Bispecific antibody pretargeting of tumor neovasculature for improved systemic radiotherapy of solid tumors

Cell-based Relay Delivery Strategy in Biomedical Applications

The relay delivery strategy is a two-step targeting approach based on two distinct modules in which the first step with an initiator is to artificially create a target/environment which can be targeted by the follow-up effector. This relay delivery concept creates opportunities to amplify existing or create new targeted signals through deploying initiators to enhance the accumulation efficiency of the following effector at the disease site. As the "live" medicines, cell-based therapeutics possess inherent tissue/cell homing abilities and favorable feasibility of biological and chemical modifications, endowing them the great potential in specifically interacting with diverse biological environments. All these unique capabilities make cellular products great candidates that can serve as either initiators or effectors for relay delivery strategies. In this review, we survey recent advances in relay delivery strategies with a specific focus on the roles of various cells in developing relay delivery systems.

Radioimmunotherapy of glioblastoma multiforme - Current status and future prospects

Glioblastoma multiforme (GBM) or grade IV astrocytoma is the most diagnosed form of primary brain tumours in adults. Radioimmunotherapy (RIT), mostly in combination with conventional therapies, is presented in the current review as a therapeutic strategy of high potential in the management of GBM. A systematic literature search was performed following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) to identify clinical studies that employed a form of radioimmunotherapy using alpha- or beta-emitting radioisotopes. The available literature on RIT in GBM and high-grade gliomas is presented and discussed. The results suggest that this promising treatment approach merits further investigation in future clinical studies.

Targeting Fibronectin for Cancer Imaging and Therapy

During cancer progression, the extracellular matrix (ECM) undergoes dramatic changes, which promote cancer cell migration and invasion. In the remodeled tumor ECM, fibronectin (FN) level is upregulated to assist tumor growth, progression, and invasion. FN serves as a central organizer of ECM molecules and mediates the crosstalk between the tumor microenvironment and cancer cells. Its upregulation is correlated with angiogenesis, cancer progression, metastasis, and drug resistance. A number of FN-targeting ligands have been developed for cancer imaging and therapy. Thus far, FN-targeting imaging agents have been tested for nuclear imaging, MRI, and fluorescence imaging, for tumor detection and localization. FN-targeting therapeutics, including nuclear medicine, chemotherapy drugs, cytokines, and photothermal moieties, were also developed in cancer therapy. Because of the prevalence of FN overexpression in cancer, FN targeting imaging agents and therapeutics have the promise of broad applications in the diagnosis, treatment, and image-guided interventions of many types of cancers. This review will summarize current understanding on the role of FN in cancer, discuss the design and development of FN-targeting agents, and highlight the applications of these FN-targeting agents in cancer imaging and therapy.

Fibronectin-targeted drug delivery in cancer

Fibronectin is an extracellular matrix protein with pivotal physiological and pathological functions in development and adulthood. Alternative splicing of the precursor mRNA, produced from the single copy fibronectin gene, occurs at three sites coding for the EDA, EDB and IIICS domains. Fibronectin isoforms comprising the EDA or EDB domains are known as oncofetal forms due to their developmental importance and their re-expression in tumors, contrasting with restricted presence in normal adult tissues. These isoforms are also recognized as important markers of angiogenesis, a crucial physiological process in development and required by tumor cells in cancer progression. Attributed to this feature, EDA and EDB domains have been extensively used for the targeted delivery of cytokines, cytotoxic agents, chemotherapy drugs and radioisotopes to fibronectin-expressing tumors to exert therapeutic effects on primary cancers and metastatic lesions. In addition to drug delivery, the EDA and EDB domains of fibronectin have also been utilized to develop imaging strategies for tumor tissues. Furthermore, EDA and EDB based vaccines seem to be promising for the treatment and prevention of certain cancer types. In this review, we will summarize recent advances in fibronectin EDA and EDB-based therapeutic strategies developed to treat cancer.

Discovery of hapten-specific scFv from a phage display library and applications for HER2-positive tumor imaging

In this study, an anti-hapten antibody (single chain Fv, scFv) against a hapten probe was developed as a unique reporter system for molecular imaging or therapy. The hapten peptide (histamine-succinyl-GSYK, Him) was synthesized for phage displayed scFv affinity selection and for conjugation with cypate (Cy-Him) for in vivo near-infrared (NIR) optical imaging. Hapten-specific scFvs were affinity selected from the human single fold phage display scFv libraries (Tomlinson I + J) with high specificity and affinity. Utilizing HER2 targeting as a model system, the highest affinity scFv (clone J42) was recombinantly fused to an anti-HER2 affibody (scFv-L-Aff) with no loss of affinity of either protein. The functionality of the hapten-scFv reporter system was tested in vitro with a HER2-positive human breast cancer cell line, SK-BR3, and in vivo with SK-BR3 xenografts. ScFv-L-Aff mediated the binding of the hapten to HER2 on SK-BR3 cells and from tissue from the SK-BR3 xenograft; however, scFv-L-Aff did not mediate uptake of the hapten in the SK-BR3 xenografted tumors, presumably due to rapid internalization of the HER2/scFv-L-Aff complex. Our results suggest that this hapten-peptide and anti-hapten scFv can be a universal reporter system in a wide range of imaging and therapeutic applications.

Radiolabeling strategies for tumor-targeting proteinaceous drugs

Owing to their large size proteinaceous drugs offer higher operative information content compared to the small molecules that correspond to the traditional understanding of druglikeness. As a consequence these drugs allow developing patient-specific therapies that provide the means to go beyond the possibilities of current drug therapy. However, the efficacy of these strategies, in particular "personalized medicine", depends on precise information about individual target expression rates. Molecular imaging combines non-invasive imaging methods with tools of molecular and cellular biology and thus bridges current knowledge to the clinical use. Moreover, nuclear medicine techniques provide therapeutic applications with tracers that behave like the diagnostic tracer. The advantages of radioiodination, still the most versatile radiolabeling strategy, and other labeled compounds comprising covalently attached radioisotopes are compared to the use of chelator-protein conjugates that are complexed with metallic radioisotopes. With the techniques using radioactive isotopes as a reporting unit or even the therapeutic principle, care has to be taken to avoid cleavage of the radionuclide from the protein it is linked to. The tracers used in molecular imaging require labeling techniques that provide site specific conjugation and metabolic stability. Appropriate choice of the radionuclide allows tailoring the properties of the labeled protein to the application required. Until the event of positron emission tomography the spectrum of nuclides used to visualize cellular and biochemical processes was largely restricted to iodine isotopes and 99m-technetium. Today, several nuclides such as 18-fluorine, 68-gallium and 86-yttrium have fundamentally extended the possibilities of tracer design and in turn caused the need for the development of chemical methods for their conjugation.

Radioimmunotherapy for high-grade glioma

Patients with high-grade glioma (HGG) still have a very poor prognosis. The infiltrative nature of the tumor and the inter- and intra-tumoral cellular and genetic heterogeneity, leading to the acquisition of new mutations over time, represent the main causes of treatment failure. Radioimmunotherapy represents an emerging approach for the treatment of HGG. Radioimmunotherapy utilizes a molecular vehicle (monoclonal antibodies) to deliver a radionuclide (the drug) to a selected cell population target. This review will provide an overview of preclinical and clinical studies to date and assess the effectiveness of radioimmunotherapy, focusing on possible future therapies for the treatment of HGG.

Diels-Alder reaction for tumor pretargeting: in vivo chemistry can boost tumor radiation dose compared with directly labeled antibody

Current pretargeting systems use noncovalent biologic interactions, which are prone to immunogenicity. We previously developed a novel approach based on the bioorthogonal reaction between a radiolabeled tetrazine and an antibody-conjugated trans-cyclooctene (TCO). However, the tumor-to-blood ratio was low due to reaction with freely circulating antibody-TCO.

METHODS

Here we developed 2 tetrazine-functionalized clearing agents that enable rapid reaction with and removal of a TCO-tagged antibody (CC49) from blood. Next, we incorporated this approach into an optimized pretargeting protocol in LS174T-bearing mice. Then we compared the pretargeted (177)Lu-labeled tetrazine with (177)Lu-labeled CC49. The biodistribution data were used for mouse and human dosimetry calculations.

RESULTS

The use of a clearing agent led to a doubling of the tetrazine tumor uptake and a 125-fold improvement of the tumor-to-blood ratio at 3 h after tetrazine injection. Mouse dosimetry suggested that this should allow for an 8-fold higher tumor dose than is possible with nonpretargeted radioimmunotherapy. Also, humans treated with CC49-TCO-pretargeted (177)Lu-tetrazine would receive a dose to nontarget tissues 1 to 2 orders of magnitude lower than with directly labeled CC49.

CONCLUSION

The in vivo performance of chemical pretargeting falls within the range of results obtained for the clinically validated pretargeting approaches in mice, with the advantage of potentially allowing for fractionated radiotherapy as a result of a lower likelihood of immunogenicity. These findings demonstrate that biologic pretargeting concepts can be translated to rapid bioorthogonal chemical approaches with retained potential.

Aqueous synthesis of color-tunable CuInS2/ZnS nanocrystals for the detection of human interleukin 6

In this Article, we present a facile microwave-assisted synthesis route for the preparation of water-soluble and high-quality CuInS2/ZnS nanocrystals (NCs) with glutathione as the stabilizer. The as-prepared CuInS2/ZnS NCs exhibited small particle sizes (~3.3 nm), long photoluminescence lifetimes, and color-tunable properties ranging from the visible to the near-infrared by varying the initial ratio of Cu/In in the precursors. The low-toxicity, highly luminescent and biocompatible CuInS2/ZnS NCs were applied to cell imaging, showing that they could be used as promising fluorescent probes. Furthermore, the CuInS2/ZnS NCs were used as the signal labels for a fluoroimmunoassay of the biomarker IL-6, showing their great potential for use as reliable point-of-care diagnostics for biomarkers of cancer and other diseases.

Antitumor effects of 32P-chromic-poly (L-lactide) brachytherapy in nude mice with human prostate cancer

The aim of the present study was to investigate the antitumor effects and tissue distribution of ³²P-chromic-poly (L-lactide) (³²P-CP-PLLA) in nude mice with human prostate cancer. Tumor models were obtained by transplantation of PC-3M tumor cells into male BALB/c nude mice. Animals were randomly divided into control, ³²P-chromic phosphate (³²P-CP) colloid and ³²P-CP-PLLA groups (all n=20). A series of indices were investigated, including apoptosis of tumor cells, rate of apoptosis, expression of caspase 3 and 8, biodistribution and intratumoral concentration of ³²P-CP-PLLA, intensity of radioactivity, tumor volume and microvessel density (MVD). Highly concentrated radioactivity of ³²P-CP-PLLA in the tumor mass was detected by single photon emission computed tomography (SPECT) scanning. The residual activities of the ³²P-CP-PLLA and ³²P-CP colloid groups were 3.02±0.32 and 1.76±0.31 MBq, respectively, on day 14 following treatment. The tumor inhibition rates were 67.24±3.55 and 55.92±7.65%, respectively (P<0.01). Necrotic changes, in conjunction with apoptosis, were observed in the treatment group. MVD values for the ³²P-CP-PLLA and ³²P-CP colloid groups were 28.24±10.07 and 36.15±11.06, respectively. ³²P-CP-PLLA showed an excellent capacity for killing tumor cells, inducing apoptosis and inhibiting angiogenesis.

³²P-chromic phosphate-Poly(L-Lactide) seeds of sustained release and their brachytherapy for prostate cancer with lymphatic metastasis

This study aims to develop a new agent, the ³²P-chromic phosphate-poly(l-lactide) (³²P-CP-PLLA) seed and to explore its anticancer effect against prostate cancer (Pca) with local lymphatic metastasis in nude mice. ³²P-CP-PLLA seeds of sustained release and nude mouse models of Pca with lymphatic metastasis were prepared. After 4 weeks, the tumor nude mouse models were randomly assigned into five groups. ³²P-CP-PLLA seeds (3.7, 7.4, 14.8, and 0 MBq) and ³²P-CP (14.8 MBq) were implanted in the tumor tissues of the nude mouse models. The following were discussed in this study: (1) the distributions of ³²P-CP-PLLA, (2) the pathological and morphological changes in the tumor and regional lymph nodes, and (3) the changes in white blood cell (WBC) and platelet counts in peripheral blood for toxic reactions. The homemade ³²P-CP-PLLA seed was a regular green cylinder, with an even distribution of mass and radioactivity. After implantation, single-photon emission computed tomograph (SPECT) showed that ³²P was mainly gathered in the tumor and regional lymph nodes. Morphological examinations revealed that necrosis and hemorrhage were around the tumor and focal lymph nodes. The tumor inhibition rates of the five groups were 70.16% ± 5.48%, 80.18% ± 5.84%, 84.97% ± 4.79%, (-), and 78.81% ± 3.13%, respectively. These values were all positive when compared with the control group. As a new homemade agent of pure β-ray, local implantation of the agent increased the focal retention of radioactivity at the target. Moreover, effective half-life showed an obvious damage to the tumor and metastatic foci of Pca.

Radioimmunotherapy of solid tumors: searching for the right target

Radioimmunotherapy of solid tumors remains a challenge despite the tremendous success of ⁹⁰Y ibritumomab tiuxetan (Zevalin) and ¹³¹I Tositumomab (Bexxar) in treating non-Hodgkin's lymphoma. For a variety of reasons, clinical trials of radiolabeled antibodies against solid tumors have not led to responses equivalent to those seen against lymphoma. In contrast, promising responses have been observed with unlabeled antibodies that target solid tumor receptors associated with cellular signaling pathways. These observations suggest that anti-tumor efficacy of the carrier antibody might be critical to achieving clinical responses. Here, we review and compare tumor antigens targeted by radiolabeled antibodies and unlabeled antibodies used in immunotherapy. The review shows that the trend for radiolabeled antibodies under pre-clinical development is to also target antigens associated with signaling pathways that are essential for the growth and survival of the tumor.

Pretargeted radioimmunotherapy for hematologic and other malignancies

Radioimmunotherapy (RIT) has emerged as one of the most promising treatment options, particularly for hematologic malignancies. However, this approach has generally been limited by a suboptimal therapeutic index (target-to-nontarget ratio) and an inability to deliver sufficient radiation doses to tumors selectively. Pretargeted RIT (PRIT) circumvents these limitations by separating the targeting vehicle from the subsequently administered therapeutic radioisotope, which binds to the tumor-localized antibody or is quickly excreted if unbound. A growing number of preclinical proof-of-principle studies demonstrate that PRIT is feasible and safe and provides improved directed radionuclide delivery to malignant cells compared with conventional RIT while sparing normal cells from nonspecific radiotoxicity. Early phase clinical studies corroborate these preclinical findings and suggest better efficacy and lesser toxicities in patients with hematologic and other malignancies. With continued research, PRIT-based treatment strategies promise to become cornerstones to improved outcomes for cancer patients despite their complexities.

Immunotherapeutic approaches for glioma

The development of effective immunotherapy strategies for glioma requires adequate understanding of the unique immunological microenvironment in the central nervous system (CNS) and CNS tumors. Although the CNS is often considered to be an immunologically privileged site and poses unique challenges for the delivery of effector cells and molecules, recent advances in technology and discoveries in CNS immunology suggest novel mechanisms that may significantly improve the efficacy of immunotherapy against gliomas. In this review, we first summarize recent advances in the CNS and CNS tumor immunology. We address factors that may promote immune escape of gliomas. We also review advances in passive and active immunotherapy strategies for glioma, with an emphasis on lessons learned from recent early-phase clinical trials. We also discuss novel immunotherapy strategies that have been recently tested in non-CNS tumors and show great potential for application to gliomas. Finally, we discuss how each of these promising strategies can be combined to achieve clinical benefit for patients with gliomas.