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80 Cards in this Set
- Front
- Back
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What are oncolytic viruses?
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Viruses used to treat cancers due to their ability to specifically infect cancer cells while leaving normal tissues largely unaffected
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What do oncolytic viruses exploit?
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Genetic abnormalities of cancer cells
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What are some genetic abnormalities that OV take advnatage of?
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Mutations in cell growth/apoptosis/antiviral capacities
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When were oncolytic viruses first observed?
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When it was noticed that canacer patients who were contracting some infectious disease were occasionally getting a brief remission period
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What are Group I Oncolytic viruses?
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Replication-defective viruses - they are used as delivery vehicles
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What are group II oncolytic viruses?
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Replication-competent: these viruses are used for their oncolytic properties, but can ALSO be used as delivery vehicles
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What are some naturally occuring oncolytic viruses?
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Reovirus, VSV
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What can improve potency of oncolytic viruses?
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Addition of therapeutic agents in combination!q
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What are some viruses that you need to delete genes to use as oncolytic viruses?
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Vaccinia, HSV, adenovirus
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Why would you make deletions in the oncolytic virus?
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To make them specific to cancer cells or to make them safer
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What is the principle that OV can kill cancer cells but not normal cells?
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The oncolytic virus infects cancer cells and will be able to replicate and kill the cells
However, in normal cells, the cell often blocks its replication or entry and is able to stop proliferation by inducing an antiviral state |
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What is important about OV ability to lyse infected cells?
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-Kills cell
-Diffuses more oncolytic viruses to neighbouring cells |
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What does the presence of the virus do?
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Causes massive inflammation - release of cytokines and infiltration of WBCs which infiltrate the tumor and cause vascular shut down -> hypoxia of tumor
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Which cells play a role in destroying tumors?
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Innate and adaptive cells (NK, Tc, macrophages)
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What are some good characteristics for an oncolytic virus to have?
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-Discriminate between normal vs. cancer cell
-Effective to wide variety of cancer cells -Sensititve to host antiviral response -Non-pathogenic in humans -Minimal side effects -Lack of neutralizing Abs in host -Genetically stable -Can be grown to high titers -Can be genetically manipulated to express the target gene |
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What is VSV?
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Vesicular Stomatitis Virus
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What type of genome does VSV have?
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ssRNA negative strand virus
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What are the 5 genes that VSV encodes?
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G-Glycoprotrein
L and P polymerase proteins M matrix protein N nucleocapsid protein |
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What is the tropism of VSV?
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Almost every cell -G protein is very potent
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What is the natural host of VSV?
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Cattle and insects
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What is beneficial about VSV being an RNA virus?
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Cytoplasmic replication - no integration steps
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What is beneficial about VSV having a small genome?
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Genetically stable (small genome)
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Which response is defective in most cancer cells, that normally VSV is sensitive to?
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The IFN antiviral response
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How does VSV partially blockl the IFN response?
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Its M protein acts to block mRNA nuclear export of the cell
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How is the ability of VSV to partially block the IFN response circumvented?
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Use VSV-AV1 - single mutation of M protein such that it cannot block the IFN mRNA transport
Use VSV-delta51 - deletionin M protein |
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Which VSV mutants are more potent inducers of the IFN response?
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M mutants
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What tumor types does VSV target?
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Many (over 60!) incl:
-Breast -Ovarian -Prostate -Melanoma -Colon -Lung |
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What are recombinant viruses?
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Viruses incorporated with genes that make them more potent, more effective at being oncolytic
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What does engineering recombinant OV allow?
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To combine their oncolytic powers to kill cells with their use as a cancer-specific delivery vehicle
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What would you have to co-transfect if you had a recombinant plasmid (made of DNA)?
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A cytoplasmic polyermase, eg. T7 cytoplasmic polymerase
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What are some advantages to using recombinant OV?
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-Allow tracking of th virus
-Improve effectiveness by combining with radiotherapy (virus expressing enzyme that concentrates radioisotope at the tumor site) -Allow recruitment of immune cells -Enzyme that allows increased cancer cell killing -Improve cancer specificity (eg. essential viral gene under control of cancer-specific promoter) |
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What is "suicide gene therapy"?
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Insert an enzyme that converts non-toxic compounds to toxic - this is local to the tumor since the OV only replicates specifically in cancer cells!
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What is an example of suicide gene therapy?
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A VSV that encodes for CD:UPRT
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What is CD:UPRT?
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Cytidine deaminase
Uracil phosphoribosyltransferase |
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What does CD do to 5FC?
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It conversts the non-toxic compound into a toxic one - 5FU- which is further degraded by mammamlian anezymes and inhibits DNA synthesis and incorporates into RNA
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Why is it good to add genes to improve anti-cancer properties?
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There is a limit to how much VSV can replicate in the host!
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What is NIS?
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Iodide symporter - if used in combionation with radiactive idodie - it will mediate iodid uptake at the tumor sites
-Allows visualization as well as being anti-cancerous |
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What is Reovirus?
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Respiratory enteric orphan virus
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What type of virus is Reovirus?
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Segmented dsRNA virus w/ capsid
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What is the natural host of Reovirus?
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Humans
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Is reovirus pathogenic to humans?
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Non-pathogenic, typically no symptoms from infection
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How is Reovirus selective for cancer cells?
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Based on the Ras-pathway whichis mutated in cancer cells
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What are tumor cells that are overactive in Ras defective in?
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The ability to activate the antiviral response - activated Ras blocks the phosphorylation of PKR -rendering it inactive and preventing it from performing its antiviral function
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What does PKR normally do when active?
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Sequeters a transcriptonal activator - blocking the transcription of viral transcripts
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Which family does Vaccinia virus belong to?
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Poxviridae
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What type of genome does Vaccinia have?
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Large (190kbp) ds DNA - enveloped virus
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Where does replication occur?
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Cytoplasmic - encodes many of its own enzymes
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What is the origin of Vaccinia?
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Cowpox virus
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What is beneficial about the large Vaccinia genome?
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Large - allows insertion of many genes to create a recombiannt virus
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Which genes are generally deleted in Vaccinia OV strains (eg vvDD straiin)?
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TK and VGF gene dletions
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What is TK?
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Involved in purine synthesis pathway
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How does a deletion in TK increase vvDD preference for cancer cells?
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This enzyem is unnecessary in dividing (cancerous) cells since there would be a large intracellular pool od deoxyribonucleotides available for virus DNA replication
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What is VGF?
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Early viral protein secred from vaccinia infected cells thart stimulates prolifration of adjacent quiestcent cells
-Unneeded in tumor cells |
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What would adding GM-CSF to the OV do?
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Increase anti-tumor immunity - attracts WBC to tumor site
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What is the JX-594 OV strain?
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vvDD also engineered to express GM-CSF and beta-galactosidase (for tracking)
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What is beneficial about the HSV genome to use it as an OV?
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-large (allows as much as 30kb to be replaced by transgenes)
-Not integrated into host genome |
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How can we transform HSV-1 into a safe OV?
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Delete:
-TK -ICP6 -ICP34.5 -ICP47 |
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What is ICP6?
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Viral ribonucleotide reductive (needed for viral DNA replication)
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What is ICP34.5?
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Neurovirulence factor: allows PKR bypass
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How does activated PKR inhibit protein synthesis? (that is required for viral replication)
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PKR phosphorylates eIF2alpha
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What is ICP47?
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Inhibiting the transporter associated with antigen presentation (TAP)
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What is OncoVex?
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HSV-1 OV strain with both ICP34.5 deleted and a GMCSF instead of ICP47
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What are some benefits of adenovirus as an OV?
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-High titers
-Does not integrate into host chromosome -Wide tropism |
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What are two approaches for ADenovirus cancer specificity?
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1) Limit expression of E1A gene product to cancer cells by putting under cancer specific promoter
2) Delete gene functions thart are critical for efficient viral replication in normal cells but are expendable in tumor cancer cells |
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What does E1A do?
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Stimulates S phase entry to transctivate both viral and cellualr genes requires for productive viral infection
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What does E1B do?
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Binds p53 and delays cell lysis during viral replication
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What is ONYX-015?
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E1B deleted virus
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How does deleting E1B ensure cancer specificity?
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Normal cells have p53 -> can inhibit viral replciation
Cancer cells are defective in p53 |
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What are some limitations to OV?
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-Certain types of cancer are non permissive to OV infection
-OV therapeutic effect may be blocked by the adaptive antivrial immune response (eg neut. Abs) -OV has a hard time reaching the tumor |
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How can we overcome these limitations?
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Combination therapies!
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What are some examples of combination therapies?
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-Recombiant viruses
-Immunosuppresive drug -Anti-cancer drug -Recombinant proteins (boosts immune response) -Improved OV delivery strategy |
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What can Rapamycin do?
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Impairs IFN response by blocking mTOR -increases OV efficacy
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What are histone deacetylase inhibitors?
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They prevent function of histone deacetylases - therefore preventing transcriptional activation of antiviral genes after IFN stimulation
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What are examples of two HDIs?
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SAHA and MS-275
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What do SAHA and MS-275 do?
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They abrogate the IFN response -restore susceptibility of cells to the virus
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What is FLT3L?
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Fms-like tyrosine kinase 3 ligand
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What does FLT3L do?
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Growth factor of hematopoietic BM cells shown to massively increase DCs
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What is the principle of using FLT3L in combination with VSV?
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VSV lyses tumor cells, and tumor Ags are released. If more DCs are around, the likelihood of capturing Ag and priming the anti-tumor immune response is increased
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Why do OV have a hard time reaching tumors?
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-Absorption into liver
-Neutralziing Abs -Blocked by complement -Absorbed by blood cells |
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What is the Trojan horse strategy?
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Take immune cells or cancer cells, inject them ex vivo and reinfuse them - virus is essentially protected
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