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Cowpox Virus: A New and Armed Oncolytic Poxvirus

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Cowpox Virus: A New and Armed Oncolytic Poxvirus

Marine Ricordel et al. Mol Ther Oncolytics.

Abstract

Oncolytic virus therapy has recently been recognized as a promising new therapeutic approach for cancer treatment. In this study, we are proposing for the first time to evaluate the in vitro and in vivo oncolytic capacities of the Cowpox virus (CPXV). To improve the tumor selectivity and oncolytic activity, we developed a thymidine kinase (TK)-deleted CPXV expressing the suicide gene FCU1, which converts the non-toxic prodrug 5-fluorocytosine (5-FC) into cytotoxic 5-fluorouracil (5-FU) and 5-fluorouridine-5'-monophosphate (5-FUMP). This TK-deleted virus replicated efficiently in human tumor cell lines; however, it was notably attenuated in normal primary cells, thus displaying a good therapeutic index. Furthermore, this new recombinant poxvirus rendered cells sensitive to 5-FC. In vivo, after systemic injection in mice, the TK-deleted variant caused significantly less mortality than the wild-type strain. A biodistribution study demonstrated high tumor selectivity and low accumulation in normal tissues. In human xenograft models of solid tumors, the recombinant CPXV also displayed high replication, inducing relevant tumor growth inhibition. This anti-tumor effect was improved by 5-FC co-administration. These results demonstrated that CPXV is a promising oncolytic vector capable of expressing functional therapeutic transgenes.

Keywords: armed; cowpox; oncolytic.

Figures

Figure 1
Figure 1
Generation of CPX Expressing the GFP::FCU1 Fusion Gene and Evaluation of the GFP-FCU1 Protein Expression (A) Schematic representation of viruses used in this study. CPXtk/gfp::fcu1 contains a deletion of TK gene replaced by a fusion gene between the eGFP and FCU1 genes. The GFP::FCU1 fusion gene is driven by the synthetic p11k7.5 early late promoter. (B) Western blot detection of the GFP-FCU1 protein by anti-FCU1 monoclonal antibody. Lane 1 (left to the right), mock-infected Lovo cells; lane 2, LoVo cells infected with CPXwt; lane 3, LoVo cells infected with CPXtk/gfp::fcu1. Molecular weight standards are shown in kDa on the left. The presence of GFP-FCU 1 protein (Mr 72,000) is indicated (arrow). (C) Conversion of 5-FC to 5-FU and release of 5-FU in the cell culture supernatant. LoVo cells were infected with the indicated vector at a MOI of 0.001 and then incubated with 0.1 mM 5-FC from day 2 to day 5 post-infection. The relative concentration of 5-FC and 5-FU in the culture supernatant was measured by HPLC. The results are expressed as the percentage of 5-FU released relative to the total amount of 5-FC+5-FU. Each data point represents the mean of triplicate determinations ± SD.
Figure 2
Figure 2
Replication and Oncolytic Activity of CPXtk/gfp::fcu1 (A) Amplification factor of CPXtk/gfp::fcu1 in a panel of human tumoral cells infected with 300 pfu and collected 72 hr post-infection. (B) Tumor cell viability by Trypan blue exclusion: 3 × 105 cells/well were infected with CPXtk/gfp::fcu1 at a MOI ranging from 0.0001 to 0.1. 5 days after, cell viability was determined by ViCell cell counter automate based on Trypan blue exclusion method. Each data point represents the mean of triplicate determinations ± SD. (C) 3D Phenion FT skin models were infected with 8 × 104 pfu of CPXwt and CPXtk/gfp::fcu1 by scarification. 7 days post infection, 3D skin and supernatant were collected and sonicated, and viral titers were determined by plaque assay. Results are expressed as viral fold increased (corresponding to output/input ratio). (D) Infection and replication of CPX TK-deleted virus on hPBMCs. Fresh hPBMCs were infected by CPXtk/gfp::fcu1 at different MOI. 16 hr post infection, eGFP level was measured on flow cytometry. 4 days post infection, cells and supernatants were harvested and sonicated. Viral titers were determined by plaque assay on Vero cells. Results are expressed as viral fold increased (corresponding to output/input ratio).
Figure 3
Figure 3
In Vitro Sensitivities of Infected Human Tumor Cells to 5-FC Combination of oncolytic and prodrug activation cytotoxicity. (A and B) LoVo (A) and A549 (B) human tumor cells were infected with the CPXwt and CPXtk/gfp::fcu1 at a MOI of 0.01 on LoVo cells and at a MOI of 0.000001 on A549 cells. After 48 hr, cells were grown in the presence of increasing concentrations of 5-FC. Cell survival was determined 3 days later, as described in the Materials and Methods section. Cell viability results are expressed as the percentage of viable cells relative to untreated/non-infected cells. Values are represented as mean ± SD of three individual determinations.
Figure 4
Figure 4
Virulence Studies and Biodistribution of CPXV in Mice (A)Virulence studies in CPXV-infected mice. Immunocompetent BalB/c mice were i.v. injected with CPXwt or CPXtk/gfp::fcu1 at concentration ranging from 1 × 105 to 1 × 107 pfu/mouse (n = 10 per group). The highest dose of deleted virus is represented. Animals were individually weighted and monitored for signs of disease for more than 60 days. Mice were euthanized when their initial weight loss reached 20% of their initial weight. Survival data are presented as Kaplan-Meier plots. p values are obtained by statistical analysis (log-rank). (B) Organ distribution of CPXVtk-/gfp::fcu1 in mice. A biodistribution experiment was performed in Swiss Nude mice bearing subcutaneous glioblastoma tumor cells. Mice were injected i.v. with CPXtk/gfp::fcu1 at 1 × 106 pfu . At days 2 and 7, 3 mice were euthanized, and tumors and organs were collected and homogenized. Viral titers were determined by plaque assay on Vero cells. Results are expressed in pfu/mg of tissue ± SEM. (C) Viral immunostaining was performed after fixation in formaldehyde (FA) as described in Materials and Methods. Cellular DNA was stained in blue (C1, C2, and C3) with DAPI, gfp::fcu1 protein was stained in red (C1 and C3), and virus was stained in green (C2 and C3). The merged picture is presented in C3.
Figure 5
Figure 5
In Vivo CPXV Anti-tumor Activity in Glioblastoma and Colorectal Xenograft Models (A and B) Immunodeficient Swiss nude mice were implanted subcutaneously with U-87 MG glioblastoma cells (A) or LoVo colorectal carcinoma cells (B). Mice (n = 10/group) were injected IT with CPXtk/gfp::fcu1 (1 × 106 pfu) or CPXwt 3 weeks after tumor cell transplantation. 5 days after viral injection, 5-FC was administered to mice by gavage at a dose of 200 mg/kg/day. Mice were monitored until sacrifice based on high tumor volume. The vertical arrow indicates the time of virus injection and the horizontal arrow indicates the duration of 5-FC treatment. Stars represent p value < 0.05 compared to control groups (buffer and buffer + 5-FC). Results are expressed in mean tumor volume ± SEM.

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References

    1. Lichty B.D., Breitbach C.J., Stojdl D.F., Bell J.C. Going viral with cancer immunotherapy. Nat. Rev. Cancer. 2014;14:559–567. - PubMed
    1. Pol J., Buqué A., Aranda F., Bloy N., Cremer I., Eggermont A., Erbs P., Fucikova J., Galon J., Limacher J.M. Trial watch-oncolytic viruses and cancer therapy. OncoImmunology. 2015;5:e1117740. - PMC - PubMed
    1. Andtbacka R.H.I., Kaufman H.L., Collichio F., Amatruda T., Senzer N., Chesney J., Delman K.A., Spitler L.E., Puzanov I., Agarwala S.S. Talimogene laherparepvec improves durable response rate in patients with advanced melanoma. J. Clin. Oncol. 2015;33:2780–2788. - PubMed
    1. Mell L.K., Yu Y.A., Brumund K.T., Advani S.J., Onyeama S., Daniels G.A., Weisman R.A., Martin P., Szalay A.A. Phase I trial of attenuated vaccinia virus (GL-ONC1) delivered intravenously with concurrent cisplatin and radiation therapy in patients with locoregionally advanced head-and-neck squamous cell carcinoma. Int. J. Radiat. Oncol. 2014;88:477–478.
    1. Mastrangelo M.J., Maguire H.C., Jr., Eisenlohr L.C., Laughlin C.E., Monken C.E., McCue P.A., Kovatich A.J., Lattime E.C. Intratumoral recombinant GM-CSF-encoding virus as gene therapy in patients with cutaneous melanoma. Cancer Gene Ther. 1999;6:409–422. - PubMed

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