🔬Nanobiotechnology Unit 2 – Nanoparticles for Drug Delivery & Therapeutics

Key Concepts in Nanoparticles for Drug Delivery

• Nanoparticles range in size from 1-100 nm and have unique physicochemical properties due to their high surface area to volume ratio
• Nanoparticles can be engineered to encapsulate, adsorb, or conjugate therapeutic agents such as small molecules, proteins, and nucleic acids
• Nanoparticle-based drug delivery systems aim to improve the pharmacokinetics, biodistribution, and therapeutic efficacy of drugs while minimizing side effects
• Nanoparticles can be designed to target specific tissues, cells, or intracellular compartments by incorporating targeting ligands (antibodies, peptides, aptamers) on their surface
• Drug release from nanoparticles can be controlled by various stimuli-responsive mechanisms (pH, temperature, enzymes, light) to achieve sustained or triggered release
• Nanoparticles can enhance the solubility, stability, and permeability of poorly water-soluble drugs, enabling their effective delivery
• Nanoparticle formulations can protect drugs from premature degradation, reduce immunogenicity, and prolong circulation time in the body

Types of Nanoparticles Used in Medicine

• Liposomes are spherical vesicles composed of lipid bilayers that can encapsulate both hydrophilic and hydrophobic drugs
• Polymeric nanoparticles, such as poly(lactic-co-glycolic acid) (PLGA) and polyethylene glycol (PEG), are biodegradable and biocompatible carriers for drug delivery
• Micelles are self-assembling nanostructures with a hydrophobic core and hydrophilic shell, suitable for delivering poorly water-soluble drugs
• Dendrimers are highly branched, monodisperse polymers with a well-defined structure and multiple functional groups for drug conjugation
• Inorganic nanoparticles, including gold, silver, and iron oxide, can be functionalized with drugs and targeting ligands for theranostic applications
  • Gold nanoparticles exhibit surface plasmon resonance and can be used for photothermal therapy and imaging
  • Iron oxide nanoparticles have magnetic properties and can be used for magnetic resonance imaging (MRI) and magnetic hyperthermia
• Virus-like particles (VLPs) are self-assembling protein nanostructures that mimic the structure of viruses and can be engineered to deliver drugs or vaccines
• Exosomes are natural, cell-derived nanoparticles that can be loaded with therapeutic agents and have inherent targeting capabilities

Nanoparticle Design and Synthesis

• Nanoparticle design involves selecting appropriate materials, sizes, shapes, and surface modifications to achieve desired properties and functions
• Top-down approaches, such as nanoprecipitation and emulsion-based methods, involve breaking down larger materials into nanoparticles
• Bottom-up approaches, such as self-assembly and chemical synthesis, involve building nanoparticles from molecular precursors
• Surface functionalization of nanoparticles can be achieved by physical adsorption, chemical conjugation, or co-polymerization of targeting ligands or functional groups
• Particle size and size distribution can be controlled by adjusting synthesis parameters (concentration, temperature, pH, surfactants) and purification methods (dialysis, centrifugation, chromatography)
• Nanoparticle characterization techniques, such as dynamic light scattering (DLS), transmission electron microscopy (TEM), and zeta potential measurements, are essential for quality control and reproducibility
• Scalability and manufacturing considerations, including batch-to-batch variability, sterilization, and storage stability, are critical for clinical translation of nanoparticle formulations

Drug Loading and Release Mechanisms

• Drug loading into nanoparticles can be achieved by physical encapsulation, chemical conjugation, or adsorption
  • Physical encapsulation involves entrapping drugs within the nanoparticle matrix during synthesis
  • Chemical conjugation involves covalently attaching drugs to the nanoparticle surface or polymer backbone
  • Adsorption involves non-covalent interactions between drugs and nanoparticle surface
• Drug loading efficiency and capacity depend on factors such as drug-nanoparticle interactions, particle size and porosity, and drug solubility
• Drug release from nanoparticles can be controlled by diffusion, erosion, or stimuli-responsive mechanisms
  • Diffusion-controlled release occurs when drugs passively diffuse out of the nanoparticle matrix based on concentration gradients
  • Erosion-controlled release occurs when the nanoparticle matrix degrades over time, releasing the encapsulated drugs
  • Stimuli-responsive release can be triggered by changes in pH (acidic tumor microenvironment), temperature (hyperthermia), enzymes (matrix metalloproteinases), or external stimuli (light, magnetic fields)
• Sustained release profiles can be achieved by optimizing nanoparticle composition, drug-polymer interactions, and release kinetics
• Pulsatile or on-demand release can be achieved by incorporating stimuli-responsive materials or triggers into the nanoparticle design

Targeting Strategies for Nanoparticles

• Passive targeting relies on the enhanced permeability and retention (EPR) effect, where nanoparticles accumulate in tumors or inflamed tissues due to leaky vasculature and poor lymphatic drainage
• Active targeting involves functionalizing nanoparticles with targeting ligands that specifically bind to receptors or antigens overexpressed on target cells
  • Antibodies, such as monoclonal antibodies (mAbs) or antibody fragments (Fab, scFv), can be conjugated to nanoparticles for targeted delivery to cancer cells expressing specific antigens (HER2, EGFR)
  • Peptides, such as RGD or NGR, can be used to target integrins or aminopeptidase N, respectively, which are overexpressed in tumor vasculature
  • Aptamers are single-stranded oligonucleotides that can fold into specific 3D structures and bind to target molecules with high affinity and specificity
  • Small molecules, such as folic acid or transferrin, can be used to target folate receptors or transferrin receptors, respectively, which are overexpressed in certain cancer cells
• Dual targeting strategies can be employed to enhance specificity and overcome biological barriers, such as targeting both tumor vasculature and cancer cells
• Intracellular targeting can be achieved by incorporating cell-penetrating peptides (CPPs) or organelle-specific targeting ligands to deliver drugs to specific subcellular compartments (nucleus, mitochondria, lysosomes)

Challenges in Nanoparticle-based Drug Delivery

• Nanoparticle stability and aggregation in biological fluids can lead to rapid clearance by the mononuclear phagocyte system (MPS) and reduced circulation time
• Protein corona formation, where serum proteins adsorb onto the nanoparticle surface, can alter nanoparticle properties, targeting efficiency, and cellular uptake
• Nonspecific uptake of nanoparticles by healthy tissues can cause off-target effects and toxicity
• Nanoparticle-induced immunogenicity can trigger immune responses, leading to rapid clearance or adverse reactions
• Incomplete drug release from nanoparticles can result in suboptimal therapeutic efficacy and drug resistance
• Batch-to-batch variability in nanoparticle synthesis and drug loading can affect reproducibility and quality control
• Scalability and manufacturing challenges, such as sterilization, storage stability, and cost-effectiveness, need to be addressed for clinical translation
• Regulatory and safety considerations, including long-term toxicity, biodegradability, and pharmacokinetics, require extensive preclinical and clinical testing

Applications in Therapeutics

• Cancer therapy: Nanoparticles can deliver chemotherapeutics, siRNA, or immunotherapeutics to tumor sites while minimizing systemic toxicity
  • Doxil, a PEGylated liposomal formulation of doxorubicin, is FDA-approved for treating ovarian cancer and multiple myeloma
  • BIND-014, a PSMA-targeted polymeric nanoparticle encapsulating docetaxel, has shown promising results in phase II clinical trials for prostate cancer
• Infectious diseases: Nanoparticles can deliver antibiotics, antivirals, or vaccines to target pathogens or infected cells
  • AmBisome, a liposomal formulation of amphotericin B, is used to treat fungal infections in immunocompromised patients
  • Polymeric nanoparticles encapsulating rifampicin and isoniazid have shown improved efficacy against intracellular Mycobacterium tuberculosis
• Cardiovascular diseases: Nanoparticles can deliver anti-inflammatory, antithrombotic, or regenerative agents to atherosclerotic plaques or damaged myocardium
• Neurodegenerative disorders: Nanoparticles can cross the blood-brain barrier and deliver neuroprotective or disease-modifying agents to the brain
  • Polymeric nanoparticles encapsulating curcumin have shown potential in treating Alzheimer's disease by reducing amyloid-β aggregation and oxidative stress
• Gene therapy: Nanoparticles can deliver nucleic acids (plasmid DNA, siRNA, miRNA) to modulate gene expression in target cells
  • Lipid nanoparticles (LNPs) encapsulating siRNA have been used to treat transthyretin amyloidosis by silencing TTR gene expression in the liver

Future Directions and Emerging Technologies

• Multifunctional nanoparticles that combine diagnostic and therapeutic capabilities (theranostics) can enable personalized medicine and real-time monitoring of treatment response
• Stimuli-responsive nanoparticles that respond to multiple external triggers (light, magnetic fields, ultrasound) can enhance drug release control and specificity
• Biomimetic nanoparticles that mimic the properties of natural entities, such as cell membranes or exosomes, can improve biocompatibility and targeting efficiency
• Nanoparticle-based vaccines that deliver antigens and adjuvants can enhance immune responses and protect against infectious diseases
• Nanoparticle-mediated gene editing, using CRISPR-Cas9 or other tools, can enable precise genome modification for treating genetic disorders
• 3D printing of nanoparticle-based scaffolds can enable the fabrication of personalized implants and tissue engineering constructs
• Microfluidic platforms for nanoparticle synthesis and screening can accelerate the discovery and optimization of novel nanoparticle formulations
• Machine learning and computational modeling can aid in the design, prediction, and optimization of nanoparticle properties and performance