial-mesenchymal transition (EMT) and sphere formation were increased in A549-Vec cells during Spry2 siRNA treatment, confirming the role of Spry2 in CUG2-induced oncogenesis. Furthermore, EMT and sphere formation were determined by the Spry2 protein levels through the regulation of EGFR-Stat1 and β-catenin-NEK2-Yap1 signaling pathways.

Conclusion

CUG2 reduces Spry2 protein levels, the negative signaling molecule of cell proliferation, via c-Cbl, possibly activating the EGFR and β-catenin signaling pathways and, in turn, contributing to the induction of cancer stem cell-like phenotypes.

CGK062, a small chemical molecule, inhibits cancer upregulated gene 2‑induced oncogenesis through NEK2 and β‑catenin

The mechanisms through which cancer‑upregulated gene 2 (CUG2), a novel oncogene, affects Wnt/β‑catenin signaling, essential for tumorigenesis, are unclear. In this study, we aimed to elucidate some of these mechanisms in A549 lung cancer cells. Under the overexpression of CUG2, the protein levels and activity of β‑catenin were evaluated by western blot analysis and luciferase assay. To examine a biological consequence of β‑catenin under CUG2 overexpression, cell migration, invasion and sphere formation assay were performed. The upregulation of β‑catenin induced by CUG2 overexpression was also accessed by xenotransplantation in mice. We first found that CUG2 overexpression increased β‑catenin expression and activity. The suppression of β‑catenin decreased cancer stem cell (CSC)‑like phenotypes, indicating that β‑catenin is involved in CUG2‑mediated CSC‑like phenotypes. Notably, CUG2 overexpression increased the phosphorylation of β‑catenin at Ser33/Ser37, which is known to recruit E3 ligase for β‑catenin degradation. Moreover, CUG2 interacted with and enhanced the expression and kinase activity of never in mitosis gene A‑related kinase 2 (NEK2). Recombinant NEK2 phosphorylated β‑catenin at Ser33/Ser37, while NEK2 knockdown decreased the phosphorylation of β‑catenin, suggesting that NEK2 is involved in the phosphorylation of β‑catenin at Ser33/Ser37. Treatment with CGK062, a small chemical molecule, which promotes the phosphorylation of β‑catenin at Ser33/Ser37 through protein kinase C (PKC)α to induce its degradation, reduced β‑catenin levels and inhibited the CUG2‑induced features of malignant tumors, including increased cell migration, invasion and sphere formation. Furthermore, CGK062 treatment suppressed CUG2‑mediated tumor formation in nude mice. Taken together, the findings of this study suggest that CUG2 enhances the phosphorylation of β‑catenin at Ser33/Ser37 by activating NEK2, thus stabilizing β‑catenin. CGK062 may thus have potential for use as a therapeutic drug against CUG2‑overexpressing lung cancer cells.

Cancer upregulated gene (CUG)2 elevates YAP1 expression, leading to enhancement of epithelial-mesenchymal transition in human lung cancer cells

Although our previous studies have showed that a novel oncogene, cancer upregulated gene (CUG)2 induced epithelial-mesenchymal transition (EMT), the detailed molecular mechanism remains unknown. Because several lines of evidence documented that Yes-Associated Protein (YAP)1 is closely associated with cancer stem cell (CSC)-like phenotypes including EMT, stemness, and drug resistance, we wondered if YAP1 is involved in CUG2-induced EMT. We herein found that the overexpression of CUG2 increased YAP1 expression at the transcriptional as well as protein levels. Chromatin immunoprecipitation assay revealed that the elevated YAP1 transcripts are attributed to c-Jun and AP2 bindings to the YAP1 promoter. Akt and MAPK kinases including ERK, JNK, and p38 MAPK enhanced the level of YAP1 protein. In spite of a close relationship between β-catenin and YAP1, not β-catenin but NEK2 played the role in increasing YAP1 expression. Silencing YAP1 inhibited CUG2-induced cell migration and invasion. N-cadherin and vimentin expressions were decreased during YAP1 knockdown. The suppression of YAP1 diminished TGF-β transcriptional activity and expression as well as phosphorylation level of Smad2 and Twist protein. Conversely, LY2109761 or Smad2 siRNA treatment reduced YAP1 protein levels, indicating a close interplay between YAP1 and TGF-β signaling. Taken together, we suggest that CUG2 induces up-regulation of YAP1 expression, leading to enhancing CUG2-induced EMT via a close crosstalk between YAP1 and TGF-β signaling.

Synthesis and Translation of Viral mRNA in Reovirus-Infected Cells: Progress and Remaining Questions

At the end of my doctoral studies, in 1988, I published a review article on the major steps of transcription and translation during the mammalian reovirus multiplication cycle, a topic that still fascinates me 30 years later. It is in the nature of scientific research to generate further questioning as new knowledge emerges. Our understanding of these fascinating viruses thus remains incomplete but it seemed appropriate at this moment to look back and reflect on our progress and most important questions that still puzzle us. It is also essential of being careful about concepts that seem so well established, but could still be better validated using new approaches. I hope that the few reflections presented here will stimulate discussions and maybe attract new investigators into the field of reovirus research. Many other aspects of the viral multiplication cycle would merit our attention. However, I will essentially limit my discussion to these central aspects of the viral cycle that are transcription of viral genes and their phenotypic expression through the host cell translational machinery. The objective here is not to review every aspect but to put more emphasis on important progress and challenges in the field.

STAT1‑HDAC4 signaling induces epithelial‑mesenchymal transition and sphere formation of cancer cells overexpressing the oncogene, CUG2

Our previous studies have shown that the novel oncogene, cancer upregulated gene 2 (CUG2), activates STAT1, which is linked to anticancer drug resistance, induces epithelial-mesenchymal transition (EMT) and cancer stem cell-like phenotypes as determined by MTT, migration and sphere formation assays. We thus aimed to ascertain whether the activation of STAT1 by CUG2 is involved in these malignant phenotypes besides drug resistance. Here, we showed that STAT1 suppression decreased the expression of N-cadherin and vimentin, biomarkers of EMT, which led to inhibition of the migration and invasion of human lung A549 cancer cells stably expressing CUG2, but did not recover E-cadherin expression. STAT1 siRNA also diminished CUG2-induced TGF-β signaling, which is critical in EMT, and TGF-β transcriptional activity. Conversely, inhibition of TGF-β signaling reduced phosphorylation of STAT1, indicating a crosstalk between STAT1 and TGF-β signaling. Furthermore, STAT1 silencing diminished sphere formation, which was supported by downregulation of stemness-related factors such as Sox2, Oct4, and Nanog. Constitutive suppression of STAT1 also inhibited cell migration, invasion and sphere formation. As STAT1 acetylation counteracts STAT1 phosphorylation, acetylation of STAT1 by treatment with trichostatin A, an inhibitor of histone deacetylases (HDACs), reduced cell migration, invasion, and sphere formation. As HDAC4 is known to target STAT1, its role was investigated under CUG2 overexpression. HDAC4 suppression resulted in inhibition of cell migration, invasion, and sphere formation as HDAC4 silencing hindered TGF-β signaling and decreased expression of Sox2 and Nanog. Taken together, we suggest that STAT1-HDAC4 signaling induces malignant tumor features such as EMT and sphere formation in CUG2-overexpressing cancer cells.

Cancer upregulated gene 2 induces epithelial-mesenchymal transition of human lung cancer cells via TGF-β signaling

Cancer upregulated gene 2 (CUG2) enhances cell migration and invasion, but the underlying mechanism has not been revealed. Herein, CUG2 decreased the expression of E-cadherin and increased the expression of N-cadherin and vimentin, characteristics of the epithelial-mesenchymal transition (EMT). A CUG2 deletion mutant, lacking interaction with nucleophosmin 1 (NPM1), or suppression of NPM1 reduced wound healing and cell invasion, indicating that CUG2-mediated EMT requires NPM1. CUG2 enhanced activation of Smad2/3 and expression of Snail and Twist, while the CUG2 silence decreased these TGF-β signaling pathways, leading to suppression of EMT. NPM silence also inhibited the CUG2-induced TGF-β signaling. These results suggest that TGF-β signaling is involved in CUG2-induced EMT. Treatment with EW-7197, a novel inhibitor of TGF-β signaling, diminished CUG2-mediated EMT and inhibition of Akt, ERK, JNK, and p38 MAPK, non-canonical TGF-β signaling molecules, also decreased expression of Smad2/3, Snail and Twist, leading to inhibition of EMT. The results confirm that TGF-β signaling is essential for CUG2-mediated EMT. Interestingly, TGF-β enhanced CUG2 expression. We further found that both CUG2-induced TGF-β production and TGF-β-induced CUG2 up-regulation required a physical interaction between Sp1 and Smad2/3 in the CUG2 and TGF-β promoter, as demonstrated by a promoter reporter assay, immunoprecipitation, and ChIP assay. These results indicated close crosstalk between CUG2 and TGF-β. Conversely, suppression of CUG2 or NPM1 did not completely inhibit TGF-β-induced EMT, indicating that the effect of TGF-β on EMT is dominant over the effect of CUG2 on EMT. Collectively, our findings suggest that CUG2 induces the EMT via TGF-β signaling.

Enhanced cytotoxicity of reovirus and radiotherapy in melanoma cells is mediated through increased viral replication and mitochondrial apoptotic signalling

Oncolytic viruses selectively target and replicate in cancer cells, providing us with a unique tool with which to target and kill tumour cells. These viruses come from a diverse range of viral families including reovirus type 3 Dearing (RT3D), a non-pathogenic human double-stranded RNA oncolytic virus, which has been shown to be an effective therapeutic agent, both as a mono-therapy and in combination with traditional chemotherapeutic drugs. This study investigated the interaction between RT3D and radiotherapy in melanoma cell lines with a BRAF mutant, Ras mutant or BRAF/Ras wild type genotype. The data indicates that RT3D combined with radiotherapy significantly increased cytotoxicity relative to either single agent, independent of genotype, both in vitro and in vivo. The mechanism of enhanced cytotoxicity was dependent on an increase in viral replication, mediated by CUG2 up-regulation and subsequent down-regulation of pPKR and p-eIF2α, leading to the activation of mitochondrial apoptotic signalling resulting in increased cell death.

Anti-tumor efficacy of oncolytic reovirus against gastrointestinal stromal tumor cells

Imatinib, a multitargeted receptor tyrosine kinase inhibitor, is used as the standard initial therapy against inoperable gastrointestinal stromal tumor (GIST). However, GIST can acquire resistance to imatinib within several years of therapy. The development of oncolytic reovirus as an anticancer agent has expanded to many clinical trials for various tumors. Here, we investigated whether reovirus has antitumor activity against GIST cells in the setting of imatinib sensitivity in vitro and in vivo. Cell proliferation and apoptosis assays were performed using a human GIST cell line, GIST-T1, and imatinib-resistant GIST (GIST-IR) cells that we established. The molecular pathways responsible for cell damage by reovirus were explored using PCR-arrays and Western blots. Reovirus significantly induced apoptotic cell death in GIST-T1 and GIST-IR cells in vitro, despite differences in the activation of receptor tyrosine kinase pathways between GIST-T1 and GIST-IR. Molecular assays indicated the possibility that reovirus induces apoptotic cell death via Fas signaling. Furthermore, in vivo mouse tumor xenograft models demonstrated a significant anti-tumor effect of reovirus on both GIST-T1 and GIST-IR cells. Our results demonstrate the therapeutic potential of reovirus against GIST.

Clinical development of reovirus for cancer therapy: An oncolytic virus with immune-mediated antitumor activity

Reovirus is a double-stranded RNA virus with demonstrated oncolysis or preferential replication in cancer cells. The oncolytic properties of reovirus appear to be dependent, in part, on activated Ras signaling. In addition, Ras-transformation promotes reovirus oncolysis by affecting several steps of the viral life cycle. Reovirus-mediated immune responses can present barriers to tumor targeting, serve protective functions against reovirus systemic toxicity, and contribute to therapeutic efficacy through antitumor immune-mediated effects via innate and adaptive responses. Preclinical studies have demonstrated the broad anticancer activity of wild-type, unmodified type 3 Dearing strain reovirus (Reolysin^®) across a spectrum of malignancies. The development of reovirus as an anticancer agent and available clinical data reported from 22 clinical trials will be reviewed.

The oncolytic virus, pelareorep, as a novel anticancer agent: a review

Pelareorep (REOLYSIN®) is an investigational new drug, a proprietary formulation consisting of a live, replication-competent, naturally occurring Reovirus Type 3 Dearing strain. Through several preclinical studies it was determined that reovirus can exhibit profound cytotoxic effects on cancer cells predominantly with an activated RAS-signalling pathway. Moreover, it was discovered that reoviruses can "hitchhike" on peripheral blood mononuclear cells and dendritic cells, thereby evading neutralizing antibodies of the host immune system. Cell carriage, targeted delivery, triggering host immune response and other inherent characteristics of the reovirus led to its further advancement into cancer therapy. When injected into Sprague-Dawley rats, the viral routes of clearance, predominantly through the spleen and liver, remained consistent with earlier studies. Toxicology findings were considered incidental and not associated with pelareorep when tested in animal models. Pelareorep demonstrated a high level of homogeneity at the amino acid level and genetic stability when compared to the master and working virus banks. The drug is manufactured in a 100 L bioreactor after which it is purified and formulated for use in pre-clinical, clinical and research studies. Over the past few decades, we have witnessed a paradigm shift from conventional therapy to the conceivable use of oncolytic viruses for the treatment of cancer. This review will detail pre-clinical evidence of anticancer activity of pelareorep that has led to extensive clinical development. Several Phase I-II clinical trials have been completed or are ongoing in cancer patients on a broad spectrum of solid tumors and hematologic malignancies.

Oncolytic reovirus combined with trastuzumab enhances antitumor efficacy through TRAIL signaling in human HER2-positive gastric cancer cells

The human epidermal growth factor receptor 2 (HER2)-targeting agent, trastuzumab, is effective for HER2-overexpressing gastric cancer therapy. As oncolytic reovirus is currently undergoing clinical trials internationally, we wanted to explore whether combination therapy using trastuzumab and reovirus might provide a novel, more effective therapeutic option for gastric cancer. Cell proliferation and cell apoptosis were examined in vitro, while molecular analysis of pathways responsible for cell damage was examined using polymerase chain reaction array. Activation of the proteins related to apoptosis, cell growth and survival was detected by Western blotting. Mouse tumor xenograft models were used to examine antitumor activity in vivo. Reovirus sensitized HER2-overexpressing gastric cancer cells to undergo apoptosis. Both in vitro and in vivo studies provided evidence that the combination therapy is a more powerful modality against HER2-overexpressing gastric cancer cells than treatment using a single agent. Molecular analysis indicated that combination therapy induced significantly higher levels of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in cancer cells. Antibody against TRAIL strongly inhibited cell toxicity caused by the combined treatment. These data suggest that reovirus may augment trastuzumab-induced cytotoxicity in gastric cancer cells.

A phase I trial of single-agent reolysin in patients with relapsed multiple myeloma

PURPOSE

Reolysin, a proprietary isolate of reovirus type III dearing, enters and preferentially induces apoptosis of malignant cells. RAS pathway activation has been associated with more efficient reoviral infectivity and enhanced oncolysis. Reovirus is currently in advanced solid tumor phase I-II trials; no clinical trials have been conducted in patients with hematologic malignancies.

EXPERIMENTAL DESIGN

A phase I trial treated 12 relapsed myeloma patients at two dose levels. Reolysin was infused daily for 5 days every 28 days. Bone marrow specimens were examined by in situ-based hybridization (ISH) for CD138, p38, caspase-3, reoviral RNA, and capsid protein at screening and cycle 1 day 8. Junctional adhesion molecule 1 (JAM-1) and cancer upregulated gene 2 (CUG2) were evaluated in patient samples and multiple myeloma cell lines. Neutralizing anti-reovirus antibody assay was performed weekly during cycle 1.

RESULTS

There were no dose-limiting toxicities, patients reached the 3 × 10(10) TCID50 daily on days 1 to 5 dose level, and grade 3 laboratory toxicities included neutropenia, thrombocytopenia, and hypophosphatemia. ISH demonstrated reoviral genome confined in multiple myeloma cells. Reoviral capsid protein and caspase-3 were rarely identified within reoviral RNA-positive cells. The longest durations of stable disease were 4, 5, and 8 months.

CONCLUSIONS

Treatment with single-agent Reolysin was well tolerated and associated with avid reoviral RNA myeloma cell entry but only minimal intracellular reoviral protein production within multiple myeloma cells. Our data support that in multiple myeloma cells, Reolysin-induced oncolysis requires combination therapy, similar to other cancers.

Tumor Restrictions to Oncolytic Virus

Oncolytic virotherapy has advanced since the days of its conception but therapeutic efficacy in the clinics does not seem to reach the same level as in animal models. One reason is premature oncolytic virus clearance in humans, which is a reasonable assumption considering the immune-stimulating nature of the oncolytic agents. However, several studies are beginning to reveal layers of restriction to oncolytic virotherapy that are present before an adaptive neutralizing immune response. Some of these barriers are present constitutively halting infection before it even begins, whereas others are raised by minute cues triggered by virus infection. Indeed, we and others have noticed that delivering viruses to tumors may not be the biggest obstacle to successful therapy, but instead the physical make-up of the tumor and its capacity to mount antiviral defenses seem to be the most important efficacy determinants. In this review, we summarize the constitutive and innate barriers to oncolytic virotherapy and discuss strategies to overcome them.

Suppression of autophagic genes sensitizes CUG2-overexpressing A549 human lung cancer cells to oncolytic vesicular stomatitis virus-induced apoptosis

We showed in our previous study that cancer upregulated gene (CUG) 2, a novel oncogene, confers resistance to infection of oncolytic vesicular stomatitis virus (VSV) by activating Stat1-mediated signal transduction. Since many studies have reported that autophagy is involved in virus replication, we investigated whether autophagy also plays a role in the antiviral activity in A549 cells overexpressing CUG2 (A549-CUG2). We suppressed Atg5 or Beclin 1 expression using siRNA and examined its effect on the susceptibility of cells to infection by oncolytic VSV. We found that A549-CUG2 cells treated with Atg5 or Beclin 1 siRNA became susceptible to VSV infection, whereas A549-CUG2 cells treated with control siRNA were resistant. This result suggests that autophagy is involved in the antiviral response of A549-CUG2 cells. Further investigation revealed that autophagy impairment enhanced the generation of reactive oxygen species (ROS), which resulted in inactivation of S6 kinase. Under these conditions, the levels of ISG15 transcript and protein decreased, which conferred on A549-CUG2 cell susceptibility to VSV infection. Finally, we found that overloading of H₂O₂ sensitized control A549-CUG2 cells to VSV-induced apoptosis. Taken together, these results indicate that autophagy impairment induces excessive ROS formation, which decreases S6 kinase activity and ISG15 expression, ultimately rendering the A549-CUG2 cells susceptible to VSV infection. We propose that autophagy impairment is a potential strategy for successful VSV virotherapy of CUG2-overexpressing tumors.

Cancer upregulated gene 2, a novel oncogene, confers resistance to oncolytic vesicular stomatitis virus through STAT1-OASL2 signaling

We have recently found a novel oncogene, named cancer upregulated gene 2 (CUG2), which activates Ras and mitogen-activated protein kinases (MAPKs), including ERK, JNK and p38 MAPK. Because activation of these signaling pathways has previously been shown to enhance cancer cell susceptibility to oncolysis by certain viruses, we examined whether vesicular stomatitis virus (VSV) could function as a potential therapeutic agent by efficiently inducing cytolysis in cells transformed by CUG2. Unexpectedly, NIH3T3 cells stably expressing CUG2 (NIH-CUG2) were resistant to VSV because of the activation of signal transducers and activators of transcription 1 (STAT1). The result was supported by evidence showing that suppression of STAT1 with short interference RNA (siRNA) renders cells susceptible to VSV. Furthermore, 2'-5' oligoadenylate synthetase-like (OASL) 2 was the most affected by STAT1 expression level among anti-viral proteins and furthermore suppression of OASL2 mRNA level caused NIH-CUG2 cells to succumb to VSV as seen in NIH-CUG2 cells treated with STAT1 siRNA. In addition, Colon26L5 carcinoma cells stably expressing CUG2 (Colon26L5-CUG2) exhibited resistance to VSV, whereas Colon26L5 stably expressing a control vector yielded to VSV infection. Moreover, Colon26L5-CUG2 cells stably suppressing STAT1 succumbed to VSV infection, resulting in apoptosis. Taken together, we propose that VSV treatment combined with the selective regulation of genes such as STAT1 and OASL2 will improve therapeutic outcomes for CUG2-overexpressing tumors.

Reovirus: a targeted therapeutic--progress and potential

Medical therapy of patients with malignancy requires a paradigm shift through development of new drugs with a good safety record and novel mechanisms of activity. While there is no dearth of such molecules, one particular agent, "reovirus" is promising by its ability to target cancer cells with aberrant signaling pathways. This double-stranded RNA virus has been therapeutically formulated and has rapidly progressed from preclinical validation of anticancer activity to a phase III registration study in platinum refractory metastatic squamous cell carcinoma of the head and neck. During this process, reovirus has shown safety both as a single agent when administered intratumorally and intravenously, as well as in combination therapy, with multiple chemotherapeutics such as gemcitabine, carboplatin/paclitaxel, and docetaxel; and similarly with radiation. The scientific rationale for its development as an anticancer agent stems from the fact that it preferentially replicates in and induces lyses of cells with an activated Kras pathway. As documented in many previous studies, the initial observation of greater tropism in Kras-compromised situation might certainly not be the sole and possibly not even the predominant reason for enhanced virulence. All the same, scientists have emphasized on Kras optimistically due to its high prevalence in various types of cancers. Incidence of Kras mutation has been found to be highest in pancreatic cancer (85%-90%) followed by colorectal (35-45%) and lung (25-30%). Reovirus, in fact has the potential not only as a therapy but also as a tool to unravel the aberrant cellular pathway leading to carcinogenicity.

Reovirus-associated reduction of microRNA-let-7d is related to the increased apoptotic death of cancer cells in clinical samples

We analyzed the in situ molecular correlates of infection from cancer patients treated with reovirus. Melanoma, colorectal, and ovarian cancer samples from such patients showed variable infection of the cancer cells but not the intermingled benign cells. RT in situ PCR showed most cancer cells contained the viral genome with threefold less having productive viral infection as documented by either tubulin or reoviral protein co-expression. Productive infection in the cancer cells was strongly correlated with co-expression of p38 and caspase-3 as well as apoptosis-related death (P<0.001). The cancer cell apoptotic death was due to a marked viral-induced inhibition of microRNA-let-7d that, in turn, upregulated caspase-3 activity. In summary, reovirus shows a striking tropism to cancer cells in clinical samples. A rate-limiting factor of reovirus-induced cancer cell death is productive viral infection that operates via the marked reduction of microRNA-let-7d and concomitant elevated caspase-3 expression.