Developing PEGylated Reversed D-Peptide as a Novel HER2-Targeted SPECT Imaging Probe for Breast Cancer Detection

Peptides in breast cancer therapy: From mechanisms to emerging drug delivery and immunotherapy strategies

Breast cancer therapy can be improved by the application of multifunctional peptides and they have unique features, such as high specificity, minimized toxicity, and the capability to influence diverse processes. The role of peptides in breas cancer therapy is highlighted in the present review, examining their functions as therapeutic agents, diagnostic tools, and drug delivery application. Therapeutic peptides have displayed the ability to regulate key pathways in breast tumor, including HER2, VEGF, and EGFR, providing ideal alternatives to the conventional chemotherapy with reduced adverse effects. Additionally, peptide-based vaccines and immune-modulating peptides have demonstrated the capacity in enhancing anti-cancer immunity. The incorporation of peptides into nanoparticles has improved the delivery of drugs and genes, enhanced anti-cancer efficacy while minimizing side impacts. The progresses in the peptide engineering, including stapled peptides, peptide-drug conjugates, and cell-penetrating peptides, have remarkably increased their therapeutic efficacy and stability, elevating their applications in breast cancer therapy. Peptides can be developed using bioinformatics and high-throughput screening technologies to optimize pharmacokinetics and bioavailability. Despite their promise, peptides demonstrate challenges such as enzymatic degradation, limited stability, and high production costs. These obstacles can be addressed through strategies such as peptide cyclization, the employement of non-natural amino acids, and nanoparticle encapsulation. This review explores these recent advancements and strategies, providing ideal insights into the clinical potential of peptides in breast tumor therapy.

Cancer Targeting Radiopeptidomimetics in Molecular Nuclear Medicine

Peptides are highly receptor-affine molecules exhibiting suitable pharmacokinetics. Additionally, low-cost production, simple protocols allowing easy modifications, and tolerance toward harsh reaction conditions make peptides ideal ligands for preparation of radiopharmaceuticals for cancer detection and treatment. However, natural peptides being substrates for enzymes are susceptible to proteolysis, which limits the in vivo lifetime and the target uptake. Therefore, the majority of peptides are not able to progress beyond preclinical research. Advancement of peptides for clinical analysis needs modification to instill improved features. Continuous increase and further expected rise in cancer cases in the next decade require development of more disease-directed and promising radiopharmaceuticals. Redesigned peptide, mimicking the original peptide with similar or improved affinity and high metabolic stability, shall have significant edge. This review outlines the design of peptidomimetics by incorporation of D-amino acids (inverso); reversal of D-amino acid sequence (retro-inverso), and reversal of L-amino acid sequence (retro). Clinically successful radiopeptidomimetics prepared using the three approaches have been elaborated to elucidate the important role of peptidomimetics in cancer management.

Development of Novel 99mTc-Labeled Hydrazinoicotinamide-Modified Ubiquicidin 29-41 Complexes with Improved Target-to-Nontarget Ratios for Bacterial Infection Imaging

To develop novel 99mTc-labeled ubiquicidin 29-41 derivatives for bacterial infection SPECT imaging aiming at achieving a high target-to-nontarget ratio and lower nontarget organ uptake, a novel 6-hydrazinoicotinamide (HYNIC) ubiquicidin 29-41 derivative (HYNIC-UBI 29-41) was designed and synthesized. It was then radiolabeled with ternary ligands, including TPPTS, PDA, 2,6-PDA, NIC, ISONIC, PSA, 4-PSA, and PES, to obtain eight 99mTc-labeled HYNIC-UBI 29-41 complexes. All the complexes demonstrated hydrophilicity, exhibited good in vitro stability, and specifically bound Staphylococcus aureus in vitro. Biodistribution studies in mice with bacterial infection demonstrated that [99mTc]Tc-tricine/TPPTS-HYNIC-UBI 29-41 resulted in increased abscess-to-muscle and abscess-to-blood ratios as well as decreased nontarget organ uptake. Furthermore, it was able to distinguish between bacterial infection and sterile inflammation. Single-photon emission computed tomography (SPECT) imaging studies in mice with bacterial infection revealed visible accumulation at the site of infection, indicating that [99mTc]Tc-tricine/TPPTS-HYNIC-UBI 29-41 is a potential radiotracer for imaging bacterial infection.

99mTc-HYNIC PEGylated Peptide Probe Targeting HER2-Expression in Breast Cancer

Increased HER2 expression during breast cancer and its metastatic spread can be checked by specific probes having high affinity towards the target. This study aimed at developing 99mTc-labelled HER2-specific molecular probe for accurate detection. The two rL-A9 peptide variants, HYNIC-rL-A9 and HYNIC-PEG12-rL-A9 were manually synthesized by solid phase methodology. 99mTc-labelling of peptides was accomplished using EDDA and tricine as co-ligands. [99mTc]Tc-HYNIC-rL-A9 showed poor uptake in HER2-expressing human breast carcinoma SKBR3 cells whereas the PEGylated counterpart [99mTc]Tc-HYNIC-PEG12-rL-A9 demonstrated high specific cellular uptake (3.01% ± 0.14%) and low nanomolar binding affinity (Kd = 17.11 ± 7.63 nM). Tumour uptake (SKBR3) of [99mTc]Tc-HYNIC-PEG12-rL-A9 was higher at 1 and 3 h in comparison to the non-PEGylated radiopeptide. Blocking studies led to 70% reduction in accumulation of radioactivity in the tumour indicating specificity of the radiopeptide. Introduction of polyethylene glycol (PEG12) as pharmacokinetic modifier led to significantly improved biological profile of the [99mTc]Tc-HYNIC-labelled rL-A9 peptide conjugate.

Advances in Preclinical Research of Theranostic Radiopharmaceuticals in Nuclear Medicine

Theranostics of nuclear medicine refers to the combination of radionuclide imaging and internal irradiation therapy, which is currently a research hotspot and an important direction for the future development of nuclear medicine. Radiopharmaceutical is a vital component of nuclear medicine and serves as one of the fundamental pillars of molecular imaging and precision medicine. At present, a variety of radiopharmaceuticals have been developed for various targets such as fibroblast activation protein (FAP), prostate-specific membrane antigen (PSMA), somatostatin receptor 2 (SSTR2), C-X-C motif chemokine receptor 4 (CXCR4), human epidermal growth factor-2 (HER2), and integrin αvβ3, and some of them have been successfully applied in clinical practice. The radiopharmaceutical with theranostic function plays an important role in the diagnosis, treatment, efficacy evaluation, and prognosis prediction of cancers and is the key to realize the personalized treatment of tumors. This Review summarizes the preclinical research progress of theranostic radiopharmaceuticals toward the above targets in the field of nuclear medicine and discusses the prospects and development directions of radiopharmaceuticals in the future.

Preclinical research progress in HER2-targeted small-molecule probes for breast cancer

Breast cancer is a malignant tumor that has the highest morbidity and mortality in women worldwide. Human epidermal growth factor receptor 2 (HER2) is a key driver of breast cancer development. Therefore, accurate assessment of HER2 expression in cancer patients and timely initiation or termination of anti-HER2 treatment are crucial for the prognosis of breast cancer patients. The emergence of radiolabeled molecular probes targeting HER2 makes this assessment possible. This article describes different types of small-molecule probes that target HER2 and are used in current preclinical applications and summarizes their advantages and disadvantages.

Influence of PEGylation on HER2-targeting retro A9 peptide analogue

Elevated levels of HER2 receptor in breast cancer can be targeted through receptor-specific peptides for precise detection and therapy by nuclear medicine approach. Previously reported retro analogue of A9 peptide had shown HER2-specificity with promising pharmacokinetic features. Hence, with an aim of further improving the circulation time of rL-A9 radiopeptide, long polyethylene glycol chain (PEG12) was introduced at the N-terminus of the peptide during solid phase synthesis and influence of PEGylation on biological profile was studied. [177Lu]Lu-DOTA-PEG12-rL-A9 demonstrated high specific cellular uptake (5.94 ± 0.09 %) in HER2-expressing human breast carcinoma SKBR3 cells and low nanomolar binding affinity (Kd = 34.58 ± 12.78 nM). Uptake in SKBR3 tumors induced in female SCID mice was higher at all the time points investigated (3, 24, 48 h) in comparison to the non-PEGylated radiopeptide, [177Lu]Lu-DOTA-rL-A9. Blocking studies led to 51 % reduction in accumulation of radioactivity in the tumor indicating specificity of the radiopeptide. Improved tumor-to-stomach and tumor-to-intestine ratios for [177Lu]Lu-DOTA-PEG12-rL-A9 compared to [177Lu]Lu-DOTA-rL-A9 at 48 h shall pave the way for better contrast and delineation of metastatic sites.

Preclinical evaluation of 68 Ga-labeled peptide CK2 for PET imaging of NRP-1 expression in vivo

PURPOSE

Neuropilin-1 (NRP-1) is a multifunctional protein involved in a variety of biological processes such as angiogenesis, tumorigenesis and immunomodulation. It was usually overexpressed in many cancer cell lines and correlated with poor prognosis of breast cancer. Positron emission tomography (PET) is an advanced imaging technique for detecting the function and metabolism of tumor-associated molecules in real time, dynamically, quantitatively and noninvasively. To improve the level of early diagnosis and evaluate the prognosis of breast cancer, an NRP-1 targeting peptide-based tracer [68 Ga]Ga-NOTA-PEG4-CK2 was designed to sensitively and specifically detect the NRP-1 expression in vivo via PET imaging.

METHODS

In silico modeling and microscale thermophoresis (MST) assay were carried out to design the NRP-1 targeting peptide NOTA-PEG4-CK2, and it was further radiolabeled with 68 Ga to prepare the tracer [68 Ga]Ga-NOTA-PEG4-CK2. The radiochemical yield (RCY), radiochemical purity (RCP), molar activity (Am), lipid-water partition coefficient (Log P) and stability of [68 Ga]Ga-NOTA-PEG4-CK2 were assessed. The targeting specificity of the tracer for NRP-1 was investigated by in vitro cellular uptake assay and in vivo PET imaging as well as blocking studies. The sensitivity of the tracer in monitoring the dynamic changes of NRP-1 expression induced by chemical drug was also investigated in vitro and in vivo. Ex vivo biodistribution, autoradiography, western blot, and immunofluorescence staining were also performed to study the specificity of [68 Ga]Ga-NOTA-PEG4-CK2 for NRP-1.

RESULTS

[68 Ga]Ga-NOTA-PEG4-CK2 was designed and synthesized with high RCY (> 98%), high stability (RCP > 95%) and high affinity to NRP-1 (KD = 25.39 ± 1.65 nM). In vitro cellular uptake assay showed that the tracer [68 Ga]Ga-NOTA-PEG4-CK2 can specifically bind to NRP-1 positive cancer cells MDA-MB-231 (1.04 ± 0.04% at 2 h) rather than NRP-1 negative cancer cells NCI-H1299 (0.43 ± 0.05%). In vivo PET imaging showed the maximum tumor uptake of [68 Ga]Ga-NOTA-PEG4-CK2 in MDA-MB-231 xenografts (4.16 ± 0.67%ID/mL) was significantly higher than that in NCI-H1299 xenografts (1.03 ± 0.19%ID/mL) at 10 min post injection, and the former exhibited higher tumor-to-muscle uptake ratio (5.22 ± 0.18) than the latter (1.07 ± 0.27) at 60 min post injection. MDA-MB-231 xenografts pretreated with nonradioactive precursor NOTA-PEG4-CK2 showed little tumor uptake of [68 Ga]Ga-NOTA-PEG4-CK2 (1.67 ± 0.38%ID/mL at 10 min post injection). Both cellular uptake assay and PET imaging revealed that NRP-1 expression in breast cancer MDA-MB-231 could be effectively suppressed by SB-203580 treatment and can be sensitively detected by [68 Ga]Ga-NOTA-PEG4-CK2. Ex vivo analysis also proved the high specificity and sensitivity of [68 Ga]Ga-NOTA-PEG4-CK2 for NRP-1 expression in MDA-MB-231 xenografts.

CONCLUSION

A promising NRP-1 targeting PET tracer [68 Ga]Ga-NOTA-PEG4-CK2 was successfully prepared. It showed remarkable specificity and sensitivity in monitoring the dynamic changes of NRP-1 expression. Hence, it could provide valuable information for early diagnosis of NRP-1 relevant cancers and evaluating the prognosis of cancer patients.

Cutting-edge approaches for targeted drug delivery in breast cancer: beyond conventional therapies

Breast cancer is a global health challenge with staggering statistics underscoring its pervasive impact. The burden of this disease is measured in terms of its prevalence and the challenges it poses to healthcare systems, necessitating a closer look at its epidemiology and impact. Current breast cancer treatments, including surgery, chemotherapy, radiation therapy, and targeted therapies, have made significant strides in improving patient outcomes. However, they are not without limitations, often leading to adverse effects and the development of drug resistance. This comprehensive review delves into the complex landscape of breast cancer, including its incidence, current treatment modalities, and the inherent limitations of existing therapeutic approaches. It also sheds light on the promising role of nanotechnology, encompassing both inorganic and organic nanoparticles equipped with the ability to selectively deliver therapeutic agents to tumor sites, in the battle against breast cancer. The review also addresses the emerging therapies, their associated challenges, and the future prospects of targeted drug delivery in breast cancer management.

Phospholipid Bilayer Integrated with Multifunctional Peptide for Ultralow-Fouling Electrochemical Detection of HER2 in Human Serum

Electrochemical biosensing devices face challenges of severe nonspecific adsorption in complex biological matrices for the detection of biomarkers, and thus, there is a significant need for sensitive and antifouling biosensors. Herein, a sensitive electrochemical biosensor with antifouling and antiprotease hydrolysis ability was constructed for the detection of human epidermal growth factor receptor 2 (HER2) by integrating multifunctional branched peptides with distearoylphosphatidylethanolamine-poly(ethylene glycol) (DSPE-PEG) self-assembled bilayer. The peptide was designed to possess antifouling, antiprotease hydrolysis, and HER2 recognizing capabilities. Molecular dynamics simulations demonstrated that the DSPE was able to effectively self-assemble into a bilayer, and the water contact angle and electrochemical experiments verified that the combination of peptide with the DSPE-PEG bilayer was conducive to enhancing the hydrophilicity and antifouling performance of the modified surface. The constructed HER2 biosensor exhibited excellent antifouling and antiprotease hydrolysis capabilities, and it possessed a linear range of 1.0 pg mL-1 to 1.0 μg mL-1, and a limit of detection of 0.24 pg mL-1. In addition, the biosensor was able to detect HER2 in real human serum samples without significant biofouling, and the assaying results were highly consistent with those measured by the enzyme-linked immunosorbent assay (ELISA), indicating the promising potential of the antifouling biosensor for clinical diagnosis.

Design, synthesis and evaluation of 177Lu-labeled inverso and retro-inverso A9 peptide variants targeting HER2-overexpression

Several HER2-specific peptides are being continuously explored to find a candidate with suitable pharmacokinetic properties for development of effective radiopharmaceutical that can find applications for clinical screening of breast cancer patients. In the present work with an aim of preparing a radiopeptide with improved metabolic stability and in vivo pharmacokinetic performance we modified our previously reported [177Lu]DOTA-L-A9 peptide. Here we designed an 'inverso' peptide with all d-amino acids and a 'retro-inverso' peptide where sequence of d-amino acids was reversed. Higher secondary structure stabilization of retro- inverso A9 variant compared to inverso A9 peptide was evident by circular dichroism studies. The two radiopeptides [177Lu]DOTA-D-A9 and [177Lu]DOTA-rD-A9 exhibited significantly improved in vivo metabolic stability over the original l-peptide. The retro-inverso variant, [177Lu]DOTA-rD-A9 demonstrated better pharmacokinetic behavior with significantly higher tumor uptake than the inverso peptide, [177Lu]DOTA-D-A9 and the original peptide, [177Lu]DOTA-L-A9. In the present case of A9 peptide, reversal of the peptide sequence of d-amino acids boosted the uptake and retention of radioactivity in HER2-positive tumor. The present study can thus guide the design and development of newer and improved versions of peptides.

Targeting HER2-Receptors with 177Lu-Labeled Triazole Stapled Cyclic Peptidomimetic

In this study on-resin Cu(I)-catalyzed click reaction was performed to synthesize triazole-stapled cyclic peptidomimetic, DOTA-c[TZ]A9 targeting HER2 receptor expression in breast cancers. Spectroscopic (circular dichroism) and docking analysis provided evidence of enhanced helicity and secondary structure stabilization along with improved HER2 affinity in comparison to the corresponding linear peptide, DOTA-[Pra¹, Aza⁷]A9. ¹⁷⁷Lu-labeled cyclic peptide, ¹⁷⁷Lu-DOTA-c[TZ]A9 displayed higher in vitro serum stability and in vivo metabolic stability and better HER2 binding affinity {K_d of 16.93 ± 3.02 nM} than the linear counterpart, [¹⁷⁷Lu]DOTA-[Pra¹, Aza⁷]A9 {K_d of 26.28 ± 2.87 nM}. Biodistribution profile in SKBR3 tumor bearing SCID mice demonstrated elevated radioactivity levels and prolonged retention of cyclic peptide in the tumor compared to the linear peptide. Thus, solid phase click cyclization technique can be extended towards preparation of triazole-stapled peptides targeting different receptors with improved stability and efficacy.

A Novel Homodimer Peptide-Drug Conjugate Improves the Efficacy of HER2-Positive Breast Cancer Therapy

Tumor-targeting peptide-drug conjugates (PDCs) have become a focus of research in recent years. However, due to the instability of peptides and their short in vivo effective half-life, they have limited clinical application. Herein, we propose a new DOX PDC based on a homodimer HER-2-targeting peptide and acid-sensitive hydrazone bond, which could enhance the anti-tumor effect of DOX and reduce systemic toxicities. The PDC could accurately deliver DOX into HER2-positive SKBR-3 cells, with it showing 2.9 times higher cellular uptake than free DOX and enhanced cytotoxicity with respect to IC₅₀ of 140 nM (vs. 410 nM for free DOX). In vitro assays showed that the PDC had high cellular internalization efficiency and cytotoxicity. In vivo anti-tumor experiments indicated that the PDC could significantly inhibit the growth of HER2-positive breast cancer xenografts in mice and reduce the side effects of DOX. In summary, we constructed a novel PDC molecule targeting HER2-positive tumors, which may overcome some deficiencies of DOX in breast cancer therapy.

An ultrasensitive dual-signal ratio electrochemical aptamer biosensor for the detection of HER2

Electrochemical ratiometric biosensors have received attention from researchers because of their self-calibration capability, which can improve the accuracy of detection. In the present study, a ratiometric dual signal electrochemical aptamer biosensor based on ZIF-67 @polydopamine (PDA) nanocomposite and Cu/UiO-66 @ 3, 3', 5, 5'-tetramethylbenzidine (TMB) nanocomposite was fabricated for the detection of breast cancer biomarker- human epidermal growth factor receptor 2 (HER2). PDA was chosen as the electroactive material with electrochemical redox activity and ZIF-67 with a high specific surface area, forming the ZIF-67 @PDA+Apt as the nanoprobe for capturing HER2 in this paper. Cu/UiO-66 is a bimetallic compound with high stability, specific surface area, and strong adsorption onto aptamer chains, and the Cu/UiO-66 @TMB+Apt nanocomposite was used as a probe for signal labeling. In the presence of HER2, the capture of HER2 by the ZIF-67 @PDA+Apt probe results in a weakening of the conductivity of the electrode, however, by attenuating the electrochemical signal from the PDA, altering the probe-Cu/UiO-66 @TMB+Apt signaling will result in the enhancement of the TMB electrochemical signal. With a sensitive detection of HER2 biomarkers in as little as 30 min with the detection range of 0.75-40 pg/mL and a limit of detection as low as 44.8 fg/mL. Dual signal ratio biosensors have a low limit of detection, short detection time, which can accurately detect targets in complex biological samples, which has important theoretical importance.

Recent advances in peptide-based therapeutic strategies for breast cancer treatment

Breast cancer is the leading cause of cancer-related fatalities in female worldwide. Effective therapies with low side effects for breast cancer treatment and prevention are, accordingly, urgently required. Targeting anticancer materials, breast cancer vaccines and anticancer drugs have been studied for many years to decrease side effects, prevent breast cancer and suppress tumors, respectively. There are abundant evidences to demonstrate that peptide-based therapeutic strategies, coupling of good safety and adaptive functionalities are promising for breast cancer therapy. In recent years, peptide-based vectors have been paid attention in targeting breast cancer due to their specific binding to corresponding receptors overexpressed in cell. To overcome the low internalization, cell penetrating peptides (CPPs) could be selected to increase the penetration due to the electrostatic and hydrophobic interactions between CPPs and cell membranes. Peptide-based vaccines are at the forefront of medical development and presently, 13 types of main peptide vaccines for breast cancer are being studied on phase III, phase II, phase I/II and phase I clinical trials. In addition, peptide-based vaccines including delivery vectors and adjuvants have been implemented. Many peptides have recently been used in clinical treatments for breast cancer. These peptides show different anticancer mechanisms and some novel peptides could reverse the resistance of breast cancer to susceptibility. In this review, we will focus on current studies of peptide-based targeting vectors, CPPs, peptide-based vaccines and anticancer peptides for breast cancer therapy and prevention.

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.

Whole-body PET tracking of a d-dodecapeptide and its radiotheranostic potential for PD-L1 overexpressing tumors

Peptides that are composed of dextrorotary (d)-amino acids have gained increasing attention as a potential therapeutic class. However, our understanding of the in vivo fate of d-peptides is limited. This highlights the need for whole-body, quantitative tracking of d-peptides to better understand how they interact with the living body. Here, we used mouse models to track the movement of a programmed death-ligand 1 (PD-L1)-targeting d-dodecapeptide antagonist (DPA) using positron emission tomography (PET). More specifically, we profiled the metabolic routes of [64Cu]DPA and investigated the tumor engagement of [64Cu/68Ga]DPA in mouse models. Our results revealed that intact [64Cu/68Ga]DPA was primarily eliminated by the kidneys and had a notable accumulation in tumors. Moreover, a single dose of [64Cu]DPA effectively delayed tumor growth and improved the survival of mice. Collectively, these results not only deepen our knowledge of the in vivo fate of d-peptides, but also underscore the utility of d-peptides as radiopharmaceuticals.

Different directions for retro-inverso peptides

Retro-inverso peptides are reversed sequences of mirror-image amino acid residues. Synthetic molecules of this type have long been considered potential mimics of functional peptides. This Peptide Highlights article examines some recent applications of the retro-inverso transformation at the interface of peptide chemistry and medicine.

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.