Role of noninvasive molecular imaging in determining response

Dendritic cell vaccination combined with irreversible electroporation for treating pancreatic cancer-a narrative review

Background and Objective

Pancreatic ductal adenocarcinoma (PDAC) is 3rd most lethal cancer in the USA leading to a median survival of six months and less than 5% 5-year overall survival (OS). As the only potentially curative treatment, surgical resection is not suitable for up to 90% of the patients with PDAC due to late diagnosis. Highly fibrotic PDAC with an immunosuppressive tumor microenvironment restricts cytotoxic T lymphocyte (CTL) infiltration and functions causing limited success with systemic therapies like dendritic cell (DC)-based immunotherapy. In this study, we investigated the potential benefits of irreversible electroporation (IRE) ablation therapy in combination with DC vaccine therapy against PDAC.

Methods

We performed a literature search to identify studies focused on DC vaccine therapy and IRE ablation to boost therapeutic response against PDAC indexed in PubMed, Web of Science, and Scopus until February 20th, 2023.

Key Content and Findings

IRE ablation destructs tumor structure while preserving extracellular matrix and blood vessels facilitating local inflammation. The studies demonstrated IRE ablation reduces tumor fibrosis and promotes CTL tumor infiltration to PDAC tumors in addition to boosting immune response in rodent models. The administration of the DC vaccine following IRE ablation synergistically enhances therapeutic response and extends OS rates compared to the use of DC vaccination or IRE alone. Moreover, the implementation of data-driven approaches further allows dynamic and longitudinal monitoring of therapeutic response and OS following IRE plus DC vaccine immunoablation.

Conclusions

The combination of IRE ablation and DC vaccine immunotherapy is a potent strategy to enhance the therapeutic outcomes in patients with PDAC.

MRI radiomics to monitor therapeutic outcome of sorafenib plus IHA transcatheter NK cell combination therapy in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is a common liver malignancy with limited treatment options. Previous studies expressed the potential synergy of sorafenib and NK cell immunotherapy as a promising approach against HCC. MRI is commonly used to assess response of HCC to therapy. However, traditional MRI-based metrics for treatment efficacy are inadequate for capturing complex changes in the tumor microenvironment, especially with immunotherapy. In this study, we investigated potent MRI radiomics analysis to non-invasively assess early responses to combined sorafenib and NK cell therapy in a HCC rat model, aiming to predict multiple treatment outcomes and optimize HCC treatment evaluations.

METHODS

Sprague Dawley (SD) rats underwent tumor implantation with the N1-S1 cell line. Tumor progression and treatment efficacy were assessed using MRI following NK cell immunotherapy and sorafenib administration. Radiomics features were extracted, processed, and selected from both T1w and T2w MRI images. The quantitative models were developed to predict treatment outcomes and their performances were evaluated with area under the receiver operating characteristic (AUROC) curve. Additionally, multivariable linear regression models were constructed to determine the correlation between MRI radiomics and histology, aiming for a noninvasive evaluation of tumor biomarkers. These models were evaluated using root-mean-squared-error (RMSE) and the Spearman correlation coefficient.

RESULTS

A total of 743 radiomics features were extracted from T1w and T2w MRI data separately. Subsequently, a feature selection process was conducted to identify a subset of five features for modeling. For therapeutic prediction, four classification models were developed. Support vector machine (SVM) model, utilizing combined T1w + T2w MRI data, achieved 96% accuracy and an AUROC of 1.00 in differentiating the control and treatment groups. For multi-class treatment outcome prediction, Linear regression model attained 85% accuracy and an AUC of 0.93. Histological analysis showed that combination therapy of NK cell and sorafenib had the lowest tumor cell viability and the highest NK cell activity. Correlation analyses between MRI features and histological biomarkers indicated robust relationships (r = 0.94).

CONCLUSIONS

Our study underscored the significant potential of texture-based MRI imaging features in the early assessment of multiple HCC treatment outcomes.

Bioanalytical Assays for Pharmacokinetic and Biodistribution Study of Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are produced by the chemical linkage of cytotoxic agents and monoclonal antibodies. The complexity and heterogeneity of ADCs and the low concentration of cytotoxic agent released in vivo poses big challenges to their bioanalysis. Understanding the pharmacokinetic behavior, exposure-safety, and exposure-efficacy relationships of ADCs is needed for their successful development. Accurate analytical methods are required to evaluate intact ADCs, total antibody, released small molecule cytotoxins, and related metabolites. The selection of appropriate bioanalysis methods for comprehensive analysis of ADCs is mainly dependent on the properties of cytotoxic agents, the chemical linker, and the attachment sites. The quality of the information about the whole pharmacokinetic profile of ADCs has been improved due to the development and improvement of analytical strategies for detection of ADCs, such as ligand-binding assays and mass spectrometry-related techniques. In this article, we will focus on the bioanalytical assays that have been used in the pharmacokinetic study of ADCs and discuss their advantages, current limitations, and potential challenges. SIGNIFICANCE STATEMENT: This article describes bioanalysis methods which have been used in pharmacokinetic study of ADCs and discusses the advantages, disadvantages and potential challenges of these assays. This review is useful and helpful and will provide insights and reference for bioanalysis and development of ADCs.

Activatable Nanoreporters for Real-Time Tracking of Macrophage Phenotypic States Associated with Disease Progression

Diagnosis of inflammatory diseases is characterized by identifying symptoms, biomarkers, and imaging. However, conventional techniques lack the sensitivities and specificities to detect disease early. Here, it is demonstrated that the detection of macrophage phenotypes, from inflammatory M1 to alternatively activated M2 macrophages, corresponding to the disease state can be used to predict the prognosis of various diseases. Activatable nanoreporters that can longitudinally detect the presence of the enzyme Arginase 1, a hallmark of M2 macrophages, and nitric oxide, a hallmark of M1 macrophages are engineered, in real-time. Specifically, an M2 nanoreporter enables the early imaging of the progression of breast cancer as predicted by selectively detecting M2 macrophages in tumors. The M1 nanoreporter enables real-time imaging of the subcutaneous inflammatory response that rises from a local lipopolysccharide (LPS) administration. Finally, the M1-M2 dual nanoreporter is evaluated in a muscle injury model, where an initial inflammatory response is monitored by imaging M1 macrophages at the site of inflammation, followed by a resolution phase monitored by the imaging of infiltrated M2 macrophages involved in matrix regeneration and wound healing. It is anticipated that this set of macrophage nanoreporters may be utilized for early diagnosis and longitudinal monitoring of inflammatory responses in various disease models.

How to 19F MRI: applications, technique, and getting started

Magnetic resonance imaging (MRI) plays a significant role in the routine imaging workflow, providing both anatomical and functional information. 19F MRI is an evolving imaging modality where instead of 1H, 19F nuclei are excited. As the signal from endogenous 19F in the body is negligible, exogenous 19F signals obtained by 19F radiofrequency coils are exceptionally specific. Highly fluorinated agents targeting particular biological processes (i.e., the presence of immune cells) have been visualised using 19F MRI, highlighting its potential for non-invasive and longitudinal molecular imaging. This article aims to provide both a broad overview of the various applications of 19F MRI, with cancer imaging as a focus, as well as a practical guide to 19F imaging. We will discuss the essential elements of a 19F system and address common pitfalls during acquisition. Last but not least, we will highlight future perspectives that will enhance the role of this modality. While not an exhaustive exploration of all 19F literature, we endeavour to encapsulate the broad themes of the field and introduce the world of 19F molecular imaging to newcomers. 19F MRI bridges several domains, imaging, physics, chemistry, and biology, necessitating multidisciplinary teams to be able to harness this technology effectively. As further technical developments allow for greater sensitivity, we envision that 19F MRI can help unlock insight into biological processes non-invasively and longitudinally.

Evaluation of 89Zr-Labeled Anti-PD-L1 Monoclonal Antibodies Using DFO and Novel HOPO Analogues as Chelating Agents for Immuno-PET

Programmed death ligand 1 (PD-L1) is a type 1 transmembrane immunosuppressive protein that is expressed on a wide range of cell types, including cancer cells. Anti-PD-L1 antibodies have revolutionized cancer therapy and have led to improved outcomes for subsets of cancer patients, including triple-negative breast cancer (TNBC) patients. As a result, PET imaging of PD-L1 protein expression in cancer patients has been explored for noninvasive detection of PD-L1 expressing tumors as well as monitoring response to anti-PD-L1 immune checkpoint therapy. Previous studies have indicated that the in vivo stability and in vivo target detection of antibody-based radio-conjugates can be dramatically affected by the chelator used. These reports demonstrated that the chelator HOPO diminishes ⁸⁹Zr de-chelation compared to DFO. Herein, we report an improved HOPO synthesis and evaluated a series of novel analogues for thermal stability, serum stability, PD-L1-specific binding using the BT-549 TNBC cell line, PET imaging in vivo, as well as biodistribution of ⁸⁹Zr-labeled anti-PD-L1 antibodies in BT-549 xenograft murine models. A new chelator, C5HOPO, demonstrated high stability in vitro and afforded effective PD-L1 targeting in vivovia immuno-PET. These results demonstrated that an improved HOPO chelator is an effective chelating agent that can be utilized to image therapeutically relevant targets in vivo.

Enhancing Cancer Diagnosis with Real-Time Feedback: Tumor Metabolism through Hyperpolarized 1-13C Pyruvate MRSI

This review article discusses the potential of hyperpolarized (HP) 13C magnetic resonance spectroscopic imaging (MRSI) as a noninvasive technique for identifying altered metabolism in various cancer types. Hyperpolarization significantly improves the signal-to-noise ratio for the identification of 13C-labeled metabolites, enabling dynamic and real-time imaging of the conversion of [1-13C] pyruvate to [1-13C] lactate and/or [1-13C] alanine. The technique has shown promise in identifying upregulated glycolysis in most cancers, as compared to normal cells, and detecting successful treatment responses at an earlier stage than multiparametric MRI in breast and prostate cancer patients. The review provides a concise overview of the applications of HP [1-13C] pyruvate MRSI in various cancer systems, highlighting its potential for use in preclinical and clinical investigations, precision medicine, and long-term studies of therapeutic response. The article also discusses emerging frontiers in the field, such as combining multiple metabolic imaging techniques with HP MRSI for a more comprehensive view of cancer metabolism, and leveraging artificial intelligence to develop real-time, actionable biomarkers for early detection, assessing aggressiveness, and interrogating the early efficacy of therapies.

MR Imaging-Based In Vivo Macrophage Imaging to Monitor Immune Response after Radiofrequency Ablation of the Liver

PURPOSE

To establish molecular magnetic resonance (MR) imaging instruments for in vivo characterization of the immune response to hepatic radiofrequency (RF) ablation using cell-specific immunoprobes.

MATERIALS AND METHODS

Seventy-two C57BL/6 wild-type mice underwent standardized hepatic RF ablation (70 °C for 5 minutes) to generate a coagulation area measuring 6-7 mm in diameter. CD68+ macrophage periablational infiltration was characterized with immunohistochemistry 24 hours, 72 hours, 7 days, and 14 days after ablation (n = 24). Twenty-one mice were subjected to a dose-escalation study with either 10, 15, 30, or 60 mg/kg of rhodamine-labeled superparamagnetic iron oxide nanoparticles (SPIONs) or 2.4, 1.2, or 0.6 mg/kg of gadolinium-160 (160Gd)-labeled CD68 antibody for assessment of the optimal in vivo dose of contrast agent. MR imaging experiments included 9 mice, each receiving 10-mg/kg SPIONs to visualize phagocytes using T2∗-weighted imaging in a horizontal-bore 9.4-T MR imaging scanner, 160Gd-CD68 for T1-weighted MR imaging of macrophages, or 0.1-mmol/kg intravenous gadoterate (control group). Radiological-pathological correlation included Prussian blue staining, rhodamine immunofluorescence, imaging mass cytometry, and immunohistochemistry.

RESULTS

RF ablation-induced periablational infiltration (206.92 μm ± 12.2) of CD68+ macrophages peaked at 7 days after ablation (P < .01) compared with the untreated lobe. T2∗-weighted MR imaging with SPION contrast demonstrated curvilinear T2∗ signal in the transitional zone (TZ) (186 μm ± 16.9), corresponsing to Iron Prussian blue staining. T1-weighted MR imaging with 160Gd-CD68 antibody showed curvilinear signal in the TZ (164 μm ± 3.6) corresponding to imaging mass cytometry.

CONCLUSIONS

Both SPION-enhanced T2∗-weighted and 160Gd-enhanced T1-weighted MR imaging allow for in vivo monitoring of macrophages after RF ablation, demonstrating the feasibility of this model to investigate local immune responses.

The Role of Molecular Imaging in Personalized Medicine

The concept of personalized medicine refers to the tailoring of medical treatment to each patient's unique characteristics. Scientific advancements have led to a better understanding of how a person's unique molecular and genetic profile makes them susceptible to certain diseases. It provides individualized medical treatments that will be safe and effective for each patient. Molecular imaging modalities play an essential role in this aspect. They are used widely in screening, detection and diagnosis, treatment, assessing disease heterogeneity and progression planning, molecular characteristics, and long-term follow-up. In contrast to conventional imaging approaches, molecular imaging techniques approach images as the knowledge that can be processed, allowing for the collection of relevant knowledge in addition to the evaluation of enormous patient groups. This review presents the fundamental role of molecular imaging modalities in personalized medicine.

Molecular Imaging and the PD-L1 Pathway: From Bench to Clinic

Programmed death-1 (PD-1) and programmed death ligand 1 (PD-L1) inhibitors target the important molecular interplay between PD-1 and PD-L1, a key pathway contributing to immune evasion in the tumor microenvironment (TME). Long-term clinical benefit has been observed in patients receiving PD-(L)1 inhibitors, alone and in combination with other treatments, across multiple tumor types. PD-L1 expression has been associated with response to immune checkpoint inhibitors, and treatment strategies are often guided by immunohistochemistry-based diagnostic tests assessing expression of PD-L1. However, challenges related to the implementation, interpretation, and clinical utility of PD-L1 diagnostic tests have led to an increasing number of preclinical and clinical studies exploring interrogation of the TME by real-time imaging of PD-(L)1 expression by positron emission tomography (PET). PET imaging utilizes radiolabeled molecules to non-invasively assess PD-(L)1 expression spatially and temporally. Several PD-(L)1 PET tracers have been tested in preclinical and clinical studies, with clinical trials in progress to assess their use in a number of cancer types. This review will showcase the development of PD-(L)1 PET tracers from preclinical studies through to clinical use, and will explore the opportunities in drug development and possible future clinical implementation.

Building the Bridge: Molecular Imaging Biomarkers for 21st Century Cancer Therapies

Precision medicine, where the molecular underpinnings of the disease are assessed for tailored therapies, has greatly impacted cancer care. In parallel, a new pillar of therapeutics has emerged with profound success, including immunotherapies such as checkpoint inhibitors and cell-based therapies. Nonetheless, it remains essential to develop paradigms to predict and monitor for therapeutic response. Molecular imaging has the potential to add substantially to all phases of cancer patient care: predicative, companion diagnostics can illuminate therapeutic target density within a tumor, and pharmacodynamic imaging biomarkers can complement traditional modalities to judge a favorable treatment response. This "Focus on Molecular Imaging" article discusses the current role of molecular imaging in oncology and highlights an additional step in clinical paradigm termed a "therapeutic biomarker," which serves to assess whether next generation drugs reach their target to elicit a favorable clinical response.

Monitoring CD8a+ T Cell Responses to Radiotherapy and CTLA-4 Blockade Using [64Cu]NOTA-CD8a PET Imaging

Purpose

Current response assessment systems for cancer patients receiving immunotherapy are limited. This is due to the associated inflammatory response that may confound the conventional morphological response evaluation criteria in solid tumors and metabolic positron emission tomography (PET) response criteria in solid. Recently, novel PET imaging techniques using radiolabeled antibodies and fragments have emerged as a particularly sensitive and specific modality for quantitative tracking of immune cell dynamics. Therefore, we sought to investigate the utility of Cu-64 labeled F(ab)′2 fragments for in vivo detection of CD8a⁺ T cells as a prognostic imaging biomarker of response to immunotherapy in an immunocompetent mouse model of colorectal cancer.

Procedures

[⁶⁴Cu]NOTA-CD8a was produced by enzymatic digestion of rat-anti-mouse CD8a antibody (clone YTS169.4), purified yielding isolated CD8a-F(ab)′2 fragments and randomly conjugated with the 2-S-(isothiocyanatbenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-SCN-Bn-NOTA) chelator. NOTA-CD8a was radiolabeled with Cu-64 and injected into CT26 tumor-bearing mice for longitudinal assessment. To investigate the value of [⁶⁴Cu]NOTA-CD8a PET imaging for assessment of treatment response, CT26 tumor-bearing mice were subjected to external radiation therapy (XRT) in combination with anti-CTLA-4 therapy. Imaging data was supported by flow cytometry and immunohistochemistry (IHC).

Results

Combination treatment with XRT and anti-CTLA-4 effectively inhibited tumor growth until day 22 post-therapy initiation (p = 0.0025) and increased the overall survival of mice compared to control (p = 0.0017). The [⁶⁴Cu]NOTA-CD8a tumor-to-heart ratio was increased in XRT + anti-CTLA-4-treated mice on day 8 after initiation of therapy (p = 0.0246). Flow cytometry and IHC confirmed the increase in tumor-infiltrating CD8a⁺ cells in XRT + anti-CTLA-4-treated mice. Furthermore, [⁶⁴Cu]NOTA-CD8a PET imaging distinguished responders and non-responders prior to treatment-induced changes in tumor volume among mice.

Conclusion

In the present study, we demonstrated that [⁶⁴Cu]NOTA-CD8a was able to detect treatment-induced changes in CD8a⁺ infiltration in murine CT26 colon tumors following a common preclinical combination treatment protocol. Overall, [⁶⁴Cu]NOTA-CD8a exhibited good prognostic and predictive value. We suggest that [⁶⁴Cu]NOTA-CD8a PET imaging can be used as an early biomarker of response to therapy in preclinical models.

Preclinical PET imaging with the novel human antibody 89Zr-DFO-REGN3504 sensitively detects PD-L1 expression in tumors and normal tissues

Background

Programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) blocking antibodies including cemiplimab have generated profound clinical activity across diverse cancer types. Tumorous PD-L1 expression, as assessed by immunohistochemistry (IHC), is an accepted predictive marker of response to therapy in some cancers. However, expression is often dynamic and heterogeneous, and therefore not reliably captured by IHC from tumor biopsies or archival samples. Thus, there is significant need for accurate whole-body quantification of PD-L1 levels.

Methods

We radiolabeled the novel human anti-PD-L1 antibody REGN3504 with zirconium-89 (⁸⁹Zr) using the chelator p-SCN-Bn-Deferoxamine to enable non-invasive immuno-positron emission tomography (immuno-PET) of PD-L1 expression. PET imaging assessed the localization of ⁸⁹Zr-REGN3504 to multiple human tumor xenografts. Mice genetically humanized for PD-1 and PD-L1 were used to assess the biodistribution of ⁸⁹Zr-REGN3504 to normal tissues and the estimated human radiation dosimetry of ⁸⁹Zr-REGN3504 was also determined. Pharmacokinetics of REGN3504 was assessed in monkeys.

Results

Clear localization of ⁸⁹Zr-REGN3504 to human tumor xenografts was observed via PET imaging and ex vivo biodistribution studies demonstrated high (fourfold to sixfold) tumor:blood ratios. ⁸⁹Zr-REGN3504 specifically localized to spleen and lymph nodes in the PD-1/PD-L1 humanized mice. ⁸⁹Zr-REGN3504 immuno-PET accurately detected a significant reduction in splenic PD-L1 positive cells following systemic treatment with clodronate liposomes. Radiation dosimetry suggested absorbed doses would be within guidelines for other ⁸⁹Zr radiolabeled, clinically used antibodies. Pharmacokinetics of REGN3504 was linear.

Conclusion

This work supports the clinical translation of ⁸⁹Zr-REGN3504 immuno-PET for the assessment of PD-L1 expression. Future clinical studies will aim to investigate the utility of ⁸⁹Zr-REGN3504 immuno-PET for predicting and monitoring response to anti-PD-1 therapy.

In vivo tracking of bioorthogonally labeled T-cells for predicting therapeutic efficacy of adoptive T-cell therapy

Non-invasive tracking of T-cells may help to predict the patient responsiveness and therapeutic outcome. Herein, we developed bioorthogonal T-cell labeling and tracking strategy using bioorthogonal click chemistry. First, ovalbumin (OVA) antigen-specific cytotoxic T-cells (CTLs) were incubated with N-azidoacetyl-D-mannosamine-tetraacylated (Ac₄ManNAz) for incorporating azide (N₃) groups on the surface of CTLs via metabolic glycoengineering. Subsequently, azide groups on the CTLs were chemically labeled with near infrared fluorescence (NIRF) dye, Cy5.5, conjugated dibenzylcyclooctyne (DBCO-Cy5.5) via bioorthogonal click chemistry, resulting in Cy5.5-labeled CTLs (Cy5.5-CTLs). The labeling efficiency of Cy5.5-CTLs could be readily controlled by changing concentrations of Ac₄ManNAz and DBCO-Cy5.5 in cultured cells. Importantly, Cy5.5-CTLs presented the strong NIRF signals in vitro and they showed no significant changes in the functional properties, such as cell viability, proliferation, and antigen-specific cytolytic activity. In ovalbumin (OVA)-expressing E.G-7 tumor-bearing immune-deficient mice, intravenously injected Cy5.5-CTLs were clearly observed at targeted solid tumors via non-invasive NIRF imaging. Moreover, tumor growth inhibition of E.G-7 tumors was closely correlated with the intensity of NIRF signals from Cy5.5-CTLs at tumors after 2-3 days post-injection. The Cy5.5-CTLs showed different therapeutic responses in E.G-7 tumor-bearing immune-competent mice, in which they were divided by their tumor growth efficacy as 'high therapeutic response (TR (+))' and 'low therapeutic response (TR (-))'. These different therapeutic responses of Cy5.5-CTLs were highly correlated with the NIRF signals of Cy5.5-CTLs at targeted tumor tissues in the early stage. Therefore, non-invasive tracking of T-cells can be able to predict and elicit therapeutic responses in the adoptive T-cell therapy.

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

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

Impact of pseudoprogression and treatment beyond progression on outcome in patients with non-small cell lung cancer treated with immune checkpoint inhibitors

Background

Immune checkpoint inhibitors (ICI) have become an important treatment option for non-small cell lung cancer (NSCLC). We aimed to evaluate the clinical impact of pseudoprogression (PsP) and treatment beyond RECIST1.1-defined progressive disease (TBP) on outcome in NSCLC patients treated with ICI.

Methods

NSCLC patients treated with ICI between Mar 2016 and July 2018 were recruited in a consecutive manner. Response was assessed every 8–12 weeks using RECIST1.1 and iRECIST. Based on iRECIST, PsP was defined as progressive disease (PD) on RECIST1.1 subsequently reset to non-PD categories. Using log-rank test, progression-free survival (PFS) was compared between patients with and without PsP, and overall survival (OS) was compared between patients treated with and without TBP. The impact of TBP on OS was evaluated through multivariate Cox proportional hazard models.

Results

Of the 189 patients, seven (3.7%) experienced PsP which mostly occurred approximately 3 months after baseline. The median PFS was significantly longer in patients with PsP (not reached) than those without PsP (3.8 months, P = .02). Among patients who demonstrated PD according to RECIST1.1, median OS was significantly longer in patients with TBP (17.2 months) than those without TBP (7.4 months, P < .001). On multivariate analysis adjusting other covariates, TBP (HR, 0.4; 95% CI, 0.2–0.7) remained as a significant protective factor for mortality.

Conclusion

PsP occurred in 3.7% of NSCLC patients under ICI treatment. Based on iRECIST scheme, PsP and TBP may be associated with survival benefit.

In vivo characterization of PD-L1 expression in breast cancer by immuno-PET with 89Zr-labeled avelumab

Programmed death protein 1 and programmed death-ligand 1 (PD-1/PD-L1) have been widely studied as one of the most critical immune check-point pairs in the cancer microenvironment. In breast cancer (BrCa), the expression of PD-L1 is regarded as a determinant biomarker for patient stratification and prediction of inhibition response. Quantitative positron emission tomography (PET) imaging of PD-L1 expression in tumors using a therapeutic antibody in the clinic seems to be a promising approach that can complement conventional histopathological methods and overcome several issues, such as the tumor heterogeneities, sampling representativeness and clear differentiation of positive and negative results. In this study, we synthesized and evaluated ⁸⁹Zr-labeled avelumab (Ave) for the in vivo characterization of PD-L1 expression in BrCa. Confocal imaging of BrCa cells and flow cytometry were employed to evaluate PD-L1 expression in MDA-MB-231 cells. The intact human monoclonal antibody targeting PD-L1, i.e., Ave, was conjugated to p-SCN-Deferoxamine (Df) and labeled with ⁸⁹Zr. After intravenous injection of ⁸⁹Zr-Df-avelumab (⁸⁹Zr-Df-Ave), PET imaging of MDA-MB-231 tumor-bearing mice, with or without blocking, was performed. High PD-L1 expression of MDA-MB-231 cells was confirmed by in vitro immuno-fluorescent staining and flow cytometry. PET imaging indicated the peak uptake of ⁸⁹Zr-Df-Ave in the tumor (6.4±1.0 %ID/g), spleen (10.2±0.7 %ID/g) and lymph nodes (6.9±1.0 %ID/g) at 48 h after injection (n=4). Blocking study using unlabeled Ave could reduce the tracer uptake in these tissues (5.2±1.0 %ID/g in the tumor, 4.9±0.5 %ID/g in the spleen and 5.8±1.1 %ID/g in lymph nodes at 48 h, n=4), which demonstrated the specificity of ⁸⁹Zr-Df-Ave. Biodistribution study and immuno-fluorescent staining were consistent with the quantitative data from PET imaging. Herein, we offer the evidence supporting the value of immuno-PET imaging using ⁸⁹Zr-Df-Ave for non-invasive characterization of PD-L1 expression in BrCa and the applicability of this tracer in BrCa for treatment evaluation after immunotherapy.

Noninvasive Tracking of Hematopoietic Stem Cells in a Bone Marrow Transplant Model

The hematopoietic stem cell engraftment depends on adequate cell numbers, their homing, and the subsequent short and long-term engraftment of these cells in the niche. We performed a systematic review of the methods employed to track hematopoietic reconstitution using molecular imaging. We searched articles indexed, published prior to January 2020, in PubMed, Cochrane, and Scopus with the following keyword sequences: (Hematopoietic Stem Cell OR Hematopoietic Progenitor Cell) AND (Tracking OR Homing) AND (Transplantation). Of 2191 articles identified, only 21 articles were included in this review, after screening and eligibility assessment. The cell source was in the majority of bone marrow from mice (43%), followed by the umbilical cord from humans (33%). The labeling agent had the follow distribution between the selected studies: 14% nanoparticle, 29% radioisotope, 19% fluorophore, 19% luciferase, and 19% animal transgenic. The type of graft used in the studies was 57% allogeneic, 38% xenogeneic, and 5% autologous, being the HSC receptor: 57% mice, 9% rat, 19% fish, 5% for dog, porcine and salamander. The imaging technique used in the HSC tracking had the following distribution between studies: Positron emission tomography/single-photon emission computed tomography 29%, bioluminescence 33%, fluorescence 19%, magnetic resonance imaging 14%, and near-infrared fluorescence imaging 5%. The efficiency of the graft was evaluated in 61% of the selected studies, and before one month of implantation, the cell renewal was very low (less than 20%), but after three months, the efficiency was more than 50%, mainly in the allogeneic graft. In conclusion, our review showed an increase in using noninvasive imaging techniques in HSC tracking using the bone marrow transplant model. However, successful transplantation depends on the formation of engraftment, and the functionality of cells after the graft, aspects that are poorly explored and that have high relevance for clinical analysis.

Molecular imaging for cancer immunotherapy

Immunotherapy has changed the treatment landscape for many cancers; however, not all patients treated have a favorable response and others can develop immune-related adverse events. A method to predict the treatment response to immunotherapeutic agents could allow for improved selection of patients more likely to benefit from treatment while sparing those who would suffer serious complications. While this has been an active area of research and has resulted in significant insights, current proposed mechanisms do not fully explain responses to therapy. One problem is that our understanding relies mostly on tumor biopsy samples that do not account for the complex spatiotemporal heterogeneity of cancers and their microenvironment. Radiolabeled probes targeting immune biomarkers and imaged using positron emission tomography with computed tomography could provide in vivo, real-time and non-invasive imaging of these biomarkers. Here we review the current field of functional nuclear imaging agents in immuno-oncology including antibodies and small molecule tracers to image PD-1, PD-L1, CTLA-4, T-cell markers and other targets being studied for potential therapies.

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Treatment response of cancers to immunotherapy is difficult to predict.

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Positron emission tomography (PET) imaging may help predict treatment response.

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PET to evaluate immunotherapeutic targets or markers of immune activation shows promise.

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Antibodies and small molecules used for PET have different imaging characteristics.

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More studies are needed to better interpret and validate PET scans for this purpose.

Current and Future Imaging Methods for Evaluating Response to Immunotherapy in Neuro-Oncology

Imaging plays a central role in evaluating responses to therapy in neuro-oncology patients. The advancing clinical use of immunotherapies has demonstrated that treatment-related inflammatory responses mimic tumor growth via conventional imaging, thus spurring the development of new imaging approaches to adequately distinguish between pseudoprogression and progressive disease. To this end, an increasing number of advanced imaging techniques are being evaluated in preclinical and clinical studies. These novel molecular imaging approaches will serve to complement conventional response assessments during immunotherapy. The goal of these techniques is to provide definitive metrics of tumor response at earlier time points to inform treatment decisions, which has the potential to improve patient outcomes. This review summarizes the available immunotherapy regimens, clinical response criteria, current state-of-the-art imaging approaches, and groundbreaking strategies for future implementation to evaluate the anti-tumor and immune responses to immunotherapy in neuro-oncology applications.

Serial T2-Weighted Magnetic Resonance Images Acquired on a 1.5 Tesla Magnetic Resonance Linear Accelerator Reveal Radiomic Feature Variation in Organs at Risk: An Exploratory Analysis of Novel Metrics of Tissue Response in Prostate Cancer

"Delta-radiomics" investigates variations in quantitative image metrics over time and can yield important clinical information. We hypothesized that in patients undergoing active radiation therapy (RT) for prostate cancer (PCa), there would exist observable variation in the quantitative metrics that describe the T₂-weighted (T_2W) intensity histogram in the prostate and surrounding organs at risk (OAR) over time. We investigated the feasibility of acquisition and subsequent analysis of the delta-radiomic profiles of these regions of interest (ROI) in serial T_2W magnetic resonance (MR) images obtained on a 1.5 Tesla (T) Magnetic Resonance Linear Accelerator (MRL). Principally, we sought to illustrate the significance of longitudinal radiomic data acquisition for tissue response monitoring and provide a framework for future hypothesis driven research.

Patients with PCa undergoing treatment with RT were compiled from an ongoing prospective observational imaging trial using a 1.5 T MRL (NCT30500081). Contiguous axial slices of prostate parenchyma were contoured and temporally normalized to sections of Sartorius muscle which served as a control. Similarly, contiguous sections of rectal and bladder wall adjacent to the prostate were contoured and temporally normalized to regions of these organs further removed from the planning target volume (PTV). First order statistical descriptors of the T_2W intensity histogram were extracted and evaluated for changes over time using linear mixed effects regression modeling and post-hoc contrasts. Benjamini-Hochberg corrections were employed to reduce the effects of multiple testing and control for the false discovery rate (FDR).

Four patients with a median age of 69 comprised this exploratory cohort. One patient had low-risk disease, two had intermediate (one favorable, one unfavorable), and one had high risk disease. Three out of four patients underwent definitive radiation to 75.6 Gray (Gy) in 42 fractions and one received hypofractionated therapy to a total dose of 70 Gy over 28 fractions, and all received treatment on a conventional linear accelerator. The most significant acute toxicity event was grade 2 GU dysfunction observed in two patients. Follow up ranged from 1 month to 10 months post treatment, and no long-term complications were reported in patients who completed treatment at least one month prior. Bladder wall adjacent to the prostate demonstrated significant variation in the mean and median metric values after the first week of treatment. In addition, rectal wall adjacent to the prostate exhibited significant variation in the mean, median, and standard deviation metric values by the second week of treatment. No significant variation in any radiomic feature was observed in the Sartorius control.

This exploratory study is one of the earliest examining the delta-radiomic characteristics of the T_2W intensity histogram in OAR extracted from images acquired on a 1.5 T MRL in patients actively being treated with RT for PCa. We demonstrated a feasible approach to longitudinal radiomic data acquisition providing limitless opportunity for future research. Analysis of the delta-radiomic profiles in OAR revealed significant variation in metrics after only one week of RT in bladder and rectal wall adjacent to the prostate. These findings must be further investigated and validated with expanded data sets with long-term follow up and correlation to clinical outcomes including toxicity and tumor control.

A Case Report of the Clinico-radiologic Challenges of Assessing Treatment Response after Stereotactic Radiation of Oligometastases Preceded by Immunotherapy: Pseudoprogression, Mixed Response Patterns, and Opportunities for Precision Radiation

As immunotherapy continues to translate to the clinic and is combined with existing modalities, such as radiation therapy, novel treatment response patterns have been observed which complicate conventional clinical assessment and management. Herein, we describe a case study of a patient with non-small cell lung cancer treated initially with definitive chemoradiation who subsequently developed oligorecurrent disease which was managed with nivolumab and then comprehensive salvage stereotactic radiation. Serial radiographic assessment had shown worsening at these limited sites of disease after initiating immunotherapy, improvement after radiation, and then heterogeneous response behavior across sites during longer-term follow-up. Given the dual effects ablative radiation may have in the context of global immune checkpoint inhibition, both cytotoxic and synergistic immune-related, assessment of treatment response to such treatment is complicated. Such assessment is further complicated by novel immunotherapy response phenomena, e.g. pseudoprogression, which are being uncovered and are not fully characterized. Current clinical and radiologic assessment strategies are inadequate to interrogate and discern between immunomodulation-influenced response behavior and further diagnostic innovation is warranted to meet the needs of evolving clinical practice in the era of immunotherapy.