ADME of Macromolecules Flashcards
Describe the differences b/w chemical-based drugs and biologics/biopharmaceutical products
Chemical-based
- MW <1000Da
- Chemically synthesized (or biosynthesized)
- Purified to homogeneity
- Chemical modifications can change activity drastically
- May have more off-target effects/side effects
Biologics
- MW in kDa
- Derived from living sources (e.g., proteins => require protein purification process)
- Unable to extract 100%
- Modifications by differing AA residue
- Behave more predictably, lesser side effects
What are the benefits of protein-based pharmaceutical products?
- Proteins control diverse cellular and physiological processes (metabolism, immune response, memory and learning)
- More naatural way of treating diseases
- Provide basis for targeted therapy/personalized medicine
Define biopharmaceuticals
Explain how clinical devices and diagnostics may make use of biopharmaceuticals
Biopharmaceuticals - recombinant proteins, monoclonal antibodies, nucleic acid-based products etc. (MACROmolecules)
Clinical devices and diagnostics may incorporate biopharmaceuticals (e.g., enzymes in glucose test strips, antibodies in immunoassays ELISA)
List the challenges of using biopharmaceuticals
- Immunogenicity
- Host cell contaminants (CHO cells etc.)
- Due to excipients (that may cause allergic reaction)
- Proteins are susceptible to denaturation and protease degradation (EXTRAcellular)
- Proteins >200kDa can be recognised by immune cells in the ECF and phagocytosized
- Proteases can also be released by activated immune cells
*Also note that protein subunits can aggregate tgt, may not exist as monomers hence they become large and easily recognized
- Proteins are susceptible to degradation by degradation systems (INTRAcellular)
- Lysosomal degradation (after endocytosis)
- Ubiquitin-proteasomal degradation
- Other activated intracellular proteases in the cytoplasm
*Intracellular half-life can only be determined by clinical trials
- Distribution of proteins (macromolecules) to tissues limited by permeability (porosity) of vasculatures
[ABSORPTION]
Proteins generally have ______ oral systemic absorption. Why?
Proteins generally have poor oral systemic absorption
- Poor protein stability
- e.g., acidic gastric fluid, digestive enzymes - Poor permeability
- e.g., through mucus layer lining the GIT (high viscosity, impeded speed of protein drug permeation)
- e.g., intestinal epithelium (-ve charge and tight junctions - restrict absorption of hydrophilic proteins) - Innate immune response
[ABSORPTION]
How does the innate immune response play a role in impeding protein drug absorption?
Mucosal epithelia lining serves as an external barrier + possess internal defenses (cellular + humoral)
- Mucosal epithelia have immune cells lying in ambush, ready to recognize and phagocytosize foreign particles (esp >200kDa), eventually degrade the proteins
[ABSORPTION]
How might proteins aggregate tgt, larger MW => more likely recognized
Partially unfolded proteins may have exposed hydrophobic surfaces, hence proteins may aggregate tgt via hydrophobic interactions
[ABSORPTION after SC administration]
Proteins are delivered to the subcutaneous tissues (aka hypodermis)
What does the hypodermis consist of?
Hypodermis:
- Adipose tissue
- Extracellular matrix: collagen (tensile strength)
- Nerves
- Blood capillaries
- Lymphatic capillaries
- Also take note of presence of immune cells that may target proteins and degrade them
[ABSORPTION after SC administration]
_____ is a major barrier that controls the rate of drug absorption into the blood capillaries
Protein drugs move through ____ via 2 transport mechanisms to reach blood or lymphatic capillaries
What are the 2 transport mechanisms?
Extracellular matrix (ECM)
2 transport mechanism to move through ECM:
1. Diffusion
2. Convection
[ABSORPTION after SC administration]
Describe diffusion (transport mechanism)
Also describe what might limit absorption via diffusion
Diffusion is the movement of single particles from high to low concentrations
It is inversely related to MW/size of proteins (smaller proteins move down conc. gradient via diffusion better)
Absorption by diffusion can be limited by:
- ECM: scarring, presence of lots of collagens and fibrous tissue
- Adipose tissue: thicker in fatter people
[ABSORPTION after SC administration]
Describe convection (transport mechanism)
Also describe what might limit absorption via convection
Convection is the collective bulk movement of large mass of particles in interstitial fluid (the flux is fluid-drive)
It is not limited by MW, though enormous proteins can get trapped in the ECM
Convection can be affected by:
- Hydrostatic pressure (higher at arterial ends, push proteins into interstitial)
- Oncotic pressure (higher at venous ends, pull interstitial fluid into blood capillaries via convection)
Absorption by convection can be limited by:
- Steric hindrance (-ve charge of ECM): negative proteins will repel the ECM and move into the capillaries faster VS positive proteins that will stay in the ECM
*Absorption by convection is LESS affected by collagen in ECM and fats in adipose tissue since it is driven by the motion of the bulk fluid
[ABSORPTION after SC administration]
Explain the absorption of larger proteins (>16-20kDa), how do they enter the circulatory system?
Larger proteins (>16-20kDa)
- Slow movement across capillary membrane
- Absorption occurs mostly via lymphatic system before draining into circulatory system
=> Protein in hypodermis can permeate the leaky endothelial membrane (as there are celfts that exist b/w the endothelial cells), and enter the lymphatic circulation
=> Lymphatic capillaries lack well-defined basement membrane, hence facilitating the permeation of the large molecules into the lymphatic circulation
*Take note that lymph nodes and lymphatics may contain lymphocytes that can attack foreign protein particles
[ABSORPTION after SC administration]
Explain the absorption of smaller proteins (<16-20kDa), how do they enter the circulatory system?
Smaller proteins (<16-20kDa)
- Absorption can occur via circulatory and lymphatic systems
=> Smaller proteins can permeate the tight endothelial membrane that lead into the blood circulation
[ABSORPTION after SC administration]
What are the considerations for absorption into the lymphatic or blood circulation?
- Perfusion of blood affects/influences capillary absorption (BLOOD CIRCULATION)
- Site of injection => tissues with high perfusion (e.g., liver, kidney)
- Patient’s peripheral perfusion (is it poor or good)
- Presence of fibrous tissue in ECM affects absorption via DIFFUSION (into LYMPHATIC or BLOOD CIRCULATION)
- Permeability of ECM from interstitial fluid in hypodermis into lymphatic or blood circulation
What are the MW of:
- Recombinant human insulin
- Recombinant cytokines
- Full-length monoclonal antibody
- Recombinant human insulin: 5-6kDa
- Recombinant cytokines: 10-12kDa
- Full-length monoclonal antibody: 160kDa (heavy chain 55kDa, light chain 25kDa)
