Non-invasive imaging of Toll-like receptor 5 expression using 131I-labeled mAb in the mice bearing H22 tumors

Immuno-PET Imaging and Pharmacokinetics of an Anti-CEA scFv-based Trimerbody and Its Monomeric Counterpart in Human Gastric Carcinoma-Bearing Mice

Monoclonal antibodies (mAbs) are currently used as therapeutic agents in different types of cancer. However, mAbs and antibody fragments developed so far show suboptimal properties in terms of circulation time and tumor penetration/retention. Here, we report the radiolabeling, pharmacokinetic evaluation, and determination of tumor targeting capacity of the previously validated anti-CEA MFE23-scFv-based N-terminal trimerbody (MFE23^N-trimerbody), and the results are compared to those obtained for the monomeric MFE23-scFv. Dissection and gamma-counting studies performed with the ¹³¹I-labeled protein scaffolds in normal mice showed slower blood clearance for the trimerbody, and accumulation in the kidneys, the spleen, and the liver for both species. These, together with a progressive uptake in the small intestine, confirm a combined elimination scheme with hepatobiliary and urinary excretion. Positron emission tomography studies performed in a xenograft mouse model of human gastric adenocarcinoma, generated by subcutaneous administration of CEA-positive human MKN45 cells, showed higher tumor accumulation and tumor-to-muscle (T/M) ratios for ¹²⁴I-labeled MFE23^N-trimerbody than for MFE23-scFv. Specific uptake was not detected with PET imaging in CEA negative xenografts as indicated by low T/M ratios. Our data suggest that engineered intermediate-sized trivalent antibody fragments could be promising candidates for targeted therapy and imaging of CEA-positive tumors.

Toll-like receptors in hepatocellular carcinoma: potential novel targets for pharmacological intervention

INTRODUCTION

Toll-like receptors (TLRs) are expressed by a wide variety of cell types including immune cells. They play a crucial role in the inflammatory and host defense response against microorganisms, and triggering TLRs can mediate the activation of innate immunity. Furthermore, research suggests that various TLRs may function differently on different tumor cells. The change in TLR activity may elicit an anti-tumor activity in hepatocellular carcinoma (HCC) cells and may serve as a novel therapeutic target for HCC therapy.

AREAS COVERED

This review discusses the role of the TLR family in HCC and the underlying signaling pathway of TLRs as a form of pattern recognition receptor in mediating inflammation and HCC immunity responses. Agonists and antagonists of TLRs, which render TLRs as potential therapeutic targets, activate downstream molecules, subsequently causing HCC cell survival. The proliferation or protection against the development of HCC is also described.

EXPERT OPINION

A series of studies have highlighted a crucial role of TLRs in HCC and consider TLR signaling pathways as potential therapeutic targets for HCC. However, the conclusions of these studies are in part paradoxical and controversial. Thus, it is necessary to extend further research to help determine the signaling pathways involved.

SPECT imaging of neuropilin receptor type-1 expression with 131I-labeled monoclonal antibody

As a novel co-receptor for vascular endothelial growth factor (VEGF), neuropilin receptor type-1 (NRP-1) is overexpressed in several cancers and metastases, and serves as an attractive target for cancer molecular imaging and therapy. Previous single photon emission computerized tomography (SPECT) studies demonstrated that the small NRP-1-targeting peptides 99mTc-MA-ATWLPPR and 99mTc-CK3 showed poor tumor imaging quality, because of their rapid blood clearance and very low tumor uptake. Compared with small peptides, monoclonal antibodies (mAbs) can improve imaging of NRP-1-expression, due to their high affinity, specificity and slow extraction. A6-11-26 is a novel monoclonal antibody against NRP-1 b1b2 domain that exhibits inhibition of tumor growth in NPR-1-expressing preclinical models. The aim of the present study was to develop the 131I-labeled anti-NRP-1 monoclonal antibody A6-11-26 as a SPECT probe for imaging of NRP-1-positive tumor. An anti-NRP-1 monoclonal antibody (A6-11-26) was produced by hybridomas and was labeled with iodine-131 by the iodogen method. In vitro, the radiolabeling efficiency, radiochemical purity, immunoreactive fraction and stability were assessed. Binding affinity and specificity of 131I‑A6-11-26 to NRP-1 were evaluated using human glioblastoma U87MG cells. In vivo, biodistribution and SPECT/CT studies were conducted on mice bearing U87MG xenografts after the injection of 131I-A6-11-26 with or without co-injection of unlabeled A6-11-26 antibody. A6-11-26 was generated successfully by hybridoma with high purity (>95%) and was labeled with iodine-131 within 60 min with high labelling efficiency (95.46±3.34%), radiochemical purity (98.23±1.41%). 131I-A6-11-26 retained its immunoreactivity and also displayed excellent stability in mouse serum and PBS solution during 1 to 96 h. Cell uptake assays showed high NRP-1-specific uptake (15.80±1.30% applied activity at 6 h) in U87MG cells. 131I-A6-11-26 bound to NRP-1 with low nanomolar affinity (KD=1.67±0.14 nM) in U87MG cells. In vivo, biodistribution study demonstrated targeting of U87MG glioma xenografts was NRP-1 specific. The tumor uptake was 6.00±1.24%ID/g at 24 h, and the tumor to muscle ratio was 3.20±0.30 at 24 h, and reached the highest level of 6.13±0.24 at 120 h after injection. SPECT imaging studies revealed that 131I-A6-11-26 could clearly identify U87MG tumors with good contrast, especially at 72-120 h after injection. The present study demonstrates that 131I-A6-11-26 is capable of detecting lesions in an NRP-1-expressing tumor with high target selectivity, and may offer a promising SPECT agent for NRP-1 expression positive tumor and encourage further investigation.