INTRODUCTION:

Cancer remains one of the most challenging and devastating diseases worldwide, necessitating the constant search for innovative and effective treatment strategies. In this research article, we present a comprehensive review of nanosuspension as a promising tool in cancer therapeutics. Nanosuspensions are submicron colloidal dispersions of nanosized drug particles stabilized by surfactants.

Nanosuspension particles can aggregate at the target site through passive or active targeting mechanisms when used as nanoparticulate drug delivery systems¹. Recently, nanosuspensions have become a potential method for the effective delivery of medicines with limited solubility. Colloidal dispersions of drug particles that are nanosized and that are created in an appropriate manner and stabilized are known as nanosuspensions by an appropriate stabilizer^2,3.

Nanosuspensions, submicron colloidal dispersions of drug particles stabilized by polymers and/or surfactants, have emerged as a promising novel strategy to overcome the limitations of conventional cancer therapies and improve treatment outcomes. Nanosuspensions offer several advantages over conventional formulations, including:

· Improved solubility:

Nanosuspensions can significantly enhance the solubility of poorly soluble drugs, thereby increasing their bioavailability and therapeutic efficacy.

· Enhanced bioavailability:

By reducing particle size, nanosuspensions can increase the surface area of drug particles, allowing for faster dissolution and absorption into the bloodstream.

· Tumor-targeted delivery:

Nanosuspensions can be surface-modified with targeting ligands to specifically bind to tumor cells, thereby reducing systemic exposure and increasing drug concentration at the tumor site.

Because of their distinct biodistribution profile in the tumor tissue, increased penetration and retention are currently thought to be key factors. Recent statistics show that surface modification of nanocarriers with poly(ethylene glycol) (PEG) has emerged as a method to significantly slow down the blood circulation half-life of the drugs, but they cannot be delivered to particular cells in a target-specific manner^4,5. Nano-carriers can have ligands or moieties attached to their surfaces, which allows for minimally invasive medication delivery into cancer cells by receptor-mediated endocytosis. accumulating at random locations. Recently, the FA receptor (FR), also known as the folate (FA) receptor, has been found to be a promising targeting location for the administration of tumor-specific drugs⁶. The most promising approach to further enhance targeting of cancer cells uses multiple targeting moieties or ligands that attach selectively to a receptor that is mainly found on cancerous cells. The production of active, targeted nanosuspensions on a large scale is challenging, to the authors' understanding.

This study's objective is to prepare active targeting: LNS, which may be directed at FR-over expressed tumor cells. On the basis of earlier experimental studies, a PEG-modified DTX-LNS (pLNS) was created in this study, and a targeted DTX-LNS (tLNS) was created utilizing a synthesized FA-PEG-distearoylphosphatidylethanolamine (FA-PEG-DSPE) conjugate. Particle size, zeta potential, and morphology of pLNS and tLNS were each characterized. The dialysis bag diffusion method was used to evaluate the in vitro drug release. A murine malignant melanoma cell line (B16), which overexpresses FR (i.e., is FR-positive [FR+]), was used for the in vitro cytotoxicity assays, as well as a human breast cancer cell line^7,8.

· Diffrence between suspension and Nanosuspension

Property	Suspension	Nanosuspension
Particle Size	Micrometer-sized particles	Nanometer-sized particles
Stability	Prone to sedimentation	Improved stability
Applications	Various industries	Pharmaceuticals, drug delivery
Solubility Enhancement	Limited	Enhanced solubility

Techniques for Preparation of Nanosuspension:

· High-Pressure homogenization:

It is the most widely used method for preparing nanosuspensions of many poorly aqueous soluble drugs⁹. It involves three steps. First, drug powders are dispersed in a stabilizer solution to form presuspension, and then the presuspension is homogenized in a high-pressure homogenizer at a low pressure for premilling, and finally homogenized at high pressure for 10 to 25 cycles until Nanosuspensions of the desired size are formed. Different methods are developed based on this. The principles for the preparation of nanosuspensions are Disso cubes, Nanopure, Nanoedge, andNanojet¹⁰.

Homogenization in aqueous media (Disso cubes):

This technology was developed by R.H. Muller using a piston-gap high-pressure homogenizer in 1999¹¹. In this method, the suspension containing a drug and surfactant is forced under pressure through a nanosized aperture valve of a high-pressure homogenizer¹¹.

Advantages:

1. It does not cause the erosion of processed materials.

2. It is applicable to drugs that are poorly soluble in both aqueous and organic media.

Disadvantages:

1. Pre-processing, like micronization of the drug, is required.

2. High-cost instruments are required, which increases the cost of the dosage form¹¹.

Homogenization in nonaqueous media (Nanopure):

Nanopure is a suspension homogenized in water-free media or water mixtures like PEG 400. PEG 1000, etc. The homogenization can be done at room temperature (00 °C) and below freezing. point (-200 °C); hence, it is known as “deep freeze” homogenization¹².

Nanoedge:

Nanoedge Technology is the combination of both precipitation and homogenization. The basic principle is same as that of precipitation and homogenization¹³. The major disadvantage of precipitation Techniques such as crystal growth and long-term stability can be overcome by using the Nanoedge technology. Particles of smaller size and better stability in a short time can be beached.

Nanojet:

It is also called opposite stream technology and uses a chamber where a stream of suspension is divided into two or more parts, which colloid with each other at high pressure due to the high¹⁴.

· Milling Techniques:

Media Milling:

This method was first developed and reported by Liversidge (1992)¹⁵. The nanosuspensions by this method are prepared by a high-shear media mill. The milling chamber was charged with the milling media, water, drug, and stabilizer and rotated at a very high shear rate under controlled temperature for at least 2–7 days¹⁶. The milling medium is composed of glass. Zirconium oxide, or highly cross-linked polystyrene resin, has high-energy shear forces. formed as a result of the impaction of milling media with the drug, which results in the breaking of the drug. microparticles to nanosized particles³⁰.

Advantages:

1. Very dilute as well as highly concentrated nanosuspensions can be prepared by handling 1 mg/ml to 400mg/ml drug quantity.

2. Nanosized distribution of the final nanosized product

Disadvantages:

1. The media milling technique is time-consuming.

2. Some fractions of particles are in the micrometer range.

3. Scale-up is not easy due to mill size and weight.

Dry-Co-grinding:

Recently, many nanosuspensions have been prepared using the dry milling technique. Dry co-grinding can be carried out easily and economically and can be conducted without organic solvents. The physicochemical properties and dissolution of poorly water-soluble drugs are improved by Co-grinding because of an improvement in the surface polarity and transformation from a crystalline to an amorphous drug.

Advantages:

1. Easy process, and no organic solvent is required.

2. Require a short grinding time.

Disadvantages

1. Generation of residue from milling media.

· Emulsification-Solvent Evaporation Technique:

This technique involves preparing a drug solution, followed by its emulsification in another liquid that is a nonsolvent for the drug. Evaporation of the solvent leads to precipitation of the drug. Crystal growth and particle aggregation can be controlled by creating high shear forces using a high-speed stirrer¹⁷.

· Precipitation:

Within the last decade, precipitation has been applied to prepare submicron particles, especially for the poorly soluble drugs¹⁸. The drug is first dissolved in a solvent, and then this solution is mixed with a miscible antisolvent in the presence of surfactants. Rapid addition of a drug solution to the antisolvent leads to sudden supersaturation of the drug and the formation of ultrafine crystalline or amorphous drug solids¹⁹.

Advantages:

1. Simple process, ease of scaling up, and

2. Economical production.

Disadvantages:

1. The growth of crystals needs to be limited by surfactant addition. A drug must be soluble at least in one solvent.

· Supercritical fluid process:

The particle size reduction was achieved more by the solubilization and nanosizing technologies. through the supercritical fluid process. Supercritical fluids (SCF) are noncondensable and dense. fluids whose temperature and pressure are greater than their critical temperature (Tc) and critical pressure (Tp). This process allows the micronization of drug particles to submicron levels. Recent Advances in the SCF process are to create nanoparticulate suspensions of particle size 5 to 2000nm in diameter²⁰. The low solubility of poorly water-soluble drugs and surfactants in supercritical CO2 and the high pressure required for these processes restrict the utility of this technology in the pharmaceutical industry²⁰.

· Melt Emulsification Method:

In this method, the drug is dispersed in the aqueous solution of stabilizer and heated above the melting point of the drug and homogenized to give an emulsion. During this process, the sample holder was enwrapped with a heating tape fitted with a temperature controller, and the The temperature of the emulsion was maintained above the melting point of the drug. The emulsion was then cooled down either slowly to room temperature or in an ice bath.

Advantages:

1. The melt emulsification technique, relative to the solvent evaporation method, is the total avoidance of organic solvents during the production process.

Disadvantages:

1. Formation of larger particles and few compliant objects than solvent evaporation.

· Solvent Evaporation:

In the solvent evaporation method, the solutions of polymers are prepared in volatile solvents and emulsions. But in the past years, dichloromethane and chloroform were used, which are now replaced by ethyl acetate, which has a better profile of toxicology. The emulsion is converted into a nanoparticle suspension by the evaporation of the solvent for the polymer, which is allowed to diffuse through the continuous phase of the emulsion. In conventional methods, two main strategies are being used for the formation of emulsions, the preparation of single-emulsions, e.g., oil-in-water (o/w), or double-emulsions, e.g., (water-in-oil)-in-Water, (w/o)/w. These methods require high-speed homogenization or ultrasonication, followed by evaporation of the solvent, either by continuous magnetic stirring at room temperature or under reduced pressure. Through ultracentrifugation, the solidified nanoparticles are collected, which was washed with distilled water to remove the additives like surfactants, and Then it was lyophilized. The particle size was influenced by the concentration of polymer, stabilizer, and the speed of the homogenizer²⁰.

Characterization Techniques for Nanosuspensions:

Several techniques are used to characterize nanosuspensions, including:

1. Particle size analysis: Particle size analysis is essential for determining the particle size distribution of nanosuspensions, which can influence their therapeutic properties. Common techniques for particle size analysis include dynamic light scattering (DLS), laser diffraction, and nanoparticle tracking analysis (NTA).

2. Zeta potential measurement: Zeta potential measurement determines the surface charge of nanosuspensions, which influences their stability and interaction with biological membranes.

3. Scanning electron microscopy (SEM): SEM provides high-resolution images of nanosuspensions, allowing for the visualization of particle morphology and size distribution.

4. Transmission electron microscopy (TEM): TEM provides even higher resolution images of nanosuspensions, allowing for detailed analysis of particle structure and composition.

Mechanism of Action:

Submicron colloidal drug dispersions in an aqueous medium stabilized by polymers or surfactants are known as nanosuspensions. Their purpose is to increase the bioavailability and solubility of poorly water-soluble medications.

The following crucial steps are involved in the mechanism of action of nanosuspensions:

1. Drug Particle Size Reduction: Using nanosuspensions, the drug's particle size is usually reduced to nanometers, usually less than 1 μm. The limits of medications that are poorly water-soluble are overcome by this expanded surface area, which promotes dissolving and saturation solubility²¹.

2. Enhanced Dissolution Rate: The medication dissolves and releases more quickly due to the tiny particle size, which increases the surface area exposed to the surrounding aqueous medium²². The nanosuspension method increases the medication's apparent solubility in the aqueous medium, resulting in a supersaturated state that can enhance drug absorption²³.

3. Enhancement of Bioavailability: Increased solubility and dissolution lead to increased bioavailability, which is especially advantageous for medications with low oral bioavailability²¹. A mixture of high-energy techniques is used in the formulation of nanosuspensions to prevent sedimentation and particle agglomeratio²⁴.

Therapeutic Action of Nanosuspension Formulations in Cancer Therapy:

Nanosuspensions offer several unique therapeutic advantages over conventional drug delivery formulations, primarily due to their ability to enhance drug solubility, bioavailability, and tumor-targeted delivery. These advantages translate into improved treatment efficacy and reduced systemic toxicity, leading to better patient outcomes.

A. Enhanced Drug Solubility: Poor drug solubility is a major challenge in cancer therapy, as it limits the amount of drug that can be administered and ultimately delivered to the tumor site. Nanosuspensions overcome this limitation by reducing the drug particle size to the submicron range, significantly increasing the surface area of the drug particles. This enhanced surface area facilitates faster dissolution and absorption of the drug into the bloodstream, leading to increased drug concentration at the tumor site.

B. Improved Bioavailability: Bioavailability refers to the proportion of an administered drug that reaches the systemic circulation and ultimately the target site. Nanosuspensions enhance drug bioavailability by increasing the surface area of drug particles, allowing for faster dissolution and absorption into the bloodstream. This improved bioavailability ensures that a larger fraction of the administered drug reaches the tumor site, maximizing its therapeutic effect.

C. Tumor-Targeted Delivery: Non-specific drug delivery often leads to systemic exposure, causing adverse effects in healthy tissues and organs. Nanosuspensions can be specifically targeted to tumor cells by surface modification with targeting ligands, such as antibodies or peptides. These targeting ligands bind to specific receptors on the surface of tumor cells, directing the nanosuspensions to the tumor site and reducing systemic exposure.

D. Sustained Release: Conventional drug delivery formulations often release the drug rapidly, leading to high initial drug concentrations followed by a rapid decline. This can result in fluctuating drug levels, potentially leading to inadequate treatment or adverse effects. Nanosuspensions can be designed to release the drug over an extended period, providing sustained drug levels at the tumor site. This sustained release profile improves treatment efficacy and reduces the frequency of administration, enhancing patient compliance.

E. Protection from Degradation: Certain drugs are susceptible to degradation by enzymes or other substances in the body, reducing their bioavailability and therapeutic efficacy. Nanosuspensions can protect the drug from degradation by encapsulating it within a protective matrix of polymers and/or surfactants. This encapsulation prevents the drug from interacting with degrading enzymes or substances, extending its shelf life and enhancing its therapeutic effectiveness.

F. Overall Therapeutic Impact: The combined effects of enhanced drug solubility, improved bioavailability, tumor-targeted delivery, sustained release, and protection from degradation contribute to the superior therapeutic efficacy of nanosuspensions in cancer therapy. By overcoming the limitations of conventional formulations, nanosuspensions offer a promising approach to improving cancer treatment outcomes and reducing patient morbidity.²⁵

The Nano-suspension’sstability^26,27:

The size of the particles affects the stability of the nanosuspension. Particles tend to clump together when their surface energy increases as they get closer to the nanoscale. In order to improve the stability of the nanosuspension and reduce the likelihood of the Ostwald ripening effect, stabilisers are utilised to create an ionic or steric barrier. Stabilisers such as cellulosics, poloxomer, polysorbates, polyoleate, povidones, and lecithin are frequently utilised in nanosuspensions.

In vivo assessment:

1. 1.Surface hydrophobicity is the first

2. Properties of adhesion

3. Interaction with proteins in the body

Stability of Nanosuspension Storage:

Zeta potential, particle size, drug content, appearance, and viscosity variations over time can be used to measure the physical characteristics of NS throughout extended storage. It seems that external factors like light and temperature are most crucial for long-term stability. In general, a dispersion needs to have a zeta potential greater than -60mV in order to stay physically stable. The ideal storage temperature is 4 oC.20 oC - Drug-loaded NS aggregation or drug loss did not occur during long-term storage.50 oC: A sharp increase in particle size was noted²⁹.

Dissolution Velocity and Saturation Solubility:

Nanosuspensions have an important advantage over other techniques, that it can increase the dissolution velocity as well as the saturation solubility. These two parameters should be determined in various physiological solutions. The assessment of saturation solubility and dissolution velocity helps in determining the in-vitro behavior of the formulation. Böhm et al. reported an increase in the dissolution pressure as well as dissolution velocity with a reduction in the particle size to the nanometer range. 17 Size reduction leads to an increase in the dissolution pressure Speed of Dissolution and Solubility at Saturation The ability of nanosuspensions to raise both the saturation solubility and the dissolving velocity above other methods is a significant benefit. Different physiological solutions should be used to determine these two parameters. The evaluation of the formulation's dissolving velocity and saturation solubility aids in figuring out how it behaves in vitro. Böhm et al. observed that when the particle size was reduced to the nanoscale range, there was an increase in both the dissolving pressure and the dissolution velocity. 17 Reduction in size causes the dissolving pressure to rise²⁸.

CONCLUSION:

Nanosuspensions represent a promising new approach to cancer treatment with the potential to overcome the limitations of conventional therapies and provide more effective and less toxic treatments for patients. Their ability to enhance drug solubility, bioavailability, and tumor-targeted delivery makes them a promising platform for the development of novel cancer therapeutics. Recent advances in nanosuspension technology, such as the development of stimuli-responsive and multifunctional nanosuspensions, further expand their potential applications. Their ability to enhance drug solubility, improve bioavailability, achieve tumor-targeted delivery, provide sustained release, and protect from degradation makes them a promising platform for developing more effective and less toxic cancer treatments. While challenges remain in optimizing nanosuspension formulations and addressing their clinical translation, the potential benefits of nanosuspensions in cancer therapy are undeniable. Continued research and development efforts are warranted to fully realize the promise of nanosuspensions in cancer therapy.

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Received on 16.11.2023 Modified on 14.02.2024

Res. J. Pharma. Dosage Forms and Tech.2024; 16(2):157-162.

DOI: 10.52711/0975-4377.2024.00025