Lec 11- Liposomes (part 2)

Question 1

Reaching tumour sites

Answer 1

1. Avoid MPS uptake
2. Long circulating
3. Escape the circulation

Question 2

3 commercial liposome formulations of anthracyclines

Myocet

Answer 2

• These are liposomes of 180nm in size entrapping doxorubicin
• They are composed of egg phosphatidylcholine and ChE (55:45mol %) so fit within the classical liposomes category
• Due to their size, the liposomes are rapidly taken up by the MPS
• This avoids peak plasma levels and reduces toxicity
• The liposomes cleared by the MPS are then thought to create an ‘MPS Depot’ from which drug re-enters the bloodstream mimicking a slow infusion
• As a result tissue concentrations are comparable to the same dose of doxorubicin HCl
• The recommended dosage is 60-75mg/m² every 3 weeks

Question 3

3 commercial liposome formulations of anthracyclines

Caelyx

Answer 3

• This contains doxorubicin entrapped within liposomes 80-100nm in size
• The liposomes are composed of hydrogenated phosphatidylcholine, cholesterol, PEG2000-distearoyl phosphatidylethanolamine, α-tocopherol (56:38:5:0.2 mol %)
• The PEG₂₀₀₀ coating gives the liposomes the stealth properties and the a-tocopherol is used as an anti-oxidant in the formulation
• This formulation is used for the treatment of solid tumours including Kaposi sarcoma and ovarian cancer
• It is supplied as a sterile, red liposomal dispersion and must be diluted in 250mL of 5% dextrose prior to administration

Question 4

DaunoXome

Answer 4

• These liposomes are composed of DSPC: ChE (2:1 mol ratio) and have a diameter of 45nm with entrapped daunorubicin
• DaunoXome is indicated for the treatment of advanced HIV-related Kaposi sarcoma
• It is available in a single-use vial for IV infusion and the liposome dispersion should appear red and translucent
• The liposome formulation helps to selectively target the daunorubicin to solid tumours
• Whilst this is not a stealth formulation tumour targeting is still noted with this formulation presumably due to the high transition temperature lipids used (DSPC) and the small vesicle size which helps pro-long blood residence time

Question 5

Surface engineering of the liposomes

Answer 5

1. MPS recognises charged surfaces on particulates avoid by formulated as a neutral surface
2. MPS recognised tagged or opsonised surfaces
   
   1. PEG coating prevents opsonisation due to steric hindrance

Question 6

Stealth tactics

Answer 6

Question 7

Why do we need long circulation

Answer 7

• Enhanced circulation allows the liposomes to target tumour sites
• This is due to the unique blood vasculature with tumour
  
  • Blood vessels in growing tumours are leaky to circulatory macromolecules and large particles
  • Allowing them easy access to the tumour’s interior

Question 8

Why do we need stealth tactics

Answer 8

• Liposomes can be recognised as foreign bodies
• They are filtered out by the liver and spleen
• The immune system recognises and destroys liposomes
• This is through a method known as opsonization

Question 9

PK data

Answer 9

• Non-modified = saturable because there is binding to a receptor
  
  • Stealth no binding so will be removed when kidney/liver
    *

Question 10

Clearance of liposomes

Answer 10

Question 11

Liver and spleen uptake

Answer 11

• Starts off fast and then plateau due to saturation
• Stealth = natural removal (kidney/liver)/ Removal is independent on concentration

Question 12

Passive targeting to tumour sites: The EPR effect

Answer 12

• Lower permeability of the blood vessel prevents the drug from escaping to area’s where it is not needed
• The high permeability of the blood vessel in the tumour site allows liposomes to escape
• Tumour tissue- the tumour tissue has poor lymphatic drainage, trapping the liposome in the cancerous tissue
• Liposome entrapped drug

Question 13

The localisation of doxorubicin in AIDS-KS lesions

Answer 13

Question 14

Liposomes bring with them new side-effects

Answer 14

• Hand-foot syndrome (Palmar-plantar erythrodysesthesia or PPE)
• Redness, swelling and sores on the palms of your hands and soles of your feet
• Reports of 48% with Caelyx v 2% with drug

Question 15

Counselling

Answer 15

• To minimise
  
  • 4-7 days after each infusion, keep hands and feet uncovered (Avoids socks/gloves/tight-fitting shoes) and soaking them in cool water when possible
  • Avoid exposing the skin to very hot water e.g. saunas and jacuzzis and avoid exercise that might cause damage to the skin e.g. jogging

Question 16

Liposome-based products

Answer 16

*

Question 17

Trigger-release liposome formulations: thermodox

Answer 17

• Heat tumour
• Liposome reaches transition temperature- gel-like structure= increased release of drug

Question 18

Visudyne: Photosensitizing agent

Answer 18

• Vertoporfin (drug)
• Egg phosphatidylglycerol
• Dimyristoyl phosphatidylcholine
• Ascorbyl palmitate
• Butylated hydroxytoluene

Question 19

Role of liposomes in Visudyne

Answer 19

• Vereportin is hydrophobic and self-aggregates
• This severely limits drug bioavailability
• Maintains vertporfin in monomeric form increasing bioavailability

Question 20

Treatment of age relatedmacular degeneration

Answer 20

• Scarring of eye tissue
• Production of faulty/leaky blood vessels

Question 21

Applications

Answer 21

• Laser enhances the release of drug by increasing flexibility of liposome membrane

Question 22

Liposomes as vaccines

Answer 22

• Virosomes are small vesicle structures, ~150nm in size, prepared from the outer coat of influenza virus and additional phospholipids
• Epaxal: This is a hepatitis A vaccine containing inactivated hepatitis A virus. The inactivated virus has been adsorbed onto virosomes

Question 23

Summary: drug delivery using lipid systems

Answer 23

• DNA delivery
• Delivery of vaccines
• Pressure probes
• Photo-sensitive liposomes
• Enhances solubility

Question 24

Summary

Answer 24

• Liposomes currently provide the ability to passively target encapsulated drugs to specific sites of disease
• This allows liposomes to improve the therapeutic index of several drugs
• However,
• alternative side-effects do arise from the use of liposomes

Question 25

Mock question

How can liposomes be used to enhance the delivery of drugs and improve their therapeutic profile. Use examples to support answer

Answer 25

• Describe the liposome
• Description of caelyx and ambisome or other
• Biodistribution by passive targeting without stealth coating
• Effect/mechanism of PEG

Question 26

Other example questions

Describe the physico-chemical factors which influence biodistribution and discuss how we can design liposomes to avoid MPS uptake

Answer 26

• Think about how the size controls fate (i.e. what size goes where)
• Also surface charge/characteristics, opsonins and phagocytosis
• What size should they be, how will er make them
• What surface properties should they have