Radioimmunotherapy of Human Colon Cancer Xenografts with 131I-Labeled Anti-CEA Monoclonal Antibody

PET imaging of Aspergillus infection using Zirconium-89 labeled anti-β-glucan antibody fragments

PURPOSE

Invasive fungal diseases, such as pulmonary aspergillosis, are common life-threatening infections in immunocompromised patients and effective treatment is often hampered by delays in timely and specific diagnosis. Fungal-specific molecular imaging ligands can provide non-invasive readouts of deep-seated fungal pathologies. In this study, the utility of antibodies and antibody fragments (Fab) targeting β-glucans in the fungal cell wall to detect Aspergillus infections was evaluated both in vitro and in preclinical mouse models.

METHODS

The binding characteristics of two commercially available β-glucan antibody clones and their respective antigen-binding Fabs were tested using biolayer interferometry (BLI) assays and immunofluorescence staining. In vivo binding of the Zirconium-89 labeled antibodies/Fabs to fungal pathogens was then evaluated using PET/CT imaging in mouse models of fungal infection, bacterial infection and sterile inflammation.

RESULTS

One of the evaluated antibodies (HA-βG-Ab) and its Fab (HA-βG-Fab) bound to β-glucans with high affinity (KD = 0.056 & 21.5 nM respectively). Binding to the fungal cell wall was validated by immunofluorescence staining and in vitro binding assays. ImmunoPET imaging with intact antibodies however showed slow clearance and high background signal as well as nonspecific accumulation in sites of infection/inflammation. Conversely, specific binding of [89Zr]Zr-DFO-HA-βG-Fab to sites of fungal infection was observed when compared to the isotype control Fab and was significantly higher in fungal infection than in bacterial infection or sterile inflammation.

CONCLUSIONS

[89Zr]Zr-DFO-HA-βG-Fab can be used to detect fungal infections in vivo. Targeting distinct components of the fungal cell wall is a viable approach to developing fungal-specific PET tracers.

In Vitro Characterization of 177Lu-DOTA-M5A Anti-Carcinoembryonic Antigen Humanized Antibody and HSP90 Inhibition for Potentiated Radioimmunotherapy of Colorectal Cancer

Carcinoembryonic antigen (CEA) is an antigen that is highly expressed in colorectal cancers and widely used as a tumor marker. ¹³¹I and ⁹⁰Y-radiolabeled anti-CEA monoclonal antibodies (mAbs) have previously been assessed for radioimmunotherapy in early clinical trials with promising results. Moreover, the heat shock protein 90 inhibitor onalespib has previously demonstrated radiotherapy potentiation effects in vivo. In the present study, a ¹⁷⁷Lu-radiolabeled anti-CEA hT84.66-M5A mAb (M5A) conjugate was developed and the potential therapeutic effects of ¹⁷⁷Lu-DOTA-M5A and/or onalespib were investigated. The ¹⁷⁷Lu radiolabeling of M5A was first optimized and characterized. Binding specificity and affinity of the conjugate were then evaluated in a panel of gastrointestinal cancer cell lines. The effects on spheroid growth and cell viability, as well as molecular effects from treatments, were then assessed in several three-dimensional (3D) multicellular colorectal cancer spheroid models. Stable and reproducible radiolabeling was obtained, with labeling yields above 92%, and stability was retained at least 48 h post-radiolabeling. Antigen-specific binding of the radiolabeled conjugate was demonstrated on all CEA-positive cell lines. Dose-dependent therapeutic effects of both ¹⁷⁷Lu-DOTA-M5A and onalespib were demonstrated in the spheroid models. Moreover, effects were potentiated in several dose combinations, where spheroid sizes and viabilities were significantly decreased compared to the corresponding monotherapies. For example, the combination treatment with 350 nM onalespib and 20 kBq ¹⁷⁷Lu-DOTA-M5A resulted in 2.5 and 2.3 times smaller spheroids at the experimental endpoint than the corresponding monotreatments in the SNU1544 spheroid model. Synergistic effects were demonstrated in several of the more effective combinations. Molecular assessments validated the therapy results and displayed increased apoptosis in several combination treatments. In conclusion, the combination therapy of anti-CEA ¹⁷⁷Lu-DOTA-M5A and onalespib showed enhanced therapeutic effects over the individual monotherapies for the potential treatment of colorectal cancer. Further in vitro and in vivo studies are warranted to confirm the current study findings.

SPECT Imaging of Hepatocellular Carcinoma Detection by the GPC3 Receptor

The glypican-3 (GPC3) receptor is a membrane protein that is highly expressed in tumor tissues but rarely expressed in the normal liver and can be used as a target for early diagnosis of hepatocellular carcinoma (HCC). Herein, we developed a GPC3-targeted ^99mTc-labeled probe for SPECT imaging in HCC. ^99mTc-HPG was rapidly radiosynthesized within 20 min with an excellent radiochemical purity (>98%), possessing good stability. Results from in vitro cell binding assays indicated that the binding specificity of ^99mTc-HPG to GPC3-positive HepG2 cells was acceptable. For SPECT/CT imaging, the HepG2 tumors were clearly visualized with the highest tumor/muscle ratio (11.55 ± 0.54) at 1 h post-injection, and the tumor uptake of ^99mTc-HPG reduced from 2.99 ± 0.15 to 1.17 ± 0.09% ID/g in the blocking study. Convenient preparation, excellent GPC3 specificity in HCC, rapid clearance from normal organs, and good biosafety profiles of ^99mTc-HPG warrant further investigations for clinical translation.

Small-animal SPECT/CT imaging of cancer xenografts and pulmonary fibrosis using a 99mTc-labeled integrin αvβ6-targeting cyclic peptide with improved in vivo stability

Abstract

Integrin αvβ6 is expressed at an undetectable level in normal tissues, but is remarkably upregulated during many pathological processes, especially in cancer and fibrosis. Noninvasive imaging of integrin αvβ6 expression using a radiotracer with favorable in vivo pharmacokinetics would facilitate disease diagnosis and therapy monitoring. Through disulfide-cyclized method, we synthesized in this study, a new integrin αvβ6-targeted cyclic peptide (denoted as cHK), and radiolabeled it with ^99mTc. The ability of the resulting radiotracer ^99mTc–HYNIC–cHK to detect integrin αvβ6 expression in pancreatic cancer xenografts and idiopathic pulmonary fibrosis was evaluated using small-animal single-photon emission computed tomography (SPECT)/computed tomography (CT). ^99mTc–HYNIC–cHK showed significantly improved in vivo metabolic stability compared to the linear peptide-based radiotracer ^99mTc–HYNIC–HK. ^99mTc–HYNIC–cHK exhibited similar biodistribution properties to ^99mTc–HYNIC–HK, but the tumor-to-muscle ratio was significantly increased (2.99 ± 0.87 vs. 1.82 ± 0.27, P < 0.05). High-contrast images of integrin αvβ6-positive tumors and bleomycin-induced fibrotic lungs were obtained by SPECT/CT imaging using ^99mTc–HYNIC–cHK. Overall, our studies demonstrate that ^99mTc–HYNIC–cHK is a promising SPECT radiotracer for the noninvasive imaging of integrin αvβ6 in living subjects.

Graphical Abstract

Nano-graphene oxide-manganese dioxide nanocomposites for overcoming tumor hypoxia and enhancing cancer radioisotope therapy

While radiotherapy (RT) is commonly used in clinics for cancer treatment, the therapeutic efficiency is not satisfactory owing to the existence of the hypoxic tumor microenvironment which seriously affects the efficiency of RT. Herein, we design polyethylene glycol (PEG)-modified reduced nano-graphene oxide-manganese dioxide (rGO-MnO₂-PEG) nanocomposites to trigger oxygen generation from H₂O₂ to reduce the tumor hypoxic microenvironments. We use the radioisotope, ¹³¹I labeled rGO-MnO₂-PEG nanocomposites as therapeutic agents for in vivo tumor radioisotope therapy (RIT), achieving excellent tumor killing and further enhancing the therapeutic efficiency of RIT. More importantly, the dissolution of MnO₂ under acidic conditions and the redox process during the catalytic pathway of H₂O₂ decomposition in the cellular microenvironment direct to the production of an enormous amount of Mn²⁺ which has been used as a contrast agent for magnetic resonance imaging (MRI). Our proposed work provides a strategy to trigger oxygen formation via an internal stimulus to enhance imaging-guided RIT efficiency.

A Label-Free Microelectrode Array Based on One-Step Synthesis of Chitosan-Multi-Walled Carbon Nanotube-Thionine for Ultrasensitive Detection of Carcinoembryonic Antigen

Carcinoembryonic antigen (CEA) has been an extensively used tumor marker responsible for clinical early diagnosis of cervical carcinomas, and pancreatic, colorectal, gastric and lung cancer. Combined with micro-electro mechanical system (MEMS) technology, it is important to develop a novel immune microelectrode array (MEA) not only for rapid analysis of serum samples, but also for cell detection in vitro and in vivo. In this work, we depict a simple approach to modify chitosan–multi-walled carbon nanotubes–thionine (CS–MWCNTs–THI) hybrid film through one-step electrochemical deposition and the CS-MWCNTs-THI hybrid films are successfully employed to immobilize anti-CEA for fabricating simple, label-free, and highly sensitive electro-chemical immune MEAs. The detection principle of immune MEA was based on the fact that the increasing formation of the antigen-antibody immunocomplex resulted in the decreased response currents and the relationship between the current reductions with the corresponding CEA concentrations was directly proportional. Experimental results indicated that the label-free MEA had good selectivity and the limit of detection for CEA is 0.5 pg/mL signal to noise ratio (SNR) = 3. A linear calibration plot for the detection of CEA was obtained in a wide concentration range from 1 pg/mL to 100 ng/mL (r = 0.996). This novel MEA has potential applications for detecting CEA for the research on cancer cells and cancer tissue slices as well as for effective early diagnosis.

Relevance of radiobiological concepts in radionuclide therapy of cancer

PURPOSE

Radionuclide therapy (RNT) is a rapidly growing area of clinical nuclear medicine, wherein radionuclides are employed to deliver cytotoxic dose of radiation to the diseased cells/tissues. During RNT, radionuclides are either directly administered or delivered through biomolecules targeting the diseased site. RNT has been clinically used for diverse range of diseases including cancer, which is the focus of the review.

CONCLUSIONS

The major emphasis in RNT has so far been given towards developing peptides/antibodies and other molecules to conjugate a variety of therapeutic radioisotopes for improved targeting/delivery of radiation dose to the tumor cells. Despite that, many of the RNT approaches have not achieved their desired therapeutic success probably due to poor knowledge about complex and dynamic (i) fate of radiolabeled molecules; (ii) radiation dose delivered; (iii) cellular heterogeneity in tumor mass; and (iv) cellular radiobiological response. Based on understanding gathered during recent years, it may be stated that besides the absorbed dose, the net radiobiological response of tumor/normal cells also determines the clinical response of radiotherapeutic modalities including RNT. The radiosensitivity of tumor/normal cells is governed by radiobiological phenomenon such as radiation-induced bystander effect, genomic instability, adaptive response and low dose hyper-radiosensitivity. These concepts have been well investigated in the context of external beam radiotherapy, but their clinical implications during RNT have received meagre attention. In this direction, a few studies performed using in vitro and in vivo models envisage the possibilities of exploiting the radiobiological knowledge for improved therapeutic outcome of RNT.

Molecularly Targeted Therapy of Human Hepatocellular Carcinoma Xenografts with Radio-iodinated Anti-VEGFR2 Murine-Human Chimeric Fab

Vascular endothelial growth factor receptor 2 (VEGFR2) is traditionally regarded as an important therapeutic target in a wide variety of malignancies, such as hepatocellular carcinoma (HCC). We previously generated a murine-human anti-VEGFR2 chimeric Fab (cFab), named FA8H1, which has the potential to treat VEGFR2-overexpressing solid tumors. Here, we investigated whether FA8H1 can be used as a carrier in molecularly targeted therapy in HCC xenograft models. FA8H1 was labeled with ¹³¹I, and two HCC xenograft models were generated using BEL-7402 (high VEGFR2-expressing) and SMMC-7721 (low VEGFR2-expressing) cells, which were selected from five HCC cell lines. The biodistribution of ¹³¹I-FA8H1 was determined in both models by Single-Photon Emission Computed Tomography and therapeutic effects were monitored in nude mice bearing BEL-7402 xenografts. Finally, we determined the involvement of necrosis and apoptotic pathways in treated mice using immunohistochemistry. ¹³¹I-FA8H1 levels were dramatically reduced in blood and other viscera. The therapeutic effect of ¹³¹I-labeled FA8H1 in the BEL-7402 model was significantly better than that by ¹³¹I and FA8H1 alone. We observed extensive necrosis in the treated tumors, and both FasL and caspase 3 were up-regulated. Thus, ¹³¹I-anti-VEGFR2 cFab has the potential to be used for molecularly targeted treatment of HCC overexpressing VEGFR2.

An RNA aptamer that binds carcinoembryonic antigen inhibits hepatic metastasis of colon cancer cells in mice

BACKGROUND & AIMS

Carcinoembryonic antigen (CEA) is expressed by many types of cancer cells; its overexpression induces cell adhesion, increases resistance to anoikis, and promotes hepatic metastasis of colon cancer cells. The amino acid sequence PELPK in its hinge region, between the N and A1 domains, is required for migration of cancer cells to the liver. We sought to identify ligands of this domain for use in diagnosis and therapy.

METHODS

We screened for RNA aptamers against the domain of CEA required for metastasis using systematic evolution of ligands by exponential enrichment. The specificity and affinity of the aptamer for CEA protein were characterized by mobility shift, uptake, and surface plasmon resonance assays. We analyzed the effects of the aptamer on metastatic properties of cells, as well as metastasis of colon cancer cells in mice.

RESULTS

Using systematic evolution of ligands by exponential enrichment, we identified an RNA aptamer that bound to the PELPK sequence in CEA with high affinity and specificity. The isolated aptamer bound specifically to CEA-positive cells and inhibited interactions between CEA and heterogeneous nuclear ribonucleoprotein M4. The aptamer inhibited homotypic aggregation, migration, and invasion by CEA-positive cancer cells, but did not affect adhesion of endothelial cells. The aptamer induced colon cancer cell anoikis by interrupting the interaction between death receptor 5 and CEA. The aptamer prevented metastasis of human colon cancer cells to the livers of mice.

CONCLUSIONS

An RNA aptamer that binds to the PELPK sequence in CEA inhibits its interactions with heterogeneous nuclear ribonucleoprotein M4 and death receptor 5, migration and invasion by colon cancer cells, and hepatic metastasis of colon cancer cells in mice. It promoted cancer cell anoikis and might be used to identify CEA-positive tumors in patients or be developed as an anti-cancer reagent.