Rational Design of Cancer Nanomedicine for Simultaneous Stealth Surface and Enhanced Cellular Uptake

Purpose: Ideal cancer nanomedicines need a stealth surface for prolonged circulation and tumor accumulation, but stealth surfaces often hinder cellular uptake. Conversely, cationic or targeting-ligand surfaces enhance uptake but cause rapid clearance and off-target interactions. This review addresses the central conflict between stealth and enhanced cellular uptake and summarizes surface-engineering strategies that integrate both properties in one system.

Hypothesis: No formal experimental hypothesis. Central thesis: “chameleon-like” drug delivery systems can turn off internalization during circulation and activate enhanced uptake at tumor sites, resolving the apparent contradiction between stealth and cellular uptake through programmed tumor-targeting strategies, stimuli-responsive surface engineering, and specific zwitterionic surfaces.

Aims: Review surface engineering of drug nanocarriers for simultaneous stealth in circulation and enhanced uptake in tumors. - Discuss programmed tumor-targeting strategies, including stimuli-sensitive nanocarriers. - Detail stealth corona-detachable systems, charge-reversal systems, tumor-acidity-protonated systems, and zwitterionic systems. - Highlight current strategies, ongoing developments, and future perspectives for clinical translation.

Delivery system: Nanocarrier types: polymeric micelles, polymeric nanoparticles, liposomes, mesoporous silica nanoparticles (MSNs), gold nanoparticles/nanorods/nanostars, carbon dots, quantum dots, PAMAM dendrimers, nanogels, upconversion nanoparticles, polymer–drug conjugates, clustered nanoparticles. - Payloads: doxorubicin (DOX), paclitaxel (PTX), docetaxel (DTX), cisplatin(IV) prodrug, gemcitabine (GEM), camptothecin (CPT), Pt prodrugs, siRNA, DNA, photosensitizers (Ce6, ALA, PpIX), imaging agents. - Surface chemistries and linkers: PEG, polyanionic peptides (EK10, polyanionic peptide), zwitterionic phosphorylcholine (PC), carboxybetaine (CB), mixed-charge ligands, DMMA, benzoic imine, MMP-cleavable peptides (GPLGIAGQ, PLGLAG, PLGVR), hyaluronic acid (HA), pHLIP, RGD, TAT, R8, iRGD, folate, biotin, iminobiotin–neutravidin. - Stimuli: tumor acidity (pH 6.5–6.8), enzymes (MMP-2/9, hyaluronidase, cathepsin B), redox/GSH, light (UV, NIR), ROS, H₂S, temperature. - Targeting mechanisms: passive EPR effect, active ligand–receptor targeting, charge reversal, size reduction, programmed tumor targeting.

Approach: Review of preclinical literature; no primary experiments. Discusses in vitro cell lines and in vivo mouse tumor models. Examples include A2780 ovarian cancer, HeLa, MCF-7, HepG2, B16F10 melanoma, 4T1 breast cancer, pancreatic cancer, lung metastasis models, and orthotopic breast cancer models. The review focuses on design principles and preclinical proof-of-concept studies; it does not report primary clinical trial data.

Key methods: Review-level synthesis of: - Nanoparticle characterization: size, zeta potential, morphology (TEM), stability. - Cellular uptake: flow cytometry, confocal laser scanning microscopy, fluorescence-activated cell sorting (FACS). - Biodistribution and tumor accumulation: ICP-MS, in vivo imaging. - Drug release: pH-, enzyme-, redox-, or light-triggered release. - Therapeutic efficacy: cytotoxicity, tumor growth inhibition, metastasis inhibition, gene silencing. - Surface property changes: zeta potential shifts, size reduction, ligand exposure, charge reversal.

Key results: Representative quantitative findings from cited studies: - MMP-2-activatable cell-penetrating peptides showed more than 10-fold increased cellular uptake after linker cleavage. - PolyHis-b-PEG micelles: DOX uptake by A2780 cells at pH 6.8 was 5 times higher than at pH 7.4 during the initial 20 min. - DMMA-modified nanocarriers reversed zeta potential from negative to positive within 10 min at pH 6.8. - PC-modified gold nanorods were internalized by cancer cells 4 times more than by normal cells; PC prodrug micelles had a drug loading content of 56.2%. - pH-responsive mixed-charge gold nanoparticles shifted zeta potential from −2 mV to +17 mV at pH 6.5, enhancing cellular uptake. - iCluster/Pt nanoparticles changed from ~104.1 nm clustered particles to small Pt-conjugated cationic PAMAM dendrimers at pH 6.8, improving tumor penetration and cellular uptake. - MMP-2-triggered PEG detachment from TAT-functionalized liposomes resulted in a 2-fold increase in cellular uptake.

Interpretation: The authors argue that stealth and enhanced cellular uptake are a “dialectical unity” in drug delivery. Tumor microenvironment-sensitive nanocarriers—including stealth corona-detachable, charge-reversal, and tumor-acidity-protonated systems—can achieve programmed targeting. Zwitterionic drug delivery systems, especially phosphorylcholine and carboxybetaine surfaces, may be the simplest and most practical route because they combine nonfouling stealth with cancer-cell-preferential uptake. The authors conclude that these strategies are promising for improved cancer nanomedicine, but clinical translation remains challenging.

Limitations: Review article; no primary data. - Complex, multi-component tumor microenvironment-sensitive nanocarriers are difficult to produce on an industrial scale. - Tumor microenvironment heterogeneity and inter-patient variability complicate universal design. - Endogenous stimuli such as pH and enzymes are difficult to control and may vary between individuals. - Protein corona formation can alter nanoparticle surface properties and targeting. - Nanoparticle stability, drug leakage during circulation, tumor penetration, and drug release after accumulation remain critical issues. - Only very few nanomedicines have been successfully translated to the clinic; clinical outcomes have often been unsatisfactory. - Response time to tumor microenvironment stimuli must be considered; protonation/deprotonation may be faster than covalent bond cleavage.