An exploratory study on 99mTc-RGD-BBN peptide scintimammography in the assessment of breast malignant lesions compared to 99mTc-3P4-RGD2

High in-vivo stability in preclinical and first-in-human experiments with [18F]AlF-RESCA-MIRC213: a 18F-labeled nanobody as PET radiotracer for diagnosis of HER2-positive cancers

PURPOSE

[18F]AlF-RESCA was introduced as a core particularly useful for 18F-labeling of heat-sensitive biomolecules. However, no translational studies have been reported up to now. Herein, we reported the first-in-human evaluation of an 18F-labeled anti-HER2 nanobody MIRC213 as a PET radiotracer for imaging HER2-positive cancers.

METHODS

MIRC213 was produced by E. coli and conjugated with ( ±)-H3RESCA-Mal. [18F]AlF-RESCA-MIRC213 was prepared at room temperature. Its radiochemical purity and stability of were determined by radio-HPLC with the size-exclusion chromatographic column. Cell uptake was performed in NCI-N87 (HER2 +) and MCF-7 (HER2-) cells and the cell-binding affinity was verified in SK-OV-3 (HER2 +) cells. Small-animal PET/CT was performed using SK-OV-3, NCI-N87, and MCF-7 tumor-bearing mice at 30 min, 1 h, and 2 h post-injection. For blocking experiment, excess MIRC213 was co-injected with radiotracer. Biodistribution were performed on SKOV-3 and MCF-7 tumor-bearing mice at 2 h post-injection. For clinical study, PET/CT images were acquired at 2 h and 4 h after injection of [18F]AlF-RESCA-MIRC213 (1.85-3.7 MBq/kg) in six breast cancer patients (3 HER2-positive and 3 HER2-negative). All patients underwent [18F]-FDG PET/CT within a week for tissue selection purpose. Distribution and dosimetry were calculated. Standardized uptake values (SUV) were measured in tumors and normal organs.

RESULTS

MIRC213 was produced with > 95% purity and modified with RESCA to obtain RESCA-MIRC213. [18F]AlF-RESCA-MIRC213 was prepared within 20 min at room temperature with the radiochemical yield of 50.48 ± 7.6% and radiochemical purity of > 98% (n > 10), and remained stable in both PBS (88%) and 5% HSA (92%) after 6 h. The 2 h cellular uptake of [18F]AlF-RESCA-MIRC213 in NCI-N87 cells was 11.22 ± 0.60 AD%/105 cells. Its binding affinity Kd value was determined to be 1.23 ± 0.58 nM. Small-animal PET/CT with [18F]AlF-RESCA-MIRC213 can clearly differentiate SK-OV-3 and NCI-N87 tumors from MCF-7 tumors and background with a high uptake of 4.73 ± 1.18 ID%/g and substantially reduced to 1.70 ± 0.13 ID%/g for the blocking group (p < 0.05) in SK-OV-3 tumors at 2 h post-injection. No significant bone radioactivity was seen in the tumor-bearing animals. In all six breast cancer patients, there was no adverse reaction during study. The uptake of [18F]AlF-RESCA-MIRC213 was mainly in lacrimal gland, parotid gland, submandibular gland, thyroid gland, gallbladder, kidneys, liver, and intestines. There was no significant bone radioactivity accumulation in cancer patients. [18F]AlF-RESCA-MIRC213 had significantly higher tumor uptake in lesions from HER2-positive patients than that lesions from HER2-negative patients (SUVmax of 3.62 ± 1.56 vs. 1.41 ± 0.41, p = 0.0012) at 2 h post-injection. The kidneys received the highest radiation dose of 2.42 × 10-1 mGy/MBq, and the effective dose was 1.56 × 10-2 mSv/MBq.

CONCLUSIONS

[18F]AlF-RESCA-MIRC213 could be prepared with high radiolabeling yield under mild conditions. [18F]AlF-RESCA-MIRC213 has relatively high stability both in vitro and in vivo. The results from clinical transformation suggest that [18F]AlF-RESCA-MIRC213 PET/CT is a safe procedure with favorable pharmacokinetics and dosimetry profile, and it is a promising new PET radiotracer for noninvasive diagnosis of HER2-positive cancers.

Clinical Evaluation of Nuclear Imaging Agents in Breast Cancer

Precision medicine is the customization of therapy for specific groups of patients using genetic or molecular profiling. Noninvasive imaging is one strategy for molecular profiling and is the focus of this review. The combination of imaging and therapy for precision medicine gave rise to the field of theranostics. In breast cancer, the detection and quantification of therapeutic targets can help assess their heterogeneity, especially in metastatic disease, and may help guide clinical decisions for targeted treatments. Positron emission tomography (PET) or single-photon emission tomography (SPECT) imaging has the potential to play an important role in the molecular profiling of therapeutic targets in vivo for the selection of patients who are likely to respond to corresponding targeted therapy. In this review, we discuss the state-of-the-art nuclear imaging agents in clinical research for breast cancer. We reviewed 17 clinical studies on PET or SPECT agents that target 10 different receptors in breast cancer. We also discuss the limitations of the study designs and of the imaging agents in these studies. Finally, we offer our perspective on which imaging agents have the highest potential to be used in clinical practice in the future.

Radionuclide-Based Imaging of Breast Cancer: State of the Art

Simple Summary

Breast cancer is one of the most commonly diagnosed malignant tumors, possessing high incidence and mortality rates that threaten women’s health. Thus, early and effective breast cancer diagnosis is crucial for enhancing the survival rate. Radionuclide molecular imaging displays its advantages for detecting breast cancer from a functional perspective. Noninvasive visualization of biological processes with radionuclide-labeled small metabolic compounds helps elucidate the metabolic state of breast cancer, while radionuclide-labeled ligands/antibodies for receptor-targeted radionuclide molecular imaging is sensitive and specific for visualization of the overexpressed molecular markers in breast cancer. This review focuses on the most recent developments of novel radiotracers as promising tools for early breast cancer diagnosis.

Abstract

Breast cancer is a malignant tumor that can affect women worldwide and endanger their health and wellbeing. Early detection of breast cancer can significantly improve the prognosis and survival rate of patients, but with traditional anatomical imagine methods, it is difficult to detect lesions before morphological changes occur. Radionuclide-based molecular imaging based on positron emission tomography (PET) and single-photon emission computed tomography (SPECT) displays its advantages for detecting breast cancer from a functional perspective. Radionuclide labeling of small metabolic compounds can be used for imaging biological processes, while radionuclide labeling of ligands/antibodies can be used for imaging receptors. Noninvasive visualization of biological processes helps elucidate the metabolic state of breast cancer, while receptor-targeted radionuclide molecular imaging is sensitive and specific for visualization of the overexpressed molecular markers in breast cancer, contributing to early diagnosis and better management of cancer patients. The rapid development of radionuclide probes aids the diagnosis of breast cancer in various aspects. These probes target metabolism, amino acid transporters, cell proliferation, hypoxia, estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), gastrin-releasing peptide receptor (GRPR) and so on. This article provides an overview of the development of radionuclide molecular imaging techniques present in preclinical or clinical studies, which are used as tools for early breast cancer diagnosis.

Clinical evaluation of kit based Tc-99m-HYNIC-RGD2 for imaging angiogenesis in breast carcinoma patients

BACKGROUND

Radiolabeled RGD peptide can be used for noninvasive in vivo imaging of αvβ3 integrin receptors leading to early detection of tumor cells and hence improving the clinical outcomes. In the present study single vial kit based HYNIC RGD2 was radiolabeled with Tc-99m and evaluated in patients with breast carcinoma.

METHODS

Radiolabeling was performed via bifunctional chelator method. Tc-99m 1110-2960 MBq (30-80 mCi) was added to the HYNIC-RGD2 vial. The reaction mixture was heated for 20 minutes at 100°C. After performing the quality checks, whole-body planar imaging was performed in 20 patients at 2-2.5 h post i.v. injection of 555-740 MBq (15-20 mCi) of the radiotracer.

RESULTS

Radiolabeling yield of ≥98% was observed in all the formulations. Quality control tests indicated the suitability of radiopharmaceutical for intravenous administration. Physiological uptake of Tc-99m HYNIC-RGD2 was observed in the nasopharynx, salivary glands, liver, spleen, and intestine. Good uptake of radiotracer was observed in breast lesions of 18 patients. Two patients were observed to be negative. Increased uptake was also seen in metastatic sites in two patients and in lymph nodes in three patients. Scintigraphy findings were in corroboration with pathological observations.

CONCLUSION

The single vial cold kit based radiolabeling of Tc-99m HYNIC-RGD2 is facile leading to its easy availability. Tc-99m HYNIC-RGD2 is a promising radiopharmaceutical which can be used for the molecular imaging of angiogenesis in breast carcinoma patients.

Theranostic Advances in Breast Cancer in Nuclear Medicine

The implication of 'theranostic' refers to targeting an identical receptor for diagnostic and therapeutic purposes, by the same radioligand, simultaneously or separately. In regard to extensive efforts, many considerable theranostic tracers have been developed in recent years. Emerging evidence strongly demonstrates the tendency of nuclear medicine towards therapies based on a diagnosis. This review is focused on the examples of targeted radiopharmaceuticals for the imaging and therapy of breast cancer.

Radiolabeled Peptides for SPECT and PET Imaging in the Detection of Breast Cancer: Preclinical and Clinical Perspectives

Breast cancer is the most common cancer in women worldwide. Due to the heterogeneous nature of breast cancer, the optimal treatment and expected response for each patient may not necessarily be universal. Molecular imaging techniques could play an important role in the early detection and targeted therapy evaluation of breast cancer. This review focuses on the development of peptides labeled with SPECT and PET radionuclides for breast cancer imaging. We summarized the current status of radiolabeled peptides for different receptors in breast cancer. The characteristics of radionuclides and major techniques for peptide labeling are also briefly discussed.

The association of 18F-fluorodeoxyglucose PET/computed tomography parameters with tissue gastrin-releasing peptide receptor and integrin αvβ3 receptor levels in patients with breast cancer

OBJECTIVE

Gastrin-releasing peptide receptor (GRPR) and integrin αvβ3 receptors are significantly associated with primary breast cancer, neovascular endothelial, and metastatic tumor cells. We aimed to evaluate GRPR and integrin αvβ3 receptor staining, F-FDG uptake patterns and possible prognostic factors in breast cancer.

METHODS

Ninety lesions of 87 subjects diagnosed with breast cancer were included in this prospective study. The sections were stained with GRPR and integrin αvβ3. Subjects were divided into four molecular subgroups: luminal A, luminal B, triple negative and HER2. PET/CT imaging was performed on all subjects. The groups were compared in terms of GRPR and integrin αvβ3 staining properties, possible prognostic factors and mean SUVmax values.

RESULTS

Increased F-FDG uptake was significantly associated with estrogen receptor and progesterone receptor negativity. Molecular subtypes were significantly associated with mean integrin scores (P = 0.030), while histopathological subtypes were significantly associated with mean GRPR scores (P = 0.029). Increased integrin αvβ3 expression is significantly associated with ER and PR negativity. Additionally, GRPR score was significantly correlated with estrogen receptor and progesterone receptor expression scores and a negative statistically significant correlation was detected between integrin and progesterone receptor scores. Mean primary lesion SUVmax had a statistically significant positive correlation with integrin αvβ3 score.

CONCLUSION

GRPR and integrin αvβ3 expression results are complementary to F-FDG PET/CT findings, and are also significantly correlated with hormone receptors associated with aggressive subtypes. These results may pave the way for GRPR and integrin αvβ3 targeted imaging with Ga-labeled molecules and systemic radionuclide treatment with Lu-labeled compounds.

Imaging and monitoring HER2 expression in breast cancer during trastuzumab therapy with a peptide probe 99mTc-HYNIC-H10F

PURPOSE

The novel molecular imaging probe ^99mTc-HYNIC-H10F was developed for patient screening and efficacy monitoring of trastuzumab therapy by SPECT imaging of HER2 expression in breast cancer.

METHODS

^99mTc-HYNIC-H10F was developed by labeling H10F peptide with ^99mTc following an optimized protocol. Biodistribution and SPECT/CT were performed in mouse models bearing HER2-positive SK-BR3 and HER2-negative MDA-MB-231 human breast cancer xenografts, respectively. The treatment response to trastuzumab was monitored and quantified by SPECT/CT in two HER2-positive breast cancer models (SK-BR3 and MDA-MB-361). The preliminary clinical study was performed in two patients with breast cancer.

RESULTS

SPECT/CT with ^99mTc-HYNIC-H10F showed that the SK-BR3 tumors were clearly visualized, while the signals from MDA-MB-231 tumors were much lower. The tumor uptake of ^99mTc-HYNIC-H10F could be blocked by excess unlabeled H10F peptide but not by excess trastuzumab. The growth of two HER2-positive tumors was prominently suppressed at day 11 post-treatment. However, SPECT/CT reflected much earlier therapy response at day 4 post-treatment. The HER2 expression in tumors of breast cancer patients could be detected by ^99mTc-HYNIC-H10F SPECT/CT imaging.

CONCLUSIONS

^99mTc-HYNIC-H10F specifically accumulates in HER2-positive tumors. Compared with trastuzumab, ^99mTc-HYNIC-H10F binds to a different domain of HER2 antigen, providing new opportunities to monitor HER2 expression levels before/during/after trastuzumab treatment for more effective personalized treatment.

Single Photon Emission Computed Tomography Tracer

Single photon emission computed tomography (SPECT) is the state-of-the-art imaging modality in nuclear medicine despite the fact that only a few new SPECT tracers have become available in the past 20 years. Critical for the future success of SPECT is the design of new and specific tracers for the detection, localization, and staging of a disease and for monitoring therapy. The utility of SPECT imaging to address oncologic questions is dependent on radiotracers that ideally exhibit excellent tissue penetration, high affinity to the tumor-associated target structure, specific uptake and retention in the malignant lesions, and rapid clearance from non-targeted tissues and organs. In general, a target-specific SPECT radiopharmaceutical can be divided into two main parts: a targeting biomolecule (e.g., peptide, antibody fragment) and a γ-radiation-emitting radionuclide (e.g., ^99mTc, ¹²³I). If radiometals are used as the radiation source, a bifunctional chelator is needed to link the radioisotope to the targeting entity. In a rational SPECT tracer design, these single components have to be critically evaluated in order to achieve a balance among the demands for adequate target binding, and a rapid clearance of the radiotracer. The focus of this chapter is to depict recent developments of tumor-targeted SPECT radiotracers for imaging of cancer diseases. Possibilities for optimization of tracer design and potential causes for design failure are discussed and highlighted with selected examples.

Peptide receptors as cancer drug targets

Neuropeptides function as neuromodulators in the brain, whereby they are released in a paracrine manner and activate G protein-coupled receptors (GPCRs) in adjacent cells. Because neuropeptides are made in, and secreted from, cancer cells, then bind to cell surface receptors, they function in an autocrine manner. Bombesin (BB)-like peptides synthesized by neuroendocrine tumor small cell lung cancer (SCLC) bind to BB receptors (BBRs), causing phosphatidylinositol turnover and phosphorylation of extracellular signal-regulated kinase (ERK). Phosphorylated ERK enters the nucleus and alters gene expression of SCLC cells, stimulating growth. Vasoactive intestinal peptide (VIP) addition to SCLC cells increases their release rate of BB-like peptides via activation of VIP receptors (VIPR), leading to activation of adenylyl cyclase and subsequent elevation of cAMP. Protein kinase A is then stimulated, leading to phosphorylation of cyclic AMP response element binding protein (CREB), which alters gene expression and stimulates proliferation. The growth of SCLC is inhibited by BBR and VIPR antagonists. This review will focus on how GPCRs for VIP and BB are molecular targets for early detection and treatment of cancer.

Comparison of [99mTc]3PRGD2 Imaging and [18F]FDG PET/CT in Breast Cancer and Expression of Integrin αvβ3 in Breast Cancer Vascular Endothelial Cells

PURPOSE

This study aimed to investigate the value of ^99mtechnetium-three polyethylene glycol spacers-arginine-glycine-aspartic acid ([^99mTc]3PRGD₂) imaging in diagnosis and staging of breast cancer compared with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) imaging, and to explore the expression of integrin α_vβ₃ in tumor vascular endothelial cells.

PROCEDURES

Forty-two women with suspected breast cancer underwent both [^99mTc]3PRGD₂ imaging and [¹⁸F]FDG imaging. Visual analysis was used to assess primary breast lesion, axillary lymph node, and distant metastasis. The tumor-blood (T/B) ratios from [^99mTc]3PRGD₂ imaging and the maximum standardized uptake value (SUVmax) from [¹⁸F]FDG imaging were analyzed for breast lesions. Integrin α_vβ₃ was analyzed through immunohistochemistry.

RESULTS

Forty-five breast lesions were found (malignant, n = 38; benign, n = 7). The sensitivity, specificity, and accuracy of [^99mTc]3PRGD₂ and [¹⁸F]FDG imaging in visual analysis for the breast lesion were 97.4, 87.5, and 95.6 % and 97.4, 71.4, and 93.3 %, respectively (P > 0.05). For semi-quantitative analysis, no significant difference of the area under the curves (AUC) was found in the imaging using the two radiopharmaceuticals (0.880 and 0.955; Z = 0.88, P > 0.05). The sensitivity, specificity, and accuracy for axillary lymph node metastasis with [^99mTc]3PRGD₂ and [¹⁸F]FDG were 78.05, 99.36, and 94.92 % and 85.37, 98.72, and 95.64 %, respectively (P > 0.05). Nine patients with distant metastases were all detected with the two radiopharmaceuticals. The expression of integrin α_vβ₃ was correlated with [^99mTc]3PRGD₂ uptake (r = 0.582, P = 0.001), which were significantly higher in the HER2-positive and stage III-IV patients (P < 0.05).

CONCLUSIONS

The prospective study demonstrated that [^99mTc]3PRGD₂ imaging seems to be valuable for diagnosis of breast cancer and its staging. It may be less sensitive for detecting small lymph node metastatic lesions when compared with [¹⁸F]FDG imaging. Integrin α_vβ₃ in tumor microvessels was associated with the breast cancer subtype and its staging.

Tumor targeting with 99m Tc radiolabeled peptides: Clinical application and recent development

Targeting overexpressed receptors on the cancer cells with radiolabeled peptides has become very important in nuclear oncology in the recent years. Peptides are small and have easy preparation and easy radiolabeling protocol with no side-effect and toxicity. These properties made them a valuable tool for tumor targeting. Based on the successful imaging of neuroendocrine tumors with ¹¹¹ In-octreotide, other receptor-targeting peptides such as bombesin (BBN), cholecystokinin/gastrin analogues, neurotensin analogues, glucagon-like peptide-1, and RGD peptides are currently under development or undergoing clinical trials. The most frequently used radionuclides for tumor imaging are ^99m Tc and ¹¹¹ In for single-photon emission computed tomography and ⁶⁸ Ga and ¹⁸ F for positron emission tomography imaging. This review presents some of the ^99m Tc-labeled peptides, with regard to their potential for radionuclide imaging of tumors in clinical and preclinical application.

Neuropeptide G Protein-Coupled Receptors as Oncotargets

Neuropeptide G protein-coupled receptors (GPCRs) are overexpressed on numerous cancer cells. In a number of tumors, such as small cell lung cancer (SCLC), bombesin (BB) like peptides and neurotensin (NTS) function as autocrine growth factors whereby they are secreted from tumor cells, bind to cell surface receptors and stimulate growth. BB-drug conjugates and BB receptor antagonists inhibit the growth of a number of cancers. Vasoactive intestinal peptide (VIP) increases the secretion rate of BB-like peptide and NTS from SCLC leading to increased proliferation. In contrast, somatostatin (SST) inhibits the secretion of autocrine growth factors from neuroendocrine tumors (NETs) and decreases proliferation. SST analogs such as radiolabeled octreotide can be used to localize tumors, is therapeutic for certain cancer patients and has been approved for four different indications in the diagnosis/treatment of NETs. The review will focus on how BB, NTS, VIP, and SST receptors can facilitate the early detection and treatment of cancer.

95gTc and 96gTc as alternatives to medical radioisotope 99mTc

We studied 95gTc and 96gTc as alternatives to the medical radioisotope 99mTc. 96gTc (95gTc) can be produced by (p, n) reactions on an enriched 96Mo (95Mo) target with a proton beam provided by a compact accelerator such as a medical cyclotron that generate radioisotopes for positron emission tomography (PET). The γ-rays are measured with an electron-tracking Compton camera (ETCC). We calculated the relative intensities of the γ-rays from 95gTc and 96gTc. The calculated γ-ray intensity of a 96gTc (95gTc) nucleus is as high as 63% (70%) of that of a 99mTc nucleus. We also calculated the patient radiation doses of 95gTc and 96gTc, which were larger than that of 99mTc by a factor of 2-3 based on the applied assumptions. A medical PET cyclotron which can provide proton beams with energies of 11-12 MeV and a current of 100 μA can produce 12 GBq (39 GBq) of 96gTc (95gTc) for operation time of 8 h, which can be used for 240 (200) diagnostic scans.

Evaluation of Tc-99m-3PRGD2 Integrin Receptor Imaging in the Differential Diagnosis of Breast Lesions and Comparison With Mammography

PURPOSE

The aims of this study were to evaluate and compare efficacies of Tc-99m-3PRGD2 integrin receptor imaging under variety of conditions for the diagnosis of breast lesions, in addition to comparison with mammography.

MATERIALS AND METHODS

Seventy-two female patients with established breast lesions were recruited. All patients were examined by Tc-99m-3PRGD2 integrin receptor imaging and mammography. Whole-body scan and SPECT/CT were acquired at dual time points of 2 and 4 h after injection using standard protocol. The processed images were evaluated by visual and semi-quantitative analysis. Mammography was performed using up and down and internal and external oblique views. The gold standard of diagnosis was based on histopathological findings.

RESULTS

Sensitivity greater than 85.0% and accuracy greater than 80.0% were observed under any technical method. For dense mammary gland, the sensitivity, specificity, and accuracy of Tc-99m-3PRGD2 SPECT/CT 4-h imaging and mammography were 95.2, 75.0, and 90.7%, and 71.4, 58.3, and 68.5% respectively. Combined two methods' sensitivity, specificity, and accuracy for detection of breast cancer can reach 98.3, 86.7, and 96.0%.

CONCLUSIONS

Tc-99m-3PRGD2-based molecular imaging is a sensitive method for the differential diagnosis of breast lesions. Particularly, Tc-99m-3PRGD2-SPECT/CT has better diagnostic value in dense mammary gland as compared with mammography. Combining two methods can significantly improve the diagnostic efficiency.

Breast Imaging Utilizing Dedicated Gamma Camera and (99m)Tc-MIBI: Experience at the Tel Aviv Medical Center and Review of the Literature Breast Imaging

The scope of the current article is the clinical role of gamma cameras dedicated for breast imaging and (99m)Tc-MIBI tumor-seeking tracer, as both a screening modality among a healthy population and as a diagnostic modality in patients with breast cancer. Such cameras are now commercially available. The technology utilizing a camera composed of a NaI (Tl) detector is termed breast-specific gamma imaging. The technology of dual-headed camera composed of semiconductor cadmium zinc telluride detectors that directly converts gamma-ray energy into electronic signals is termed molecular breast imaging. Molecular breast imaging system has been installed at the Department of Nuclear medicine at the Tel Aviv Sourasky Medical Center, Tel Aviv in 2009. The article reviews the literature well as our own experience.

Interrogating the Role of Receptor-Mediated Mechanisms: Biological Fate of Peptide-Functionalized Radiolabeled Gold Nanoparticles in Tumor Mice

To get a better insight on the transport mechanism of peptide-conjugated nanoparticles to tumors, we performed in vivo biological studies of bombesin (BBN) peptide functionalized gold nanoparticles (AuNPs) in human prostate tumor bearing mice. Initially, we sought to compare AuNPs with thiol derivatives of acyclic and macrocyclic chelators of DTPA and DOTA types. The DTPA derivatives were unable to provide a stable coordination of (67)Ga, and therefore, the functionalization with the BBN analogues was pursued for the DOTA-containing AuNPs. The DOTA-coated AuNPs were functionalized with BBN[7-14] using a unidentate cysteine group or a bidentate thioctic group to attach the peptide. AuNPs functionalized with thioctic-BBN displayed the highest in vitro cellular internalization (≈ 25%, 15 min) in gastrin releasing peptide (GRP) receptor expressing cancer cells. However, these results fail to translate to in vivo tumor uptake. Biodistribution studies following intravenous (IV) and intraperitoneal (IP) administration of nanoconjugates in tumor bearing mice indicated that the presence of BBN influences to some degree the biological profile of the nanoconstructs. For IV administration, the receptor-mediated pathway appears to be outweighed by the EPR effect. By contrast, in IP administration, it is reasoned that the GRPr-mediated mechanism plays a role in pancreas uptake.

Bombesin related peptides/receptors and their promising therapeutic roles in cancer imaging, targeting and treatment

INTRODUCTION

Despite remarkable advances in tumor treatment, many patients still die from common tumors (breast, prostate, lung, CNS, colon, and pancreas), and thus, new approaches are needed. Many of these tumors synthesize bombesin (Bn)-related peptides and over-express their receptors (BnRs), hence functioning as autocrine-growth-factors. Recent studies support the conclusion that Bn-peptides/BnRs are well-positioned for numerous novel antitumor treatments, including interrupting autocrine-growth and the use of over-expressed receptors for imaging and targeting cytotoxic-compounds, either by direct-coupling or combined with nanoparticle-technology.

AREAS COVERED

The unique ability of common neoplasms to synthesize, secrete, and show a growth/proliferative/differentiating response due to BnR over-expression, is reviewed, both in general and with regard to the most frequently investigated neoplasms (breast, prostate, lung, and CNS). Particular attention is paid to advances in the recent years. Also considered are the possible therapeutic approaches to the growth/differentiation effect of Bn-peptides, as well as the therapeutic implication of the frequent BnR over-expression for tumor-imaging and/or targeted-delivery.

EXPERT OPINION

Given that Bn-related-peptides/BnRs are so frequently ectopically-expressed by common tumors, which are often malignant and become refractory to conventional treatments, therapeutic interventions using novel approaches to Bn-peptides and receptors are being explored. Of particular interest is the potential of reproducing with BnRs in common tumors the recent success of utilizing overexpression of somatostatin-receptors by neuroendocrine-tumors to provide the most sensitive imaging methods and targeted delivery of cytotoxic-compounds.

99mTc-Glu-c(RGDyK)-Bombesin SPECT Can Reduce Unnecessary Biopsy of Masses That Are BI-RADS Category 4 on Ultrasonography

Masses that, on ultrasonography, are category 4 according to the Breast Imaging Reporting and Data System (BI-RADS) represent possible malignancy, and a biopsy is recommended. This study explored the value of (99m)Tc-Glu-c(RGDyK)-bombesin ((99m)Tc-RGD-bombesin) in reducing unnecessary biopsy of these masses.

METHODS

Ninety women with a BI-RADS 4 mass on ultrasonography were enrolled in this study to undergo breast SPECT using (99m)Tc-RGD-bombesin. The images were independently interpreted using qualitative visual and semiquantitative analyses. The final diagnosis was based on histopathologic examination of surgically excised or percutaneous biopsy specimens. Fractions of the samples were immunohistochemically analyzed to evaluate expression of integrin αvβ3 and gastrin-releasing peptide receptor (GRPR). The receptor-positive group was further divided into 3 subgroups (GRPR(+)/αvβ3 (+), GRPR(+)/αvβ3 (-), and αvβ3 (+)/GRPR(-)).

RESULTS

Ninety-four masses (22 malignant and 72 benign) were confirmed by histopathologic examination. On qualitative analysis, 20 of the malignant masses showed high (99m)Tc-RGD-bombesin accumulation and 48 of the benign masses showed no (99m)Tc-RGD-bombesin accumulation. The optimal cutoff for qualitative analysis was a score of 2. Semiquantitative analysis revealed that 20 of the malignant masses and 16 of the benign masses had a relatively high tumor-to-normal-tissue ratio (T/N). The optimal cutoff was a T/N of 2.26. The mean T/N was higher for malignant masses than for benign masses (3.17 ± 0.86 vs. 1.89 ± 0.71, P < 0.05). T/Ns did not differ among the 3 subgroups (P > 0.05). The areas under the receiver-operating-characteristic curves for the qualitative and semiquantitative analyses were 0.788 and 0.865, respectively, and the overall diagnostic performance did not significantly differ between these analyses (P > 0.05).

CONCLUSION

(99m)Tc-RGD-bombesin SPECT can differentiate benign from malignant BI-RADS 4 masses with high specificity. Further study of the application of this test to clinical breast cancer appears warranted.