99mTc-Evans blue dye for mapping contiguous lymph node sequences and discriminating the sentinel lymph node in an ovine model

Sentinel lymph node detection by combining nonradioactive techniques with contrast agents: State of the art and prospects

The status of sentinel lymph nodes (SLNs) has a substantial prognostic value because these nodes are the first place where cancer cells accumulate along their spreading route. Routine SLN biopsy ("gold standard") involves peritumoral injections of radiopharmaceuticals, such as technetium-99m, which has obvious disadvantages. This review examines the methods used as "gold standard" analogs to diagnose SLNs. Nonradioactive preoperative and intraoperative methods of SLN detection are analyzed. Promising photonic tools for SLNs detection are reviewed, including NIR-I/NIR-II fluorescence imaging, photoswitching dyes for SLN detection, in vivo photoacoustic detection, imaging and biopsy of SLNs. Also are discussed methods of SLN detection by magnetic resonance imaging, ultrasonic imaging systems including as combined with photoacoustic imaging, and methods based on the magnetometer-aided detection of superparamagnetic nanoparticles. The advantages and disadvantages of nonradioactive SLN-detection methods are shown. The review concludes with prospects for the use of conservative diagnostic methods in combination with photonic tools.

Lymphatic targeting by albumin-hitchhiking: Applications and optimisation

The lymphatic system plays an integral role in the development and progression of a range of disease conditions, which has impelled medical researchers and clinicians to design, develop and utilize advanced lymphatic drug delivery systems. Following interstitial administration, most therapeutics and molecules are cleared from tissues via the draining blood capillaries. Macromolecules and delivery systems >20 kDa in size or 10-100 nm in diameter are, however, transported from the interstitium via draining lymphatic vessels as they are too large to cross the blood capillary endothelium. Lymphatic uptake of small molecules can be promoted by two general approaches: administration in association with synthetic macromolecular constructs, or through hitchhiking on endogenous cells or macromolecular carriers that are transported from tissues via the lymphatics. In this paper we review the latter approach where molecules are targeted to lymph by hitchhiking on endogenous albumin transport pathways after subcutaneous, intramuscular or intradermal injection. We describe the properties of the lymphatic system and albumin that are relevant to lymphatic targeting, the characteristics of drugs and delivery systems designed to hitchhike on albumin trafficking pathways and how to further optimise these properties, and finally the current applications and potential future directions for albumin-hitchhiking approaches to target the lymphatics.

Preparation of a multi-modal agent for sentinel lymph node mapping using Evans blue and 99mTc-labeled mannosylated human serum albumin conjugate

INTRODUCTION

The identification of sentinel lymph nodes (SLNs) is important in deciding the resection range during surgery. ^99mTc-labeled mannosylated human serum albumin ([^99mTc]Tc-MSA) is a radiopharmaceutical developed for SLN detection by targeting macrophages. Evans blue (EB) is a blue dye binding strongly to albumin and has been used for SLN detection. [^99mTc]Tc-MSA-EB conjugate was prepared as a multi-modal imaging agent and tested its performance by visual investigation, fluorescence imaging and SPECT/CT for SLN mapping in mice.

METHODS

EB was mixed with various concentration of MSA to prepare MSA-EB conjugates. The binding efficiencies were determined using thin-layer chromatography. The UV-VIS spectra and molar extinction coefficient of the conjugate were obtained. The fluorescence was monitored at the excitation wavelength range 420-780 nm and the emission wavelength range 520-845 nm. The [^99mTc]Tc-MSA-EB conjugate and EB were injected into the footpads of normal BALB/c mice to check the lymph node (LN) uptakes. The visible, fluorescence, and SPECT/CT images were obtained after injection.

RESULTS

The conjugation of EB with MSA increased by time and was saturated within 10 min. The molar extinction coefficient of the conjugate was 99,259.3/M/cm at 620 nm. The uptake of conjugate into the popliteal LN after injection into the footpads of mice was investigated visually and fluorescence imaging. SPECT/CT images showed that the standardized uptake values of [^99mTc]Tc-MSA-EB conjugate in popliteal LN were about 4 times higher than in sciatic LN at all timepoints. It was confirmed by investigating resected LN that the blue color, fluorescence, and radioactivity of the [^99mTc]Tc-MSA-EB conjugate were retained only on the LN and did not spread to adjoining tissues.

CONCLUSION

[^99mTc]Tc-MSA-EB conjugate has a great potential as a multi-modal SLN mapping agent which could be detected by visual investigation, fluorescence imaging, and SPECT/CT.

Hybrid 99mTc-magnetite tracer for dual modality sentinel lymph node mapping

Accuracy of sentinel lymph node identification using radioactive tracers in non-superficial cancers can be limited by radiation shine through and low spatial resolution of detection systems such as intraoperative gamma probes. By utilising a dual radioactive/magnetic tracer, sensitive lymphoscintigraphy can be paired with high spatial resolution intraoperative magnetometer probes to improve the accuracy of sentinel node detection in cancers with complex multidirectional lymphatic drainage. Dextran-coated magnetite nanoparticles (33 nm mean hydrodynamic diameter) were labelled with ^99mTc and applied as a lymphotropic tracer in small and large animal models. The dual tracer could be radiolabelled with 98 ± 2% efficiency after 10 min of incubation at room temperature. Biodistribution studies of the tracer were conducted in normal rats (subdermal and intravenous tail delivery, n = 3) and swine (subdermal hind limb delivery, n = 5). In rats the dual tracer migrated through four tiers of lymph node, 20 min after subdermal injection. Results from intravenous biodistribution test for radiocolloids demonstrated no aggregation in vivo, however indicated the presence of some lower-molecular weight radioactive impurities (^99mTc-dextran). In swine, the dual tracer could be effectively used to map lymphatic drainage from hind hoof to popliteal and inguinal basins using intraoperative gamma and magnetometer probes. Of the eight primary nodes excised, eight were positively identified by gamma probe and seven by magnetometer probe. The high-purity dual tracer shows early promise for sentinel node identification in complex lymphatic environments by combining sensitive preoperative lymphoscintigraphy with a high-resolution intraoperative magnetometer probe.

Evans Blue Dye: A Revisit of Its Applications in Biomedicine

Evans blue (EB) dye has owned a long history as a biological dye and diagnostic agent since its first staining application by Herbert McLean Evans in 1914. Due to its high water solubility and slow excretion, as well as its tight binding to serum albumin, EB has been widely used in biomedicine, including its use in estimating blood volume and vascular permeability, detecting lymph nodes, and localizing the tumor lesions. Recently, a series of EB derivatives have been labeled with PET isotopes and can be used as theranostics with a broad potential due to their improved half-life in the blood and reduced release. Some of EB derivatives have even been used in translational applications in clinics. In addition, a novel necrosis-avid feature of EB has recently been reported in some preclinical animal studies. Given all these interesting and important advances in EB study, a comprehensive revisiting of EB has been made in its biomedical applications in the review.

An Albumin-binding Polypeptide Both Targets Cytotoxic T Lymphocyte Vaccines to Lymph Nodes and Boosts Vaccine Presentation by Dendritic Cells

Rationale: Albumin-binding carriers have been shown to target cytotoxic T lymphocyte (CTL) vaccines to lymph nodes (LNs) and improve the efficacy of the vaccines. However, it was not clear whether the improved efficacy is solely due to the LN targeting, which prompted this study.

Methods: First, we generated a fusion protein consisting of an albumin-binding domain (ABD) and an immune-tolerant elastin-like polypeptide (iTEP). Then, we examined the binding between this fusion protein, termed ABD-iTEP, and mouse serum albumin (MSA). Next, we evaluated the accumulation of ABD-iTEP in LNs and dendritic cells (DCs) in the LNs. We also analyzed antigen presentation and in vitro T cell activation of vaccines that were delivered by ABD-iTEP and investigated possible underlying mechanisms of the presentation and activation results. Last, we measured CTL responses induced by ABD-iTEP-delivered vaccines in vivo.

Results: ABD-iTEP bound with MSA strongly with an affinity of 1.41 nM. This albumin-binding carrier, ABD-iTEP, accumulated in LNs 3-fold more than iTEP, a control carrier that did not bind with albumin. ABD-iTEP also resulted in 4-fold more accumulation in DCs in the LNs than iTEP. Most importantly, ABD-iTEP drastically enhanced the antigen presentation of its vaccine payloads and the T cell activation induced by its payloads. The enhancement was dependent on the formation of the complex between MSA and ABD-iTEP. Meanwhile, the MSA/ABD-iTEP complex was found to have increased stability in acidic subcellular compartments and increased cytosolic accumulation in DCs, which might explain the enhanced vaccine presentation resulting from the complex. Finally, when ABD-iTEP was used to deliver CTL vaccines derived from both self- and non-self-antigens, it boosted the vaccine-induced responses by 2-fold in either case.

Conclusion: ABD-iTEP not only targets vaccines to LNs but also promotes the presentation of the vaccines by DCs. Albumin-binding carriers have more than one mechanism to boost the efficacy of CTL vaccines.

Potential Applications of Using 68Ga-Evans Blue PET/CT in the Evaluation of Lymphatic Disorder: Preliminary Observations

PURPOSE

Potentials of 68Ga-NEB as a PET tracer in the evaluation of a variety of lymphatic drainage disorders were analyzed.

METHODS

68Ga-NEB was injected subcutaneously, and the PET/CT images were acquired in 13 patients with different suspected lymphatic drainage abnormality. The 68Ga-NEB PET/CT findings were compared with Tc-SC lymphoscintigraphy.

RESULTS

68Ga-NEB activity could be clearly observed in the lymphatic route on the PET/CT images from all the patients. In 5 (38.5%) of 13 patients tested, 68Ga-NEB PET/CT provided more information than the Tc-SC lymphoscintigraphy.

CONCLUSIONS

68Ga-NEB PET/CT can be used as an alternative of Tc-SC lymphoscintigraphy in the evaluation of lymphatic disorders, which enables fast results and might be more accurate than the conventional Tc-SC lymphoscintigraphy.

Lymphatic imaging: focus on imaging probes

In view of the importance of sentinel lymph nodes (SLNs) in tumor staging and patient management, sensitive and accurate imaging of SLNs has been intensively explored. Along with the advance of the imaging technology, various contrast agents have been developed for lymphatic imaging. In this review, the lymph node imaging agents were summarized into three groups: tumor targeting agents, lymphatic targeting agents and lymphatic mapping agents. Tumor targeting agents are used to detect metastatic tumor tissue within LNs, lymphatic targeting agents aim to visualize lymphatic vessels and lymphangionesis, while lymphatic mapping agents are mainly for SLN detection during surgery after local administration. Coupled with various signal emitters, these imaging agents work with single or multiple imaging modalities to provide a valuable way to evaluate the location and metastatic status of SLNs.

In vivo albumin labeling and lymphatic imaging

The ability to accurately and easily locate sentinel lymph nodes (LNs) with noninvasive imaging methods would assist in tumor staging and patient management. For this purpose, we developed a lymphatic imaging agent by mixing fluorine-18 aluminum fluoride-labeled NOTA (1,4,7-triazacyclononane-N,N',N''-triacetic acid)-conjugated truncated Evans blue ((18)F-AlF-NEB) and Evans blue (EB) dye. After local injection, both (18)F-AlF-NEB and EB form complexes with endogenous albumin in the interstitial fluid and allow for visualizing the lymphatic system. Positron emission tomography (PET) and/or optical imaging of LNs was performed in three different animal models including a hind limb inflammation model, an orthotropic breast cancer model, and a metastatic breast cancer model. In all three models, the LNs can be distinguished clearly by the apparent blue color and strong fluorescence signal from EB as well as a high-intensity PET signal from (18)F-AlF-NEB. The lymphatic vessels between the LNs can also be optically visualized. The easy preparation, excellent PET and optical imaging quality, and biosafety suggest that this combination of (18)F-AlF-NEB and EB has great potential for clinical application to map sentinel LNs and provide intraoperative guidance.

Clinical relevance of novel imaging technologies for sentinel lymph node identification and staging

The sentinel lymph node (SLN) concept has become a standard of care for patients with breast cancer and melanoma, yet its clinical application to other cancer types has been somewhat limited. This is mainly due to the reduced accuracy of conventional SLN mapping techniques (using blue dye and/or radiocolloids as lymphatic tracers) in cancer types where lymphatic drainage is more complex, and SLNs are within close proximity to other nodes or the tumour site. In recent years, many novel techniques for SLN mapping have been developed including fluorescence, x-ray, and magnetic resonant detection. Whilst each technique has its own advantages/disadvantages, the role of targeted contrast agents (for enhanced retention in the SLN, or for immunostaging) is increasing, and may represent the new standard for mapping the SLN in many solid organ tumours. This review article discusses current limitations of conventional techniques, limiting factors of nanoparticulate based contrast agents, and efforts to circumvent these limitations with modern tracer architecture.

Sentinel lymph node biopsy in early breast cancer surgery--working with the risks of vital blue dye to reap the benefits

AIMS

Sentinel lymph node biopsy (SLNB) is an important method of staging early breast cancer because of the inherent benefits it confers on patients in terms of arm function and quality of life. Its success depends on a high level of accuracy in detecting the sentinel node. This is achieved by a dual mapping technique that employs a radio-labelled nanocolloid and a vital blue dye. The vital dyes however carry the risk of anaphylaxis, and as more surgeons employ SLNB in their daily practice, a proportionate rise in the number of anaphylactic reactions can be expected. A comprehensive review of risks and benefits associated with using vital blues dyes has not been published and therefore a retrospective review was undertaken of the different levels of anaphylaxis associated with vital dyes as well as their benefits in SLNB.

METHODS

An OVID MEDLINE search was performed of the English published literature using appropriate search terms to find published trial data and case series that focused on adverse reactions to vital blue dyes.

RESULTS

The risk of severe anaphylaxis (grade 3) can be as low as 0.06%, and up to 0.4% for patients undergoing SLNB when data is analysed from large trials. Furthermore, adverse reactions associated with blue dyes are reversible with appropriate management.

CONCLUSIONS

Surgeons should continue to use vital dyes to ensure that SLNB remains a highly sensitive procedure.

Feasibility study of sentinel lymph node biopsy in esophageal cancer with conservative lymphadenectomy

INTRODUCTION

Lymphoscintigraphy and sentinel node mapping is established in breast cancer and melanoma but not in esophageal cancer, even though many centers have shown that occult tumor deposits in lymph nodes influence prognosis. We report our initial experience with lymphoscintigraphy and sentinel lymph node biopsy in patients undergoing resection for esophageal cancer.

METHODS

Sixteen of 17 consecutive patients underwent resection for invasive esophageal cancer along with sentinel lymph node retrieval (resection rate, 94%). Peritumoral injection of (99m)Tc antimony colloid was performed by upper endoscopy prior to the operation. A two-surgeon synchronous approach via right thoracotomy and laparotomy was performed with conservative lymphadenectomy. Sentinel lymph nodes were identified using a gamma probe both in vivo and ex vivo. Sentinel lymph nodes were sent off separately for serial sections and immunohistochemistry.

RESULTS

Median patient age was 60.4 years (range, 45-75 years). Fifteen were male, and thirteen had adenocarcinoma. At least one sentinel lymph node (median, 2) was identified in 14 of 16 patients (success rate, 88%). Sentinel nodes were present in more than one nodal station in five patients (31%). In all 14 patients, the sentinel lymph node accurately predicted findings in non-sentinel nodes (accuracy, 100%). Three patients with positive sentinel lymph nodes had metastases identified in non-sentinel nodes (sensitivity, 100%).

CONCLUSIONS

Sentinel lymph node biopsy is feasible in esophageal resection with conservative lymphadenectomy, and initial results suggest it is accurate in predicting overall nodal status. Further study is needed to assess impact on patient management and prognosis.

In vivo antitumor and antimetastatic activities of camptothecin encapsulated with N-trimethyl chitosan in a preclinical mouse model of liver cancer

Application of camptothecin (CPT) is hampered due to its extreme water insolubility and unpredictable side effects. Therefore, it is essential to establish an efficient and safe protocol for the administration of camptothecin against tumor growth and metastasis. Here, we encapsulated camptothecin with N-trimethyl chitosan (CPT-TMC) and tested it on BALB/c mice subcutaneously injected with murine hepatocellular carcinoma cells at the hindlimb feet pad. CPT-TMC effectively inhibited tumor growth and lymphatic metastasis, prolonged survival time, yet without apparent toxic effects. Thus, CPT-TMC may provide a novel and effective therapeutic strategy against human advanced hepatic cancer without conspicuous systemic toxic effects.

Lymphatic mapping with 99mTc-Evans Blue dye in sheep

OBJECTIVE

99mTc-Evans Blue (EB) is an agent that contains both radioactive and color signals in a single dose. Earlier studies in animal models have suggested that this agent when compared with the dual-injection technique of radiocolloid/blue dye can successfully discriminate the sentinel lymph node. The aim of this study was to investigate the potential of 99mTc-EB as an agent to map the lymphatic system in an ovine model.

METHODS

Doses of 99mTc-EB (23 MBq) containing EB dye (4 mg) were administered intradermally to the limbs of four anesthetized sheep, and they were then imaged over 20-30 min using a gamma camera. The study protocol was repeated using 99mTc-antimony trisulfide colloid (ATC) and Patent Blue V dye. The lymph nodes (popliteal, inguinal, and iliac for hind limbs or prescapular for fore limbs) were identified with a gamma probe during the operative exposure, then dissected and counted in a large volume counter.

RESULTS

Simple and complex (dual) drainage patterns were visible on the scans, and the sentinel node was more radioactive than higher tier nodes in a chain, for both radiotracers. For 99mTc-EB, maximum radioactive uptake was achieved at 3-6 min for popliteal lymph nodes, 12-14 min for iliac nodes, and 13-14 min for prescapular nodes. 99mTc-ATC resulted in maximum radioactive uptake at 4-6 min for popliteal lymph nodes, 13 min for an inguinal node, 13-20 min for iliac nodes, and 18 min for a prescapular node. Following 99mTc-EB injection, 15/15 lymph nodes harvested were all radioactive and blue. For 99mTc-radiocolloid/Patent Blue V injection, 8/14 nodes were radioactive and blue, and 6/14 nodes were radioactive only.

CONCLUSIONS

The soluble radiotracer 99mTc-EB appeared to be a useful lymphoscintigraphic agent in sheep, in which radioactive counts from superficial lymphatic channels and lymph nodes were sufficient for planar imaging. In comparison with 99mTc-antimony trisulfide colloid, both tracers discriminated the sentinel lymph node up to 50 min after administration; however, 99mTc-EB had the advantage of providing radioactive (gamma probe) and color signals simultaneously during the operative exposure.

A tumor-selective biotherapy with prolonged impact on established metastases based on cytokine gene-engineered MSCs

The poor prognosis for patients with advanced malignancy relates partly to the inability to reverse cancer metastasis. In this study we have investigated an integrated immunotherapy method against pre-established metastases in three kinds of advanced cancer models including B16 melanoma, 4T1 breast tumor, and Hca hepatoma. The progression of metastases into multistep lymph nodes (LN) and internal organs was, markedly impeded in the midway stage and reversed in the ultimate stage following a 20-day course of intravenous immunotherapy [with interleukin-12 (IL-12) gene-engineered mesenchymal stem cells (MSCs), administered once every 5 days P < 0.05)]; the therapy was without systemic toxic effects. As the control, obvious systemic toxicity was observed in the free AdIL-12 group, yet metastasis was partly delayed only in the midway stage but not in the ultimate stage. Enzyme-linked immunosorbent assay (ELISA) showed that the intratumoral expression levels of IL-12 were enhanced by cytokine-engineered MSCs to be tenfold greater than that of free AdIL-12 groups in the ultimate stage; conversely, free AdIL-12 groups showed elevated serum, but not intratumoral levels of IL-12, during the midway stage. Furthermore, histomorphometric analysis revealed a reductive tendency toward reversion of tumor-associated lymphatic sprouts and an increased tumor apoptosis index in engineered MSC groups (P < 0.05). These data indicate the potential of cytokine-engineered MSCs to be considered as an integrated therapeutic weapon for targeting advanced malignancies.