Oncolytic Viruses II - Potency Flashcards
how does changing serotypes improve virus replication in cancer cells/how is this done? explain with adenovirus example
Directed evolution: passage on HT-29 –> selected “ColoAd1” = Ad3/Ad11p chimeric virus –> uses CD46 R which is higher in cancers that the Ad5 CAR receptor which is low on cancers
Ad3 and Ad11p have reduced seroprevelance –> less preexisiting immunity
how was Ad5 adapted towards cancer through mutations?
PCR Ad5 on “mutator cells” which express error-prone pol. –> mutants –> select best mutant on human cancer cell line (largest plaque = better virus/highly prolific)
best mutatns changed splicing ratio –> increased expression of ADP (adenovirus death protein) which is a transmembrane protein that induces nuclear membrane instability –> cell lysis (proinflammatory) and virus release
decreased 6.7K = inhibitor of extrinisc cell death/induced apoptosis
decreased 19K = inhibitor of MHC peptide loading
which mutation in virus could promote replication/killing/spread in cancer cells?
SV5 (mutant) binds less to cells –> spreads a farther distance before re-infection –> infects more layers than WT
why would different binding efficiencies favour different niches?
in gut: bind or be eliminated – fast flow, few input viruses, lots of immune cells –> binding efficiency must be strong here
in tumor: bind too strong and never move – limited flow (dense and high pressure), lots of input viruses, less immune cells –> efficient binding restrcits distance of spread
what are two ways to increase immunity against tumor Ags?
- add stimulatory genes
- delete immunomodulatory genes
how does HSV ICP47 block MHC1-peptide loading?
- bind the transporters associated with antigen processing (TAP)
- blocks loading of peptides onto MHC-1 molecules in the ER
- infected cells are masked for immune recognition of cytotoxic T cells
what do the viroreceptors and virokines (immunomodulatory genes ) in poxviruses do?
- viroreceptors: solube or cell-surface decoys that bind host-cell cytokines or chemokines –> block: IFN signaling, cytokine activity, complement
- virokines: secreted agonistic or antagonisitic ligands for host cellular receptors –> activates EGRF/Ras signaling
what are 6 general ways for resisting neutralization by Abs or complement?
- high dose – admin so much virus –> takes a while for body to catch up
- immunosuppressive drugs (downside: susceptible to other pathogens + need IS to clear cancer cells)
- specific inhibitors
- genetic – change epitopes
- biochemical virus shielding
- change oncolytic virus at every treatment
what components of human serum inactivate oncolytic VV? what does heating serum do?
complements and Abs
heating serum denatures complement
does inhibiting complement promote oncolysis by VV? how can we inhibit complement, why is this not the best solution?
CVF = cobra venom factor – C3 complement depleting –> cobras are an endagered species
when complement is reduced, virus reduced tumor size –> once intitial virus gets to tumor, it can subdue complement because it expresses its own complement inhibitor
biochemical targeting was not ideal for an oncolytic virus, why is biochemical shielding a good approach?
helps hide the virus so it can get to its target
what are 3 challenges for changing OV at every treatment?
- overwhelming the IS, forgets about the tumor?
- politics, patent your virus
- can only use the one’s that are approved, takes a while to develop
what effect do factors in breast tumor environments have on reovirus?
when mouse breast tunor extracellular extract (tumor juice) is combined with reovirus in a mouse –> smaller viral titre than virus alone
how do breast cancer factor inactivate reovirus?
breast tumor metalloproteases cleave the attatchment protein of reovirus: cleaves sigma1’s C-term head off –> tail (sialic acid) –> can’t bind to cells
can we overcome the cleavage of sigma1 and inactivation by breast cancer proteases in reovirus?
point mutation to remove proteolysis-sensitive site –> no cleavage by proteases –> reovirus can bind to cells
