THE CHEMISTRY OF DRUG DELIVERY SYSTEMS (hoá học các hệ dẫn truyền thuốc)

Đây là bài giảng về hoá học các hệ dẫn truyền thuốc dành cho các lớp cao học của Dr. Le Thanh Dung, bài giảng được trình bày bằng tiếng Anh giúp các bạn tiếp cận với cách trình bày bằng tiếng anh trong các bài báo cáo khoa học của mình, bài rất hay.

Email: ltdung@hcmut.edu.vn

OBJECTIVES

On the completion of this course, the student should be able

to have a deep understanding of the chemical aspects of drug delivery systems that have recently attracted attention from the chemistry and chemical engineering community

EVALUATION

 Seminar: 70%

 Final exam: 30%

Students have to work in group for the preparation and the presentation

of their seminar subject Evaluation will be given based on individual contribution (preparation, discussion), the oral presentation and the answers to the questions

Students will receive a publication on drug delivery system at least one week before the day of the exam The exam questions will be based on the given article

REFERENCES

1 Martin Malmsten, Surfactants and polymers in drug delivery,

Marcel Dekker, New York, 2002

2 Glen S Kwon, Polymeric drug delivery systems, Taylor &

Francis Group, New York, 2005

3 Ram B Gupta, Uday B Kompella, Nanoparticle technology for

drug delivery, Taylor & Francis Group, New York, 2006

4 Publications in Elsevier, Royal Society of Chemistry, American Chemical Society, Wiley InterScience journals…

CONTENTS

1 Generalities of drug delivery

2 Liposomes as drug delivery systems

3 Polymers and polymeric systems for drug delivery

4 Dendrimers for drug delivery

GENERALITIES OF DRUG DELIVERY

DRUG DELIVERY SYSTEM

brings a therapeutic agent to a specific body site at a certain rate to achive an effective concentration at the site of drug action

ROUTES OF DRUG ADMINISTRATION

Topical delivery

ORAL DELIVERY (GASTROINTESTINAL ADMINISTRATION)

ORAL DELIVERY (GASTROINTESTINAL ADMINISTRATION)

 poorly absorption of large, highly charged molecules

 degradation of drug by stomach acid, various enzymes in the GI tract

ORAL DELIVERY (GASTROINTESTINAL ADMINISTRATION)

Dosage forms:

 liquids (rapid aborsoped)

 dispersed systems: emulsions, suspensions

 solids (less absorped): powders, tablets, caplets, capsules

 controlled release drug delivery systems

TRANSDERMAL ADMINISTRATION

Advantages:

 solution for drugs that can not be administered by oral delivery

 reliability, precision of dosage

 time control of the onset of action

MUCOSAL DRUG DELIVERY

Advantages:

 avoid the first-pass effect of drug cleareance

ORAL MUCOSAL ROUTE

SUBLINGUAL AND BUCCAL DELIVERY

High permeability Less permeability

Higher rate of absorption Low rate of absorption

Higher drug bioavailability Low drug bioavailability

Rapid onset of action Sustained-release approaches

Constantly washed by saliva Relatively immobile

More permeable drug Less permeable drug (peptides)

Not include penetration enhancers Normally include penetration enhancers

What do you know about saliva?

 Saliva: protective aqueous fluid, 1% organic & 99% inorganic materials

 Salivary pH: 5.5 – 7 depending on the flow rate

Flow rate increases  [HCO3] increases  pH increases

 Daily salivary volume: 0.5 – 2 L

Oral cavity is a water-rich environment Selection of hydrophylic matrices as drug carriers

PULMONARY ADMINISTRATION

Large mucosal surface of respitory system for drug absorption

« Taking advantage of the body’s ability to transfer large molecules through the lung is a better way to deliver drugs than sticking people with needles »

Patton, Chemtech 1997, 27, 34

PULMONARY ADMINISTRATION

Advantages:

 larger surface area (70 m2)

 very fast onset of action (comparable to intravenous route)

Disadvantages:

 lack of reproducibility of the administered dose

 variable rate of absorption of drug at different regions

TRANSDERMAL AND TOPICAL ADMINISTRATION

STRUCTURE OF THE SKIN

TRANSDERMAL AND TOPICAL ADMINISTRATION

STRUCTURE OF THE SKIN Epidermis structure:

TRANSDERMAL AND TOPICAL ADMINISTRATION

STRUCTURE OF THE SKIN Stratum corneum structure:

Penetration barriers: lipid self-assemblies in the stratum

corneum (10%)

TRANSDERMAL AND TOPICAL ADMINISTRATION

PERMEABILITY ENHANCEMENT

 By surfactant-based formulations (penetration enhancers,

liposomes,…):

 By hydration of the stratum corneum:

Surfactant-based formulations can interact with lipids and alter

their structure  enhance drug penetration

Water can interact with the polar headgroups of lipids through hydrogen

bonding  loosen the lipid packing  the lipid region becomes more fluid

 Enhance drug penetration

PENETRATION ENHANCEMENT

Barry, Int J Cosmet Sci 1988, 10, 281

PENETRATION (PERMEABILITY) ENHANCERS Definition:

Compounds that promote the absorption of drugs through the skin or mucosae, usually by reversibly altering the permeability of the barrier

PENETRATION (PERMEABILITY) ENHANCERS Common penetration enhancers:

Aprotinin

Dextrans

PENETRATION (PERMEABILITY) ENHANCERS Common penetration enhancers:

SELECTION OF ROUTE OF DRUG

ADMINISTRATION

 Affects the onset and duration of drug action

 Depends on the desired drug concentration profiles to be achieve, patient and disease

Ex: Administration of nitroglycerin

CLASSIFICATION OF DRUG DELIVERY SYSTEM

By the way of delivery:

 Targeted drug delivery systems: deliver drug to a desired

body location, organ, tissue, specific cells…

 Controlled-release drug delivery systems: preprogramed

drug release

By the route of delivery:

 Topical (local) drug delivery systems: drugs are delivered

locally to the target organ/tissue without entering the

systemic circulation

 Systemic drug delivery systems: drugs are delivered to

the whole body via the general blood circulation

DIFFERENT KINDS OF DRUG

Tablets, pills Capsules Suppositories

Creams

Repeat administration Fluctuation of drug concentration in the body

DRUG RELEASE PROFILE FLUCTUATION IN DRUG CONCENTRATION

A 1 A 2

A 3

A 4 Drug concentration

Frequencies of dosing

B Toxic level

Adverse side effects

PRODRUG

 Prodrug is an inactive precursor of a drug

 Prodrug reconversion occurs in the body inside a specific

organ, tissue or cell

What is a prodrug?

Prodrug = Drug + Drug delivery system

How to design a prodrug?

 Increase solubility or absorption

 Increase chemical and metabolic stability

 Mask irritation or taste

MAIN TYPES OF PRODRUGS FOR

TARGETED DRUG DELIVERY

(a): Classic prodrugs: prodrugs are transformed into one or

more active substances inside the cell

(b): Two or more substances react to form the active drug under specific intracellular conditions

(c): Advanced forms of prodrugs containing 3 components

ADVANCED FORMS OF PRODRUGS

 Carrier: binding other components and altering the

physicochemical properties (ex solubility) of prodrug

 Targeting moiety:  enhancing the specific activity of the drug

ADVANTAGES OF PRODRUG OF TYPE (c)

 The conditions of drug release can be precisely controlled by modifying the bonds and each constituent

 Prevent the degradation of the active component, reduce its total body clearance

 Release the drug inside targeted cells

DRUG DELIVERY SYSTEMS

LIPOSOMES IN DRUG DELIVERY

WHAT ARE LIPOSOMES?

 First described by Bangham and Horne after their study of lipid phase structures in the electron microscope in 1964

Bangham, Horne, J Mol Biol 1964, 8, 660

 Liposomes are concentric bilayered vesicles in which an

 Liposomes are formed spontaneously when lipids are dispersed

in an aqueous medium (auto-assembly)

Why liposmes are used in drug delivery ?

Phospholipid bilayer

Aqueous cavity

Polar head group

Hydrophobic tail

 Storage ability of hydrophilic substances in the aqueous cavity

and hydrophobic drugs in the membrane

 Similarity of structure to phospholipid membranes in living cells

 Avoid the hydrolytic degradation of drugs in water

 Reduce the RES uptake due to the rapid clearance of drugs

from bloodstream circulation (especially in intravenous administration)

STRUCTURAL COMPONENTS OF LIPOSOMES

 The main components of liposomes are phospholipids and

sterols

 Phospholipids are the major strutural components of

biological membranes such as cell membranes

 The most common phospholipids in biological membranes:

 Phosphoglycerides

 Sphingolipids

SPHINGOLIPIDS

Sphingosine

Sphingolipids

N-acylsphingosine, ceramide

R 2 = polar head group

STEROLS

Basic core of sterols

Cholesterol

 Fluidity buffer for membrane with respect to temperature

 Hydroxyl group in position 3 allows functionalization by various functional groups

INFLUENCE OF CHOLESTEROL

ON THE STABILITY OF LIPOSOMES

 Reduce the membrane permeability of phospholipid bilayers

Needham and Nunn, 1990

Grit and Crommelin, 1993

Increase the stability of liposomes in vitro and in vivo

Cholesterol is added in lipid mixtures used to produce

Lamellar phase

Inverse micelles

CLASSIFICATION OF LIPOSOMES

Liposomes are classified depending on their size

Liposomes SUVs - Small

Uni-lamellar Vesicles

LUVs - Large Uni-lamellar Vesicles

MLVs – Multilamellar Large Vesicles Diameter

(nm)

Cross

section

PREPARATION OF LIPOSOME

DELIVERY SYSTEM

By the lipid film rehydration method

Minko et al J Appl Physiol 2002, 93, 1550 Pakunlu et al Pharm Res 2003, 20, 351

MLVs

Sonication

22 kHz SUVs

Filters SUVs of

homogenous size

Lipid-soluble drug Water-soluble drug

PHYSICOCHEMICAL PROPERTIES

OF LIPOSOMES

Phase transition Temperature (Tc)

Gel phase (solid) Liquid crystalline phase (fluid)

 Better ability of self-assembly

 Higher permeability to aqueous solution

Tc depends on the properties of lipids:

polarity

structure of fatty acid chain (length, level of unsaturation,

branching, presence of cycles)

adsorption of ions or proteins

Viniegra et al Int J Biochem 1984 Papahadjopoulos et al Biochim Biophys Acta 1973

INCORPORATION OF DRUGS IN LIPOSOMES

 Through a drug concentration gradient

 Before the formation of liposomes

 Through a pH gradient

Drug: weak base

ACTIVE LOADING OF DRUG INTO PREFORMED

LIPOSOMES BY pH GRADIENT

ACTIVE LOADING OF DRUG INTO PREFORMED

LIPOSOMES BY pH GRADIENT Drug = weak base:

Doxorubicin Adriamycin (cancer chemotherapy)

Vincristine (cancer chemotherapy)

CHARACTERIZATION OF LIPOSOME SYSTEMS

Properties of liposomes Analysis

Physical size, shape and its distribution Cryo-TEM

Laser light scattering Size exclusion chromatography (SEC) NMR

Surface charge, zeta potential Free flow electrophoresis

Extent of drug entrapped Size exclusion chromatography (SEC)

NMR Entrapped volume/lipid weight NMR

Carboxyfluorescene

31 P NMR Phase transition temperature (Tc) Differential scanning calorimetry (DSC)

Purity of phospholipids Thin layer chromatography (TLC)

HPLC NMR

CHARACTERIZATION OF LIPOSOME SYSTEMS

 Light scattering techniques

 NMR

 Cryogenic transmission electron microscopy (Cryo-TEM)

 Differential Scanning Calorimetry (DSC)

 Drug release

 Fluorescene spectroscopy

CONTROL OF LIPOSOME FORMATION BY NMR

By 31 P solid-state NMR:

DSPC: DPPE-PEG2000 :cholesterol = 60: 15 :25 mol%

High PEG-lipid content

C Leal et al J Colloid Interface Sci 2008, 325, 485

By 31 P solid-state NMR:

DSPC: DPPE-PEG5000 :cholesterol = 78: 4.5 :17.5 mol%

65  C Low PEG-lipid content

C Leal et al J Colloid Interface Sci 2008, 325, 485

CONTROL OF LIPOSOME FORMATION BY NMR

By 31 P solid-state NMR:

DSPC: DPPE-PEG2000 :cholesterol = 67: 8 :25 mol%

65  C Intermediate PEG-lipid content

C Leal et al J Colloid Interface Sci 2008, 325, 485

CONTROL OF LIPOSOME FORMATION BY NMR

C Leal et al J Colloid Interface Sci 2008, 325, 485

DSPC: DPPE-PEG2000 :cholesterol

65  C

By 31 P solid-state NMR:

The higher the PEG-lipid content, the smaller the micelles are

CONTROL OF LIPOSOME FORMATION BY NMR

M Delcea et al http://arxiv.org/abs/0904.1662v1, 2009

By 1 H NMR:

CONTROL OF LIPOSOME FORMATION BY NMR

DOPC lipid in chloroform DOPC vesicles in HEPES buffer Also confirmed by DOSY NMR

M Delcea et al http://arxiv.org/abs/0904.1662v1, 2009

By 1 H NMR:

CONTROL OF LIPOSOME FORMATION BY NMR

The higher the line width, the bigger the molecules are

DMPG vesicles in HEPES buffer Also confirmed by DOSY NMR

DMPG lipid in chloroform

EVALUATION OF LIPOSOME SIZE BY DIFFUSION NMR SPECTROSCOPY

 The (mean) hydrodynamic radius R of a particle can be derived

DIFFUSION ORDERED SPECTROSCOPY (DOSY)

– NMR CHROMATOGRAPHY

 Means for “virtual separation” of compounds

 One axis is the chemical shift, the other is that of the diffusion

coefficient

2D DOSY spectrum

Y Cohen et al Angew Chem Int Ed 2005, 44, 520

EVALUATION OF LIPOSOME SIZE BY

DIFFUSION NMR SPECTROSCOPY

C Leal et al J Colloid Interface Sci 2008, 325, 485

EVALUATION OF LIPOSOME SIZE BY

EVALUATION OF LIPOSOME SIZE BY DIFFUSION NMR SPECTROSCOPY

C Leal et al J Colloid Interface Sci 2008, 325, 485

CPEG: PEG-lipid content in the liposomes

DLIP/10 12, DMIC/10 12 : micelle and liposome diffusion coefficients x 10 12

dLIP, dMIC: micelle and liposome diameters

dPCS : liposome diameters obtained by photon correlation spectroscopy

 MIC: fraction of micelles

EVALUATION OF DRUG ENCAPSULATION BY

DIFFUSION NMR SPECTROSCOPY

Y Cohen et al Angew Chem Int Ed 2005, 44, 520

Principles:

 Drug size << liposome size

 In free state: Ddrug >> Dliposome

 In encapsulated state: Ddrug  Dliposome

The quantity of drug encapsulated in liposomes can be evaluated

CRYOGENIC TRANSMISSION ELECTRON

MICROSCOPY (CRYO-TEM)

CRYOGENIC TRANSMISSION ELECTRON

MICROSCOPY (CRYO-TEM) Information:

state

Applications:

 Identify new morphologies and phases in the solution state

 Characterize the interplay between different objets in solution

 Used as complement to scattering techiniques:

 to improve the modeling of scattering data

 to discern the polydispersity in size and shape of assembled structure

 characterize intermediate structures

Zhong and Pochan, Polym Rev 2010, 50, 287

CRYOGENIC TRANSMISSION ELECTRON

MICROSCOPY (CRYO-TEM) Advantages:

Zhong and Pochan, Polym Rev 2010, 50, 287

 characterize in situ, in the solution state

 without the need of modeling as required in scattering

techniques (neutron, X-ray, light scattering)

Disadvantages:

 heavy technical skills for sample preparation and observation

CRYOGENIC TRANSMISSION ELECTRON

MICROSCOPY (CRYO-TEM)

Sample preparation:

 place a drop of sample onto an EM-grid

 remove excess solution by a filter paper, leaving a thin film of the solution on the EM-grid

 Plunge rapidly the grid into liquid ethane held just above the freezing point (cooled by liquide nitrogen) to vitrify the sample and avoid sample’s crystallization

 Transfer the vitrified sample at low temperature to the

microscope

CRYOGENIC TRANSMISSION ELECTRON

MICROSCOPY (CRYO-TEM) Sample preparation:

CRYO-TEM IMAGES OF LIPOSOMES FORMED BY

EPC : CHOLESTEROL = 60 : 40 MOL%

Edwards et al Biophys J 1997, 73, 258

EPC: egg yolk lecithin

Liposomes have spherical shapes

Ice crystal deposited on the sample surface after vitrification

100 nm