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Drug Delivery Systems and Targeting — Materials, Surfaces and Delivery Limits

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DDS controls where drugs travel and how they are released. The 0.7% median from an animal-study review highlights a delivery constraint, while approved formulations demonstrate the importance of carrier materials.

Drug Delivery Systems and Targeting — Materials, Surfaces and Delivery Limits

Based on regulatory documents and peer-reviewed primary sources / text-source review: September 2026 / illustration and English editorial revision: October 2026.

Composition: FDA approved attachments (DailyMed), Drugs@FDA, FDA product guidance, review papers (Cancer Research/Nature Reviews Materials/Nature Communications/Nature Materials/Journal of Controlled Release etc.) as primary information / last updated September 2026

ImageGen educational illustration of targeted drug delivery to tissue
ImageGen-generated educational illustration. A conceptual depiction of targeted drug delivery to tissue. It is not a photograph of an actual device, product, or specimen, nor a precise molecular structure, scale drawing, or measured dataset.
Composition of this article
  1. What is DDS?
  2. Four nanocarrier classes
  3. Passive targeting and EPR: the 1986 report
  4. The EPR debate: relevance to human tumors
  5. Author calculations: interpreting 0.7%
  6. Materials viewpoint: surfaces and clearance
  7. Active targeting: accumulation versus uptake
  8. Small ligand–drug conjugates
  9. Release control and payload state
  10. Carrier-to-drug mass ratios
  11. Materials viewpoint: requirements for generic liposomes
  12. Challenges and unresolved questions
  13. Glossary / references / source audit
Notation used in this article

Facts are statements in cited publications. Author calculations use explicitly stated assumptions. Unresolved/future items have not been confirmed as established outcomes. Interpretations are this article’s organization and reading of materials and process design, not statements by the cited authors. Source fact Author calculation Unresolved / future

Medical disclaimer

This is an explanation of materials and formulation technology, not an assessment or comparison of treatment efficacy or safety, and not medical advice. Product composition and approval dates are taken from regulatory documents. Animal-study findings must not be treated as human outcomes.

1. What is DDS?

  • DDS changes distribution and release by encapsulating, conjugating or embedding a drug. It is a delivery technology, distinct from the drug modality, and can be used with different modalities.
  • Duncan describes polymer therapeutics in the 5–100 nm range: polymer–drug conjugates, polymer–protein conjugates, micelles with covalently bound drugs, and DNA-delivery polyplexes. Liposomes and albumin particles are additional carrier classes.
  • Wilhelm et al. found a median of 0.7% of the administered nanoparticle dose reaching solid tumors in a review of ten years of preclinical studies. Delivery to the intended site is a major constraint.
    • Source fact
The key engineering point

Targeting does not automatically mean greater nanoparticle accumulation in the target tissue. Animal studies report that ligand attachment changed cancer-cell uptake without substantially changing total tumor accumulation. Separately, calculations from the compositions of approved products give carrier-material masses about 2–9 times the drug mass. This article interprets these observations as evidence that carrier design and manufacture matter alongside the drug itself. Source fact Author calculation

2. Four nanocarrier classes

Nanocarriers have several different structures. Rosenblum et al. list clinical examples of passive targeting: Doxil, Abraxane, Marqibo, DaunoXome and Onivyde in the United States; Myocet and Mepact in Europe; Genexol-PM in Korea; and SMANCS in Japan. These are examples discussed in their 2018 paper, not a newly verified comprehensive approval list. Source fact

ImageGen educational illustration of targeted drug delivery to tissue (figure 1)
Figure 1. ImageGen-generated educational illustration. A conceptual depiction of targeted drug delivery to tissue. It is not a photograph of an actual device, product, or specimen, nor a precise molecular structure, scale drawing, or measured dataset. The original schematic with its data and sources is available below.
View the original schematic and source annotations
Four nanocarrier classes (schematic) Red: drug; blue/green/brown: carrier material 1 Liposome 2 Albumin particle 3 Polymeric micelle 4 Polymer conjugate Lipid-bilayer vesicle Drug in aqueous interior Doxil / Onivyde / Vyxeos Albumin–drug particles Solvent-free formulation Abraxane Block copolymers assemble into core and shell Genexol-PM (Korea) Drug or protein attached covalently to a polymer Oncaspar / SMANCS Examples: Rosenblum (2018) [3]; compositions: FDA labels [16–20]; classifications: Duncan (2003) [12] and Cabral (2018) [13]. Four classes are this article’s organization, not an exhaustive taxonomy. Schematic only: not actual molecular shapes, relative sizes or payload positions.

Figure 1. Original vector schematic. Product examples: Rosenblum (2018) [3]; compositions: FDA labels [16–20]; carrier classifications: Duncan (2003) [12] and Cabral (2018) [13]. The four classes are organized here for explanation, not an exhaustive taxonomy. Molecular shapes, sizes and payload positions are schematic.

TypeFDA-approved exampleComposition in the labelInitial U.S. approval
PEGylated liposomeDOXIL (doxorubicin hydrochloride)STEALTH liposomes: cholesterol 3.19 mg/mL, HSPC 9.58 mg/mL, MPEG-DSPE 3.19 mg/mL. More than 90% of drug is encapsulated.November 17, 1995
PEGylated liposomeONIVYDE (irinotecan)Approximately 110 nm unilamellar liposomes: DSPC 6.81 mg/mL, cholesterol 2.22 mg/mL, MPEG-2000-DSPE 0.12 mg/mL. Irinotecan sucrose-octasulfate salt forms a gel or precipitate.October 22, 2015
Two-drug liposomeVYXEOS (daunorubicin/cytarabine)Drug molar ratio 1:5; DSPC/DSPG/cholesterol molar ratio 7:2:1. Per vial: lipid 618 mg, copper gluconate 100 mg and sucrose 2,054 mg.2017
Albumin-bound particlesABRAXANE (paclitaxel)Mean size approximately 130 nm; amorphous paclitaxel. Per vial: paclitaxel 100 mg and approximately 900 mg human albumin. Solvent-free formulation.2005
Polymer–protein conjugateONCASPAR (pegaspargase)Four 34.5 kDa enzyme subunits with 69–82 mPEG chains of approximately 5 kDa.1994

Sources: FDA labels [References 16–20], Drugs@FDA [References 24 and 26], and Initial U.S. Approval dates in the labels. Anselmo and Mitragotri describe VYXEOS as a 100 nm bilamellar liposome [Reference 15]. The table concerns formulation composition, not efficacy or clinical outcomes. Source fact

Cabral et al. describe polymeric micelles assembled from block copolymers through multicomponent interactions with drugs, proteins and nucleic acids. Interaction types and block-copolymer chemistry are central to design. The materials-engineering interpretation here is that self-assembly is used to incorporate the payload. Source fact

3. Passive targeting and EPR: the 1986 report

The idea of tumor nanocarriers has roots in Japanese research. Yasuhiro Matsumura and Hiroshi Maeda reported their findings in Cancer Research in 1986. Source fact

Matsumura and Maeda (1986): reported findings

The initial observation was that SMANCS, a polymer conjugate of the anticancer protein neocarzinostatin, accumulated in tumor tissue more than the unmodified protein. Radiolabeled proteins with molecular weights of 12,000–160,000 were examined; many accumulated progressively, reaching tumor-to-blood concentration ratios of 5 within 19–72 hours. Source fact

By contrast, neocarzinostatin, a small protein with a molecular weight of 12,000, did not reach tumor-to-blood ratios of either 1 or 5. Source fact

The authors proposed abundant tumor vasculature, increased permeability to macromolecules, and limited retrieval through blood vessels and lymphatics as contributing factors. Source fact

This is the enhanced permeability and retention (EPR) effect. Rosenblum et al. attribute the original 1986 description to Matsumura and Maeda. Preferential retention of larger conjugates provided a rationale for passive targeting with nanocarriers. Source fact

Larger is not always better. Very small constructs may undergo renal clearance, while larger ones face other transport and clearance constraints.

Published sizes on a logarithmic scale Particle diameter (nm); each major interval is tenfold 1 10 100 1,000 10,000 nm 5.5 nm Below this: rapid urinary clearance in the QD study 82–241 Liposome diameters compared in animals Product examples: 100 / 110 / 130 nm VYXEOS / ONIVYDE / ABRAXANE Tumor endothelial gaps Reported up to 2,000 nm 5.5 nm: Choi (2007) [9]; 82–241 nm: Charrois and Allen (2003) [10]. 2,000 nm: Sindhwani (2020) abstract [5]. 110/130 nm: FDA labels [17/18]; 100 nm: Anselmo and Mitragotri (2019) [15]. The 5.5 nm finding concerns quantum dots in rodents, not a universal cutoff.
Figure 2. Published diameters on a logarithmic reference axis: Choi [9], Charrois and Allen [10], Sindhwani [5], FDA labels [17/18], Anselmo and Mitragotri [15]. Different experimental systems are compared; this is not a tumor-delivery eligibility threshold.

At the small-size end, Choi et al. reported rapid urinary elimination of quantum dots with final hydrodynamic diameters below 5.5 nm in rodents. Zwitterionic or neutral coatings prevented serum-protein adsorption; adsorption increased hydrodynamic size beyond 15 nm and prevented renal clearance. Surface-bound proteins can therefore change the effective size seen in the body. Source fact

Charrois and Allen compared 82, 101, 154 and 241 nm liposomes in mice. The three smaller sizes showed similar tumor accumulation, each significantly higher than the 241 nm particles. Source fact

4. The EPR debate: relevance to human tumors

The EPR effect underpinned nanomedicine design for decades, but papers since the late 2010s have questioned its implications. The following comparison presents different published positions rather than declaring one side the winner.

PublicationReported argument / findingsPosition summarized by this article
Wilhelm et al. (2016)Median solid-tumor delivery was 0.7% of injected nanoparticle dose in a ten-year preclinical review, with implications for manufacture, cost, toxicity, imaging and therapeutic outcomes.Highlights low delivery
Danhier (2016)Argues that EPR observed in rodents does not translate effectively to human tumors and that improved efficacy should not simply be attributed to EPR.Critical of EPR-based translation
Rosenblum et al. (2018)Despite low absolute delivery, discusses relative advantage over conventional drugs; one preclinical paclitaxel example is 0.6%ID for a nanocarrier versus 0.2%ID for free drug.Potential relative advantage despite low absolute values
Sindhwani et al. (2020)Reports that endothelial gaps, previously described up to 2,000 nm, did not explain transport; up to 97% entered via active endothelial-cell processes in the studied models.Questions the gap-leakage mechanism

Sources: Wilhelm et al. [Reference 2], Danhier [4], Rosenblum et al. [3], and Sindhwani et al. [5]. The position column is this article’s summary, not an outcome directly measured by all four authors. Source fact

Rosenblum et al. discuss PET/CT imaging of copper-64-labeled liposomes in 19 patients with HER2-positive metastatic breast cancer. Uptake peaked at 24–48 hours, with potential stratification by accumulation. Their review also describes animal studies showing heterogeneity within and between tumors. Source fact

Interpreting the debate in materials terms

The disagreement concerns reproducibility and applicability across tumors, not merely whether accumulation can occur. Patient-to-patient variation motivates discussion of imaging-based selection. The analogy with a coating whose adhesion depends on the substrate is this article’s interpretation.

5. Author calculations: interpreting 0.7%

Author calculations

The following arithmetic uses published values with stated assumptions; the resulting ratios are author calculations. Author calculation

  • Assumption: 0.7% median tumor delivery in Wilhelm et al.’s animal-study review. Source fact
  • Outside the tumor: 100 − 0.7 = 99.3%.
  • Outside/tumor ratio: 99.3 ÷ 0.7 ≈ 142.
  • One preclinical relative-delivery example: 0.6% ÷ 0.2% = 3.

Limitations: 0.7% is a median from animal studies, mainly mice, not a human delivery value. The fraction outside the tumor includes liver and spleen uptake, renal elimination and material still circulating; the arithmetic does not separate these destinations. The threefold ratio comes from one specific preclinical comparison.

Nanoparticle tumor delivery (includes author calculations) 0.7% Median reaching solid tumors Ten-year animal-study review Published by Wilhelm et al. Approximately 142× Outside-tumor / tumor ratio 99.3 ÷ 0.7 = 141.9 Author calculation 3× Compared with free drug 0.6% ÷ 0.2% (one preclinical example) Author calculation Illustrative destinations per 100 units Red band: 0.7 units; remaining 99.3: liver, spleen, kidneys, blood and other sites. 0.7%: Wilhelm (2016) [2]; 0.6%/0.2%: preclinical example in Rosenblum (2018) [3]. 142× and 3× are author calculations from animal data, not human outcomes. Band length is proportional to 0.7%; other destinations are not apportioned.
Figure 3. Animal-study values from Wilhelm [2] and Rosenblum [3]. Approximately 142× and 3× are author calculations, not human delivery or treatment outcomes.

6. Materials viewpoint: surfaces and clearance

Materials viewpoint: the protein-covered surface in blood

Rosenblum et al. discuss removal by the mononuclear phagocyte system (MPS), trapping in liver sinusoids, and uptake by hepatocytes and Kupffer cells. Adsorbed serum proteins and opsonins form a protein corona that can influence targeting. Source fact

The interpretation here is that cells encounter the adsorbed protein layer rather than only the engineered bare particle surface. Choi et al. showed that protein adsorption can increase hydrodynamic size beyond 15 nm, while zwitterionic or neutral coatings can prevent it. Surface chemistry is therefore a design variable. Source fact

PEG surface modification is familiar to materials engineers. FDA doxorubicin-liposome guidance describes an MPEG coating that protects liposomes from MPS clearance and prolongs circulation. It estimates a thermodynamically limited PEG-layer thickness of a few nanometers. Source fact

A nanometer-scale polymer brush can affect distribution in the body. The analogy with dispersion stabilizers and antifouling coatings is this article’s interpretation; the evaluation environment here contains thousands of plasma proteins rather than a simple contaminant.

7. Active targeting: accumulation versus uptake

Active targeting attaches affinity ligands to a carrier to promote local accumulation, retention or uptake by selected cells. Rosenblum et al. discuss targets including HER2, folate receptors and CD44. Source fact

The same review stresses that an actively targeted carrier must first reach the target site: effective passive delivery remains a prerequisite. A ligand does not pull a particle through the body to the tumor. The next two studies illustrate this distinction. Source fact

StudyComparisonTumor accumulationCellular distribution and uptake
Kirpotin et al. (2006)PEG-terminal anti-HER2 Fab′/scFv liposomes versus untargeted liposomes in HER2-overexpressing human breast-cancer xenograft mice.Both 7–8%ID/g; antibody attachment did not change overall biodistribution or prolonged circulation.Targeted particles entered cancer cells; untargeted particles remained mainly in stroma/macrophages. Cancer-cell uptake up to sixfold higher.
Moreira et al. (2001)Antagonist-G peptide-bearing stealth liposomes versus untargeted liposomes in human small-cell-lung-cancer xenograft mice.Size-dependent, not ligand-dependent; up to 2–4%ID/g.Binding to tumor-derived cells increased 30–44-fold.

Sources: Kirpotin et al. [Reference 6] and Moreira et al. [7]. Both used mouse models. %ID/g denotes the percentage of injected dose per gram of tissue. Source fact

ImageGen educational illustration of targeted drug delivery to tissue (figure 4)
Figure 4. ImageGen-generated educational illustration. A conceptual depiction of targeted drug delivery to tissue. It is not a photograph of an actual device, product, or specimen, nor a precise molecular structure, scale drawing, or measured dataset. The original schematic with its data and sources is available below.
View the original schematic and source annotations
Ligands can change cellular uptake without changing tumor accumulation Schematic of Kirpotin et al.’s mouse study (2006) No ligand (passive) Antibody fragment (active) Often outside cancer cells (brown) Taken up into cancer cells Tumor accumulation 7–8%ID/g Stroma and macrophages Tumor accumulation 7–8%ID/g Cancer-cell uptake Up to 6× Size and surface influence arrival; ligands can act after arrival. 7–8%ID/g, distributions and up to 6×: Kirpotin (2006) abstract [6]; mouse data. Counts and positions are schematic, not measured proportions. Bottom line is author interpretation.

Figure 4. Original vector schematic of Kirpotin (2006) [6]. Tumor accumulation, distribution and uptake values are from mouse experiments. Particle counts and positions are illustrative; the concluding interpretation is this article’s. These findings do not establish identical behavior in humans.

In their 2018 review, Rosenblum et al. reported 15 approved passive-targeting nanocarriers, while active-targeting carriers had not progressed beyond clinical trials. Two Phase II trials of the PSMA-targeted docetaxel nanoparticle BIND-014 missed their primary endpoints. The review discusses tumor penetration, heterogeneity, hypoxia and endosomal escape, along with regulatory and manufacturing-scale-up complexity. This is a dated report, not a claim about the complete approval landscape in 2026. Source fact

Moreira et al. studied post-insertion of peptide ligands from PEG-lipid micelles into preformed liposomes. Up to about 0.3 µg ligand per µmol phospholipid produced cytotoxicity similar to conventional conjugation. The paper stresses scalable manufacture for clinical application. Separating particle formation from ligand attachment is the process-engineering question highlighted here. Source fact

8. Small ligand–drug conjugates

Ligand targeting has not universally failed. Approved products also exist in which the ligand is conjugated directly to a drug rather than attached to a nanoparticle.

ProductTargeting componentPayload / conjugationInitial U.S. approval
GIVLAARI (givosiran)Three N-acetylgalactosamine (GalNAc) residues target hepatocytes.Covalently conjugated siRNA.2019
PLUVICTO (lutetium Lu 177 vipivotide tetraxetan)PSMA-binding ligand.Lutetium-177 radiolabeled through a chelator; whole-compound molecular weight approximately 1,216.2022
Antibody–drug conjugate (ADC)Antibody.Drug linked to an antibody; see the separate ADC article.See the ADC article.

GIVLAARI and PLUVICTO data come from FDA labels [References 22 and 23], including Initial U.S. Approval dates. The table does not compare clinical efficacy. GalNAc nucleic-acid medicines are discussed separately in this series. Source fact

Interpreting small-molecule targeting

The animal studies above distinguish delivery of the particle to a tumor from ligand-mediated uptake after arrival. A smaller carrier or conjugate may have a different distribution regime; GalNAc-siRNA, around 16 kDa, is unlike a 100 nm liposome. However, no direct primary-source comparison establishing why one approach succeeded clinically was found in this article’s survey. This is an interpretation of separate observations, not causal proof. Source fact

ImageGen educational illustration of targeted drug delivery to tissue (figure 5)
Figure 5. ImageGen-generated educational illustration. A conceptual depiction of targeted drug delivery to tissue. It is not a photograph of an actual device, product, or specimen, nor a precise molecular structure, scale drawing, or measured dataset.

9. Release control and payload state

Release control is another pillar of DDS. Regulatory labels and papers show that the physical state of an encapsulated drug varies substantially among formulations.

(1) Crystals and salts in liposomes

Barenholz organizes DOXIL around three independent principles: Source fact

  • PEGylated nanoliposomes prolong circulation and reduce reticuloendothelial-system clearance.
  • An ammonium-sulfate gradient drives remote loading, stable doxorubicin retention and subsequent release.
  • High-transition-temperature phosphatidylcholine (53°C) with cholesterol produces a liquid-ordered lipid bilayer.

FDA guidance describes doxorubicin-sulfate crystals inside liposomes. ONIVYDE contains irinotecan as sucrose-octasulfate salt in a gel or precipitated state. The interpretation here is that controlling a solid-like internal state can limit leakage and influence release. Source fact

(2) Embedding in biodegradable microspheres

LUPRON DEPOT 3.75 mg is a lyophilized microsphere powder containing leuprolide acetate 3.75 mg, purified gelatin 0.65 mg, PLGA 33.1 mg and D-mannitol 6.6 mg. It is a monthly formulation. Drugs@FDA records approval of NDA 019732 on January 26, 1989. Source fact

Fredenberg et al. describe PLGA as the most widely used biodegradable polymer for controlled release of encapsulated drugs. Its release mechanisms are complex, making generalization and prediction difficult. Source fact

(3) Conjugation changes molecular size

ONCASPAR conjugates an enzyme with 69–82 mPEG chains of approximately 5 kDa. Increasing macromolecular size to alter clearance is the interpretation here. SMANCS is also a polymer–protein conjugate. Source fact

ImageGen educational illustration of targeted drug delivery to tissue (figure 6)
Figure 6. ImageGen-generated educational illustration. A conceptual depiction of targeted drug delivery to tissue. It is not a photograph of an actual device, product, or specimen, nor a precise molecular structure, scale drawing, or measured dataset. The original schematic with its data and sources is available below.
View the original schematic and source annotations
Payload state: three release-control concepts 1 Solid-like state in a vesicle 2 Embedded in degradable polymer 3 Polymer conjugation An ion gradient drives loading into crystals, salts or gel DOXIL / ONIVYDE Drug dispersed in PLGA microspheres Complex release mechanisms LUPRON DEPOT (monthly) Multiple PEG chains increase molecular size and alter circulation ONCASPAR / SMANCS 1: Barenholz (2012) [11], FDA guidance [28], ONIVYDE label [17]; 2: LUPRON label [21] and Fredenberg (2011) [14]; 3: ONCASPAR label [20], Matsumura and Maeda (1986) [1]. Three classes are author organization; no actual crystal shape, particle size or chain count is shown.

Figure 6. Original vector schematic. Vesicle loading: Barenholz (2012) [11], FDA guidance [28] and ONIVYDE label [17]; polymer microspheres: LUPRON DEPOT label [21] and Fredenberg (2011) [14]; conjugates: ONCASPAR label [20] and Matsumura and Maeda (1986) [1]. The three explanatory classes do not show actual dimensions or molecular structures.

10. Carrier-to-drug mass ratios

First, the quantities in the labels
  • DOXIL per mL: doxorubicin hydrochloride 2 mg; cholesterol 3.19 mg; HSPC 9.58 mg; MPEG-DSPE 3.19 mg; sucrose 94 mg. Source fact
  • ONIVYDE per mL: irinotecan free base 4.3 mg; DSPC 6.81 mg; cholesterol 2.22 mg; MPEG-2000-DSPE 0.12 mg. Source fact
  • VYXEOS per vial: daunorubicin 44 mg; cytarabine 100 mg; DSPC 454 mg; DSPG 132 mg; cholesterol 32 mg; sucrose 2,054 mg. Source fact
  • ABRAXANE per vial: paclitaxel 100 mg and approximately 900 mg human albumin. Source fact
  • LUPRON DEPOT 3.75 mg: leuprolide acetate 3.75 mg and PLGA 33.1 mg. Source fact
  • ONCASPAR: four 34.5 kDa enzyme subunits conjugated with 69–82 mPEG chains of approximately 5 kDa. Source fact
Author calculations

The following calculations compare carrier-material mass with drug mass using the published compositions. Author calculation

  • DOXIL: total lipid 3.19 + 9.58 + 3.19 = 15.96 mg; lipid/drug ≈ 8.0; PEG lipid 3.19 ÷ 15.96 ≈ 20% of lipid mass.
  • ONIVYDE: total lipid 6.81 + 2.22 + 0.12 = 9.15 mg; lipid/drug ≈ 2.1; PEG lipid 0.12 ÷ 9.15 ≈ 1.3% of lipid mass.
  • VYXEOS: lipid 454 + 132 + 32 = 618 mg; drugs 44 + 100 = 144 mg; lipid/drug ≈ 4.3.
  • ABRAXANE: 900 ÷ 100 ≈ 9 (albumin/paclitaxel).
  • LUPRON DEPOT: 33.1 ÷ 3.75 ≈ 8.8 (PLGA/drug).
  • ONCASPAR: enzyme 34.5 × 4 = 138 kDa; PEG 5 × (69–82) = 345–410 kDa. PEG contributes approximately 71–75% of conjugate mass.

Limitations: DOXIL uses a hydrochloride-salt mass, whereas ONIVYDE uses free-base mass; these bases are not normalized. ABRAXANE’s approximately 900 mg albumin is a label approximation that includes sodium caprylate and sodium acetyltryptophanate. ONCASPAR estimates simply add enzyme-subunit and mPEG molecular weights. These are materials-composition comparisons, not comparisons of efficacy or safety.

Carrier/drug mass ratios (author calculations) Bar lengths follow ratios (1× = 50 drawing units); values calculated from labels ABRAXANE LUPRON DEPOT DOXIL VYXEOS ONIVYDE ≈9× 8.8× 8.0× 4.3× 2.1× Albumin PLGA Lipids (PEG lipid ≈20%) Lipids Lipids ONCASPAR: PEG ≈71–75% of conjugate mass (≈2.5–3.0× enzyme mass). Component masses: FDA labels [16–21]. Ratios and percentages are author calculations. DOXIL uses hydrochloride mass; ONIVYDE uses free-base mass. Sucrose and other excipients excluded. Materials-composition comparison, not clinical efficacy or safety.
Figure 7. Masses from FDA labels [16–21]; ratios and percentages calculated by the author. Salt bases are not normalized and other excipients, such as sucrose, are excluded. Not an efficacy or safety comparison.

11. Materials viewpoint: requirements for generic liposomes

Materials viewpoint: equal ingredients need not mean equal structures

Drugs@FDA records DOXIL (NDA 050718) approval on November 17, 1995, and the first generic, Sun Pharma ANDA 203263, on February 4, 2013. The interval is approximately 17 years and two months, calculated here. Barenholz’s 2012 review noted the absence of a generic two years after relevant patent expiry. Source fact Author calculation

FDA’s product-specific doxorubicin-liposome guidance, revised as a draft in May 2022, sets out material and process requirements for subsequent products. These requirements help explain the engineering challenge but do not establish the cause of the approval interval. Source fact

  • Composition: qualitatively the same excipients (Q1), with concentrations within ±5% (Q2).
  • Process: ammonium-sulfate-gradient active loading; liposome formation with ammonium sulfate, size reduction, gradient formation, then active drug loading.
  • Lipid raw materials: match the reference product’s natural/synthetic route category and compare molecular-species distributions, not only specification compliance.
  • Properties: composition, doxorubicin-sulfate crystal state, internal volume/pH/ion concentrations, morphology and lamellarity, bilayer phase transitions, size distribution, PEG-layer thickness, surface potential and leakage under multiple conditions.
  • Size distribution: measure D10, D50 and D90; compare D50 and SPAN = (D90−D10)/D50 using at least 30 vials of each product.

Matching the ingredient list is not enough: internal structure and interfaces also matter. Crystal state, bilayer phase behavior, PEG-layer thickness and size distribution depend on processing. The guidance recommends identifying critical process parameters and material attributes by assessing liposome-property sensitivity. Source fact

For lipid suppliers, the comparison can extend to molecular-species distributions and whether raw materials arise from natural or synthetic routes. This materials interpretation connects with the separate discussion of equivalence in the biosimilars article.

What is compared for a subsequent liposomal product? FDA doxorubicin-liposome guidance: May 2022 revised draft Initial requirements Qualitatively matched excipients (Q1) Concentrations within ±5% (Q2) Ammonium-sulfate gradient for active loading Same lipid-route category Compare molecular-species distributions Interior Composition / loading / drug:lipid Doxorubicin-sulfate crystals Internal volume / pH / ions Membrane Morphology and lamellarity Lipid-bilayer phase transition Leakage under multiple conditions Surface PEG thickness (a few nm) Potential and charge Size Measure D10 / D50 / D90 Compare D50 and SPAN At least 30 vials each Reference approval: Nov 17, 1995 → first generic: Feb 4, 2013 (≈17 years 2 months). Properties: FDA guidance [28]; dates: Drugs@FDA [24/25]. Interval calculated here. Four boxes are author organization. Guidance also calls for human bioequivalence testing.
Figure 8. Properties from FDA draft guidance [28]; dates from Drugs@FDA [24/25]. The approximately 17-year, two-month interval is calculated here, not a causal explanation of the development delay.

12. Challenges and unresolved questions

(1) Unresolved EPR implications

The significance of EPR remains debated. Sindhwani et al. suggest that understanding active transport through endothelial cells could open delivery strategies. This article’s September 2026 survey did not confirm a clinical product exploiting that pathway; this remains unresolved here. Source fact Unresolved / future

(2) Clinical value of particle-bound ligands

Rosenblum et al.’s statement about active-targeting approval was made in 2018. This article did not comprehensively verify whether such nanocarriers had subsequently received FDA approval as of September 2026; current approval status is unresolved, not evidence of nonapproval. Source fact Unresolved / future

(3) Imaging-based patient selection

Rosenblum et al. discuss imaging-based patient selection. This article’s survey did not confirm primary evidence that the approach had become a standard clinical procedure. Source fact Unresolved / future

Summary
  • DDS is delivery engineering. Liposomes, albumin particles, polymeric micelles and polymer conjugates include clinical-product examples. Source fact
  • EPR was reported in 1986; tumor/blood protein concentration ratios reached 5 in 19–72 hours in the reported experiments. Source fact
  • Median nanoparticle tumor delivery was 0.7% in the animal-study review; the outside/tumor ratio is approximately 142 by author calculation. Author calculation
  • Mouse studies distinguish ligand-mediated cellular uptake from total tumor accumulation. Source fact
  • Calculated carrier/drug mass ratios in the examples are approximately 2–9. Author calculation
  • Subsequent liposomal products must address internal structure and interfaces, not only ingredients. The first DOXIL generic approval came approximately 17 years and two months later. Author calculation

13. Glossary

DDS
Drug delivery systems: control of drug distribution and release.
Nanocarrier
Nanoscale particle or macromolecule that encapsulates or conjugates a payload.
Liposome
A lipid-bilayer vesicle with an aqueous interior and membrane that can carry drugs.
Polymeric micelle
A self-assembled block-copolymer particle with core and shell.
Polymer conjugate
Drug or protein covalently attached to a polymer chain.
Passive targeting
Distribution influenced by carrier size and surface properties.
Active targeting
Ligand-mediated binding or uptake by cells bearing a selected receptor.
EPR effect
Enhanced permeability and retention of macromolecules or particles in tumors; reported by Matsumura and Maeda in 1986.
Ligand
A selectively binding component, such as an antibody, peptide or sugar.
Protein corona
Adsorbed protein layer that changes a particle’s effective biological properties.
MPS
Mononuclear phagocyte system involved in removal of foreign material, including in liver and spleen.
PEGylation
Attachment of polyethylene glycol to alter aggregation and clearance.
%ID/g
Percentage of injected dose per gram of tissue.
Remote loading
Loading into preformed liposomes driven by an ion gradient across the membrane.
PLGA
Biodegradable copolymer of lactic and glycolic acids used for controlled release.
Q1/Q2
In this guidance, qualitatively matched excipients and concentrations within ±5%.
SPAN
Distribution-width metric: (D90−D10)/D50.

14. Primary references

  1. Matsumura, Y., Maeda, H.“A new concept for macromolecular therapeutics in cancer chemotherapy: mechanism of tumoritropic accumulation of proteins and the antitumor agent smancs”Cancer Research 46(12 Pt 1), 6387–6392 (1986). PMID 2946403 — pubmed.ncbi.nlm.nih.gov
  2. Wilhelm, S. et al.“Analysis of nanoparticle delivery to tumours”Nature Reviews Materials 1, 16014 (2016). doi:10.1038/natrevmats.2016.14 — nature.com
  3. Rosenblum, D., Joshi, N., Tao, W., Karp, J.M., Peer, D.“Progress and challenges towards targeted delivery of cancer therapeutics”Nature Communications 9, 1410 (2018). doi:10.1038/s41467-018-03705-y — nature.com
  4. Danhier, F.“To exploit the tumor microenvironment: Since the EPR effect fails in the clinic, what is the future of nanomedicine?”Journal of Controlled Release 244(Pt A), 108–121 (2016). doi:10.1016/j.jconrel.2016.11.015 — pubmed.ncbi.nlm.nih.gov
  5. Sindhwani, S. et al.“The entry of nanoparticles into solid tumours”Nature Materials 19(5), 566–575 (2020). doi:10.1038/s41563-019-0566-2 — pubmed.ncbi.nlm.nih.gov
  6. Kirpotin, D.B. et al.“Antibody targeting of long-circulating lipidic nanoparticles does not increase tumor localization but does increase internalization in animal models”Cancer Research 66(13), 6732–6740 (2006). doi:10.1158/0008-5472.CAN-05-4199 — pubmed.ncbi.nlm.nih.gov
  7. Moreira, J.N., Gaspar, R., Allen, T.M.“Targeting Stealth liposomes in a murine model of human small cell lung cancer”Biochimica et Biophysica Acta 1515(2), 167–176 (2001). doi:10.1016/s0005-2736(01)00411-4 — pubmed.ncbi.nlm.nih.gov
  8. Moreira, J.N., Ishida, T., Gaspar, R., Allen, T.M.“Use of the post-insertion technique to insert peptide ligands into pre-formed stealth liposomes with retention of binding activity and cytotoxicity”Pharmaceutical Research 19(3), 265–269 (2002). doi:10.1023/a:1014434732752 — pubmed.ncbi.nlm.nih.gov
  9. Choi, H.S. et al.“Renal clearance of quantum dots”Nature Biotechnology 25(10), 1165–1170 (2007). doi:10.1038/nbt1340 — pubmed.ncbi.nlm.nih.gov
  10. Charrois, G.J., Allen, T.M.“Rate of biodistribution of STEALTH liposomes to tumor and skin: influence of liposome diameter and implications for toxicity and therapeutic activity”Biochimica et Biophysica Acta 1609(1), 102–108 (2003). doi:10.1016/s0005-2736(02)00661-2 — pubmed.ncbi.nlm.nih.gov
  11. Barenholz, Y.“Doxil® — The first FDA-approved nano-drug: Lessons learned”Journal of Controlled Release 160(2), 117–134 (2012). doi:10.1016/j.jconrel.2012.03.020 — pubmed.ncbi.nlm.nih.gov
  12. Duncan, R.“The dawning era of polymer therapeutics”Nature Reviews Drug Discovery 2(5), 347–360 (2003). doi:10.1038/nrd1088 — pubmed.ncbi.nlm.nih.gov
  13. Cabral, H., Miyata, K., Osada, K., Kataoka, K.“Block Copolymer Micelles in Nanomedicine Applications”Chemical Reviews 118(14), 6844–6892 (2018). doi:10.1021/acs.chemrev.8b00199 — pubmed.ncbi.nlm.nih.gov
  14. Fredenberg, S., Wahlgren, M., Reslow, M., Axelsson, A.“The mechanisms of drug release in poly(lactic-co-glycolic acid)-based drug delivery systems — a review”International Journal of Pharmaceutics 415(1-2), 34–52 (2011). doi:10.1016/j.ijpharm.2011.05.049 — pubmed.ncbi.nlm.nih.gov
  15. Anselmo, A.C., Mitragotri, S.“Nanoparticles in the clinic: An update”Bioengineering & Translational Medicine 4(3), e10143 (2019). doi:10.1002/btm2.10143 — pmc.ncbi.nlm.nih.gov
  16. FDA/NLM DailyMed“DOXIL (doxorubicin hydrochloride liposome injection) prescribing information” — dailymed.nlm.nih.gov
  17. FDA/NLM DailyMed“ONIVYDE (irinotecan liposome injection) prescribing information” — dailymed.nlm.nih.gov
  18. FDA/NLM DailyMed“ABRAXANE (paclitaxel protein-bound particles) prescribing information” — dailymed.nlm.nih.gov
  19. FDA/NLM DailyMed“VYXEOS (daunorubicin and cytarabine liposome) prescribing information” — dailymed.nlm.nih.gov
  20. FDA/NLM DailyMed“ONCASPAR (pegaspargase) prescribing information” — dailymed.nlm.nih.gov
  21. FDA/NLM DailyMed“LUPRON DEPOT 3.75 mg (leuprolide acetate for depot suspension) prescribing information” — dailymed.nlm.nih.gov
  22. FDA/NLM DailyMed“GIVLAARI (givosiran) prescribing information” — dailymed.nlm.nih.gov
  23. FDA/NLM DailyMed“PLUVICTO (lutetium Lu 177 vipivotide tetraxetan) prescribing information” — dailymed.nlm.nih.gov
  24. FDA Drugs@FDA“NDA 050718 DOXIL (LIPOSOMAL)”approval history — accessdata.fda.gov
  25. FDA Drugs@FDA“ANDA 203263 Doxorubicin Hydrochloride (liposomal), Sun Pharma”approval history — accessdata.fda.gov
  26. FDA Drugs@FDA“NDA 207793 ONIVYDE”approval history — accessdata.fda.gov
  27. FDA Drugs@FDA“NDA 019732 LUPRON DEPOT”approval history — accessdata.fda.gov
  28. FDA“Draft Guidance on Doxorubicin Hydrochloride(Injectable, liposomal)”product-specific draft guidance, revised May 2022(PDF) — accessdata.fda.gov

15. Claim–source correspondence (audit)

Claim in this articleEvidence / limitationsClassification
The initial observation was that SMANCS, a polymer conjugate of the anticancer protein neocarzinostatin, accumulated in tumor tissue more than the unmodified protein. Radiolabeled proteins with molecular weights of 12,000–160,000 were examined; many accumulated progressively, reaching tumor-to-blood concentration ratios of 5 within 19–72 hours. By contrast, neocarzinostatin, a small protein with a molecular weight of 12,000, did not reach tumor-to-blood ratios of either 1 or 5. The authors proposed abundant tumor vasculature, increased permeability to macromolecules, and limited retrieval through blood vessels and lymphatics as contributing factors.Matsumura and Maeda (1986) [Reference 1] https://pubmed.ncbi.nlm.nih.gov/2946403/ Source fact Source fact
Wilhelm et al. found a median of 0.7% of the administered nanoparticle dose reaching solid tumors in a review of ten years of preclinical studies. Delivery to the intended site is a major constraint. The review discusses implications for manufacture, cost, toxicity, imaging and therapy.Wilhelm et al. (2016) [Reference 2] https://www.nature.com/articles/natrevmats201614 Source fact Source fact
Nanocarriers have several different structures. Rosenblum et al. list clinical examples of passive targeting: Doxil, Abraxane, Marqibo, DaunoXome and Onivyde in the United States; Myocet and Mepact in Europe; Genexol-PM in Korea; and SMANCS in Japan. These are examples discussed in their 2018 paper, not a newly verified comprehensive approval list. This is the enhanced permeability and retention (EPR) effect. Rosenblum et al. attribute the original 1986 description to Matsumura and Maeda. Preferential retention of larger conjugates provided a rationale for passive targeting with nanocarriers. Rosenblum et al. discuss PET/CT imaging of copper-64-labeled liposomes in 19 patients with HER2-positive metastatic breast cancer. Uptake peaked at 24–48 hours, with potential stratification by accumulation. Their review also describes animal studies showing heterogeneity within and between tumors. Rosenblum et al. discuss removal by the mononuclear phagocyte system (MPS), trapping in liver sinusoids, and uptake by hepatocytes and Kupffer cells. Adsorbed serum proteins and opsonins form a protein corona that can influence targeting. Active targeting attaches affinity ligands to a carrier to promote local accumulation, retention or uptake by selected cells. Rosenblum et al. discuss targets including HER2, folate receptors and CD44. The same review stresses that an actively targeted carrier must first reach the target site: effective passive delivery remains a prerequisite. A ligand does not pull a particle through the body to the tumor. The next two studies illustrate this distinction. In their 2018 review, Rosenblum et al. reported 15 approved passive-targeting nanocarriers, while active-targeting carriers had not progressed beyond clinical trials. Two Phase II trials of the PSMA-targeted docetaxel nanoparticle BIND-014 missed their primary endpoints. The review discusses tumor penetration, heterogeneity, hypoxia and endosomal escape, along with regulatory and manufacturing-scale-up complexity. This is a dated report, not a claim about the complete approval landscape in 2026. Rosenblum et al. discuss imaging-based patient selection. This article’s survey did not confirm primary evidence that the approach had become a standard clinical procedure. The review contrasts 0.6%ID nanocarrier with 0.2%ID free-drug delivery in one preclinical example and discusses heterogeneous accumulation.Rosenblum et al. (2018) [Reference 3] https://www.nature.com/articles/s41467-018-03705-y Source fact Source fact
Argues that EPR observed in rodents does not translate effectively to human tumors and that improved efficacy should not simply be attributed to EPR.Danhier (2016) [Reference 4] https://pubmed.ncbi.nlm.nih.gov/27871992/ Source fact Source fact
Reports that endothelial gaps, previously described up to 2,000 nm, did not explain transport; up to 97% entered via active endothelial-cell processes in the studied models.Sindhwani et al. (2020) [Reference 5] https://pubmed.ncbi.nlm.nih.gov/31932672/ Source fact Source fact
PEG-terminal anti-HER2 Fab′/scFv liposomes versus untargeted liposomes in HER2-overexpressing human breast-cancer xenograft mice. Both 7–8%ID/g; antibody attachment did not change overall biodistribution or prolonged circulation. Targeted particles entered cancer cells; untargeted particles remained mainly in stroma/macrophages. Cancer-cell uptake up to sixfold higher.Kirpotin et al. (2006) [Reference 6] https://pubmed.ncbi.nlm.nih.gov/16818648/ Source fact Source fact
Antagonist-G peptide-bearing stealth liposomes versus untargeted liposomes in human small-cell-lung-cancer xenograft mice. Size-dependent, not ligand-dependent; up to 2–4%ID/g. Binding to tumor-derived cells increased 30–44-fold.Moreira et al. (2001) [Reference 7] https://pubmed.ncbi.nlm.nih.gov/11718672/ Source fact Source fact
Moreira et al. studied post-insertion of peptide ligands from PEG-lipid micelles into preformed liposomes. Up to about 0.3 µg ligand per µmol phospholipid produced cytotoxicity similar to conventional conjugation. The paper stresses scalable manufacture for clinical application. Separating particle formation from ligand attachment is the process-engineering question highlighted here.Moreira et al. (2002) [Reference 8] https://pubmed.ncbi.nlm.nih.gov/11934232/ Source fact Source fact
At the small-size end, Choi et al. reported rapid urinary elimination of quantum dots with final hydrodynamic diameters below 5.5 nm in rodents. Zwitterionic or neutral coatings prevented serum-protein adsorption; adsorption increased hydrodynamic size beyond 15 nm and prevented renal clearance. Surface-bound proteins can therefore change the effective size seen in the body.Choi et al. (2007) [Reference 9] https://pubmed.ncbi.nlm.nih.gov/17891134/ Source fact Source fact
Charrois and Allen compared 82, 101, 154 and 241 nm liposomes in mice. The three smaller sizes showed similar tumor accumulation, each significantly higher than the 241 nm particles.Charrois and Allen (2003) [Reference 10] https://pubmed.ncbi.nlm.nih.gov/12507764/ Source fact Source fact
Barenholz organizes DOXIL around three independent principles: PEGylated nanoliposomes prolong circulation and reduce reticuloendothelial-system clearance. An ammonium-sulfate gradient drives remote loading, stable doxorubicin retention and subsequent release. High-transition-temperature phosphatidylcholine (53°C) with cholesterol produces a liquid-ordered lipid bilayer.Barenholz (2012) [Reference 11] https://pubmed.ncbi.nlm.nih.gov/22484195/ Source fact Source fact
Duncan describes polymer therapeutics in the 5–100 nm range: polymer–drug conjugates, polymer–protein conjugates, micelles with covalently bound drugs, and DNA-delivery polyplexes. Liposomes and albumin particles are additional carrier classes.Duncan (2003) [Reference 12] https://pubmed.ncbi.nlm.nih.gov/12750738/ Source fact Source fact
Cabral et al. describe polymeric micelles assembled from block copolymers through multicomponent interactions with drugs, proteins and nucleic acids. Interaction types and block-copolymer chemistry are central to design. The materials-engineering interpretation here is that self-assembly is used to incorporate the payload.Cabral et al. (2018) [Reference 13] https://pubmed.ncbi.nlm.nih.gov/29957926/ Source fact Source fact
Fredenberg et al. describe PLGA as the most widely used biodegradable polymer for controlled release of encapsulated drugs. Its release mechanisms are complex, making generalization and prediction difficult.Fredenberg et al. (2011) [Reference 14] https://pubmed.ncbi.nlm.nih.gov/21640806/ Source fact Source fact
VYXEOS described as a 100 nm bilamellar liposome; the paper summarizes approved nanomedicine examples.Anselmo and Mitragotri (2019) [Reference 15] https://pmc.ncbi.nlm.nih.gov/articles/PMC6764803/ Source fact Source fact
DOXIL per mL: doxorubicin hydrochloride 2 mg; cholesterol 3.19 mg; HSPC 9.58 mg; MPEG-DSPE 3.19 mg; sucrose 94 mg. More than 90% drug encapsulation; label indicates 1995 initial approval.DOXIL label [Reference 16] https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1c153e9e-4cf2-4ac7-9cf9-16f9b48d7dce Source fact Source fact
ONIVYDE per mL: irinotecan free base 4.3 mg; DSPC 6.81 mg; cholesterol 2.22 mg; MPEG-2000-DSPE 0.12 mg. Approximately 110 nm unilamellar vesicles containing irinotecan sucrose-octasulfate gel/precipitate; 2015 initial approval.ONIVYDE label [Reference 17] https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=c8b58efa-1820-48a4-b70d-62918fc4abfc Source fact Source fact
ABRAXANE per vial: paclitaxel 100 mg and approximately 900 mg human albumin. Approximately 130 nm particles, amorphous paclitaxel, solvent-free formulation; 2005 initial approval.ABRAXANE label [Reference 18] https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=24d10449-2936-4cd3-b7db-a7683db721e4 Source fact Source fact
VYXEOS per vial: daunorubicin 44 mg; cytarabine 100 mg; DSPC 454 mg; DSPG 132 mg; cholesterol 32 mg; sucrose 2,054 mg. DSPC/DSPG/cholesterol molar ratio 7:2:1; copper gluconate 100 mg; drug molar ratio 1:5; 2017 initial approval.VYXEOS label [Reference 19] https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=7ea701ce-e7d3-4349-a9c2-642a501d45c8 Source fact Source fact
ONCASPAR: four 34.5 kDa enzyme subunits conjugated with 69–82 mPEG chains of approximately 5 kDa. 1994 initial approval.ONCASPAR label [Reference 20] https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ac7b6a6f-6ddb-48c6-8088-d8a8e3fea6ce Source fact Source fact
LUPRON DEPOT 3.75 mg is a lyophilized microsphere powder containing leuprolide acetate 3.75 mg, purified gelatin 0.65 mg, PLGA 33.1 mg and D-mannitol 6.6 mg. It is a monthly formulation. Drugs@FDA records approval of NDA 019732 on January 26, 1989.LUPRON DEPOT label [Reference 21] https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=00c486b0-bd7b-4898-834d-8c656e5e73cb Source fact Source fact
GIVLAARI: GalNAc three-residue ligand conjugated to siRNA, molecular weight approximately 16,000; 2019 initial approval.GIVLAARI label [Reference 22] https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=167e663c-11e1-497b-a3fc-951d65d58eaa Source fact Source fact
PLUVICTO: PSMA ligand radiolabeled with lutetium-177 through a chelator; whole-compound molecular weight approximately 1,216; 2022 initial approval.PLUVICTO label [Reference 23] https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=14908037-2892-4d98-a053-253ce35afb1a Source fact Source fact
DOXIL NDA 050718 approved November 17, 1995.Drugs@FDA [Reference 24] https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=050718 Source fact Source fact
Sun Pharma generic ANDA 203263 approved February 4, 2013.Drugs@FDA [Reference 25] https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=203263 Source fact Source fact
ONIVYDE NDA 207793 approved October 22, 2015.Drugs@FDA [Reference 26] https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=207793 Source fact Source fact
LUPRON DEPOT NDA 019732 approved January 26, 1989.Drugs@FDA [Reference 27] https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=019732 Source fact Source fact
Composition: qualitatively the same excipients (Q1), with concentrations within ±5% (Q2). Process: ammonium-sulfate-gradient active loading; liposome formation with ammonium sulfate, size reduction, gradient formation, then active drug loading. Lipid raw materials: match the reference product’s natural/synthetic route category and compare molecular-species distributions, not only specification compliance. Properties: composition, doxorubicin-sulfate crystal state, internal volume/pH/ion concentrations, morphology and lamellarity, bilayer phase transitions, size distribution, PEG-layer thickness, surface potential and leakage under multiple conditions. Size distribution: measure D10, D50 and D90; compare D50 and SPAN = (D90−D10)/D50 using at least 30 vials of each product. PEG surface modification is familiar to materials engineers. FDA doxorubicin-liposome guidance describes an MPEG coating that protects liposomes from MPS clearance and prolongs circulation. It estimates a thermodynamically limited PEG-layer thickness of a few nanometers. Matching the ingredient list is not enough: internal structure and interfaces also matter. Crystal state, bilayer phase behavior, PEG-layer thickness and size distribution depend on processing. The guidance recommends identifying critical process parameters and material attributes by assessing liposome-property sensitivity. Guidance revised as a draft in May 2022.FDA doxorubicin-liposome product-specific draft guidance [Reference 28] https://www.accessdata.fda.gov/drugsatfda_docs/psg/PSG_050718.pdf Source fact Source fact
Outside the tumor: 100 − 0.7 = 99.3%. Outside/tumor ratio: 99.3 ÷ 0.7 ≈ 142. One preclinical relative-delivery example: 0.6% ÷ 0.2% = 3. DOXIL: total lipid 3.19 + 9.58 + 3.19 = 15.96 mg; lipid/drug ≈ 8.0; PEG lipid 3.19 ÷ 15.96 ≈ 20% of lipid mass. ONIVYDE: total lipid 6.81 + 2.22 + 0.12 = 9.15 mg; lipid/drug ≈ 2.1; PEG lipid 0.12 ÷ 9.15 ≈ 1.3% of lipid mass. VYXEOS: lipid 454 + 132 + 32 = 618 mg; drugs 44 + 100 = 144 mg; lipid/drug ≈ 4.3. ABRAXANE: 900 ÷ 100 ≈ 9 (albumin/paclitaxel). LUPRON DEPOT: 33.1 ÷ 3.75 ≈ 8.8 (PLGA/drug). ONCASPAR: enzyme 34.5 × 4 = 138 kDa; PEG 5 × (69–82) = 345–410 kDa. PEG contributes approximately 71–75% of conjugate mass. Carrier/drug ratios approximately 2–9. ONCASPAR PEG/enzyme mass approximately 2.5–3.0. DOXIL-to-first-generic interval approximately 17 years and two months.Limitations: DOXIL uses a hydrochloride-salt mass, whereas ONIVYDE uses free-base mass; these bases are not normalized. ABRAXANE’s approximately 900 mg albumin is a label approximation that includes sodium caprylate and sodium acetyltryptophanate. ONCASPAR estimates simply add enzyme-subunit and mPEG molecular weights. These are materials-composition comparisons, not comparisons of efficacy or safety.Author calculation Author calculation
Clinical products exploiting active endothelial transport, post-2018 active-targeting FDA approvals, and established imaging-based patient selection were not confirmed comprehensively in the September 2026 survey.Rosenblum et al.’s statement about active-targeting approval was made in 2018. This article did not comprehensively verify whether such nanocarriers had subsequently received FDA approval as of September 2026; current approval status is unresolved, not evidence of nonapproval.Unresolved / future Unresolved / future
The animal studies above distinguish delivery of the particle to a tumor from ligand-mediated uptake after arrival. A smaller carrier or conjugate may have a different distribution regime; GalNAc-siRNA, around 16 kDa, is unlike a 100 nm liposome. However, no direct primary-source comparison establishing why one approach succeeded clinically was found in this article’s survey. This is an interpretation of separate observations, not causal proof.No direct comparative primary study was confirmed; the discussion is an interpretation of separate published observations.Interpretation / scope note
Author organization of DDS as delivery engineering, carrier classes, the EPR debate, surface/protein-corona effects, PEG analogies, post-arrival ligand effects, payload-state and release-control categories, internal-structure/interface equivalence, and separation of carrier formation from ligand attachment for scale-up.Author interpretation based on published material; not a position of the cited authors or regulators.Interpretation / scope note
This is an explanation of materials and formulation technology, not an assessment or comparison of treatment efficacy or safety, and not medical advice. Product composition and approval dates are taken from regulatory documents. Animal-study findings must not be treated as human outcomes.Author interpretation based on published material; not a position of the cited authors or regulators.Interpretation / scope note
Educational ImageGen illustrations and vector schematics are distinguished from real specimens and measured data.Author interpretation based on published material; not a position of the cited authors or regulators.Interpretation / scope note

Text-source review: September 26, 2026. Sources include regulatory labels, Drugs@FDA, FDA guidance and peer-reviewed literature. Author interpretations and calculations are distinguished from source facts. Animal-study values, including 0.7% and %ID/g, are not human clinical outcomes. The EPR debate, subsequent active-targeting approvals and imaging-based selection remain unresolved in the stated survey. This is an explanation of materials and formulation technology, not an assessment or comparison of treatment efficacy or safety, and not medical advice. Product composition and approval dates are taken from regulatory documents. Animal-study findings must not be treated as human outcomes. ImageGen illustrations are educational models, not photographs, micrographs or measured data; original quantitative schematics are retained.

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