BONE MARROW TARGETING AND TARGETING TO LYSOSOMAL DISEASES

By

SOMESHWAR.K M.PHARM.

II - SEMESTER

Department of PharmaceuticsUniversity College of Pharmaceutical

Sciences,KAKATIYA UNIVERSITY

Warangal - 506009

CONTENTS

Introduction Physiology of bone marrow Bone marrow targets for drug delivery Colloidal carriers for bone marrow targeting Nanospheres/nanoparticles Liposomes Lysosomal storage diseases Targeting exogenous enzymes Conclusion References

INTRODUCTION

The main problems currently associated with systemic drug administration are: 1. Even biodistribution of pharmaceuticals throughout

the body;

2. The lack of drug specific affinity toward a pathological site;

3. The necessity of a large total dose of a drug;

4. Non-specific toxicity and other adverse side-effects.

Drug targeting Targeted drug delivery (TDD) is an event

where, a drug-carrier complex or conjugate delivers the drug(s) exclusively to preselected cells in a specified manner.

TDD implies for selective and effective localization of pharmacologically active moiety at a predetermined target in a therapeutic concentration, while restricting its access to non-target normal cellular linings, thus minimizing the toxic effects and maximizing therapeutic index.

The concept of drug targeting includes a coordinated behavior of three components:

(a) Drug;

(b) Targeting moiety - cell, tissue, inside of a cell, etc.

(c) Pharmaceutical carrier - colloidal carriers, cellular carriers, polymer

based systems, macromolecular carriers.

LEVELS OF TARGETING Passive targeting

Inverse targeting

Active targeting - First order targeting - Second order targeting - Third order targeting

Physical targeting

Dual targeting

PHYSIOLOGY OF BONE MARROW Bone marrow is the flexible tissue found in the hollowinterior of bones. In adults, marrow in large bones producesnew blood cells. It constitutes 4% of total body weight, i.e.approximately 2.6 kg in adults.

There are two types of bone marrow: - Red marrow - Yellow marrow

Red bone marrow consists of hematopoietic or blood forming tissue which produces white blood cells and red blood cells.

Within the marrow haemopoietic progenitor cells at various stages of development replenish the peripheral blood cells populations.

The major vascular constituents of bone marrow are called as sinuses.

These blood vessels are relatively large forming a barrier i.e. Marrow Blood Barrier (MBB) between the Hematopoietic compartment and the circulation.

The walls of MBB consists of continuous endothelium and a discontinuous adventitial cell layer . The MBB serves to control cellular traffic in and out of the marrow.

BONE MARROW TARGETS FOR DRUG DELIVERY

The RES of organism is usually very effective in removing small foreign colloidal particles administered intravenously.

The kupffer cells of liver and the macrophages of the spleen constitute 80-95% of phagocytic cells of this system and it is here that the particles are normally deposited.

For the particles to reach the bone marrow this uptake by kupffer cells and macrophages should be prevented.

1. Reticuloendothelial system (RES)

The endothelium of bone marrow sinusoids removes particulate materials from the blood.

The endothelium is not only capable of phagocytic uptake and storage of particles but also provides for the transmural passage of particulate material to the extra vascular spaces where the particles are phagocytosed by central macrophages.

2. Sinusoidal capillaries

.

Capillary endothelial barrier

MARROW (STEM CELL) TRANSPLANTATION The homing of progenitor cells to the marrow has

provided the basis for treatment of certain diseases of haemopoietic origin by bone marrow transplantation.

Certain genetic diseases which are characterised by a generalized absence of a specific enzyme such as adenosine deaminase (ADA) deficiency in severe combined immunodeficiency, and glucose cerebrosidase deficiency in Gaucher’s disease are treated.

COLLOIDAL CARRIERS FOR BONE MARROW TARGETING

The ability of the bone marrow to remove the particulate matters from the circulation, opens up an idea for the delivery of therapeutic agents by means of colloidal drug carrier systems such as

Liposomes Nanospheres Emulsions Microspheres

With all these carrier systems a high proportions of the dose still reaches the liver and spleen within few minutes after intravenous administration.

Since intravenously administered colloidal particles are normally removed efficiently by RES cells of liver and spleen , only a small fraction of these particles reaches the bone marrow.

Modification of the surfaces of the particles by a polymer in order to provide a hydrophilic barrier minimize the uptake of the plasma components.

E.g. poly(ethylene oxide) (PEO), polysorbate (Tween-80) and lauryl ethers (Brij-35).

NANOSPHERES/NANOPARTICLES

Poloxomer 407 Non-ionic block copolymer.

It contains a central block of hydrophobic polyoxypropylene ( POP) flanked by blocks of hydrophilic polyoxyethylene (POE).

Polystyrene microspheres are surface labeled with iodine-131 .these labeled particles are incubated for 24hours with a 2% w/v solution of poloxomer 407.

This provides a coating layer over the particles

Both the coated and uncoated particles were administered intravenously to rabbits.

The blood samples were taken and radioactivity was measured using gamma counter.

Gamma camera scans of rabbits clearly demonstrated that the uncoated polystyrene particles were largely taken up by liver and spleen after injection while the Poloxomer 407 coated particles were apparently deposited in bone marrow.

The uptake of uncoated particles by liver/spleen region occurred rapidly and efficiently with 90% of the particles being deposited in these organs within 2 min.

The Poloxomer 407 coated particles showed a marked decreased liver/spleen activity.

Polyalkylcyanoacrylate nanoparticles (Gibaud Et al., 1999) Doxorubicin & stimulating growth factor (rhG-CSF) are the

model compounds

Histological studies showed rapid capture of nanoparticles by bone marrow macrophages as soon as 15 min after injection

Doxorubicin nanoparticles administered were more toxic than free doxorubicin on all blood and marrow cells

LIPOSOMES

Phospholipids vesicles (Liposomes) have been widely investigated as potential carriers for drugs, genes , proteins because their capsular structure permits encapsulation of various therapeutic agents.

Advantage of using Liposomes as drug delivery carriers is that their pharmacokinetics can be controlled by modifying surface characteristics.

Liposomes composed of equimolar amounts of cholesterol and either saturated phospholipids or sphingomyelin exhibited low tendency for accumulation in kupffer cells following intravascular administration.

Their uptake from blood to spleen and bone marrow remains relatively high.

25% of the injected dose of vesicles, formed from equimolar amounts of cholesterol and disteroyl phosphatidylcholine , were localized in rat bone marrow 72 hours post intravenous administration.

Immunoliposomes Liposomes appended with antibodies or their fragments,

as target oriented moieties are known as immunoliposomes. Immunoliposomes bearing poly-(ethylene glycol)-

coupled monoclonal antibody linked via cleavable disulphide bond can be used for ex vivo applications as sorting of hematopoietic stem cells

LYSOSOMAL STORAGE DISEASES

Lysosomal storage diseases (LSDs) are a group of approximately 40 rare inherited metabolic disorders that result from defects in lysosomal function.

LSDs are caused by lysosomal dysfunction usually as a consequence of deficiency of a single enzyme required for the metabolism of lipids, glycoproteins (sugar containing proteins) or mucopolysaccharides.

Like other genetic diseases, individuals inherit lysosomal storage diseases from their parents. Although each disorder results from different gene mutations that translate into a deficiency in enzyme activity, they all share a common biochemical characteristic – all lysosomal disorders originate from an abnormal accumulation of substances inside the lysosome.

Based on the chemical nature of the accumulating materials LSDs are categorized into:

Lipid storage disorders (Sphingolipidoses) - Sphingolipidoses are caused by genetic defects in a series of lysosomal enzymes and other proteins essential for the catabolism of sphingolipids.

E.g. Gaucher’s disease, Niemann -Pick disease, Fabry’s disease, Tay-sach’s disease.

Mucopolysaccharidoses - Mucopolysaccharidoses are caused by genetic enzymatic defects in the degradation of carbohydrate chains of glycosaminoglycans. E.g. Hurler Syndrome, Hunter syndrome, Mucolipidosis.

Glycogen storage disorders - Glycoprotein disorders result from defects in lysosomal hydrolases.

E.g. Pompe disease, Sialidosis.

DISEASE SIGNS AND SYMPTOMS

MAJOR LIPID ACCUMULATION

ENZYME DEFECT

Faber’s disease

Mental retardation, dermatitis

ceramide ceramidase

Gaucher’s disease

Spleen and liver enlargement, erosion of long bones

glucoceribroside Glucoceribroside β- glucosidase

Niemann -pick disease

Spleen and liver enlargement

sphingomyelin sphingomyelinase

Fabry’s disease

Reddish purple skin rashes, kidney failure

ceramidetrihexoside Ceramidetrihexosideα- galactosidase

Tay-sach’s disease

Red spot in retina, blindness, muscular weakness

ganglioside Hexosaminidase A

Principal manifestations, stored lipids in sphingolipidoses

TARGETING EXOGENOUS ENZYMES

Direct the major portion of enzymes to the storage cells.

Intracellular trafficking of the enzyme.

ConclusionImprovement of existing approaches to diagnosis and treatment of various diseases

involving bone marrow.

Combination with gene delivery and controlled expression of enzymes and carrier proteins is a promising strategy.

References S.P.Vyas and Roop K. Khar; targeted &

Controlled drug delivery: Novel Carrier Systems,

S.P.Vyas and V.K.Dixit; pharmaceutical biotechnology,

James Swarbrick and James C.Boylan; Encyclopedia of pharmaceutical technology; third edition; volume2,

Garret M. Ihler; methods of drug delivery.

S.M. Moghimi; Exploiting bone marrow microvascular structure for drug delivery and future therapies; Advanced Drug Delivery Reviews 17 (1995) 61-73,

P.B. Malafaya, G.A. Silva, E.T. Baran, R.L. Reis; Drug delivery therapies I: General trends and its importance on bone tissue engineering applications; Current Opinion in Solid State and Materials Science 6 (2002) 283–295

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