Ligand-Based Active Targeting: Mechanisms, Advantages, and Applications

Ligand-based active targeting is transforming drug delivery by enabling carriers to recognize and bind specifically to diseased cells through ligand–receptor interactions. This precise targeting improves drug efficacy and minimizes unwanted side effects compared to passive approaches. Among the most promising tools in this field, immunoliposomes combine the versatility of liposomes with the specificity of antibodies, paving the way for more intelligent, more efficient therapeutic delivery systems. In this article, Creative Biolabs explores the mechanisms, advantages, and diverse applications of ligand-based active targeting in next-generation nanomedicine.

Introduction: The Promise of Ligand-Based Active Targeting

Conventional chemotherapy for cancer, such as doxorubicin (DOX) and cisplatin (CDDP) for osteosarcoma treatment, has limited efficacy due to poor targeting and severe systemic toxicity. As a result, the 5-year survival rate for osteosarcoma patients is only 60-70%. Passive targeting via the enhanced permeability and retention (EPR) effect improves drug localization but is variable across tumors and fails to ensure specific cellular uptake. In comparison with non-targeted controls, targeted delivery by iron oxide nanoparticles (IONPs) with a size of 30 nm only exhibited 1.15-fold higher tumor accumulation. Therefore, targeted delivery that enables advanced delivery precisions are needed.

Ligand-based active targeting addresses these issues by conjugating ligands (proteins, peptides, etc.) to carriers, enabling specific binding to overexpressed tumor receptors. For example, alendronate (ALN)-modified nanoparticles have fivefold higher affinity for the bone tumor microenvironment, and transferrin (Tf)-conjugated sub-5nm ultrafine IONPs (uIONPs) show 6-fold greater tumor retention. As most carriers are modulable, various ligands can be integrated into the delivery systems to target specific biomarkers (Figure 1). For instance, folate (FA) can bind to folate receptors (FRs) in ovarian and breast cancers; hyaluronic acid (HA) can target CD44 in pancreatic and osteosarcoma cancer stem cells; RGD peptides can recognize integrins in angiogenesis-dependent tumors. Moreover, ligand-based active targeted systems could improve hydrophobic drug solubility, protect payloads, prolong circulation, and enable stimuli-responsive release.

Creative Biolabs supports every step, including ligand discovery, conjugation, formulation, and characterization, under one roof. Explore our capabilities: Targeted Delivery.

Fig.1 Nanocarriers modified by different functional ligands.¹

How Ligand-Based Active Targeting Works

Ligand-based active targeting, as a core strategy for precise nano-drug delivery in cancer therapy, operates through a sequence of highly specific molecular interactions and cellular processes to address the limitations of conventional chemotherapy (non-selective toxicity) and passive targeting (variable EPR effect efficiency). It leverages "lock-and-key" binding between bioactive ligands and overexpressed biomarkers on tumor cells or tumor-associated tissues, enabling stepwise, controllable drug delivery.

Ligand-biomarker specificity

The first step hinges on ligand-biomarker specificity. Ligands are selected based on the unique expression profile of tumor targets. For instance, bisphosphonates (BPs), such as alendronate (ALN) and zoledronate (ZOL), can bind to hydroxyapatite (HAp), the main inorganic component of bone tissue. Therefore, BPs are ideal for osteosarcoma targeting. It has been proven that ALN-modified nanoparticles exhibited a fivefold higher affinity for the bone tumor microenvironment than unmodified carriers. Another typical example is folic acid (FA), a ligand commonly used in the treatment of ovarian, breast, and lung cancers. It is selected as it can target folate receptors (FRs), which are overexpressed in ovarian, breast, and lung cancers.

Receptor-Mediated Endocytosis

Once ligands bind to their cognate receptors, the second step, receptor-mediated endocytosis, is triggered. This active cellular process internalizes ligand-modified nanocarriers into tumor cells via specialized pathways (e.g., clathrin-dependent or caveolin-mediated endocytosis), avoiding non-specific uptake by normal cells. For example, in osteosarcoma, RGD-modified nanocarriers can bind to integrins on tumor cells, inducing lattice-protein-mediated endocytosis to enter the cytoplasm; Tf-uIONPs can also be internalized via TfR-mediated pathways.

Controllable Drug Release

The last step is controllable drug release, which is typically facilitated by the tumor microenvironment. To this end, many ligand-modified nanocarriers were designed for stimuli-responsive release. For example, HA-modified nanogels co-loaded with doxorubicin (DOX) and cisplatin (CDDP) rely on the acidic pH of the tumor microenvironment (pH 6.0-6.5) to trigger the release of the payloads, thus further improving the on-target cytotoxicity while minimizing the systemic toxicity.

In conclusion, ligand-based active targeting concisely integrates three key features: ligand specificity, receptor-mediated internalization, and microenvironment-responsive release into one orchestrated process. Therefore, it can overcome various limitations in traditional cancer delivery. Its inherent dependency on well-characterized ligand-biomarker pairs (FA-FR, HA-CD44, RGD-integrin, etc.) also makes it broadly applicable to various cancer types, thus setting the foundation for personalized cancer treatment.

Major Ligand Types and Their Applications in Modern Drug Delivery

Different classes of ligands are utilized in ligand-based active targeting. Each of these ligand classes uses its unique physiologic properties to target and bind to tumor-specific biomarkers (Figure 2). The principal ligand categories encompass proteins, peptides, aptamers, carbohydrates, and small molecules.

Fig.2 Different biological ligands for active targeting.⁴

Proteins and Antibodies

Description:

Protein and antibody ligands are bioactive proteins that can bind specifically to receptors overexpressed on target cells.

Common formats:

Key examples include transferrin (Tf, an iron-transporting protein), trastuzumab (a monoclonal antibody against HER2), Fab/scFv ( fragments of antibodies), and Z-domains (engineered high-affinity proteins smaller than full antibodies).

Properties:

• They exhibit high target specificity and strong receptor affinity; Z-domains further offer advantages, such as small size (avoiding clearance by the mononuclear phagocyte system, MPS) and lower immunogenicity compared to full antibodies.

Applications:

• Tf-conjugated sub-5 nm ultrafine iron oxide nanoparticles (Tf-uIONPs) can bind to Tf receptors (TfR) on osteosarcoma cells, triggering receptor-mediated endocytosis and achieving 6-fold greater tumor retention than unmodified uIONPs.
• Trastuzumab-modified graphene oxide (GO) nanocomposites can induce dual antitumor effects against osteosarcoma cells via HER2-mediated cytotoxicity and GO-induced oxidative stress.
• Mesoporous silica nanoparticles (MSNs) modified with HER2-binding affinity proteinsbodies have an increased accumulation in SK-BR-3 breast cancer tumors by ~90% compared to unmodified MSNs.

Peptides

Description:

Peptide ligands are short amino acid sequences (5–30 residues) that bind tumor receptors via specific motifs. They are designed or screened (e.g., via phage display) to match overexpressed tumor biomarkers.

Common formats:

Widely used variants include RGD (Arg-Gly-Asp, targeting integrins), YSA (YSAYPDSVPMMS, targeting EphA2), and iRGD (CRGDK/R, a tumor-penetrating peptide with dual binding motifs).

Properties:

• Low immunogenicity, easy chemical synthesis, and good tissue penetration;
• Some (e.g., iRGD) can switch binding targets post-cleavage to enhance deep tumor penetration.

Applications:

• RGD-modified polymeric micelles (RGD-DOX-PM) can load doxorubicin (DOX) with 57%-73% efficiency, and induce 6-fold higher inhibition of MG-63 osteosarcoma cell proliferation when compared to non-targeted micelles.
• YSA-conjugated liposomes loaded with DOX can promote cell uptake of Saos-2 osteosarcoma, thus increasing on-target cytotoxicity by nearly 2-fold.
• iRGD can bind to ɑv integrins on tumor endothelial cells. After being cleaved in tumor cells, it can expose a CendR motif that binds to neuropilin-1 (NRP-1). This switch in affinity can promote tumor-specific penetration of molecules.

Aptamers

Description:

Aptamer ligands are single-stranded DNA or RNA oligonucleotides (15-60 nucleotides) that can fold into 3D structures to bind tumor biomarkers (e.g., proteins, receptors) with high specificity. They are considered "chemical antibodies" in modern drug delivery.

Common formats:

Representative examples include AS-1411 (binds nucleolin), CD133 aptamers (targets CD133⁺ cancer stem cells), and GBI-10 (binds tenascin-C in pancreatic cancer).

Properties:

• Low immunogenicity, easy chemical modification (e.g., conjugation to nanocarriers), and high target selectivity;
• Their small size also aids tumor penetration.

Applications:

• AS-1411-modified mesoporous silica nanoparticles (MSNs) can load CX-5461 (an rRNA synthesis inhibitor) and accumulate in the nucleolus of HeLa cells, inducing pro-death autophagy and suppressing tumor growth in xenografts.
• CD133 aptamer-conjugated PLGA nanoparticles (Ap-SaL-NP) can deliver salinomycin to CD133⁺ osteosarcoma stem cells (OSCs), thereby reducing tumor sphere formation by 40%.
• GBI-10 aptamers in combination with cell-penetrating peptides (CPPs) can enhance camptothecin prodrug (CPTD) delivery to pancreatic ductal adenocarcinoma, thereby improving tumor penetration.

Carbohydrates

Description:

Carbohydrate ligands (polysaccharides or monosaccharides) are biocompatible ligands that bind carbohydrate-specific receptors on tumor cells. They leverage the Warburg effect (tumor cells' high demand for sugar) for targeting.

Common formats:

Key examples include hyaluronic acid (HA, a glycosaminoglycan), mannose (a monosaccharide), and fructose (a hexose sugar).

Properties:

• Biodegradable, non-toxic, and often responsive to tumor microenvironments (e.g., acidic pH);
• HA can act as a "double-functional" ligand (targeting CD44 and serving as a nanocarrier backbone).

Applications:

• HA-modified nanogels co-loaded with cisplatin (CDDP) and DOX can release drugs in acidic osteosarcoma microenvironments (pH-responsive release), thus reducing lung metastasis by 71.4% in K7M2 tumor models.
• Mannose-coupled lamellar layered double hydroxide (LDH) nanocomposites can deliver siRNA to U2OS osteosarcoma cells via lectin receptor-mediated endocytosis, resulting in a 66% cell-killing efficiency (2.5-fold higher than unmodified LDH).
• Fructose-modified MnP nanocomplexes (Fru-MnP) can bind GLUT5 transporters on 143B osteosarcoma cells, thus catalyzing Fenton-like reactions to generate hydroxyl radicals for chemodynamic therapy.

Small molecules (Vitamins)

Description:

Small-molecule ligands, particularly vitamins, can target nutrient receptors that are overexpressed on tumor cells (which demand more vitamins for rapid proliferation), offering low-cost, easy-to-conjugate options for targeting.

Common formats:

Primary examples include folic acid (FA, vitamin B9), cobalamin (vitamin B12), and biotin (vitamin B7, targeting sodium-dependent multivitamin transporters, SMVT).

Properties:

• They have small molecular weights (avoiding steric hindrance during conjugation), high receptor affinity, and low production costs;
• Their natural role in cell metabolism ensures minimal off-target binding to normal cells.

Applications:

• FA-modified liposomes loaded with DOX and edelfosine can enhance intracellular uptake in FR-positive MG63 osteosarcoma cells and result in synergistic apoptosis.
• Cobalamin-conjugated insulin nanoparticles can avoid gastrointestinal digestion and target transcobalamin receptors (TCR) on leukemia cells, improving insulin delivery to tumors.
• Biotin-modified PLGA nanoparticles loaded with gemcitabine can bind to SMVT on AsPC-1 pancreatic cancer cells, leading to increased drug accumulation in tumors.

Tip: When in doubt, run a ligand panel screen against your receptor and compare binding, internalization, and downstream potency under matched payload loading.

Immunoliposomes: GPS for Lipid Nanocarriers

Immunoliposomes are lipid-based nanocarriers modified with antibodies or their fragments (e.g., Fab', scFv) via conjugation/adsorption. Acting as "GPS" for lipid nanocarriers, they guide precise drug delivery to tumors through antibody-antigen binding.

Fig.3 Structure of immunoliposomes.3

There are three key properties of immunoliposomes:

1. High Targeting Specificity
   The binding of an antibody with its antigen is highly specific, and therefore, off-target drug accumulation is reduced. For instance, HER2 antibody-conjugated immunoliposomes were found to be exclusively internalized in HER2-positive SK-BR-3 breast cancer cells and were not internalized in HER2-negative MCF-10A normal breast cells. This treatment methodology resulted in a 30% decrease in systemic toxicity (e.g., cardiotoxicity of doxorubicin) compared to traditional methods.
2. Enhanced Cellular Uptake
   Compared to unmodified liposomes, immunoliposomes significantly improve tumor cell uptake via receptor-mediated endocytosis. For instance, anti-EGFR antibody-modified liposomes loaded with paclitaxel (PTX) have a 3.2-fold higher uptake rate in EGFR-positive MG63 osteosarcoma cells than non-targeted liposomes.
3. Low Immunogenicity
   Instead of full-length antibodies, antibody fragments (e.g., Fab') are used to avoid activating the complement system or inducing anti-antibody immune responses. For example, Fab'-modified immunoliposomes show no detectable antibody-dependent cell-mediated cytotoxicity (ADCC) against normal cells.

By leveraging the unique properties, immunoliposomes are extensively applied in cancer therapy.

1. Breast Cancer Targeting
   In SK-BR-3 breast cancer xenograft mice, anti-HER2 antibody-modified immunoliposomes can encapsulate docetaxel, achieving an 8-fold higher tumor drug concentration than free docetaxel. As a result, the tumor growth was inhibited by 78% and the peripheral neuropathy (a common side effect of docetaxel) was reduced by 50%.
2. Osteosarcoma Therapy
   CD44, a key driver of drug resistance, is overexpressed in osteosarcoma stem cells (OSCs). In K7M2 osteosarcoma-bearing mice, anti-CD44 antibody-modified immunoliposomes loaded with doxorubicin (DOX) can reduce OSC populations by 60% and lung metastasis nodules by 65%, with no significant damage to normal osteoblasts (hFOB 1.19 cells).
3. Pancreatic Cancer Penetration
   Tenascin-C is abundant in the dense stroma of pancreatic ductal adenocarcinoma (PDAC), which blocks drug penetration. Anti-tenascin-C antibody-modified immunoliposomes carrying gemcitabine can target tenascin-C to "navigate" through the stroma, thus increasing gemcitabine's intratumoral penetration depth by 2.3-fold and inhibiting PDAC growth by 62%.

Practical Workflow: From Target Idea to In Vivo Proof

1. Define the target (expression, internalization, safety window).
2. Screen ligands (antibody/fragment, peptide, aptamer, small molecule) for binding and uptake.
3. Select the carrier (liposome vs. polymer NP) based on payload and release profile.
4. Pick a linker/conjugation method that preserves ligand orientation and activity.
5. Formulate and load the drug; optimize size, PDI, zeta potential, and encapsulation efficiency.
6. Characterize (binding kinetics, receptor competition, internalization rate, release kinetics, serum stability).
7. Evaluate in vitro (target vs. off-target cells; quantitative uptake; potency shift).
8. Evaluate in vivo (biodistribution, target engagement, PK/PD markers).
9. Iterate on ligand density, PEG length, and lipid composition to balance stealth and binding.

Need a turnkey program?

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Why Creative Biolabs

Creative Biolabs brings end-to-end targeted delivery capabilities to your HA research:

Creative Biolabs supports ligand selection, immunoliposome design, conjugation chemistry, and microfluidic production under strong analytical controls. Because we cover discovery through scale-ready workflows, teams can move faster with fewer unknowns.

Explore more: Targeting Module Development Services at Creative Biolabs.

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Conclusion: A Smarter Way to Deliver

Ligand-based active targeting moves us from broad exposure to precise engagement, and immunoliposomes are one of the most practical vehicles to realize that vision. When you align the right receptor, the right ligand, and the right carrier, you raise intracellular drug levels where it counts and lower exposure where it does not. With an integrated partner, you can design, build, and verify a targeted system with confidence.

Ready to accelerate your program?

Partner with Creative Biolabs to design and validate your ligand-based active targeting system, including immunoliposome development, conjugation chemistry, and fit-for-purpose analytics. Start here: Targeting Module Development Services.

References

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2. Shi, P. et al. "Active targeting schemes for nano-drug delivery systems in osteosarcoma therapeutics." J Nanobiotechnol 21, 103 (2023). https://jnanobiotechnology.biomedcentral.com/articles/10.1186/s12951-023-01826-1.
3. Vera-López, K. J., Aranzamendi-Zenteno, M., Davila-Del-Carpio, G. & Nieto-Montesinos, R. "Using Immunoliposomes as Carriers to Enhance the Therapeutic Effectiveness of Macamide N-3-Methoxybenzyl-Linoleamide." Neurology International 17, 38 (2025). https://www.mdpi.com/2035-8377/17/3/38. Distributed under Open Access license CC BY 4.0, without modification.
4. Yoo, J., Park, C., Yi, G., Lee, D. & Koo, H. "Active Targeting Strategies Using Biological Ligands for Nanoparticle Drug Delivery Systems." Cancers 11, 640 (2019). https://www.mdpi.com/2072-6694/11/5/640. Distributed under Open Access license CC BY 4.0, without modification.
5. Xu, Y. et al. "Probing and Enhancing Ligand-Mediated Active Targeting of Tumors Using Sub-5 nm Ultrafine Iron Oxide Nanoparticles." Theranostics 10, 2479–2494 (2020). http://www.thno.org/v10p2479.htm.