Bio 6 Flashcards
What can gene therapy be used for?
Gene repair Pro-drug metabolising enzyme therapy to sensitize cancer cells Viral oncolysis Modification of tumour microenvironment Drug resistance therapy Immunotherapy
What are the commerical barriers to gene therapy?
Costs are high for materials
Small market of suitable patients
Costs of patents and licences
Biological barriers to gene therapy
Many genes may be mutated
Variation within tumour
Variation between patients
Require majority of cancer cells to be affected
What are microRNAs?
short RNA molecules that bind to mRNA targets and repress gene expression
Oncomirs
Repress TS genes
Tumour suppressor miRs
Repress oncogenes
How can microRNAs be exploited for cancer therapies?
Block oncomirs: increase tumour suppressor genes
Increase tumour suppressor microRNAs: downregulate oncogenes
Anti-miRs (antagomirs)?
Inactive oncomirs, bind and sequesters
Oligonucleotides complementary to miRs
MicroRNA sponges?
Mop up oncomirs
They have multiple decoy binding sites for miR
RNA sequence is complementary to multiple target miRs
MicroRNA mask?
Block oncomirs
Oligonucleotide complementary to target mRNA
Binds to mRNA to block access to miRs
Upregulate tumour suppressor miRs?
Oligonucleotide to mimic TS miRs
Replacement therapy
What are the barriers to miR therapies?
- Stability: oligonucleotides only last a few minutes in blood stream; chemical modification into liposomes can increase increase half-life
- Excretion: modications to increase albumin binding, slows renal clearance
- Cellular uptake and targeting: large size and polar make it difficult to get across membranes, therefore use carrier- active uptake
What are the biologial issues with miR therapies?
High dose is required
Transient inhibition; repeated doses needed
Off-target effects; multiple targets for each miRs
Pro-drug metabolising enzyme therapy example and how it works?
Herpes Simplex TK
Phosphorylates prodrugs such as valaciclovir to toxic nucleotides
Uses gamma retroviral vector or cancer cell surface antigen to target cells
Not licenced
Viral oncolysis example
Adenovirus dl1520; uses defective p53 pathway
Only replicates in cancer cells
How does targeting the tumour microenvironment as a therapy work?
Prevents angiogenesis by modifying normal cells
Doesn’t require high efficiency of transduction
Modify immune response and metastatic potential?
Cancer cells don’t exist in isolation
What doesnt require such high energy transduction?
When you target the host, not the cancer
How can gene therapy reduce toxicity?
By increasing the therapeutic index
What is the recent progress for ALL (acute lymphoblastic leukemia)?
donor T-cells from healthy volunteer, genetically modified to attack CD19+ cells and resistant to immunotherapy which would otherwise kill all T-cells
this is transplanted into patient and immune system kills all cancer cells and also donor T-cells and so is free from genetic modification as well as cance
What are monoclonal antibodies?
proteins produced by the immune system to bind specifically to foreign antigens
produced by B lymphocytes
come from single clone of B lymphocytes and target a single epitope
Polyclonal antibodies
come from many clones of B lymphocytes
target multiple epitopes
Draw structure of antibody (immunoglobulin)
Antigen binding site
Variable and constant regions
Light chain and heavy chain
Disulphide bonfs
What are MAbs used for?
Make cells visable to immune system: mark
Stop cells dividing: against growth receptors
Target therapies: conjugated to enzyme
Diagnosis: hormone receptors
What is rituximab?
targets CD20 on B cells and kills them in lymphomas and leukemias.
- causes antibody dependent cell mediated cytotoxicity
- causes complement mediated cytotoxicity
How are MAbs used as delivery systems?
Radioimmunotherapy (RIT) to deliver radioisotopes
Antibody drug conjugates (ADC): deliver drug to target
Antibody directed enzyme pro-drug therapy (ADEPT): delivers activating enzyme of pro drug to target
What characteristics are needed for therapeutic antibodies?
Good specificity
Large quantities
Well defined purity
What are the benefits of recombinant Mabs?
Not recognised as foreign
Different species have differences in Fc region which is recognised by immune system
Smaller molecules distribute more easily
You can remove unwanted functions (Fc activation) and add additional functions
You can reduce size by getting rid of amino acids
What are the fragments of recombinant antibodies based on?
Fab fragment or an Fv fragment of an anitbody
Disadvantages of antibody fragments?
Reduced circulation; half-life is controlled by Fc region and glycosylation
Loss of immune receptor function (ADCC, CDC)
Reduced binding activity
What are third-generation molecules?
They remove non-essential regions from MAbs, but retain effector functions, so there is increased tumour penetration (small)
What are cancer vaccines?
A tumour-associated antigen (TAA) induces an immune response against tumour cells specifically
Host immune is often compromised
How does Provenge (Sipuleucel-T) work?
PAP (prostatic acid phosphatase) is a fusion protein and is cultured with immune cells from patient with prostate CA
Then it is returned back to patient, the monocyte presents the fusion protein at surfuce and matures into activated antigen and presents tumour associated antigen on the surface - activates APC, then it evokes an immune response to attack prostate cancer cells; involcing CD4 and CD8 T cells and cytokines to lysis the cell.
Why would you want to induce cytotoxic T-lymphocytes?
So tumour-associated antigen (TAA) can be expressed on Antibody presenting cell (APC), and can modify tumour cells to act as or attrack APCs
