Drug Delivery Systems: Biological Approaches PDF

Drug Delivery Systems: Dr. Mohammad Obeid Ayasrah E-Mail: [email protected] 1 The Biological approach: The concept of drug carriers The biological approach includes the use of biological material for controlled drug delivery. Drug targeting...

Drug Delivery Systems: Dr. Mohammad Obeid Ayasrah E-Mail: [email protected] 1 The Biological approach: The concept of drug carriers The biological approach includes the use of biological material for controlled drug delivery. Drug targeting using biological carriers have been used to enhance the effectiveness and reduce side effects of drugs. Biological carriers include: liposomes and other nanoparticles, polysaccharides, lipoprotein, and glycoproteins. Examples of drugs incorporated into biological carriers include: methotrexate and Adriamycin as well as agents which are of macromolecular size such as enzymes and nucleic acids. 2 The biological carrier can be used to achieve the following: - Sustained and controlled systemic drug levels - Can introduce the drug directly into the systemic system (selective distribution) - Can produce localized drug action by introducing carrier into appropriate organ or body cavity - Liposomes can promote the cellular uptake of drugs that don't penetrate cell membrane easily - Biological carrier used to deliver agents which are of macromolecular size such as enzymes and nucleic acid - Can be combined with antibodies to develop target drug carrier complex - Protect the drug from degradation (stabilization) - Reduce side effect of drugs and decrease nonspecific cytotoxicity - Changing the agent’s solubility - Reduction in immunogenicity & antigenicity of enzymes. 3 3 Characteristics of a carrier system The properties of a carrier system may vary from one application to another depending on the drug (or enzyme) used. However there are general characteristics that a drug-carrier system must possess: 1.The carrier-agent conjugate must retain the agent’s activity (unless it can be degraded at the site of desired action with the release of the agent in its active form). 2.The carrier must be biocompatible (i.e., non-toxic, non-immunogenic and non antigenic) should not change the antigenicity of the compound carried. 3.The carrier must be biodegradable 4.The carrier must retain its own desirable characteristics following conjugation with a drug. E.g. antibodies must retain their ability to complex to a specific antigen 4 Questions to be made when developing DDS using Biological Approach 1. What is the mode of action of a carrier- drug combination? 2. How does the conjugate act, is it on plasma, cell surface or within the cells of target tissue? 3. Is the drug exhibiting intracellular action when transported into the cell? Is this action due drug alone or due to the combination with the carrier? (i.e.) is the agent acting within the cell as part of conjugate or does it act following its cleavage from the carrier? 4. Are carriers specific or non-specific? 5. What are the chemical linkages between drug and the carrier?  Answers to these questions are essential for the rational development of drug- carrier combination. 5 5 Types of carriers 1. Specific: carriers of highly specific binding to cell surface receptors. These are used to direct drugs or enzymes to cells bearing specific receptors, such as antibodies. 2. Non-specific: Carriers that do not have high specificity of binding. The majority of carriers are of this type. Such carriers are normally taken by cells by phagocytosis.  In this case, the target cells should have a well-developed phagocytic function. 6 In order to have better therapeutic effect with less side effects, we need the target cells to have a well-developed phagocytic function, while non-target cells to have less well developed phagocytic function. 7 SEM images showing the phagocytosis of microparticles by macrophages: (d) Microparticles lying on the cell surface, (e&f) being phagocyted and (g&h) allegedly located inside the cell. 8 The cross-linking between the carrier & drug molecules could be: 1. Covalent binding 2. Non - covalent (i.e., entrapment or encapsulation of the drug). The desirable characteristics of the cross linkage reaction: 1. The reaction should allow effective control of the size of drug - carrier complex. 2. It should maintain the site specificity of the carrier portion. 3. It should not change the normal activity of the drug or enzyme. 4. The cross-linking must be readily broken if the drug is to be released. 9 The distribution of non- specific carriers in vivo depends on the following properties: 1.Size & size distribution of the carrier 0.1- 7.0 μm  goes for liver, spleen and kidney < 0.1 μm  to bone marrow > 7 μm  lung (circulation, monocyte) 2.Lipophilicity & hydrophilicity of the carrier The more hydrophobic carriers go to the liver. 3.Surface charge of the carrier The more negatively charged carriers go to the liver. 10 The use of nanoparticles in drug delivery Nanoparticles have different classifications, some based on particle size, shape, and origin, while others are based on chemical structure as either organic or non-organic. However, regardless of the classification, nanoparticles possess pertinent features, namely their high surface-to-volume ratio, which is much greater than other particles (such as micron- or larger-sized particles). This feature provides nano-sized particles with a very limited volume for transportation of cargo, but a large surface area for interactions with biological membranes. 11 12 The use of nanoparticles in drug delivery The major challenge in drug delivery is to get the drug to the site of action and avoiding off-target, collateral effects on non-diseased tissues. This is critical in improving chemotherapies where for example tumour metastases may lie deep in different organs. In terms of drug targeting, nanoparticles have different characteristics, such as controllable size, which facilitate accumulation in tumour tissues, enable penetration of different biological barriers and cell membranes. Furthermore, after delivering their payload, nanoparticles should be eliminated from the body safely and in a reasonable time with minimal side effects. Therefore, the ideal nanoparticle should be non-toxic, biocompatible, biodegradable, non-immunogenic, and be able to escape early hepatic or renal clearance. All these properties make nanoparticles an optimal drug carrier. 13 The use of nanoparticles in drug delivery AmBisome (liposomal amphotericin B, used to treat cancer patients with fungal infections) and Doxil (liposomal doxorubicin) were among the first anti-cancer medications on the market using lipid-based nanoparticles. The US Food and Drug Administration (FDA) have approved several nanoparticle-based drugs for human use with many others now in different phases of clinical development. It is believed that nanotechnology-based drug delivery will have a growing share of the anticancer therapeutics in the coming years. 14 Types of Nanoparticles for Drug Delivery There are many types of nanoparticles used for drug delivery, among them include:  Lipid-based nanoparticles such as liposomes, niosomes, and micelles.  Silica nanoparticles  Quantum dot  Amphiphilic nanoparticles  Dendrimers  Carbon nanotubes  Metal-core nanoparticles such as gold nanoparticles  Oligopeptides  Poly (lactic-so-glycolic acid) (PLGA) 15 16 Liposomes : HISTORICAL BACKGROUND  1965: Discovery by Alex Bangham , who was studying phospholipids from biological membranes.  Phospholipids + Formation of Water spherical structures (in excess) (onion-shaped vesicle): Water LIPOSOMES Water Liposomes : HISTORICAL BACKGROUND Bangham found that liposomes shrink in hypertonic media & swell in hypotonic media; i.e., acting as “osmometers”. This indicated that the liposomal membrane is semipermeable; as cell membranes. Bangham and his coworkers studied liposomes and used them as models for cell membranes. Since then, liposomes became very versatile tools in biology, biochemistry and medicine. 18 Liposomes : HISTORICAL BACKGROUND  From the 1970s: study of liposomes for the delivery of drugs to specific sites of the body Over 30 000 articles published to date  In the 1990s: liposomal formulations on the market - Amphotericin B (AmBisome ®) - Cytarabine (DepoCyt ® ) WHAT IS A LIPOSOME? Lipid bilayer membrane Aqueous compartment = Spherical vesicles in which a lipid bilayer membrane delimitates a central aqueous compartment WHAT IS A LIPOSOME? Lipid bilayer membrane Aqueous compartment Hydrophilic drug Antibody Lipophilic drug = Spherical vesicles in which a lipid bilayer membrane delimitates a central aqueous compartment Encapsulation of drugs WHAT IS A LIPOSOME? 4 to 5 nm From 15 to 1000 nm = Spherical vesicles in which a lipid bilayer membrane delimitates a central aqueous compartment Encapsulation of drugs LIPID COMPOSITION  Phospholipids -major structural component of a liposome O Phosphate R 2 C group O CH 2 O CH O Glycerol or R 1 C p CH 2 O R Fatty O O acids LIPID COMPOSITION  Phospholipids Major structural component of a liposome O O R 2 Phosphate C R C 2 O group CH O CH 2 Hydrophilic 2 O CH O O CH O Glycerol R C or p R 1 C p 1 CH O R CH 2 O R 2 O O O Fatty O Hydrophobic acids LIPID COMPOSITION Phospholipids  Phospholipids are the basic building block of every cell membrane in the human body.  There are two types of phospholipids in our bodies, existing together with their metabolites: 1. Sphingosine based (sphingomeylin): do not form liposomes. 2. Glycerol based (phosphoglycerides), which are of two types:  Monacylphosphglycerides: do not form liposomes.  Diacyl phosphglyceride: form liposomes. These include: phosphatidyl choline (PC; Lecithin) and phosphatidyl ethanolamine (PE; Cephalin). 25 LIPID COMPOSITION O R2 C O CH 2 O CH O R1 C CH 2 O p R O O Common Name: Phosphatidyl- (suffix) Where R is: Name of head Phospholipid name group OH Acid Phosphatidic acid CH3 Choline Phosphatidylcholine OCH2 CH2 NCH3 CH3 Ethanolamine Phosphatidyl- OCH2 CH2 NH3 ethanolamine OCH2 CH CH2 Glycerol Phosphatidylglycerol OH OH Serine Phosphatidylserine NH3 OCH COO LIPID COMPOSITION O R1 C O CH2 O CH O CH3 R2 C C O p OCH2 CH2 NCH3 O O CH3 Phosphatidylcholine Common name: (prefix)-phosphatidylcholine Where R and R are: Name of 1 2 Phospholipid name fatty acid O C Myristic Dimyristoylphosphatidylcholine O C Palmitic Dipalmitoylphosphatidylcholine O C Stearic Distearoylphosphatidylcholine O C Oleic Dioleoylphosphatidylcholine O C Linolenic Dilinoleoylphosphatidylcholine Liposomes formation Liposomes are formed spontaneously (within fractions of a second) when phospholipids are dispersed in aqueous media, in order to reduce their surface free energy, because this the most thermodynamically stable aggregation. When phospholipids are placed in an aqueous media the hydrophilic heads of the phospholipids line together, side by side with their tails behind, forming a monolayer, as shown here. 28  Liposomes formation Another phospholipid layer will line itself up tail-to-tail, in response to the same aqueous environment, forming a tightly fitted phospholipid bilayer, as shown below. This phospholipid bilayers is similar to that forming the the biological membranes in our bodies (each bilayer is about (1/1000) the thickness of a page; i.e., in the range of 4-5 nm). Phospholipids aggregate into a bilayer shape due to their cylindrical geometry. 29 Liposomes formation In order to prevent any hydrophobic contact with water (i.e., to further reduce surface free energy), the bilayers fold on themselves, forming long tubules, which upon slight shaking, break down forming “liposomes”. 30 Liposomes formation Phospholipid chemistry determines the bilayer permeability of the liposome Effect on drug entrapment Below phospholipid phase Above phospholipid phase transition temperature transition temperature +DT - DT Solid (gel) phase Liquid crystalline phase Liposomes formation Phase transition temperature is influenced by:  Hydrocarbon chain length of fatty acids (PT increases with increasing chain length)  Degree of fatty acid insaturation (PT increases with increasing saturation)  Phospholipid head group Liposomes formation  Sterols  Most commonly used sterol: cholesterol - Low biological toxicity - Inexpensive and available in high purity grades  Used to improve the mechanical strength of the bilayer (optimal : equimolar concentration to phospholipids) Above phospholipid phase transition temperature + Chol - Chol SIZE AND NUMBER OF LIPID BILAYERS Liposome morphology controlled by:  manufacturing technique :++++++  chemical composition :+ Three types of liposomal structure CLASSIFICATION OF LIPOSOMES Multilamellar vesicles (MLV) - number of concentric bilayers - size range: 200-1000 nm -usually composed of 5 or more bilayers Unilamellar vesicles (ULV) - single bilayer - size range: up to 1000 nm Small unilamellar vesicles (SUV) - single bilayer - size range: 15-50 nm SIZE AND NUMBER OF LIPID BILAYERS As liposomal size decreases, the drug payload per mass of lipid decreases Note that:  MLVs are the easiest to prepare, and they were the first to be prepared by Bangham.  SUVs may be prepared from MLVs by sonication.  ULVs are the most difficult to prepare, because they consist of single bilayer membrane holding large volume of aqueous space.  SUV are the least physically stable, as they tend to undergo vesicle to vesicle fusion more readily than MLVs or LUVs, due to their high radius of curvature and to the asymmetry of lipid distribution between the two monolayers. 37  Images of multilamellar liposomes Freeze Fracture Electron Microscopy Typical liposomes as observed under the bright field microscope 38  Images of unilamellar vesicles Freeze Fracture Negative staining Electron Microscopy Electron Microscopy 39  The average size and size distribution of liposomes is very important because it influences: physical properties, biological fate, and entrapment capacity Since the body is literally held together with phospholipids, these liposomal spheres are readily accepted by the body as essential building materials. Because of their tiny size, they are able to be quickly assimilated into the bloodstream for delivery throughout the body. Then, as a needy cell "borrows" the fresh phospholipid molecules from the liposome for rebuilding, the contents of the liposome are delivered to the same needy cells. 40 Stability of Liposomes Phospholipids are susceptible to hydrolytic and oxidative degradations, which could affect their physical stability and permeability. Although liposomes are thermodynamically stable, there are several circumstances where liposomes instability can occur:  Liposomes containing acidic lipids can undergo vesicle to vesicle fusion in presence of Ca+2.  SUVs represent a somewhat unstable configuration because of the strain induced in the membrane by their small radius of curvature.  Liposomes are unstable when subjected to mechanical force or ultrasonication or hydrodynamic shear that can rapidly release their contents & reduce their size. 41 Liposomes as drug carriers Liposomes have shown a great potential as drug carriers due to following:  They are biocompatible & biodegradable.  They can entrap a wide range of drugs (within their aqueous compartments or within the lipid membrane) and subsequently release them at variable rate.  They generally provide better controlled delivery of drugs or enzymes; enhancing their efficacy and reducing their adverse effects  They can be administered by different routes as: oral, parenteral, nasal, and topical to skin & eye.  They may be introduced into cells by different mechanisms such as endocytosis and fusion.  They were reported to enhance in vivo stability of entrapped drugs and enzymes. 42  Their size, lamellarity, and lipid composition influence many of their important properties like fluidity, permeability, stability and structure. These can be customized to serve specific needs. Their properties are also influenced by external parameters like temperature, ionic strength and presence of certain molecules nearby. It is the sub-microscopic liposomes that are actually used in Liposomal Technology, which are able to be quickly assimilated into bloodstream for the delivery throughout the body. 43 Drug incorporation into liposomes The ability to incorporate drugs into liposomes depends on the characteristics of liposomes as well as on the drug’s physicochemical properties. Polar drugs are entrapped within the aqueous compartments and non-polar drugs are incorporate in the lipid membrane. 44 Drug incorporation into liposomes The ability to incorporate drugs into liposomes depends not only on the characteristics of the liposomes but also on the chemical and physical properties of the drug Polar drugs such as methotroxate or fluorodeoxyuridine are trapped within the internal aqueous compartment of liposome Non polar drugs as actinomycin D or vinblastine bind to lipid membrane of the vesicles. Polar drugs are released from liposomes when the bilayer membrane has been bleached Non polar drugs remain attached with liposomes unless there is a gross disruption of the membrane structure 45 45  Non polar drugs can cause marked changes in the physical properties of liposomes membrane. Despite these differences, the encapsulation of both polar and non polar drugs shares a number of properties. For example, the efflux of both types polar and non polar drugs is maximal at the lipid phase transition. 46 46 THANK YOU 47