MEMBRANES AND TRANSPORT PROCESSES Lecture #6

permeability Membrane

drug- bound protein Protein-Mediated Transport Types Transcytosis (Macromolecules) caveolae

Transport Types Paracellular Transcellular – Diffusion (Small Molecules) – Protein-Mediated (Small Molecules) – Transcytosis (Macromolecules)

Diffusion Transcellular: Passive Diffusion

Factors that Influence Passive Diffusion Hydrophobicity Permeability

Factors that Influence Passive Diffusion: pH partition hypothesis

Permeability Properties Membranehydrophobicityionizationmolecular weight Blood Capillaries*independent < 5 kD Renal glomerulusdependent Nasal mucosadependent Buccal mucosadependent GI Tractdependent Lungdependent Hepatocytehighly dependent Renal Tubulehighly dependent Blood Brain Barrierhighly dependent * Except testes, placenta and CNS.

Hydrophobicity Permeability

Passive TransportActive Transport Membrane Equilibrative Concentrative

Protein-Mediated Transcellular Facilitated Diffusion (Energy-Independent) Active Transport (Energy-Dependent) Equilibrative TransportersConcentrating Transporters

Regulation of Facilitated Diffusion Voltage-gated Ligand-gated Mechanically-gated Light-gated Pore Closed Pore Open Ligand-gated Transporter GABA A receptor

Active Transport Primary – ATP Secondary – Electrochemical Gradient (ion-coupled) Multidrug Resistance Protein (Primary) Peptide Transporter (Secondary)

Classes of Protein Transporters Carriers – active (energy-dependent) or passive (energy-independent) – bind solute on one site and release it on the other Channels – passive (energy-independent) – solutes diffuse through the protein Channel Carrier

[Drug], mg/L Transport Rate Not Saturable Saturable Differences Between Passive and Protein-Mediated Transport Carriers Channels and Passive Diffusion

Modes of Transport cotransporter (symporter) exchanger (antiporter) uniporter Coupled Transport ABC

BCRP = Breast Cancer Resistance Protein LAT = Large Neutral Amino Acids Transporter OAT = Organic Anionic Transporter OATP = Organic Anionic Transporting Polypeptide OCT = Organic Cationic Transporter MDR = Multidrug Resistance Protein MRP = Multidrug Resistance Protein SVCT = Sodium-Dependent Vitamin C Transporter Most Important Transporters in PK

Transporters ASBT = Ileal Apical Sodium/Bile Acid Co-Transporter BCRP = Breast Cancer Resistance Protein OAT = Organic Anionic Transporter OATP = Organic Anionic Transporting Polypeptide OCT = Organic Cationic Transporter MATE = Multidrug and Toxin Extrusion Protein MCT = Monocarboxylic Acid Transporter MDR (P-gp) = Multidrug Resistance Protein MRP = Multidrug Resistance Protein PEPT = Peptide Transporter URAT = Urate Transporter

Brain Blood Plasma Brain [Drug], nM [Drug] varies with Tissue HIV Protease Inhibitor Volume Distribution (V) = 122 L

Distribution Rate varies with Tissues Drug Amount, ug

Drugs: Biologics Not typically produced by chemical synthesis and macromolecules originating from a biological organism Extracted from living systems – Antibodies – Pig insulin – Heparin (Sugar) Protein from Recombinant DNA (modified/unmodified) – Erythropoietin – Human growth hormone – Blood clotting factors Engineered Viruses – Gene Therapy – Oncolytic Virus DNA/RNA – Vaccines – Control Gene Expression Are engineered viruses drugs?

Transcytosis Transcytosis of IgA, an immunoglobin

Transcytosis Mechanisms Caveolae-Mediated (Receptor Independent) Clathrin-mediated (Receptor-Dependent) AP2=Adaptor Protein 2 Absorptive Transcytosis Receptor-mediated Transcytosis Other Proteins Involved

Methods: Drug Delivery and Transcytosis Chemical Linkage to Targeting Vector Non-covalent streptavidin/biotin linkage – Biotin  streptavidin (1-10 fM) – Biotinylated drug  Streptavidin- Targeting Vector Liposome with Targeting Vector – Drug inside liposome Nanoparticles (polymers) – Coated for drug delivery Drug Targeting Vector Streptavidin Biotin

Targets: Drug Delivery and Transcytosis Transferrin Receptor – Transferrin-Drug Insulin Receptor and Insulin-like Growth Factor Receptor – Insulin-Drug Low Density Lipoprotein Receptor Related Proteins 1 and 2 – LDL (Drug Inside) Diphtheria toxin receptor/Heparin binding epidermal growth factor – Non-toxic diphtheria toxin mutant-Drug – Heparin-Drug

Examples: Directed-Drug Delivery and Transcytosis Melanotransferrin (Protein) (p97) – Covalently linked with anti-cancer drugs – GPI-anchor – Transferrin Receptor Angiopeps (Peptide) – small/large molecule delivery – alpha-2-macroglobulin receptor Leptin (Peptide) – Leptin receptor Glycosylphosphatidylinositol (GPI anchor)

Distribution is Reversible Anti-arthritis Prodrug Activated Charcoal Known since early 1800s Adverse Drug Reaction (ADR): Severe Skin Reaction t 1/2 = 2 weeksvein artery