Radiolabeling of trastuzumab with 177Lu via DOTA, a new radiopharmaceutical for radioimmunotherapy of breast cancer

In Vitro Assessment of 177Lu-Labeled Trastuzumab-Targeted Mesoporous Carbon@Silica Nanostructure for the Treatment of HER2-Positive Breast Cancer

This study assessed the effectiveness of a trastuzumab-targeted 177Lu-labeled mesoporous Carbon@Silica nanostructure (DOTA@TRA/MC@Si) for HER2-positive breast cancer treatment, focusing on its uptake, internalization, and efflux in breast cancer cells. The synthesized PEI-MC@Si nanocomposite was reacted with DOTA-NHS-ester, confirmed by the Arsenazo(III) assay. Following this, TRA was conjugated to the DOTA@PEI-MC@Si for targeting. DOTA@PEI-MC@Si and DOTA@TRA/MC@Si nanocomposites were labeled with 177Lu, and their efficacy was evaluated through in vitro radiolabeling experiments. According to the results, the DOTA@TRA/MC@Si nanocomposite was successfully labeled with 177Lu, yielding a radiochemical yield of 93.0 ± 2.4%. In vitro studies revealed a higher uptake of the [177Lu]Lu-DOTA@TRA/MC@Si nanocomposite in HER2-positive SK-BR-3 cells (44.0 ± 4.6% after 24 h) compared to MDA-MB-231 cells (21.0 ± 2.3%). The IC50 values for TRA-dependent uptake in the SK-BR-3 and BT-474 cells were 0.9 µM and 1.3 µM, respectively, indicating affinity toward HER-2 receptor-expressing cells. The lipophilic distribution coefficients of the radiolabeled nanocomposites were determined to be 1.7 ± 0.3 for [177Lu]Lu-DOTA@TRA/MC@Si and 1.5 ± 0.2 for [177Lu]Lu-DOTA@PEI-MC@Si, suggesting sufficient passive transport through the cell membrane and increased accumulation in target tissues. The [177Lu]Lu-DOTA@TRA/MC@Si nanocomposite showed an uptake into HER2-positive cell lines, marking a valuable step toward the development of a nanoparticle-based therapeutic agent for an improved treatment strategy for HER2-positive breast cancer.

Formulation of patient dose of [177Lu]Lu-Trastuzumab using in-house developed freeze-dried kit: A path forward for clinical translation

Trastuzumab is a US-FDA-approved humanized monoclonal antibody used for the treatment of human epidermal growth factor receptor 2 (HER2)-positive breast cancer. The aim of the present work is to optimize a freeze-dried formulation of DOTA-Trastuzumab conjugate for the preparation of patient doses of [177Lu]Lu-Trastuzumab for radioimmunotherapy of breast cancer. The formulation of [177Lu]Lu-Trastuzumab usually takes a long time, and thus, such a process is not suitable for the routine preparation of this agent in hospital radiopharmacies. To circumvent this, a pre-synthesized DOTA-Trastuzumab conjugate as a freeze-dried formulation is proposed. In the present work, DOTA-Trastuzumab conjugate was subjected to a freeze-drying process after the addition of optimized amounts of radioprotectant and cryoprotectant. [177Lu]Lu-DOTA-Trastuzumab was prepared by incubating the lyophilized powder of the kit vial with medium-specific activity 177LuCl3. The final radiochemical purity of [177Lu]Lu-DOTA-Trastuzumab, prepared using freeze-dried kit, was determined to be >95%. To ascertain the reproducibility of the procedure, six consecutive batches of the freeze-dried formulation were prepared, radiolabeled, and evaluated by carrying out both in vitro and ex vivo studies. The consistency of the results of all the six consecutive batches confirmed the robustness and utility of the in-house optimized freeze-dried formulation for the preparation of patient doses of [177Lu]Lu-Trastuzumab at hospital radiopharmacies.

Development of Novel Trifunctional Chelating Agents That Enhance Tumor Retention of Radioimmunoconjugates

Chelator-containing radioimmunoconjugates (RICs) composed of monoclonal antibodies, chelators, and radiometals exhibit broad potential for cancer diagnosis or therapy. In this study, we developed novel trifunctional chelating agents that enhance the tumor retention of RICs, MDPEI2, and MDPEI4, which contain the metal chelator DOTA, a maleimide moiety, and diethylenetriamine (PEI2) or tetraethylenepentamine (PEI4), respectively, as a poly(ethylenimine) (PEI) scaffold for the addition of positive charges to the radiometabolites of RICs to reduce their release from tumor cells. Trastuzumab radiolabeled by [111In]In-MDPEI2 ([111In]In-TMDPEI2) or [111In]In-MDPEI4 ([111In]In-TMDPEI4) showed high immunoreactivity and lower rates of exportations of their radiometabolites from tumor cells than RICs without PEI scaffolds. The tumor uptake of [111In]In-TMDPEI2 and [111In]In-TMDPEI4 was enhanced compared with RICs without PEI scaffolds, and [111In]In-TMDPEI2 exhibited the highest tumor/blood ratio. These results indicate the utility of MDPEI2 to synthesize RICs with favorable tumor-targeting properties in vivo by controlling the radioactivity distribution in tumor cells.

PET/CT and SPECT/CT Imaging of HER2-Positive Breast Cancer

HER2 (Human Epidermal Growth Factor Receptor 2)-positive breast cancer is characterized by amplification of the HER2 gene and is associated with more aggressive tumor growth, increased risk of metastasis, and poorer prognosis when compared to other subtypes of breast cancer. HER2 expression is therefore a critical tumor feature that can be used to diagnose and treat breast cancer. Moving forward, advances in HER2 in vivo imaging, involving the use of techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT), may allow for a greater role for HER2 status in guiding the management of breast cancer patients. This will apply both to patients who are HER2-positive and those who have limited-to-minimal immunohistochemical HER2 expression (HER2-low), with imaging ultimately helping clinicians determine the size and location of tumors. Additionally, PET and SPECT could help evaluate effectiveness of HER2-targeted therapies, such as trastuzumab or pertuzumab for HER2-positive cancers, and specially modified antibody drug conjugates (ADC), such as trastuzumab-deruxtecan, for HER2-low variants. This review will explore the current and future role of HER2 imaging in personalizing the care of patients diagnosed with breast cancer.

Homodimer 99mTc-HYNIC-E(SSSLTVPWY)2 peptide improved HER2-overexpressed tumor targeting and imaging

We hypothesized that a novel design of the LTVPWY (LY) peptide might exhibit a great potential for improving binding affinity and targeting HER2-overexpressed tumors. Hence, new dimer construction of ^99mTc-labeled LY [^99mTc-HYNIC-E(SSSLTVPWY)₂] (^99mTc-DLY) was introduced. Afterward, a head-to-head comparison of in vitro and in vivo experiments was performed between ^99mTc-DLY and ^99mTc-HYNIC-SSSLTVPWY as the monomer analog. The blocking dosage of trastuzumab reduced the uptake of the dimer about 20% more efficiently than the monomer in the SKOV-3 cell line. A twofold increase in competitive binding affinity and biological half-life was observed for ^99mTc-DLY. The ovarian-tumor-bearing mice were detected with high contrast where the tumor-to-muscle ratio of ^99mTc-DLY was notably increased about 40% using a gamma camera. The biodistribution experiment revealed an approximately 10% enhancement in tumor/blood, tumor/muscle, and tumor/bone ratios for the dimer. More rapid blood clearance was another achievement of the homodimer design. Overall, ^99mTc-DLY successfully affected the pharmacokinetics and consequently the visualization of HER2-overexpressing tumors.

Template directed synthesis of antibody Fc conjugates with concomitant ligand release

Antibodies are an attractive therapeutic modality for cancer treatment as they allow the increase of the treatment response rate and avoid the severe side effects of chemotherapy. Notwithstanding the strong benefit of antibodies, the efficacy of anti-cancer antibodies can dramatically vary among patients and ultimately result in no response to the treatment. Here, we have developed a novel means to regioselectively label the Fc domain of any therapeutic antibody with a radionuclide chelator in a single step chemistry, with the aim to study by SPECT/CT imaging if the radiolabeled antibody is capable of targeting cancer cells in vivo. A Fc-III peptide was used as bait to bring a carbonate electrophilic site linked to a metal chelator and to a carboxyphenyl leaving group in close proximity with an antibody Fc nucleophile amino acid (K317), thereby triggering the covalent linkage of the chelator to the antibody lysine, with the concomitant release of the carboxyphenyl Fc-III ligand. Using CHX-A′′-DTPA, we radiolabeled trastuzumab with indium-111 and showed in biodistribution and imaging experiments that the antibody accumulated successfully in the SK-OV-3 xenograft tumour implanted in mice. We found that our methodology leads to homogeneous conjugation of CHX-A′′-DTPA to the antibody, and confirmed that the Fc domain can be selectively labeled at K317, with a minor level of unspecific labeling on the Fab domain. The present method can be developed as a clinical diagnostic tool to predict the success of the therapy. Furthermore, our Fc-III one step chemistry concept paves the way to a broad array of other applications in antibody bioengineering.

A method is reported to attach a radionuclide chelator in a single step chemistry to the Fc domain of any therapeutic antibody.

Analysis of absorbed dose in radioimmunotherapy with 177Lu-trastuzumab using two different imaging scenarios: a pilot study

OBJECTIVES

Internal organ dosimetry is an important procedure to demonstrate the reliable application of 177Lu-trastuzumab radioimmunotherapy for human epidermal growth factor receptor-positive metastatic breast cancers. We are reporting the first human dosimetry study for 177Lu-trastuzumab. Another objective of our study was to calculate and compare the absorbed doses for normal organs and tumor lesions in patients before radioimmunotherapy with 177Lu-trastuzumab using two different imaging scenarios.

METHODS

Eleven patients (48.27 ± 8.95 years) with a history of metastatic breast cancer were included in the study. Postadministration of 177Lu-trastuzumab (351.09 ± 23.89 MBq/2 mg), acquisition was performed using planar and hybrid imaging scenarios at 4, 24, 72 and 168 h. Single-photon emission computed tomography/computed tomography imaging was performed at 72 h postinjection. Acquired images were processed using Dosimetry Toolkit software for the estimation of normalized cumulated activity in organs and tumor lesions. OLINDA/EXM 2.0 software was used for absorbed dose calculation in both scenarios.

RESULTS

Significant difference in normalized cumulated activity and the absorbed dose is noted between two imaging scenarios for the organs and tumor lesions (P < 0.05). Mean absorbed dose (mGy/MBq) estimated from heart, lungs, liver, spleen, kidney, adrenal, pancreas and colon using planar and hybrid scenarios were 0.81 ± 0.19 and 0.63 ± 0.17; 0.75 ± 0.13 and 0.32 ± 0.06; 1.26 ± 0.25 and 1.01 ± 0.17; 0.68 ± 0.22 and 0.53 ± 0.16; 0.91 ± 0.3 and 0.69 ± 0.24; 0.18 ± 0.04 and 0.11 ± 0.02; 0.25 ± 0.22 and 0.09 ± 0.02 and 0.75 ± 0.61 and 0.44 ± 0.28, respectively.

CONCLUSIONS

On the basis of our dosimetric evaluation, we concluded that radioimmunotherapy with 177Lu-trastuzumab is well tolerated to be implemented in routine clinical practice against HER2 positive metastatic breast cancer. Liver is the main critical organ at risk. Hybrid scenario demonstrated significantly lower absorbed doses in organs and tumors compared to the multiplanar method.

Radioimmunotheranostic Pair Based on the Anti-HER2 Monoclonal Antibody: Influence of Chelating Agents and Radionuclides on Biological Properties

The oncogene HER2 is an important molecular target in oncology because it is associated with aggressive disease and the worst prognosis. The development of non-invasive imaging techniques and target therapies using monoclonal antibodies is a rapidly developing field. Thus, this work proposes the study of the radioimmunotheranostic pair, [111In]In-DTPA-trastuzumab and [177Lu]Lu-DOTA-trastuzumab, evaluating the influence of the chelating agents and radionuclides on the biological properties of the radioimmunoconjugates (RICs). The trastuzumab was immunoconjugated with the chelators DTPA and DOTA and radiolabeled with [111In]InCl3 and [177Lu]LuCl3, respectively. The stability of the RICs was evaluated in serum, and the immunoreactive and internalization fractions were determined in SK-BR-3 breast cancer cells. The in vivo pharmacokinetics and dosimetry quantification and the ex vivo biodistribution were performed in normal and SK-BR-3 tumor-bearing mice. The data showed that there was no influence of the chelating agents and radionuclides on the immunoreactive and internalization fractions of RICs. In contrast, they influenced the stability of RICs in serum, as well as the pharmacokinetics, dosimetry and biodistribution profiles. Therefore, the results showed that the nature of the chelating agent and radionuclide could influence the biological properties of the radioimmunotheranostic pair.

Site-specific radioiodination of an anti-HER2 single domain antibody fragment with a residualizing prosthetic agent

INTRODUCTION

As a consequence of their small size, high stability and high affinity, single domain antibody fragments (sdAbs) are appealing targeting vectors for radiopharmaceutical development. With sdAbs binding to internalizing receptors like HER2, residualizing prosthetic agents can enhance tumor retention of radioiodine, which until now has been done with random labeling approaches. Herein we evaluate a site-specific strategy utilizing a radioiodinated, residualizing maleimido moiety and the anti-HER2 sdAb 5F7 bearing a GGC tail for conjugation.

METHODS

Maleimidoethyl 3-(guanidinomethyl)-5-iodobenzoate ([131I]MEGMB) and its N-succinimidyl ester analogue, iso-[125I]SGMIB, were labeled by halodestannylation and conjugated with 5F7GGC and 5F7, respectively. Radiochemical purity, immunoreactivity and binding affinity were determined. Paired-label experiments directly compared iso-[125I]SGMIB-5F7 and [131I]MEGMIB-5F7GGC with regard to internalization/residualization and affinity on HER2-expressing SKOV-3 ovarian carcinoma cells as well as biodistribution and metabolite distribution in athymic mice with subcutaneous SKOV-3 xenografts.

RESULTS

[131I]MEGMIB-5F7GGC had an immunoreactivity of 81.3% and Kd = 0.94 ± 0.27 nM. Internalization assays demonstrated high intracellular trapping for both conjugates, For example, at 1 h, intracellular retention was 50.30 ± 3.36% for [131I]MEGMIB-5F7GGC and 55.95 ± 3.27% for iso-[125I]SGMIB-5F7, while higher retention was seen for iso-[125I]SGMIB-5F7 at later time points. Peak tumor uptake was similar for both conjugates (8.35 ± 2.66%ID/g and 8.43 ± 2.84%ID/g for iso-[125I]SGMIB-5F7 and [131I]MEGMIB-5F7GGC at 1 h, respectively); however, more rapid normal tissue clearance was seen for [131I]MEGMIB-5F7GGC, with a 2-fold higher tumor-to-kidney ratio and a 3-fold higher tumor-to-liver ratio compared with co-injected iso-[125I]SGMIB-5F7. Consisted with this, generation of labeled catabolites in the kidneys was higher for [131I]MEGMIB-5F7GGC.

CONCLUSION

[131I]MEGMIB-5F7GGC offers similar tumor targeting as iso-[125I]SGMIB-5F7 but with generally lower normal tissue uptake.

ADVANCES IN KNOWLEDGE AND IMPLICATION FOR PATIENT CARE

The site specific nature of the [131I]MEGMIB reagent may facilitate clinical translation, particularly for sdAb with compromised affinity after random labeling.

Introduction of an Aldehyde Handle on Nanobodies by Affinity-Guided Labeling

Chemically modified antigen-binding proteins are widely applied for their targeting abilities in the fields of biotechnology, medicine, and diagnostics. However, the production of site-selectively modified proteins remains a challenge. Here, we have designed a chemical probe for the introduction of a reactive aldehyde on nanobodies by metal-complex-guided conjugation. The probe design allows for purification of the conjugates, and the aldehyde constitutes an efficient handle for further modification of the nanobodies. In vitro experiments confirmed the binding activity and selectivity of fluorescent conjugates toward the native antigen. Furthermore, the modification strategy allowed for production of a nanobody-drug conjugate that was active in vitro.

Comparative In Vitro Cytotoxicity Studies of 177Lu-CHX-A″-DTPA-Trastuzumab and 177Lu-CHX-A″-DTPA-F(ab')2-Trastuzumab in HER2-Positive Cancer Cell Lines

Background: Human epidermal growth factor receptor 2 (HER2) is found to be amplified in ∼15%-20% of breast cancers. In this study, the authors report the synthesis and comparative in vitro therapeutic efficacy of ¹⁷⁷Lu-CHX-A″-DTPA-trastuzumab and ¹⁷⁷Lu-CHX-A″-DTPA-F(ab')₂-trastuzumab to determine their potential as theranostic agents for patients with breast cancer. Materials and Methods: Bivalent F(ab')₂-trastuzumab was produced by enzymatic digestion of trastuzumab, conjugated with p-SCN-Bn-CHX-A″-DTPA and subsequently radiolabeled with ¹⁷⁷Lu. Cell viability, membrane toxicity assays, and apoptosis analysis were carried out with ¹⁷⁷Lu-CHX-A″-DTPA-trastuzumab and ¹⁷⁷Lu-CHX-A″-DTPA-F(ab')₂-trastuzumab in HER2-positive ovarian (SK-OV-3) and breast cancer (SK-BR-3 and MDA-MB-453) cells. Results: In vitro cell binding studies showed ∼20%-25% binding of ¹⁷⁷Lu-CHX-A″-DTPA-trastuzumab and ¹⁷⁷Lu-CHX-A″-DTPA-F(ab')₂-trastuzumab to SK-OV-3, SK-BR-3, and MDA-MB-453 cells. The cells exhibited similar degree of membrane integrity and cellular toxicity when treated with same amount (activity) of ¹⁷⁷Lu-CHX-A″-DTPA-F(ab')₂-trastuzumab and ¹⁷⁷Lu-CHX-A″-DTPA-trastuzumab, and the toxicity was dose dependent. The mode of cell death was predominantly by apoptosis and necrosis with both the radioimmunoconjugates. Conclusions: The results indicated that the efficacy of both the radioimmunoconjugates, in terms of inducing cell death, was similar thereby ascertaining their potential as good therapeutic agents for patients with breast cancer.

Preparation of 177Lu-Trastuzumab injection for treatment of breast cancer

The objective of this study was the facile preparation of ¹⁷⁷Lu-CHX-A''-DTPA-Trastuzumab injection for breast cancer therapy. Trastuzumab conjugated with CHX-A''-DTPA-NCS was radiolabeled with ¹⁷⁷Lu in >95% radiochemical purity. In vitro studies in SKBR3 and MDA-MB-453 cells confirmed specificity of ¹⁷⁷Lu-CHX-A''-DTPA-Trastuzumab to HER2 positive cells. The radioimmunoconjugate showed good immunoreactivity, in vitro stability in saline and K_d of 1.01 ± 0.13 nM in SKBR3 cells. Clearance of ¹⁷⁷Lu-CHX-A''-DTPA-Trastuzumab in Swiss mice was predominantly through the hepatobiliary route with minimal bone uptake.

Imidazole carbamate probes for affinity guided azide-transfer to metal-binding proteins

Probes for affinity guided conjugation have shown great promise for the preparation of high-quality protein conjugates.

Targeting HER2 in Nuclear Medicine for Imaging and Therapy

Since its discovery, the human epidermal growth factor 2 (HER2) has been extensively studied. Presently, there are 2 standard diagnostic techniques to assess HER2 status in biopsies: immunohistochemistry and fluorescence in situ hybridization. While these techniques have played an important role in the treatment of patients with HER2-positive cancer, they both require invasive biopsies for analysis. Moreover, the expression of HER2 is heterogeneous in breast cancer and can change over the course of the disease. Thus, the degree of HER2 expression in the small sample size of biopsied tumors at the time of analysis may not represent the overall status of HER2 expression in the whole tumor and in between tumor foci in the metastatic setting as the disease progresses. Unlike biopsy, molecular imaging using probes against HER2 allows for a noninvasive, whole-body assessment of HER2 status in real time. This technique could potentially select patients who may benefit from HER2-directed therapy and offer alternative treatments to those who may not benefit. Several antibodies and small molecules against HER2 have been labeled with different radioisotopes for nuclear imaging and/or therapy. This review presents the most recent advances in HER2 targeting in nuclear medicine focusing on preclinical and clinical studies.

MANOTA: a promising bifunctional chelating agent for copper-64 immunoPET

A comparison of four bifunctional chelating agents showed superior behaviour of a new NOTA derivative for ⁶⁴Cu labelling of antibody fragments.

Preparation and preclinical evaluation of 131 I-trastuzumab for breast cancer

Trastuzumab that targets the human epidermal growth factor receptor type 2 (HER2) is known to benefit patients with HER2+ metastatic breast cancer. The objective was to explore the potential of ¹³¹ I-trastuzumab for treatment of breast cancers. Radioiodination of trastuzumab was carried out by chloramine-T method, purified by using PD-10 column, and characterized by size exclusion high-performance liquid chromatography on a gel column. In vitro studies were carried out in HER2+ cells to determine the specificity of the radioimmunoconjugate. Uptake and retention of ¹³¹ I-trastuzumab were determined by biodistribution studies in tumor-bearing non-obese diabetic/severe combined immunodeficiency and normal severe combined immunodeficiency mice. The radiochemical purity (RCP) of ¹³¹ I-trastuzumab was 98 ± 0.4% with retention time of 17 minutes by high-performance liquid chromatography. In vitro stability studies exhibited RCP of more than 90% in serum at 37°C after 120 hours of radioiodination. In vitro cell binding with ¹³¹ I-trastuzumab in HER2+ cells showed binding of 28% to 35% which was inhibited significantly, with unlabeled trastuzumab confirming its specificity. K_d value of ¹³¹ I-trastuzumab was 0.5 nM, while its immunoreactivity was more than 80%. Uptake of more than 12% and retention were observed in the tumors up to 120 hours p.i. ¹³¹ I-trastuzumab prepared in-house-exhibited RCP of more than 98%, excellent immunoreactivity, affinity to HER2+ cell lines and good tumor uptake thereby indicating its potential for further evaluation in HER2+ breast cancers.

Imaging Diagnostic and Therapeutic Targets: Human Epidermal Growth Factor Receptor 2

Since the approval of trastuzumab, a humanized monoclonal antibody against the extracellular domain of human epidermal growth factor receptor 2 (HER2), 3 other HER2-targeting agents have gained regulatory approval: lapatinib, pertuzumab, and trastuzumab-emtansine. These agents have revolutionized the management of HER2-positive breast cancer, highlighting the concept that targeted therapies are successful when patients exhibit tumor-selective expression of a molecular target-in this case, HER2. However, response prediction and innate or acquired resistance remain serious concerns. Predictive biomarkers of a response-which could help in the selection of patients who might benefit from a selected targeted therapy-are currently lacking. Molecular imaging with anti-HER2 probes allows the noninvasive, whole-body assessment of HER2 tumor burden and has the potential to improve patient selection, optimize the dose and schedule, and rationalize assessment of the response to anti-HER2 therapies. Furthermore, unlike biopsy-based HER2 assessment, this approach can reveal inter- or intratumoral heterogeneity as well as variations in HER2 expression over time. This review summarizes the available literature and the current status of molecular imaging as a tool for the assessment of HER2 (target) expression or the prediction of an early treatment response in early and advanced HER2-positive breast cancer.

The interaction of NOTA as a bifunctional chelator with competitive alkali metal ions: a DFT study

This work investigates NOTA–alkali metal (Li⁺, Na⁺ and K⁺ and Rb⁺) complexation using density functional theory.

Activity estimation in radioimmunotherapy using magnetic nanoparticles

OBJECTIVE

Estimation of activity accumulated in tumor and organs is very important in predicting the response of radiopharmaceuticals treatment. In this study, we synthesized (177)Lutetium ((177)Lu)-trastuzumab-iron oxide nanoparticles as a double radiopharmaceutical agent for treatment and better estimation of organ activity in a new way by magnetic resonance imaging (MRI).

METHODS

(177)Lu-trastuzumab-iron oxide nanoparticles were synthesized and all the quality control tests such as labeling yield, nanoparticle size determination, stability in buffer and blood serum up to 4 d, immunoreactivity and biodistribution in normal mice were determined. In mice bearing breast tumor, liver and tumor activities were calculated with three methods: single photon emission computed tomography (SPECT), MRI and organ extraction, which were compared with each other.

RESULTS

The good results of quality control tests (labeling yield: 61%±2%, mean nanoparticle hydrodynamic size: 41±15 nm, stability in buffer: 86%±5%, stability in blood serum: 80%±3%, immunoreactivity: 80%±2%) indicated that (177)Lu-trastuzumab-iron oxide nanoparticles could be used as a double radiopharmaceutical agent in mice bearing tumor. Results showed that (177)Lu-trastuzumab-iron oxide nanoparticles with MRI had the ability to measure organ activities more accurate than SPECT.

CONCLUSIONS

Co-conjugating radiopharmaceutical to MRI contrast agents such as iron oxide nanoparticles may be a good way for better dosimetry in nuclear medicine treatment.

[(64) Cu]-labelled trastuzumab: optimisation of labelling by DOTA and NODAGA conjugation and initial evaluation in mice

The human epidermal growth factor receptor‐2 (HER2) is overexpressed in 20–30% of all breast cancer cases, leading to increased cell proliferation, growth and migration. The monoclonal antibody, trastuzumab, binds to HER2 and is used for treatment of HER2‐positive breast cancer. Trastuzumab has previously been labelled with copper‐64 by conjugation of a 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA) chelator. The aim of this study was to optimise the ⁶⁴Cu‐labelling of DOTA‐trastuzumab and as the first to produce and compare with its 1,4,7‐triazacyclononane, 1‐glutaric acid‐5,7 acetic acid (NODAGA) analogue in a preliminary HER2 tumour mouse model. The chelators were conjugated to trastuzumab using the activated esters DOTA mono‐N‐hydroxysuccinimide (NHS) and NODAGA‐NHS. ⁶⁴Cu‐labelling of DOTA‐trastuzumab was studied by varying the amount of DOTA‐trastuzumab used, reaction temperature and time. Full ⁶⁴Cu incorporation could be achieved using a minimum of 10‐µg DOTA‐trastuzumab, but the fastest labelling was obtained after 15 min at room temperature using 25 µg of DOTA‐trastuzumab. In comparison, 80% incorporation was achieved for ⁶⁴Cu‐labelling of NODAGA‐trastuzumab. Both [⁶⁴Cu]DOTA‐trastuzumab and [⁶⁴Cu]NODAGA‐trastuzumab were produced after purification with radiochemical purities of >97%. The tracers were injected into mice with HER2 expressing tumours. The mice were imaged by positron emission tomography and showed high tumour uptake of 3–9% ID/g for both tracers.

Production of (177)Lu for Targeted Radionuclide Therapy: Available Options

BACKGROUND

This review provides a comprehensive summary of the production of (177)Lu to meet expected future research and clinical demands. Availability of options represents the cornerstone for sustainable growth for the routine production of adequate activity levels of (177)Lu having the required quality for preparation of a variety of (177)Lu-labeled radiopharmaceuticals. The tremendous prospects associated with production of (177)Lu for use in targeted radionuclide therapy (TRT) dictate that a holistic consideration should evaluate all governing factors that determine its success.

METHODS

While both "direct" and "indirect" reactor production routes offer the possibility for sustainable (177)Lu availability, there are several issues and challenges that must be considered to realize the full potential of these production strategies.

RESULTS

This article presents a mini review on the latest developments, current status, key challenges and possibilities for the near future.

CONCLUSION

A broad understanding and discussion of the issues associated with (177)Lu production and processing approaches would not only ensure sustained growth and future expansion for the availability and use of (177)Lu-labeled radiopharmaceuticals, but also help future developments.

Demonstration of dose dependent cytotoxic activity in SW480 colon cancer cells by ¹⁷⁷Lu-labeled siRNA targeting IGF-1R

PURPOSE

The radiolabeling of targeting biomolecules with gamma emitter radionuclides for tracing and beta emitters for therapy involves the conjugation of such biomolecules to the chelating agents to form complexes with the radionuclide of interest. In this study, radioconjugate of IGF-1R siRNA with lutetium-177 ((177)Lu) was produced, and the anti-proliferation and apoptosis effects elicited by this (177)Lu-siRNA complex in the SW480 colon cancer cells were evaluated.

METHODS

IGF-1R and Luciferase siRNAs were conjugated with p-SCN-Bn-DTPA, and then radiolabeled with (177)Lu. The effects of labeled and non-labeled IGF-1R siRNAs on IGF-1R expression were assessed with RT-PCR analysis and ELISA assay. IGF-1R siRNAs induced cell death and apoptosis were investigated using MTT assay and Annexin-V/propidium iodide (PI) double staining, respectively.

RESULTS

Combined purification using Vivaspin and PD-10 columns resulted in a radiochemical purity of 97.32% ± 1.97%. Knockdown effect of the labeled IGF-1R siRNA was not significantly different from the non-labeled duplex of the same sequence (P<0.05), but it was significant compared to the Luciferase siRNAs (P<0.001). Proliferation decreased significantly, but apoptosis increased in the cells treated with the (177)Lu-IGF-1R siRNA in comparison with either (177)Lu or IGF-1R siRNA (P<0.001).

CONCLUSION

Radioconjugate of IGF-1R siRNA, p-SCN-Bn-DTPA and (177)Lu was successfully produced and characterized as radiopharmaceutical. The present study demonstrates the involvement of (177)Lu-labeled IGF-1R siRNA in the inhibition of cell growth and induction of apoptosis in colon cancer cells.

Radioimmunotherapy with ¹³¹I-bevacizumab as a specific molecule for cells with overexpression of the vascular endothelial growth factor

Bevacizumab is a humanized monoclonal antibody that inhibits vascular endothelial growth factor A and is used for the treatment of several cancers. We labeled this monoclonal antibody with Iodine-131 (¹³¹I) and performed in vitro quality control and tumor cell growth inhibition tests. Bevacizumab was labeled with ¹³¹I using chloramine T. Radiochemical purity and stability in phosphate-buffered saline and human blood serum were determined using thin-layer chromatography and radio-sodium dodecyl sulfate-polyacrylamide gel electrophoresis, respectively, performed at different times. Cell-specific binding, internalization, and toxicity of the radiolabeled antibody were tested using the SKOV-3 ovarian cancer cell line. The biodistribution of ¹³¹I-bevacizumab was investigated using male mice. The radiochemical purity of the complex was 99% ± 0.7%. Its stability in phosphate-buffered saline and human blood serum at 48 hours postpreparation was 78% ± 1.2% and 93% ± 0.6%, respectively. (131)I-bevacizumab was significantly bound to SKOV-3. The internalization of ¹³¹I-bevacizumab was time dependent, and it was cleared from the blood after 24 hours. Significant reductions in SKOV-3 cell viability were achieved with (131)I-bevacizumab at a concentration of 500 nM. A low accumulation of ¹³¹I-bevacizumab was observed in the stomach and salivary glands after 24 hours and 48 hours. These findings indicate that the new radiolabeled antibody should be further evaluated in animals and, possibly, in humans as a new radiopharmaceutical agent for use in radioimmunotherapy for ovarian cancer.

DOTAGA-trastuzumab. A new antibody conjugate targeting HER2/Neu antigen for diagnostic purposes

Improved bifunctional chelating agents (BFC) are required for indium-111 radiolabeling of monoclonal antibodies (mAbs) under mild conditions to yield stable, target-specific agents. 2,2',2"-(10-(2,6-Dioxotetrahydro-2H-pyran-3-yl)-1,4,7,10-tetraazacyclododecane-1,4,7-triyl)triacetic acid (DOTAGA-anhydride) was evaluated for mAb conjugation and labeling with indium-111. The DOTA analogue was synthesized and conjugated to trastuzumab-which targets the HER2/neu receptor-in mild conditions (PBS pH 7.4, 25 °C, 30 min) and gave a mean degree of conjugation of 2.6 macrocycle per antibody. Labeling of this immunoconjugate with indium-111 was performed in 75% yield after 1 h at 37 °C, and the proportion of (111)In-DOTAGA-trastuzumab reached 97% after purification. The affinity of DOTAGA-trastuzumab was 5.5 ± 0.6 nM as evaluated by in vitro saturation assays using HCC1954 breast cancer cell line. SPECT/CT imaging and biodistribution studies were performed in mice bearing breast cancer BT-474 xenografts. BT-474 tumors were clearly visualized on SPECT images at 24, 48, and 72 h postinjection. The tumor uptake of [(111)In-DOTAGA]-trastuzumab reached 65%ID/g 72 h postinjection. These results show that the DOTAGA BFC appears to be a valuable tool for biologics conjugation.

Pre-Clinical Assessment of Lu-Labeled Trastuzumab Targeting HER2 for Treatment and Management of Cancer Patients with Disseminated Intraperitoneal Disease

Studies from this laboratory have demonstrated the potential of targeting HER2 for therapeutic and imaging applications with medically relevant radionuclides. To expand the repertoire of trastuzumab as a radioimmunoconjugate (RIC) vector, use of (177)Lu was investigated. The combination of a 6.7 d half-life, lower energy β(-)-emissions (500 keV max; 130 keV ave), and an imagable γ-emission make (177)Lu an attractive candidate for radioimmunotherapy (RIT) regimens for treatment of larger tumor burdens not possible with α-zparticle radiation. Radiolabeling trastuzumab-CHX-A"-DTPA with (177)Lu was efficient with a specific binding of 60.8 ± 6.8% with HER2 positive SKOV-3 cells. Direct quantitation of tumor targeting and normal tissue uptake was performed with athymic mice bearing subcutaneous and intraperitoneal LS-174T xenografts; a peak tumor %ID/g of 24.70 ± 10.29 (96 h) and 31.70 ± 16.20 (72 h), respectively, was obtained. Normal tissue uptake of the RIC was minimal. Tumor targeting was also demonstrated by γ-scintigraphy. A therapy study administering escalating doses of (177)Lu-trastuzumab to mice bearing three day LS-174T i.p. xenografts established the effective therapeutic dose of i.p. administered (177)Lu-trastuzumab at 375 μCi with a median survival of 124.5 d while a median survival of 10 d was noted for the control (untreated) group. In conclusion, trastuzumab radiolabeled with (177)Lu has potential for treatment of disseminated, HER2 positive, peritoneal disease.

Preclinical evaluation of (177)lu-nimotuzumab: a potential tool for radioimmunotherapy of epidermal growth factor receptor-overexpressing tumors

BACKGROUND

The humanized monoclonal antibody Nimotuzumab (h-R3) has demonstrated an exceptional and better clinical profile than other monoclonal antibodies for immunotherapy of epidermal growth factor receptor-overexpressing tumors. This work deals with the preparation and radiolabeling optimization of (177)Lu-Nimotuzumab and their preclinical evaluation.

METHODS

Nimotuzumab was conjugated with S-2-(4-isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane tetraacetic acid (p-SCN-Bn-DOTA), testing different molar ratios. The immunoconjugates were characterized. The radiolabeling with (177)Lu was optimized. Radioimmunoconjugates stability was tested in 2-[bis[2-[bis(carboxymethyl)amino]ethyl]amino]acetic acid (DTPA) excess and human serum. In vitro studies were performed in tumor model cell lines. Receptor-specific binding was tested by competitive inhibition. (177)Lu-Nimotuzumab in vivo studies were conducted in healthy and xenograft animals.

RESULTS

Nimotuzumab conjugates were obtained with high purity. Radiolabeling yield and specific activities ranged from 63.6% to 94.5% and from 748 to 1142 MBq/mg, respectively. The stability in DTPA excess and human serum was 95.9% and 93.2% after 10 days, respectively. The radioimmunoconjugate showed specific receptor binding in tumor cell lines. Biodistribution in healthy animals showed the typical behavior of the immunoconjugates based on monoclonal antibodies. The study in xenografts mice demonstrated uptake of (177)Lu-Nimotuzumab in the tumor and reticuloendothelial organs.

CONCLUSIONS

(177)Lu-Nimotuzumab was obtained with high purity and specific activities under optimal conditions without significant loss in immunoreactivity and might be a potential radioimmunoconjugate for radioimmunotherapy of tumors with epidermal growth factor receptor overexpression.

A pretherapy biodistribution and dosimetry study of indium-111-radiolabeled trastuzumab in patients with human epidermal growth factor receptor 2-overexpressing breast cancer

PURPOSE

The purposes of this study were to evaluate the organ biodistribution, pharmacokinetics, immunogenicity, and tumor uptake of (111)Indium ((111)In)-MxDTPA-trastuzumab in patients with human epidermal growth factor receptor 2 (HER2)-overexpressing breast cancers and to determine whether (90)Y-MxDTPA-trastuzumab should be evaluated in subsequent clinical therapy trials.

EXPERIMENTAL DESIGN

Patients with HER2-overexpressing breast cancers who were to undergo planned trastuzumab therapy first received unlabeled trastuzumab (4-8 mg/kg IV), followed 4 hours later by 5 mCi (111)In-MxDTPA-trastuzumab (10 mg antibody). Serial blood samples, 24-hour urine collections, and nuclear scans were performed at defined time points for 7 days.

RESULTS

Eight (8) patients received (111)In-MxDTPA-trastuzumab, which was well tolerated with no adverse side-effects. Three (3) of 7 patients with known lesions demonstrated positive imaging on nuclear scans. No antiantibody responses were observed for 2 months postinfusion. Organ doses (cGy/mCi) assuming radiolabeling with (90)Y were 19.9 for heart wall, 17.6 for liver, 4.6 for red marrow, and 2.8 for the whole body. Tumor doses ranged from 24 to 172 cGy/mCi.

CONCLUSIONS

In summary, results from this study indicate that (90)Y-MxDTPA-trastuzumab is an appropriate agent to evaluate in therapy trials. No evidence of an immune response to (111)In-MxDTPA-trastuzumab was detected, predicting for the ability to administer multiple cycles. With the exception of cardiac uptake, pharmacokinetics and organ biodistribution were comparable to other (90)Y-labeled monoclonal antibodies previously evaluated in the clinic. Cardiac uptake was comparable to hepatic uptake and therefore predicted to not be prohibitively high as to result in dose-limiting cardiotoxicity.

177Lu labeling of Herceptin and preclinical validation as a new radiopharmaceutical for radioimmunotherapy of breast cancer

INTRODUCTION

In the present study, Herceptin was labeled with lutetium-177 via DOTA, and the necessary preclinical quality control tests (in vitro and in vivo) were performed to evaluate its use as a radioimmunotherapy agent.

MATERIAL AND METHODS

Herceptin was conjugated to DOTA as a chelator in three different conjugation buffers (ammonium acetate, carbonate and HEPES buffer); each of the resulting conjugates was compared with respect to in vitro characteristics such as number of chelates per antibody, incorporated activity, immunoreactivity and in vitro stability in PBS buffer and blood serum. The biodistribution study and gamma camera imaging were performed in mice bearing breast tumors. To assess the therapeutic effects of (177)Lu-Herceptin, cytotoxicity was investigated for 7 days in a SKBr3 breast cancer cell line.

RESULTS

Carbonate buffer was the best conjugation buffer (number of chelates per antibody: 6; incorporated activity: 81%; immunoreactivity: 87%; buffer stability: 86%; serum stability: 81%, after 4 days). The efficient tumor uptake observed in the biodistribution studies was consistent with the gamma camera image results. At a concentration of 4 μg ml(-1), (177)Lu-Herceptin (surviving cells: 5 ± 0.6% of the total cells) of the total cells corresponded to an approximately eightfold increase in cytotoxicity in comparison to unmodified Herceptin (surviving cells: 43 ± 3.9%).

CONCLUSION

The new complex described herein could be considered for further evaluation in animals and potentially in humans as a radiopharmaceutical for use in the radioimmunotherapy of breast cancer. These results may be important for patients who cannot tolerate the therapeutic dosage of Herceptin currently used because of heart problems.

Toxicity of trastuzumab labeled 177Lu on MCF7 and SKBr3 cell lines

In this study, we labeled trastuzumab with (177)Lu to synthesize a new radiopharmaceutical for therapy of breast cancer and at the first stage investigated its therapeutic effects on SKBr3 and MCF7 breast cancer cell lines. Trastuzumab-(177)Lu showed very good in-vitro characteristics such as high radiochemical purity (91+/-0.9%), good stability in PBS buffer (86+/-2.3%) and blood serum (81+/-2.7%) up to 96 h, appropriate immunoreactivity (85.4+/-1.1%) and high cytotoxicity in HER2 expression cells. 5 fold increase in toxicity of trastuzumab-(177)Lu was observed when compared with unlabeled trastuzumab on SKBr3 cells.