New small 99mTc-labeled peptides for HER2 receptor imaging

Peptides Targeting HER2-Positive Breast Cancer Cells and Applications in Tumor Imaging and Delivery of Chemotherapeutics

Breast cancer represents the most common cancer type and one of the major leading causes of death in the female worldwide population. Overexpression of HER2, a transmembrane glycoprotein related to the epidermal growth factor receptor, results in a biologically and clinically aggressive breast cancer subtype. It is also the primary driver for tumor detection and progression and, in addition to being an important prognostic factor in women diagnosed with breast cancer, HER2 is a widely known therapeutic target for drug development. The aim of this review is to provide an updated overview of the main approaches for the diagnosis and treatment of HER2-positive breast cancer proposed in the literature over the past decade. We focused on the different targeting strategies involving antibodies and peptides that have been explored with their relative outcomes and current limitations that need to be improved. The review also encompasses a discussion on targeted peptides acting as probes for molecular imaging. By using different types of HER2-targeting strategies, nanotechnology promises to overcome some of the current clinical challenges by developing novel HER2-guided nanosystems suitable as powerful tools in breast cancer imaging, targeting, and therapy.

The preclinical study of 177Lu-DOTA-LTVSPWY as a potential therapeutic agent against HER2 overexpressed cancer

BACKGROUND

Peptide receptor radionuclide therapy (PRRT) has evolved in cancer therapy and diagnosis. LTVSPWY, as a peptide, can target HER2 receptor; on the other hand, ¹⁷⁷Lu emits β^- which is helpful for cancer therapy. The radiolabeling of LTVSPWY with ¹⁷⁷Lu results in a therapeutic agent (¹⁷⁷Lu-DOTA-LTVSPWY) capable of cancer treatment.

METHODS

¹⁷⁷Lu-DOTA-LTVSPWY was prepared with high radiochemical purity (RCP). The stability was investigated in saline and human serum. The radiotracer affinity toward the SKOV-3 cell line with overexpression of the HER2 receptor was evaluated. Then the impact of the radiotracer on the colony formation of the SKOV-3 cell line was investigated with colony assay. Moreover, the biodistribution of this radiotracer in SKOV-3 xenograft tumor-bearing nude mice were also studied to determine the radiotracer accumulation in the tumor site. The mice were treated with ¹⁷⁷Lu-DOTA-LTVSPWY and subjected to histopathological evaluation.

RESULTS

The RCP of ¹⁷⁷Lu-DOTA-LTVSPWY after radiolabeling and stability tests was more than 97.7%. The radiotracer displayed high affinity toward the SKOV-3 cell line (K_D = 6.6 ± 3.2 nM). Treatment of the SKOV-3 cell line with the radiotracer reduces the SKOV-3 colony survival to less than 3% for 5 MBq of the radiotracer. Tumor-to-muscle (T/M) ratio is the highest at 48 h and 1 h post-injection (2.3 and 4.75, respectively). The histopathological study also confirms the cellular damage to the tumor tissue.

CONCLUSIONS

¹⁷⁷Lu-DOTA-LTVSPWY can recognize HER2 receptors in vivo and in vitro; hence, it can serve as a therapeutic agent.

Molecular Imaging of HER2 Expression in Breast Cancer patients Using the [99mTc] Tc-Labeled Small Peptide

PURPOSE

The accurate determination of human epidermal growth factor receptor 2 (HER2) status can predict response to treatment with HER2-targeted therapy for HER2-positive breast cancer patients. [^99mTc]Tc-HYNIC-(Ser)₃-LTVPWY ([^99mTc]Tc-HYNIC-LY) is a small synthetic peptide molecule targeting of the HER2 receptor. This clinical study evaluated the pharmacokinetic, dosimetry, and efficacy of [^99mTc]Tc-HYNIC-LY for determining the HER2 status in primary breast cancer patients.

MATERIALS AND METHODS

In total, 24 women with suspected primary breast cancer received an intravenous injection of approximately 20 µg (∼740 MBq) of [^99mTc]Tc-HYNIC-LY. In the first 3 patients, blood levels of radioactivity were analyzed for pharmacokinetic evaluation and planar gamma camera imaging was conducted at 30 min and 1, 2, 4, and 24 hour after injection for dosimetry assessment. In the last 21 patients, planar imaging was performed at the baseline, as well as 1, 2, 3, and 4 hour, followed by single-photon emission computed tomography (SPECT) imaging after 4 hour to evaluate the tumor-targeting potential in primary lesions.

RESULTS

Injection of [^99mTc]Tc-HYNIC-LY was safe and well tolerated. Fast blood clearance provided high-contrast HER2 imaging within 1 to 4 hour. The highest absorbed radiation dose was found for kidneys (6.78E-03 ± 2.62E-04 mSv/MBq), followed by the heart (3.73E-03 ± 1.98E-04 mSv/MBq). The [^99mTc]Tc-HYNIC-LY peptide was able to detect HER2 status in primary tumors at an acceptable level.

CONCLUSION

The findings of this study indicated that [^99mTc]Tc-HYNIC-LY SPECT is safe and feasible for the identification of HER2-positive lesions in primary breast cancer patients, and may provide an accurate and non-invasive modality for guiding HER2 targeted therapy.

Evaluation of 68Ga-Radiolabeled Peptides for HER2 PET Imaging

One in eight women will be diagnosed with breast cancer in their lifetime and approximately 25% of those cases will be HER2-positive. Current methods for diagnosing HER2-positive breast cancer involve using IHC and FISH from suspected cancer biopsies to quantify HER2 expression. HER2 PET imaging could potentially increase accuracy and improve the diagnosis of lesions that are not available for biopsies. Using two previously discovered HER2-targeting peptides, we modified each peptide with the chelator DOTA and a PEG2 linker resulting in DOTA-PEG2-GSGKCCYSL (P5) and DOTA-PEG2-DTFPYLGWWNPNEYRY (P6). Each peptide was labeled with 68Ga and was evaluated for HER2 binding using in vitro cell studies and in vivo tumor xenograft models. Both [68Ga]P5 and [68Ga]P6 showed significant binding to HER2-positive BT474 cells versus HER2-negative MDA-MB-231 cells ([68Ga]P5; 0.68 ± 0.20 versus 0.47 ± 0.05 p < 0.05 and [68Ga]P6; 0.55 ± 0.21 versus 0.34 ± 0.12 p < 0.01). [68Ga]P5 showed a higher percent injected dose per gram (%ID/g) binding to HER2-positive tumors two hours post-injection compared to HER2-negative tumors (0.24 ± 0.04 versus 0.12 ± 0.06; p < 0.05), while the [68Ga]P6 peptide showed significant binding (0.98 ± 0.22 versus 0.51 ± 0.08; p < 0.05) one hour post-injection. These results lay the groundwork for the use of peptides to image HER2-positive 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.

Synthesis and comparative evaluation of 177Lu-labeled PEG and non-PEG variant peptides as HER2-targeting probes

Highest global cancer incidence of female breast cancer is a matter of great concern. HER2-positive breast cancers have high mortality rate hence detection at an early stage is vital for successful treatment, improved cancer care and survival rate. Radiolabeled peptides have emerged as new alternatives to radiolabeled antibodies to overcome the limitations of slow clearance and uptake in non-target tissues. Herein, DOTA-A9 peptide and its pegylated variant were constructed on solid phase and radiolabeled with [177Lu]LuCl3. [177Lu]DOTA-A9 and [177Lu]DOTA-PEG4-A9 displayed high binding affinity (Kd = 48.4 ± 1.4 and 55.7 ± 12.3 nM respectively) in human breast carcinoma SKBR3 cells. Two radiopeptides exhibited renal excretion and rapid clearance from normal organs. Uptake in SKBR3 tumor and tumor-to-background ratios were significantly higher (p < 0.05) for [177Lu]DOTA-PEG4-A9 at the three time points investigated. Xenografts could be clearly visualized by [177Lu]DOTA-PEG4-A9 in SPECT images at 3, 24 and 48 h p.i. indicating the potential for further exploration as HER2-targeting probe. The encouraging in vivo profile of PEG construct, [177Lu]DOTA-PEG4-A9 incentivizes future studies for clinical applications.

Initial preclinical evaluation of 68 Ga-DOTA-(Ser) 3 -LTVSPWY peptide as a PET radiotracer for glioblastoma targeting and imaging

PURPOSE

Imaging of glioblastoma multiform (GBM) tumor using 68 -Galium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaceticacid-Ser-Ser-Ser-Leu-Thr-Val-Ser-Pro-Trp-Tyr ( 68 Ga-DOTA-(Ser)3-LTVSPWY) as a PET radiotracer for HER2 receptor due to fact that this receptor plays a pivotal role in the tumorigenesis and tumor progression in a wide range of cancer.

METHODS

68 Ga-DOTA-(Ser) 3 -LTVSPWY was produced with high radiochemical purity. The affinity and specificity of this radiotracer toward HER2 receptor on the surface of glioma glioblastoma (U-87 MG) cell line were evaluated. Furthermore, the biodistribution and PET imaging of this radiolabeled peptide were investigated on xenografted U-87 MG tumor-bearing mice.

RESULTS

The in-vitro specific binding study revealed that the 68 Ga-DOTA-(Ser) 3 -LTVSPWY binds to different cell lines with respect to their level of HER2 expression. The calculated K D and B max of radiolabeled peptide toward U-87 MG cell line were 5.5 ± 2.4 nmol/l and (2.4 ± 0.3) × 10 5 receptors per cell, respectively. The highest tumor uptake was observed at 30-min postinjection, whereas the tumor-to-muscle ratio was about four-fold. The acquired PET images distinctively show tumor site, which was blocked with excess nonlabeled peptide that revealed specific in-vivo targeting of 68 Ga-DOTA-(Ser) 3 -LTVSPWY for glioma.

CONCLUSION

68 Ga-DOTA-(Ser) 3 -LTVSPWY specifically recognizes HER2 receptors and could be a potential candidate for GBM imaging.

The influence of kidneys ion transport inhibitors on the pharmacokinetic and tumor uptake behaviors of a HER2-targeted small size radiolabeled peptide

BACKGROUND

HER2 over-expression plays a crucial role in the cancer treatment protocol. This study evaluates the effectiveness of kidney organic anion and cation transport inhibitors on the tumor uptake of 99mTc-HYNIC-(Ser)3-LTVPWY radiotracer in SKOV-3 tumor-bearing nude mice.

METHODS

Before the injection of the radiolabeled peptide, SKOV-3 tumor-bearing nude mice were treated with furosemide, cimetidine, para-amino hippuric acid, and saline. The inhibition effects of the organic anion and cation transport inhibitors were compared with the control group. In both treatment and control groups, the tumor and renal accumulation of radiopeptide in mice bearing SKOV-3 tumors were assessed in biodistribution and SPECT imaging studies.

RESULTS

The biodistribution and imaging results suggested that all treated groups showed a higher tumor and higher normal tissue radioactivity compared to the control group. According to the tumor imaging study, the furosemide-treated group had slightly better tumor uptake and a higher tumor to muscle uptake ratio than the other treatment groups.

CONCLUSIONS

Administration of furosemide (an OAT inhibitor) increased radioactivity accumulation in the kidneys and blood and improved tumor radioactivity uptake. PAH (an anion transporter substrate) and cimetidine (an OCT inhibitor) have a minor effect on the accumulation of radioactivity in the kidneys and the acquired images.

Review: Radionuclide Molecular Imaging Targeting HER2 in Breast Cancer with a Focus on Molecular Probes into Clinical Trials and Small Peptides

As the most frequently occurring cancer worldwide, breast cancer (BC) is the leading cause of cancer-related death in women. The overexpression of HER2 (human epidermal growth factor receptor 2) is found in about 15% of BC patients, and it is often associated with a poor prognosis due to the effect on cell proliferation, migration, invasion, and survival. As a result of the heterogeneity of BC, molecular imaging with HER2 probes can non-invasively, in real time, and quantitatively reflect the expression status of HER2 in tumors. This will provide a new approach for patients to choose treatment options and monitor treatment response. Furthermore, radionuclide molecular imaging has the potential of repetitive measurements, and it can help solve the problem of heterogeneous expression and conversion of HER2 status during disease progression or treatment. Different imaging probes of targeting proteins, such as monoclonal antibodies, antibody fragments, nanobodies, and affibodies, are currently in preclinical and clinical development. Moreover, in recent years, HER2-specific peptides have been widely developed for molecular imaging techniques for HER2-positive cancers. This article summarized different types of molecular probes targeting HER2 used in current clinical applications and the developmental trend of some HER2-specific peptides.

Peptide Based Imaging Agents for HER2 Imaging in Oncology

Breast cancer continues to be the most lethal cancer type in women and one of the most diagnosed. Understanding Breast cancer receptor status is one of the most vital processes for determining treatment options. One type of breast cancer, human epidermal growth factor receptor 2 (HER2) positive, has approved receptor-based therapies including trastuzumab and pertuzumab that can significantly increase the likelihood of survival. Current methods to determine HER2 status include biopsies with immunohistochemical staining and/or fluorescence in situ hybridization. However, positron emission tomography (PET) imaging techniques using ⁸⁹Zr-trastuzumab or ⁸⁹Zr-pertuzumab are currently in clinical trials for a non-invasive, full body diagnostic approach. Although the antibodies have strong specificity to the HER2 positive lesions, challenges involving long post-injection time for imaging due to the blood circulation of the antibodies and matching of long-live isotopes leading to increased dose to the patient leave opportunities for alternative PET imaging probes. Peptides have been shown to allow for shorter injection-to-imaging time and can be used with shorter lived isotopes. HER2 specific peptides under development will help improve the diagnosis and potentially therapy options for HER2 positive breast cancer. Peptides showing specificity for HER2 could start widespread development of molecular imaging techniques for HER2 positive cancers.

PET and SPECT Imaging of the EGFR Family (RTK Class I) in Oncology

The human epidermal growth factor receptor family (EGFR-family, other designations: HER family, RTK Class I) is strongly linked to oncogenic transformation. Its members are frequently overexpressed in cancer and have become attractive targets for cancer therapy. To ensure effective patient care, potential responders to HER-targeted therapy need to be identified. Radionuclide molecular imaging can be a key asset for the detection of overexpression of EGFR-family members. It meets the need for repeatable whole-body assessment of the molecular disease profile, solving problems of heterogeneity and expression alterations over time. Tracer development is a multifactorial process. The optimal tracer design depends on the application and the particular challenges of the molecular target (target expression in tumors, endogenous expression in healthy tissue, accessibility). We have herein summarized the recent preclinical and clinical data on agents for Positron Emission Tomography (PET) and Single Photon Emission Tomography (SPECT) imaging of EGFR-family receptors in oncology. Antibody-based tracers are still extensively investigated. However, their dominance starts to be challenged by a number of tracers based on different classes of targeting proteins. Among these, engineered scaffold proteins (ESP) and single domain antibodies (sdAb) show highly encouraging results in clinical studies marking a noticeable trend towards the use of smaller sized agents for HER imaging.

Radiolabeled nanobodies for tumor targeting: From bioengineering to imaging and therapy

So far, numerous molecules and biomolecules have been evaluated for tumor targeting purposes for radionuclide-based imaging and therapy modalities. Due to the high affinity and specificity against tumor antigens, monoclonal antibodies are appropriate candidates for tumor targeting. However, their large size prevents their comprehensive application in radionuclide-based tumor imaging or therapy, since it leads to their low tumor penetration, low blood clearance, and thus inappropriate tumor-to-background ratio. Nowadays, the variable domain of heavy-chain antibodies from the Camelidae family, known as nanobodies (Nbs), turn into exciting candidates for medical research. Considering several innate advantages of these new tumor-targeting agents, including excellent affinity and specificity toward antigen, high solubility, high stability, fast washout from blood, convenient production, ease of selection, and low immunogenicity, it assumes that they may overcome generic problems of monoclonal antibodies, their fragments, and other vectors used for tumor imaging/therapy. After three decades of Nbs discovery, the increasing number of their preclinical and clinical investigations, which have led to outstanding results, confirm their application for tumor targeting purposes. This review describes Nbs characteristics, the diagnostic and therapeutic application of their radioconjugates, and their recent advances.

The emerging role of radionuclide molecular imaging of HER2 expression in breast cancer

Targeting of human epidermal growth factor type 2 (HER2) using monoclonal antibodies, antibody-drug conjugates and tyrosine kinase inhibitors extends survival of patients with HER2-expressing metastatic breast cancer. High expression of HER2 is a predictive biomarker for such specific treatment. Accurate determination of HER2 expression level is necessary for stratification of patients to targeted therapy. Non-invasive in vivo radionuclide molecular imaging of HER2 has a potential of repetitive measurements, addressing issues of heterogeneous expression and conversion of HER2 status during disease progression or in response to therapy. Imaging probes based of several classes of targeting proteins are currently in preclinical and early clinical development. Both preclinical and clinical data suggest that the most promising are imaging agents based on small proteins, such as single domain antibodies or engineered scaffold proteins. These agents permit a very specific high-contrast imaging at the day of injection.

Targeting and imaging of HER2 overexpression tumor with a new peptide-based 68Ga-PET radiotracer

Human epidermal growth factor receptor 2 (HER2) overexpression, as a predictive biomarker, is associated with more tumor aggressiveness and worse clinical outcomes in cancer, whereas it's accurate identification has led to the choice of effective treatments in many patients. In this study, a peptide-based PET probe (⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY) was developed for imaging HER2 expression in tumors. The DOTA-(Ser)₃-LTVSPWY was labeled with ⁶⁸Ga and then was evaluated in vitro with HER2-positive SKOV-3 cell line; moreover, the in vivo biodistribution and PET/CT imaging were performed in xenografted tumor-bearing nude mice. The ⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY displayed the high radiochemical purity greater than 95% and good stability in normal saline and human serum. The cellular binding experiments showed that the cell uptake in HER2-positive ovarian cancer cells could be effectively blocked by non-labeled peptide. The K_d and B_max values for radiolabeled peptide were obtained at 2.5 ± 0.6 nM and (3.4 ± 0.2) × 10⁵ sites per cell, respectively. Biodistribution study demonstrated that tumor-to-blood and tumor-to-muscle ratios were about 1.73 ± 0.36 and 3.78 ± 0.17 at 120 min after the injection of the radiolabeled peptide, respectively. Tumor imaging by PET/CT exhibited high contrast tumor image at 60 min after injection in animal models. Consequently, the results were indicative of the specific accumulation of ⁶⁸Ga-DOTA-(Ser)₃-LTVSPWY peptide in HER2-positive tumors and the suitability of its application as a PET probe for the diagnosis of HER2-overexpression tumor.

Strategies for improving stability and pharmacokinetic characteristics of radiolabeled peptides for imaging and therapy

Tumor cells overexpress a variety of receptors that are emerging targets in cancer chemotherapy. Radiolabeled peptides with high affinity and selectivity for these overexpressed receptors have been designed for both imaging and therapy purposes. Such peptides display advantages such as high selectivity for tumor cells, rapid tumor tissue penetration, and rapid clearance from non-target tissues and the circulation. However, the very short in vivo half-life of radiolabeled peptides, arising from enzymatic degradation and/or efficient clearance by the kidney, limits their accumulation in tumors. This review presents various strategies that have been applied to extend the half-life extension and improve the pharmacokinetic characteristics of radiolabeled peptides. These include amino acid substitution, modification of the peptide termini, dimerization and multimerization of the peptide, cyclization, conjugation with polymers, sugars and albumin and use of peptidase inhibitors.

Synthesis of a novel 99mTc labeled GE11 peptide for EGFR SPECT imaging

PURPOSE

This study investigated a novel SPECT agent for the noninvasive imaging of EGFR-overexpressing tumors.

METHODS

The EGFR-targeting peptide GE11 was synthesized with the introduction of four amino acids (GGGC) to its C-terminal to act as a strong chelator and radiolabeled using ^99mTc. The radiochemical yield of the ^99mTc-peptide-GE11 were evaluated using RP-HPLC. Cellular assays of the probe were performed on two NSCLC cell lines: A549 (high expression) and H23 (low expression). Biodistribution and SPECT imaging were performed in BALB/c nude mice bearing A549 and H23 NSCLC xenografts.

RESULTS

The ^99mTc-peptide-GE11 was prepared at high efficiency with radiochemical yield of 98.40 ± 1.00 % and it showed favorable stability. The cellular uptake was significantly higher in A549 than in H23 at all time points (especially at 1 h, which was 10.34 ± 0.72 and 2.04 ± 0.18, respectively). A nearly 56% reduction in probe uptake was observed after pretreatment with excess unlabeled peptides. The performance of SPECT imaging and biodistribution demonstrated higher uptake of the ^99mTc-peptide-GE11 in A549 xenograft than in H23 xenografts.

CONCLUSION

The new SPECT tracer ^99mTc-peptide-GE11 showed EGFR specificity, favorable pharmacokinetics and great potential for EGFR-targeted imaging.

Biologicals to direct nanotherapeutics towards HER2-positive breast cancers

HER2-positive breast cancer, an aggressive cancer, is treated with combinations of conventional anticancer drugs viz., cytotoxic drugs, nibs, and mAbs. Major limitations associated with this therapy are patient non-compliance due to the adverse drug reactions and rapid development of resistance by the HER2-positive malignant cells. While the former is addressed by the nano-formulations of the anticancer-drugs to some extent, the latter is still at large. This is because the nanocarriers of the anticancer drugs, by and large, lack the target specificity and selectivity. Thus, nowadays, to overcome these problems, various safe and efficacious biological agents are being used to direct the nanotherapeutics towards the HER2-positive breast cancers. The present review describes the potentials of such biological agents.

99mTc-radiolabeled HER2 targeted exosome for tumor imaging

Exosomes represent unique features including nontoxicity, non-immunogenicity, biodegradability, and targeting ability that make them suitable candidates for clinical applications. Therefore, in this study, ^99mTc-radiolabel HER2 targeted exosomes (^99mTc-exosomes) were provided for tumor imaging. These exomes are obtained from genetically engineered cells and possessed DARPin G3 as a ligand for HER2 receptors. These exosomes were radiolabeled using fac-[^99mTc(CO)₃(H₂O)₃]⁺ synthon. The quality control showed high radiochemical purity (RCP) for ^99mTc-exosomes (>96%). ^99mTc-exosomes displayed a higher affinity toward SKOV-3 cells (higher HER2 expression) in comparison with MCF-7, HT29, U87-MG, A549 cell lines at different levels of HER2 expression. Trastuzumab (an antibody with a high affinity toward HER2) inhibited the binding of ^99mTc-exosomes to SKOV-3 cells up to 40%. Biodistribution study in SKOV-3 tumor bearing nude mice confirmed the ability of ^99mTc-exosomes for accumulation in the tumor. ^99mTc-exosomes can visualize tumor in SKOV-3 tumor-bearing nude mouse. The blockage of HER2 receptors using trastuzumab (excessive amount) suggests the ^99mTc-exosomes binding to the receptors and reduced the accumulation of ^99mTc-exosomes in the tumor site. This suggest that ^99mTc-exosomes interact with HER2 receptors and act through specific targeting.

Preclinical pharmacokinetic, biodistribution, radiation dosimetry, and toxicity studies of 99mTc-HYNIC-(Ser)3-LTVPWY: A novel HER2-targeted peptide radiotracer

Accurate assessment of the HER2 expression is an essential issue for predicting response to anti-HER2 therapy in breast cancer patients. The aim of this study was to evaluate ^99mTc-HYNIC-(Ser)₃-LTVPWY (^99mTc-HYNIC-LY) peptide as a novel HER2-targeted radiolabeled peptide in healthy mice to examine the applicability of this imaging agent in a first-in-human clinical trial. To this end, pharmacokinetic and dosimetry studies were performed according to the ICH guideline M3 (R2) with ^99mTc-HYNIC-LY. To estimate the radiation-absorbed doses in humans, the accumulated activity in each mouse organ was calculated based on biodistribution data. In addition, toxicology assessment was performed based on mortality events, body weights, and serum biochemical, hematological, and histopathological assays. The pharmacokinetic study showed rapid blood clearance. Based on the results of biodistribution study, the highest radioactivity was observed in the kidneys. The projected absorbed doses to the kidneys, liver, lungs, stomach, and spleen were obtained as 1.70E-02, 1.42E-02, 1.02E-02, 8.62E-03, and 8.34E-03 mSv/MBq, respectively. The results also revealed that serum biochemical and hematological parameters were in the normal range. No significant morphologic alterations were observed in the liver, kidneys, and spleen tissues. Consequently, the results were indicative of the suitability of ^99mTc-HYNIC-LY peptide for advancement to a first-in-human clinical trial.

Basic and practical concepts of radiopharmaceutical purification methods

The presence of radiochemical impurities in a radiopharmaceutical contributes to an unnecessary radiation burden for the patients or to an undesirable high radioactivity background, which reduces the imaging contrast or therapeutic efficacy. Therefore, if the radiolabeling process results in unsatisfactory radiochemical purity, a purification step is unavoidable. A successful purification process requires a profound knowledge about the radiopharmaceuticals of interest ranging from structural features to susceptibility to different conditions. Most radiopharmaceutical purification methods are based on solid-phase extraction (SPE), high-performance liquid chromatography (HPLC), size exclusion chromatography (SEC), ion-exchange chromatography (IEC), and liquid-liquid extraction (LLE). Here, we discuss the basic and applied concepts of these purifications methods as well as their advantages and limitations.

99mTc-HYNIC-(tricine/EDDA)-FROP peptide for MCF-7 breast tumor targeting and imaging

Background

Breast cancer is the most common malignancy among women in the world. Development of novel tumor-specific radiopharmaceuticals for early breast tumor diagnosis is highly desirable. In this study we developed ^99mTc-HYNIC-(tricine/EDDA)-Lys-FROP peptide with the ability of specific binding to MCF-7 breast tumor.

Methods

The FROP-1 peptide was conjugated with the bifunctional chelator hydrazinonicotinamide (HYNIC) and labeled with ^99mTc using tricine/EDDA co-ligand. The cellular specific binding of ^99mTc-HYNIC-FROP was evaluated on different cell lines as well as with blocking experiment on MCF-7 (human breast adenocarcinoma). The tumor targeting and imaging of this labeled peptide were performed on MCF-7 tumor bearing mice.

Results

Radiochemical purity for ^99mTc-HYNIC-(tricine/EDDA)-FROP was 99% which was determined with ITLC method. This radiolabeled peptide showed high stability in normal saline and serum about 98% which was monitored with HPLC method. In saturation binding experiments, the binding constant (K_d) to MCF-7 cells was determined to be 158 nM. Biodistribution results revealed that the ^99mTc-HYNIC-FROP was mainly exerted from urinary route. The maximum tumor uptake was found after 30 min post injection (p.i.); however maximum tumor/muscle ratio was seen at 15 min p.i. The tumor uptake of this labeled peptide was specific and blocked by co-injection of excess FROP. According to the planar gamma imaging result, tumor was clearly visible due to the tumor uptake of ^99mTc-HYNIC-(tricine/EDDA)-FROP in mouse after 15 min p.i.

Conclusions

The ^99mTc-HYNIC-(tricine/EDDA)-FROP is considered a promising probe with high specific binding to MCF-7 breast cancer cells.

Nanomedicine: An effective tool in cancer therapy

Various types of nanoparticles (NPs) have been used in delivering anticancer drugs to the site of action. This area has become more attractive in recent years due to optimal size and negligible undesirable side effects caused by the NPs. The focus of this review is to explore various types of NPs and their surface/chemical modifications as well as attachment of targeting ligands for tuning their properties in order to facilitate targeted delivery to the cancer sites in a rate-controlled manner. Heme compatibility, biodistribution, longer circulation time, hydrophilic lipophilic balance for high bioavailability, prevention of drug degradation and leakage are important in transporting drugs to the targeted cancer sites. The review discusses advantages of polymeric, magnetic, gold, and mesoporous silica NPs in delivering chemotherapeutic agents over the conventional dosage formulations along with their shortcomings/risks and possible solutions/alternatives.

99mTc-HYNIC-(Ser)3-LTVPWY peptide bearing tricine as co-ligand for targeting and imaging of HER2 overexpression tumor

Human epidermal growth factor receptor 2 (HER2) is overexpressed in several cancers. Today’s tumor targeting is receiving more attention due to its specificity to target receptor-dependent cancers. The aim of this study was to evaluate the 99mTc-HYNIC-(tricine)-(Ser)3-LTVPWY peptide for tumor targeting and imaging with overexpression of HER2. HYNIC-(Ser)3-LTVPWY peptide was labeled with 99mTc using tricine as a co-ligand at room temperature. Specific binding of this radiolabeled peptide was assessed on four cancer cell lines with different levels of HER2 receptor expression. Also the affinity of 99mTc-HYNIC-(tricine)-(Ser)3-LTVPWY peptide to the HER2 receptor was evaluated in the SKOV-3 cell line. Biodistribution study of this radiolabeled peptide was performed in SKOV-3 tumor bearing nude mice. The HYNIC conjugated peptide was simply labeled with 99mTc radionuclide with high labeling efficiency about 98±1% showing favorable stability in normal saline and human serum. In the presence of unlabeled peptide as competitor, the HER2 binding capacity of the radiolabeled peptide reduced (approximately five-fold). The KD and Bmax values were found 2.6±0.5 nM and (2.6±0.1)×106, respectively. The tumor/muscle ratios for this radiotracer were determined 1.17±0.77, 1.15±0.32 and 2.65±0.32 at 1, 2 and 4 h after injection, respectively. Presaturation of HER2 receptors in SKOV-3 xenografted nude mice showed a reduction in the tumor/muscle ratio confirming in vivo specificity of the peptide. According to SPECT imaging, the tumor was visualized in mouse after 4 h postinjection of radiolabeled peptide. 99mTc-HYNIC-(tricine)-(Ser)3-LTVPWY peptide exhibited overexpressed HER2 tumor targeting.

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.

An improved 99mTc-HYNIC-(Ser)3-LTVSPWY peptide with EDDA/tricine as co-ligands for targeting and imaging of HER2 overexpression tumor

Overexpression of human epidermal receptor 2 (HER2) has given the opportunity for targeting and delivering of imaging radiotracers. The aim of this study was to evaluate the ^99mTc-HYNIC-(EDDA/tricine)-(Ser)₃-LTVSPWY peptide for tumor targeting and imaging of tumor with overexpression of HER2. The HYNIC-(Ser)₃-LTVSPWY was labeled with ^99mTc in presence of EDDA/tricine mixture as co-ligands. The in vitro and in vivo studies of this radiolabeled peptide were performed for cellular specific binding and tumor targeting. The high radiochemical purity of ^99mTc-HYNIC (EDDA/tricine)-(Ser)₃-LTVSPWY was obtained to be 99%. It exhibited high stability in normal saline and human serum. In HER2 binding affinity study, a significant reduction in uptake of radiolabeled peptide (7.7 fold) was observed by blocking SKOV-3 cells receptors with unlabeled peptide. The K_D and B_max values for this radiolabeled peptide were determined as 3.3 ± 1.0 nM and 2.9 ± 0.3 × 10⁶ CPM/pMol, respectively. Biodistribution study revealed tumor to blood and tumor to muscle ratios about 6.9 and 4 respectively after 4 h. Tumor imaging by gamma camera demonstrated considerable high contrast tumor uptake. This developed ^99mTc-HYNIC-(Ser)₃-LTVSPWY peptide selectively targeted on HER2 tumor and exhibited a high target uptake combined with acceptable low background activity for tumor imaging in mice. The results of this study and its comparison with another study showed that ^99mTc-HYNIC-(EDDA/tricine)-(Ser)₃-LTVSPWY is much better than previously reported radiolabeled peptide as ^99mTc-CSSS-LTVSPWY for HER2 overexpression tumor targeting and imaging.

Novel Linear Peptides with High Affinity to αvβ3 Integrin for Precise Tumor Identification

Development of alternative linear peptides for targeting αvβ3 integrin has attracted much attention, as the traditional peptide ligand, cyclic RGD, is limited by inferior water-solubility and complex synthesis. Using pharmacophore-based virtual screening and high-throughput molecular docking, we identified two novel linear small peptides RWr and RWrNM with high affinity and specificity to αvβ3 integrin. The competitive binding with cyclic RGD (c(RGDyK)) and cellular uptake related to the integrin expression levels verified their affinity to αvβ3 integrin. The intermolecular interaction measurement and dynamics simulation demonstrated the high binding affinity and stability, especially for RWrNM. In vivo peptide-guided tumor imaging and targeted therapy further confirmed their specificity. Results indicated that the newly identified small linear peptide RWrNM, with high affinity and specificity to αvβ3 integrin, better water-solubility, and simplified synthetic process, could overcome limitations of the current cyclic RGD peptides, paving the way for diverse use in diagnosis and therapy.