GX1 targeting delivery of rmhTNFα evaluated using multimodality imaging

68Ga-Labeled GX1 Dimer: A Novel Probe for PET/Cerenkov Imaging Targeting Gastric Cancer

Purpose

To synthesize the dimer of GX1 and identify whether its affinity and targeting are better than those of GX1. To prepare ⁶⁸Ga-DOTA-KEK-(GX1)₂ and to apply it to PET and Cerenkov imaging of gastric cancer.

Methods

⁶⁸Ga-DOTA-KEK-(GX1)₂ was prepared, and the labeling yield and stability were determined. Its specificity and affinity were verified using an in vitro cell binding assay and competitive inhibition test, cell immunofluorescence, and cell uptake and efflux study. Its tumor-targeting ability was determined by nano PET/CT and Cerenkov imaging, standardized uptake value (SUV), signal-to-background ratio (SBR) quantification, and a biodistribution study in tumor-bearing nude mice.

Results

⁶⁸Ga-DOTA-KEK-(GX1)₂ was successfully prepared, and the labeling yield was more than 97%. It existed stably for 90 min in serum. The binding of ⁶⁸Ga-DOTA-KEK-(GX1)₂ to cocultured HUVECs (Co-HUVECs) was higher than that to human umbilical vein endothelial cells (HUVECs), BGC823 cells, and GES cells. It was also higher than that of ⁶⁸Ga-DOTA-GX1, indicating that the dimer did improve the specificity and affinity of GX1. The binding of KEK-(GX1)₂ to Co-HUVECs was significantly higher than that of GX1. Additionally, the uptake of ⁶⁸Ga-DOTA-KEK-(GX1)₂ by Co-HUVECs was higher than that of ⁶⁸Ga-DOTA-GX1 and reached a maximum at 60 min. Nano PET/CT and Cerenkov imaging showed that the tumor imaging of the nude mice injected with ⁶⁸Ga-DOTA-KEK-(GX1)₂ was clear, and the SUV and SBR value of the tumor sites were significantly higher than those of the nude mice injected with ⁶⁸Ga-DOTA-GX1, indicating that the probe had better targeting in vivo. Finally, the biodistribution showed quantitatively that when organs such as the kidney and liver metabolized rapidly, the radioactivity of the tumor site of the nude mice injected with ⁶⁸Ga-DOTA-KEK-(GX1)₂ decreased relatively slowly. At the same time, the percentage of injected dose per gram (%ID/g) of the tumor site was higher than that of other normal organs except the liver and kidney at 60 min, which indicated that the tumor had good absorption of the probe.

Conclusion

GX1 was modified successfully, and the in vivo and in vitro properties of the GX1 dimer were significantly better than those of GX1. The imaging probe, ⁶⁸Ga-DOTA-KEK-(GX1)₂, was successfully prepared, which provides a candidate probe for PET and Cerenkov diagnosis of gastric cancer.

188Re-labeled GX1 dimer as a novel dual-functional probe targeting TGM2 for imaging and antiangiogenic therapy of gastric cancer

PURPOSE

The GX1 peptide (CGNSNPKSC) can specifically bind to TGM2 and possesses the ability to target the blood vessels of gastric cancer. This study intends to develop an integrated dual-functional probe with higher affinity, specificity and targeting and to characterize it in vivo and in vitro.

METHODS

The dimer and tetramer of GX1 were prepared using cross-linked PEG and labeled with ^99mTc. The best targeting probe [PEG-(GX1)₂] was selected by gamma camera imaging in nude mouse models of gastric cancer. ¹⁸⁸Re-PEG-(GX1)₂ was prepared and characterized through cell binding analysis and competitive inhibition experiments, gamma camera imaging, MTT analysis and flow cytometry, BLI, immunohistochemistry, HE staining and biochemical analysis.

RESULTS

PEG-(GX1)₂ bound specifically to Co-HUVEC with higher affinity than GX1. ¹⁸⁸Re-PEG-(GX1)₂ had better ability to target gastric cancer in tumor-bearing nude mice and higher T/H ratios than ¹⁸⁸Re-GX1. ¹⁸⁸Re-PEG-(GX1)₂ inhibited the growth of Co-HUVEC and induced apoptosis, and its effects were more robust than those of ¹⁸⁸Re-GX1. BLI showed that ¹⁸⁸Re-PEG-(GX1)₂ inhibited tumor proliferation in vivo with a stronger effect than ¹⁸⁸Re-GX1. Compared with ¹⁸⁸Re-GX1, ¹⁸⁸Re-PEG-(GX1)₂ suppressed tumor angiogenesis and tumor cell proliferation and induced tumor cell apoptosis in vivo. The ¹⁸⁸Re-PEG-(GX1)₂ group did not cause visible changes in liver and kidney morphology and function in vivo.

CONCLUSION

The dimer of GX1 was synthesized by using cross-linked PEG, and then ¹⁸⁸Re-PEG-(GX1)₂ was prepared. This radiopharmaceutical played both diagnostic and therapeutic functions, and gamma camera imaging could be utilized to detect the distribution of drugs in vivo during treatment. Through a series of experiments in vitro and in vivo, the feasibility of the drug was confirmed, and these results laid the foundation for the subsequent development and application of GX1.

Vascular-homing peptides for cancer therapy

In the past 30 years, a variety of phage libraries have been extensively utilized to identify and develop tumor homing peptides (THPs). THPs specifically bind to tumor cells or elements of the tumor microenvironment while no or low affinity to normal cells. In this regard, the efficacy of therapeutic agents in cancer therapy can be enhanced by targeting strategies based on coupling with THPs that recognize receptors expressed by tumor cells or tumor vasculature. Especially, vascular-homing peptides, targeting tumor vasculature, have their receptors expressed on or around the blood vessel including pro-angiogenic factors, metalloproteinase, integrins, fibrin-fibronectin complexes, etc. This review briefly summarizes recent studies on identification and therapeutic applications of vascular-homing peptides targeting common angiogenic markers or with unknown vascular targets in some certain types of cancers. These newly discovered vascular-homing peptides are promising candidates which could provide novel strategies for cancer therapy.

Evaluation of Magnetonanoparticles Conjugated with New Angiogenesis Peptides in Intracranial Glioma Tumors by MRI

Angiogenesis plays a critical role in progression of malignant gliomas. The development of glioma-specific labeling molecules that can aid detection and visualization of angiogenesis can help surgical planning and improve treatment outcome. The aim of this study was to evaluate if two peptides (GX1 and RGD-GX1) linked to angiogenesis can be used as an MR-imaging markers of angiogenesis. MR imaging was performed in U87 glioblastoma-bearing NOD-SCID mice at different time points between 15 and 120 min post-injection to visualize particle distribution. GX1 and RGD-GX1 exhibited the highest accumulation in U87 glioblastoma at 120 min post i.v. administration. GX1-conjugated agents lead to higher decrease in transverse relaxation time (T ₂) (i.e., stronger contrast enhancement) than RGD-GX1-conjugated agents in U87 glioblastoma tumor model. In addition, we tested if U87-IDH1^R132 mutated cell line had different pattern of GX1 or RGD-GX1 particle accumulation. Responses in U87-IDH1^WT followed a similar pattern with GX1 contrast agents; however, lower contrast enhancement was observed with RGD-GX1 agents. The specific binding of these peptides to human glioblastoma xenograft in the brain was confirmed by magnetic resonance imaging. The contrast enhancement following injection of magnetonanoparticles conjugated to GX1 peptide matched well with CD31 staining and iron staining.

Heterogeneous dimer peptide-conjugated polylysine dendrimer-Fe3O4 composite as a novel nanoscale molecular probe for early diagnosis and therapy in hepatocellular carcinoma

A novel nanoscale molecular probe is formulated in order to reduce toxicity and side effects of antitumor drug doxorubicin (DOX) in normal tissues and to enhance the detection sensitivity during early imaging diagnosis. The mechanism involves a specific targeting of Arg-Gly-Asp peptide (RGD)-GX1 heterogeneous dimer peptide-conjugated dendrigraft poly-l-lysine (DGL)-magnetic nanoparticle (MNP) composite by α_vβ₃-integrin/vasculature endothelium receptor-mediated synergetic effect. The physicochemical properties of the nanoprobe were characterized by using transmission electron microscope, Fourier transform infrared spectroscopy, X-ray diffraction, dynamic light scattering (DLS), and vibrating sample magnetometer. The average diameter of the resulting MNP-DGL-RGD-GX1-DOX nanoparticles (NPs) was ~150-160 nm by DLS under simulate physiological medium. In the present experimental system, the loading amount of DOX on NPs accounted for 414.4 mg/g for MNP-DGL-RGD-GX1-DOX. The results of cytotoxicity, flow cytometry, and cellular uptake consistently indicated that the MNP-DGL-RGD-GX1-DOX NPs were inclined to target HepG2 cells in selected three kinds of cells. In vitro exploration of molecular mechanism revealed that cell apoptosis was associated with the overexpression of Fas protein and the significant activation of caspase-3. In vivo magnetic resonance imaging and biodistribution study showed that the MNP-DGL-RGD-GX1-DOX formulation had high affinity to the tumor tissue, leading to more aggregation of NPs in the tumor. In vivo antitumor efficacy research verified that MNP-DGL-RGD-GX1-DOX NPs possessed significant antitumor activity and the tumor inhibitory rate reached 78.5%. These results suggested that NPs could be promising in application to early diagnosis and therapy in hepatocellular carcinoma as a specific nanoprobe.

Evaluation of GX1 and RGD-GX1 peptides as new radiotracers for angiogenesis evaluation in experimental glioma models

Gliomas are the most common type among all central nervous system tumors. The aggressiveness of gliomas is correlated with the level of angiogenesis and is often associated with prognosis. The aim of this study is to evaluate the novel GX1 peptide and the heterodimer RGD-GX1 radiolabeled with technetium-99m, for angiogenesis detection in glioma models. Radiolabeling and radiochemical controls were assessed for both radioconjugates. In vitro binding studies in glioma tumor cells were performed, as well as biodistribution in SCID mice bearing tumor cells, in order to evaluate the biological behavior and tumor uptake of the radiocomplexes. Blocking and imaging studies were also conducted. MicroSPECT/CT images were acquired in animals with experimentally implanted intracranial tumor. Open field activity was performed to evaluate behavior, as well as perfusion and histology analysis. The radiochemical purity of both radiotracers was greater than 96 %. In vitro binding studies revealed rather similar binding profi le for each molecule. The highest binding was for RGD-GX1 peptide at 120 min in U87MG cells (1.14 ± 0.35 %). Tumor uptake was also favorable for RGD-GX1 peptide in U87MG cells, reaching 2.96 ± 0.70 % at 1 h p.i. with 47 % of blocking. Imaging studies also indicated better visualization for RGD-GX1 peptide in U87MG cells. Behavior evaluation pointed brain damage and histology studies confirmed actual tumor in the uptake site. The results with the angiogenesis seeking molecule (99m)Tc-HYNIC-E-[c(RGDfk)-c(GX1)] were successful, and better than with (99m)Tc-HYNIC-PEG4-c(GX1). Future studies targeting angiogenesis in other glioma and nonglioma tumor models are recommended.

GX1-conjugated poly(lactic acid) nanoparticles encapsulating Endostar for improved in vivo anticolorectal cancer treatment

Tumor angiogenesis plays a key role in tumor growth and metastasis; thus, targeting tumor-associated angiogenesis is an important goal in cancer therapy. However, the efficient delivery of drugs to tumors remains a key issue in antiangiogenesis therapy. GX1, a peptide identified by phage-display technology, is a novel tumor vasculature endothelium-specific ligand and possesses great potential as a targeted vector and antiangiogenic agent in the diagnosis and treatment of human cancers. Endostar, a novel recombinant human endostatin, has been shown to inhibit tumor angiogenesis. In this study, we developed a theranostic agent composed of GX1-conjugated poly(lactic acid) nanoparticles encapsulating Endostar (GPENs) and labeled with the near-infrared dye IRDye 800CW to improve colorectal tumor targeting and treatment efficacy in vivo. The in vivo fluorescence molecular imaging data showed that GPENs (IRDye 800CW) more specifically targeted tumors than free IRDye 800CW in colorectal tumor-bearing mice. Moreover, the antitumor efficacy was evaluated by bioluminescence imaging and immunohistology, revealing that GPENs possessed improved antitumor efficacy on subcutaneous colorectal xenografts compared to other treatment groups. Thus, our study showed that GPENs, a novel GX1 peptide guided form of nanoscale Endostar, can be used as a theranostic agent to facilitate more efficient targeted therapy and enable real-time monitoring of therapeutic efficacy in vivo.

Radiolabeling and biological evaluation of the GX1 and RGD-GX1 peptide sequence for angiogenesis targeting

INTRODUCTION

Aiming to develop a novel (99m)Tc-labeled imaging agent, for angiogenesis and tumor receptors, two peptides obtained from phage display library, namely GX1 and the heterodimer RGD-GX1, were synthesized in a cyclic conformation. They were radiolabeled with (99m)Tc, employing the HYNIC chelator, for radiochemical evaluation and biological properties.

METHODS

Radiolabeling, radiochemical control, plasma protein binding, and partition coefficient were assessed for both radioconjugates. Biodistribution in healthy Balb/c mice was carried out, in order to evaluate the biological behaviour of the radiocomplexes.

RESULTS

The conjugates displayed a rather similar pharmacokinetic profile. They were prepared with high radiochemical purity (>96%), and both were hydrophilic (log P of -2.25 and -2.51 respectively). Preferential renal excretion was observed. Kidney uptake (42.31±5.35 %ID/g) for (99m)Tc-HYNIC-E-[c(RGDfk)-c(GX1)], 1h post-injection was about three times higher than the uptake of (99m)Tc-HYNIC-PEG4-c(GX1) (11.92±4.77%ID/g). Total blood, bone and muscle values revealed a slightly slower clearance for the RGD-GX1 radiocomplex.

CONCLUSION

The high radiochemical purity achieved, and the similar in vivo profile observed for both radioconjugates, make them potential candidates for radiopharmaceuticals for tumor imaging. Further investigations of binding affinity, and uptake of GX1 and RGD-GX1 peptides in tumor models, are warranted.