Targeting Cell Cycle Facilitates E1A-Independent Adenoviral Replication

DNA replication of E1-deleted first-generation adenoviruses (AdV) in cultured cancer cells has been reported repeatedly and it was suggested that certain cellular proteins could functionally compensate for E1A, leading to the expression of the early region 2 (E2)-encoded proteins and subsequently virus replication. Referring to this, the observation was named E1A-like activity. In this study, we investigated different cell cycle inhibitors with respect to their ability to increase viral DNA replication of dl70-3, an E1-deleted adenovirus. Our analyses of this issue revealed that in particular inhibition of cyclin-dependent kinases 4/6 (CDK4/6i) increased E1-independent adenovirus E2-expression and viral DNA replication. Detailed analysis of the E2-expression in dl70-3 infected cells by RT-qPCR showed that the increase in E2-expression originated from the E2-early promoter. Mutations of the two E2F-binding sites in the E2-early promoter (pE2early-LucM) caused a significant reduction in E2-early promoter activity in trans-activation assays. Accordingly, mutations of the E2F-binding sites in the E2-early promoter in a virus named dl70-3/E2Fm completely abolished CDK4/6i induced viral DNA replication. Thus, our data show that E2F-binding sites in the E2-early promoter are crucial for E1A independent adenoviral DNA replication of E1-deleted vectors in cancer cells. IMPORTANCE E1-deleted AdV vectors are considered replication deficient and are important tools for the study of virus biology, gene therapy, and large-scale vaccine development. However, deletion of the E1 genes does not completely abolish viral DNA replication in cancer cells. Here, we report, that the two E2F-binding sites in the adenoviral E2-early promoter contribute substantially to the so-called E1A-like activity in tumor cells. With this finding, on the one hand, the safety profile of viral vaccine vectors can be increased and, on the other hand, the oncolytic property for cancer therapy might be improved through targeted manipulation of the host cell.

The oncolytic adenovirus XVir-N-31 joins forces with CDK4/6 inhibition augmenting innate and adaptive antitumor immunity in Ewing sarcoma

PURPOSE

Ewing sarcoma (EwS) is a highly malignant pediatric tumor characterized by a non-T cell-inflamed immune-evasive phenotype. When relapsed or metastasized, survival is poor, emphasizing the need for novel treatment strategies. Here, we analyze the novel combination approach using the YB-1-driven oncolytic adenovirus XVir-N-31 and CDK4/6 inhibition to augment EwS immunogenicity.

EXPERIMENTAL DESIGN

In vitro, viral toxicity, replication, and immunogenicity were studied in several EwS cell lines. In vivo tumor xenograft models with transient humanization were applied to evaluate tumor control, viral replication, immunogenicity, and dynamics of innate as well as human T cells after treatment with XVir-N-31 combined with CDK4/6 inhibition. Furthermore, immunological features of dendritic cell maturation and T cell-stimulating capacities were assessed.

RESULTS

The combination approach significantly increased viral replication and oncolysis in vitro, induced HLA-I upregulation, and interferon-gamma-induced protein 10 expression and enhanced maturation of monocytic dendritic cells with superior capacities to stimulate tumor antigen-specific T cells. These findings were confirmed in vivo showing tumor-infiltration by (1) monocytes with antigen-presenting capacities and M1 macrophage marker genes, (2) TReg suppression in spite of adenovirus infection (3) superior engraftment and (4) tumor-infiltration by human T cells. Consequently, survival was improved over controls with signs of an abscopal effect after combination treatment.

CONCLUSION

The joint forces of the YB-1-driven oncolytic adenovirus XVir-N-31 and CDK4/6 inhibition induce therapeutically relevant local and systemic antitumor effects. Innate as well as adaptive immunity against EwS is boosted in this preclinical setting, pointing towards high therapeutic potential in the clinic.

Identification of the KIF and MCM protein families as novel targets for combination therapy with CDK4/6 inhibitors in bladder cancer

CDK4/6 inhibitors have proven their potency for the treatment of cancer but only in combination with hormone or targeted therapies. The aim of this study was the identification of molecules that are involved in response mechanisms to CDK4/6 inhibitors and the development of novel combination therapies with corresponding inhibitors in bladder cancer. Genes of response to therapy and genes that confer resistance to the CDK4/6 inhibitor palbociclib were identified by performing an analysis of published literature and own published data using a CRISPR-dCas9 genome wide gain of function screen. Genes that were down-regulated upon treatment were compared with genes that confer resistance when up-regulated. Two of the top 5 genes were validated by quantitative PCR and western blotting upon treatment with palbociclib in the bladder cancer cell lines T24, RT112 and UMUC3. As inhibitors for combination therapy, we used ciprofloxacin, paprotrain, ispinesib and SR31527. Analysis of synergy was done using the "zero interaction potency" model. Cell growth was examined using sulforhodamine B staining. A list of genes that met the requirements for inclusion in the study was generated from 7 publications. Of the 5 most relevant genes, MCM6 and KIFC1 were chosen and their down-regulation upon treatment with palbociclib was confirmed by qPCR and immunoblotting. The combination of inhibitors against both, KIFC1 and MCM6 with PD resulted in a synergistic inhibition of cell growth. We have identified 2 molecular targets whose inhibition has promising potential for effective combination therapies with the CDK4/6 inhibitor palbociclib.

Genome-Wide CRISPR Screening for the Identification of Therapy Resistance-Associated Genes in Urothelial Carcinoma

The application of CRISPR (clustered regularly interspaced short palindromic repeats)-Cas9 technology with pooled guide RNA libraries enables genome-wide screening, which has some advantages over other screening methods using chemical DNA mutagens for inducing genetic changes, RNA interference, or arrayed screens. Here we describe the use of genome-wide knockout and transcriptional activation screening enabling the CRISPR-Cas9 system to discover resistance mechanisms to CDK4/6 inhibition in bladder cancer along with next-generation sequencing (NGS) analysis. We will describe the approach for transcriptional activation in the bladder cancer cell line T24 and provide guidance on critical points during the experimental workflow.

The Oncolytic Adenovirus XVir-N-31, in Combination with the Blockade of the PD-1/PD-L1 Axis, Conveys Abscopal Effects in a Humanized Glioblastoma Mouse Model

Glioblastoma (GBM) is an obligatory lethal brain tumor with a median survival, even with the best standard of care therapy, of less than 20 months. In light of this fact, the evaluation of new GBM treatment approaches such as oncolytic virotherapy (OVT) is urgently needed. Based on our preliminary preclinical data, the YB-1 dependent oncolytic adenovirus (OAV) XVir-N-31 represents a promising therapeutic agent to treat, in particular, therapy resistant GBM. Preclinical studies have shown that XVir-N-31 prolonged the survival of GBM bearing mice. Now using an immunohumanized mouse model, we examined the immunostimulatory effects of XVir-N-31 in comparison to the wildtype adenovirus (Ad-WT). Additionally, we combined OVT with the inhibition of immune checkpoint proteins by using XVir-N-31 in combination with nivolumab, or by using a derivate of XVir-N-31 that expresses a PD-L1 neutralizing antibody. Although in vitro cell killing was higher for Ad-WT, XVir-N-31 induced a much stronger immunogenic cell death that was further elevated by blocking PD-1 or PD-L1. In vivo, an intratumoral injection of XVir-N-31 increased tumor infiltrating lymphocytes (TILs) and NK cells significantly more than Ad-WT not only in the virus-injected tumors, but also in the untreated tumors growing in the contralateral hemisphere. This suggests that for an effective treatment of GBM, immune activating properties by OAVs seem to be of greater importance than their oncolytic capacity. Furthermore, the addition of immune checkpoint inhibition (ICI) to OVT further induced lymphocyte infiltration. Consequently, a significant reduction in contralateral non-virus-injected tumors was only visible if OVT was combined with ICI. This strongly indicates that for an effective eradication of GBM cells that cannot be directly targeted by an intratumoral OV injection, additional ICI therapy is required.

Targeting the Retinoblastoma/E2F repressive complex by CDK4/6 inhibitors amplifies oncolytic potency of an oncolytic adenovirus

CDK4/6 inhibitors (CDK4/6i) and oncolytic viruses are promising therapeutic agents for the treatment of various cancers. As single agents, CDK4/6 inhibitors that are approved for the treatment of breast cancer in combination with endocrine therapy cause G1 cell cycle arrest, whereas adenoviruses induce progression into S-phase in infected cells as an integral part of the their life cycle. Both CDK4/6 inhibitors and adenovirus replication target the Retinoblastoma protein albeit for different purposes. Here we show that in combination CDK4/6 inhibitors potentiate the anti-tumor effect of the oncolytic adenovirus XVir-N-31 in bladder cancer and murine Ewing sarcoma xenograft models. This increase in oncolytic potency correlates with an increase in virus-producing cancer cells, enhanced viral genome replication, particle formation and consequently cancer cell killing. The molecular mechanism that regulates this response is fundamentally based on the reduction of Retinoblastoma protein expression levels by CDK4/6 inhibitors.

Neither CDK4/6 inhibitors nor oncolytic adenoviruses show high efficiency as monotherapy in the treatment of cancer. Authors show here that when combined, CDK4/6 inhibitors deplete Retinoblastoma protein levels, which leads to more efficient virus replication and an increase in oncolytic virus-producing cancer cells and thus to efficient anti-tumor response in mouse xenograft sarcoma models.

The Oncolytic Adenovirus XVir-N-31 as a Novel Therapy in Muscle-Invasive Bladder Cancer

Muscle-invasive bladder cancer represents approximately 25% of diagnosed bladder cancer cases and carries a significant risk of death. Oncolytic viruses are novel antitumor agents with the ability to selectively replicate and lyse tumor cells while sparing healthy tissue. We explored the efficiency of the oncolytic YB-1-selective adenovirus XVir-N-31 in vitro and in an orthotopic mouse model for bladder cancer by intramural injection under ultrasound guidance. We demonstrated that XVir-N-31 replicated in bladder cancer cells and induced a stronger immunogenic cell death than wild-type adenovirus by facilitating enhanced release of HMGB1 and exosomal Hsp70. The intratumoral delivery of XVir-N-31 by ultrasound guidance delayed tumor growth in an immunodeficient model, demonstrating the feasibility of this approach to deliver oncolytic viruses directly into the tumor.

YB-1 dependent oncolytic adenovirus efficiently inhibits tumor growth of glioma cancer stem like cells

Background

The brain cancer stem cell (CSC) model describes a small subset of glioma cells as being responsible for tumor initiation, conferring therapy resistance and tumor recurrence. In brain CSC, the PI3-K/AKT and the RAS/mitogen activated protein kinase (MAPK) pathways are found to be activated. In consequence, the human transcription factor YB-1, knowing to be responsible for the emergence of drug resistance and driving adenoviral replication, is phosphorylated and activated. With this knowledge, YB-1 was established in the past as a biomarker for disease progression and prognosis. This study determines the expression of YB-1 in glioblastoma (GBM) specimen in vivo and in brain CSC lines. In addition, the capacity of Ad-Delo3-RGD, an YB-1 dependent oncolytic adenovirus, to eradicate CSC was evaluated both in vitro and in vivo.

Methods

YB-1 expression was investigated by immunoblot and immuno-histochemistry. In vitro, viral replication as well as the capacity of Ad-Delo3-RGD to replicate in and, in consequence, to kill CSC was determined by real-time PCR and clonogenic dilution assays. In vivo, Ad-Delo3-RGD-mediated tumor growth inhibition was evaluated in an orthotopic mouse GBM model. Safety and specificity of Ad-Delo3-RGD were investigated in immortalized human astrocytes and by siRNA-mediated downregulation of YB-1.

Results

YB-1 is highly expressed in brain CSC lines and in GBM specimen. Efficient viral replication in and virus-mediated lysis of CSC was observed in vitro. Experiments addressing safety aspects of Ad-Delo3-RGD showed that (i) virus production in human astrocytes was significantly reduced compared to wild type adenovirus (Ad-WT) and (ii) knockdown of YB-1 significantly reduced virus replication. Mice harboring othotopic GBM developed from a temozolomide (TMZ)-resistant GBM derived CSC line which was intratumorally injected with Ad-Delo3-RGD survived significantly longer than mice receiving PBS-injections or TMZ treatment.

Conclusion

The results of this study supported YB-1 based virotherapy as an attractive therapeutic strategy for GBM treatment which will be exploited further in multimodal treatment concepts.

Impact of radiation therapy on the oncolytic adenovirus dl520: implications on the treatment of glioblastoma

BACKGROUND AND PURPOSE

Viral oncolytic therapy is emerging as a new form of anticancer therapy and has shown promising preclinical results, especially in combination with radio- and chemotherapy. We recently reported that nuclear localization of the human transcription factor YB-1 in multidrug-resistant cells facilitates E1-independent adenoviral replication. The aim of this study was to evaluate the combined treatment of the conditionally-replicating adenovirus dl520 and radiotherapy in glioma cell lines in vitro and in human tumor xenografts. Furthermore, the dependency of YB-1 on dl520 replication was verified by shRNA directed down regulation of YB-1.

METHODS AND MATERIAL

Localization of YB-1 was determined by immunostaining. Glioma cell lines LN-18, U373 and U87 were infected with dl520. Induction of cytopathic effect (CPE), viral replication, viral yield and viral release were determined after viral infection, radiation therapy and the combination of both treatment modalities. The capacity of treatments alone or combined to induce tumor growth inhibition of subcutaneous U373 tumors was tested also in nude mice.

RESULTS

Quantitative real-time PCR demonstrated that the shRNA-mediated down regulation of YB-1 is leading to a dramatic decrease in adenoviral replication of dl520. Immunostaining analysis showed that the YB-1 protein was predominantly located in the cytoplasm in the perinuclear space and less abundant in the nucleus. After irradiation we found an increase of nuclear YB-1. The addition of radiotherapy increased the oncolytic effect of dl520 with enhanced viral replication, viral yield and viral release. The oncolytic activity of dl520 plus radiation inhibited the growth of subcutaneous U373 tumors in a xenograft mouse model.

CONCLUSIONS

Radiation mediated increase of nuclear YB-1 in glioma cells enhanced the oncolytic potential of adenovirus dl520.

Novel three-pronged strategy to enhance cancer cell killing in glioblastoma cell lines: histone deacetylase inhibitor, chemotherapy, and oncolytic adenovirus dl520

Resistance to radiation and chemotherapy remains an obstacle to the treatment of brain tumors. We have demonstrated that the replication-deficient adenovirus d1520, which lacks the E1A 13S protein, replicates efficiently and exhibits oncolytic potential in multidrug-resistant cells with nuclear localization of the human transcription factor YB-1. However, besides others, key factors regarding oncolytic virotherapy are limited tumor transduction rate and low replication efficiency. The objective of this study was to determine whether the chemotherapeutic agent irinotecan, by enhancing nuclear localization of YB-1, and the histone deacetylase inhibitor trichostatin A, by upregulating coxsackievirus-adenovirus receptor (CAR) expression, could augment replication of and cell lysis by adenovirus dl520 in glioblastomas in vitro. We found that trichostatin A upregulated CAR expression and that irinotecan caused increased nuclear localization of YB-1 in both glioblastoma cell lines. Irinotecan alone, and trichostatin A alone, enhanced replication of and cell lysis by dl520. Importantly, when combining both agents, the replication efficiency (maximum, 27-fold) and induction of cytopathic effect (maximum, 3.8-fold) of dl520 were further augmented significantly. These results support the hypothesis that the enhanced oncolytic effect of dl520, after incubation with chemotherapeutic agents, is mediated by an increased accumulation of YB-1 in the nucleus (due to irinotecan) and by upregulation of CAR (due to trichostatin A). Thus, therapy combining virotherapy, chemotherapy, and histone deacetylase inhibitor treatment is a novel approach to enhance the oncolytic efficacy of dl520.

Inhibition of the multidrug-resistant phenotype by targeting YB-1 with a conditionally oncolytic adenovirus: implications for combinatorial treatment regimen with chemotherapeutic agents

Bearing in mind the limited success of available treatment modalities for the therapy of multidrug-resistant tumor cells, alternative and complementary strategies need to be developed. It is known that the transcriptional activation of genes, such as MDR1 and MRP1, which play a major role in the development of a multidrug-resistant phenotype in tumor cells, involves the Y-box protein YB-1. Thus, YB-1 is a promising target for new therapeutic approaches to defeat multidrug resistance. In addition, it has been reported previously that YB-1 is an important factor in adenoviral replication because it activates transcription from the adenoviral E2-late promoter. Here, we report that an oncolytic adenovirus, named Xvir03, expressing the viral proteins E1B55k and E4orf6, leads to nuclear translocation of YB-1 and in consequence to viral replication and cell lysis in vitro and in vivo. Moreover, we show that Xvir03 down-regulates the expression of MDR1 and MRP1, indicating that recruiting YB-1 to the adenoviral E2-late promoter for viral replication is responsible for this effect. Thus, nuclear translocation of YB-1 by Xvir03 leads to resensitization of tumor cells to cytotoxic drugs. These data reveal a link between chemotherapy and virotherapy based on the cellular transcription factor YB-1 and provide the basis for formulating a model for a novel combined therapy regimen named Mutually Synergistic Therapy.

Characterization of the recombinant adenovirus vector AdYB-1: implications for oncolytic vector development

Conditionally replicating adenoviruses are a promising new modality for the treatment of cancer. However, early clinical trials demonstrate that the efficacy of current vectors is limited. Interestingly, DNA replication and production of viral particles do not always correlate with virus-mediated cell lysis and virus release depending on the vector utilized for infection. However, we have previously reported that nuclear accumulation of the human transcription factor YB-1 by regulating the adenoviral E2 late promoter facilitates viral DNA replication of E1-deleted adenovirus vectors which are widely used for cancer gene therapy. Here we report the promotion of virus-mediated cell killing as a new function of the human transcription factor YB-1. In contrast to the E1A-deleted vector dl312 the first-generation adenovirus vector AdYB-1, which overexpresses YB-1 under cytomegalovirus promoter control, led to necrosis-like cell death, virus production, and viral release after infection of A549 and U2OS tumor cell lines. Our data suggest that the integration of YB-1 in oncolytic adenoviruses is a promising strategy for developing oncolytic vectors with enhanced potency against different malignancies.

Multidrug-resistant cancer cells facilitate E1-independent adenoviral replication: impact for cancer gene therapy

Resistance to chemotherapy is responsible for a failure of current treatment regimens in cancer patients. We have reported previously that the Y-box protein YB-1 regulates expression of the P-glycoprotein gene mdr1, which plays a major role in the development of a multidrug resistant-tumor phenotype. YB-1 predicts drug resistance and patient outcome in breast cancer. Thus, YB-1 is a promising target for new therapeutic approaches to defeat multidrug resistance. In drug-resistant cancer cells and in adenovirus-infected cells YB-1 is found in the nucleus. Nuclear accumulation of YB-1 in adenovirus-infected cells is a function of the E1 region, and we have shown that YB-1 facilitates adenovirus replication. Here we report that E1A-deleted or mutant adenovirus vectors, such as Ad312 and Ad520, replicate efficiently in multidrug-resistant (MDR) cancer cells and induce an adenovirus cytopathic effect resulting in host cell lysis. Thus, replication-defective adenoviruses are a previously unrecognized vector system for a selective elimination of MDR cancer cells. Our work forms the basis for the development of novel oncolytic adenovirus vectors for the treatment of MDR malignant diseases in the clinical setting.

YB-1 relocates to the nucleus in adenovirus-infected cells and facilitates viral replication by inducing E2 gene expression through the E2 late promoter

The adenovirus early proteins E1A and E1B-55kDa are key regulators of viral DNA replication, and it was thought that targeting of p53 by E1B-55kDa is essential for this process. Here we have identified a previously unrecognized function of E1B for adenovirus replication. We found that E1B-55kDa is involved in targeting the transcription factor YB-1 to the nuclei of adenovirus type 5-infected cells where it is associated with viral inclusion bodies believed to be sites of viral transcription and replication. We show that YB-1 facilitates E2 gene expression through the E2 late promoter thus controlling E2 gene activity at later stages of infection. The role of YB-1 for adenovirus replication was demonstrated with an E1-minus adenovirus vector containing a YB-1 transgene. In infected cells, AdYB-1 efficiently replicated and produced infectious progeny particles. Thus, adenovirus E1B-55kDa protein and the host cell factor YB-1 act jointly to facilitate adenovirus replication in the late phase of infection.

Identification of differentially expressed genes in human melanoma cells with acquired resistance to various antineoplastic drugs

Malignant melanoma displays strong resistance against various antineoplastic drugs. The mechanisms conferring this intrinsic resistance are unclear. To better understand the molecular events associated with drug resistance in melanoma, a panel of human melanoma cell variants exhibiting low and high levels of resistance to 4 commonly used drugs in melanoma treatment, i.e., vindesine, etoposide, fotemustine and cisplatin, was characterized by differential display reverse transcription-polymerase chain reaction (DDRT-PCR). Of 269 mRNA fragments found to be altered in expression level by DDRT-PCR, a total of 11 cDNA clones was characterized after confirmation of a differential expression pattern by Northern blot analyses. These clones include 3 genes (DSM-1, DSM-3 and DSM-5) of known function, 4 previously sequenced genes (DSM-2, DSM-4, DSM-6 and DSM-7) of uncharacterized function and 4 novel genes (DSM-8-DSM-11) without match in GenBank. All of these genes exhibited altered mRNA expression in high level etoposide-resistant cells, whereby 7 genes (DSM-1-DSM-6 and DSM-8) were found to be decreased in the transcription rate in these etoposide-resistant cells. The mRNA synthesis of the remaining genes (DSM-7 and DSM-9-DSM11) was enhanced in high level etoposide-resistant melanoma cells. The expression of 5 (DSM-5 and DSM-7-DSM-10) of the cloned cDNA encoding mRNAs was modulated in various independently established drug-resistant melanoma cells, indicating to be associated with drug resistance. Further characterization of these genes may yield inside into the biology and development of drug resistance in malignant melanoma.

Characterization of a MAb to ovarian cancer and its possible diagnostic application

We report the distribution pattern of the target antigen of an IgG1 monoclonal antibody, Ki-OC III raised in BALB/C mice against solubilised ovarian adenocarcinoma, in normal tissue and in a collection of human tumour types. Special reference was made to benign and malignant ovarian tumours. The reactive antigen protein purified to homogeneity for a planned amino acid analysis showed three bands between 37-40 kDa. Immunohistochemical analysis revealed a specificity of 98% and a sensitivity of 77%. The tracer kinetics of the radiolabelled antibody were tested on a human ovarian carcinoma cell line in athymic mice. The results were compared to cell lines derived from breast and stomach carcinomas as well as to a human glioblastoma cell line. The results show the preferential uptake by ovarian cancer cells followed by breast cancer cell lines. In animal models, scintigraphic monitoring and direct measurement of the radio-labelled monoclonal antibody showed a preferential accumulation in tumours, in addition to high level signals in the liver, kidney, spleen and heart which were related to degradation, excretion and high circulation. The Ki-OC III reactive antigen could be a potential candidate for immunomonitoring of ovarian and possibly also of breast cancer, for in vivo tumour imaging as well as for histopathologic examinations.