Module 1-b Biological Barriers

Biological Barriers Human barriers Cellular Delivery Skin Mucosa DRUG PROBE DRUG PROBE External barriers Cellular Delivery En route barriers Blood Extracellular matrix Cellular barriers Endosomal/lysosomal degradation Inefficient translocation to the targeted sub-cellular organelles

Human Barrier (Errors)

Common Routes of Administration

First Pass Mechanism Metabolism occurs during the absorption process. The fraction of the initial dose appearing in the portal vein is the fraction absorbed, and the fraction reaching the blood circulation after the first-pass through the liver defines the bioavailability of the drug.

Histologic image of human epidermis Source: Grays Anatomy

Composition of gastric mucus Source: DOI: 10.5772/23951

Possible destabilization and degradation pathways of probes during in vivo circulation Immunoglobulins, complement proteins, albumin, apolipoprotein and fibrinogen. adsorbs on the surface of nanoparticles and tag them for attack by the MPS. Scavengers to engulf foreign particles Mononuclear phagocyte system: (MPS)

Renal Clearance Renal molecular weight cut-off: 48kDa Renal size cut-off: ~10 nm Anything beyond >10-20 nm may not be excreted Size: ~10 nm

Blood Brain Barrier (BBB) Blood and brain junction, endothelial cells are tightly stitched together Composed of smaller subunits, e.g. biochemical dimers, transmembrane proteins, occludin, claudins, junctional adhesion molecule (JAM), ZO-1 protein Crossing BBB: disruption by osmotic means; biochemically by the use of vasoactive substances such as bradykinin; localized exposure to high-intensity focused ultrasound (HIFU) Pore size upper limit ~12 nm (malignant glioma) Polyethylenglycol, peptides….. A cortical microvessel stained for blood-brain barrier protein ZO-1

Degraded nanoparticle Cellular Barriers Excretion Degraded nanoparticle SUCCESS FALIURE Possible degradation routes Acidic pH and enzymes (late endosomes -lysosomes). Viscosity and intracellular enzymes of the cytosol. Recycling (exocytosis) of the vesicle contents.

Charged molecule: activity of specific transport and channel proteins Diffusion of Agents Through Cellular Bilayer Hydrophobic molecule Charged molecule Polar (large) Glucose Polar (small) H2O, ethanol (a) ibuprofen, (b) aspirin, (c) erythromycin Charged molecule: activity of specific transport and channel proteins Polar (large) Gases Hydrophobic molecule Charged molecule Polar (small)

Can There be a Direct Access to the Cytoplasm? How can we avoid endosomal escape pathway? Direct translocation across the plasma membrane is another suggested endocytic pathway Does not depend on the metabolic activity of the cells. Energy-independent Receptor-independent Transduction Cell penetration peptides

Cell Penetrating Peptides (CPPs) 1988 1994 1996 1997 2000 2001 2004 2006 2008 Discovery TAT Covalent approach PENETRATIN TRANSPORTAN Complex MPG POLY R TP10 In vivo PEP-1 Clinical Trial PPTG SAP SynB M918 PrPr EB1 CADY Phase IIb-3

Extra Vascular NP: How Far Below We Could Drive the Size Down? Hydrophobic Hydrophillic Self-assembly Diblock copolymer Micelle Cross-linking PTD PTD-SCK-FTSC 40-60 nm Shell cross-linked nanoparticles (SCKs) Pan, Turner, Wooley Macromolecules, 2004, 37 (19), pp 7109–7115 Becker, Pan, Wooley Bioconjugate Chemistry 2003

Its all about ‘CONTROL’

A perfect Therapeutic Approach Precise Targeting (Tissue/Cell/Molecular) Precise Action (Maximize therapeutic action and minimize toxicity and side effects) Precise Timing (On when it is needed, Off when it is not needed) Implicit in these design goals is the requirement for precise control mechanisms that can either respond to local environments automatically or respond to signals sent remotely.

Characteristics of an ideal tumor-targeted Agent (1) Increase drug localization in the tumor through: (a) Passive targeting (b) Active targeting (2) Decrease drug localization in sensitive, non-target tissues (3) Ensure minimal drug leakage during transit to target (4) Protect the drug from degradation and from premature clearance (5) Retain the drug at the target site for the desired period of time (6) Facilitate cellular uptake and intracellular trafficking (7) Biocompatible and biodegradable Lammers T, et al. British Journal of Cancer 2008;99:392-397.

Absorption, Distribution, Metabolism, and Excretion (ADME) Describes the disposition of a pharmaceutical compound within an organism. The four criteria all influence the drug levels and kinetics of drug exposure to the tissues. Influence the performance and pharmacological activity of the compound as a drug. LADME: L stands for "liberation" and deals with details of the route of administration such as what a tablet will do at a given gastric pH level, the creation of extended-release injectables for IM or SC use etc.

ADME Other RES sites Distribution Absorption Liver Systemic Local barriers Distribution Absorption Liver Systemic Circulation Target tissue Metabolism Kidney Excretion

Clinically Utilized Drug Targeting Strategies

Targeting Approaches There is a search dual-mode probes that can detect a tumor imaging) and destroy it (therapy) Redox-potential Ultrasound Temperature DRUG PROBE pH-sensitive DRUG PROBE DRUG PROBE Physical Targeting Active Targeting Passive Targeting Based on nanoparticle functionalization for specific targeting of disease cells Based on retention effect of particle of certain hydrodynamic size in cancerous tissues (e.g. Doxil) Proteins (antibodies and their fragments such as TAT), nucleic acids (aptamers), receptor ligands (peptides, vitamins, and carbohydrates

EPR: Taking advantage of retention A. Tumorous tissues suffer of Enhanced Permeability and Retention effect (RES) B. Nanoparticles injected in the blood stream do not permeate through healthy tissues C. Blood vessels in the surrounding of tumorous tissues are defective and porous D. Nanoparticles injected in the blood permeate through blood vessels toward tumorous tissues, wherein they accumulate Annu. Rev. Biomed. Eng. 2007. Vol. 9, pp. 257–88

Clinical Example of EPR Doxil is a polyethylene glycol coated liposomal formulation of doxorubicin. Marketed by Ben Venue Laboratories  of J&J. Outside the US, Doxil is known as Caelyx (Janssen). Approved by the FDA for treatment of ovarian cancer and multiple myeloma and an AIDS-related cancer.