Emerging Treatments Flashcards
Inborn errors of metabolism
The largest group of genetic diseases that affect various pathways including carbohydrate, fatty acid and protein metabolism
For example PKU MCAD deficiency maple syrup urine disease and homocystinuria
PKU
lack of phenylaline hydroxylase which converted phenylaline to tyrosine
Untreated PKU causes major cognitive impairment,behavioural difficulties,fairer skin and hair
Treated with low protein diet and tyrosine supplements
Haemophilia
- Blood clotting disorder known since ancient times
- Causes uncontrolled bleeding
- Bleeding into joints (Causes excruciating pain), into brain and internal bleeding occurs
Stages of drug development
- Phase I: first in healthy volunteers less than 100 to see safety
- Phase II: check therapeutic effect on few patients 100-300
- Phase III: large scale therapeutic trials 200-3000
Pharmacological chaperones
Fix misfolded proteins
- Some mutations prevent proteins folding properly
- Chaperones aid in folding process and sometimes proteins misfold after which it is subject to degradation by various pathways
- If correctly folded, protein is active and moved down secretory pathway and then moved into cytoplasm or out of cell
Fabrys disease
Deficiency of alpha galactosidase A causing build up of globotriaosylceramide
Cause protein misfold
Treat with small molecule chaperone migalastat which is a substrate for for alpha galactosidase A
Mutation specific
Pharmacological modulators
- Commonly used drugs
- Can be receptor agonists/antagonists
- Can be ion channel activators/blockers
- Firstly designed to have these effects on mutant receptor or channel e.g. Bcl-abl Kinase inhibitors for treatment of cancers caused by Ph chromosome
How have pharmacological modulators helped with cystic fibrosis treatment
Defective chloride ion channel can open if we make a drug that causes activation called Ivacaftor
combination therapy of chaperone and activator can be used for treatment
What does stop codon readthrough treat?
- Diseases caused by a non-sense mutation (aka stop mutation) that introduces a stop codon prematurely in the protein sequence
- This prevents protein production.
What drugs red through premature stop codons
Eg aminoglycosides that bind to bacterial ribosomes and cause mistranslations
DMD involvement in stop codon read through
- DMD caused by a premature stop codon and you get truncated dystrophin
- In BMD there is a missing section
- Theory is if we read through premature stop codon we get a phenotype more like BMD which is much more mild phenotype
What is gene therapy
- For a recessive disease we replace defective gene
- For a dominant disease we delete the defective gene
Much easier in vitro (in glass in a lab) + ex vivo (out of the living) than in vivo (in the living)
Mitochondrial inherited disease therapy
Requires IVF chromosomes from unfertilised egg with mutated mitochondrial DNA and transfer to unfertilised donor egg with removed nucleus which is then fertilised in vitro and develops to form an embryo (maternal spindle transfer)
Second way is fertilising egg with mutated mitochondrial DNA, removing the resulting pronucleus and transferring it to a fertilised donor egg with a removed pronucleus and letting it develop normally (pronucleur transfer)
How does viral gene therapy work
Can engineer a virus’s DNA to carry a therapeutic gene
Ex vivo gene therapies
Tread diseases Affecting haemopoitetc cells
Eg SCID aka bubble baby disease where both B and T cell mediated responses are lacking
Treated with bone marrow transplant
In vivo gene therapies
Can insert genes in vivo to replace defective genes, useful for treating recessive diseases
Can use injection systemically but most successful in vivo therapies have been local injections in eye, brain or spine
Treats for lack of defective gene
Leber congenital amaurosis (in vivo)
It’s a recessive disease cause by mutation in RPE65 (retinal pigment epithelium-specific kilodalton 65 which is involved in generation of visual pigment) which causes progressive blindness through loss of retinal cells
Inject luxturna into eye behind retina which is taken up by cells to make RPE65 proteins
Anti sense oligonucleotides
Target against gene
Used for dominant disease caused by gain of function
Are short modified nucleic acids that are complementary to mRNA of gene were interested in. They bind to and block translation of target mRNA destroying it
Cheap
Exon skipping using oligonucleotides
Treats deletions for large proteins
DMD therapy exon skipping
- DMD is caused by a small deletion that shifts the reading frame and causes a truncated protein
- BMD is caused by a large deletion but the reading frame is left intact
- So exon skipping tries to convert DMD into BMD - much more mild and survivable phenotype
Eteplirsen drug does this- oligonucleotide causes skipping of exon 51 which results in a partially active form of dystrophin
Lentivirus
Infected in humans for use in gene therapy
RNAi
Regulates activity of gene by silencing or downregulating activity through dSRNA molecules
In vitro gene therapy for ADA-SCID
- Treatment called strimvelis and is similar to autologous transplant
- Take bone marrow from patient, isolate HSCs and isolate and expand CD34+ cells
- Transfect them with a lentivirus that encodes ADA and grow transformed cells
- Treat patient with busulfan to kill their own HSCs then reinfuse transformed cells into patient to replace the faults HSCs with healthy ones
All functions
Pharmacological chaperons are used to treat protein misfolding. Pharmacological modulators activate or inhibit ion channels. Stop codon read through treats mutations that introduce an early stop codon.ex vivo treats haemopoetic cells via reading and then inserting functional gene. In vivo gene therapy directly introduce the functions, gene which treats recessive disorders. Anti sense oligonucleotides treats dominant disease by destroying faulty mRNA. Exon skipping treats deleterious for large proteins RNAi treats dominant disorders by silencing genes
