Imaging the pharmacology of nanomaterials by intravital microscopy: Toward understanding their biological behavior

Using imaging modalities to predict nanoparticle distribution and treatment efficacy in solid tumors: The growing role of ultrasound

Nanomedicine in oncology has not had the success in clinical impact that was anticipated in the early stages of the field's development. Ideally, nanomedicines selectively accumulate in tumor tissue and reduce systemic side effects compared to traditional chemotherapeutics. However, this has been more successful in preclinical animal models than in humans. The causes of this failure to translate may be related to the intra- and inter-patient heterogeneity of the tumor microenvironment. Predicting whether a patient will respond positively to treatment prior to its initiation, through evaluation of characteristics like nanoparticle extravasation and retention potential in the tumor, may be a way to improve nanomedicine success rate. While there are many potential strategies to accomplish this, prediction and patient stratification via noninvasive medical imaging may be the most efficient and specific strategy. There have been some preclinical and clinical advances in this area using MRI, CT, PET, and other modalities. An alternative approach that has not been studied as extensively is biomedical ultrasound, including techniques such as multiparametric contrast-enhanced ultrasound (mpCEUS), doppler, elastography, and super-resolution processing. Ultrasound is safe, inexpensive, noninvasive, and capable of imaging the entire tumor with high temporal and spatial resolution. In this work, we summarize the in vivo imaging tools that have been used to predict nanoparticle distribution and treatment efficacy in oncology. We emphasize ultrasound imaging and the recent developments in the field concerning CEUS. The successful implementation of an imaging strategy for prediction of nanoparticle accumulation in tumors could lead to increased clinical translation of nanomedicines, and subsequently, improved patient outcomes. This article is categorized under: Diagnostic Tools In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery Emerging Technologies.

Recent advancements in the targeted delivery of etoposide nanomedicine for cancer therapy: A comprehensive review

Etoposide (ETO), a popular anticancer drug that inhibits topoisomerase II enzymes, may be administered more effectively and efficiently due to nanomedicine. The therapeutic application of ETO is constrained by its limited solubility, weak absorption, and severe side effects. This article summarizes substantial progress made in the development of ETO nanomedicine for the treatment of cancer. It discusses various organic and inorganic nanostructures used to load or affix ETOs, such as lipids, liposomes, polymeric nanoparticles (NPs), dendrimers, micelles, gold NPs, iron oxide NPs, and silica NPs. In addition, it evaluates the structural properties of these nanostructures, such as their size, zeta potential, encapsulation efficiency, and drug release mechanism, as well as their in vitro or in vivo performance. The article also emphasizes the co-delivery of ETO with other medications or agents to produce synergistic effects or combat drug resistance in the treatment of cancer. It concludes with a discussion of the challenges and potential avenues for clinical translation of ETO nanomedicine.

Role of in vivo imaging in Head and Neck cancer management

Intravital microscopy (IVM) and optical coherency tomography (OCT) are powerful optical imaging tools that allow visualization of dynamic biological activities in living subjects with subcellular resolutions. They have been used in preclinical and clinical cancer imaging, providing insights into the complex physiological, cellular, and molecular behaviors of tumors. They have revolutionized cancer diagnosis and therapies, allowing for real-time observation of biologic processes in vivo, including angiogenesis and immune cell interactions. Recent developments in techniques for observing deep tissues of living animals have improved bioluminescent proteins, fluorescent proteins, fluorescent dyes, and detection technologies like two-photon excitation microscopy. These technologies have become indispensable tools in basic sciences, preclinical research, and modern drug development. In Vivo imaging can detect subcellular signaling or metabolic events in living animals, but depth-dependent signal attenuation limits the depth from which significant data can be obtained. Cancer cell motility and invasion are key features of metastatic tumors, but only a small portion of tumor cells are motile and metastasize due to genetic, epigenetic, and microenvironmental heterogeneities.

Current status of Cancer Nanotheranostics: Emerging strategies for cancer management

Cancer diagnosis and management have been a slow-evolving area in medical science. Conventional therapies have by far proved to have various limitations. Also, the concept of immunotherapy which was thought to revolutionize the management of cancer has presented its range of drawbacks. To overcome these limitations nanoparticulate-derived diagnostic and therapeutic strategies are emerging. These nanomaterials are to be explored as they serve as a prospect for cancer theranostics. Nanoparticles have a significant yet unclear role in screening as well as therapy of cancer. However, nanogels and Photodynamic therapy is one such approach to be developed in cancer theranostics. Photoactive cancer theranostics is a vivid area that might prove to help manage cancer. Also, the utilization of the quantum dots as a diagnostic tool and to selectively kill cancer cells, especially in CNS tumors. Additionally, the redox-sensitive micelles targeting the tumor microenvironment of the cancer are also an important theranostic tool. This review focuses on exploring various agents that are currently being studied or can further be studied as cancer theranostics.

Supermagnetic Human Serum Albumin (HSA) Nanoparticles and PLGA-Based Doxorubicin Nanoformulation: A Duet for Selective Nanotherapy

Predicting the ability of nanoparticles (NP) to access the tumor is key to the success of chemotherapy using nanotherapeutics. In the present study, the ability of the dual NP-based theranostic system to accumulate in the tumor was evaluated in vivo using intravital microscopy (IVM) and MRI. The system consisted of model therapeutic doxorubicin-loaded poly(lactide-co-glycolide) NP (Dox-PLGA NP) and novel hybrid Ce^3/4+-doped maghemite NP encapsulated within the HSA matrix (hMNP) as a supermagnetic MRI contrasting agent. Both NP types had similar sizes of ~100 nm and negative surface potentials. The level of the hMNP and PLGA NP co-distribution in the same regions of interest (ROI, ~2500 µm²) was assessed by IVM in mice bearing the 4T1-mScarlet murine mammary carcinoma at different intervals between the NP injections. In all cases, both NP types penetrated into the same tumoral/peritumoral regions by neutrophil-assisted extravasation through vascular micro- and macroleakages. The maximum tumor contrasting in MRI scans was obtained 5 h after hMNP injection/1 h after PLGA NP injection; the co-distribution level at this time reached 78%. Together with high contrasting properties of the hMNP, these data indicate that the hMNP and PLGA NPs are suitable theranostic companions. Thus, analysis of the co-distribution level appears to be a useful tool for evaluation of the dual nanoparticle theranostics, whereas assessment of the leakage areas helps to reveal the tumors potentially responsive to nanotherapeutics.

Clinical translational barriers against nanoparticle-based imaging agents

Nanoparticle based imaging agents (NIAs) have been intensively explored in bench studies. Unfortunately, only a few cases have made their ways to clinical translation. In this review, clinical trials of NIAs were investigated for understanding possible barriers behind that. First, the complexity of multifunctional NIAs is considered a main barrier because it brings uncertainty to batch-to-batch fabrication, and results in sophisticated in vivo behaviors. Second, inadequate biosafety studies slow down the translational work. Third, NIA uptake at disease sites is highly heterogeneous, and often exhibits poor targeting efficiency. Focusing on the aforementioned problems, key design parameters were analyzed including NIAs' size, composition, surface characteristics, dosage, administration route, toxicity, whole-body distribution and clearance in clinical trials. Possible strategies were suggested to overcome these barriers. Besides, regulatory guidelines as well as scale-up and reproducibility during manufacturing process were covered as they are also key factors to consider during clinical translation of NIAs.

Intravital microscopy for real-time monitoring of drug delivery and nanobiological processes

Intravital microscopy (IVM) expands our understanding of cellular and molecular processes, with applications ranging from fundamental biology to (patho)physiology and immunology, as well as from drug delivery to drug processing and drug efficacy testing. In this review, we highlight modalities, methods and model organisms that make up today's IVM landscape, and we present how IVM - via its high spatiotemporal resolution - enables analysis of metabolites, small molecules, nanoparticles, immune cells, and the (tumor) tissue microenvironment. We furthermore present examples of how IVM facilitates the elucidation of nanomedicine kinetics and targeting mechanisms, as well as of biological processes such as immune cell death, host-pathogen interactions, metabolic states, and disease progression. We conclude by discussing the prospects of IVM clinical translation and examining the integration of machine learning in future IVM practice.

In Vivo Click Chemistry Enables Multiplexed Intravital Microscopy

The ability to observe cells in live organisms is essential for understanding their function in complex in vivo milieus. A major challenge today has been the limited ability to perform higher multiplexing beyond four to six colors to define cell subtypes in vivo. Here, a click chemistry-based strategy is presented for higher multiplexed in vivo imaging in mouse models. The method uses a scission-accelerated fluorophore exchange (SAFE), which exploits a highly efficient bioorthogonal mechanism to completely remove fluorescent signal from antibody-labeled cells in vivo. It is shown that the SAFE-intravital microscopy imaging method allows 1) in vivo staining of specific cell types in dorsal and cranial window chambers of mice, 2) complete un-staining in minutes, 3) in vivo click chemistries at lower (µm) and thus non-toxic concentrations, and 4) the ability to perform in vivo cyclic imaging. The potential utility of the method is demonstrated by 12 color imaging of immune cells in live mice.

Mapping and Validation of scRNA-Seq-Derived Cell-Cell Communication Networks in the Tumor Microenvironment

Recent advances in single-cell technologies, particularly single-cell RNA-sequencing (scRNA-seq), have permitted high throughput transcriptional profiling of a wide variety of biological systems. As scRNA-seq supports inference of cell-cell communication, this technology has and continues to anchor groundbreaking studies into the efficacy and mechanism of novel immunotherapies for cancer treatment. In this review, we will highlight methods developed to infer inter- and intracellular signaling from scRNA-seq and discuss how they have contributed to studies of immunotherapeutic intervention in the tumor microenvironment (TME). However, a central challenge remains in validating the hypothesized cell-cell interactions. Therefore, this review will also cover strategies for integration of these scRNA-seq-derived interaction networks with existing experimental and computational approaches. Integration of these networks with imaging, protein secretion measurements, and network analysis and mathematical modeling tools addresses challenges that remain with scRNA-seq to enhance studies of immunosuppressive and immunotherapy-altered signaling in the TME.

Nanotechnology Tools Enabling Biological Discovery

Over the years, the engineering aspect of nanotechnology has been significantly exploited. Medical intervention strategies have been developed by leveraging existing molecular biology knowledge and combining it with nanotechnology tools to improve outcomes. However, little attention has been paid to harnessing the strengths of nanotechnology as a biological discovery tool. Fundamental understanding of controlling dynamic biological processes at the subcellular level is key to developing personalized therapeutic and diagnostic interventions. Single-cell analyses using intravital microscopy, expansion microscopy, and microfluidic-based platforms have been helping to better understand cell heterogeneity in healthy and diseased cells, a major challenge in oncology. Also, single-cell analysis has revealed critical signaling pathways and biological intracellular components with key biological functions. The physical manipulation enabled by nanotools can allow real-time monitoring of biological changes at a single-cell level by sampling intracellular fluid from the same cell. The formation of intercellular highways by nanotube-like structures has important clinical implications such as metastasis development. The integration of nanomaterials into optical and molecular imaging techniques has rendered valuable morphological, structural, and biological information. Nanoscale imaging unravels mechanisms of temporality by enabling the visualization of nanoscale dynamics never observed or measured between individual cells with standard biological techniques. The exceptional sensitivity of nanozymes, artificial enzymes, make them perfect components of the next-generation mobile diagnostics devices. Here, we highlight these impactful cancer-related biological discoveries enabled by nanotechnology and producing a paradigm shift in cancer research and oncology.

Advanced Tumor Imaging Approaches in Human Tumors

The management of cancer has always relied heavily on the imaging modalities used to detect and monitor it. While many of these modalities have been around for decades, the technology surrounding them is always improving, and much has been discovered in recent years about the nature of tumors because of this. There have been several areas that have aided those discoveries. The use of artificial intelligence has already helped immensely in the quality of images taken but has not yet been widely implemented in clinical settings. Molecular imaging has proven to be useful in diagnosing different types of cancers based on the specificity of the probes/contrast agents used. Intravital imaging has already uncovered new information regarding the heterogeneity of the tumor vasculature. These three areas have provided a lot of useful information for the diagnosis and treatment of cancer, but further research and development in human trials is necessary to allow these techniques to fully utilize the information obtained thus far.

Confocal Imaging of Single-Cell Signaling in Orthotopic Models of Ovarian Cancer

Ovarian cancer (OVCA) is frequently detected at late stages of disease, often with dissemination throughout the peritoneal cavity surface, abdomen, and ascites fluid. Tumor signaling via mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways can promote OVCA progression and depend on local microenvironmental cues. To better study OVCA in situ within native tissue contexts, here we describe confocal microscopy techniques to image mouse models of intraperitoneal disease at a single-cell resolution. As a proof of principle demonstration, examples are highlighted for simultaneously imaging tumor vascularization, infiltrating and often immunosuppressive immune cells (tumor-associated macrophages), and OVCA kinase activity.

Neuroprotective effects of fluorophore-labelled manganese complexes: Determination of ROS production, mitochondrial membrane potential and confocal fluorescence microscopy studies in neuroblastoma cells

In this work, four manganese(II) complexes derived from the ligands H₂L¹-H₂L⁴, that incorporate dansyl or tosyl fluorescent dyes, have been investigated in term of their antioxidant properties. Two of the manganese(II) complexes have been newly prepared using the asymmetric half-salen ligand H₂L² and the thiosemicarbazone ligand H₂L³. The four organic strands and the manganese complexes have been characterized by different analytical and spectroscopic techniques. The study of the antioxidant behaviour of these two new complexes and other two fluorophore-labelled analogues was tested in SH-SY5Y neuroblastoma cells. These four model complexes 1-4 were found to protect cells from oxidative damage in this human neuronal model, by reducing the release of reactive oxygen species. Complexes 1-4 significantly improved cell survival, with levels between 79.1 ± 0.8% and 130.9 ± 4.1%. Moreover, complexes 3 and 4 were able to restore the mitochondrial membrane potential at 1 μM, with 4 reaching levels higher than 85%, similar to the percentages obtained by the positive control agent cyclosporin A. The incorporation of the fluorescent label in the complexes allowed the study of their ability to enter the human neuroblastoma cells by confocal microscopy.

Preclinical Studies in Small Animals for Advanced Drug Delivery Using Hyperthermia and Intravital Microscopy

This paper presents three devices suitable for the preclinical application of hyperthermia via the simultaneous high-resolution imaging of intratumoral events. (Pre)clinical studies have confirmed that the tumor micro-environment is sensitive to the application of local mild hyperthermia. Therefore, heating is a promising adjuvant to aid the efficacy of radiotherapy or chemotherapy. More so, the application of mild hyperthermia is a useful stimulus for triggered drug release from heat-sensitive nanocarriers. The response of thermosensitive nanoparticles to hyperthermia and ensuing intratumoral kinetics are considerably complex in both space and time. To obtain better insight into intratumoral processes, longitudinal imaging (preferable in high spatial and temporal resolution) is highly informative. Our devices are based on (i) an external electric heating adaptor for the dorsal skinfold model, (ii) targeted radiofrequency application, and (iii) a microwave antenna for heating of internal tumors. These models, while of some technical complexity, significantly add to the understanding of effects of mild hyperthermia warranting implementation in research on hyperthermia.

Imaging therapeutic peptide transport across intestinal barriers

Oral delivery is a highly preferred method for drug administration due to high patient compliance. However, oral administration is intrinsically challenging for pharmacologically interesting drug classes, in particular pharmaceutical peptides, due to the biological barriers associated with the gastrointestinal tract. In this review, we start by summarizing the pharmacological performance of several clinically relevant orally administrated therapeutic peptides, highlighting their low bioavailabilities. Thus, there is a strong need to increase the transport of peptide drugs across the intestinal barrier to realize future treatment needs and further development in the field. Currently, progress is hampered by a lack of understanding of transport mechanisms that govern intestinal absorption and transport of peptide drugs, including the effects of the permeability enhancers commonly used to mediate uptake. We describe how, for the past decades, mechanistic insights have predominantly been gained using functional assays with end-point read-out capabilities, which only allow indirect study of peptide transport mechanisms. We then focus on fluorescence imaging that, on the other hand, provides opportunities to directly visualize and thus follow peptide transport at high spatiotemporal resolution. Consequently, it may provide new and detailed mechanistic understanding of the interplay between the physicochemical properties of peptides and cellular processes; an interplay that determines the efficiency of transport. We review current methodology and state of the art in the field of fluorescence imaging to study intestinal barrier transport of peptides, and provide a comprehensive overview of the imaging-compatible in vitro, ex vivo, and in vivo platforms that currently are being developed to accelerate this emerging field of research.

Effect of Acoustic Radiation Force on the Distribution of Nanoparticles in Solid Tumors

Acoustic radiation force (ARF) might improve the distribution of nanoparticles (NPs) in tumors. To study this, tumors growing subcutaneously in mice were exposed to focused ultrasound (FUS) either 15 min or 4 h after the injection of NPs, to investigate the effect of ARF on the transport of NPs across the vessel wall and through the extracellular matrix. Quantitative analysis of confocal microscopy images from frozen tumor sections was performed to estimate the displacement of NPs from blood vessels. Using the same experimental exposure parameters, ARF was simulated and compared with the experimental data. Enhanced interstitial transport of NPs in tumor tissues was observed when FUS (10 MHz, acoustic power 234 W/cm², 3.3% duty cycle) was given either 15 min or 4 h after NP administration. According to acoustic simulations, the FUS generated an ARF per unit volume of 2.0×10⁶ N/m³. The displacement of NPs was larger when FUS was applied 4 h after NP injection compared with after 15 min. This study shows that ARF might contribute to a modest improved distribution of NPs into the tumor interstitium.

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.

Role of intravital imaging in nanomedicine-assisted anti-cancer therapy

Although nanomedicines have provided promising anti-tumor effects in cancer animal models, their clinical success remains limited. One of the most significant barriers in the clinical translation of nanomedicines is that they consist of multiple components, each of which may have different toxicities and therapeutic effects. Intravital imaging provides high spatial and temporal resolution for visualizing nanomedicine-mediated interactions between immune cells and tumor cells in real-time. Intravital imaging can facilitate the in vivo evaluation of the properties and effects of nanomedicines, such as their ability to cross the tumor vasculature, specifically eliminate the cancer cells, and modulate the immune cells found in the tumor microenvironment (TME). Thus, intravital imaging can provide direct evidence of nanomedicine's intravital behavior to better understand mechanism and accelerate clinical translation. In this review, we summarize several applications and latest advances in intravital imaging in nanomedicine-assisted anti-cancer therapy and discuss future perspectives in the field.

Quantification of Cellular Drug Biodistribution Addresses Challenges in Evaluating in vitro and in vivo Encapsulated Drug Delivery

Nanoencapsulated drug delivery to solid tumors is a promising approach to overcome pharmacokinetic limitations of therapeutic drugs. However, encapsulation leads to complex drug biodistribution and delivery making analysis of delivery efficacy challenging. As proxies, nanocarrier accumulation or total tumor drug uptake in the tumor are used to evaluate delivery. Yet, these measurements fail to assess delivery of active, released drug to the target, and thus it commonly remains unknown if drug-target occupancy has been achieved. Here, we develop an approach to evaluate the delivery of encapsulated drug to the target, where residual drug target vacancy is measured using a fluorescent drug analog. In vitro measurements reveal that burst release governs drug delivery independent of nanoparticle uptake, and highlight limitations of evaluating nanoencapsulated drug delivery in these models. In vivo, however, our approach captures successful nanoencapsulated delivery, finding that tumor stromal cells drive nanoparticle accumulation and mediate drug delivery to adjacent cancer cells. These results, and generalizable approach, provide a critical advance to evaluate delivery of encapsulated drug to the drug target - the central objective of nanotherapeutics.

Manipulating dynamic tumor vessel permeability to enhance polymeric micelle accumulation

Selectively delivering anticancer drugs to solid tumors while avoiding their accumulation in healthy tissues is a major goal in polymeric micelle research. We have recently discovered that the extravasation and permeation of polymeric micelles occur in a dynamic manner characterized by vascular bursts followed by a brief and vigorous outward flow of fluid (called "nano-eruptions"). Nano-eruptions allow delivery of polymeric micelle-associated drugs, though delivery can be heterogeneous both among tumors and within an individual tumor, leading to suboptimal intratumoral distribution. Manipulation of nano-eruptions is expected to improve the efficiency of drug delivery systems (DDSs). By using compounds that affect the intratumoral environment, i.e. a TGF-β inhibitor and chloroquine, the possibility of manipulating nano-eruptions to improve delivery efficiency was investigated. Both compounds were tested in a mouse xenograft model of GFP-labeled pancreatic tumor cells by tracing nano-eruption events and extravasation of size-modulated polymeric micelles in real-time through intravital confocal laser scanning microscopy. The TGF-β inhibitor increased the number of dynamic vents, extended duration time, and generated dynamic vents with a wide range of sizes. Chloroquine did not affect the frequency of nano-eruptions, but it increased tumor vessel diameter, maximum nano-eruption area, and maximum radial increase. Both the TGF-β inhibitor and chloroquine augmented nano-eruptions to diffuse polymeric micelles through tumor stroma, and these medications had a greater effect on the polymeric micelles with larger size, i.e. 70-nm, than on the smaller polymeric micelles having a 30-nm diameter. The results indicate that TGF-β inhibition and chloroquine refashion the intratumoral distribution of DDSs by different mechanisms.

Nanoparticle delivery in vivo: A fresh look from intravital imaging

Nanomedicine has proven promising in preclinical studies. However, only few formulations have been successfully translated to clinical use. A thorough understanding of how nanoparticles interact with cells in vivo is essential to accelerate the clinical translation of nanomedicine. Intravital imaging is a crucial tool to reveal the mechanisms of nanoparticle transport in vivo, allowing for the development of new strategies for nanomaterial design. Here, we first review the most recent progress in using intravital imaging to answer fundamental questions about nanoparticle delivery in vivo. We then elaborate on how nanoparticles interact with different cell types and how such interactions determine the fate of nanoparticles in vivo. Lastly, we discuss ways in which the use of intravital imaging can be expanded in the future to facilitate the clinical translation of nanomedicine.

In vivo microscopy reveals macrophage polarization locally promotes coherent microtubule dynamics in migrating cancer cells

Microtubules (MTs) mediate mitosis, directional signaling, and are therapeutic targets in cancer. Yet in vivo analysis of cancer cell MT behavior within the tumor microenvironment remains challenging. Here we developed an imaging pipeline using plus-end tip tracking and intravital microscopy to quantify MT dynamics in live xenograft tumor models. Among analyzed features, cancer cells in vivo displayed higher coherent orientation of MT dynamics along their cell major axes compared with 2D in vitro cultures, and distinct from 3D collagen gel cultures. This in vivo MT phenotype was reproduced in vitro when cells were co-cultured with IL4-polarized MΦ. MΦ depletion, MT disruption, targeted kinase inhibition, and altered MΦ polarization via IL10R blockade all reduced MT coherence and/or tumor cell elongation. We show that MT coherence is a defining feature for in vivo tumor cell dynamics and migration, modulated by local signaling from pro-tumor macrophages.

The regulation of microtubule (MT) dynamics in cancer cells within the tumor microenvironment is less understood. Here, the authors develop an imaging platform to examine MT dynamics in live xenograft models and show that pro-tumor macrophages modulate MT coherence and alignment to promote cancer cell migration.

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.

The expanding landscape of inflammatory cells affecting cancer therapy

Tumour-infiltrating myeloid cells (TIMCs) are critical regulators of cancer growth. The different phenotypes, functions and therapeutic effects of these phagocytes have, however, been difficult to study. With the advent of single-cell-based technologies, a new 'worldview' is emerging: the classification of TIMCs into subtypes that are conserved across patients and across species. As the landscape of TIMCs is beginning to be understood, it opens up questions about the function of each TIMC subtype and its drugability. In this Perspective, we outline the current map of TIMC populations in cancer and their known and presumed functions, and discuss their therapeutic implications and the biological research questions that they give rise to. The answers should be particularly relevant for bioengineers, materials scientists and the chemical and pharmaceutical communities developing the next generation of cancer therapies.

Neutrophil-mediated transport is crucial for delivery of short-circulating magnetic nanoparticles to tumors

Recently neutrophil-based nanoparticles (NPs) drug delivery systems have gained considerable attention in cancer therapy. Numerous studies have been conducted to identify optimal NPs parameters for passive tumor targeting, while there is a fundamental dearth of knowledge about the factors governing cell-mediated delivery. Here, by using intravital microscopy and magnetic resonance imaging, we describe accumulation dynamics of 140 nm magnetic cubes and clusters in murine breast cancer (4T1) and colon cancer (CT26) models. Notwithstanding rapid clearance from the blood flow, NPs readily accumulated in tumors at later time points. Both NPs types were captured mostly by intravascular neutrophils immediately after injection, and transmigration of NPs-bound neutrophils through the vessel wall was first shown in real-time. A dramatic drop in NPs accumulation upon Ly6G and Gr1 depletion further confirmed the role of neutrophils as a biocarrier for targeting tumors. Of note, for shorter circulating NPs, a cell-dependent delivery route was more impactful, while the accumulation of longer circulating counterpart was less compromised by neutrophil depletion. Neutrophil-mediated transport was also shown to depend on tumor type, with more efficiency noted in neutrophil-rich tumors. Revealing NPs characteristics and host factors influencing the neutrophil-based tumor targeting will help to rationally design drug delivery systems for improved cancer treatment. STATEMENT OF SIGNIFICANCE: Utilizing host cells as trojan horses for delivery nanodrugs to tumor site is a promising approach for cancer therapy. However, it is not clear yet how nanoparticles characteristics and tumor properties affect the efficiency of cell-based nanoparticles transport. Here, we compare neutrophil-based delivery of different-shaped magnetic nanoparticles (cubes and clusters) in two tumor models. The results suggest that neutrophil-mediated route is more impactful for rapidly cleared cubes, than for longer circulating clusters. The efficiency of cell-based accumulation also correlated with the level of neutrophils recruitment to different tumor types. These finding are important for rationale design of nanocarriers and predicting the efficiency of neutrophil-mediated drug delivery between patients and tumor types.

Nanotherapeutic Shots through the Heart of Plaque

The past several decades have brought significant advances in the application of clinical and preclinical nanoparticulate drugs in the field of cancer, but nanodrug development in cardiovascular disease has lagged in comparison. Improved understanding of the spatiotemporal kinetics of nanoparticle delivery to atherosclerotic plaques is required to optimize preclinical nanodrug delivery and to drive their clinical translation. Mechanistic studies using super-resolution and correlative light microscopy/electron microscopy permit a broad, ultra-high-resolution picture of how endothelial barrier integrity impacts the enhanced permeation and retention (EPR) effect for nanoparticles as a function of both atherosclerosis progression and metabolic therapy. Studies by Beldman et al. in the December issue of ACS Nano suggest atherosclerotic plaque progression supports endothelial junction stabilization, which can reduce nanoparticle entry into plaques, and metabolic therapy may induce similar effects. Herein, we examine the potential for advanced dynamic intravital microscopy-based mechanistic studies of nanoparticle entry into atherosclerotic plaques to shed light on the advantages of free extravasation versus immune-mediated nanoparticle uptake for effective clinical translation. We further explore the potential combination of metabolic therapy with another emerging cardiovascular disease treatment paradigm-efferocytosis stimulation-to enhance atherosclerotic plaque regression.

Optical Microscopy and Coherence Tomography of Cancer in Living Subjects

Intravital microscopy (IVM) and optical coherency tomography (OCT) are two powerful optical imaging tools that allow visualization of dynamic biological activities in living subjects with subcellular resolutions. Recent advances in labeling and label-free techniques empower IVM and OCT for a wide range of preclinical and clinical cancer imaging, providing profound insights into the complex physiological, cellular, and molecular behaviors of tumors. Preclinical IVM and OCT have elucidated many otherwise inscrutable aspects of cancer biology, while clinical applications of IVM and OCT are revolutionizing cancer diagnosis and therapies. We review important progress in the fields of IVM and OCT for cancer imaging in living subjects, highlighting key technological developments and their emerging applications in fundamental cancer biology research and clinical oncology investigation.

Spatial heterogeneity of nanomedicine investigated by multiscale imaging of the drug, the nanoparticle and the tumour environment

Genetic and phenotypic tumour heterogeneity is an important cause of therapy resistance. Moreover, non-uniform spatial drug distribution in cancer treatment may cause pseudo-resistance, meaning that a treatment is ineffective because the drug does not reach its target at sufficient concentrations. Together with tumour heterogeneity, non-uniform drug distribution causes “therapy heterogeneity”: a spatially heterogeneous treatment effect. Spatial heterogeneity in drug distribution occurs on all scales ranging from interpatient differences to intratumour differences on tissue or cellular scale. Nanomedicine aims to improve the balance between efficacy and safety of drugs by targeting drug-loaded nanoparticles specifically to tumours. Spatial heterogeneity in nanoparticle and payload distribution could be an important factor that limits their efficacy in patients. Therefore, imaging spatial nanoparticle distribution and imaging the tumour environment giving rise to this distribution could help understand (lack of) clinical success of nanomedicine. Imaging the nanoparticle, drug and tumour environment can lead to improvements of new nanotherapies, increase understanding of underlying mechanisms of heterogeneous distribution, facilitate patient selection for nanotherapies and help assess the effect of treatments that aim to reduce heterogeneity in nanoparticle distribution.

In this review, we discuss three groups of imaging modalities applied in nanomedicine research: non-invasive clinical imaging methods (nuclear imaging, MRI, CT, ultrasound), optical imaging and mass spectrometry imaging. Because each imaging modality provides information at a different scale and has its own strengths and weaknesses, choosing wisely and combining modalities will lead to a wealth of information that will help bring nanomedicine forward.

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.

Extravasating Neutrophils Open Vascular Barrier and Improve Liposomes Delivery to Tumors

Liposomes are the most extensively used nanocarriers in cancer therapy. Despite the advantages these vehicles provide over free drugs, there are still limitations with regards to the efficiency of liposomes delivery to tumors and off-target accumulation. A better understanding of nanodrugs extravasation mechanisms in different tumor types and normal vessels is needed to improve their antitumor activity. We used intravital microscopy to track for fluorescent liposomes behavior in xenograft tumor models (murine breast cancer 4T1 and melanoma B16, human prostate cancer 22Rv1) and normal skin and identified two distinct extravasation patterns. Microleakage, a local perivascular nanoparticle deposition, was found both in malignant and healthy tissues. This type of liposomes leakage does not provide access to tumor cells and is presumably responsible for drug deposition in normal tissues. In contrast, macroleakage penetrated deep into tissues and localized predominantly on the tumor-host interface. Although neutrophils did not uptake liposomes, their extravasation appeared to initiate both micro- and macroleakages. Based on neutrophils and liposomes extravasation dynamics, we hypothesized that microleakage and macroleakage are subsequent steps of the extravasation process corresponding to liposomes transport through endothelial and subendothelial barriers. Of note, extravasation spots were detected more often in the proximity of neutrophils, and across studied tumor types, neutrophils counts correlated with leakage frequencies. Reduced liposomes accumulation in 4T1 tumors upon Ly6G depletion further corroborated neutrophils role in nanoparticles delivery. Elucidating liposomes extravasation routes has a potential to help improve existing strategies and develop effective nanodrugs for cancer therapy.

NIR-II-Excited Intravital Two-Photon Microscopy Distinguishes Deep Cerebral and Tumor Vasculatures with an Ultrabright NIR-I AIE Luminogen

Intravital fluorescence imaging of vasculature morphology and dynamics in the brain and in tumors with large penetration depth and high signal-to-background ratio (SBR) is highly desirable for the study and theranostics of vascular-related diseases and cancers. Herein, a highly bright fluorophore (BTPETQ) with long-wavelength absorption and aggregation-induced near-infrared (NIR) emission (maximum at ≈700 nm) is designed for intravital two-photon fluorescence (2PF) imaging of a mouse brain and tumor vasculatures under NIR-II light (1200 nm) excitation. BTPETQ dots fabricated via nanoprecipitation show uniform size of around 42 nm and a high quantum yield of 19 ± 1% in aqueous media. The 2PF imaging of the mouse brain vasculatures labeled by BTPETQ dots reveals a 3D blood vessel network with an ultradeep depth of 924 µm. In addition, BTPETQ dots show enhanced 2PF in tumor vasculatures due to their unique leaky structures, which facilitates the differentiation of normal blood vessels from tumor vessels with high SBR in deep tumor tissues. Moreover, the extravasation and accumulation of BTPETQ dots in deep tumor (more than 900 µm) is visualized under NIR-II excitation. This study highlights the importance of developing NIR-II light excitable efficient NIR fluorophores for in vivo deep tissue and high contrast tumor imaging.

Fluorescence anisotropy imaging in drug discovery

Non-invasive measurement of drug-target engagement can provide critical insights in the molecular pharmacology of small molecule drugs. Fluorescence polarization/fluorescence anisotropy measurements are commonly employed in protein/cell screening assays. However, the expansion of such measurements to the in vivo setting has proven difficult until recently. With the advent of high-resolution fluorescence anisotropy microscopy it is now possible to perform kinetic measurements of intracellular drug distribution and target engagement in commonly used mouse models. In this review we discuss the background, current advances and future perspectives in intravital fluorescence anisotropy measurements to derive pharmacokinetic and pharmacodynamic measurements in single cells and whole organs.

Screening for new macrophage therapeutics

Myeloid derived macrophages play a key role in many human diseases, and their therapeutic modulation via pharmacological means is receiving considerable attention. Of particular interest is the fact that these cells are i) dynamic phenotypes well suited to therapeutic manipulation and ii) phagocytic, allowing them to be efficiently targeted with nanoformulations. However, it is important to consider that macrophages represent heterogeneous populations of subtypes with often competing biological behaviors and functions. In order to develop next generation therapeutics, it is therefore essential to screen for biological effects through a combination of in vitro and in vivo assays. Here, we review the state-of-the-art techniques, including both cell based screens and in vivo imaging tools that have been developed for assessment of macrophage phenotype. We conclude with a forward-looking perspective on the growing need for noninvasive macrophage assessment and laboratory assays to be put into clinical practice and the potential broader impact of myeloid-targeted therapeutics.

Preparation and Testing of Cells Expressing Fluorescent Proteins for Intravital Imaging of Tumor Microenvironment

Intravital microscopy is widely used for in vivo studies of the mechanisms of carcinogenesis and response to antitumor therapy. For visualization of tumor cells in vivo, cell lines expressing fluorescent proteins are needed. Expression of exogenous proteins can affect cell growth rate and their tumorigenic potential. Therefore, comprehensive analysis of the morphofunctional properties of transduced cells is required for creating appropriate models of tumor microenvironment. In the present study, six lines of mouse tumor cells expressing green and red fluorescent proteins were derived. Analysis of cells morphology, growth kinetics, and response to chemotherapy in vitro revealed no significant differences between wild-type and transduced cell lines. Introduction of fluorescent proteins into the genome of 4T1 (murine breast cancer) and B16-F10 (murine melanoma) cells did not affect tumor growth rate after subcutaneous implantation to mice, while both CT26-GFP and CT26-RFP cells (murine colon cancer) were rejected starting from day 8 after implantation. Elucidation of the mechanisms underlying CT26-GFP/RFP rejection is required to modify transduction technique for creating the models of tumor microenvironment accessible for in vivo visualization. Transduced 4T1 and B16-F10 cell lines can be used for intravital microscopic imaging of tumor cells, neoplastic vasculature, and leukocyte subpopulations.

Intravital imaging of glioma border morphology reveals distinctive cellular dynamics and contribution to tumor cell invasion

The pathogenesis of glioblastoma (GBM) is characterized by highly invasive behavior allowing dissemination and progression. A conclusive image of the invasive process is not available. The aim of this work was to study invasion dynamics in GBM using an innovative in vivo imaging approach. Primary brain tumor initiating cell lines from IDH-wild type GBM stably expressing H2B-Dendra2 were implanted orthotopically in the brains of SCID mice. Using high-resolution time-lapse intravital imaging, tumor cell migration in the tumor core, border and invasive front was recorded. Tumor cell dynamics at different border configurations were analyzed and multivariate linear modelling of tumor cell spreading was performed. We found tumor border configurations, recapitulating human tumor border morphologies. Not only tumor borders but also the tumor core was composed of highly dynamic cells, with no clear correlation to the ability to spread into the brain. Two types of border configurations contributed to tumor cell spreading through distinct invasion patterns: an invasive margin that executes slow but directed invasion, and a diffuse infiltration margin with fast but less directed movement. By providing a more detailed view on glioma invasion patterns, our study may improve accuracy of prognosis and serve as a basis for personalized therapeutic approaches.

A Supramolecular Nanocarrier for Delivery of Amiodarone Anti-Arrhythmic Therapy to the Heart

Amiodarone is an effective antiarrhythmic drug used to treat and prevent different types of cardiac arrhythmias. However, amiodarone can have considerable side effects resulting from accumulation in off-target tissues. Cardiac macrophages are highly prevalent tissue-resident immune cells with importance in homeostatic functions, including immune response and modulation of cardiac conduction. We hypothesized that amiodarone could be more efficiently delivered to the heart via cardiac macrophages, an important step toward reducing overall dose and off-target tissue accumulation. Toward this goal, we synthesized a nanoparticle drug carrier composed of l-lysine cross-linked succinyl-β-cyclodextrin that demonstrates amiodarone binding through supramolecular host-guest interaction as well as a high macrophage affinity. Biodistribution analyses at the organ and single-cell level demonstrate accumulation of nanoparticles in the heart resulting from rapid uptake by cardiac macrophages. Nanoparticle assisted delivery of amiodarone resulted in a 250% enhancement in the selective delivery of the drug to cardiac tissue in part due to a concomitant decrease of pulmonary accumulation, the main source of off-target toxicity.

Multiplex Three-Dimensional Mapping of Macromolecular Drug Distribution in the Tumor Microenvironment

Macromolecular cancer drugs such as therapeutic antibodies and nanoparticles are well known to display slow extravasation and incomplete penetration into tumors, potentially protecting cancer cells from therapeutic effects. Conventional assays to track macromolecular drug delivery are poorly matched to the heterogeneous tumor microenvironment, but recent progress on optical tissue clearing and three-dimensional (3D) tumor imaging offers a path to quantitative assays with cellular resolution. Here, we apply transparent tissue tomography (T3) as a tool to track perfusion and delivery in the tumor and to evaluate target binding and vascular permeability. Using T3, we mapped anti-programmed cell death protein-ligand 1 (PD-L1) antibody distribution in whole mouse tumors. By measuring 3D penetration distances of the antibody drug out from the blood vessel boundaries into the tumor parenchyma, we determined spatial pharmacokinetics of anti-PD-L1 antibody drugs in mouse tumors. With multiplex imaging of tumor components, we determined the distinct distribution of anti-PD-L1 antibody drug in the tumor microenvironment with different PD-L1 expression patterns. T3 imaging revealed CD31+ capillaries are more permeable to anti-PD-L1 antibody transport compared with the blood vessels composed of endothelium supported by vascular fibroblasts and smooth muscle cells. T3 analysis also confirmed that isotype IgG antibody penetrates more deeply into tumor parenchyma than anti-Her2 or anti-EGFR antibody, which were restrained by binding to their respective antigens on tumor cells. Thus, T3 offers simple and rapid access to 3D, quantitative maps of macromolecular drug distribution in the tumor microenvironment, offering a new tool for development of macromolecular cancer therapeutics.

Multispectral optoacoustic tomography (MSOT) for imaging the particle size-dependent intratumoral distribution of polymeric micelles

PURPOSE

This study proposes the utilization of multispectral optoacoustic tomography (MSOT) to investigate the intratumoral distribution of polymeric micelles and effect of size on the biodistribution and antitumor efficacy (ATE).

MATERIALS AND METHODS

Docetaxel and/or optoacoustic agent-loaded polymeric micelles (with diameters of 22, 48, and 124 nm) were prepared using amphiphilic block copolymers poly (ethylene glycol) methyl ether-block-poly (D,L lactide) (PEG2000-PDLLAx). Subcutaneous 4T1 tumor-bearing mice were monitored with MSOT imaging and IVIS® Spectrum in vivo live imaging after tail vein injection of micelles. The in vivo results and ex vivo confocal imaging results were then compared. Next, ATE of the three micelles was found and compared.

RESULTS

We found that MSOT imaging offers spatiotemporal and quantitative information on intratumoral distribution of micelles in living animals. All the polymeric micelles rapidly extravasated into tumor site after intravenous injection, but only the 22-nm micelle preferred to distribute into the inner tumor tissues, leading to a superior ATE than that of 48- and 124-nm micelles.

CONCLUSION

This study demonstrated that MSOT is theranostically a powerful imaging modality, offering quantitative information on size-dependent spatiotemporal distribution patterns after the extravasation of nanomedicine from tumor blood vessels.

Magnetite-Gold nanohybrids as ideal all-in-one platforms for theranostics

High-quality, 25 nm octahedral-shaped Fe3O4 magnetite nanocrystals are epitaxially grown on 9 nm Au seed nanoparticles using a modified wet-chemical synthesis. These Fe3O4-Au Janus nanoparticles exhibit bulk-like magnetic properties. Due to their high magnetization and octahedral shape, the hybrids show superior in vitro and in vivo T2 relaxivity for magnetic resonance imaging as compared to other types of Fe3O4-Au hybrids and commercial contrast agents. The nanoparticles provide two functional surfaces for theranostic applications. For the first time, Fe3O4-Au hybrids are conjugated with two fluorescent dyes or the combination of drug and dye allowing the simultaneous tracking of the nanoparticle vehicle and the drug cargo in vitro and in vivo. The delivery to tumors and payload release are demonstrated in real time by intravital microscopy. Replacing the dyes by cell-specific molecules and drugs makes the Fe3O4-Au hybrids a unique all-in-one platform for theranostics.

Radiation therapy primes tumors for nanotherapeutic delivery via macrophage-mediated vascular bursts

Efficient delivery of therapeutic nanoparticles (TNPs) to tumors is critical in improving efficacy, yet strategies that universally maximize tumoral targeting by TNP modification have been difficult to achieve in the clinic. Instead of focusing on TNP optimization, we show that the tumor microenvironment itself can be therapeutically primed to facilitate accumulation of multiple clinically relevant TNPs. Building on the recent finding that tumor-associated macrophages (TAM) can serve as nanoparticle drug depots, we demonstrate that local tumor irradiation substantially increases TAM relative to tumor cells and, thus, TNP delivery. High-resolution intravital imaging reveals that after radiation, TAM primarily accumulate adjacent to microvasculature, elicit dynamic bursts of extravasation, and subsequently enhance drug uptake in neighboring tumor cells. TAM depletion eliminates otherwise beneficial radiation effects on TNP accumulation and efficacy, and controls with unencapsulated drug show that radiation effects are more pronounced with TNPs. Priming with combined radiation and cyclophosphamide enhances vascular bursting and tumoral TNP concentration, in some cases leading to a sixfold increase of TNP accumulation in the tumor, reaching 6% of the injected dose per gram of tissue. Radiation therapy alters tumors for enhanced TNP delivery in a TAM-dependent fashion, and these observations have implications for the design of next-generation tumor-targeted nanomaterials and clinical trials for adjuvant strategies.

Coating Matters: Review on Colloidal Stability of Nanoparticles with Biocompatible Coatings in Biological Media, Living Cells and Organisms

Within the last two decades, the field of nanomedicine has not developed as successfully as has widely been hoped for. The main reason for this is the immense complexity of the biological systems, including the physico-chemical properties of the biological fluids as well as the biochemistry and the physiology of living systems. The nanoparticles' physicochemical properties are also highly important. These differ profoundly from those of freshly synthesized particles when applied in biological/living systems as recent research in this field reveals. The physico-chemical properties of nanoparticles are predefined by their structural and functional design (core and coating material) and are highly affected by their interaction with the environment (temperature, pH, salt, proteins, cells). Since the coating material is the first part of the particle to come in contact with the environment, it does not only provide biocompatibility, but also defines the behavior (e.g. colloidal stability) and the fate (degradation, excretion, accumulation) of nanoparticles in the living systems. Hence, the coating matters, particularly for a nanoparticle system for biomedical applications, which has to fulfill its task in the complex environment of biological fluids, cells and organisms. In this review, we evaluate the performance of different coating materials for nanoparticles concerning their ability to provide colloidal stability in biological media and living systems.

Engineering and physical sciences in oncology: challenges and opportunities

The principles of engineering and physics have been applied to oncology for nearly 50 years. Engineers and physical scientists have made contributions to all aspects of cancer biology, from quantitative understanding of tumour growth and progression to improved detection and treatment of cancer. Many early efforts focused on experimental and computational modelling of drug distribution, cell cycle kinetics and tumour growth dynamics. In the past decade, we have witnessed exponential growth at the interface of engineering, physics and oncology that has been fuelled by advances in fields including materials science, microfabrication, nanomedicine, microfluidics, imaging, and catalysed by new programmes at the National Institutes of Health (NIH), including the National Institute of Biomedical Imaging and Bioengineering (NIBIB), Physical Sciences in Oncology, and the National Cancer Institute (NCI) Alliance for Nanotechnology. Here, we review the advances made at the interface of engineering and physical sciences and oncology in four important areas: the physical microenvironment of the tumour and technological advances in drug delivery; cellular and molecular imaging; and microfluidics and microfabrication. We discussthe research advances, opportunities and challenges for integrating engineering and physical sciences with oncology to develop new methods to study, detect and treat cancer, and we also describe the future outlook for these emerging areas.

Targeting tumor associated macrophages: The new challenge for nanomedicine

The engineering of new nanomedicines with ability to target and kill or re-educate Tumor Associated Macrophages (TAMs) stands up as a promising strategy to induce the effective switching of the tumor-promoting immune suppressive microenvironment, characteristic of tumors rich in macrophages, to one that kills tumor cells, is anti-angiogenic and promotes adaptive immune responses. Alternatively, the loading of monocytes/macrophages in blood circulation with nanomedicines, may be used to profit from the high infiltration ability of myeloid cells and to allow the drug release in the bulk of the tumor. In addition, the development of TAM-targeted imaging nanostructures, can be used to study the macrophage content in solid tumors and, hence, for a better diagnosis and prognosis of cancer disease. The major challenges for the effective targeting of TAM with nanomedicines and their application in the clinic have already been identified. These challenges are associated to the undesirable clearance of nanomedicines by, the mononuclear phagocyte system (macrophages) in competing organs (liver, lung or spleen), upon their intravenous injection; and also to the difficult penetration of nanomedicines across solid tumors due to the abnormal vasculature and the excessive extracellular matrix present in stromal tumors. In this review we describe the recent nanotechnology-base strategies that have been developed to target macrophages in tumors.

A hindsight reflection on the clinical studies of poly(l-glutamic acid)-paclitaxel

Chemotherapy for cancer treatment is limited by the excessive toxicity to normal tissues. The design of chemodrug-loaded nanoformulations provides a unique approach to improve the treatment efficacy while minimizing toxicity. Despite the numerous publications of nanomedicine for the last several decades, however, only a small fraction of the developed nanoformulations have entered clinical trials, with even fewer being approved for clinical application. Poly(l-glutamic acid)-paclitaxel (PG-TXL) belongs to the few formulations that reached phase III clinical trials. Unfortunately, the development of PG-TXL stopped in 2016 due to the inability to show significant improvement over current standard care. This review will provide an overview of the preclinical and clinical evaluations of PG-TXL, and discuss lessons to be learned from this ordeal. The precise identification of suitable patients for clinical trial studies, deep understanding of the mechanisms of action, and an effective academic-industry partnership throughout all phases of drug development are important for the successful bench-to-bedside translation of new nanoformulations. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Peptide-Based Structures.