SARS-CoV-2 and oncolytic EV-D68-encoded proteases differentially regulate pyroptosis.

Pyroptosis, a pro-inflammatory programmed cell death, has been implicated in the pathogenesis of coronavirus disease 2019 and other viral diseases. Gasdermin family proteins (GSDMs), including GSDMD and GSDME, are key regulators of pyroptotic cell death. However, the mechanisms by which virus infection modulates pyroptosis remain unclear. Here, we employed a mCherry-GSDMD fluorescent reporter assay to screen for viral proteins that impede the localization and function of GSDMD in living cells. Our data indicated that the main protease NSP5 of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) blocked GSDMD-mediated pyroptosis via cleaving residues Q29 and Q193 of GSDMD. While another SARS-CoV-2 protease, NSP3, cleaved GSDME at residue G370 but activated GSDME-mediated pyroptosis. Interestingly, respiratory enterovirus EV-D68-encoded proteases 3C and 2A also exhibit similar differential regulation on the functions of GSDMs by inactivating GSDMD but initiating GSDME-mediated pyroptosis. EV-D68 infection exerted oncolytic effects on human cancer cells by inducing pyroptotic cell death. Our findings provide insights into how respiratory viruses manipulate host cell pyroptosis and suggest potential targets for antiviral therapy as well as cancer treatment.IMPORTANCEPyroptosis plays a crucial role in the pathogenesis of coronavirus disease 2019, and comprehending its function may facilitate the development of novel therapeutic strategies. This study aims to explore how viral-encoded proteases modulate pyroptosis. We investigated the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and respiratory enterovirus D68 (EV-D68) proteases on host cell pyroptosis. We found that SARS-CoV-2-encoded proteases NSP5 and NSP3 inactivate gasdermin D (GSDMD) but initiate gasdermin E (GSDME)-mediated pyroptosis, respectively. We also discovered that another respiratory virus EV-D68 encodes two distinct proteases 2A and 3C that selectively trigger GSDME-mediated pyroptosis while suppressing the function of GSDMD. Based on these findings, we further noted that EV-D68 infection triggers pyroptosis and produces oncolytic effects in human carcinoma cells. Our study provides new insights into the molecular mechanisms underlying virus-modulated pyroptosis and identifies potential targets for the development of antiviral and cancer therapeutics.

Assessing and Overcoming Resistance Phenomena against a Genetically Modified Vaccinia Virus in Selected Cancer Cell Lines.

Genetically modified vaccinia viruses (VACVs) have been shown to possess profound oncolytic capabilities. However, tumor cell resistance to VACVs may endanger broad clinical success. Using cell mass assays, viral replication studies, and fluorescence microscopy, we investigated primary resistance phenomena of cell lines of the NCI-60 tumor cell panel to GLV-1h94, a derivative of the Lister strain of VACV, which encodes the enzyme super cytosine deaminase (SCD) that converts the prodrug 5-fluorocytosine (5-FC) into the chemotherapeutic compound 5-fluorouracil (5-FU). After treatment with GLV-1h94 alone, only half of the cell lines were defined as highly susceptible to GLV-1h94-induced oncolysis. When adding 5-FC, 85% of the cell lines became highly susceptible to combinatorial treatment; none of the tested tumor cell lines exhibited a "high-grade resistance" pattern. Detailed investigation of the SCD prodrug system suggested that the cytotoxic effect of converted 5-FU is directed either against the cells or against the virus particles, depending on the balance between cell line-specific susceptibility to GLV-1h94-induced oncolysis and 5-FU sensitivity. The data provided by this work underline that cellular resistance against VACV-based virotherapy can be overcome by virus-encoded prodrug systems. Phase I/II clinical trials are recommended to further elucidate the enormous potential of this combination therapy.

Actin-resistant DNAse I Expression From Oncolytic Adenovirus Enadenotucirev Enhances Its Intratumoral Spread and Reduces Tumor Growth.

Spread of oncolytic viruses through tumor tissue is essential to effective virotherapy. Interstitial matrix is thought to be a significant barrier to virus particle convection between "islands" of tumor cells. One way to address this is to encode matrix-degrading enzymes within oncolytic viruses, for secretion from infected cells. To test the hypothesis that extracellular DNA provides an important barrier, we assessed the ability of DNase to promote virus spread. Nonreplicating Ad5 vectors expressing actin-resistant DNase (aDNAse I), proteinase K (PK), hyaluronidase (rhPH20), and chondroitinase ABC (CABC) were injected into established DLD human colorectal adenocarcinoma xenografts, transcomplemented with a replicating Ad5 virus. Each enzyme improved oncolysis by the replicating adenovirus, with no evidence of tumor cells being shed into the bloodstream. aDNAse I and rhPH20 hyaluronidase were then cloned into conditionally-replicating group B adenovirus, Enadenotucirev (EnAd). EnAd encoding each enzyme showed significantly better antitumor efficacy than the parental virus, with the aDNAse I-expressing virus showing improved spread. Both DNase and hyaluronidase activity was still measurable 32 days postinfection. This is the first time that extracellular DNA has been implicated as a barrier for interstitial virus spread, and suggests that oncolytic viruses expressing aDNAse I may be promising candidates for clinical translation.

Synergistic antitumor effect of adenovirus armed with Drosophila melanogaster deoxyribonucleoside kinase and nucleoside analogs for human breast carcinoma in vitro and in vivo.

BACKGROUND: Suicide gene therapy in cancer can selectively kill tumors without damaging normal tissues. Drosophila melanogaster multisubstrate deoxyribonucleoside kinase (Dm-dNK), an original suicide kinase, makes use of the carcinomatous suicide gene therapy for broader substrate specificity and a higher catalytic rate. METHODS: To enhance the anti-tumor efficacy of Dm-dNK and maintain its substrate specificity and safety control in the meantime, the conditionally replicative gene-viral system, ZD55-dNK (which contains the selective replication adenovirus, ZD55, encoded with Dm-dNK), was investigated in pushing a deeper development of this strategy. Selective replication, cell killing efficacy, and cytotoxicity, in combination with chemotherapy, were applied to two breast cell lines (MDA231 and MCF7 cells), two normal cell lines (WI38 and MRC5 cells), and the MCF7 xenograft model in vivo. RESULTS: The preclinical study showed that ZD55-dNK, combined with 2',2'-difluorodeoxycytidine (DFDC), synergistically inhibited adenovirus replication in vitro but maintained specifically cancer cell killing efficacy. ZD55-dNK also greatly improved the antineoplastic effect in vitro and in breast cancer xenograft in vivo. CONCLUSION: The concomitant use of ZD55-dNK and DFDC is possibly a novel and promising approach to breast cancer treatment, and further investigation on the safe control of excessive virus replication and the efficacy of this approach in humans is warranted.

Replicating retroviral vectors for oncolytic virotherapy of experimental hepatocellular carcinoma.

Gene therapy mediated by murine leukemia virus (MLV)-based replicating retrovirus vector (RRV) was previously proven to be highly effective in tumor cell killing, resulting in significant suppression of tumor growth in vivo. Recently, we developed a different form of RRV which is derived from another retrovirus, gibbon ape leukemia virus (GALV), as a cancer therapeutic agent. We compared the gene delivery efficiency and antitumor effects in the two types of RRV in experimental hepatocellular carcinoma (HCC). Our results show that both RRVs can efficiently spread throughout entire HCC cell populations in vitro and achieve high transduction efficiency in HCC xenografts in vivo, while GALV RRV, in general, exhibited more rapid replication kinetics in the tumors. In vitro, substantial HCC cell killing was achieved even when initially only 1% of the HCC cells were producing RRVs that express the yeast cytosine deaminase suicide gene, indicating that the high efficiency of gene transfer by replicative spread of RRVs greatly increased suicide gene toxicity. In vivo, GALV RRV-mediated suicide gene therapy efficiently suppressed HCC tumor growth and no detectable RRV signals were observed in extratumoral tissues, showing promise in using GALV RRV as a cancer therapeutic agent.

Enhanced cytotoxicity with a novel system combining the paclitaxel-2'-ethylcarbonate prodrug and an HSV amplicon with an attenuated replication-competent virus, HF10 as a helper virus.

We previously demonstrated that HF10, which is a natural, non-engineered HSV-1, has potent oncolytic activity in the treatment of solid malignant tumors in vitro and in vivo [H. Takakuwa, F. Goshima, N. Nozawa, T. Yoshikawa, H. Kimata, A. Nakao, et al., Oncolytic viral therapy using a spontaneously generated herpes simplex virus type 1 variant for disseminated peritoneal tumor in immunocompetent mice, Arch. Virol. 148 (2003) 813-825; S. Kohno, C. Lou, F. Goshima, Y. Nishiyama, T. Sata, Y. Ono, Herpes simplex virus type 1 mutant HF10 oncolytic viral therapy for bladder cancer, Urology 66 (2005) 1116-1121; D. Watanabe, F. Goshima, I. Mori, Y. Tamada, Y. Matsumoto, Y. Nishiyama, Oncolytic virotherapy for malignant melanoma with herpes simplex virus type 1 mutant HF10, J. Dermatol. Sci. 50 (2008) 185-196; A. Nawa, C. Luo, L. Zhang, Y. Ushijima, D. Ishida, M. Kamakura, et al., Non-engineered, naturally oncolytic herpes simplex virus HSV1 HF10: applications for cancer gene therapy, Curr. Gene. Ther. 8 (2008) 208-221]. Previous reports have also shown that a combination of HF10 and paclitaxel (TAX) was more efficacious than either regimen alone for some types of malignant tumors [S. Shimoyama, F. Goshima, O. Teshigahara, H. Kasuya, Y. Kodera, A. Nakao, et al., Enhanced efficacy of herpes simplex virus mutant HF10 combined with paclitaxel in peritoneal cancer dissemination models, Hepatogastroenterology 54 (2007) 1038-1042]. In this study, we investigated the efficacy of gene-directed enzyme prodrug therapy (GDEPT) using a novel system that combines the paclitaxel-2'-ethylcarbonate prodrug (TAX-2'-Et) and an HSV amplicon expressing rabbit-carboxylesterase (CES) with HF10 as a helper virus. This GDEPT system aims to produce high level of CES at the tumor site, resulting in efficient local conversion of the TAX-2'-Et prodrug into the active drug TAX [A. Nawa, T. Tanino, C. Lou, M. Iwaki, H. Kajiyama, K. Shibata, et al., Gene directed enzyme prodrug therapy for ovarian cancer: could GDEPT become a promising treatment against ovarian cancer?, Anti-Cancer Agents Med Chem 8 (2008) 232-239]. We demonstrated that the green fluorescent protein (GFP) gene, as a trace maker, was more efficiently introduced by the HSV amplicon compared to the expression vector, pHGCX, and that the HSV amplicon system expressed an active CES enzyme that could convert TAX-2'-Et to TAX in Cos7 cells. Furthermore, although the cytotoxicity of this amplicon system was not enhanced in virus-sensitive tumor cells, it was significantly enhanced in low virus-sensitive tumor cells in the presence of the prodrug in a concentration-dependent manner, compared to the control virus alone (p<0.05). These results indicate that the addition of a prodrug converting enzyme may be a feasible approach to further enhance the efficacy of HF10 as a cancer therapeutics in low HF10-sensitive malignancies.

The nitroreductase prodrug SN 28343 enhances the potency of systemically administered armed oncolytic adenovirus ONYX-411(NTR).

Conditionally replicating adenoviruses (CRAd) 'armed' with prodrug-activating genes have the potential to augment the efficacy of virotherapy. An Escherichia coli nitroreductase (NTR) gene (nfsB) was introduced into the E3B region of the systemically active CRAd ONYX-411, to produce ONYX-411(NTR), which had single agent oncolytic activity equivalent to unarmed virus in vitro and in vivo. A fluorogenic probe (SN 29884) developed to monitor NTR expression revealed robust, durable NTR expression in ONYX-411(NTR) infected neoplastic but not primary human cell lines. NTR expression occurred >24 h post-infection in parallel with fiber and was sensitive to ara-C indicating transcriptional linkage to viral replication. A novel NTR prodrug, the 3,5-dinitrobenzamide-2-bromomustard SN 27686, was shown to be more dose potent and selective than CB 1954 and provided a superior bystander effect in 3D multicellular layer cultures. Its water-soluble phosphate ester SN 28343 was substantially more active than CB 1954 against xenografts containing a minority of stable NTR-expressing cells. A single intravenous dose of ONYX-411(NTR) (10(8) PFU) to nude mice bearing large H1299 xenografts (>350 mm(3)) resulted in tumor-specific NTR expression which increased over time. Despite extensive viral spread by day 14, this conservative virus dose and schedule was unable to control such well-established tumors. However, subsequent administration of SN 28343 resulted in the majority of mice (62.5%) being tumor-free on day 120.

Modulation of telomerase promoter tumor selectivity in the context of oncolytic adenoviruses.

The telomerase RNA (hTR) and reverse transcriptase (hTERT) promoters are active in most cancer cells, but not in normal cells, and are useful for transcriptional targeting in gene therapy models. Telomerase-specific conditionally replicating adenoviruses (CRAd) are attractive vectors because they should selectively lyse tumor cells. Here, we compare CRAds, in which either the hTR or hTERT promoter controls expression of the adenovirus E1A gene. In replication-defective reporter adenoviruses, the hTR promoter was up to 57-fold stronger in cancer cells than normal cells and up to 49-fold stronger than hTERT. In normal cells, hTERT promoter activity was essentially absent. Doses of telomerase-specific CRAds between 1.8 and 28 infectious units per cell efficiently killed cancer cells, but normal cells required higher doses. However, CRAd DNA replication and E1A expression were detected in both cancer and normal cells. Overall, tumor specificity of the CRAds was limited compared with nonreplicating vectors. Surprisingly, both CRAds expressed similar E1A levels and functional behavior, despite known differentials between hTR and hTERT promoter activities, suggesting that the promoters are deregulated. Rapid amplification of cDNA ends analysis of hTR-/hTERT-E1A transcripts ruled out cryptic transcription from the vector backbone. Blocking E1A translation partially restored the hTR-/hTERT-E1A mRNA differential, evidencing feedback regulation by E1A.