Nuclear medicine in primary breast cancer imaging

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.

Nanobody-Based Theranostic Agents for HER2-Positive Breast Cancer: Radiolabeling Strategies

The overexpression of human epidermal growth factor 2 (HER2) in breast cancer (BC) has been associated with a more aggressive tumor subtype, poorer prognosis and shorter overall survival. In this context, the development of HER2-targeted radiotracers is crucial to provide a non-invasive assessment of HER2 expression to select patients for HER2-targeted therapies, monitor response and identify those who become resistant. Antibodies represent ideal candidates for this purpose, as they provide high contrast images for diagnosis and low toxicity in the therapeutic setting. Of those, nanobodies (Nb) are of particular interest considering their favorable kinetics, crossing of relevant biological membranes and intratumoral distribution. The purpose of this review is to highlight the unique characteristics and advantages of Nb-based radiotracers in BC imaging and therapy. Additionally, radiolabeling methods for Nb including direct labeling, indirect labeling via prosthetic group and indirect labeling via complexation will be discussed, reporting advantages and drawbacks. Furthermore, the preclinical to clinical translation of radiolabeled Nbs as promising theranostic agents will be reported.

Synthesis and preliminary evaluation of a 18 F-labeled ethisterone derivative [18 F]EAEF for progesterone receptor targeting

To develop a novel progesterone receptor-targeting probe for positron emission tomography imaging, an ethisterone derivative [¹⁸ F]EAEF was designed and prepared in high decay-corrected radiochemical yield (30-35%) with good radiochemical purity (>98%). [¹⁸ F]EAEF is a lipophilic tracer (logP = 0.53 ± 0.06) with very good stability in saline and serum. In the biodistribution study, high radioactivity accumulation of [¹⁸ F]EAEF were found in uterus (5.73 ± 1.83% ID/g) and ovary (4.05 ± 0.73% ID/g) at 2 hr postinjection (p.i.), which have high progesterone receptor expression after treated with estradiol, while the muscle background has very low uptake (0.50 ± 0.17% ID/g). For positron emission tomography imaging, [¹⁸ F]EAEF showed high uptake in progesterone receptor-positive MCF-7 tumor (3.15 ± 0.07% ID/g at 2 hr p.i.) with good tumor to muscle ratio (2.90), and obvious lower tumor uptakes were observed in MCF-7 with EAEF blocking (1.84 ± 0.05% ID/g at 2 hr p.i.) or in progesterone receptor-negative MDA-MB-231 tumor (1.80 ± 0.03% ID/g at 2 hr p.i.). Based on the good stability and specificity of [¹⁸ F]EAEF, it may be a good candidate for imaging progesterone receptor and worth further investigation.

Modern breast cancer detection: a technological review

Breast cancer is a serious threat worldwide and is the number two killer of women in the United States. The key to successful management is screening and early detection. What follows is a description of the state of the art in screening and detection for breast cancer as well as a discussion of new and emerging technologies. This paper aims to serve as a starting point for those who are not acquainted with this growing field.

Preoperative Staging of Large Primary Breast Cancer With [18F]Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography Compared With Conventional Imaging Procedures

Purpose

To evaluate the utility of positron emission tomography (PET) and [18F]fluorodeoxyglucose in the initial staging of large primary breast tumors.

Patients and Methods

This prospective study was approved by the ethics committee, and all patients gave their informed consent before enrollment. Sixty consecutive patients with large (> 3 cm) primary breast cancer diagnosed by clinical examination and breast magnetic resonance imaging (MRI) were entered onto the study. The mean age was 57 ± 13 years. Chest computed tomography (CT), liver ultrasonography, bone scan, and PET/CT were performed in all patients. All findings were histologically confirmed, and/or at least 1 year of follow-up was required. Correlation between parameters was calculated using Pearson's correlation coefficient. P < .05 was considered statistically significant.

Results

Primary tumor was identified by both PET/CT and MRI in all patients. Multifocal and/or multicentric tumors were found in 19 patients by MRI. Axillary lymph node metastases were found in 20 of 52 patients. Extra-axillary metastatic lymph nodes were also found in three patients. One patient showed an infiltrated lymph node in the contralateral axilla. The sensitivity and specificity for PET/CT to detect axillary lymph nodes metastases were 70% and 100%, respectively. PET/CT diagnosed all extra-axillary lymph nodes. The overall sensitivity and specificity of PET/CT in detecting distant metastases were 100% and 98%, respectively; whereas the sensitivity and specificity of conventional imaging were 60% and 83%, respectively. PET led to a change in the initial staging in 42% of patients.

Conclusion

PET/CT underestimates locoregional lymph node staging in large primary breast cancer patients. PET/CT is a valuable tool to discard unsuspected extra-axillary lymph nodes and distant metastases.

Weaving single photon imaging into new drug development

The specific aim of this review is to assess the potential contribution of single photon emitting radiopharmaceutical technologies to new drug development. For each phase of therapeutic drug development, published literature was sought that shows single photon emitters can add value by quantifying pharmacokinetics, visualizing mechanisms of drug action, estimating therapeutic safety indices, or measuring dose-dependent pharmacodynamic effects. Not any published reports were found that describe using nuclear medicine techniques to help manage the progress of a new drug development program. As a consequence, most of the case in favor of weaving single photon imaging into the process had to be built on extrapolations from studies that showed feasibility post hoc. The strongest evidence of potential value was found for drug candidates that hope to influence diseases characterized by cell proliferation or cell death, particularly in the fields of oncology, cardiology, nephrology, and inflammation. Receptor occupancy studies were observed to occasionally offer unique advantages over analogous studies with positron emission tomography (PET). Enough hard data sets were found to justify the costs of using single photon imaging in a variety of new drug development paradigms.

Positron emission tomography in the staging and management of breast cancer

Background

Breast cancer is the commonest cause of cancer death in women in the Western world, and imaging is essential in its diagnosis and staging. Metabolic imaging is a novel approach to improving the detection of cancers, as malignant transformation of cells is often associated with increased metabolic activity. This review assesses the possible role of positron emission tomography (PET) as a single non-invasive imaging modality to replace or complement current imaging and surgical practices in the diagnosis and staging of breast cancer.

Methods and results

A Medline search was performed and articles were cross-referenced with other relevant material. Evaluation of primary breast cancer with PET has shown a sensitivity of between 64 and 100 per cent and a specificity of 33–100 per cent; diagnostic accuracy appears to be related to tumour size. Difficulties arise in altered fluorodeoxyglucose uptake in lobular carcinoma, carcinoma in situ and benign inflammatory breast disease. In axillary staging, sensitivities of between 25 and 100 per cent have been reported, but with a false-negative of up to 20 per cent. In the assessment of distant metastasis and asymptomatic patients with raised levels of tumour markers, PET was superior to conventional imaging modalities.

Conclusion

PET is not a single diagnostic and staging tool that can replace current surgical, histological and radiological staging. Its main role in breast cancer lies in the investigation of metastatic disease and the evaluation of pathological response to various chemotherapeutic regimens.

Breast imaging in the new era

In the last decade,there have been huge advances in the field of breast imaging.Full field digital mammography systems optimise lesion to background contrast with resultant improvement in the sensitivity of the technique for cancer detection, facilitated by computer-aided detection.Though mammography remains the only established modality for population-based screening, preliminary results from several large studies indicate that magnetic resonance imaging(MRI) has a role in high-risk patients.On the other hand, advances in ultrasound, MRI and nuclear medicine have the potential to greatly improve the specificity of breast imaging with regard to cancer detection and lesion characterisation.A number of new and experimental techniques are being developed which may have great impact in this area and these will be discussed. Though MRI now has an established place in the diagnosis of breast cancer, it is becoming clear that it can directly affect surgical and medical management by enabling assessment of response to chemotherapy and endocrine therapy, and facilitating choice of the most appropriate surgery.Just as the role of MRI has evolved,so too the place of nuclear medicine, particularly positron emission tomography and radio-immunoscintigraphy should become clearer in the next few years.