MRI monitoring of nanocarrier accumulation and release using Gadolinium-SPIO co-labelled thermosensitive liposomes

A Facile NMR Method for Pre-MRI Evaluation of Trigger-Responsive T1 Contrast Enhancement

There is a growing interest in developing paramagnetic nanoparticles as responsive magnetic resonance imaging (MRI) contrast agents, which feature switchable T1 image contrast of water protons upon biochemical cues for better discerning diseases. However, performing an MRI is pragmatically limited by its cost and availability. Hence, a facile, routine method for measuring the T1 contrast is highly desired in early-stage development. This work presents a single-point inversion recovery (IR) nuclear magnetic resonance (NMR) method that can rapidly evaluate T1 contrast change by employing a single, optimized IR pulse sequence that minimizes water signal for "off-state" nanoparticles and allows for sensitively measuring the signal change with "switch-on" T1 contrast. Using peptide-induced liposomal gadopentetic acid (Gd3+-DTPA) release and redox-sensitive manganese oxide (MnO2) nanoparticles as a demonstration of generality, this method successfully evaluates the T1 shortening of water protons caused by liposomal Gd3+-DTPA release and Mn2+ formation from MnO2 reduction. Furthermore, the NMR measurement is highly correlated to T1-weighted MRI scans, suggesting its feasibility to predict the MRI results at the same field strength. This NMR method can be a low-cost, time-saving alternative for pre-MRI evaluation for a diversity of responsive T1 contrast systems.

Fe-Based Theranostic Agents Respond to the Tumor Microenvironment for MRI-Guided Ferroptosis-/Apoptosis-Inducing Anticancer Therapy

Tumor microenvironment-specific magnetic resonance imaging (MRI) contrast agents are conducive to accurate diagnoses by visualization of biochemical and pathological changes for suitable treatment. Herein, we reported a pH-responsive contrast agent DFeZd NP with MRI diagnosis and tumor treatment capabilities. DFeZd NPs can map the pH change by modulating the MR signal in different acid-base environments. Moreover, T1 signals are stronger in the tumor site, which proves efficient in distinguishing malignant tumors from normal tissues, as well as demarcating the tumor boundary. Subsequently, sustained supply of Fe through the Fe-based contrast agent leads to Fe redox cycling and lipid peroxides, inducing ferroptosis in tumor cells. Furthermore, under an acidic tumor microenvironment, in the presence of ascorbic acid, increased Fe²⁺ is generated, which serves as a stronger inducer of ferroptosis. Moreover, due to the different relaxivity of Fe³⁺ and Fe²⁺, redox cycling and ferroptosis in tumors can be monitored by MRI. Therefore, we propose DFeZd NPs as accessible and promising Fe-based dopamine-derived contrast agents for specific MRI imaging and ferroptosis induction for anticancer therapy.

Organic nanoparticle tracking during pharmacokinetic studies

To understand how nanoparticles (NPs) interact with biological barriers and to ensure they maintain their integrity over time, it is crucial to study their in vivo pharmacokinetic (PK) profiles. Many methods of tracking have been used to describe the in vivo fate of NPs and to evaluate their PKs and structural integrity. However, they do not deliver the same level of information and this may cause misinterpretations. Here, the authors review and discuss the different methods for in vivo tracking of organic NPs. Among them, Förster resonance energy transfer (FRET) presents great potential to track NPs' integrity. However, FRET still requires validated methods to extract and quantify NPs in biological fluids and tissues.

Liposomal Fe(III) Macrocyclic Complexes with Hydroxypropyl Pendants as MRI Probes

Paramagnetic liposomes containing Fe(III) complexes were prepared by incorporation of mononuclear (Fe(L1) or Fe(L3)) or dinuclear (Fe2(L2)) coordination complexes of 1,4,7-triazacyclononane macrocycles containing 2-hydroxypropyl pendant groups. Two different types of paramagnetic liposomes were prepared. The first type, LipoA, has the mononuclear Fe(L1) complex loaded into the internal aqueous core. The second type, LipoB, has the amphiphilic Fe(L3) complex inserted into the liposomal bilayer and the internal aqueous core loaded with either Fe(L1) (LipoB1) or Fe2(L2) (LipoB2). LipoA enhances both T1 and T2 water proton relaxation rates. Treatment of LipoA with osmotic gradients to produce a nonspherical liposome produces a liposome with a chemical exchange saturation transfer effect as shown by an asymmetry analysis but only at high osmolarity. LipoB1, which contains an amphiphilic complex in the liposomal bilayer, produced a broadened Z-spectrum upon treatment of the liposome with osmotic gradients. The r1 relaxivity of LipoB1 and LipoB2 were higher than the r1 relaxivity of LipoA on a per Fe basis, suggesting an important contribution from the amphiphilic Fe(III) center. The r1 relaxivities of paramagnetic liposomes are relatively constant over a range of magnetic field strengths (1.4-9.4 T), with the ratio of r2/r1 substantially increasing at high field strengths. MRI studies of LipoB1 in mice showed prolonged contrast enhancement in blood compared to the clinically employed Gd(DOTA), which was injected at a 2-fold higher dose per metal than the Fe(III)-loaded liposomes.

Imaging Beyond Seeing: Early Prognosis of Cancer Treatment

Assessing cancer response to therapeutic interventions has been realized as an important course to early predict curative efficacy and treatment outcomes due to tumor heterogeneity. Compared to the traditional invasive tissue biopsy method, molecular imaging techniques have fundamentally revolutionized the ability to evaluate cancer response in a spatiotemporal manner. The past few years has witnessed a paradigm shift on the efforts from manufacturing functional molecular imaging probes for seeing a tumor to a vantage stage of interpreting the tumor response during different treatments. This review is to stand by the current development of advanced imaging technologies aiming to predict the treatment response in cancer therapy. Special interest is placed on the systems that are able to provide rapid and noninvasive assessment of pharmacokinetic drug fates (e.g., drug distribution, release, and activation) and tumor microenvironment heterogeneity (e.g., tumor cells, macrophages, dendritic cells (DCs), T cells, and inflammatory cells). The current status, practical significance, and future challenges of the emerging artificial intelligence (AI) technology and machine learning in the applications of medical imaging fields is overviewed. Ultimately, the authors hope that this review is timely to spur research interest in molecular imaging and precision medicine.

Comparative study on contrast enhancement of Magnevist and Magnevist-loaded nanoparticles in pancreatic cancer PDX model monitored by MRI

Background:

The aim of this study was to compare contrast enhancement of Magnevist® (gadopentate dimeglumine (Mag)) to that of PEGylated Magnevist®-loaded liposomal nanoparticles (Mag-Lnps) in pancreatic cancer patient-derived xenograft (PDX) mouse model via magnetic resonance imaging (MRI).

Methods:

Mag-Lnps formulated by thin-film hydration and extrusion was characterized for the particle size and zeta potential. A 21.1 T vertical magnet was used for all MRI. The magnet was equipped with a Bruker Advance console and ParaVision 6.1 acquisitions software. Mag-Lnps phantoms were prepared and imaged with a 10-mm birdcage coil. For in vivo imaging, animals were sedated and injected with a single dose (4 mg/kg) of Mag or Mag-Lnps with Mag equivalent dose. Using a 33-mm inner diameter birdcage coil, T₁ maps were acquired, and signal to noise ratio (SNR) measured for 2 h.

Results:

Mag-Lnps phantoms showed a remarkable augmentation in contrast with Mag increment. However, in in vivo imaging, no significant difference in contrast was observed between Mag and MRI. While Mag-Lnps was observed to have fairly high tumor/muscle (T/M) ratio in the first 30 min, free Mag exhibited higher T/M ratio over the time-period between 30 and 120 min. Overall, there was no statistically significant difference between Mag and Mag-Lnp in rating MR image quality. Low payload of Mag entrapment by Lnps and restricted access of water (protons) to Mag-Lnps may have affected the performance of Mag-Lnps as an effective contrast agent.

Conclusion:

This study showed no significance difference in MRI contrast between Mag and Mag-Lnp pancreatic cancer PDX mouse models.

In Vivo Evaluation of Magnetic Targeting in Mice Colon Tumors with Ultra-Magnetic Liposomes Monitored by MRI

PURPOSE

The development of theranostic nanocarriers as an innovative therapy against cancer has been improved by targeting properties in order to optimize the drug delivery to safely achieve its desired therapeutic effect. The aim of this paper is to evaluate the magnetic targeting (MT) efficiency of ultra-magnetic liposomes (UML) into CT26 murine colon tumor by magnetic resonance imaging (MRI).

PROCEDURES

Dynamic susceptibility contrast MRI was applied to assess the bloodstream circulation time. A novel semi-quantitative method called %I_0.25, based on the intensity distribution in T₂^*-weighted MRI images was developed to compare the accumulation of T₂ contrast agent in tumors with or without MT. To evaluate the efficiency of magnetic targeting, the percentage of pixels under the intensity value I_0.25 (I_0.25 = 0.25(I_max - I_min)) was calculated on the intensity distribution histogram.

RESULTS

This innovative method of processing MRI images showed the MT efficiency by a %I_0.25 that was significantly higher in tumors using MT compared to passive accumulation, from 15.3 to 28.6 %. This methodology was validated by ex vivo methods with an iron concentration that is 3-fold higher in tumors using MT.

CONCLUSIONS

We have developed a method that allows a semi-quantitative evaluation of targeting efficiency in tumors, which could be applied to different T₂ contrast agents.

Current developments in drug delivery with thermosensitive liposomes

Thermosensitive liposomes (TSLs) have been an important research area in the field of tumor targeted chemotherapy. Since the first TSLs appeared that using 1,2-dipalmitoyl-sn-glyce-ro-3-phosphocholine (DPPC) as the primary liposomal lipid, many studies have been done using this type of liposome from basic and practical aspects. While TSLs composed of DPPC enhance the cargo release near the phase transition temperature, it has been shown that many factors affect their temperature sensitivity. Thus numerous attempts have been undertaken to develop new TSLs for improving their thermal response performance. The main objective of this review is to introduce the development and recent update of innovative TSLs formulations, including combination of radiofrequency ablation (RFA), high-intensity focused ultrasound (HIFU), magnetic resonance imaging (MRI) and alternating magnetic field (AMF). In addition, various factors affecting the design of TSLs, such as lipid composition, surfactant, size and serum components are also discussed.

An update on nanoparticle-based contrast agents in medical imaging

Despite the great value of current exogenous contrast agents for providing main diagnostic information, they still have certain drawbacks such as short blood half life, nonspecific biodistribution, fast clearance, slight renal toxicity and poor contrast in fat patients. Nanoparticles (NPs) are used as novel contrast agents that represent a promising strategy for the non invasive diagnosis. As a platform, nanoparticulates are compatible for developing targeted contrast agents. Advances in nanotechnology will provide enhanced sensitivity and specificity for tumor imaging enabling earlier detection of metastases. This article focuses on fundamental issue such as biological interactions, clearance routes, coating of NPs and presents a wide discussion about most recent category of NPs that are used as contrast agents and thebenefits/concerns issues associated with their use in clinical procedures.

Molecular imaging of brain localization of liposomes in mice using MALDI mass spectrometry

Phospholipids have excellent biocompatibility and are therefore often used as main components of liposomal drug carriers. In traditional bioanalytics, the in-vivo distribution of liposomal drug carriers is assessed using radiolabeled liposomal constituents. This study presents matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) as an alternative, label-free method for ex-vivo molecular imaging of liposomal drug carriers in mouse tissue. To this end, indocyanine green as cargo and two liposomal markers, 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine conjugated with monodisperse polyethylene glycol (PEG36-DSPE) were incorporated into liposomal carriers and administered to mice. We used MALDI MSI of the two lipid markers in both positive and negative ion mode for visualization of liposome integrity and distribution in mouse organs. Additional MSI of hemoglobin in the same tissue slice and pixel-by-pixel computational analysis of co-occurrence of lipid markers and hemoglobin served as indicator of liposome localization either in parenchyma or in blood vessels. Our proof-of-concept study suggests that liposomal components and indocyanine green distributed into all investigated organs.