Integrin-Targeted Theranostic Nanoparticles for Clinical MRI-Traceable Treatment of Liver Fibrosis

Liver fibrosis is the critical stage in the development of chronic liver disease (CLD), from simple injury to irreversible cirrhosis. Timely detection and intervention of liver fibrosis are crucial for preventing CLD from progressing into a fatal condition. Herein, we developed iron oxide (Fe3O4) nanoparticles (IONPs) and ferulic acid (FA) coencapsulated poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs), followed by surface modification with cRGD peptides (cRGD-PLGA/IOFA) for integrin-targeted clinical magnetic resonance imaging (MRI)-traceable treatment of liver fibrosis. The cRGD peptide linked on the surface of the PLGA/IOFA NPs could specifically bind to the overexpressed integrin αvβ3 on activated hepatic stellate cells (HSCs) in the fibrotic liver, enabling the high-sensitive clinical MR imaging (3 T) and precise staging of liver fibrosis. The FA encapsulated in cRGD-PLGA/IOFA showed excellent efficacy in reducing oxidative stress and inhibiting the activation of HSCs through the transforming growth factor-β (TGF-β)/Smad pathway. Notably, the IONPs encapsulated in cRGD-PLGA/IOFA NPs could alleviate liver fibrosis by regulating hepatic macrophages through the NF-κB pathway, lowering the proportion of Ly6Chigh/CD86+, and degrading collagen fibers. The FA and IONPs in the cRGD-PLGA/IOFA produced a synergistic enhancement effect on collagen degradation, which was more effective than the IONPs treatment alone. This study demonstrates that cRGD-PLGA/IOFA NPs could effectively relieve liver fibrosis by acting on macrophages and HSCs and provide a new strategy for the clinical MRI-traceable treatment of liver fibrosis.

A Manganese Porphyrin Platform for the Design and Synthesis of Molecular and Targeted MRI Contrast Agents

Magnetic resonance imaging (MRI) contrast agents, in contrast to the plethora of fluorescent agents available to target disease biomarkers or exogenous implants, have remained predominantly non-specific. That is, they do not preferentially accumulate in specific locations in vivo because doing so necessitates longer contrast retention, which is contraindicated for current gadolinium (Gd) agents. This double-edge sword implies that Gd agents can offer either rapid elimination (but lack specificity) or targeted accumulation (but with toxicity risks). For this reason, MRI contrast agent innovation has been severely constrained. Gd-free alternatives based on manganese (Mn) chelates have been largely ineffective, as they are inherently unstable. In this study, we present a Mn(III) porphyrin (MnP) platform for bioconjugation, offering the highest stability and chemical versatility compared to any other T₁ contrast agent. We exploit the inherent metal stability conferred by porphyrins and the absence of pendant bases (found in Gd or Mn chelates) that limit versatile functionalization. As proof-of-principle, we demonstrate labeling of human serum albumin, a model protein, and collagen hydrogels for applications in in-vivo targeted imaging and material tracking, respectively. In-vitro and in-vivo results confirm unprecedented metal stability, ease of functionalization, and high T₁ relaxivity. This new platform opens the door to ex-vivo validation by fluorescent imaging and multipurpose molecular imaging in vivo.

Corrigendum: Progress of photoacoustic imaging combined with targeted photoacoustic contrast agents in tumor molecular imaging

[This corrects the article DOI: 10.3389/fchem.2022.1077937.].

Progress of photoacoustic imaging combined with targeted photoacoustic contrast agents in tumor molecular imaging

Molecular imaging visualizes, characterizes, and measures biological processes at the molecular and cellular level. In oncology, molecular imaging is an important technology to guide integrated and precise diagnosis and treatment. Photoacoustic imaging is mainly divided into three categories: photoacoustic microscopy, photoacoustic tomography and photoacoustic endoscopy. Different from traditional imaging technology, which uses the physical properties of tissues to detect and identify diseases, photoacoustic imaging uses the photoacoustic effect to obtain the internal information of tissues. During imaging, lasers excite either endogenous or exogenous photoacoustic contrast agents, which then send out ultrasonic waves. Currently, photoacoustic imaging in conjunction with targeted photoacoustic contrast agents is frequently employed in the research of tumor molecular imaging. In this study, we will examine the latest advancements in photoacoustic imaging technology and targeted photoacoustic contrast agents, as well as the developments in tumor molecular imaging research.

Magnetic resonance imaging of tumor-infiltrating lymphocytes by anti-CD3-conjugated iron oxide nanoparticles

Immune checkpoint blockade, considered a revolutionary approach in cancer treatment, is only effective in patients with high tumor-infiltrating lymphocytes (TILs). This work aimed to investigate the feasibility of targeted contrast agent (CA) based on dextran-coated superparamagnetic iron oxide nanoparticles (SPIONs-DEX) for TILs detection by magnetic resonance imaging (MRI) studies. To do so, we synthesized an MRI CA by conjugating SPIONs-DEX to an anti-CD3 monoclonal antibody via cyanogen bromide as a cross-linker. In vitro assessments demonstrated the higher labeling efficiency of the developed CA to CD3+ lymphocytes compared to SPIONs-DEX. In vivo MRI of a xenograft model of CD3+ lymphocytes revealed the significant signal loss after the intravenous injection of the bioconjugate by ~ 34% and 21% in T 2 * -weighted and T 2 -weighted images, respectively. The histopathological evaluation of xenograft tumors confirmed the labeling of lymphocytes by the targeted CA. This approach could open up a new horizon in the non-invasive assessment of TILs to identify patients eligible for immunotherapy.

GdDO3NI Enhanced Magnetic Resonance Imaging Allows Imaging of Hypoxia After Brain Injury

BACKGROUND

Brain tissue hypoxia is a common consequence of traumatic brain injury (TBI) due to the rupture of blood vessels during impact and it correlates with poor outcome. The current magnetic resonance imaging (MRI) techniques are unable to provide a direct map of tissue hypoxia.

PURPOSE

To investigate whether GdDO3NI, a nitroimidazole-based T₁ MRI contrast agent allows imaging hypoxia in the injured brain after experimental TBI.

STUDY TYPE

Prospective.

ANIMAL MODEL

TBI-induced mice (controlled cortical impact model) were intravenously injected with either conventional T₁ agent (gadoteridol) or GdDO3NI at 0.3 mmol/kg dose (n = 5 for each cohort) along with pimonidazole (60 mg/kg) at 1 hour postinjury and imaged for 3 hours following which they were euthanized.

FIELD STRENGTH/SEQUENCE

7 T/T₂ -weighted spin echo and T₁ -weighted gradient echo.

ASSESSMENT

Injured animals were imaged with T₂ -weighted spin-echo sequence to estimate the extent of the injury. The mice were then imaged precontrast and postcontrast using a T₁ -weighted gradient-echo sequence for 3 hours postcontrast. Regions of interests were drawn on the brain injury region, the contralateral brain as well as on the cheek muscle region for comparison of contrast kinetics. Brains were harvested immediately post-imaging for immunohistochemical analysis.

STATISTICAL TESTS

One-way analysis of variance and two-sample t-tests were performed with a P < 0.05 was considered statistically significant.

RESULTS

GdDO3NI retention in the injury region at 2.5-3 hours post-injection was significantly higher compared to gadoteridol (mean retention fraction 63.95% ± 27.43% vs. 20.68% ± 7.43% for gadoteridol at 3 hours) while it rapidly cleared out of the muscle region. Pimonidazole staining confirmed the presence of hypoxia in both gadoteridol and GdDO3NI cohorts, and the later cohort showed good agreement with MRI contrast enhancement.

DATA CONCLUSION

GdDO3NI was successfully shown to visualize hypoxia in the brain post-TBI using T₁ -weighted MRI at 2.5-3 hours postcontrast.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 1.

Exploring the Unique Contrast Properties of Aptamer-Gadolinium Conjugates in Magnetic Resonance Imaging for Targeted Imaging of Thrombi

Objective: An important clinical question in the determination of the extent of thrombosis-related vascular conditions is the identification of blood clot location. Fibrin is a major molecular constituent of blood clots and can, therefore, be utilized in molecular imaging. In this proof-of-concept study, we sought to prepare a fibrin-targeting magnetic resonance imaging contrast agent, using a Gd(III)-loaded fibrinogen aptamer (FA) chelate conjugate (Gd(III)-NOTA-FA) (NOTA = 1,4,7-triazacyclononane-1,4,7-triacetic acid), to endow the ability to specifically accumulate at the location of blood clots, thereby enhancing contrast capabilities. Methods: The binding affinity of FA for fibrin was confirmed by fluorescence microscopy and microscale thermophoresis. The preparation and effective loading of the chelate-aptamer conjugates were confirmed by mass spectrometry and a xylenol orange colorimetric test. Longitudinal and transverse relaxivities and the effects of target binding were assessed using T1- and T2-map sequences at 7 T. T1- and T2-weighted images were acquired after blood clots were treated with Gd(III)-NOTA-FA. Collagen was used as the protein control, while an unrelated aptamer sequence, FB139, was used as the aptamer control. Results: FA demonstrated a high affinity and selectivity toward the polymeric protein, with a K_d of 16.6 nM, confirming an avidity over fibrinogen. The longitudinal (r1) and transverse (r2) relaxivities of Gd(III)-NOTA-FA demonstrated that conjugation to the long aptamer strand shortened T1 relaxation times and increased T2 relaxation times (3.04 and 38.7 mM^-1 s^-1, respectively). These effects were amplified by binding to the fibrin target (1.73 and 46.5 mM^-1 s^-1, respectively). In vitro studies with thrombin-polymerized human blood (clots) in whole blood showed an unexpected enhancement of signal intensity (hyperintense) produced exclusively at the location of the clot during the T2-weighted scan, while the presence of fibrinogen within a whole blood pool resulted in T1 signal intensity enhancement throughout the pool. This is advantageous, as simply reversing the type of a scan from a typical T1-weighted to a T2-weighted would allow to selectively highlight the location of blood clots. Conclusions: Gd(III)-NOTA-FA can be used for molecular imaging of thrombi, through fibrin-targeted delivery of contrast to the location of blood clots in T2-weighted scans.

Environment-specific spectral modeling: A new tool for the analysis of biological specimens

The recent discovery of fluorescent dyes for improving pathologic tissues identification has highlighted the need of robust methods for performance validation especially in the field of fluorescence-guided surgery. Optical imaging of excised tissue samples is the reference tool to validate the association between dyes localization and the underlying histology in a controlled environment. Spectral unmixing may improve the validation process discriminating dye from endogenous signal. Here, an innovative spectral modeling approach that weights the spectral shifts associated with changes in chemical environment is described. The method is robust against spectral shift variations and its application leads to unbiased spectral weights estimates as demonstrated by numerical simulations. Finally, spectral shifts values computed pixel-wise from spectral images are used to display additional information with potential diagnostic value.

Synthesis and Assessment of Peptide Gd-DOTA Conjugates Targeting Extradomain B Fibronectin for Magnetic Resonance Molecular Imaging of Prostate Cancer

Contrast enhanced MRI is commonly used in imaging and treatment planning of prostate cancer. However, no tumor targeting contrast agent is commercially available for accurate detection and characterization of prostate cancer with MRI. Extradomain B fibronectin (EDB-FN), an oncoprotein present in aggressive tumors, is a promising molecular target for detection and stratification of high-risk prostate cancer. In this work, we have identified four small peptides (GVK, IGK, SGV, and ZD2) specific to EDB-FN for tumor targeting. In silico simulations of the binding patterns and affinities of peptides to the EDB protein fragment revealed different binding site to different peptide in the ligand-receptor interactions. Tumor specificity and organ distribution of the peptides were assessed using fluorescence imaging in male mice bearing PC-3 human prostate cancer xenografts. Targeted contrast agents were synthesized by conjugating tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) to the peptides in the solid phase, followed by complexation with GdCl₃. The contrast agents were characterized by MALDI-TOF mass spectrometry and relaxivity measurements. All four peptide Gd-DOTA conjugates resulted in robust tumor contrast enhancement in MR imaging of the PC3 mouse prostate cancer model. The peptide Gd-DOTA conjugates specific to EDB-FN are promising targeted small molecular macrocyclic contrast agents for MR molecular imaging of prostate cancer.

Site-Specific In Vivo Bioorthogonal Ligation via Chemical Modulation

A critical limitation of bioorthogonal click chemistry for in vivo applications has been its low reaction efficiency due to the pharmacokinetic barriers, such as blood distribution, circulation, and elimination in living organisms. To identify key factors that dominate the efficiency of click chemistry, here a rational design of near-infrared fluorophores containing tetrazine as a click moiety is proposed. Using trans-cyclooctene-modified cells in live mice, it is found that the in vivo click chemistry can be improved by subtle changes in lipophilicity and surface charges of intravenously administered moieties. By controlling pharmacokinetics, biodistribution, and clearance of click moieties, it is proved that the chemical structure dominates the fate of in vivo click ligation.

Peptide targeted high-resolution molecular imaging of prostate cancer with MRI

Non-invasive accurate detection of prostate cancer is critical for clinical management of the disease. Molecular MRI has a potential for accurate detection of prostate cancer with high spatial resolution. Fibronectin is a hallmark of epithelial-mesenchymal transition occurred in aggressive prostate cancer and highly expressed in malignant tumors. A pentapeptide CREKA targeted contrast agent CREKA-dL-(DOTA-Gd)4 was synthesized and evaluated to target fibrin-fibronectin complexes in tumor extracellular matrix for molecular MRI of prostate cancer. The contrast agent was synthesized by solid-phase peptide synthesis. The T1 relaxivity of CREKA-(DOTA-Gd)4 at 1.5 T was 33.2 mM(-1)s(-1) per molecule (8.3 per Gd). The fluorescence imaging showed that CREKA specifically bound to orthotopic PC3 prostate tumor in athymic nude mice. Strong enhancement was observed in the tumor tissue injected with CREKA-(DOTA-Gd)4 in the first 5 minutes post-injection before MR signal became visible in the bladder at a low dose of 0.03 mmol-Gd/kg. The targeted contrast agent exhibited minimal Gd retention in the main organs and tissues 2 days after injection. The peptide targeted contrast agent CREKA-(DOTA-Gd)4 is promising for high-resolution molecular MRI of prostate cancer.

Molecular MRI of atherosclerotic plaque progression in an ApoE(-/-) mouse model with a CLT1 peptide targeted macrocyclic Gd(III) chelate

Molecular imaging of atherosclerotic biomarkers is critical for non-invasive detection and diagnosis of atherosclerotic plaques and therapeutic management. Fibrin and fibronectin accumulate at elevated levels in atherosclerotic plaques and are associated with atherogenesis and disease progression. Molecular imaging of these biomarkers has the potential to non-invasively characterize plaque burden. In this work, we investigated the effectiveness of a peptide-targeted macrocyclic Gd(III) chelate, CLT1-dL-(DOTA-Gd)4, specific to fibrin-fibronectin complexes for molecular MRI of atherosclerosis. Atherosclerotic plaques were induced in Apolipoprotein E-knockout (ApoE(-/-)) mice by feeding with high fat and cholesterol-enriched diet (HFD) for up to 30 weeks. MRI of the vessel wall in the arch aorta was performed at 10, 20 and 30 weeks after the onset of HFD. High spatial-resolution MRI was performed prior and up to 35 minutes after i.v. injection of CLT1-dL-(DOTA-Gd)4 or a nonspecific control agent at a dose of 0.1 mmol-Gd/kg. CLT1-dL-(DOTA-Gd)4 produced stronger enhancement in the atherosclerotic lesions of the aortic wall than the control at all time points in the mice. Cross sectional MR images of the aortic arch revealed progressive thickening of the atherosclerotic vessel wall in the mice on HFD for up to 30 weeks. This progression correlated well to histological staining, as well as fibrin and fibronectin immunochemical stained images. Molecular MRI with CLT1-dL-(DOTA-Gd)4 has a potential for detecting atherosclerosis and non-invasive monitoring of the progression of the plaques.

Design considerations for targeted optical contrast agents

Optical fluorescence imaging with the right combination of imaging modality and targeted contrast agents offers tremendous improvement in intraoperative imaging and clinical output (i.e., image-guided cancer surgery). Therefore, it is of paramount importance to gain an in-depth knowledge in the design of targeted contrast agents to meet clinical requirements. Currently, there are several clinically approved contrast agents available; however, none perform optimally in vivo by providing optimum sensitivity, stability, specificity, and safety for target imaging, diagnosis, and therapy. In this review, we discuss basic design considerations for targeted contrast agents in terms of optical and physicochemical properties, biological and physiological interactions, and biodistribution and targeting.

Molecular ultrasound imaging using a targeted contrast agent for assessing early tumor response to antiangiogenic therapy

OBJECTIVES

Contrast-enhanced ultrasound (US) and targeted microbubbles have been shown to be advantageous for angiogenesis evaluation and disease staging in cancer. This study explored molecular US imaging of a multitargeted microbubble for assessing the early tumor response to antiangiogenic therapy.

METHODS

Target receptor expression of 2LMP breast cancer cells was quantified by flow cytometric analysis and characterization established with antibodies against mouse α(V)β3- integrin, P-selectin, and vascular endothelial growth factor receptor 2. Tumor-bearing mice (n = 15 per group) underwent contrast-enhanced US imaging of multitargeted microbubbles. Microbubble accumulation was calculated by destruction-replenishment techniques and time-intensity curve analysis. On day 0, mice underwent baseline imaging. Next, therapy group mice were injected with a 0.2-mg dose of bevacizumab, and controls received matched saline injections. Imaging was repeated on days 1 and 3. After imaging was completed on day 3, the mice were euthanized and tumors excised. Histologic analysis of microvessel density and intratumoral necrosis was completed on tumor sections.

RESULTS

On day 3 after bevacizumab dosing, a 71.8% change in tumor vasculature was shown between the therapy and control groups (P = .01). The therapy group had a 15.4% decrease in tumor vascularity, whereas the control group had a 56.4% increase.

CONCLUSIONS

Molecular US imaging of angiogenic markers can detect the early tumor response to drug therapy.