Heparanase‑Targeted Magnetic Gold Nanoparticle Probe Enhances MRI Detection of Tumor Metastasis

Abstract

Heparanase (HPA) is widely expressed in metastatic malignancies and has emerged as a promising tumor‑associated antigen (TAA) for both immunotherapy and molecular imaging. We engineered a magnetic gold nanoparticle probe conjugated with an anti‑HPA monoclonal antibody (HPA&GoldMag) to enable specific visualization of HPA‑positive tumors via magnetic resonance imaging (MRI). In vitro studies confirmed that the probe selectively bound HPA‑expressing cancer cell lines, producing a pronounced T2 signal reduction. In vivo, intravenous injection of HPA&GoldMag into MKN45 tumor‑bearing nude mice resulted in significant signal attenuation in tumor, liver, kidney, and lung tissues compared with baseline scans. These findings demonstrate the probe’s robust physicochemical properties, immune specificity, and its potential as a platform for early, non‑invasive detection of metastatic tumors.

Background

Metastatic spread remains the leading cause of cancer mortality, yet current imaging modalities—ultrasound, CT, and conventional MRI—detect only macroscopic lesions once disease is advanced. Molecular imaging, particularly MRI using targeted contrast agents, offers superior soft‑tissue resolution and the capacity for early disease detection. Superparamagnetic nanoparticles conjugated to tumor‑specific antibodies have shown promise in enhancing contrast and enabling antigen‑specific imaging. HPA, an endoglycosidase that degrades heparan sulfate proteoglycans, is up‑regulated in many metastatic tumors and drives extracellular matrix remodeling, angiogenesis, and invasion. Prior work has validated HPA as a therapeutic TAA; here, we investigate its utility as a universal target for MRI‑guided tumor imaging.

Methods

Cell Lines and Animal Model

Seven human cancer cell lines were evaluated, including HPA‑positive lines (HepG2, MKN45, SGC‑7901, SW480, U2OS) and HPA‑negative controls (MCF‑7, HF). Cells were cultured under standard conditions. Fifteen BALB/c nude mice (4–5 wk) were subcutaneously inoculated with 2 × 10^6 MKN45 cells and monitored until tumor volumes reached ~1 cm before imaging.

Western Blot and Immunocytochemistry

HPA expression was quantified by Western blot (anti‑HPA, 1:200) and immunocytochemistry. Protein lysates were resolved on 10% SDS‑PAGE, transferred to PVDF, and probed with chemiluminescent detection. Cytoplasmic HPA localization was confirmed by DAB staining.

Probe Synthesis and Characterization

The HPA&GoldMag probe was assembled using the GoldMag™‑CS kit (30 nm magnetic gold nanoparticles). Atomic force microscopy (AFM) revealed an increase in hydrodynamic diameter from 13.8 nm (unlabeled) to 24.8 nm (antibody‑conjugated), confirming successful coupling.

Specificity Assessment

Immunofluorescence and flow cytometry demonstrated 95 % binding to HPA‑positive cells and <10 % to HPA‑negative cells, with no binding observed for control IgG‑GoldMag probes.

In Vitro MRI

Serial dilutions of the probe in 1 % agarose were imaged on a 3.0 T scanner using T1 and T2 sequences. Significant T2 signal loss was observed at a 1:640 dilution, indicating high sensitivity.

In Vivo MRI

After tail‑vein injection of HPA&GoldMag, mice underwent pre‑ and 2‑hour post‑injection T2‑weighted scans. Tumor, liver, kidney, and lung signals were markedly reduced compared to baseline (p < 0.05).

Statistical Analysis

Data were expressed as mean ± SD; comparisons were made by one‑way ANOVA (SPSS 13.0), with p < 0.05 considered significant.

Results

HPA Expression Across Cell Lines

Western blot and immunohistochemistry confirmed high HPA expression in HepG2, SGC‑7901, MKN45, SW480, and U2OS, whereas MCF‑7 displayed minimal expression (Figure 1).

Expression of HPA proteins in various cell lines. a Western blot (65 kDa) of HPA in HepG2, SGC‑7901, MKN45, MCF‑7, SW480, U2OS. b Immunohistochemistry of HPA in the same lines.

Probe Construction and AFM Analysis

AFM images confirmed uniform 30 nm nanoparticles and a size increase to ~25 nm after antibody conjugation, indicating successful probe fabrication (Figure 2).

a Schematic of HPA antibody conjugation. b AFM scan of HPA&GoldMag.

Specific Binding to HPA

Immunofluorescence revealed intense red staining in HPA‑positive cells; negligible signal in HPA‑negative lines and no binding for IgG‑GoldMag controls. Flow cytometry corroborated these findings, with 95 % positive binding in HPA‑positive cells (Figure 3).

a Immunofluorescence images. b Flow cytometry histograms.

In Vitro MRI Signal Reduction

Serial dilutions of the probe produced dose‑dependent T2 signal loss, with significant contrast at a 1:640 dilution (p < 0.05) (Figure 4a‑b). Cell‑labelled MRI demonstrated markedly reduced T2 signal in HPA‑positive cells compared to controls (Figure 4c‑e).

a Dilution series MRI. b Statistical analysis. c MRI of labelled cells. d T1 comparison. e T2 comparison.

In Vivo MRI of Tumor‑Bearing Mice

Post‑injection scans showed significant T2 signal attenuation in tumors, liver, kidney, and lung tissues relative to pre‑injection images (p < 0.05), confirming in vivo targeting (Figure 5).

a Pre‑ and post‑injection images. b Quantitative signal comparison.

Discussion

Our data establish HPA as a viable universal TAA for targeted MRI, overcoming the size limitations of conventional modalities. The HPA&GoldMag probe harnesses the superparamagnetic Fe_3O_4@Au core‑shell architecture to generate strong T2 contrast while retaining antibody specificity. Compared with iron oxide alone, the gold shell improves biocompatibility and functionalization efficiency, enabling robust antibody conjugation (200 µg HPA mAb per mg nanoparticles). The probe’s high affinity and low off‑target binding in vitro and in vivo underscore its potential for early metastasis detection and possibly theranostic applications.

Conclusions

We demonstrate that HPA‑conjugated magnetic gold nanoparticles possess superior physicochemical properties, high targeting specificity, and potent T2 MRI contrast. This platform offers a promising strategy for the non‑invasive, early detection of metastatic tumors and may serve as a foundation for future theranostic interventions.

Abbreviations

AFM

Atomic force micrograph

BM

Basement membrane

CT

Computed tomography

ECM

Extracellular matrix

HPA

Heparanase

HSPG

Heparan sulfate proteoglycan

MRI

Magnetic resonance imaging

PVDF

Polyvinylidene fluoride

TAA

Tumor‑associated antigen