Imaging approaches to optimize molecular therapies

Preparation and identification of a fluorescent probe with CsPbBr3perovskite quantum dots and CD44v6 specific peptide for gastric cancer imaging

Since the sensitivity and accuracy of traditional detection for early gastric cancer diagnosis are still insufficient, it is significant to continuously optimize the optical molecular imaging detection technology based on an endoscopic platform. The signal intensity and stability of traditional chemical fluorescent dyes are low, which hinders the clinical application of molecular imaging detection technology. This work developed a probe based on perovskite quantum dots (PQDs) and peptide ligands. By utilizing CsPbBr3perovskite PQDs modified by azithromycin (AZI), combined with the specific polypeptide ligand of CD44v6, a gastric cancer biomarker, the perovskite-based probe (AZI-PQDs probe) which can specifically identify gastric cancer tumor was prepared. Owing to the high photoluminescence quantum yield of CsPbBr3PQDs, the naked eye can observe the imaging under the excitation of the hand-held ultraviolet light source. AZI-PQDs probe can accurately identify gastric cancer cells, tissues, and xenograft models with experiments ofex vivoandin vivofluorescence imaging detection. It also exhibited low toxicity and immunogenicity, indicating the safety of the probe. This work provides a probe combined with cancer specificity and a reliable fluorescent signal that has the potential for application in gastric cancer optical molecular imaging.

A cancer immunoprofiling strategy using mass spectrometry coupled with bioorthogonal cleavage

The accurate quantification of biomarkers is paramount in modern medicine, particularly in cancer where precise diagnosis is imperative for targeted therapy selection. In this paper we described a multiplexed analysis diagnostic approach based on cleavable MS-tagged antibodies. The technology uses MS-tag isotopologues and the sydnonimine-cyclooctyne click-and-release bioorthogonal reaction. In a proof of concept study, we demonstrated the potential of this approach for cancer cell immunoprofiling in culture cells, tissues and in vivo as well, thereby unveiling promising diagnostic avenues.

Harnessing Biopolymer Gels for Theranostic Applications: Imaging Agent Integration and Real-Time Monitoring of Drug Delivery

Biopolymer gels have gained tremendous potential for therapeutic applications due to their biocompatibility, biodegradability, and ability to adsorb and bind biological fluids, making them attractive for drug delivery and therapy. In this study, the versatility of biopolymer gels is explored in theranostic backgrounds, with a focus on integrating imaging features and facilitating real-time monitoring of drug delivery. Different methods of delivery are explored for incorporating imaging agents into biopolymer gels, including encapsulation, surface functionalization, nanoparticle encapsulation, and layer-by-layer assembly techniques. These methods exhibit the integration of agents and real-time monitoring drug delivery. We summarize the synthesis methods, general properties, and functional mechanisms of biopolymer gels, demonstrating their broad applications as multimodal systems for imaging-based therapeutics. These techniques not only enable multiple imaging but also provide signal enhancement and facilitate imaging targets, increasing the diagnostic accuracy and therapeutic efficacy. In addition, current techniques for incorporating imaging agents into biopolymer gels are discussed, as well as their role in precise drug delivery and monitoring.

Engineering focusing on cancer

While cancer research and care have benefited from revolutionary advances in the ability to manipulate and study living systems, the field is limited by a lack of synergy to leverage the power of engineering approaches. Cancer engineering is an emerging subfield of biomedical engineering that unifies engineering and cancer biology to better understand, diagnose, and treat cancer. We highlight cancer engineering's unique challenges, the importance of creating dedicated centers and departments that enable translational collaboration, and educational approaches to arm a new generation of scientists with engineering expertise and a fundamental understanding of cancer biology to transform clinical cancer care.

Construction of truncated PSMA as a PET reporter gene for CAR T cell trafficking

In solid tumors, there are multiple barriers for a chimeric antigen receptor (CAR) T cell to surmount in order to reach the tumor site. For better understanding whether CAR T cells effectively infiltrate into tumor site, and simultaneously, whether there are off-target effects, real-time monitoring technologies need to be established. Cell-based positron emission tomography reporter genes have been developed to monitor engineered cells in living subjects. In this study, we reported the construction of a novel reporter gene truncated prostate-specific membrane antigen (ΔPSMA) pending for monitoring CAR T cells using 68Ga-PSMA-617 and a method for tracking the distribution of CAR T cells in vivo was developed. Data were provided to demonstrate that ΔPSMA was predominantly localized on the plasma membrane and could take up 68Ga-PSMA-617 in vitro in a time-dependent manner. And the expression of ΔPSMA did not affect CAR expression and cytolytic capacity of CAR T cells. CAR-ΔPSMA T cell xenografts in nude mice were clearly imaged by positron emission tomography 60 min after injection of 68Ga-PSMA-617. PSMA paired with 68Ga-PSMA-617 was capable of identifying approximately 1 × 104 engineered CAR T cells. The ability to image small numbers of CAR T cells in vivo would be helpful to accelerate the translation of cell-based therapies into the clinic, and it may reinforce our understanding of treatment success, failure, and toxicity.

Perspectives of Evidence-Based Therapy Management

BACKGROUND

Therapeutics that specifically address biological processes often require a much finer selection of patients and subclassification of diseases. Thus, diagnostic procedures must describe the diseases in sufficient detail to allow selection of appropriate therapy and to sensitively track therapy response. Anatomical features are often not sufficient for this purpose and there is a need to image molecular and pathophysiological processes.

METHOD

Two imaging strategies can be pursued: molecular imaging attempts to image a few biomarkers that play key roles in pathological processes. Alternatively, patterns describing a biological process can be identified from the synopsis of multiple (non-specific) imaging markers, possibly in combination with omics and other clinical findings. Here, AI-based methods are increasingly being used.

RESULTS

Both strategies of evidence-based therapy management are explained in this review article and examples and clinical successes are presented. In this context, reviews of clinically approved molecular diagnostics and decision support systems are listed. Furthermore, since reliable, representative, and sufficiently large datasets are further important prerequisites for AI-assisted multiparametric analyses, concepts are presented to make data available in a structured way, e. g., using Generative Adversarial Networks to complement databases with virtual cases and to build completely anonymous reference databases.

CONCLUSION

Molecular imaging and computer-assisted cluster analysis of diagnostic data are complementary methods to describe pathophysiological processes. Both methods have the potential to improve (evidence-based) the future management of therapies, partly on their own but also in combined approaches.

KEY POINTS

· Molecular imaging and radiomics provide valuable complementary disease biomarkers.. · Data-driven, model-based, and hybrid model-based integrated diagnostics advance precision medicine.. · Synthetic data generation may become essential in the development process of future AI methods..

Small-molecule probes from bench to bedside: advancing molecular analysis of drug-target interactions toward precision medicine

Over the past decade, remarkable advances have been witnessed in the development of small-molecule probes. These molecular tools have been widely applied for interrogating proteins, pathways and drug-target interactions in preclinical research. While novel structures and designs are commonly explored in probe development, the clinical translation of small-molecule probes remains limited, primarily due to safety and regulatory considerations. Recent synergistic developments - interfacing novel chemical probes with complementary analytical technologies - have introduced and expedited diverse biomedical opportunities to molecularly characterize targeted drug interactions directly in the human body or through accessible clinical specimens (e.g., blood and ascites fluid). These integrated developments thus offer unprecedented opportunities for drug development, disease diagnostics and treatment monitoring. In this review, we discuss recent advances in the structure and design of small-molecule probes with novel functionalities and the integrated development with imaging, proteomics and other emerging technologies. We further highlight recent applications of integrated small-molecule technologies for the molecular analysis of drug-target interactions, including translational applications and emerging opportunities for whole-body imaging, tissue-based measurement and blood-based analysis.

Advances in PET imaging of cancer

Molecular imaging has experienced enormous advancements in the areas of imaging technology, imaging probe and contrast development, and data quality, as well as machine learning-based data analysis. Positron emission tomography (PET) and its combination with computed tomography (CT) or magnetic resonance imaging (MRI) as a multimodality PET-CT or PET-MRI system offer a wealth of molecular, functional and morphological data with a single patient scan. Despite the recent technical advances and the availability of dozens of disease-specific contrast and imaging probes, only a few parameters, such as tumour size or the mean tracer uptake, are used for the evaluation of images in clinical practice. Multiparametric in vivo imaging data not only are highly quantitative but also can provide invaluable information about pathophysiology, receptor expression, metabolism, or morphological and functional features of tumours, such as pH, oxygenation or tissue density, as well as pharmacodynamic properties of drugs, to measure drug response with a contrast agent. It can further quantitatively map and spatially resolve the intertumoural and intratumoural heterogeneity, providing insights into tumour vulnerabilities for target-specific therapeutic interventions. Failure to exploit and integrate the full potential of such powerful imaging data may lead to a lost opportunity in which patients do not receive the best possible care. With the desire to implement personalized medicine in the cancer clinic, the full comprehensive diagnostic power of multiplexed imaging should be utilized.

Nanomedicines for cardiovascular disease

The leading cause of death in the world, cardiovascular disease (CVD), remains a formidable condition for researchers, clinicians and patients alike. CVD comprises a broad collection of diseases spanning the heart, the vasculature and the blood that runs through and interconnects them. Limitations in CVD therapeutic and diagnostic landscapes have generated excitement for advances in nanomedicine, a field focused on improving patient outcomes through transformative therapies, imaging agents and ex vivo diagnostics. CVD nanomedicines are fundamentally shaped by their intended clinical application, including (1) cardiac or heart-related biomaterials, which can be functionally (for example, mechanically, immunologically, electrically) improved by incorporating nanomaterials; (2) the vasculature, involving systemically injected nanotherapeutics and imaging nanodiagnostics, nano-enabled biomaterials or tissue-nanoengineered solutions; and (3) improving the sensitivity and/or specificity of ex vivo diagnostic devices for patient samples. While immunotherapy has developed into a key pillar of oncology in the past dozen years, CVD immunotherapy and immunoimaging are recently emergent and likely to factor substantially in CVD management in the coming decade. The nanomaterials in CVD-related clinical trials and many promising preclinical strategies indicate that nanomedicine is on the cusp of greatly impacting patients with CVD. Here we review these recent advances, highlighting key clinical opportunities in the rapidly emerging field of CVD nanomedicine.

A tumor-targetable NIR probe with photoaffinity crosslinking characteristics for enhanced imaging-guided cancer phototherapy

Spatiotemporally manipulating the in situ immobilization of theranostic agents within cancer cells to improve their bioavailability is highly significant yet challenging in tumor diagnosis and treatment. Herein, as a proof-of concept, we for the first time report a tumor-targetable near-infrared (NIR) probe DACF with photoaffinity crosslinking characteristics for enhanced tumor imaging and therapeutic applications. This probe possesses great tumor-targeting capability, intensive NIR/photoacoustic (PA) signals, and a predominant photothermal effect, allowing for sensitive imaging and effective photothermal therapy (PTT) of tumors. Most notably, upon 405 nm laser illumination, DACF could be covalently immobilized within tumor cells through a photocrosslinking reaction between photolabile diazirine groups and surrounding biomolecules resulting in enhanced tumor accumulation and prolonged retention simultaneously, which significantly facilitates the imaging and PTT efficacy of tumor in vivo. We therefore believe that our current approach would provide a new insight for achieving precise cancer theranostics.

Gallium-68-labeled Peptide PET Quantifies Tumor Exposure of PD-L1 Therapeutics

PURPOSE

Immune checkpoint therapy (ICT) is currently ineffective in a majority of patients. Tumor drug exposure measurements can provide vital insights into mechanisms involved in the resistance of solid tumors to those therapeutics; however, tools to quantify in situ drug exposure are few. We have investigated the potential of programmed death-ligand 1 (PD-L1) pharmacodynamics, quantified using PET, to inform on the tumor exposure of anti-PD-L1 (aPD-L1) therapeutics.

EXPERIMENTAL DESIGN

To noninvasively quantify PD-L1 levels, we first developed a novel peptide-based gallium-68-labeled binder, [68Ga]Ga-DK223, and evaluated its in vivo distribution, pharmacokinetics, and PD-L1 specificity in preclinical models of triple-negative breast cancer and urothelial carcinoma with variable PD-L1 expression. We then quantified baseline and accessible PD-L1 levels in tumors as a noninvasive pharmacodynamic measure to assess tumor exposure to two aPD-L1 antibodies (avelumab and durvalumab).

RESULTS

DK223 exhibited a KD of 1.01±0.83 nmol/L for PD-L1 and inhibited the PD-1:PD-L1 interaction in a dose-dependent manner. [68Ga]Ga-DK223 provides high-contrast PET images within 60 minutes of administration and detects PD-L1 in an expression-dependent manner in xenograft models. PD-L1 pharmacodynamics measured using [68Ga]Ga-DK223-PET revealed that avelumab and durvalumab had similar exposure early during therapy, but only durvalumab exhibited sustained exposure at the tumor.

CONCLUSIONS

[68Ga]Ga-DK223 detected variable PD-L1 levels and exhibited salient features required for clinical translation. [68Ga]Ga-DK223-PET could be useful for quantifying total PD-L1 levels at baseline and accessible PD-L1 levels during therapy to understand drug exposure at the tumor, thus supporting its use for guiding and optimizing ICT.

A Hoechst Reporter Enables Visualization of Drug Engagement In Vitro and In Vivo: Toward Safe and Effective Nanodrug Delivery

Assessment of drug activation and subsequent interaction with targets in living tissues could guide nanomedicine design, but technologies enabling insight into how a drug reaches and binds its target are limited. We show that a Hoechst-based reporter system can monitor drug release and engagement from a nanoparticle delivery system in vitro and in vivo, elucidating differences in target-bound drug distribution related to drug-linker and nanoparticle properties. Drug engagement is defined as chemical detachment of drug or reporter from a nanoparticle and subsequent binding to a subcellular target, which in the case of Hoechst results in a fluorescence signal. Hoechst-based nanoreporters for drug activation contain prodrug elements such as dipeptide linkers, conjugation handles, and nanoparticle modifications such as targeting ligands to determine how nanomedicine design affects distribution of drug engaged with a subcellular target, which is tracked via cellular nuclear fluorescence in situ. Furthermore, the nanoplatform is amenable toward common maleimide-based linkers found in many prodrug-based delivery systems including polymer-, peptide-, and antibody-drug conjugates. Findings from the Hoechst reporter system were applied to develop highly potent, targeted, anticancer micelle nanoparticles delivering a monomethyl auristatin E (MMAE) prodrug comprising the same linkers employed in Hoechst studies. MMAE nanomedicine with the optimal drug-linker resulted in effective tumor growth inhibition in mice without associated acute toxicity, whereas the nonoptimal linker that showed broader drug activation in Hoechst reporter studies resulted in severe toxicity. Our results demonstrate the potential to synergize direct visualization of drug engagement with nanomedicine drug-linker design to optimize safety and efficacy.

Optimized 68Ga-Labeled Urea-Based PSMA-Targeted PET Tracers for Prostate Cancer

Prostate-specific membrane antigen (PSMA)-targeting radiopharmaceuticals have become some of the most promising tools for the diagnosis and therapy prostate cancer (PCa). The structure of existing PSMA-targeted PET tracers still needs to be optimized to improve their pharmacokinetic properties and tumor-to-background ratio. In this study, we modified the structure of a well-studied PSMA tracer, and six novel tracers with variable hydrophilicity and pharmacokinetics were developed and evaluated both in vitro and in vivo. All of the novel tracers showed high hydrophilicity (log p = −2.99 ± 0.33 to −3.49 ± 0.01), rapid clearance rates (elimination half-times = 15.55 to 35.97 min), and high affinity for PSMA (Ki = 8.11 ± 0.49 to 42.40 ± 2.11 nM) in vitro. Specific cell binding and micro-PET experiments showed that [⁶⁸Ga]Ga-PSMA-Q displayed the highest specific PSMA+ cell uptake (3.75 ± 0.35 IA%/10⁶ at 60 min), tumor uptake (SUVmax = 0.97 ± 0.24 at 60 min p.i.), and tumor-to-muscle ratio (59.33 ± 5.72 at 60 min p.i.), while the tumor-to-muscle ratio was much higher than that of [⁶⁸Ga]Ga-PSMA-617. The results of this study validate the clinical potential of [⁶⁸Ga]Ga-PSMA-Q for PET imaging and further targeted therapy of prostate cancer.

Hydrogel Stamping for Rapid, Multiplexed, Point-of-Care Immunostaining of Cells and Tissues

In the era of precision oncology, multicolor fluorescence imaging has become a core technology for multiplexed molecular analysis of cellular and tissue specimens. However, conventional solution-based staining is labor-intensive and time-consuming and requires considerable expertise to yield optimal results, which creates difficulties for employing this technology in resource-limited settings. Here, we report a new immunostaining method based on hydrogel stamping, which is simple, fast, easy to use, and reproducible. We showed that a hydrophilic hydrogel stamp could effectively transfer fluorescent antibodies to targets and withdraw an excess solution when the reaction is completed, obviating the need for extra washing. This unique property allows for quality immunostaining in 5 min for cells using one-eighth of antibody consumption compared to the conventional solution-based method. Furthermore, we implemented fluorescence quenching and immunocycling with hydrogel staining for multiplexed analysis of 9 protein markers at a single cell level. Finally, we applied the immunocycling method to human breast cancer tissue samples and showed quality immunostaining over a large area (∼2 cm²) in 30 min for molecular subtyping of breast cancer. The hydrogel immunostaining could open new opportunities for rapid, automated, and multiplexed profiling in compact point-of-care systems for molecular cancer diagnosis.

Perspectives of Evidence-Based Therapy Management

BACKGROUND

 Therapeutics that specifically address biological processes often require a much finer selection of patients and subclassification of diseases. Thus, diagnostic procedures must describe the diseases in sufficient detail to allow selection of appropriate therapy and to sensitively track therapy response. Anatomical features are often not sufficient for this purpose and there is a need to image molecular and pathophysiological processes.

METHOD

 Two imaging strategies can be pursued: molecular imaging attempts to image a few biomarkers that play key roles in pathological processes. Alternatively, patterns describing a biological process can be identified from the synopsis of multiple (non-specific) imaging markers, possibly in combination with omics and other clinical findings. Here, AI-based methods are increasingly being used.

RESULTS

 Both strategies of evidence-based therapy management are explained in this review article and examples and clinical successes are presented. In this context, reviews of clinically approved molecular diagnostics and decision support systems are listed. Furthermore, since reliable, representative, and sufficiently large datasets are further important prerequisites for AI-assisted multiparametric analyses, concepts are presented to make data available in a structured way, e. g., using Generative Adversarial Networks to complement databases with virtual cases and to build completely anonymous reference databases.

CONCLUSION

 Molecular imaging and computer-assisted cluster analysis of diagnostic data are complementary methods to describe pathophysiological processes. Both methods have the potential to improve (evidence-based) the future management of therapies, partly on their own but also in combined approaches.

KEY POINTS

· Molecular imaging and radiomics provide valuable complementary disease biomarkers.. · Data-driven, model-based, and hybrid model-based integrated diagnostics advance precision medicine.. · Synthetic data generation may become essential in the development process of future AI methods..

CITATION FORMAT

· Kiessling F, Schulz V, . Perspectives of Evidence-Based Therapy Management. Fortschr Röntgenstr 2022; DOI: 10.1055/a-1752-0839.

Multiplexed imaging in oncology

In oncology, technologies for clinical molecular imaging are used to diagnose patients, establish the efficacy of treatments and monitor the recurrence of disease. Multiplexed methods increase the number of disease-specific biomarkers that can be detected simultaneously, such as the overexpression of oncogenic proteins, aberrant metabolite uptake and anomalous blood perfusion. The quantitative localization of each biomarker could considerably increase the specificity and the accuracy of technologies for clinical molecular imaging to facilitate granular diagnoses, patient stratification and earlier assessments of the responses to administered therapeutics. In this Review, we discuss established techniques for multiplexed imaging and the most promising emerging multiplexing technologies applied to the imaging of isolated tissues and cells and to non-invasive whole-body imaging. We also highlight advances in radiology that have been made possible by multiplexed imaging.

Optical Imaging of Epigenetic Modifications in Cancer: A Systematic Review

Increasing evidence has demonstrated that abnormal epigenetic modifications are strongly related to cancer initiation. Thus, sensitive and specific detection of epigenetic modifications could markedly improve biological investigations and cancer precision medicine. A rapid development of molecular imaging approaches for the diagnosis and prognosis of cancer has been observed during the past few years. Various biomarkers unique to epigenetic modifications and targeted imaging probes have been characterized and used to discriminate cancer from healthy tissues, as well as evaluate therapeutic responses. In this study, we summarize the latest studies associated with optical molecular imaging of epigenetic modification targets, such as those involving DNA methylation, histone modification, noncoding RNA regulation, and chromosome remodeling, and further review their clinical application on cancer diagnosis and treatment. Lastly, we further propose the future directions for precision imaging of epigenetic modification in cancer. Supported by promising clinical and preclinical studies associated with optical molecular imaging technology and epigenetic drugs, the central role of epigenetics in cancer should be increasingly recognized and accepted.

Fundamentals and developments in fluorescence-guided cancer surgery

Fluorescence-guided surgery using tumour-targeted imaging agents has emerged over the past decade as a promising and effective method of intraoperative cancer detection. An impressive number of fluorescently labelled antibodies, peptides, particles and other molecules related to cancer hallmarks have been developed for the illumination of target lesions. New approaches are being implemented to translate these imaging agents into the clinic, although only a few have made it past early-phase clinical trials. For this translational process to succeed, target selection, imaging agents and their related detection systems and clinical implementation have to operate in perfect harmony to enable real-time intraoperative visualization that can benefit patients. Herein, we review key aspects of this imaging cascade and focus on imaging approaches and methods that have helped to shed new light onto the field of intraoperative fluorescence-guided cancer surgery with the singular goal of improving patient outcomes.

Pharmacodynamic measures within tumors expose differential activity of PD(L)-1 antibody therapeutics

Macromolecules such as monoclonal antibodies (mAbs) are likely to experience poor tumor penetration because of their large size, and thus low drug exposure of target cells within a tumor could contribute to suboptimal responses. Given the challenge of inadequate quantitative tools to assess mAb activity within tumors, we hypothesized that measurement of accessible target levels in tumors could elucidate the pharmacologic activity of a mAb and could be used to compare the activity of different mAbs. Using positron emission tomography (PET), we measured the pharmacodynamics of immune checkpoint protein programmed-death ligand 1 (PD-L1) to evaluate pharmacologic effects of mAbs targeting PD-L1 and its receptor programmed cell death protein 1 (PD-1). For PD-L1 quantification, we first developed a small peptide-based fluorine-18-labeled PET imaging agent, [¹⁸F]DK222, which provided high-contrast images in preclinical models. We then quantified accessible PD-L1 levels in the tumor bed during treatment with anti-PD-1 and anti-PD-L1 mAbs. Applying mixed-effects models to these data, we found subtle differences in the pharmacodynamic effects of two anti-PD-1 mAbs (nivolumab and pembrolizumab). In contrast, we observed starkly divergent target engagement with anti-PD-L1 mAbs (atezolizumab, avelumab, and durvalumab) that were administered at equivalent doses, correlating with differential effects on tumor growth. Thus, we show that measuring PD-L1 pharmacodynamics informs mechanistic understanding of therapeutic mAbs targeting PD-L1 and PD-1. These findings demonstrate the value of quantifying target pharmacodynamics to elucidate the pharmacologic activity of mAbs, independent of mAb biophysical properties and inclusive of all physiological variables, which are highly heterogeneous within and across tumors and patients.

Converting an Anti-Mouse CD4 Monoclonal Antibody into an scFv Positron Emission Tomography Imaging Agent for Longitudinal Monitoring of CD4+ T Cells

Immuno-positron emission tomography (PET), a noninvasive imaging modality, can provide a dynamic approach for longitudinal assessment of cell populations of interest. Transformation of mAbs into single-chain variable fragment (scFv)-based PET imaging agents would allow noninvasive tracking in vivo of a wide range of possible targets. We used sortase-mediated enzymatic labeling in combination with PEGylation to develop an anti-mouse CD4 scFv-based PET imaging agent constructed from an anti-mouse CD4 mAb. This anti-CD4 scFv can monitor the in vivo distribution of CD4+ T cells by immuno-PET. We tracked CD4+ and CD8+ T cells in wild-type mice, in immunodeficient recipients reconstituted with monoclonal populations of OT-II and OT-I T cells, and in a B16 melanoma model. Anti-CD4 and -CD8 immuno-PET showed that the persistence of both CD4+ and CD8+ T cells transferred into immunodeficient mice improved when recipients were immunized with OVA in CFA. In tumor-bearing animals, infiltration of both CD4+ and CD8+ T cells increased as the tumor grew. The approach described in this study should be readily applicable to convert clinically useful Abs into the corresponding scFv PET imaging agents.

Joint Modeling of RNAseq and Radiomics Data for Glioma Molecular Characterization and Prediction

RNA sequencing (RNAseq) is a recent technology that profiles gene expression by measuring the relative frequency of the RNAseq reads. RNAseq read counts data is increasingly used in oncologic care and while radiology features (radiomics) have also been gaining utility in radiology practice such as disease diagnosis, monitoring, and treatment planning. However, contemporary literature lacks appropriate RNA-radiomics (henceforth, radiogenomics ) joint modeling where RNAseq distribution is adaptive and also preserves the nature of RNAseq read counts data for glioma grading and prediction. The Negative Binomial (NB) distribution may be useful to model RNAseq read counts data that addresses potential shortcomings. In this study, we propose a novel radiogenomics-NB model for glioma grading and prediction. Our radiogenomics-NB model is developed based on differentially expressed RNAseq and selected radiomics/volumetric features which characterize tumor volume and sub-regions. The NB distribution is fitted to RNAseq counts data, and a log-linear regression model is assumed to link between the estimated NB mean and radiomics. Three radiogenomics-NB molecular mutation models (e.g., IDH mutation, 1p/19q codeletion, and ATRX mutation) are investigated. Additionally, we explore gender-specific effects on the radiogenomics-NB models. Finally, we compare the performance of the proposed three mutation prediction radiogenomics-NB models with different well-known methods in the literature: Negative Binomial Linear Discriminant Analysis (NBLDA), differentially expressed RNAseq with Random Forest (RF-genomics), radiomics and differentially expressed RNAseq with Random Forest (RF-radiogenomics), and Voom-based count transformation combined with the nearest shrinkage classifier (VoomNSC). Our analysis shows that the proposed radiogenomics-NB model significantly outperforms (ANOVA test, p < 0.05) for prediction of IDH and ATRX mutations and offers similar performance for prediction of 1p/19q codeletion, when compared to the competing models in the literature, respectively.

Exploring the Influence of Different Albumin Binders on Molecular Imaging Probe Distribution

The biodistribution of molecular imaging probes or tracers mainly depends on the chemical nature of the probe and the preferred metabolization and excretion routes. Small molecules have rather short half-lives while antibodies reside inside the organism for a longer period of time. An excretion via kidneys and bladder is faster than a mainly hepatobiliary elimination. To manipulate the biodistribution behavior of probes, different strategies have been pursued, including utilizing serum albumin as an inherent transport mechanism for small molecules. Here, we modified an existing small molecular fluorescent probe targeted to the endothelin-A receptor (ET_AR) with three different albumin-binding moieties to search for an optimal modification strategy. A diphenylcyclohexyl (DPCH) group, a p-iodophenyl butyric acid (IPBA), and a fatty acid (FA) group were attached via amino acid linkers. All three modifications result in transient albumin binding of the developed compounds, as concluded from gel electrophoresis investigations. Spectrophotometric measurements applying variable amounts of bovine, murine, and human serum albumin (BSA, MSA, and HSA) reveal distinct variations of absorption and emission intensities and shifts of their maximum wavelengths. Binding to MSA results in the weakest effects, while binding to HSA leads to the strongest. Cell-based in vitro investigations utilizing ET_AR-positive HT-1080 fibrosarcoma and ET_AR-negative BT-20 breast adenocarcinoma cells support a retained specific target-binding capacity of the modified compounds and different degrees of unspecific binding. In vivo analysis of a HT-1080 xenograft model in nude mice over the course of 1 week by fluorescence reflectance imaging illustrates noticeable differences between the four examined probes. While the IPBA-modified probe shows the highest absolute signal intensity values, the FA-modified probe exhibits the most favorable tumor-to-organ ratios. In summary, reversible binding to albumin enhances the biological half-life of the designed probes substantially and enables near infrared optical imaging of subcutaneous tumors for several days in vivo. Because the unmodified probe already exhibits reasonable results, the attachment of albumin-binding moieties does not lead to a substantially improved imaging outcome in terms of target-to-background ratios. On the other hand, because the implemented transient albumin binding results in an overall higher amount of probe inside tumor lesions, this strategy might be adaptable for theranostic or therapeutic approaches in a future clinical routine.

More Than Meets the Eye: Scientific Rationale behind Molecular Imaging and Therapeutic Targeting of Prostate-Specific Membrane Antigen (PSMA) in Metastatic Prostate Cancer and Beyond

Simple Summary

Prostate-specific membrane antigen (PSMA) is a transmembrane protein that is overexpressed in prostate cancer and correlates with the aggressiveness of the disease. PSMA is a promising target for imaging and therapeutics in prostate cancer patients validated in prospective trials. However, the role of PSMA in prostate cancer progression is poorly understood. In this review, we discuss the biology and scientific rationale behind the use of PSMA and other targets in the detection and theranostics of metastatic prostate cancer.

Abstract

Prostate cancer is the second most common cancer type in men globally. Although the prognosis for localized prostate cancer is good, no curative treatments are available for metastatic disease. Better diagnostic methods could help target therapies and improve the outcome. Prostate-specific membrane antigen (PSMA) is a transmembrane glycoprotein that is overexpressed on malignant prostate tumor cells and correlates with the aggressiveness of the disease. PSMA is a clinically validated target for positron emission tomography (PET) imaging-based diagnostics in prostate cancer, and during recent years several therapeutics have been developed based on PSMA expression and activity. The expression of PSMA in prostate cancer can be very heterogeneous and some metastases are negative for PSMA. Determinants that dictate clinical responses to PSMA-targeting therapeutics are not well known. Moreover, it is not clear how to manipulate PSMA expression for therapeutic purposes and develop rational treatment combinations. A deeper understanding of the biology behind the use of PSMA would help the development of theranostics with radiolabeled compounds and other PSMA-based therapeutic approaches. Along with PSMA several other targets have also been evaluated or are currently under investigation in preclinical or clinical settings in prostate cancer. Here we critically elaborate the biology and scientific rationale behind the use of PSMA and other targets in the detection and therapeutic targeting of metastatic prostate cancer.

One-pot green synthesis of I@CNDs-Fe3O4 hybrid nanoparticles from kelp for multi-modal imaging in vivo

Multi-modal imaging technologies are playing an increasingly important role in biomedical research. However, there remains a demanding challenge to develop biocompatible contrast agents via a simple, green synthetic route for multi-modal imaging. Here we report the synthesis and applications of a new contrast agent for triple-modal imaging, that is, iodine-containing N-doping carbon nano-dots hybridized with Fe3O4 nanoparticles (I@CNDs-Fe3O4). We develop a one-pot, environment friendly hydrothermal method to synthesize the hybrid nanoparticles, primarily using kelp as the bioresource. I@CNDs-Fe3O4 nanoparticles have been demonstrated to exhibit excellent multi-modal imaging capabilities, including wavelength-tunable fluorescent imaging, X-ray attenuation for CT imaging enhancement, and T2-Weighted MR imaging. Importantly, the formulation of the hybrid nanoparticle provides an optimal solution to address the disequilibrium of osmotic pressure caused by the conventional CT imaging contrast agents of iodine compounds. The I@CNDs-Fe3O4 nanoparticles promise important applications in multi-modal imaging technologies in vivo as a versatile and biocompatible contrast agent.

Preclinical Applications of Multi-Platform Imaging in Animal Models of Cancer

In animal models of cancer, oncologic imaging has evolved from a simple assessment of tumor location and size to sophisticated multimodality exploration of molecular, physiologic, genetic, immunologic, and biochemical events at microscopic to macroscopic levels, performed noninvasively and sometimes in real time. Here, we briefly review animal imaging technology and molecular imaging probes together with selected applications from recent literature. Fast and sensitive optical imaging is primarily used to track luciferase-expressing tumor cells, image molecular targets with fluorescence probes, and to report on metabolic and physiologic phenotypes using smart switchable luminescent probes. MicroPET/single-photon emission CT have proven to be two of the most translational modalities for molecular and metabolic imaging of cancers: immuno-PET is a promising and rapidly evolving area of imaging research. Sophisticated MRI techniques provide high-resolution images of small metastases, tumor inflammation, perfusion, oxygenation, and acidity. Disseminated tumors to the bone and lung are easily detected by microCT, while ultrasound provides real-time visualization of tumor vasculature and perfusion. Recently available photoacoustic imaging provides real-time evaluation of vascular patency, oxygenation, and nanoparticle distributions. New hybrid instruments, such as PET-MRI, promise more convenient combination of the capabilities of each modality, enabling enhanced research efficacy and throughput.

Photoacoustic Tomography Opening New Paradigms in Biomedical Imaging

After the emergence of the ultrasound, X-ray CT, PET, and MRI, photoacoustic tomography (PAT) is now in the phase of its exponential growth, with its expected full maturation being another form of mainstream clinical imaging modality. By combining the high contrast benefit of optical imaging and the high-resolution deep imaging capability of ultrasound, PAT can provide unprecedented anatomical image contrasts at clinically relevant depths as well as enable the use of a variety of functional and molecular imaging information, which is not possible with conventional imaging modalities. With these strengths, PAT has achieved numerous breakthroughs in various biomedical applications and also provided new technical platforms that may be able to resolve unmet issues in clinics. In this chapter, we provide an overview of the development of PAT technology for several major biomedical applications and provide an approximate projection of the future of PAT.

PET/CT Imaging of 89Zr-N-sucDf-Pembrolizumab in Healthy Cynomolgus Monkeys

Purpose

Programmed cell death-1 receptor (PD-1) and its ligand (PD-L1) are the targets for immunotherapy in many cancer types. Although PD-1 blockade has therapeutic effects, the efficacy differs between patients. Factors contributing to this variability are PD-L1 expression levels and immune cells present in tumors. However, it is not well understood how PD-1 expression in the tumor microenvironment impacts immunotherapy response. Thus, imaging of PD-1-expressing immune cells is of interest. This study aims to evaluate the biodistribution of Zirconium-89 (⁸⁹Zr)-labeled pembrolizumab, a humanized IgG4 kappa monoclonal antibody targeting PD-1, in healthy cynomolgus monkeys as a translational model of tracking PD-1-positive immune cells.

Procedures

Pembrolizumab was conjugated with the tetrafluorophenol-N-succinyl desferal-Fe(III) ester (TFP-N-sucDf) and subsequently radiolabeled with ⁸⁹Zr. Four cynomolgus monkeys with no previous exposure to humanized monoclonal antibodies received tracer only or tracer co-injected with pembrolizumab intravenously over 5 min. Thereafter, a static whole-body positron emission tomography (PET) scan was acquired with 10 min per bed position on days 0, 2, 5, and 7. Image-derived standardized uptake values (SUV_mean) were quantified by region of interest (ROI) analysis.

Results

⁸⁹Zr-N-sucDf-pembrolizumab was synthesized with high radiochemical purity (> 99 %) and acceptable molar activity (> 7 MBq/nmol). In animals dosed with tracer only, ⁸⁹Zr-N-sucDf-pembrolizumab distribution in lymphoid tissues such as mesenteric lymph nodes, spleen, and tonsils increased over time. Except for the liver, low radiotracer distribution was observed in all non-lymphoid tissue including the lung, muscle, brain, heart, and kidney. When a large excess of pembrolizumab was co-administered with a radiotracer, accumulation in the lymph nodes, spleen, and tonsils was reduced, suggestive of target-mediated accumulation.

Conclusions

⁸⁹Zr-N-sucDf-pembrolizumab shows preferential uptake in the lymphoid tissues including the lymph nodes, spleen, and tonsils. ⁸⁹Zr-N-sucDf-pembrolizumab may be useful in tracking the distribution of a subset of immune cells in non-human primates and humans.

Trial Registration

ClinicalTrials.gov Identifier: NCT02760225

Supplementary Information

The online version contains supplementary material available at 10.1007/s11307-020-01558-w.

In vivo detection of antigen-specific CD8+ T cells by immuno-positron emission tomography

The immune system's ability to recognize peptides on major histocompatibility molecules contributes to the eradication of cancers and pathogens. Tracking these responses in vivo could help evaluate the efficacy of immune interventions and improve mechanistic understanding of immune responses. For this purpose, we employ synTacs, which are dimeric major histocompatibility molecule scaffolds of defined composition. SynTacs, when labeled with positron-emitting isotopes, can noninvasively image antigen-specific CD8+ T cells in vivo. Using radiolabeled synTacs loaded with the appropriate peptides, we imaged human papillomavirus-specific CD8+ T cells by positron emission tomography in mice bearing human papillomavirus-positive tumors, as well as influenza A virus-specific CD8+ T cells in the lungs of influenza A virus-infected mice. It is thus possible to visualize antigen-specific CD8+ T-cell populations in vivo, which may serve prognostic and diagnostic roles.

Update on the development of molecular imaging and nanomedicine in China: Optical imaging

Molecular imaging has received increased attention worldwide, including in China, because it offers noninvasive characterization of widely diverse clinically significant pathologies. To achieve these goals, nanomedicine has evolved into a broad interdisciplinary field with flexible designs to accommodate and concentrate imaging and therapeutic payloads into pathological cells through selective binding to disease specific cell membrane biomarkers. This concept of personalized medicine reflects the vision of "magic bullets" proposed by German biochemist Paul Ehrlich over 100 years ago. As happening worldwide, Chinese scientists are contributing to this tsunami of science and technologies through impactful national programs and international research collaborations. This review provides a comprehensive update of Chinese innovations to address intractable unmet medical need in China and worldwide in the optical sciences. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Development of [18F]FPy-WL12 as a PD-L1 Specific PET Imaging Peptide

Expression of programmed cell death ligand 1 (PD-L1) within tumors is an important biomarker for guiding immune checkpoint therapies; however, immunohistochemistry-based methods of detection fail to provide a comprehensive picture of PD-L1 levels in an entire patient. To facilitate quantification of PD-L1 in the whole body, we developed a peptide-based, high-affinity PD-L1 imaging agent labeled with [¹⁸F]fluoride for positron emission tomography (PET) imaging. The parent peptide, WL12, and the nonradioactive analog of the radiotracer, ¹⁹FPy-WL12, inhibit PD-1/PD-L1 interaction at low nanomolar concentrations (half maximal inhibitory concentration [IC₅₀], 26-32 nM). The radiotracer, [¹⁸F]FPy-WL12, was prepared by conjugating 2,3,5,6-tetrafluorophenyl 6-[¹⁸F]fluoronicotinate ([¹⁸F]FPy-TFP) to WL12 and assessed for specificity in vitro in 6 cancer cell lines with varying PD-L1 expression. The uptake of the radiotracer reflected the PD-L1 expression assessed by flow cytometry. Next, we performed the in vivo evaluation of [¹⁸F]FPy-WL12 in mice bearing cancer xenografts by PET imaging, ex vivo biodistribution, and blocking studies. In vivo data demonstrated a PD-L1-specific uptake of [¹⁸F]FPy-WL12 in tumors that is reduced in mice receiving a blocking dose. The majority of [¹⁸F]FPy-WL12 radioactivity was localized in the tumors, liver, and kidneys indicating the need for optimization of the labeling strategy to improve the in vivo pharmacokinetics of the radiotracer.

Recent Advances in Rare-Earth-Doped Nanoparticles for NIR-II Imaging and Cancer Theranostics

Fluorescence imaging in the second near infrared window (NIR-II, 1,000-1,700 nm) has been widely used in cancer diagnosis and treatment due to its high spatial resolution and deep tissue penetration depths. In this work, recent advances in rare-earth-doped nanoparticles (RENPs)-a novel kind of NIR-II nanoprobes-are presented. The main focus of this study is on the modification of RENPs and their applications in NIR-II in vitro and in vivo imaging and cancer theranostics. Finally, the perspectives and challenges of NIR-II RENPs are discussed.

Ultra-fast cycling for multiplexed cellular fluorescence imaging

Rapid analysis of single and scant cell populations is essential in modern diagnostics, yet existing methods are often limited and slow. Here we describe an ultra-fast, highly efficient cycling method for the analysis of single cells based on unique linkers for tetrazine (Tz) / trans-cyclooctene (TCO) mediated quenching. Surprisingly, the quenching reaction rates were more than 3 orders of magnitude faster (t1/2 < 1 sec) than predicted. This allowed multi-cycle staining and immune cell profiling within an hour, leveraging the accelerated kinetics to open new diagnostic possibilities for rapid cellular analyses.

Ultra-fast Cycling for Multiplexed Cellular Fluorescence Imaging

Rapid analysis of single and scant cell populations is essential in modern diagnostics, yet existing methods are often limited and slow. Herein, we describe an ultra-fast, highly efficient cycling method for the analysis of single cells based on unique linkers for tetrazine (Tz)/trans-cyclooctene (TCO)-mediated quenching. Surprisingly, the quenching reaction rates were more than 3 orders of magnitude faster (t1/2 <1 s) than predicted. This allowed multi-cycle staining and immune cell profiling within an hour, leveraging the accelerated kinetics to open new diagnostic possibilities for rapid cellular analyses.

Spatial heterogeneity of oxygenation and haemodynamics in breast cancer resolved in vivo by conical multispectral optoacoustic mesoscopy

The characteristics of tumour development and metastasis relate not only to genomic heterogeneity but also to spatial heterogeneity, associated with variations in the intratumoural arrangement of cell populations, vascular morphology and oxygen and nutrient supply. While optical (photonic) microscopy is commonly employed to visualize the tumour microenvironment, it assesses only a few hundred cubic microns of tissue. Therefore, it is not suitable for investigating biological processes at the level of the entire tumour, which can be at least four orders of magnitude larger. In this study, we aimed to extend optical visualization and resolve spatial heterogeneity throughout the entire tumour volume. We developed an optoacoustic (photoacoustic) mesoscope adapted to solid tumour imaging and, in a pilot study, offer the first insights into cancer optical contrast heterogeneity in vivo at an unprecedented resolution of <50 μm throughout the entire tumour mass. Using spectral methods, we resolve unknown patterns of oxygenation, vasculature and perfusion in three types of breast cancer and showcase different levels of structural and functional organization. To our knowledge, these results are the most detailed insights of optical signatures reported throughout entire tumours in vivo, and they position optoacoustic mesoscopy as a unique investigational tool linking microscopic and macroscopic observations.

NIRF Nanoprobes for Cancer Molecular Imaging: Approaching Clinic

Near-IR fluorescence imaging (NIRFI) is a highly promising technique for improving cancer theranostics in the era of precision medicine. Through the combination with cutting-edge bionanotechnologies, the potential of NIRFI can be greatly broadened. A variety of novel NIRF nanoprobes has been developed with ultimate goals of addressing unmet medical needs. Here, we present recent breakthroughs on the fundamental aspects of NIRFI, such as imaging at long wavelengths (1000-1700 nm), and the use of new approaches (X-rays, chemiluminescence, radioluminescence, etc.) for the excitation of novel nanoprobes. Within two decades, research on NIRF nanoprobes has translated to clinical trials and it will further translate to cancer management.

Improving nanotherapy delivery and action through image-guided systems pharmacology

Despite recent advances in the translation of therapeutic nanoparticles (TNPs) into the clinic, the field continues to face challenges in predictably and selectively delivering nanomaterials for the treatment of solid cancers. The concept of enhanced permeability and retention (EPR) has been coined as a convenient but simplistic descriptor of high TNP accumulation in some tumors. However, in practice EPR represents a number of physiological variables rather than a single one (including dysfunctional vasculature, compromised lymphatics and recruited host cells, among other aspects of the tumor microenvironment) — each of which can be highly heterogenous within a given tumor, patient and across patients. Therefore, a clear need exists to dissect the specific biophysical factors underlying the EPR effect, to formulate better TNP designs, and to identify patients with high-EPR tumors who are likely to respond to TNP. The overall pharmacology of TNP is governed by an interconnected set of spatially defined and dynamic processes that benefit from a systems-level quantitative approach, and insights into the physiology have profited from the marriage between in vivo imaging and quantitative systems pharmacology (QSP) methodologies. In this article, we review recent developments pertinent to image-guided systems pharmacology of nanomedicines in oncology. We first discuss recent developments of quantitative imaging technologies that enable analysis of nanomaterial pharmacology at multiple spatiotemporal scales, and then examine reports that have adopted these imaging technologies to guide QSP approaches. In particular, we focus on studies that have integrated multi-scale imaging with computational modeling to derive insights about the EPR effect, as well as studies that have used modeling to guide the manipulation of the EPR effect and other aspects of the tumor microenvironment for improving TNP action. We anticipate that the synergistic combination of imaging with systems-level computational methods for effective clinical translation of TNPs will only grow in relevance as technologies increase in resolution, multiplexing capability, and in the ability to examine heterogeneous behaviors at the single-cell level.

Recent advances in tissue imaging for cancer research

Image analysis in clinical research has evolved at fast pace in the last decade. This review discusses basic concepts ranging from immunohistochemistry to advanced techniques such as multiplex imaging, digital pathology, flow cytometry and intravital microscopy. Tissue imaging ex vivo is still one of the gold-standards in the field due to feasibility. We describe here different protocols and applications of digital analysis providing basic and clinical researchers with an overview on how to analyse tissue images. In vivo imaging is not easily accessible to researchers; however, it provides invaluable dynamic information. Overall, we discuss a plethora of techniques that - when combined - constitute a powerful platform for basic and translational cancer research.

Imaging CAR T Cell Trafficking with eDHFR as a PET Reporter Gene

Cell-based therapeutics have considerable promise across diverse medical specialties; however, reliable human imaging of the distribution and trafficking of genetically engineered cells remains a challenge. We developed positron emission tomography (PET) probes based on the small-molecule antibiotic trimethoprim (TMP) that can be used to image the expression of the Escherichia coli dihydrofolate reductase enzyme (eDHFR) and tested the ability of [¹⁸F]-TMP, a fluorine-18 probe, to image primary human chimeric antigen receptor (CAR) T cells expressing the PET reporter gene eDHFR, yellow fluorescent protein (YFP), and Renilla luciferase (rLuc). Engineered T cells showed an approximately 50-fold increased bioluminescent imaging signal and 10-fold increased [¹⁸F]-TMP uptake compared to controls in vitro. eDHFR-expressing anti-GD2 CAR T cells were then injected into mice bearing control GD2^- and GD2⁺ tumors. PET/computed tomography (CT) images acquired on days 7 and 13 demonstrated early residency of CAR T cells in the spleen followed by on-target redistribution to the GD2⁺ tumors. This was corroborated by autoradiography and anti-human CD8 immunohistochemistry. We found a high sensitivity of detection for identifying tumor-infiltrating CD8 CAR T cells, ∼11,000 cells per mm³. These data suggest that the [¹⁸F]-TMP/eDHFR PET pair offers important advantages that could better allow investigators to monitor immune cell trafficking to tumors in patients.

Small molecules as theranostic agents in cancer immunology

With further research into the molecular mechanisms and roles linking immune suppression and restraint of (pre)malignancies, immunotherapies have revolutionized clinical strategies in the treatment of cancer. However, nearly 70% of patients who received immune checkpoint therapeutics showed no response. Complementary and/or synergistic effects may occur when extracellular checkpoint antibody blockades combine with small molecules targeting intracellular signal pathways up/downstream of immune checkpoints or regulating the innate and adaptive immune response. After radiolabeling with radionuclides, small molecules can also be used for estimating treatment efficacy of immune checkpoint blockades. This review not only highlights some significant intracellular pathways and immune-related targets such as the kynurenine pathway, purinergic signaling, the kinase signaling axis, chemokines, etc., but also summarizes some attractive and potentially immunosuppression-related small molecule agents, which may be synergistic with extracellular immune checkpoint blockade. In addition, opportunities for small molecule-based theranostics in cancer immunology will be discussed.

Light-Addressable Nanoclusters of Ultrasmall Iron Oxide Nanoparticles for Enhanced and Dynamic Magnetic Resonance Imaging of Arthritis

Design of novel nanoplatforms with single imaging elements for dynamic and enhanced T 1/T 2-weighted magnetic resonance (MR) imaging of diseases still remains significantly challenging. Here, a facile strategy to synthesize light-addressable ultrasmall Fe3O4 nanoparticles (NPs) that can form nanoclusters (NCs) under laser irradiation for enhanced and dynamic T 1/T 2-weighted MR imaging of inflammatory arthritis is reported. Citric acid-stabilized ultrasmall Fe3O4 NPs synthesized via a solvothermal approach are linked with both the arthritis targeting ligand folic acid (FA) and light-addressable unit diazirine (DA) via polyethylene glycol (PEG) spacer. The formed ultrasmall Fe3O4-PEG-(DA)-FA NPs are cytocompatible, display FA-mediated targeting specificity to arthritis-associated macrophage cells, and can form NCs upon laser irradiation to have tunable r 1 and r 2 relaxivities by varying the laser irradiation duration. With these properties owned, the designed Fe3O4-PEG-(DA)-FA NPs can be used for T 1-weighted MR imaging of arthritis without lasers and enhanced dual-mode T 1/T 2-weighted MR imaging of arthritis under laser irradiation due to the formation of NCs that have extended accumulation within the arthritis region and limited intravasation back to the blood circulation. The designed light-addressable Fe3O4-PEG-(DA)-FA NPs may be used as a promising platform for dynamic and precision T 1/T 2-weighted MR imaging of other diseases.

Concurrent fluorescence and volumetric optoacoustic tomography of nanoagent perfusion and bio-distribution in solid tumors

Intravenously administered liposomes and other nano-sized particles are known to passively accumulate in solid tumors via the enhanced permeability and retention (EPR) effect, which is extensively explored toward the improvement of diagnosis and drug delivery in oncology. Agent extravasation into tumors is often hampered by the mononuclear phagocytic and renal systems, which sequester and/or eliminate most of the nanoparticles from the body. Dynamic imaging of the tumor microcirculation and bolus perfusion can thus facilitate optimization of the nanoparticle delivery. When it comes to non-invasive visualization of rapid biological dynamics in whole tumors, the currently available pre-clinical imaging modalities are commonly limited by shallow penetration, lack of suitable contrast or otherwise insufficient spatial or temporal resolution. Herein, we demonstrate the unique capabilities of a combined epi-fluorescence and optoacoustic tomography (FLOT) system for characterizing contrast agent dynamics in orthotopic breast tumors in mice. A liposomal indocyanine green (Lipo-ICG) preparation was administered intravenously with the time-lapse data continuously acquired during and after the injection procedure. In addition to the highly sensitive detection of the fluorescence agent by the epi-fluorescence modality, the volumetric multi-spectral optoacoustic tomography readings further enabled resolving deep-seated vascular structures with high spatial resolution and hence provided accurate readings of the dynamic bio-distribution of nanoparticles in the entire tumor in 3D. The synergetic combination of the two modalities can become a powerful tool in cancer research and potentially aid the diagnosis, staging and treatment guidance of certain types of cancer in the clinical setting.

Calcium phosphate nanocarriers for drug delivery to tumors: imaging, therapy and theranostics

Calcium phosphate (CaP) was engineered as a drug delivery nanocarrier nearly 50 years ago due to its biocompatibility and biodegradability. In recent years, several approaches have been developed for the preparation of size-controllable, stable and multifunctional CaP nanocarriers, and several targeting moieties have also been decorated on the surface of these nanocarriers for active targeting. The CaP nanocarriers have been utilized for loading probes, nucleic acids, anticancer drugs and photosensitizers for cancer imaging, therapy and theranostics. Herein, we reviewed the recent advances in the preparation strategies of CaP nanocarriers and the applications of these nanocarriers in tumor diagnosis, gene delivery, drug delivery and theranostics and finally provided perspectives.

Integrin α6 targeted positron emission tomography imaging of hepatocellular carcinoma in mouse models

Integrin α6 emerges to be a diagnostic biomarker for hepatocellular carcinoma (HCC). Here, we translated our previously identified integrin α6 targeted peptide RWY into a positron emission tomography (PET) tracer ¹⁸F-RWY for the detection of HCC lesions in following four HCC mouse models including subcutaneous, orthotopic, genetically engineered and chemical induced HCC mice. ¹⁸F-RWY produced high PET signals in liver tumor tissues that were reduced by blocking studies using nonradiolabeled RWY peptide. We compared the integrin α6 targeted PET tracer ¹⁸F-RWY with the integrin αvβ3-targeted PET tracer ¹⁸F-3PRGD₂ and the clinical PET tracer ¹⁸F-FDG in chemical induced HCC mice. Among 12 HCC identified by enhanced magnetic resonance imaging (MRI) with hepatocellular specific gadoxetate disodium Gd-EOB-DTPA, the sensitivities of ¹⁸F-RWY, ¹⁸F-3PRGD₂ and ¹⁸F-FDG were approximately 92%, 73% and 50% while the tumor-to-liver ratios were 4.36 ± 1.41, 1.97 ± 0.43 and 1.63 ± 0.23 respectively. Additionally, PET imaging with the integrin α6 targeted ¹⁸F-RWY enabled to visualize small HCC lesions with diameters approximately 0.2 cm that was hard to be distinguished from surround hepatic vascular by enhanced MRI with Gd-EOB-DTPA. These findings potentiate the use of integrin α6 targeted PET tracer ¹⁸F-RWY for the detection of HCC.

Photoacoustic imaging as a tool to probe the tumour microenvironment

The tumour microenvironment (TME) is a complex cellular ecosystem subjected to chemical and physical signals that play a role in shaping tumour heterogeneity, invasion and metastasis. Studying the roles of the TME in cancer progression would strongly benefit from non-invasive visualisation of the tumour as a whole organ in vivo, both preclinically in mouse models of the disease, as well as in patient tumours. Although imaging techniques exist that can probe different facets of the TME, they face several limitations, including limited spatial resolution, extended scan times and poor specificity from confounding signals. Photoacoustic imaging (PAI) is an emerging modality, currently in clinical trials, that has the potential to overcome these limitations. Here, we review the biological properties of the TME and potential of existing imaging methods that have been developed to analyse these properties non-invasively. We then introduce PAI and explore the preclinical and clinical evidence that support its use in probing multiple features of the TME simultaneously, including blood vessel architecture, blood oxygenation, acidity, extracellular matrix deposition, lipid concentration and immune cell infiltration. Finally, we highlight the future prospects and outstanding challenges in the application of PAI as a tool in cancer research and as part of a clinical oncologist's arsenal.

Recent Advances in Targeting Nuclear Molecular Imaging Driven by Tetrazine Bioorthogonal Chemistry

Molecular imaging techniques apply sophisticated technologies to monitor, directly or indirectly, the spatiotemporal distribution of molecular or cellular processes for biomedical, diagnostic, or therapeutic purposes. For example, Single-Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) imaging, the most representative modalities of molecular imaging, enable earlier and more accurate diagnosis of cancer and cardiovascular diseases. New possibilities for noninvasive molecular imaging in vivo have emerged with advances in bioorthogonal chemistry. For example, tetrazine-related Inverse Electron Demand Diels-Alder (IEDDA) reactions can rapidly generate short-lived radioisotope probes in vivo that provide strong contrast for SPECT and PET. Here, we review pretargeting strategies for molecular imaging and novel radiotracers synthesized via tetrazine bioorthogonal chemistry. We systematically describe advances in direct radiolabeling and pretargeting approaches in SPECT and PET using metal and nonmetal radioisotopes based on tetrazine bioorthogonal reactions, and we discuss prospects for the future of such contrast agents.

Liposome-based probes for molecular imaging: from basic research to the bedside

Molecular imaging is very important in disease diagnosis and prognosis. Liposomes are excellent carriers for different types of molecular imaging probes. In this work, we summarize current developments in liposome-based probes used for molecular imaging and their applications in image-guided drug delivery and tumour surgery, including computed tomography (CT), ultrasound imaging (USI), magnetic resonance imaging (MRI), positron emission tomography (PET), fluorescence imaging (FLI) and photoacoustic imaging (PAI). We also summarized liposome-based multimodal imaging probes and new targeting strategies for liposomes. This work will offer guidance for the design of liposome-based imaging probes for future clinical applications.