Imaging of innate immunity activation in vivo with a redox-tuned PET reporter

Dual Enzyme-Driven Cascade Reactions Modulate Immunosuppressive Tumor Microenvironment for Catalytic Therapy and Immune Activation

Lactate-enriched tumor microenvironment (TME) fosters an immunosuppressive milieu to hamper the functionality of tumor-associated macrophages (TAMs). However, tackling the immunosuppressive effects wrought by lactate accumulation is still a big challenge. Herein, we construct a dual enzyme-driven cascade reaction platform (ILH) with immunosuppressive TME modulation for photoacoustic (PA) imaging-guided catalytic therapy and immune activation. The ILH is composed of iridium (Ir) metallene nanozyme, lactate oxidase (LOx), and hyaluronic acid (HA). The combination of Ir nanozyme and LOx can not only efficiently consume lactate to reverse the immunosuppressive TME into an immunoreactive one by promoting the polarization of TAMs from the M2 to M1 phenotype, thus enhancing antitumor defense, but also alleviate tumor hypoxia as well as induce strong oxidative stress, thus triggering immunogenic cell death (ICD) and activating antitumor immunity. Furthermore, the photothermal performance of Ir nanozyme can strengthen the cascade catalytic ability and endow ILH with a PA response. Based on the changes in PA signals from endogenous molecules, three-dimensional multispectral PA imaging was utilized to track the process of cascade catalytic therapy in vivo. This work provides a nanoplatform for dual enzyme-driven cascade catalytic therapy and immune activation by regulating the immunosuppressive TME.

Development of STING probes and visualization of STING in multiple tumor types

PURPOSE

The stimulator of interferon genes (STING) is a critical component of the innate immune system and plays a pivotal role in tumor immunotherapy. Developing non-invasive in vivo diagnostic methods for visualizing STING is highly valuable for STING-related immunotherapy. This work aimed to build a noninvasive imaging platform that can dynamically and quantitatively monitor tumor STING expression.

METHODS

We investigated the in vivo positron emission tomography (PET) imaging of STING-expressing tumors (B16F10, MC38, and Panc02) with STING-targeted radioprobe ([18F]F-CRI1). The expression of STING in tumors was quantified, and correlation analysis was performed between these results and the outcomes of PET imaging. Furthermore, we optimized the structure of [18F]F-CRIn with polyethylene glycol (PEG) to improve the pharmacokinetic characteristics in vivo. A comprehensive comparison of the imaging and biodistribution results obtained with the optimized probes was conducted in the B16F10 tumors.

RESULTS

The PET imaging results showed that the uptake of [18F]F-CRI1 in tumors was positively correlated with the expression of STING in tumors (r = 0.9184, P < 0.001 at 0.5 h). The lipophilicity of the optimized probes was significantly reduced. As a result of employing optimized probes, B16F10 tumor-bearing mice exhibited significantly improved tumor visualization in PET imaging, along with a marked reduction in retention within non-target areas such as the gallbladder and intestines. Biodistribution experiments further validated the efficacy of probe optimization in reducing uptake in non-target areas.

CONCLUSION

In summary, this work demonstrated a promising pathway for the development of STING-targeted radioprobes, advancing in vivo PET imaging capabilities.

Application of copper (I) selective ligands for PET imaging of reactive oxygen species through metabolic trapping

INTRODUCTION

Reactive oxygen species (ROS) are attractive targets for clinical PET imaging. In this study, we hypothesized that PET imaging of ROS would be possible by using chelating ligands (L) that form stable complexes with copper (I) but not with copper (II), based on metabolic trapping. Namely, when [64Cu][CuI(L)2]+ is oxidized by ROS, the oxidized complex will release [64Cu]Cu2+. Then, the released [64Cu]Cu2+ will be trapped inside the cell, resulting in PET signal depending on the redox potential of ROS. To examine the potential of this novel molecular design for ROS imaging, we synthesized copper (I) complexes with bicinchoninic acid (BCA) disodium salt and bathocuproinedisulfonic acid (BCS) disodium salt and evaluated their reactivity with several kinds of ROS. In addition, the cellular uptake of [64Cu][CuI(BCS)2]3- and the stability of [64Cu][CuI(BCS)2]3- in a biological condition were also evaluated.

METHODS

[64Cu]Cu2+ was reduced to [64Cu]Cu+ by ascorbic acid and coordinated with BCA and BCS in the acetate buffer to synthesize [64Cu][CuI(BCA)2]3- and [64Cu][CuI(BCS)2]3-. The radiochemical yields were determined by thin-layer chromatography (TLC). After [64Cu][CuI(BCS)2]3- was incubated with hydroxyl radical, lipid peroxide, superoxide, and hydrogen peroxide, the percentage of released [64Cu]Cu2+ from the parent complex was evaluated by TLC. HT-1080 human fibrosarcoma cells were treated with 0.1 % Dimethyl sulfoxide (control), imidazole ketone erastin (IKE), or IKE + ferrostatin-1 (Fer-1). Then, the uptake of [64Cu][CuI(BCS)2]3- to HT-1080 cells in each group was evaluated as %Dose/mg protein. Lastly, [64Cu][CuI(BCS)2]3- was incubated in human plasma, and its intact ratio was determined by TLC.

RESULTS

The radiochemical yield of [64Cu][CuI(BCS)2]3- (86 ± 1 %) was higher than that of [64Cu][CuI(BCA)2]3- (44 ± 3 %). [64Cu][CuI(BCA)2]3- was unstable and partially decomposed on TLC. After [64Cu][CuI(BCS)2]3- was reacted with hydroxyl radical, lipid peroxide, and superoxide, 67 ± 2 %, 44 ± 13 %, and 22 ± 3 % of total radioactivity was detected as [64Cu]Cu2+, respectively. On the other hand, the reaction with hydrogen peroxide did not significantly increase the ratio of [64Cu]Cu2+ (4 ± 1 %). These results suggest that [64Cu][CuI(BCS)2]3- could be used for detecting high-redox-potential ROS such as hydroxyl radical and lipid peroxide with high selectivity. The cellular uptake values of [64Cu][CuI(BCS)2]3- in the control, IKE, and Fer-1 group were 42 ± 2, 54 ± 2, and 47 ± 5 %Dose/mg protein (n = 3), respectively, suggesting the ROS specific uptake of [64Cu][CuI(BCS)2]3-. On the other hand, the intact ratio after the incubation of [64Cu][CuI(BCS)2]3- in human plasma was 9 ± 5 %.

CONCLUSION

PET imaging of ROS would be possible by using a copper (I) selective ligand, based on metabolic trapping. Although improvement of the membrane permeability and the stability of copper (I) complexes is required, the present results pave the way for the development of novel 64Cu-labeled complexes for PET imaging of ROS.

Symptomatic pseudoprogression in metastatic colorectal cancer

A man in his 70s with metastatic colorectal cancer presented with worsening clinical symptoms and imaging studies concerning for disease progression. He had received two cycles of pembrolizumab, but due to his symptomatic presentation and significant decline in performance status, there was concern for worsening disease. Transitioning to hospice was briefly considered, given his clinical decline and the notable increase in tumour size. Despite the presence of clinical symptoms and radiographic findings, pseudoprogression-defined as an increase in the size(s) of and/or visual appearance of new lesion(s), followed by a response-was also considered as part of the diagnostic possibilities. Consequently, the decision was made to proceed with a third cycle of pembrolizumab. During his subsequent outpatient follow-up, the patient showed significant symptomatic improvement and reported a decrease in his palpable right flank mass. With further immunotherapy, the patient continued to demonstrate symptomatic and radiological improvement.

A FRET-Based Ratiometric H2S Sensor for Sensitive Optical Molecular Imaging in Second Near-Infrared Window

Second near-infrared (NIR-II) window optical molecular imaging kicks off a new revolution in high-quality imaging in vivo, but always suffers from the hurdles of inevitable tissue autofluorescence background and NIR-II probe development. Here, we prepare a Förster resonance energy transfer-based ratiometric NIR-II window hydrogen sulfide (H2S) sensor through the combination of an H2S-responsive NIR-II cyanine dye (acceptor, LET-1055) and an H2S-inert rhodamine hybrid polymethine dye (donor, Rh930). This sensor not only exhibits high sensitivity and selectivity, but also shows rapid reaction kinetics (~20 min) and relatively low limit of detection (~96 nM) toward H2S, allowing in vivo ratiometric NIR-II fluorescence imaging of orthotopic liver and colon tumors and visualization of the drug-induced hepatic H2S fluctuations. Our findings provide the potential for advancing the feasibility of NIR-II activity-based sensing for in vivo clinical diagnosis.

Augmenting Immunotherapy via Bioinspired MOF-Based ROS Homeostasis Disruptor with Nanozyme-Cascade Reaction

Despite its remarkable clinical breakthroughs, immune checkpoint blockade (ICB) therapy remains limited by the insufficient immune response in the "cold" tumor. Nanozyme-based antitumor catalysis is associated with precise immune activation in the tumor microenvironment (TME). In this study, a cascade-augmented nanoimmunomodulator (CMZM) with multienzyme-like activities, which includes superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and glutathione oxidase (GSHOx), that dissociates under an acidic and abundant GSH TME, is proposed for multimodal imaging-guided chemodynamic therapy (CDT)/photodynamic therapy (PDT) enhanced immunotherapy. Vigorous multienzyme-like activities can not only produce O2 to alleviate hypoxia and promote the polarization of M2 to M1 macrophages, but also generate ROS (•OH and 1 O2 ) and deplete GSH in the TME to expose necrotic cell fragments and reverse immunosuppressive TME by eliciting the maturation of dendritic cells and infiltration of cytotoxic T lymphocytes (CTLs) in tumors. Therefore, inhibitory effects on both primary and distant tumors are achieved through synergy with an α-PD-L1 blocking antibody. This cascade multienzyme-based nanoplatform provides a smart strategy for highly efficient ICB immunotherapy against "cold" tumors by revising immunosuppressive TME.

Myeloperoxidase-Sensitive Magnetic Resonance Imaging Assesses Inflammatory Activation State in Experimental Mouse Acute Gout

BACKGROUND

A novel myeloperoxidase-activatable manganese-based (MPO-Mn) MRI probe may enable the activation state of inflammatory foci to be detected and monitored noninvasively.

PURPOSE

To evaluate the inflammatory response in a mouse model of acute gout using MPO as an imaging biomarker and a potential therapeutic target.

STUDY TYPE

Prospective.

ANIMAL MODEL

A total of 40 male Swiss mice with monosodium urate crystals induced acute gout.

FIELD STRENGTH/SEQUENCE

A 3.0 T/T1-weighted imaging with 2D fast spoiled gradient recalled echo and T2-weighted imaging with fast recovery fast spin-echo sequences.

ASSESSMENT

The difference in contrast-to-noise ratio between left hind limb (lesion) and right hind limb (internal reference) (ΔCNR), and normalized signal-to-noise ratio (nSNR) on the right hind limb were calculated and compared. The expression level and activity of myeloperoxidase (MPO) were analyzed using western blotting and spectrophotometric quantitation activity assay. MPO-positive cell infiltration and lesion volume were evaluated using immunofluorescence staining and T2-weighted images, respectively.

STATISTICAL TESTS

Student's t test. A P-value less than 0.05 was considered to be statistically significant.

RESULTS

MPO-Mn resulted in a significantly higher ΔCNR than Gd-DTPA (22.54 ± 1.86 vs. 13.90 ± 2.22) but lower nSNR on the reference right hind limb (1.08 ± 0.07 vs. 1.21 ± 0.08). Compared to the nontreatment group, MPO-inhibition resulted in a significantly reduced contrast enhancement at the lesion (17.81 ± 1.58 vs. 22.96 ± 3.12), which was consistent with a remission of the inflammatory response, as evidenced by a substantial reduction of lesion volume (0.55 ± 0.16 mm3 /g vs. 1.14 ± 0.15 mm3 /g), myeloperoxidase expression level (0.98 ± 0.09 vs. 1.48 ± 0.19) and activity (0.75 ± 0.12 vs. 1.12 ± 0.07), and inflammatory cell recruitment.

DATA CONCLUSION

MPO-Mn MRI has potential to evaluate the activation state of inflammatory foci in the experimental model of acute gout.

EVIDENCE LEVEL

1.

TECHNICAL EFFICACY

Stage 1.

Gender Differences in a Mouse Model of Hepatocellular Carcinoma Revealed Using Multi-Modal Imaging

The worldwide incidence of hepatocellular carcinoma (HCC) continues to rise, in part due to poor diet, limited exercise, and alcohol abuse. Numerous studies have suggested that the loss or mutation of PTEN plays a critical role in HCC tumorigenesis through the activation of the PI3K/Akt signaling axis. The homozygous knockout of PTEN in the livers of mice results in the accumulation of fat (steatosis), inflammation, fibrosis, and eventually progression to HCC. This phenotype bears a striking similarity to non-alcoholic steatohepatitis (NASH) which is thought to occupy an intermediate stage between non-alcoholic fatty liver disease (NAFLD), fibrosis, and HCC. The molecular and physiological phenotypes that manifest during the transition to HCC suggest that molecular imaging could provide a non-invasive screening platform to identify the hallmarks of HCC initiation prior to the presentation of clinical disease. We have carried out longitudinal imaging studies on the liver-specific PTEN knockout mouse model using CT, MRI, and multi-tracer PET to interrogate liver size, steatosis, inflammation, and apoptosis. In male PTEN knockout mice, significant steatosis was observed as early as 3 months using both magnetic resonance spectroscopy (MRS) and computed tomography (CT). Enhanced uptake of the apoptosis tracer 18F-TBD was also observed in the livers of male PTEN homozygous knockout mice between 3 and 4 months of age relative to heterozygous knockout controls. Liver uptake of the inflammation tracer [18F]4FN remained relatively low and constant over 7 months in male PTEN homozygous knockout mice, suggesting the suppression of high-energy ROS/RNS with PTEN deletion relative to heterozygous males where the [18F]4FN liver uptake was elevated at early and late time points. All male PTEN homozygous mice developed HCC lesions by month 10. In contrast to the male cohort, only 20% (2 out of 10) of female PTEN homozygous knockout mice developed HCC lesions by month 10. Steatosis was significantly less pronounced in the female PTEN homozygous knockout mice relative to males and could not accurately predict the eventual occurrence of HCC. As with the males, the [18F]4FN uptake in female PTEN homozygous knockout mice was low and constant throughout the time course. The liver uptake of 18F-TBD at 3 and 4.5 months was higher in the two female PTEN knockout mice that would eventually develop HCC and was the most predictive imaging biomarker for HCC in the female cohort. These studies demonstrate the diagnostic and prognostic role of multi-modal imaging in HCC mouse models and provide compelling evidence that disease progression in the PTEN knockout model is highly dependent on gender.

CAR T-cells and macrophages in large B-cell lymphoma: impact on toxicity and efficacy

Chimeric antigen receptor (CAR) T-cell therapy targeting CD19 is the current standard of care for the treatment of relapsed refractory large B cell lymphoma, demonstrating impressive response rates in the second- and third-line setting. Despite these advances, this treatment strategy can result in significant toxicities, such as cytokine release syndrome or immune effector cell associated neurotoxicity syndrome. While the exact mechanisms of these immune-mediated toxicities are not clearly understood, emerging pre-clinical and clinical studies have revealed the pivotal role of myeloid cells, particularly macrophages, as key contributors to the efficacy of treatments and as crucial mediators of toxicity. In this review, we discuss the current understanding of how macrophages mediate these effects, highlighting specific mechanisms of macrophage biology relevant to CAR T-cell therapy activity and side effects. These findings are resulting in novel treatment strategies that target macrophages, and able to mitigate toxicity while preserving CAR T-cell therapy efficacy.

The 'stealth-bomber' paradigm for deciphering the tumour response to carbon-ion irradiation

Numerous studies have demonstrated the higher biological efficacy of carbon-ion irradiation (C-ions) and their ballistic precision compared with photons. At the nanometre scale, the reactive oxygen species (ROS) produced by radiation and responsible for the indirect effects are differentially distributed according to the type of radiation. Photon irradiation induces a homogeneous ROS distribution, whereas ROS remain condensed in clusters in the C-ions tracks. Based on this linear energy transfer-dependent differential nanometric ROS distribution, we propose that the higher biological efficacy and specificities of the molecular response to C-ions rely on a 'stealth-bomber' effect. When biological targets are on the trajectories of the particles, the clustered radicals in the tracks are responsible for a 'bomber' effect. Furthermore, the low proportion of ROS outside the tracks is not able to trigger the cellular mechanisms of defence and proliferation. The ability of C-ions to deceive the cellular defence of the cancer cells is then categorised as a 'stealth' effect. This review aims to classify the biological arguments supporting the paradigm of the 'stealth-bomber' as responsible for the biological superiority of C-ions compared with photons. It also explains how and why C-ions will always be more efficient for treating patients with radioresistant cancers than conventional radiotherapy.

Engineered Nanoprobes for Immune Activation Monitoring

The activation of the immune system is critical for cancer immunotherapy and treatments of inflammatory diseases. Non-invasive visualization of immunoactivation is designed to monitor the dynamic nature of the immune response and facilitate the assessment of therapeutic outcomes, which, however, remains challenging. Conventional imaging modalities, such as positron emission tomography, computed tomography, etc., were utilized for imaging immune-related biomarkers. To explore the dynamic immune monitoring, probes with signals correlated to biomarkers of immune activation or prognosis are urgently needed. These emerging molecular probes, which turn on the signal only in the presence of the intended biomarker, can improve the detection specificity. These probes with "turn on" signals enable non-invasive, dynamic, and real-time imaging with high sensitivity and efficiency, showing significance for multifunctionality/multimodality imaging. As a result, more and more innovative engineered nanoprobes combined with diverse imaging modalities were developed to assess the activation of the immune system. In this work, we comprehensively review the recent and emerging advances in engineered nanoprobes for monitoring immune activation in cancer or other immune-mediated inflammatory diseases and discuss the potential in predicting the efficacy following treatments. Research on real-time in vivo immunoimaging is still under exploration, and this review can provide guidance and facilitate the development and application of next-generation imaging technologies.

Imaging strategies for monitoring the immune response

Real-time monitoring of the immune response can be used to evaluate the immune status of the body and to distinguish immune responders and non-responders, so as to better guide immunotherapy. Through direct labelling of immune cells and imaging specific biomarkers of different cells, the activation status of immune cells and immunosuppressive status of tumor cells can be visualized. The immunotherapeutic regimen can then be adjusted accordingly in a timely manner to improve the efficacy of immunotherapy. In this review, various imaging methods, immune-related imaging probes, current challenges and opportunities are summarized and discussed.