Tumor targetting
- 1. TUMOR TARGETING Presented By K. TRIDEVA SASTRI M.Pharm 2nd semester (Pharmaceutics) Reg No. 121725101005 1 GITAM INSTITUTE OF PHARMACY GITAM (DEEMED TO BE UNIVERSITY) VISAKHAPATNAM 530045 November 2018
- 2. What is TUMOR ? • Crudely, it is a pathophysiological condition in which the normal cells transform into immortal cells that grow without any control, often referred to as carcinogenesis. • Principally, persistent tissue injury and/or genetic factors such as mutations, epigenetic and global transcriptome changes contribute to carcinogenesis. • Cumulatively, it could be considered as multistep (comprising a variety of genetic alterations), multipath (including various apoptotic and angiogenesis pathways), and multifocal (constitutive of both field carcinogenesis and clonal expansion) 2
- 3. Tumors classified as…. • Benign • Benign: They are- • Slow growing • Capsulated • Non- invasive • Do not metastasize • Well differentiated • Suffix “oma” • Example : Fibroma, Adenoma, Emangioma, Ipoma, Eningioma • Malignant • Malignant: They are- • Fast growing • Non-capsulated • Invasive & infiltrate • Metastasize • Poorly differtiated • Suffix “carcinoma” or “sarcoma” They can be classified in two forms. These are- 3
- 4. Key contributing factors of carcinogenesis 4
- 5. • Subsequently these changes lead to distinct tumor microenvironment as compared to normal cells. This discriminatory microenvironment and altered pathophysiological signaling pathways have been classically used in the recent drug discovery approaches and set the genesis of molecularly targeted therapies. • Unfortunately, most of the anticancer drugs till time target the DNA or other biologicals actively involved in cell division and thereby control the rapidly diving cancer cells. • However, in the course of that, the normal host tissues are also not spared and nonspecific generalized toxicity is noted which may be severely intense at times and may lead to either early termination of therapy or other secondary complications 5
- 6. • Firstly, main targets include rapidly dividing lymphohematopoietic cells, epithelial linings and other mucus secreting regions of gut, hair follicular regions, etc. These complexities lead to low chemotherapeutic index of the anticancer drugs. • Secondly, rapid emergence of drug resistance also contributes majorly to the poor cancer chemotherapeutics. 6
- 7. TUMOR TARGETING (a) preferentially localizing its pharmacological activities at the site of action, (b) recognition and interaction with target cells, and (c) achieving cellular concentrations so as to exhibit therapeutic response • Very often a variety of homing devices are being employed to direct the drug and/or carriers to the particular site of action. • Mechanistically, these homing devices are the special molecular signatures that are expressed to a greater extent at the tumor tissues such as folic acid, etc. 7
- 8. • The principal need for tumor targeting is required due to limited accessibility of drugs to tumor tissues, requirement of high doses, intolerable cytotoxicity, development of multidrug resistance and nonspecific targeting. WHY TUMOR TARGETING …..? 8
- 9. Normal Vs Tumor Vasculature • Prominent homeostasis among the proangiogenic and antiangiogenic molecules in the normal tissues which are responsible for balanced organization of the blood vessels. • This system works in tandem with lymphatics for clearance of the cellular by- products. • Carcinogenesis leads to imbalances in these systems leading to a variety of alterations. • Subsequently, compromised basal membrane, disorganized pericyte layer, downregulation of the adhesion molecules and endothelial linings contribute to high permeability of the tumor tissues. • The principal barriers for the conventional chemotherapeutic agents to access the tumor tissues are malformed tumor vasculature which leads to altered vascular permeability, high interstitial pressure, extracellular acidosis, and hypoxia (due to high mitochondrial oxygen consumption) 9
- 10. • In case of tumors interstitial pressure shoots up to 100 mmHg owing to three principal reasons. These include (a) compromised functionalities of the blood vessel and lymphatics, (b) osmotic pressure generated by drainage of solutes from tissues, and (c) high contractile characteristics of tumor tissues • The pH of the tumor microenvironment is usually dropped relatively towards acidic, as evident from the direct measurement by placing sensitive electrodes into the solid tumors 10
- 11. Barriers to Tumor Targeting 11
- 12. • Nonuniform distribution of blood vessels across the tumor, • Uneven distribution of administered therapeutics often leading to poor therapeutic response. • Overexpression of efflux transporters, often referred to as ATP binding cassette (ABC) transporters such as P-glycoprotein, multidrug resistance proteins (MRP-1, -2), etc. Most of the anticancer drugs are substrates of such efflux transporters. • Subsequently, other factors such as diffusional barrier due to high intercapillary distance, cell density, and extracellular matrix components also pose potential barrier to tumor delivery of therapeutics. 12
- 13. A) Conventional Strategies for Tumor Targeting • Selective accumulation of the drug at preferred site is also majorly affected by its physicochemical properties. • Most of the anticancer drugs fall in the category II/IV of Biopharmaceutical Classification Systems (BCS), thereby posing pharmaceutical problems while water soluble drugs pose problems related to permeability across various biological barriers. • Major approaches could be employed which include (a) subtle structural modifications for improving the physicochemical properties in accordance with structure–activity relationships (SAR), (b) conjugating homing ligands for predetermined bio-distribution patterns, and (c) involvement of carrier based approaches 13
- 14. Passive Targeting • The natural biodistribution pattern of the drug delivery carrier is exploited for its preferential localization in the vicinity of the tumors such as enhanced permeation and retention effects, phagocytosis of particulate carrier by mononuclear phagocytosis systems (MPS) and preferential localization in the organs of reticuloendothelial system (RES). • In addition, other typical properties of the tumor microenvironment such as low extracellular pH, relative micro-acidosis, mild hyperthermia, etc. could also be employed for availing passive targeting of therapeutics. 14
- 15. Enhanced Permeation and Retention ( EPR ) Effect • Classically, the cell proliferation leads to formation of solid mass and upon reaching a specific size, cells in the interior starts getting deprived of the nutrients. Release of growth mediators signaling the development of the blood vessels within tumor. • The formed blood vessels are often leaky owing to absence of basal membrane leading to fenestrations within the size of 200–2,000 nm • The principal factors affecting EPR effect includes vessel architecture, interstitial fluid composition, extracellular matrix composition, phagocyte infiltration, presence of necrotic domains, factors pertaining to the colloidal carriers such as blood circulation time, particle size, particle shape, surface charge, and surface functionalization, if any, (e.g., stealth characteristics by PEGylation ) 15
- 16. • The presence of fenestrations results in poor resistance to the extravasation of macromolecules to the tumor microenvironment and contributes to the enhanced permeation part of EPR. • Simultaneously, it has also been found that tumor mass is associated with nonuniform lymphatic drainage and experience a huge physical stress owing to rapid growth in the dimensions of the tumor mass. This leads to the severe compromise in the drainage functionality of the vessels and contributes to the retention part of EPR effect 16
- 17. Surface Engineering of Colloidal Carriers for Stealth Characteristics • Drastic reduction in RES uptake and significant appreciation in the EPR effect of the colloidal carriers can be achieved by surface engineering. • Usually, the opsonins interact with the colloidal carriers via forces such as van der Waal’s forces, weak electrostatic forces, ionic forces, and hydrophobic/hydrophilic forces. • In purview of this, hydrophobic and charged particles are rapidly processed by RES and significant prolongation in the circulation half-life can be achieved by surface functionalizing PEG chains forming “stealth” systems. • Mechanistically, the stealth characteristics are imparted by steric barrier, shielding of anionic charge, and binding with dysopsonins 17
- 18. Active Targeting • Active targeting refers to the attachment of marker component to the colloidal carrier system which is specifically recognized by the target in concern may it be either from organelle or organ. • Usually molecular targets are employed such as overexpression of surface receptors on tumor cells for site specific delivery of therapeutics such as dietary ligands (carbohydrate based, folate , etc.), monoclonal antibodies and their fragments, non-antibody ligands (peptidic ligands), etc. • The active targeting could be divided into various levels depending upon extent of penetration, i.e., organ level, cellular level, and subcellular level. 18
- 19. Albumin Based Targeting • Albumin plays a critical role in maintaining the homeostasis by mobilizing key endogenous hydrophobic molecules. It specially binds via non-covalent interactions and executes the transport of molecules in concern by transcytosis across the endothelial cells into interstitial space. • Paclitaxel bound albumin nanoparticle represents the classical example for establishing the potential of albumin based delivery of anticancer drugs. • The principal advantages associated with albumin based targeting include superior stability over a wide range of pH (4–9) and temperature (10–60 °C), biodegradation, non-immunogenic, and nontoxic. • A striking advantage includes its additional cryoprotectant effect which makes the lyophilization of formulation in concern quite easier than other systems in race. 19
- 20. Vitamin Based Targeting • The vitamins employed for targeting potential includes folate, vitamin B 12 , thiamine, and biotin. • The principal advantages associated with vitamins, particularly folic acid, includes stability over shelf and physiological conditions, relatively inexpensive, nontoxic, non-immunogenic, endogenous homing ligand, wide flexibility for diverse chemical reactions, and relatively higher overexpression of folate receptors on most of the cancers. • It has been noted that folate functionalized colloidal carrier systems are preferably absorbed by receptor mediated endocytosis. 20
- 22. Transferrin Based Targeting • Transferrin receptors are also exclusively overexpressed in most of major types of tumors including lung, lymphomas and breast cancers in the order of ~10-fold. • The important feature of employing transferrin as targeting ligand is its capability for enabling the transcytosis across blood brain barrier 22
- 23. Transferrin conjugated nanoparticles for improved tumor delivery of therapeutics 23
- 24. Lectin Based Targeting • Lectins represent a class of cyto-adhesive targeting ligands which is moderately recognized by glycans on the glycosylated cell surface proteins and lipids. • Most of the cell surface expresses peculiar glycan arrays which can be sensed differentially and hence this could be a viable strategy as regards targeting perspectives 24
- 25. Peptide Based Targeting • The tumor specific peptides could be broadly categorized into two categories, one targeting tumor cell surface while other targeting tumor vasculature. • The cell surface targets could be either lymphomas, myelomas, neuroblastomas, breast cancer, head cancer, neck cancer, prostrate cancer, endothelial cells, or human laryngeal carcinomas whereas the • Tumor vasculature targets could be α v β 3 , α v β 5 ,aminopeptidases, proteoglycans, gelatinases, and vascular endothelial growth factors 25
- 26. Physical Targeting • The physical stimuli for drug targeting may either be endogenous such as pH, temperature, redox potentials, etc., or be exogenous, i.e., employment of external forces such as magnetic, ultrasound, etc. • The tumor microenvironment is slightly acidic and exhibits mild hyperthermia which could be specifically exploited as a stimulus for physical targeting. • Magnet assisted tumor targeting approaches have also widely been explored considering its immense potential. The drug in concern is immobilized on ferromagnetic colloidal carriers and allowed to circulate in body. • Similarly, the circulating colloidal carrier may be accumulated at the desired site of action using ultrasound energy. 26
- 27. B) Recent Advances in Tumor Targeting Approaches • Molecular Targeted Therapies • Inhibition of the CDKs is an important target. • Strategic inhibitors could be designed to compete via inhibition of the ATP binding sites or upregulation of the native CDK inhibitors. • Molecular targeted therapies, the available bioactives could be crudely categorized among three broad generations • First generation comprising ones that act predominantly via DNA damage, synthesis and/or other linked processes such as tubulins, • Second generation comprising agents that target cancer growth signaling mechanisms such as kinases, etc., and • Third generation, comprising agents which act on cellular pathways indirectly related to cancer growth such as chromatin modifiers, protein chaperones, proteasome inhibitors, etc. 27
- 28. Agents Acting on Protein Folding and Proteotoxic Stresses • Considering the typical microenvironment in the vicinity of tumor, cancer cells constantly experience a variety of stresses, especially permanent proteotoxic stress which is generally caused by the misfolding and aggregation of proteins. • The latter effect is predominantly observed in cancer cells owing to molecular crowding of the cellular milieu. • Usually such stresses are counterfeited by a group of molecules inclusive of chaperones and protein remodeling factors 28
- 29. Tumor Angiogenesis • In routine physiological conditions, the vascular network develops in three phases, viz., vasculogenesis, angiogenesis, and vascular remodelling. • Angiogenesis is initiated in tumor upon reaching the size 1–2 mm and is typically coordinated by the hypoxic microenvironment of the tumor. Hypoxia inducible factors (HIFs), heterodimeric transcription factors, direct the expression of VEGF -A for angiogenic sequences 29
- 30. Targeting tumor vasculature to inhibit angiogenesis. ( a ) Inhibition of binding to proangiogenic receptors and/or altering the interaction of angiogenic factors with co-receptors. ( b ) Penetration into the cells followed by binding with tyrosine kinase receptors ( c ) Direct activation of receptors, e.g., thrombospondin peptide mimetics ( d ) Extracellular matrix receptors, e.g., αvβ3 integrins. ( e ) Nonspecific inhibitors of proliferation 30
- 31. Cancer Immunotherapy • Principally, these act through antibody dependent cellular cytotoxicity (ADCC) and complement-activation- dependent cytotoxicity (CDC) for imparting cytotoxicity and play a crucial role in efficient management of a variety of cancers 31
- 32. Radioimmunotherapy (RAIT) • RAIT or Radioimmunoconjugates refer to the macromolecular entities where monoclonal antibodies (mAbs) are covalently attached to high linear energy transfer (LET) radionuclides. • The radionuclides could either be alpha emitters such as • 213 bismuth, 211 astatine, 223 radium, 149 terbium, 225 actinium, 227 thorium, 230 uranium or beta emitters such as 131 iodine, 90 yttrium, 60 cobalt, 99m technetium capable of damaging DNA either by strand breakage or by other effects ultimately resulting in cell death. 32
- 33. General architecture of multifunctional nanoparticles and associated principal advantages. 33
- 34. Immunotoxins • Immunotoxins represents a group of macromolecular species essentially comprising toxin conjugates and targeting antibodies linked via gene fusions, peptide bonds, disulfide bonds, thioether bonds, etc. • Upon successful internalization within target cells, the immunotoxins releases toxin by a variety of mechanisms such as degradation by proteases, reduction of disulfide bonds, or acid hydrolysis. 34
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- 36. Antibody Directed Enzyme Prodrug Therapy ADEPT 36
- 37. Immunoliposomes • Internalization of liposomal drug delivery systems. (A) Plain liposomes are entitled for either specific adsorption ( a ), nonspecificc adsorption at cell surface ( b ) fusion with cell membrane ( c ), destabilized of liposomes upon adsorption at cell surface by internal components ( d ), direct or transfer-protein-mediated exchange of lipid component ( e ) and endocytosis ( f ). The endocytosed liposomes either fuses with lysosomes ( g ) or leads to endosomal escape and drug delivery to cytoplasm ( h ). (B) Surface functionalization of the liposomes with appropriate ligands can be performed ( a ) to interact with target receptors ( b ), followed by endocytosis ( c ), and drug release ( d ) 37
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Editor's Notes
- #7: Hence, there lies a strong need to develop selective anticancer therapeutics which would principally act to cancer cells without affecting the normal tissues.