topic 21 - Biologics Flashcards
Biomacromolecules as drugs
Small molecule drugs are:
<500 Da
Moderately hydrophobic
Synthetic
Uniform.
Biological drugs are:
Many kDa
Very hydrophilic
Synthetic or biologically sourced
Can be disperse
insulin
Insulin is a small protein/peptide produced within the pancreas. Its role is to regulate the metabolism of fats, carbohydrates and sugars by promoting glucose absorption.
In diabetes reduced, or no insulin is released into the bloodstream. Insulin is administered to counter this.
First isolation and administration of insulin to diabetic patients by Banting and Best in 1922 – resulting in a huge benefits for people with diabetes and a Nobel prize just one year later.
Usually self-administered as subcutaneous injection
Obtained from pig pancreas, or through expression in bacteria.
antibodies
The role of antibodies in nature is to bind strongly and selectively to foreign material (antigen) and illicit an immune response
Medicinal uses all exploit selective binding, some use the immune system too.
The chemical unit recognised is called the epitope
antibodies - production
Polyclonal antibodies are many sequences, but all bind the same antigen
Polyclonal antibodies are produced by the body’s natural immune system.
antibodies - production - pt 2
Monoclonal antibodies (mAbs) are all identical and are produced using biotechnological methods.
Most medical uses employ mAbs which are easier to regularise.
Both processes involve use of animals.
Smaller, single-chain antibodies (“nanobodies”) can be obtained using camelids and cartilaginous fish.
antibodies - blocking receptors
Antibodies can bind cell-surface receptor proteins and prevent their hormones binding.
HER2 is a cell surface receptor similar to EGFR which is overexpressed in 30% of breast cancers leading to excessive cell proliferation.
Herceptin / trastuzumab binds and blocks HER2 activity
antibodies - blocking receptors - pt 2
Large protein – intravenous, or subcutaneous (if tumour site accessible).
No known metabolic pathways – long circulation time (28 day half life) means injections can be infrequent.
Reduces risk of return of early stage cancer after surgery by ~10%
Adds ~5 months to late stage cancers.
Common side effects are flu-like.
2-7% of patients have cardiac problems.
No benefit if cancer does not overexpress HER2 – side effects remain. Patients must be tested first.
antibodies - blocking receptors - pt 3
If you know the biochemistry, and you have a target which is extracellular, it can be treated with an antibody:
Adalimumab – blocks TNF, a protein which is involved in inflammation – treats rheumatoid arthritis
Ixekizumab – binds interleukin 17A, a protein involved in inflammation – treats psoraiasis
Alirocumab – binds PCSK6, which is stops removal of LDL chlosterol from circulation – treats high cholesterol
No requirement for structural knowledge – just need to raise an immune response in mice to the target.
antibody - drug conjugates
The recognition properties of antibodies can be used to bring drugs to the right site.
Compounds which would otherwise have unacceptable side effects can be used
Also used to radiotherapy.
antibody - drug conjugates - pt 2
Many amines (Lys) displayed on surface
React these at random to make amides
Does not give uniform product
E.g. trastuzumab emtansine
Partial reduction of disulfides give free thiols (Cys)
React these specifically with maleimides
More uniform product
E.g. Brentuximab vedotin
Engineer new Cys in specific locations to give free thiols
React these specifically with maleimides
Uniform product
E.g. Vadastuximab talirine
Nucleic acids
It is usually the proteins which cause diseases.
But all proteins are produced based on DNA RNA sequences
Can we block production of overactive or faulty proteins?
Can we produce new or fixed proteins?
✔ No need for structural knowledge of the protein or finding a druggable site
✔ Easy to programme in specificity for proteins/mutations/conditions
– just make right sequence
✘ Do need to get nucleic acids into the cells – not membrane soluble
✘ Nucleic acids subject to enzymatic degradation
what are antisense oligos (ASO’s) - nucleic acids?
Administer a DNA oligomer complementary (antisense) to the mRNA which encodes the gene of interest (sense) which we want to silence
- RNAse H cleaves DNA/RNA duplexes
- DNA gets in the way of the ribosome when the mRNA comes to be translated
- DNA can stop the mRNA being processed (spliced) in the right way before translation, again by getting in the way
what is an RNA interference - Nucleic acids
Uses a natural pathway for degradation of double-stranded RNAs (dsRNAs)
Long dsRNAs are broken into smaller (~20mer) units (small interfering RNAs = siRNAs) by Dicer, and one strand (guide) is incorporated into the RNA-induced silencing complex (RISC)
The other (passenger) strand is degraded
RISC cleaves any mRNAs in the cell complementary to the guide strand – silencing those genes.
Drugs introduce synthetic siRNAs
Patirsan treats polyneuropathy in patients with hereditary transthyretin-mediated amyloidosis – a rare, fatal disease
what are mRNA - nucleic acids?
Instead of silencing genes, new proteins can be produced if new mRNA can be given to a cell.
First approvals in the mRNA vaccines for COVID.
what are CRISPR/Cas 9?
CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats (i.e. DNA sequences).
Cas9: An enzyme which cuts DNA at a pre-specified point.
Gene editing:
Use guide RNA/Cas9 to cleave DNA at desired point
Use DNA repair mechanisms to fill in gap with donor DNA.
