[177Lu]Bz-DTPA-EGF: Preclinical Characterization of a Potential Radionuclide Targeting Agent Against Glioma

A Novel Dual-labeled Peptide for Multimodal Imaging of EGFR with L858R Mutation

BACKGROUND

The development of molecular imaging agents targeting epidermal growth factor receptor (EGFR) with L858R mutation may help with the selection of non-small cell lung carcinoma (NSCLCL) patients who may benefit from EFGR tyrosine kinase inhibitor (TKI) therapy.

OBJECTIVE

In this study, we developed 99mTc STHHYYP-GHEG-ECGK-tetramethylrhodamine (STHHYYP-ECGK-TAMRA) to target EGFR with L858R mutation in NSCLC tumors and verified its probability as a molecular imaging agent.

METHODS

Fmoc solid-phase peptide synthesis was used to synthesize STHHYYP-ECGKTAMRA. 99mTc labelled STHHYYP-ECGK-TAMRA was prepared. Gamma imaging, fluorescent imaging and biodistribution were performed in murine models bearing NCI-H1975 and NCI-H1650 tumors.

RESULTS

The binding affinity value (Kd) of 99mTc STHHYYP-ECGK-TAMRA was estimated to be 130.6 ± 29.2 nM in NCI-H1975 cells. The gamma camera images showed a substantial uptake of 99mTc STHHYYP-ECGK-TAMRA in the NCI-H1975 tumor. The % injected dose/gram of the NCI-H1975 tumor tissue was 2.77 ± 0.70 and 3.48 ± 1.01 at 1 and 3 h, respectively.

CONCLUSION

Specific binding of 99mTc STHHYYP-ECGK-TAMRA to L858R-mutated EGFRpositive NCI-H1975 cells and tumors was demonstrated in in vivo and in vitro studies. The results suggest that 99mTc STHHYYP-ECGK-TAMRA is a good candidate agent for dualmodality imaging targeting EGFR with L858R mutation.

Single domain Camelid antibody fragments for molecular imaging and therapy of cancer

Despite innovations in cancer therapeutics, cancer remains associated with high mortality and is one of biggest health challenges worldwide. Therefore, developing precise cancer imaging and effective treatments is an unmet clinical need. A relatively novel type of therapeutics are heavy chain variable domain antibody fragments (VHHs) derived from llamas. Here, we explored the suitability of VHHs for cancer imaging and therapy through reviewing the existing literature. We searched the MEDLINE, EMBASE and Cochrane databases and identified 32 papers on molecular imaging and 41 papers on therapy that were suitable for comprehensive reviewing. We found that VHHs harbor a higher specificity and affinity compared to mAbs, which contributes to high-quality imaging and less side-effects on healthy cells. The employment of VHHs in cancer imaging showed remarkably shorter times between administration and imaging. Studies showed that 18F and 99mTc are two optimal radionuclides for imaging with VHHs and that site-specific labelling is the optimal conjugation modality for VHHs with radionuclide or fluorescent molecules. We found different solutions for reducing kidney retention and immunogenicity of VHHs. VHHs as anticancer therapeutics have been tested in photodynamic therapy, targeted radionuclide therapy, immunotherapy and molecular targeted therapy. These studies showed that VHHs target unique antigen epitopes, which are distinct from the ones recognized by mAbs. This advantage means that VHHs may be more effective for targeted anticancer therapy and can be combined with mAbs. We found that high cellular internalization and specificity of VHHs contributes to the effectiveness and safety of VHHs as anticancer therapeutics. Two clinical trials have confirmed that VHHs are effective and safe for cancer imaging and therapy. Together, VHHs seem to harbor several advantages compared to mAbs and show potential for application in personalized treatment for cancer patients. VHH-based imaging and therapy are promising options for improving outcomes of cancer patients.

A novel dual-labeled small peptide as a multimodal imaging agent for targeting wild-type EGFR in tumors

The epidermal growth factor receptor (EGFR) is over-expressed in various human cancer. The over-expression of EGFR in tumors is an excellent target for the development of cancer imaging agents. In the present study, we developed Tc-99m SYPIPDT-GHEG-ECG-K-tetramethylrhodamine (SYPIPDT-ECG-TAMRA) as a molecular imaging agent targeting wild-type EFGR (wtEGFR)-positive tumor cells, and verified its feasibility as molecular imaging agent. SYPIPDT-ECG-TAMRA was synthesized using Fmoc solid-phase peptide synthesis. The radiolabeling of SYPIPDT-ECG-TAMRA with Tc-99m was accomplished using ligand exchange via tartrate. Cellular uptake and binding affinity studies were performed. In vivo gamma camera imaging, ex vivo imaging and biodistribution studies were performed using NCI-H460 and SW620 tumor-bearing murine models. After radiolabeling procedures with Tc-99m, Tc-99m SYPIPDT-ECG-TAMRA complexes were prepared at high yield (> 95%). The binding affinity value (K_d) of Tc-99m SYPIPDT-ECG-TAMRA for NCI-H460 cells was estimated to be 76.5 ± 15.8 nM. In gamma camera imaging, the tumor to normal muscle uptake ratios of Tc-99m SYPIPDT-ECG-TAMRA increased with time (2.7 ± 0.6, 4.0 ± 0.9, and 6.2 ± 1.0 at 1, 2, and 3 h, respectively). The percentage injected dose per gram of wet tissue for the NCI-H460 tumor was 1.91 ± 0.11 and 1.70 ± 0.22 at 1 and 3 h, respectively. We developed Tc-99m SYPIPDT-ECG-TAMRA, which is dual-labeled with both radioisotope and fluorescence. In vivo and in vitro studies demonstrated specific uptake of Tc-99m SYPIPDT-ECG-TAMRA into wtEGFR-positive NCI-H460 cells and tumors. Thus, the results of the present study suggest that Tc-99m SYPIPDT-ECG-TAMRA is a potential dual-modality imaging agent targeting wtEGFR.

Chemoradiation therapy using cyclopamine-loaded liquid-lipid nanoparticles and lutetium-177-labeled core-crosslinked polymeric micelles

Cyclopamine (CPA), a potent inhibitor of the Hedgehog pathway, has produced promising anticancer results in a number of preclinical studies. CPA has also been found to enhance tumor response to radiation therapy. However, CPA is water insoluble. A drug delivery system suitable for systemic administration of CPA is needed before CPA can be considered for clinical translation. We hypothesized that CPA solubilized in a liquid-lipid nanoparticle system (CPA-LLP) for intravenous injection would have desirable pharmacokinetic properties and increased anticancer efficacy. We further hypothesized that CPA-LLP would enhance the response of tumor cells to targeted radiotherapy delivered selectively through intratumoral injection of lutetium-177 bound to core-crosslinked polymeric micelles (CCPM-(177)Lu). We tested the combination therapy in 4T1 murine breast cancer and Miapaca-2 human pancreatic adenocarcinoma models. The results showed that CPA-LLP had higher antitumor cytotoxicity than free CPA (IC50 values [mean±SEM]: 2.7±0.2μM vs. 11.3±1.2μM against 4T1 cells; 1.8±0.2 vs. 17.1±1.26μM against Miapaca-2 cells; p<0.0001). In both cell lines, CPA-LLP resulted in significantly lower clonogenicity than free CPA (p<0.05). Moreover, in both cell lines, CPA-LLP significantly enhanced the cell response to CCPM-(177)Lu radiotherapy as measured by clonogenic assay (p<0.05). In 4T1 and Miapaca-2 mouse xenograft models, the combination of CPA-LLP and CCPM-(177)Lu delayed tumor growth more than either monotherapy did alone. In the 4T1 tumor model, tumor size at 16days after treatment was significantly smaller with the combination therapy than with all the other treatments. In the Miapaca-2 model, the combination therapy resulted in the highest rate of mouse survival and prevented tumor relapse. In conclusion, the combination of CPA-LLP and CCPM-(177)Lu was an effective strategy for treating breast and pancreatic cancer and deserves further investigation.

Molecular pathways and molecular imaging in breast cancer: an update

Breast cancer is a heterogenic cancer being characterized by a variability of somatic mutations and in particular by different receptor expressions, such as estrogen, progesterone and human epidermal receptor. These phenotype characteristics play a crucial role in determining tumour response to various chemotherapies and other treatments and in the development of resistance to therapies. Positron emission tomography (PET) as a nuclear medicine technique, has recently demonstrated the advantages in determining the severity of disease and in evaluating the efficacy of treatments in a variety of neoplasm, including breast cancer. Because this procedure is able to pinpoint molecular activity within the body, it offers the potential to identify disease in its earliest stages as well as a patient's immediate response to therapeutic interventions in a non-invasive way. In this paper we performed an extended view about the correlation between molecular factors of breast cancer and PET tracers; in particular, we focalized our attention on their possible advantages in terms of 1) early detection of primary or recurrent cancer; 2) as a guide for target therapies and 3) for the evaluation of response to specific and now-available molecular treatments.

PET imaging of EGF receptors using [18F]FBEM-EGF in a head and neck squamous cell carcinoma model

PURPOSE

To prepare and evaluate a new radiotracer for molecular imaging of cell surface receptors for epidermal growth factor (EGF).

METHODS

Cys-tagged EGF (cEGF) was labeled with (18)F by coupling the free thiol group of the Cys tag with N-[2-(4-[(18)F]fluorobenzamido)ethyl]maleimide ([(18)F]FBEM) to form [(18)F]FBEM-cEGF. Cell uptake, internalization and efflux of [(18)F]FBEM-cEGF were tested in human head and neck squamous carcinoma UM-SCC1 cells. In vivo tumor targeting and pharmacokinetics of the radiotracers were evaluated in UM-SCC1 tumor-bearing athymic nude mice by static and dynamic microPET imaging. Ex vivo biodistribution assays were performed to confirm the noninvasive imaging results.

RESULTS

The radiolabeling yield for [(18)F]FBEM-cEGF was over 60%, based on starting [(18)F]FBEM. [(18)F]FBEM-cEGF exhibited rapid blood clearance through both hepatobiliary and renal excretion. UM-SCC1 tumors were clearly visualized and showed modest tracer uptake of 2.60 ± 0.59 %ID/g at 30 min after injection. Significantly higher tumor uptake of [(18)F]FBEM-cEGF (5.99 ± 1.61%ID/g at 30 min after injection, p < 0.01) and tumor/nontumor ratio were achieved by coinjection of 50 μg of unlabeled EGF. Decreased liver uptake of [(18)F]FBEM-cEGF was observed when unlabeled EGF was coadministered.

CONCLUSION

With optimized liver blocking, [(18)F]FBEM-cEGF has the potential to be used in a noninvasive and quantitative manner for detection of malignant lesions and evaluation of EGFR activity.

SPECT imaging with 99mTc-labeled EGFR-specific nanobody for in vivo monitoring of EGFR expression

PURPOSE

Overexpression of the epidermal growth factor receptor (EGFR) occurs with high incidence in various carcinomas. The oncogenic expression of the receptor has been exploited for immunoglobulin-based diagnostics and therapeutics. We describe the use of a llama single-domain antibody fragment, termed Nanobody, for the in vivo radioimmunodetection of EGFR overexpressing tumors using single photon emission computed tomography (SPECT) in mice.

METHODS

Fluorescence-activated cell sorting (FACS) analysis was performed to evaluate the specificity and selectivity of 8B6 Nanobody to bind EGFR on EGFR overexpressing cells. The Nanobody was then labeled with (99m)Tc via its C-terminal histidine tail. Uptake in normal organs and tissues was assessed by ex vivo analysis. In vivo tumor targeting of (99m)Tc-8B6 Nanobody was evaluated via pinhole SPECT in mice bearing xenografts of tumor cells with either high (A431) or moderate (DU145) overexpression of EGFR.

RESULTS

FACS analysis indicated that the 8B6 Nanobody only recognizes cells overexpressing EGFR. In vivo blood clearance of (99m)Tc-8B6 Nanobody is relatively fast (half-life, 1.5 h) and mainly via the kidneys. At 3 h postinjection, total kidney accumulation is high (46.6+/-0.9%IA) compared to total liver uptake (18.9+/-0.6%IA). Pinhole SPECT imaging of mice bearing A431 xenografts showed higher average tumor uptake (5.2+/-0.5%IA/cm(3)) of (99m)Tc-8B6 Nanobody compared to DU145 xenografts (1.8+/-0.3%IA/cm(3), p<0.001).

CONCLUSION

The EGFR-binding Nanobody investigated in this study shows high specificity and selectivity towards EGFR overexpressing cells. Pinhole SPECT analysis with (99m)Tc-8B6 Nanobody enabled in vivo discrimination between tumors with high and moderate EGFR overexpression. The favorable biodistribution further corroborates the suitability of Nanobodies for in vivo tumor imaging.

Planning for intracavitary anti-EGFR radionuclide therapy of gliomas. Literature review and data on EGFR expression

Targeting with radionuclide labelled substances that bind specifically to the epidermal growth factor receptor, EGFR, is considered for intracavitary therapy of EGFR-positive glioblastoma multiforme, GBM. Relevant literature is reviewed and examples of EGFR expression in GBM are given. The therapeutical efforts made so far using intracavitary anti-tenascin radionuclide therapy of GBM have given limited effects, probably due to low radiation doses to the migrating glioma cells in the brain. Low radiation doses might be due to limited penetration of the targeting agents or heterogeneity in the expression of the target structure. In this article we focus on the possibilities to target EGFR on the tumour cells instead of an extracellular matrix component. There seems to be a lack of knowledge on the degree of intratumoral variation of EGFR expression in GBM, although the expression seemed rather homogeneous over large areas in most of the examples (n=16) presented from our laboratory. The observed homogeneity was surprising considering the genomic instability and heterogeneity that generally characterises highly malignant tumours. However, overexpression of EGFR is, at least in primary GBMs, one of the steps in the development of malignancy, and tumour cells that lose or downregulate EGFR will probably be outgrown in an expanding tumour cell population. Thus, loss of EGFR expression might not be the critical factor for successful intracavitary radionuclide therapy. Instead, it is likely that the penetration properties of the targeting agents are critical, and detailed studies on this are urgent.

Angiogenesis in gliomas: imaging and experimental therapeutics

Much of the interest in angiogenesis and hypoxia has led to investigating diagnostic imaging methodologies and developing efficacious agents against angiogenesis in gliomas. In many ways, because of the cytostatic effects of these agents on tumor growth and tumor-associated endothelial cells, the effects of therapy are not immediately evident. Hence finding clinically applicable imaging tools and pathologic surrogate markers is an important step in translating glioma biology to therapeutics. There are a variety of strategies in the approach to experimental therapeutics that target the hypoxia-inducible factor pathway, the endogenous antiangiogenic and proangiogenic factors and their receptors, adhesion molecules, matrix proteases and cytokines, and the existing vasculature. We discuss the rationale for antiangiogenesis as a treatment strategy, the preclinical and clinical assessment of antiangiogenic interventions and finally focus on the various treatment strategies, including combining antiangiogenic drugs with radiation and chemotherapy.