Cancer remains a major global health challenge and includes a diverse group of diseases characterized by abnormal cell proliferation, invasion, and metastatic dissemination.

Chemotherapy, targeted therapy, radiotherapy, immunotherapy, and surgery have improved outcomes for many patients. However, systemic treatment is frequently associated with significant limitations.

Many anticancer drugs have poor aqueous solubility and unfavorable pharmacokinetic properties. Their distribution throughout the body can expose healthy tissues to toxic concentrations.

The therapeutic effectiveness of a drug depends not only on its intrinsic anticancer activity but also on whether sufficient concentrations can reach the tumor.

Nanotechnology has introduced new opportunities to address these problems.

Nanoparticles are nanoscale delivery systems capable of carrying therapeutic molecules and modifying their biological distribution.

Depending on their composition and design, nanoparticles can improve drug solubility, protect drugs from degradation, prolong circulation, facilitate tumor accumulation, and provide controlled drug release.

More advanced systems can incorporate targeting ligands that recognize molecules preferentially expressed by tumor cells or tumor-associated stromal cells.

Nanoparticle-based delivery is therefore an important component of modern cancer nanomedicine.

Principles of Nanoparticle-Based Drug Delivery

Nanoparticles can function as carriers for small-molecule drugs, nucleic acids, proteins, peptides, and combinations of therapeutic agents.

Their physicochemical characteristics—including particle size, shape, surface charge, composition, and hydrophobicity—can influence biological behavior.

Particle size can affect circulation, tissue penetration, cellular uptake, and clearance.

Surface modification can alter interactions with plasma proteins and immune cells.

Encapsulation can protect drugs from premature degradation and may reduce exposure of healthy tissues.

Controlled-release mechanisms can provide sustained drug exposure at the target site.

These properties allow nanoparticle systems to be designed according to the requirements of particular therapeutic applications.

Major Types of Nanoparticles

Several nanoparticle platforms have been developed for cancer treatment.

Liposomal Drug Delivery

Liposomes are among the most extensively investigated nanocarriers.

They consist of lipid bilayers surrounding an aqueous compartment.

Hydrophilic drugs can be incorporated into the aqueous interior, whereas hydrophobic compounds can associate with the lipid bilayer.

Liposomal encapsulation can alter the pharmacokinetic behavior of drugs and may reduce exposure of healthy tissues.

Surface modification with polyethylene glycol can increase circulation time in some formulations.

Liposomal systems have therefore become an important clinically relevant platform for anticancer drug delivery.

Polymeric Nanoparticles and Micelles

Polymeric nanoparticles can be constructed from biodegradable materials capable of encapsulating therapeutic compounds.

Drug release can be controlled by polymer degradation, diffusion, or environmental conditions.

Polymeric micelles contain hydrophobic cores surrounded by hydrophilic shells.

They are particularly useful for improving the apparent solubility of poorly water-soluble anticancer drugs.

The chemical properties of polymers can be modified to control stability, circulation, and release.

Lipid Nanoparticles

Lipid nanoparticles have received considerable attention because of their ability to deliver nucleic acids and other therapeutic molecules.

They can incorporate messenger RNA, small interfering RNA, or other molecular cargos.

In cancer therapy, these systems are being investigated for delivery of gene-regulating molecules, tumor antigens, and therapeutic nucleic acids.

Lipid composition and surface characteristics can be adjusted to influence cellular uptake and intracellular release.

Targeted Nanoparticle Delivery

Targeted delivery aims to increase the concentration of therapeutic agents at tumor sites while reducing exposure to normal tissues.

Two broad strategies are commonly considered: passive targeting and active targeting.

Passive targeting is associated with the physicochemical and vascular characteristics of tumors.

Active targeting involves attachment of specific ligands to the nanoparticle surface.

These ligands may recognize receptors or antigens expressed by tumor cells or tumor-associated cells.

Passive Targeting

Many solid tumors contain abnormal blood vessels and impaired lymphatic drainage.

These characteristics can facilitate accumulation of some nanoscale materials within tumor tissue.

This phenomenon has traditionally been associated with the enhanced permeability and retention effect.

However, the extent of this effect varies substantially among tumor types and individual patients.

Tumor vascular heterogeneity, interstitial pressure, extracellular matrix density, and blood flow can all influence nanoparticle accumulation.

Consequently, passive targeting alone may not provide sufficient tumor selectivity in every clinical situation.

Active Targeting

Active targeting involves attaching a molecular ligand to the nanoparticle surface.

Potential targeting molecules include antibodies, antibody fragments, peptides, aptamers, carbohydrates, and small molecules.

After reaching the tumor, these ligands can interact with specific receptors.

Receptor-mediated uptake may increase internalization of nanoparticles into cancer cells.

Examples of investigated molecular targets include HER2, EGFR, folate receptors, transferrin receptors, and prostate-specific membrane antigen.

Active targeting can therefore provide an additional layer of specificity beyond passive tumor accumulation.

Stimuli-Responsive Nanoparticles

Tumors possess several characteristics that can be exploited for controlled drug release.

The extracellular environment of many tumors is more acidic than normal tissues.

Tumor cells may also exhibit elevated reactive oxygen species and increased activity of certain enzymes.

Nanoparticles can be engineered to respond to these differences.

Stimuli-responsive systems may reduce premature drug release and improve local drug exposure.

Nanoparticles for Combination Therapy

Cancer cells frequently develop resistance when exposed to a single therapeutic agent.

Nanoparticles can carry multiple therapeutic molecules within one delivery platform.

For example, a nanoparticle may simultaneously deliver a chemotherapeutic drug and a nucleic-acid-based inhibitor of a resistance pathway.

Combination systems can also integrate chemotherapy with immunomodulatory agents.

Co-delivery can potentially improve synchronization of drug exposure and increase therapeutic activity.

Nanoparticles for Nucleic Acid Delivery

Nucleic-acid therapeutics have considerable potential in cancer treatment.

Small interfering RNA can suppress expression of specific genes.

Messenger RNA can be used to produce therapeutic proteins or stimulate immune responses.

MicroRNA mimics or inhibitors can modify regulatory pathways involved in tumor progression.

However, nucleic acids are vulnerable to enzymatic degradation and may have difficulty crossing cellular membranes.

Nanoparticles can protect these molecules and facilitate intracellular delivery.

Figure 1. Nanoparticle-Based Targeted Cancer Drug Delivery

                    NANOPARTICLE

                         │

        ┌────────────────┼────────────────┐

        ▼                ▼                ▼

     Drug Cargo      Targeting Ligand   Surface Design

        │                │                │

        └────────────────┼────────────────┘

                         ▼

                  Tumor Vasculature

                         │

                         ▼

                Tumor Accumulation

                         │

                         ▼

               Receptor Recognition

                         │

                         ▼

                  Cellular Uptake

                         │

                         ▼

                Intracellular Release

                         │

             ┌───────────┴───────────┐

             ▼                       ▼

       Molecular Target          Cancer Cell

          Inhibition                Death

             │                       │

             └───────────┬───────────┘

                         ▼

                  Reduced Tumor

                     Growth

Figure 1: General mechanism of targeted nanoparticle-based drug delivery, including tumor accumulation, molecular recognition, cellular uptake, intracellular drug release, and anticancer activity.

Nanoparticles and the Tumor Microenvironment

The tumor microenvironment presents several biological barriers to effective drug delivery.

Cancer-associated fibroblasts can produce dense extracellular matrix components that restrict nanoparticle penetration.

High interstitial fluid pressure can reduce transport from blood vessels into tumor tissue.

Abnormal vasculature can produce heterogeneous drug distribution.

Hypoxic and necrotic regions may be poorly accessible.

Nanoparticle design must therefore consider not only cancer-cell targeting but also transport through the tumor microenvironment.

Nanoparticles and Multidrug Resistance

Multidrug resistance is a major obstacle in cancer treatment.

Cancer cells may overexpress drug-efflux transporters, modify drug metabolism, enhance DNA repair, or activate anti-apoptotic pathways.

Nanoparticles may help overcome some resistance mechanisms by improving intracellular drug delivery.

Encapsulation can also alter the interaction between therapeutic molecules and drug-efflux systems.

Co-delivery of chemotherapy with gene-silencing molecules targeting resistance-associated genes represents another potential strategy.

Review Design

The present article was prepared as a narrative review of nanoparticle-based drug delivery systems for targeted cancer therapy.

Literature Search

Relevant scientific literature was considered from major biomedical databases and peer-reviewed journals.

Search terms included combinations of “nanoparticle drug delivery,” “cancer nanomedicine,” “targeted cancer therapy,” “liposomes,” “polymeric nanoparticles,” “lipid nanoparticles,” “stimuli-responsive nanoparticles,” “nanoparticle-mediated drug delivery,” and “tumor targeting.”

Inclusion Criteria

Research addressing nanoparticle formulation, drug encapsulation, targeted delivery, tumor accumulation, controlled release, molecular targeting, therapeutic resistance, or cancer applications was considered relevant.

Data Synthesis

The literature was organized according to nanoparticle platforms, targeting mechanisms, tumor microenvironment interactions, therapeutic applications, and translational challenges.

Results

The reviewed evidence indicates that nanoparticle systems can improve several properties of anticancer drugs.

Encapsulation can increase stability and modify pharmacokinetics.

Targeting ligands can facilitate receptor-mediated uptake in appropriate tumor models.

Stimuli-responsive systems can provide controlled drug release in response to tumor-associated conditions.

Lipid and polymeric nanoparticles can also deliver nucleic acids and combination therapies.

However, nanoparticle accumulation remains highly dependent on tumor biology.

Variations in vascular permeability, extracellular matrix density, interstitial pressure, immune clearance, and tumor heterogeneity can significantly affect delivery.

Therefore, nanoparticle performance cannot be predicted solely from physicochemical characteristics

Nanoparticle-based drug delivery represents one of the most promising areas of cancer nanomedicine.

The fundamental advantage of nanoparticles is their ability to modify the biological behavior of therapeutic molecules.

A conventional drug may be rapidly metabolized or distributed throughout the body.

Encapsulation within a nanoparticle can protect the drug and alter its pharmacokinetic profile.

This may increase drug exposure at the tumor while reducing exposure to some healthy tissues.

However, nanoparticle delivery is not inherently equivalent to selective cancer targeting.

Tumors differ substantially in vascular structure, blood flow, extracellular matrix composition, and immune-cell infiltration.

The enhanced permeability and retention effect can therefore vary between patients.

Active targeting provides an additional strategy.

Ligands attached to nanoparticles can recognize tumor-associated receptors and potentially increase cellular uptake.

Nevertheless, receptor expression is often heterogeneous.

A target may be highly expressed in one region of a tumor but absent from another.

This can limit the effectiveness of a single targeting ligand.

Stimuli-responsive systems offer another promising approach.

Instead of relying exclusively on receptor expression, nanoparticles can respond to environmental characteristics such as acidity, enzymes, or reactive oxygen species.

These systems can potentially reduce premature drug release.

Another important application is combination therapy.

Cancer cells frequently use multiple mechanisms to survive treatment.

A nanoparticle capable of delivering two or more therapeutic agents may simultaneously interfere with different survival pathways.

Nucleic-acid delivery is particularly promising.

RNA-based molecules can theoretically regulate genes involved in proliferation, metastasis, immune suppression, or drug resistance.

Nanoparticles can protect these molecules from degradation and facilitate cellular uptake.

Despite these advantages, significant challenges remain.

Nanoparticles may be recognized and removed by the mononuclear phagocyte system.

Protein adsorption can modify nanoparticle behavior in biological fluids.

Manufacturing complexity can influence batch-to-batch consistency.

Long-term toxicity and biodegradation must also be carefully evaluated.

Therefore, successful clinical translation requires integration of nanomaterial science, pharmacology, molecular oncology, and toxicology.

Advantages and Limitations of Nanoparticle Delivery

Safety and Toxicological Considerations

The clinical development of nanoparticles requires careful assessment of safety.

Particle composition, size, surface charge, biodegradability, and dose can influence toxicity.

Nanoparticles may accumulate in organs involved in filtration and clearance.

Some inorganic nanomaterials may persist for extended periods.

Potential immune reactions and inflammatory responses must also be considered.

Biodegradable materials may offer advantages because they can be metabolized or eliminated after fulfilling their delivery function.

Comprehensive pharmacokinetic and toxicological studies are therefore essential before clinical application.

Future Perspectives

Future nanoparticle systems are likely to become increasingly multifunctional.

Nanoparticles may simultaneously carry therapeutic drugs, imaging agents, and molecular regulators.

Personalized nanomedicine could use tumor-specific molecular information to select appropriate targeting ligands and therapeutic cargos.

Artificial intelligence and computational modeling may help optimize nanoparticle composition and predict tumor accumulation.

Biomimetic nanoparticles, including systems designed to mimic biological membranes, are also being investigated.

Another important direction is the development of nanoparticles capable of targeting the tumor microenvironment rather than cancer cells alone.

Such approaches could modify stromal cells, tumor-associated macrophages, angiogenesis, or extracellular matrix components.

The integration of nanoparticles with immunotherapy may also provide new opportunities for improving antitumor immune responses

Nanoparticle-based drug delivery systems offer important opportunities for improving targeted cancer therapy.

Liposomes, polymeric nanoparticles, micelles, lipid nanoparticles, dendrimers, inorganic nanoparticles, and stimuli-responsive systems can modify drug distribution, improve stability, and facilitate controlled release.

Active targeting can enhance interaction with specific molecular receptors, while environmental responsiveness may provide tumor-associated drug release.

Nanoparticles can also facilitate delivery of nucleic acids and combination therapies, potentially addressing mechanisms of therapeutic resistance.

However, tumor heterogeneity, biological barriers, immune clearance, toxicity, manufacturing complexity, and variability in nanoparticle accumulation remain important challenges.

Future progress will require more precise understanding of nanoparticle–tumor interactions and integration of nanotechnology with molecular profiling and personalized medicine.

The development of safer, biodegradable, multifunctional, and patient-specific nanocarriers may ultimately improve the effectiveness and selectivity of cancer treatment.

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