Ocular Effects of MEK Inhibitor Therapy: Literature Review, Clinical Presentation, and Best Practices for Mitigation.

MEK signaling pathway targeting has emerged as a valuable addition to the options available for the treatment of advanced cancers including melanoma and non-small cell lung cancer. Ophthalmologic monitoring of patients taking part in clinical trials of MEK inhibitors has shown that while ocular effects are common, generally emerging during the first days to weeks of treatment, the majority are either asymptomatic or have minimal visual impact and are benign, resolving without intervention or the need to reduce or stop MEK inhibitor therapy. However rare cases of serious, potentially vision-threatening ocular toxicities have been reported during MEK inhibitor therapy. There is currently no recommendation for routine ophthalmologic screening or monitoring of patients with advanced cancer who are initiating MEK inhibitor therapy. However, baseline ophthalmologic examination may be useful for all patients initiating MEK inhibitor therapy to allow the differentiation of preexisting pathology versus the development of MEK inhibitor-associated retinopathy in the event of the emergence of symptomatic ocular events. Regular ophthalmologic examination may be appropriate for patients at increased risk for ocular events, such as patients with a history of ocular inflammation, infection, or underlying macular/retinal disease. All patients reporting visual disturbance should be referred for prompt ophthalmologic review to determine the potential seriousness of any underlying abnormalities and whether there is a need for treatment modification or specific intervention. Understanding the potential consequences of ocular toxicities is of particular importance in the context of decision-making for the continuation of potentially life-prolonging medications such as MEK inhibitors.

Sustained and Localized Drug Depot Release Using Radiation-Activated Scintillating Nanoparticles.

Clinical treatment of cancer commonly incorporates X-ray radiation therapy (XRT), and developing spatially precise radiation-activatable drug delivery strategies may improve XRT efficacy while limiting off-target toxicities associated with systemically administered drugs. Nevertheless, achieving this has been challenging thus far because strategies typically rely on radical species with short lifespans, and the inherent nature of hypoxic and acidic tumor microenvironments may encourage spatially heterogeneous effects. It is hypothesized that the challenge could be bypassed by using scintillating nanoparticles that emit light upon X-ray absorption, locally forming therapeutic drug depots in tumor tissues. Thus a nanoparticle platform (Scintillating nanoparticle Drug Depot; SciDD) that enables the local release of cytotoxic payloads only after activation by XRT is developed, thereby limiting off-target toxicity. As a proof-of-principle, SciDD is used to deliver a microtubule-destabilizing payload MMAE (monomethyl auristatin E). With as little as a 2 Gy local irradiation to tumors, MMAE payloads are released effectively to kill tumor cells. XRT-mediated drug release is demonstrated in multiple mouse cancer models and showed efficacy over XRT alone (p < 0.0001). This work shows that SciDD can act as a local drug depot with spatiotemporally controlled release of cancer therapeutics.

Thyroid Cancers Exhibit Oncogene-Enhanced Macropinocytosis that Is Restrained by IGF1R and Promote Albumin-Drug Conjugate Response.

PURPOSE: Oncogene-driven macropinocytosis fuels nutrient scavenging in some cancer types, yet whether this occurs in thyroid cancers with prominent MAPK-ERK and PI3K pathway mutations remains unclear. We hypothesized that understanding links between thyroid cancer signaling and macropinocytosis might uncover new therapeutic strategies. EXPERIMENTAL DESIGN: Macropinocytosis was assessed across cells derived from papillary thyroid cancer (PTC), follicular thyroid cancer (FTC), non-malignant follicular thyroid, and aggressive anaplastic thyroid cancer (ATC), by imaging fluorescent dextran and serum albumin. The impacts of ectopic BRAFV600E and mutant RAS, genetic PTEN silencing, and inhibitors targeting RET, BRAF, and MEK kinases were quantified. BrafV600E p53-/- ATC tumors in immunocompetent mice were used to measure efficacy of an albumin-drug conjugate comprising microtubule-destabilizing monomethyl auristatin E (MMAE) linked to serum albumin via a cathepsin-cleavable peptide (Alb-vc-MMAE). RESULTS: FTC and ATC cells showed greater macropinocytosis than non-malignant and PTC cells. ATC tumors accumulated albumin at 8.8% injected dose per gram tissue. Alb-vc-MMAE, but not MMAE alone, reduced tumor size by >90% (P < 0.01). ATC macropinocytosis depended on MAPK/ERK activity and nutrient signaling, and increased by up to 230% with metformin, phenformin, or inhibition of IGF1Ri in monoculture but not in vivo. Macrophages also accumulated albumin and express the cognate IGF1R ligand, IGF1, which reduced ATC responsiveness to IGF1Ri. CONCLUSIONS: These findings identify regulated oncogene-driven macropinocytosis in thyroid cancers and demonstrate the potential of designing albumin-bound drugs to efficiently treat them.

Polymeric microneedles enable simultaneous delivery of cancer immunomodulatory drugs and detection of skin biomarkers.

Background: Immune-modulating therapies impart positive outcomes in a subpopulation of cancer patients. Improved delivery strategies and non-invasive monitoring of anti-tumor effects can help enhance those outcomes and understand the mechanisms associated with the generation of anti-tumor immune responses following immunotherapy. Methods: We report on the design of a microneedle (MN) platform capable of simultaneous delivery of immune activators and collection of interstitial skin fluid (ISF) to monitor therapeutic responses. While either approach has shown promise, the integration of the therapy and diagnostic arms into one MN platform has hardly been explored before. MNs were synthesized out of crosslinked hyaluronic acid (HA) and loaded with a model immunomodulatory nanoparticle-containing drug, CpG oligodinucleotides (TLR9 agonist), for cancer therapy in melanoma and colon cancer models. The therapeutic response was monitored by longitudinal analysis of entrapped immune cells in the MNs following patch retrieval and digestion. Results: Transdermal delivery of CpG-containing NPs with MNs induced anti-tumor immune responses in multiple syngeneic mouse cancer models. CpG-loaded MNs stimulated innate immune cells and reduced tumor growth. Intravital microscopy showed deposition and spatiotemporal co-localization of CpG-NPs within the tumor microenvironment when delivered with MNs. Analysis of MN-sampled ISF revealed similar immune signatures to those seen in the bulk tumor homogenate, such as increased populations of macrophages and effector T cells following treatment. Conclusions: Our hydrogel-based MNs enable effective transdermal drug delivery into immune cells in the tumor microenvironment, and upon retrieval, enable studying the immune response to the therapy over time. This platform has the theranostic potential to deliver a range of combination therapies while detecting biomarkers.

Dual Immunostimulatory Pathway Agonism through a Synthetic Nanocarrier Triggers Robust Anti-Tumor Immunity in Murine Glioblastoma.

Myeloid cells are abundant, create a highly immunosuppressive environment in glioblastoma (GBM), and thus contribute to poor immunotherapy responses. Based on the hypothesis that small molecules can be used to stimulate myeloid cells to elicit anti-tumor effector functions, a synthetic nanoparticle approach is developed to deliver dual NF-kB pathway-inducing agents into these cells via systemic administration. Synthetic, cyclodextrin-adjuvant nanoconstructs (CANDI) with high affinity for tumor-associated myeloid cells are dually loaded with a TLR7 and 8 (Toll-like receptor, 7 and 8) agonist (R848) and a cIAP (cellular inhibitor of apoptosis protein) inhibitor (LCL-161) to dually activate these myeloid cells. Here CANDI is shown to: i) readily enter the GBM tumor microenvironment (TME) and accumulate at high concentrations, ii) is taken up by tumor-associated myeloid cells, iii) potently synergize payloads compared to monotherapy, iv) activate myeloid cells, v) fosters a "hot" TME with high levels of T effector cells, and vi) controls the growth of murine GBM as mono- and combination therapies with anti-PD1. Multi-pathway targeted myeloid stimulation via the CANDI platform can efficiently drive anti-tumor immunity in GBM.

Radiation Cleaved Drug-Conjugate Linkers Enable Local Payload Release.

Conjugation of therapeutic payloads to biologics including antibodies and albumin can enhance the selectively of drug delivery to solid tumors. However, achieving activity in tumors while avoiding healthy tissues remains a challenge, and payload activity in off-target tissues can cause toxicity for many such drug-conjugates. Here, we address this issue by presenting a drug-conjugate linker strategy that releases an active therapeutic payload upon exposure to ionizing radiation. Localized X-ray irradiation at clinically relevant doses (8 Gy) yields 50% drug (doxorubicin or monomethyl auristatin E, MMAE) release under hypoxic conditions that are traditionally associated with radiotherapy resistance. As proof-of-principle, we apply the approach to antibody- and albumin-drug conjugates and achieve >2000-fold enhanced MMAE cytotoxicity upon irradiation. Overall, this work establishes ionizing radiation as a strategy for spatially localized cancer drug delivery.

Vasculopathy and Increased Vascular Congestion in Fatal COVID-19 and Acute Respiratory Distress Syndrome.

Rationale: The leading cause of death in coronavirus disease 2019 (COVID-19) is severe pneumonia, with many patients developing acute respiratory distress syndrome (ARDS) and diffuse alveolar damage (DAD). Whether DAD in fatal COVID-19 is distinct from other causes of DAD remains unknown. Objective: To compare lung parenchymal and vascular alterations between patients with fatal COVID-19 pneumonia and other DAD-causing etiologies using a multidimensional approach. Methods: This autopsy cohort consisted of consecutive patients with COVID-19 pneumonia (n = 20) and with respiratory failure and histologic DAD (n = 21; non-COVID-19 viral and nonviral etiologies). Premortem chest computed tomography (CT) scans were evaluated for vascular changes. Postmortem lung tissues were compared using histopathological and computational analyses. Machine-learning-derived morphometric analysis of the microvasculature was performed, with a random forest classifier quantifying vascular congestion (CVasc) in different microscopic compartments. Respiratory mechanics and gas-exchange parameters were evaluated longitudinally in patients with ARDS. Measurements and Main Results: In premortem CT, patients with COVID-19 showed more dilated vasculature when all lung segments were evaluated (P = 0.001) compared with controls with DAD. Histopathology revealed vasculopathic changes, including hemangiomatosis-like changes (P = 0.043), thromboemboli (P = 0.0038), pulmonary infarcts (P = 0.047), and perivascular inflammation (P < 0.001). Generalized estimating equations revealed significant regional differences in the lung microarchitecture among all DAD-causing entities. COVID-19 showed a larger overall CVasc range (P = 0.002). Alveolar-septal congestion was associated with a significantly shorter time to death from symptom onset (P = 0.03), length of hospital stay (P = 0.02), and increased ventilatory ratio [an estimate for pulmonary dead space fraction (Vd); p = 0.043] in all cases of ARDS. Conclusions: Severe COVID-19 pneumonia is characterized by significant vasculopathy and aberrant alveolar-septal congestion. Our findings also highlight the role that vascular alterations may play in Vd and clinical outcomes in ARDS in general.

Deciphering albumin-directed drug delivery by imaging.

Albumin is the most abundant plasma protein, exhibits extended circulating half-life, and its properties have long been exploited for diagnostics and therapies. Many drugs intrinsically bind albumin or have been designed to do so, yet questions remain about true rate limiting factors that govern albumin-based transport and their pharmacological impacts, particularly in advanced solid cancers. Imaging techniques have been central to quantifying - at a molecular and single-cell level - the impact of mechanisms such as phagocytic immune cell signaling, FcRn-mediated recycling, oncogene-driven macropinocytosis, and albumin-drug interactions on spatial albumin deposition and related pharmacology. Macroscopic imaging of albumin-binding probes quantifies vessel structure, permeability, and supports efficiently targeted molecular imaging. Albumin-based imaging in patients and animal disease models thus offers a strategy to understand mechanisms, guide drug development and personalize treatments.

Overcoming differential tumor penetration of BRAF inhibitors using computationally guided combination therapy.

BRAF-targeted kinase inhibitors (KIs) are used to treat malignancies including BRAF-mutant non-small cell lung cancer, colorectal cancer, anaplastic thyroid cancer, and, most prominently, melanoma. However, KI selection criteria in patients remain unclear, as are pharmacokinetic/pharmacodynamic (PK/PD) mechanisms that may limit context-dependent efficacy and differentiate related drugs. To address this issue, we imaged mouse models of BRAF-mutant cancers, fluorescent KI tracers, and unlabeled drug to calibrate in silico spatial PK/PD models. Results indicated that drug lipophilicity, plasma clearance, faster target dissociation, and, in particular, high albumin binding could limit dabrafenib action in visceral metastases compared to other KIs. This correlated with retrospective clinical observations. Computational modeling identified a timed strategy for combining dabrafenib and encorafenib to better sustain BRAF inhibition, which showed enhanced efficacy in mice. This study thus offers principles of spatial drug action that may help guide drug development, KI selection, and combination.

New and Emerging Research on Solute Carrier and ATP Binding Cassette Transporters in Drug Discovery and Development: Outlook From the International Transporter Consortium.

Enabled by a plethora of new technologies, research in membrane transporters has exploded in the past decade. The goal of this state-of-the-art article is to describe recent advances in research on membrane transporters that are particularly relevant to drug discovery and development. This review covers advances in basic, translational, and clinical research that has led to an increased understanding of membrane transporters at all levels. At the basic level, we describe the available crystal structures of membrane transporters in both the solute carrier (SLC) and ATP binding cassette superfamilies, which has been enabled by the development of cryogenic electron microscopy methods. Next, we describe new research on lysosomal and mitochondrial transporters as well as recently deorphaned transporters in the SLC superfamily. The translational section includes a summary of proteomic research, which has led to a quantitative understanding of transporter levels in various cell types and tissues and new methods to modulate transporter function, such as allosteric modulators and targeted protein degraders of transporters. The section ends with a review of the effect of the gut microbiome on modulation of transporter function followed by a presentation of 3D cell cultures, which may enable in vivo predictions of transporter function. In the clinical section, we describe new genomic and pharmacogenomic research, highlighting important polymorphisms in transporters that are clinically relevant to many drugs. Finally, we describe new clinical tools, which are becoming increasingly available to enable precision medicine, with the application of tissue-derived small extracellular vesicles and real-world biomarkers.

Probing immune infiltration dynamics in cancer by in vivo imaging.

Cancer immunotherapies typically aim to stimulate the accumulation and activity of cytotoxic T-cells or pro-inflammatory antigen-presenting cells, reduce immunosuppressive myeloid cells or regulatory T-cells, or elicit some combination of effects thereof. Notwithstanding the encouraging results, immunotherapies such as PD-1/PD-L1-targeted immune checkpoint blockade act heterogeneously across individual patients. It remains challenging to predict and monitor individual responses, especially across multiple sites of metastasis or sites of potential toxicity. To address this need, in vivo imaging of both adaptive and innate immune cell populations has emerged as a tool to quantify spatial leukocyte accumulation in tumors non-invasively. Here we review recent progress in the translational development of probes for in vivo leukocyte imaging, focusing on complementary perspectives provided by imaging of T-cells, phagocytic macrophages, and their responses to therapy.

ADAM8-Dependent Extracellular Signaling in the Tumor Microenvironment Involves Regulated Release of Lipocalin 2 and MMP-9.

The metalloprotease-disintegrin ADAM8 is critically involved in the progression of pancreatic cancer. Under malignant conditions, ADAM8 is highly expressed and could play an important role in cell-cell communication as expression has been observed in tumor and immune cells of the tumor microenvironment (TME) such as macrophages. To analyze the potential role of ADAM8 in the TME, ADAM8 knockout PDAC tumor cells were generated, and their release of extracellular vesicles (EVs) was analyzed. In EVs, ADAM8 is present as an active protease and associated with lipocalin 2 (LCN2) and matrix metalloprotease 9 (MMP-9) in an ADAM8-dependent manner, as ADAM8 KO cells show a lower abundance of LCN2 and MMP-9. Sorting of ADAM8 occurs independent of TSG101, even though ADAM8 contains the recognition motif PTAP for the ESCRTI protein TSG101 within the cytoplasmic domain (CD). When tumor cells were co-cultured with macrophages (THP-1 cells), expression of LCN2 and MMP-9 in ADAM8 KO cells was induced, suggesting that macrophage signaling can overcome ADAM8-dependent intracellular signaling in PDAC cells. In co-culture with macrophages, regulation of MMP-9 is independent of the M1/M2 polarization state, whereas LCN2 expression is preferentially affected by M1-like macrophages. From these data, we conclude that ADAM8 has a systemic effect in the tumor microenvironment, and its expression in distinct cell types has to be considered for ADAM8 targeting in tumors.

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.

Cell-Cell Communication Networks in Tissue: Toward Quantitatively Linking Structure with Function.

Forefront techniques for molecular interrogation of mammalian tissues, such as multiplexed tissue imaging, intravital microscopy, and single-cell RNA sequencing (scRNAseq), can combine to quantify cell-type abundance, co-localization, and global levels of receptors and their ligands. Nonetheless, it remains challenging to translate these various quantities into a more comprehensive understanding of how cell-cell communication networks dynamically operate. Therefore, construction of computational models for network-level functions - including niche-dependent actions, homeostasis, and multi-scale coordination - will be valuable for productively integrating the battery of experimental approaches. Here, we review recent progress in understanding cell-cell communication networks in tissue. Featured examples include ligand-receptor dissection of immunosuppressive and mitogenic signaling in the tumor microenvironment. As a future direction, we highlight an unmet potential to bridge high-level statistical approaches with low-level physicochemical mechanisms.

Meningeal B Cell Clusters Correlate with Submeningeal Pathology in a Natural Model of Multiple Sclerosis.

Multiple sclerosis (MS) is an idiopathic demyelinating disease in which meningeal inflammation correlates with accelerated disease progression. The study of meningeal inflammation in MS has been limited because of constrained access to MS brain/spinal cord specimens and the lack of experimental models recapitulating progressive MS. Unlike induced models, a spontaneously occurring model would offer a unique opportunity to understand MS immunopathogenesis and provide a compelling framework for translational research. We propose granulomatous meningoencephalomyelitis (GME) as a natural model to study neuropathological aspects of MS. GME is an idiopathic, progressive neuroinflammatory disease of young dogs with a female bias. In the GME cases examined in this study, the meninges displayed focal and disseminated leptomeningeal enhancement on magnetic resonance imaging, which correlated with heavy leptomeningeal lymphocytic infiltration. These leptomeningeal infiltrates resembled tertiary lymphoid organs containing large B cell clusters that included few proliferating Ki67+ cells, plasma cells, follicular dendritic/reticular cells, and germinal center B cell-like cells. These B cell collections were confined in a specialized network of collagen fibers associated with the expression of the lympho-organogenic chemokines CXCL13 and CCL21. Although neuroparenchymal perivascular infiltrates contained B cells, they lacked the immune signature of aggregates in the meningeal compartment. Finally, meningeal B cell accumulation correlated significantly with cortical demyelination reflecting neuropathological similarities to MS. Hence, during chronic neuroinflammation, the meningeal microenvironment sustains B cell accumulation that is accompanied by underlying neuroparenchymal injury, indicating GME as a novel, naturally occurring model to study compartmentalized neuroinflammation and the associated pathology thought to contribute to progressive MS.

Therapeutically reprogrammed nutrient signalling enhances nanoparticulate albumin bound drug uptake and efficacy in KRAS-mutant cancer.

Nanoparticulate albumin bound paclitaxel (nab-paclitaxel, nab-PTX) is among the most widely prescribed nanomedicines in clinical use, yet it remains unclear how nanoformulation affects nab-PTX behaviour in the tumour microenvironment. Here, we quantified the biodistribution of the albumin carrier and its chemotherapeutic payload in optically cleared tumours of genetically engineered mouse models, and compared the behaviour of nab-PTX with other clinically relevant nanoparticles. We found that nab-PTX uptake is profoundly and distinctly affected by cancer-cell autonomous RAS signalling, and RAS/RAF/MEK/ERK inhibition blocked its selective delivery and efficacy. In contrast, a targeted screen revealed that IGF1R kinase inhibitors enhance uptake and efficacy of nab-PTX by mimicking glucose deprivation and promoting macropinocytosis via AMPK, a nutrient sensor in cells. This study thus shows how nanoparticulate albumin bound drug efficacy can be therapeutically improved by reprogramming nutrient signalling and enhancing macropinocytosis in cancer cells.

The hedgehog pathway suppresses neuropathogenesis in CD4 T cell-driven inflammation.

The concerted actions of the CNS and the immune system are essential to coordinating the outcome of neuroinflammatory responses. Yet, the precise mechanisms involved in this crosstalk and their contribution to the pathophysiology of neuroinflammatory diseases largely elude us. Here, we show that the CNS-endogenous hedgehog pathway, a signal triggered as part of the host response during the inflammatory phase of multiple sclerosis and experimental autoimmune encephalomyelitis, attenuates the pathogenicity of human and mouse effector CD4 T cells by regulating their production of inflammatory cytokines. Using a murine genetic model, in which the hedgehog signalling is compromised in CD4 T cells, we show that the hedgehog pathway acts on CD4 T cells to suppress the pathogenic hallmarks of autoimmune neuroinflammation, including demyelination and axonal damage, and thus mitigates the development of experimental autoimmune encephalomyelitis. Impairment of hedgehog signalling in CD4 T cells exacerbates brain-brainstem-cerebellum inflammation and leads to the development of atypical disease. Moreover, we present evidence that hedgehog signalling regulates the pathogenic profile of CD4 T cells by limiting their production of the inflammatory cytokines granulocyte-macrophage colony-stimulating factor and interferon-γ and by antagonizing their inflammatory program at the transcriptome level. Likewise, hedgehog signalling attenuates the inflammatory phenotype of human CD4 memory T cells. From a therapeutic point of view, our study underlines the potential of harnessing the hedgehog pathway to counteract ongoing excessive CNS inflammation, as systemic administration of a hedgehog agonist after disease onset effectively halts disease progression and significantly reduces neuroinflammation and the underlying neuropathology. We thus unveil a previously unrecognized role for the hedgehog pathway in regulating pathogenic inflammation within the CNS and propose to exploit its ability to modulate this neuroimmune network as a strategy to limit the progression of ongoing neuroinflammation.

p53 dynamics vary between tissues and are linked with radiation sensitivity.

Radiation sensitivity varies greatly between tissues. The transcription factor p53 mediates the response to radiation; however, the abundance of p53 protein does not correlate well with the extent of radiosensitivity across tissues. Given recent studies showing that the temporal dynamics of p53 influence the fate of cultured cells in response to irradiation, we set out to determine the dynamic behavior of p53 and its impact on radiation sensitivity in vivo. We find that radiosensitive tissues show prolonged p53 signaling after radiation, while more resistant tissues show transient p53 activation. Sustaining p53 using a small molecule (NMI801) that inhibits Mdm2, a negative regulator of p53, reduced viability in cell culture and suppressed tumor growth. Our work proposes a mechanism for the control of radiation sensitivity and suggests tools to alter the dynamics of p53 to enhance tumor clearance. Similar approaches can be used to enhance killing of cancer cells or reduce toxicity in normal tissues following genotoxic therapies.

Macrophage imaging and subset analysis using single-cell RNA sequencing.

Macrophages have been associated with drug response and resistance in diverse settings, thus raising the possibility of using macrophage imaging as a companion diagnostic to inform personalized patient treatment strategies. Nanoparticle-based contrast agents are especially promising because they efficiently deliver fluorescent, magnetic, and/or radionuclide labels by leveraging the intrinsic capacity of macrophages to accumulate nanomaterials in their role as professional phagocytes. Unfortunately, current clinical imaging modalities are limited in their ability to quantify broad molecular programs that may explain (a) which particular cell subsets a given imaging agent is actually labeling, and (b) what mechanistic role those cells play in promoting drug response or resistance. Highly multiplexed single-cell approaches including single-cell RNA sequencing (scRNAseq) have emerged as resources to help answer these questions. In this review, we query recently published scRNAseq datasets to support companion macrophage imaging, with particular focus on using dextran-based nanoparticles to predict the action of anti-cancer nanotherapies and monoclonal antibodies.

Detecting Immune Response to Therapies Targeting PDL1 and BRAF by Using Ferumoxytol MRI and Macrin in Anaplastic Thyroid Cancer.

Background Anaplastic thyroid cancer (ATC) is aggressive with a poor prognosis, partly because of the immunosuppressive microenvironment created by tumor-associated macrophages (TAMs). Purpose To understand the relationship between TAM infiltration, tumor vascularization, and corresponding drug delivery by using ferumoxytol-enhanced MRI and macrin in an ATC mouse model. Materials and Methods ATC tumors were generated in 6-8-week-old female B6129SF1/J mice through intrathyroid injection to model orthotopic tumors, or intravenously to model hematogenous metastasis, and prospectively enrolled randomly into treatment cohorts (n = 94 total; August 1, 2018, to January 15, 2020). Mice were treated with vehicle or combined serine/threonine-protein kinase B-Raf (BRAF) kinase inhibitor (BRAFi) and anti-PDL1 antibody (aPDL1). A subset was cotreated with therapies, including an approximately 70-nm model drug delivery nanoparticle (DDNP) to target TAM, and an antibody-neutralizing colony stimulating factor 1 receptor (CSF1R). Imaging was performed at the macroscopic level with ferumoxytol-MRI and microscopically with macrin. Genetically engineered BrafV600E/WT p53-null allografts were used and complemented by a GFP-transgenic derivative and human xenografts. Tumor-bearing organs were processed by using tissue clearing and imaged with confocal microscopy and MRI. Two-tailed Wilcoxon tests were used for comparison (≥five per group). Results TAM levels were higher in orthotopic thyroid tumors compared with pulmonary metastatic lesions by 79% ± 23 (standard deviation; P < .001). These findings were concordant with ferumoxytol MRI, which showed 136% ± 88 higher uptake in thyroid lesions (P = .02) compared with lung lesions. BRAFi and aPDL1 combination therapy resulted in higher tumor DDNP delivery by 39% ± 14 in pulmonary lesions (P = .004). Compared with the untreated group, tumors following BRAFi, aPDL1, and CSF1R-blocking antibody combination therapy did not show greater levels of TAM or DDNP (P = .82). Conclusion In a mouse model of anaplastic thyroid cancer, ferumoxytol MRI showed 136% ± 88 greater uptake in orthotopic thyroid tumors compared with pulmonary lesions, which reflected high vascularization and greater tumor-associated macrophage (TAM) levels. Serine/threonine-protein kinase B-Raf inhibitor and anti-programmed death ligand 1 antibody elicited higher local TAM levels and 43% ± 20 greater therapeutic nanoparticle delivery but not higher vascularization in pulmonary tumors. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Luker in this issue.