Targeted molecular imaging of VEGF receptors overexpressed in ischemic microvasculature using chitosan-DC101 conjugates

The anti-glypican 1 AT101 antibody as targeting agent to effectively deliver chitosan nanobubbles to glioblastoma cells

BACKGROUND

Recently, we developed AT101, an IgM-class mouse monoclonal antibody directed against glypican-1 (GPC1), a proteoglycan that can be considered as useful target for glioblastoma multiforme (GBM) treatment being specifically and highly expressed on GBM cell surface. Here, we proposed the use of AT101 as targeting agent in a drug delivery nanoplatfom to effectively deliver chitosan nanobubbles (NBs) for GBM treatment.

METHODS

Chitosan NBs were prepared and conjugated with AT101 or left unconjugated as control.

RESULTS

The ability of AT101 to bind the GPC1 protein was demonstrated by flow cytometry and immunofluorescence analysis in the "GBM-like" GPC1-expressing cell lines U-87 MG and T98G. AT101 was shown to bind GPC1-expressing GBM tumor samples by immunofluorescence. In-vivo experiments in the U-87 MG xenograft model showed that AT101 was able to bind GPC1 on cell surface and accumulate in U-87 MG tumor masses (p = 0.0002 respect to control). Moreover, in-vivo experiments showed that AT101 is able to target GPC1 when conjugated to chitosan NBs, thus increasing their specific deliver to GPC1-expressing cells of U-87 MG tumor, as compared to chitosan NBs not conjugated to AT101 (p = 0.02).

CONCLUSIONS

AT101 is an useful targeting agent for the development of drug delivery nanoplatforms for GBM treatment.

The Role of VEGF Receptors as Molecular Target in Nuclear Medicine for Cancer Diagnosis and Combination Therapy

Simple Summary

The rapid development of diagnostic and therapeutic methods of the cancer treatment causes that these diseases are becoming better known and the fight against them is more and more effective. Substantial contribution in this development has nuclear medicine that enables very early cancer diagnosis and early start of the so-called targeted therapy. This therapeutic concept compared to the currently used chemotherapy, causes much fewer undesirable side effects, due to targeting a specific lesion in the body. This review article discusses the possible applications of radionuclide-labelled tracers (peptides, antibodies or synthetic organic molecules) that can visualise cancer cells through pathological blood vessel system in close tumour microenvironment. Hence, at a very early step of oncological disease, targeted therapy can involve in tumour formation and growth.

Abstract

One approach to anticancer treatment is targeted anti-angiogenic therapy (AAT) based on prevention of blood vessel formation around the developing cancer cells. It is known that vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptors (VEGFRs) play a pivotal role in angiogenesis process; hence, application of angiogenesis inhibitors can be an effective approach in anticancer combination therapeutic strategies. Currently, several types of molecules have been utilised in targeted VEGF/VEGFR anticancer therapy, including human VEGF ligands themselves and their derivatives, anti-VEGF or anti-VEGFR monoclonal antibodies, VEGF binding peptides and small molecular inhibitors of VEGFR tyrosine kinases. These molecules labelled with diagnostic or therapeutic radionuclides can become, respectively, diagnostic or therapeutic receptor radiopharmaceuticals. In targeted anti-angiogenic therapy, diagnostic radioagents play a unique role, allowing the determination of the emerging tumour, to monitor the course of treatment, to predict the treatment outcomes and, first of all, to refer patients for AAT. This review provides an overview of design, synthesis and study of radiolabelled VEGF/VEGFR targeting and imaging agents to date. Additionally, we will briefly discuss their physicochemical properties and possible application in combination targeted radionuclide tumour therapy.

The Alginate Layer for Improving Doxorubicin Release and Radiolabeling Stability of Chitosan Hydrogels

PURPOSE

Chitosan hydrogels (CSH) formed through ionic interaction with an anionic molecule are suitable as a drug carrier and a tissue engineering scaffold. However, the initial burst release of drugs from the CSH due to rapid swelling after immersing in a biofluid limits their wide application as a drug delivery carrier. In this study, alginate layering on the surface of the doxorubicin (Dox)-loaded and I-131-labeled CSH (DI-CSH) was performed. The effect of the alginate layering on drug release behavior and radiolabeling stability was investigated.

METHODS

Chitosan was chemically modified using a chelator for I-131 labeling. After labeling of I-131 and mixing of Dox, the chitosan solution was dropped into tripolyphosphate (TPP) solution using an electrospinning system to prepare spherical microhydrogels. The DI-CSH were immersed into alginate solution for 30 min to form the crosslinking layer on their surface. The formation of alginate layer on the DI-CSH was confirmed by Fourier transform infrared spectroscopy (FT-IR) and zeta potential analysis. In order to investigate the effect of alginate layer, studies of in vitro Dox release from the hydrogels were performed in phosphate buffered in saline (PBS, pH 7.4) at 37 °C for 12 days. The radiolabeling stability of the hydrogels was evaluated using ITLC under different experimental condition (human serum, normal saline, and PBS) at 37 °C for 12 days.

RESULTS

Formatting the alginate-crosslinked layer on the CSH surface did not change the spherical morphology and the mean diameter (150 ± 10 μm). FT-IR spectra and zeta potential values indicate that alginate layer was formed successfully on the surface of the DI-CSH. In in vitro Dox release studies, the total percentage of the released Dox from the DI-CSH for 12 days were 60.9 ± 0.8, 67.3 ± 1.4, and 71.8 ± 2.5 % for 0.25, 0.50, and 1.00 mg Dox used to load into the hydrogels, respectively. On the other hand, after formatting alginate layer, the percentage of the released Dox for 12 days was decreased to 47.6 ± 1.4, 51.1 ± 1.4, and 57.5 ± 1.6 % for 0.25, 0.50, and 1.00 mg Dox used, respectively. The radiolabeling stability of DI-CSH in human serum was improved by alginate layer.

CONCLUSIONS

The formation of alginate layer on the surface of the DI-CSH is useful for improving the drug release behavior and radiolabeling stability.

Imaging key biomarkers of tumor angiogenesis

Angiogenesis is a fundamental requirement for tumor growth and therefore it is a primary target for anti-cancer therapy. Molecular imaging of angiogenesis may provide novel opportunities for early diagnostic and for image-guided optimization and management of therapeutic regimens. Here we reviewed the advances in targeted imaging of key biomarkers of tumor angiogenesis, integrins and receptors for vascular endothelial growth factor (VEGF). Tracers for targeted imaging of these biomarkers in different imaging modalities are now reasonably well-developed and PET tracers for integrin imaging are currently in clinical trials. Molecular imaging of longitudinal responses to anti-angiogenic therapy in model tumor systems revealed a complex pattern of changes in targeted tracer accumulation in tumor, which reflects drug-induced tumor regression followed by vascular rebound. Further work will define the competitiveness of targeted imaging of key angiogenesis markers for early diagnostic and image-guided therapy.

Imaging key biomarkers of tumor angiogenesis

Angiogenesis is a fundamental requirement for tumor growth and therefore it is a primary target for anti-cancer therapy. Molecular imaging of angiogenesis may provide novel opportunities for early diagnostic and for image-guided optimization and management of therapeutic regimens. Here we reviewed the advances in targeted imaging of key biomarkers of tumor angiogenesis, integrins and receptors for vascular endothelial growth factor (VEGF). Tracers for targeted imaging of these biomarkers in different imaging modalities are now reasonably well-developed and PET tracers for integrin imaging are currently in clinical trials. Molecular imaging of longitudinal responses to anti-angiogenic therapy in model tumor systems revealed a complex pattern of changes in targeted tracer accumulation in tumor, which reflects drug-induced tumor regression followed by vascular rebound. Further work will define the competitiveness of targeted imaging of key angiogenesis markers for early diagnostic and image-guided therapy.

Dextran-conjugated vascular endothelial growth factor receptor antibody for in vivo melanoma xenografted mouse imaging

Intact immunoglobulin G antibody has a relatively large molecule size of approximately 150 kDa that remains in the bloodstream for many weeks, which is a considerable disadvantage when it is used to carry radioactive materials for imaging. To lower background activity and increase the contrast of images, we investigated antivascular endothelial growth factor (VEGF) receptor 2 antibody (DC101) conjugated dextran for VEGF receptor 2 imaging in tumor xenografted mice. DTPA-conjugated aminodextran was synthesized, reacted with sulfo-LC-SPDP, and then reacted with DC101. The binding affinity of DTPA-dextran-DC101 to Flk-1 was measured. The gamma imaging and biodistributions of (99m)Tc-DTPA-dextran-DC101, (99m)Tc-DTPA-DC101, and (125)I-DC101 were studied in B16F10 melanoma xenografted mice. The dissociation values for DC101, DTPA-DC101, and DTPA-dextran-DC101 were 22.48, 3.05, and 14.74 pM, respectively. In gamma images, (99m)Tc-DTPA-dextran-DC101 showed weak liver uptake and rapid kidney elimination. In biodistribution results, the liver uptake of (99m)Tc-DTPA-dextran-DC101 was similar with that of (99m)Tc-DTPA-DC101 at each time point. However, the blood activity of (99m)Tc-DTPA-dextran-DC101 has shown significant differences, compared with (99m)Tc-DTPA-DC101 at all time points. The tumor accumulation of dextran-conjugated antibody was increased with time, whereas that of dextran nonconjugated antibody decreased. In particular, the pattern of tumor uptake of (99m)Tc-DTPA-dextran-DC101 was similar to that of (125)I-DC101, so this was thought to reflect the kinetics of DC101, unlike the nonconjugated form. The results of this study suggested that introduction of dextran moiety to make (99m)Tc-radiolabeled DC101 imaging agent could provide better images with the impaired background and the steady increasing binding to the receptor. However, further studies are necessary to improve clinical pharmacokinetics, such as enhancement of tumor uptake and impaired renal uptake.

Advances in bio-optical imaging for the diagnosis of early oral cancer

Oral cancer is among the most common malignancies worldwide, therefore early detection and treatment is imperative. The 5-year survival rate has remained at a dismal 50% for the past several decades. The main reason for the poor survival rate is the fact that most of the oral cancers, despite the general accessibility of the oral cavity, are not diagnosed until the advanced stage. Early detection of the oral tumors and its precursor lesions may be the most effective means to improve clinical outcome and cure most patients. One of the emerging technologies is the use of non-invasive in vivo tissue imaging to capture the molecular changes at high-resolution to improve the detection capability of early stage disease. This review will discuss the use of optical probes and highlight the role of optical imaging such as autofluorescence, fluorescence diagnosis (FD), laser confocal endomicroscopy (LCE), surface enhanced Raman spectroscopy (SERS), optical coherence tomography (OCT) and confocal reflectance microscopy (CRM) in early oral cancer detection. FD is a promising method to differentiate cancerous lesions from benign, thus helping in the determination of adequate resolution of surgical resection margin. LCE offers in vivo cellular imaging of tissue structures from surface to subsurface layers and has demonstrated the potential to be used as a minimally invasive optical biopsy technique for early diagnosis of oral cancer lesions. SERS was able to differentiate between normal and oral cancer patients based on the spectra acquired from saliva of patients. OCT has been used to visualize the detailed histological features of the oral lesions with an imaging depth down to 2–3 mm. CRM is an optical tool to noninvasively image tissue with near histological resolution. These comprehensive diagnostic modalities can also be used to define surgical margin and to provide a direct assessment of the therapeutic effectiveness.