Lecture 11 - gene therapy Flashcards
what is gene therapy ?
Introduction of genetic material into a person’s somatic cells to treat or prevent a disease
gene therapy is used to overcomee limitations associated with the administration of therapeutic proteins: Low bioavailability, Inadequate pharmacokinetics profile (fast degradation) and High cost of manufacture
what is gene augmentation therapy?
replacing a non-functional gene that causes the disease with a healthy copy of the gene
Suitable for the treatment of inherited disorders
Only if the pathogenic effects are reversible
Ex: cystic fibrosis: replacing the inactive Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene
what is gene inhibition therapy?
inhibition of the expression of the pathogenic gene
Suitable for the treatment of infectious diseases, cancer, inherited disorders caused by inappropriate gene activity
Introduction of short nucleic acids (DNAs or RNAs) with regulatory function, to inhibit the expression of the pathogenic gene
what are the 6 classes of non coding nucleic acids in gene inhibition therapy?
- oligonucleotides and modified oligonucleotides (antisenses)
- small catalytic RNAs and DNAs (ribozymes and DNAzymes)
- small regulatory RNAs (siRNAs and microRNAs)
- long antisense RNAs
- decoy RNAs and DNAs
- RNAs binding to other molecules thanks to their tridimensional structure (aptamers)
describe non coding nucleic acid class antisense
oligonucleotides designed to bind to mRNA:
- Formation of double-stranded RNA/DNA hybrid -
- Blockage of the translation of the mRNA
- Stimulation of the degradation of the RNA:DNA hybrid by cellular RNase H enzymes
Ex in clinical trials: drug G3139 (Oblimersen), a phosphorothioate targeting Bcl-2 for inhibiting apoptosis in melanoma and chronic lymphatic leukaemia
sIRNA
Small interfering RNA (siRNA): short, 21-23 nucleotide double stranded pieces of RNA
Use: recognition of complementary mRNA, post-translational silencing of gene expression by multiple mechanisms:
- cleavage of target RNA
- inhibition of translation
- sequestration into specific cytoplasmic compartments (P bodies), in which RNA degradation is believed to occur
Ex : siRNA against Bcr-Abl for the treatment of chronic myeloid leukaemia (CML)
explain the approach killing of specific cells
Suitable for cancer
Strategies for cancer gene therapy:
- to target the cancer cells themselves
- to improve the efficacy of the immune system in recognizing and destroying the cancer cells: immunotherapy
what are the 3 strategies for gene therapy of cancer cells ?
Strategy 1: Inhibition of cancer cell proliferation
Tranfer of genes or non ocndign neucleic aicds into the cancer cells to inhibit their porlfieration of induce apoptosis
* Ex: tumour suppressor p53, retinoblastoma tumor suppressor (Rb)
2- Strategy 2: Transfer of suicide genes into cancer cells
delivery of genes inducing cell death or activating a cytotoxic pro-drug directly into the cancer cell
* Ex: thymidine kinase gene of the herpes simplex virus (HSV-TK) which activates ganciclovir
3- Strategy 3: Oncolytic viruses
Exploit the property of virus mutants to selectively replicate and lyse cancer cells
explain the development of a suitable even therapy approach
Choice of the correct therapeutic gene (a vast spectrum of nucleic acids with potential therapeutic function is now available to gene therapy)
Administration route
Two general routes of administration:
- Isolation of the patient’s cells followed by gene transfer in the laboratory (ex vivo gene therapy)
- Direct delivery of the therapeutic gene into the patients (in vivo gene therapy)
Persistence of gene transfer (rapid disappearance of RNA from circulation and elimination via the liver, kidney and reticulo-endothelial system)
Delivery system (need to specific delivery to the target tissues/ cells)
what are barrier to DNA delivery tissues ?
Degradation of DNA by nucleases after intravenous injection
Inability of DNA to reach the target
tissue following intravenous injection
Poor ability of DNA to cross biological membranes :
- very large molecule
- carries a charge
what is entry of DNA into cell limited and facilitated by ?
Entry of DNA into cell is :
- limited by size and charge
but facilitated when DNA is associated with:
- cationic liposomes
- cationic polymers and dendrimers
- viruses
what is endocytosis ?
endocytosis is formation of membrane vesicles at the cell surface, followed by their internalization and intracellular trafficking
4 different endocytosis
Mechanisms:
- Phagocytosis
- Macropinocytosis
- Clathrin-mediated endocytosis
- Caveolar endocytosis
describe the 4 different endocytosis mechanisms
macropinocytosis - Formation of large
endocytic vacuoles (>500 nm)
phagocytosis - Internalization of large particles
(>500 nm)
clathrin-mediated endocytosis - More specific, active event
where the plasma membrane folds inward to form pits coated with the cytosolic protein clathrin
- Formation of small vesicles (~ 100 nm)
Caveolar endocytosis - Non-clathrin-coated, plasma membrane flask-shaped invaginations (~50 nm)
what are rate limiting steps in the DNA delivery to the nucleus?
Escape of DNA from the endosomes and translocation to the nucleus are the rate-limiting steps.
Transport of DNA from the cytoplasm to the nucleus is an active, carrier-mediated and saturable process with an apparent size limitation of< 25nm.
only very little DNA arrives in the nucleus
what are Properties of an ideal gene delivery vector
safe
able of delivering DNA to the cell nucleus
amenable to scale up
economical production to pharmaceutical standards
high transfection efficiency
targeting of desired tissue type for localised transfection
what are. factors limiting the progress of gene therapy?
Effective and safe delivery
Significant gene expression and targeting
what are available vectors for even delivery ?
non-viral - lipids, polymers, dendrimers
- relative lower efficiency
- poor nuclear targeting (DNA stays trapped in the endosome)
- safer in vivo
- no limit to the size of the carried nucleic acid
- no immune response, allowing repeated injections
- ease to prepare and scale up
- rapid uptake and elimination by the cells of the reticuloendothelial system
viral - Adenoviruses, Retroviruses, Lentiviruses, Adeno-associated viruses, Herpes simplex viruses
- generally higher efficiency - - variable nuclear targeting
- limitation to the size of the carried nucleic acid (max 30 kB)
- risk of immune response
- risk of generating the infectious form
- risk of inducing tumorigenic mutations
- difficulty to scale up
what are problems linked to viruses?
Therapy- limiting immune response on administration of the second dose of adenoviruses
death of patient - Traces of adenovirus present in organs outside the target organ (liver), even though adenovirus injected into liver
explain gene delivery for non viral vectors
charged + to dna -
when lipids as used as a vector, they go from lipids to liposomes (lipoplexes)
polymers charged + to particles (polyplexes) charged -
dendrimers charged positive to particles (dendriplexes) charged negative
what are cationic liposomes
Electrostatic complexes with the negatively
charged DNA
- Neutralisation of the charges
- Facilitation of DNA transfer
- (also protection of DNA against degradation)
Ex: Lipofectin®
Polymers
Polymers protonated at physiological pH
ex: polyethylenimine
- Polyethylenimine (branched)
- Polyethylenimine (linear)
Densely positively charged
Efficacious DNA binding
Enhancement of the cellular endocytosis of DNA
Facilitation of endosomal escape
But: cytotoxicity
Dendrimers
Polymers composed of multiple branched monomers that emerge radially from the central core
Electrostatic interactions of the terminal primary amines with DNA
Monodisperse size
Modifiable surface functionality
Water solubility
Available internal cavity for drug delivery
Enhancement of the release of the dendrimer-DNA complex from the endosome
Gendicine
Viral replacement gene therapeutic
for human use in China
Disease: treatment of head and neck squamous cell carcinomas
Gene: wild type p53 gene, causing tumour apoptosis
(Strategy 1: Inhibition of cancer cell proliferation)
Vector: adenoviral vector
what is Head and neck squamous cell carcinoma
Cancer originating from the epithelium of the upper aerodigestive tract (lip, oral cavity, mouth, nasal cavity, pharynx and larynx)
Mainly strikes men over 50 years of age
80% of the world’s cases of head and neck squamous cell carcinoma occur in China
(about 300 000 new patients diagnosed with this cancer each year in China)
Main cause in China: tobacco and betel nut chewing
Treatment
- Combined surgery and chemotherapy
- Radiation therapy
Tumour resistance to these treatments
Poor prognostic
Need for an alternative treatment
