Protein formulations

Question 1

Problems with protein delivery

Answer 1

Large hydrophilic molecules

Extra-vascular access difficult

Poor stability

Purity of recombinant products

Complex pharmacological action

Question 2

Barriers to protein drug delivery

Answer 2

LMW drugs reach sites of action by diffusion + partition

HMW + hydrophilic drugs, anatomy + physiology present many barriers

Question 3

Size + shape of macromolecule + proteins

Answer 3

Relationships between Mw + size depends on shape

• e.g. polysaccharides, branching, loose random, coils
• Proteins = globular + tightly packed; smaller than same Mw polsaccharides

Bigger the Mw, bigger the size (nm)

IgM = large; acts as small particle

• o transit through basement membrane + little extravasation

Question 4

Factors determining biodistribution of macromolecules

Answer 4

Ability of macromolecules to be transported across endothelium

Differences in relative blood flow to different tissues

Amount reaching tissues also affected by rate of elimination by kidneys + metabolism

Question 5

How are macromolecules eliminated?

Answer 5

Small proteins, oligonucleotides = kidney (by glomerular filtration)

• Larger macromolecules are not eliminated by kidney filtration

Cut-off for glomerular filtration

• 60kDa - proteins
• 40kDa - dextrans (polysaccharides)

Question 6

Metabolism of macromolecules

Answer 6

Removing old serum proteins + unwanted macromolecules (by dying cells) mainly by receptors on parenchymal cells + macrophages

e.g. Asialoglycoprotein (ASGPR)

Sugars below terminal sugar residue, sialic acid, are recognised by specific receptors when terminal sugar is cleaved off

ASGPR recognises D-galactose

Question 7

Materials cleared by ASGP receptor

Answer 7

Hormones

Carrier molecules

Protease inhibitors

Immunological

• Other receptors = N-Acetylgalactosamine recetor on macrophages + fucose receptor on liver parenchymal cells*
• Other proteins e.g. albumin + LDL have no sugar residue. These proteins age + are acetylated + cleared by a receptor recognising acetylated proteines*
• There is a receptor that removes unwanted DNA from circulation*

Question 8

How are macromolecules cleared + metabolised?

Answer 8

After binding to receptor, proteins endocystose + sent to lysosomes

Macromolecules are regulated + metabolised by the liver

Question 9

Importance of clearance receptors to drug delivery?

Answer 9

Protein drugs cleared from circulation using normal homeostatic mechanism

Specific receptors used to target drugs to liver

Cytotoxic drugs could cause liver toxicity

Question 10

Propterties of protein + peptide drugs

Answer 10

Large, hydrophilic molecules

Not well transported across biological membranes (<2& bioavailability)

Physical, chemical + biological instabilities

Major disadvantages compared with small MW drugs

Question 11

Physical stability of proteins

Answer 11

Proteins lose native 3D structure

Unfolding/denaturation due to:

• hydrophobic conditions, surfactants
• pH, solvent, temperature
• dehydration, lyophilisation

Adsorption

• polar + non-polar residues
• Adsorbed + interfaces
  
  • aire-water-foaming
  • air-solid

Aggregation

• denatured, unfolded proteins may interact
• Aggregation becomes precipitation @ macroscopic level

Question 12

Routes of admin.

Question 13

How to improve oral bioavailability of proteins/peptides

Question 14

Potential adverse effects of inhaled insulin

Question 15

Inhaled insulin pharmacokinetics/dynamics

Question 16

Why inhalation delivery for insulin?

Question 17

Parental delivery systems

Question 18

Implantable delvery system