Ultrasound targeted apoptosis imaging in monitoring early tumor response of trastuzumab in a murine tumor xenograft model of her-2-positive breast cancer(1.)

Dynamic surveillance of tamoxifen-resistance in ER-positive breast cancer by CAIX-targeted ultrasound imaging

Tamoxifen‐based hormone therapy is central for the treatment of estrogen receptor positive (ER⁺) breast cancer. However, the acquired tamoxifen resistance, typically co‐exists with hypoxia, remains a major challenge. We aimed to develop a non‐invasive, targeted ultrasound imaging approach to dynamically monitory of tamoxifen resistance. After we assessed acquired tamoxifen resistance in 235 breast cancer patients and a list of breast cancer cell lines, we developed poly(lactic‐co‐glycolic acid)‐poly(ethylene glycol)‐carbonic anhydrase IX mono antibody nanobubbles (PLGA‐PEG‐mAb_CAIX NBs) to detect hypoxic breast cancer cells upon exposure of tamoxifen in nude mice. We demonstrate that carbonic anhydrase IX (CAIX) expression is associated with breast cancer local recurrence and tamoxifen resistance both in clinical and cellular models. We find that CAIX overexpression increases tamoxifen tolerance in MCF‐7 cells and predicts early tamoxifen resistance along with an oscillating pattern in intracellular ATP level in vitro. PLGA‐PEG‐mAb_CAIX NBs are able to dynamically detect tamoxifen‐induced hypoxia and tamoxifen resistance in vivo. CAIX‐conjugated NBs with noninvasive ultrasound imaging is powerful for dynamically monitoring hypoxic microenvironment in ER⁺ breast cancer with tamoxifen resistance.

Annexin V conjugated nanobubbles: A novel ultrasound contrast agent for in vivo assessment of the apoptotic response in cancer therapy

In vivo assessment of apoptotic response to cancer therapy is believed to be very important for optimizing management of treatment. However, few noninvasive strategies are currently available to monitor the therapeutic response in vivo. Ultrasonography has been used to detect apoptotic cell death in vivo, but a high-frequency transducer is needed. Fortunately, the capability of ultrasound contrast agents (UCAs) to exit the leaky vasculature of tumors enables ultrasound-targeted imaging of molecular events in response to cancer therapy. In this study, we prepared a novel nano-sized UCA, namely, Annexin V-conjugated nanobubbles (AV-NBs, 635.5 ± 25.4 nm). In vitro studies revealed that AV-NBs were relatively stable and highly echogenic. Moreover, these AV-NBs could easily extravasate into the tumor vasculature and recognize the apoptotic cells with high specificity and affinity in tumors sensitive to chemotherapy. Ultrasound imaging results demonstrated that AV-NBs had higher echogenicity and significantly greater enhancement compared with the untargeted control NBs (P < 0.01) inside the tumors after chemotherapy. Taken together, this study provides a promising method to accurately evaluate therapeutic effects at the molecular level to support cancer management.

Synthesis and evaluation of a radiolabeled bis-zinc(II)-cyclen complex as a potential probe for in vivo imaging of cell death

The exposition of phosphatidylserine (PS) from the cell membrane is associated with most cell death programs (apoptosis, necrosis, autophagy, mitotic catastrophe, etc.), which makes PS an attractive target for overall cell death imaging. To this end, zinc(II) macrocycle coordination complexes with cyclic polyamine units as low-molecular-weight annexin mimics have a selective affinity for biomembrane surfaces enriched with PS, and are therefore useful for detection of cell death. In the present study, a ¹¹C-labeled zinc(II)-bis(cyclen) complex (¹¹C-CyclenZn2) was prepared and evaluated as a new positron emission tomography (PET) probe for cell death imaging. ¹¹C-CyclenZn2 was synthesized by methylation of its precursor, 4-methoxy-2,5-di-[10-methyl-1,4,7,10-tetraazacyclododecane-1,4,7-tricarboxylic acid tri-tert-butyl ester] phenol (Boc-Cyclen2) with ¹¹C-methyl triflate as a prosthetic group in acetone, deprotection by hydrolysis in aqueous HCl solution, and chelation with zinc nitrate. The cell death imaging capability of ¹¹C-CyclenZn2 was evaluated using in vitro cell uptake assays with camptothecin-treated PC-3 cells, biodistribution studies, and in vivo PET imaging in Kunming mice bearing S-180 fibrosarcoma. Starting from ¹¹C-methyl triflate, the total preparation time for ¹¹C-CyclenZn2 was ~40 min, with an uncorrected radiochemical yield of 12 ± 3% (based on ¹¹C-CH₃OTf, n = 10), a radiochemical purity of greater than 95%, and the specific activity of 0.75-1.01 GBq/μmol. The cell death binding specificity of ¹¹C-CyclenZn2 was demonstrated by significantly different uptake rates in camptothecin-treated and control PC-3 cells in vitro. Inhibition experiments for ¹⁸F-radiofluorinated Annexin V binding to apoptotic/necrotic cells illustrated the necessity of zinc ions for zinc(II)-bis(cyclen) complexation in binding cell death, and zinc(II)-bis(cyclen) complexe and Annexin V had not identical binding pattern with apoptosis/necrosis cells. Biodistribution studies of ¹¹C-CyclenZn2 revealed a fast clearance from blood, low uptake rates in brain and muscle tissue, and high uptake rates in liver and kidney, which provide the main metabolic route. PET imaging using ¹¹C-CyclenZn2 revealed that cyclophosphamide-treated mice (CP-treated group) exhibited a significant increase of uptake rate in the tumor at 60 min postinjection, compared with control mice (Control group). The results indicate that the ability of ¹¹C-CyclenZn2 to detect cell death is comparable to Annexin V, and it has potential as a PET tracer for noninvasive evaluation and monitoring of anti-tumor chemotherapy.

Prediction of survival prognosis of non-small cell lung cancer by APE1 through regulation of Epithelial-Mesenchymal Transition

The DNA base excision repair gene APE1 involves in DNA damage repair pathway and overexpression in a variety of human cancers. Analyses of patients with non-small cell lung cancer (NSCLC) suggested that multiple factors associated with prognosis of NSCLC patients. Further investigation showed that APE1 expression was able to predict the progression-free survival and overall survival in patients with NSCLC and correlated with lymph node metastasis. Intriguingly, as a stratification of APE1-141 SNPs in APE1 positive expression, we also found APE1-141 GT/GG was identified as a marker for prediction of poor survival in NSCLC patients. In the in vitro experiments, the results showed that when APE1 expression was inhibited by siRNA or AT101 (an APE1 inhibitor), the migration and invasion of NSCLC cells were suppressed. Furthermore, epithelial-mesenchymal transition (EMT) markers was tested to provide evidence that APE1 promoted NSCLC EMT through interaction with SirT1. Using NSCLC xenograft models, we confirmed that AT101 shrank tumor volumes and inhibited lymph node metastasis. In conclusion, APE1 could be a potential target for patients with NSCLC metastasis and AT101 is a potent inhibitor in further treatment of NSCLC patients.

Recent advances in ultrasound-based diagnosis and therapy with micro- and nanometer-sized formulations

Ultrasound (US) is one of the most frequently used imaging methods in the clinic. The broad spectrum of its applications can be increased by the use of gas-filled microbubbles (MB) as ultrasound contrast agents (UCA). In recent years, also nanoscale UCA like nanobubbles (NB), echogenic liposomes (ELIP) and nanodroplets have been developed, which in contrast to MB, are able to extravasate from the vessels into the tissue. New disease-specific UCA have been designed for the assessment of tissue biomarkers and advanced US to a molecular imaging modality. For this purpose, specific binding moieties were coupled to the UCA surface. The vascular endothelial growth factor receptor-2 (VEGFR-2) and P-/E-selectin are prominent examples of molecular US targets to visualize tumor blood vessels and inflammatory diseases, respectively. Besides their application in contrast-enhanced imaging, MB can also be employed for drug delivery to tumors and across the blood-brain barrier (BBB). This review summarizes the development of micro- and nanoscaled UCA and highlights recent advances in diagnostic and therapeutic applications, which are ready for translation into the clinic.

Bench to bedside molecular functional imaging in translational cancer medicine: to image or to imagine?

Ongoing research on malignant and normal cell biology has substantially enhanced the understanding of the biology of cancer and carcinogenesis. This has led to the development of methods to image the evolution of cancer, target specific biological molecules, and study the anti-tumour effects of novel therapeutic agents. At the same time, there has been a paradigm shift in the field of oncological imaging from purely structural or functional imaging to combined multimodal structure-function approaches that enable the assessment of malignancy from all aspects (including molecular and functional level) in a single examination. The evolving molecular functional imaging using specific molecular targets (especially with combined positron-emission tomography [PET] computed tomography [CT] using 2- [(18)F]-fluoro-2-deoxy-D-glucose [FDG] and other novel PET tracers) has great potential in translational research, giving specific quantitative information with regard to tumour activity, and has been of pivotal importance in diagnoses and therapy tailoring. Furthermore, molecular functional imaging has taken a key place in the present era of translational cancer research, producing an important tool to study and evolve newer receptor-targeted therapies, gene therapies, and in cancer stem cell research, which could form the basis to translate these agents into clinical practice, popularly termed "theranostics". Targeted molecular imaging needs to be developed in close association with biotechnology, information technology, and basic translational scientists for its best utility. This article reviews the current role of molecular functional imaging as one of the main pillars of translational research.

Targeted ultrasound contrast agents for ultrasound molecular imaging and therapy

Ultrasound contrast agents (UCAs) are used routinely in the clinic to enhance contrast in ultrasonography. More recently, UCAs have been functionalised by conjugating ligands to their surface to target specific biomarkers of a disease or a disease process. These targeted UCAs (tUCAs) are used for a wide range of pre-clinical applications including diagnosis, monitoring of drug treatment, and therapy. In this review, recent achievements with tUCAs in the field of molecular imaging, evaluation of therapy, drug delivery, and therapeutic applications are discussed. We present the different coating materials and aspects that have to be considered when manufacturing tUCAs. Next to tUCA design and the choice of ligands for specific biomarkers, additional techniques are discussed that are applied to improve binding of the tUCAs to their target and to quantify the strength of this bond. As imaging techniques rely on the specific behaviour of tUCAs in an ultrasound field, it is crucial to understand the characteristics of both free and adhered tUCAs. To image and quantify the adhered tUCAs, the state-of-the-art techniques used for ultrasound molecular imaging and quantification are presented. This review concludes with the potential of tUCAs for drug delivery and therapeutic applications.

Biomarkers in preclinical cancer imaging

In view of the trend towards personalized treatment strategies for (cancer) patients, there is an increasing need to noninvasively determine individual patient characteristics. Such information enables physicians to administer to patients accurate therapy with appropriate timing. For the noninvasive visualization of disease-related features, imaging biomarkers are expected to play a crucial role. Next to the chemical development of imaging probes, this requires preclinical studies in animal tumour models. These studies provide proof-of-concept of imaging biomarkers and help determine the pharmacokinetics and target specificity of relevant imaging probes, features that provide the fundamentals for translation to the clinic. In this review we describe biological processes derived from the “hallmarks of cancer” that may serve as imaging biomarkers for diagnostic, prognostic and treatment response monitoring that are currently being studied in the preclinical setting. A number of these biomarkers are also being used for the initial preclinical assessment of new intervention strategies. Uniquely, noninvasive imaging approaches allow longitudinal assessment of changes in biological processes, providing information on the safety, pharmacokinetic profiles and target specificity of new drugs, and on the antitumour effectiveness of therapeutic interventions. Preclinical biomarker imaging can help guide translation to optimize clinical biomarker imaging and personalize (combination) therapies.