The preoperative detection of axillary lymph node metastases in breast cancer by isotope imaging

Radiolabeled Liposomes for Nuclear Imaging Probes

Quantitative nuclear imaging techniques are in high demand for various disease diagnostics and cancer theranostics. The non-invasive imaging modality requires radiotracing through the radioactive decay emission of the radionuclide. Current preclinical and clinical radiotracers, so-called nuclear imaging probes, are radioisotope-labeled small molecules. Liposomal radiotracers have been rapidly developing as novel nuclear imaging probes. The physicochemical properties and structural characteristics of liposomes have been elucidated to address their long circulation and stability as radiopharmaceuticals. Various radiolabeling methods for synthesizing radionuclides onto liposomes and synthesis strategies have been summarized to render them biocompatible and enable specific targeting. Through a variety of radionuclide labeling methods, radiolabeled liposomes for use as nuclear imaging probes can be obtained for in vivo biodistribution and specific targeting studies. The advantages of radiolabeled liposomes including their use as potential clinical nuclear imaging probes have been highlighted. This review is a comprehensive overview of all recently published liposomal SPECT and PET imaging probes.

Enhanced Efficacy of Radiopharmaceuticals When Using Technetium-99m-Labeled Liposomal Agents: Synthesis and Pharmacokinetic Properties

Challenges posed by the retention of radiopharmaceuticals in unintended organs affect the quality of patient procedures when undergoing diagnostics and therapeutics. The aim of this study was to formulate a suitable tracer encapsulated in liposomes using different techniques and compounds to enhance the stability, uptake, clearance, and cytotoxic effect of the radiopharmaceutical. Cationic liposomes were prepared by a thin-film method using dipalmitoyl phosphatidylcholine (DPPC) and cholesterol. Whole-body gamma camera images were acquired of intravenously injected New Zealand rabbits. Additionally, liposomes were assessed using stability, toxicity, zeta potential, and particle size tests. In the control cases, Technetium-99m (^99mTc)-sestamibi exhibited the lowest heart uptake the blood pool and delayed images compared to both ^99mTc-liposomal agents. Liver and spleen uptake in the control samples with ^99mTc-sestamibi increased in 1-h-delayed images, unlike with ^99mTc-liposomal agents, which were decreased in delayed images. The mean maximum count in the bladder for ^99mTc-sestamibi loaded liposomes 1 h post-injection was 2354.6 (±2.6%) compared to 178.4 (±0.54%) for ^99mTc-sestamibi without liposomes. Liposomal encapsulation reduced the cytotoxic effect of the sestamibi. ^99mTc-MIBI-cationic liposomes exhibited excellent early uptake and clearance compared to ^99mTc-MIBI without liposomes. Adding cholesterol during liposome formation enhanced the stability and specificity of the targeted organs.

Macrometastasis at selective lymph node biopsy: A practical going-for-the-one clinical scoring system to personalize decision making

BACKGROUND

Axillary sentinel lymph node biopsy (SLNB) is standard treatment for patients with clinically and pathological negative lymph nodes. However, the role of completion axillary lymph node dissection (cALND) following positive sentinel lymph node biopsy (SLNB) is debated.

AIM

To identify a subgroup of women with high axillary tumor burden undergoing SLNB in whom cALND can be safely omitted in order to reduce the risk of long-term complications and create a Preoperative Clinical Risk Index (PCRI) that helps us in our clinical practice to optimize the selection of these patients.

METHODS

Patients with positive SLNB who underwent a cALND were included in this study. Univariate and multivariate analysis of prognostic and predictive factors were used to create a PCRI for safely omitting cALND.

RESULTS

From May 2007 to April 2014, we performed 1140 SLN biopsies, of which 125 were positive for tumor and justified to practice a posterior cALND. Pathologic findings at SLNB were micrometastases (mic) in 29 cases (23.4%) and macrometastasis (MAC) in 95 cases (76.6%). On univariate analysis of the 95 patients with MAC, statistically significant factors included: age, grade, phenotype, histology, lymphovascular invasion, lymph-node tumor size, and number of positive SLN. On multivariate analysis, only lymph-node tumor size (≤ 20 mm) and number of positive SLN (> 1) retained significance. A numerical tool was created giving each of the parameters a value to predict preoperatively which patients would not benefit from cALND. Patients with a PCRI ≤ 15 has low probability (< 10%) of having additional lymph node involvement, a PRCI between 15-17.6 has a probability of 43%, and the probability increases to 69% in patients with a PCRI > 17.6.

CONCLUSION

The PCRI seems to be a useful tool to prospectively estimate the risk of nodal involvement after positive SLN and to identify those patients who could omit cALND. Further prospective studies are necessary to validate PCRI clinical generalization.

Radiolabelling of nanomaterials for medical imaging and therapy

Nanomaterials offer unique physical, chemical and biological properties of interest for medical imaging and therapy. Over the last two decades, there has been an increasing effort to translate nanomaterial-based medicinal products (so-called nanomedicines) into clinical practice and, although multiple nanoparticle-based formulations are clinically available, there is still a disparity between the number of pre-clinical products and those that reach clinical approval. To facilitate the efficient clinical translation of nanomedicinal-drugs, it is important to study their whole-body biodistribution and pharmacokinetics from the early stages of their development. Integrating this knowledge with that of their therapeutic profile and/or toxicity should provide a powerful combination to efficiently inform nanomedicine trials and allow early selection of the most promising candidates. In this context, radiolabelling nanomaterials allows whole-body and non-invasive in vivo tracking by the sensitive clinical imaging techniques positron emission tomography (PET), and single photon emission computed tomography (SPECT). Furthermore, certain radionuclides with specific nuclear emissions can elicit therapeutic effects by themselves, leading to radionuclide-based therapy. To ensure robust information during the development of nanomaterials for PET/SPECT imaging and/or radionuclide therapy, selection of the most appropriate radiolabelling method and knowledge of its limitations are critical. Different radiolabelling strategies are available depending on the type of material, the radionuclide and/or the final application. In this review we describe the different radiolabelling strategies currently available, with a critical vision over their advantages and disadvantages. The final aim is to review the most relevant and up-to-date knowledge available in this field, and support the efficient clinical translation of future nanomedicinal products for in vivo imaging and/or therapy.

Nuclear imaging of liposomal drug delivery systems: A critical review of radiolabelling methods and applications in nanomedicine

The integration of nuclear imaging with nanomedicine is a powerful tool for efficient development and clinical translation of liposomal drug delivery systems. Furthermore, it may allow highly efficient imaging-guided personalised treatments. In this article, we critically review methods available for radiolabelling liposomes. We discuss the influence that the radiolabelling methods can have on their biodistribution and highlight the often-overlooked possibility of misinterpretation of results due to decomposition in vivo. We stress the need for knowing the biodistribution/pharmacokinetics of both the radiolabelled liposomal components and free radionuclides in order to confidently evaluate the images, as they often share excretion pathways with intact liposomes (e.g. phospholipids, metallic radionuclides) and even show significant tumour uptake by themselves (e.g. some radionuclides). Finally, we describe preclinical and clinical studies using radiolabelled liposomes and discuss their impact in supporting liposomal drug development and clinical translation in several diseases, including personalised nanomedicine approaches.

Techniques for Loading Technetium-99m and Rhenium-186/188 Radionuclides into Preformed Liposomes for Diagnostic Imaging and Radionuclide Therapy

Liposomes can serve as carriers of radionuclides for diagnostic imaging and therapeutic applications. Herein, procedures are outlined for radiolabeling liposomes with the gamma-emitting radionuclide, technetium-99m (^99mTc), for noninvasive detection of disease and for monitoring the pharmacokinetics and biodistribution of liposomal drugs, and/or with therapeutic beta-emitting radionuclides, rhenium-186/188 (^186/188Re), for radionuclide therapy. These efficient and practical liposome radiolabeling methods use a post-labeling mechanism to load ^99mTc or ^186/188Re into preformed liposomes prepared in advance of the labeling procedure. For all liposome radiolabeling methods described, a lipophilic chelator is used to transport ^99mTc or ^186/188Re across the lipid bilayer of the preformed liposomes. Once within the liposome interior, the pre-encapsulated glutathione or ammonium sulfate (pH) gradient provides for stable entrapment of the ^99mTc and ^186/188Re within the liposomes. In the first method, ^99mTc is transported across the lipid bilayer by the lipophilic chelator, hexamethylpropyleneamine oxime (HMPAO) and ^99mTc-HMPAO becomes trapped by interaction with the pre-encapsulated glutathione within the liposomes. In the second method, ^99mTc or ^186/188Re is transported across the lipid bilayer by the lipophilic chelator, N,N-bis(2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA), and ^99mTc-BMEDA or ^186/188Re-BMEDA becomes trapped by interaction with pre-encapsulated glutathione within the liposomes. In the third method, an ammonium sulfate (pH) gradient loading technique is employed using liposomes with an extraliposomal pH of 7.4 and an interior pH of 5.1. BMEDA, which is lipophilic at pH 7.4, serves as a lipophilic chelator for ^99mTc or ^186/188Re to transport the radionuclides across the lipid bilayer. Once within the more acidic liposome interior, ^99mTc/^186/188Re-BMEDA complex becomes protonated and more hydrophilic, which results in stable entrapment of the ^99mTc/^186/188Re-BMEDA complex within the liposomes. Since many commercially available liposomal drugs use an ammonium sulfate (pH) gradient for drug loading, these liposomal drugs can be directly radiolabeled with ^99mTc-BMEDA for noninvasive monitoring of tissue distribution during treatment or with ^186/188Re-BMEDA for combination chemo-radionuclide therapy.

Radiolabeled lipid nanoparticles for diagnostic imaging

BACKGROUND

Nanoparticles are increasingly being incorporated into the design of diagnostic imaging agents. Significant research efforts have been conducted with one class of lipid nanoparticle (liposomes) radiolabeled with gamma-emitting radionuclides as radiopharmaceuticals for scintigraphic imaging of cancer, inflammation/infection and sentinel lymph node detection.

OBJECTIVE

This article reviews the current literature with special emphasis on the clinical studies performed with liposome radiopharmaceuticals for detection of tumors, infectious/inflammatory sites or metastatic lymph nodes. Future uses of liposome radiopharmaceuticals are also described.

METHODS

Characteristics required of the radionuclide, liposome formulation and radiolabeling method for an effective radiopharmaceutical are discussed. A description of the procedures and instrumentation for conducting an imaging study with liposome radiopharmaceutical is included. Clinical studies using liposome radiopharmaceuticals are summarized. Future imaging applications of first- and second-generation radiolabeled liposomes for chemodosimetry and the specific targeting of a disease process are also described.

RESULTS/CONCLUSION

The choice of radionuclide, liposome formulation and radiolabeling method must be carefully considered during the design of a liposome radiopharmaceutical for a given application. After-loading and surface chelation methods are the most efficient and practical. Clinical studies with liposome radiopharmaceuticals demonstrated that a wide variety of tumors could be detected with good sensitivity and specificity. Liposome radiopharmaceuticals could also clearly detect various soft tissue and bone inflammatory/infectious lesions, and performed equal to or better than infection imaging agents that are approved at present. Yet, despite these favorable results, no liposome radiopharmaceutical has been approved for any indication. Some of the reasons for this can be attributed to reports of an unexpected infusion-related adverse reaction in two studies, the requirement of more complex liposome manufacturing procedures, and the adoption of other competing imaging procedures. Continued research of liposome radiopharmaceutical design based on a better understanding of liposome biology, improved radiolabeling methodologies and advances in gamma camera technology is warranted.

Techniques for loading technetium-99m and rhenium-186/188 radionuclides into pre-formed liposomes for diagnostic imaging and radionuclide therapy

Liposomes can serve as carriers of radionuclides for diagnostic imaging and therapeutic applications. Herein, procedures are outlined for radiolabeling liposomes with the gamma-emitting radionuclide, technetium-99m ((99m)Tc), for non-invasive detection of disease and for monitoring the pharmacokinetics and biodistribution of liposomal drugs, and/or with therapeutic beta-emitting radionuclides, rhenium-186/188 ((186/188)Re), for radionuclide therapy. These efficient and practical liposome radiolabeling methods use a post-labeling mechanism to load (99m)Tc or (186/188)Re into pre-formed liposomes prepared in advance of the labeling procedure. For all liposome radiolabeling methods described, a lipophilic chelator is used to transport (99m)Tc or (186/188)Re across the lipid bilayer of the pre-formed liposomes. Once within the liposome interior, the pre-encapsulated glutathione or ammonium sulfate (pH) gradient provides for stable entrapment of the (99m)Tc and (186/188)Re within the liposomes. In the first method, (99m)Tc is transported across the lipid bilayer by the lipophilic chelator, hexamethylpropyleneamine oxime (HMPAO) and (99m)Tc-HMPAO becomes trapped by interaction with the pre-encapsulated glutathione within the liposomes. In the second method, (99m)Tc or (186/188)Re is transported across the lipid bilayer by the lipophilic chelator, N,N-bis(2-mercaptoethyl)-N',N'-diethylethylenediamine (BMEDA), and (99m)Tc-BMEDA or (186/188)Re-BMEDA becomes trapped by interaction with pre-encapsulated glutathione within the liposomes. In the third method, an ammonium sulfate (pH) gradient loading technique is employed using liposomes with an extraliposomal pH of 7.4 and an interior pH of 5.1. BMEDA, which is lipophilic at pH 7.4, serves as a lipophilic chelator for (99m)Tc or (186/188)Re to transport the radionuclides across the lipid bilayer. Once within the more acidic liposome interior, (99m)Tc/(186/188)Re-BMEDA complex becomes protonated and more hydrophilic, which results in stable entrapment of the (99m)Tc/(186/188)Re-BMEDA complex within the liposomes. Since many commercially available liposomal drugs use an ammonium sulfate (pH) gradient for drug loading, these liposomal drugs can be directly radiolabeled with (99m)Tc-BMEDA for non-invasive monitoring of tissue distribution during treatment or with (186/188)Re-BMEDA for combination chemo-radionuclide therapy.

Preparation and characterization of radioactive dirhenium decacarbonyl-loaded PLLA nanoparticles for radionuclide intra-tumoral therapy

This study describes the development of biocompatible radioactive rhenium-loaded nanoparticles for radionuclide anti-cancer therapy. To achieve this goal, dirhenium decacarbonyl [Re2(CO)10] has been encapsulated in poly(L-lactide) based nanoparticles by an oil-in-water emulsion-solvent evaporation method. A 3(3) factorial design method was applied to investigate the influence of both the proceeding and formulation parameters including the stirring speed and the concentration of both the PLLA polymer and the poly(vinyl alcohol) stabiliser on both nanoparticles size and the Re2(CO)10 encapsulation efficacy. The factorial design results attributed a clear negative effect for the stirring speed and the stabiliser concentration on the nanoparticles size while the polymer concentration exhibited a positive one. Regarding the Re2(CO)10 encapsulation efficacy, higher values were obtained when higher polymer concentrations, lower stabiliser concentrations or slower stirring speeds were applied in the preparation. Different tests were thereafter performed to characterize the Re2(CO)10-loaded nanoparticles. The nanoparticles size, being experimentally controlled by the above mentioned parameters, ranged between 330 and 1500 nm and the maximum rhenium loading was 24% by nanoparticles weight as determined by atomic emission assays and neutron activation analysis. Furthermore, the rhenium distribution within nanoparticles has been shown to be homogeneous as confirmed by the energy dispersive X-ray spectrometry. DSC assays demonstrated that Re2(CO)10 was encapsulated in its crystalline initial state. Other experiments including FT-IR and NMR did not show interactions between PLLA and Re2(CO)10. To render them radioactive, these nanoparticles have been bombarded with a neutron flux of 1.45x10(13) n/cm2/s during 1 h. The SEM micrographs of nanoparticles after neutron bombardment showed that the nanoparticles remained spherical and separated but slightly misshaped. These applied neutron activation conditions yielded a specific activity of about 32.5 GBq per gram of nanoparticles. Preliminary estimations allow us to think that a sole injection of 50 mg of these activated nanoparticles into a brain tumor model (4.2 cm diameter) would deliver a tumor absorbed dose of up to 47 Gy. In conclusion, these dirhenium decacarbonyl-loaded nanoparticles represent a novel promising tool for radionuclide anti-cancer therapy.

Pelvic lymphoscintigraphy: contribution to the preoperative staging of rectal cancer

PURPOSE

Preservation of the anal sphincter in surgery for cancer of the distal rectum in an attempt to avoid colostomy has been a main concern of colorectal surgeons. Various proposed procedures contradict oncological principles, especially with respect to pelvic lymphadenectomy. Therefore, prior knowledge of pelvic lymph node involvement is an important factor in choosing the operative technique, i.e., radical or conservative resection. Introduction of ultrasound, computerized tomography, and magnetic resonance have made preoperative study of the area possible. Nevertheless, these resources offer information of an anatomical nature only. Lymphoscintigraphy enables the morphological and functional evaluation of the pelvic area and contributes toward complementing the data obtained with the other imaging techniques. The objective of this prospective study is twofold: to standardize the lymphoscintigraphy technique and to use it to differentiate patients with rectal cancer from those with other coloproctologic diseases.

CASUISTIC AND METHODS

Sixty patients with various coloproctologic diseases were studied prospectively. Ages ranged from 21 to 96 years (average, 51 and median, 55 years). Twenty-six patients were male and 34 were female. Thirty patients had carcinoma of the distal rectum as diagnosed by proctologic and anatomic-pathologic examinations, 20 patients had hemorrhoids, 5 had chagasic megacolon, 2 had diverticular disease, 2 had neoplasm of the right colon, and 1 had ulcerative colitis as diagnosed by proctologic exam and/or enema. The lymphoscintigraphy method consisted of injecting 0.25 mL of a dextran solution marked with radioactive technetium-99m into the right and left sides of the perianal region and obtaining images with a gamma camera. The results were analyzed statistically with a confidence level of 95% (P <.05) using the following statistical techniques: arithmetic and medium average, Fisher exact test, chi-square test corrected for continuity according to Yates, and distribution tables for the number of patients.

RESULTS

In rectal cancer, the tracer progresses unilaterally or is absent; in other patients, the progress of the tracer is bilateral and symmetrical, although its progress may be slow. Statistical tests showed with high significance that the agreement index between the clinical diagnosis and the result of the lymphoscintigraphic exam was 93%.

CONCLUSIONS

Lymphoscintigraphy is a standardized, painless, and harmless test that can be performed in all cases; it differentiates patients with rectal cancer from those with other coloproctological diseases.

Preoperative lymphoscintigraphy during lymphatic mapping for breast cancer: improved sentinel node imaging using subareolar injection of technetium 99m sulfur colloid

BACKGROUND

Preoperative lymphoscintigraphy has been recommended to confirm the successful uptake and direction of migration of radiotracer into sentinel nodes during lymphatic mapping for breast cancer. In addition, preoperative lymphatic mapping may provide a visually useful aid to the relative location of sentinel nodes within a nodal basin. One common method of breast lymphoscintigraphy involves injections of unfiltered technetium 99m sulfur colloid (Tc-99m-SC) directly into parenchymal tissues surrounding a tumor or biopsy cavity (IP injection). Because of the many imaging failures and prolonged imaging times of IP lymphoscintigraphy, the procedure has fallen into disfavor by oncologic surgeons. The purpose of this study is to document the increased success rate of preoperative breast lymphoscintigraphy using a new anatomic site of injection, the subareolar lymphatic plexus (SA injection).

STUDY DESIGN

In the 12 months between December 1, 1998, and December 29, 1999, 42 women with stage I and II breast cancer underwent preoperative lymphoscintigraphy by either the IP (n = 12, December 1998 to May 1999) or SA (n = 30, May 1999 to December 1999) route of injection. Both groups were injected with 1 mCi (37 MBq) of unfiltered Tc-99m-SC followed immediately by external gamma-camera imaging. The success rate for preoperative sentinel node imaging and the total imaging time were recorded in both groups.

RESULTS

The success rate of identifying a sentinel node by SA lymphoscintigraphy was 90% (n = 27 of 30 patients), compared with 50% (n = 6 of 12 patients) for IP lymphoscintigraphy (p = 0.009). The imaging time in the SA injection group was 34 +/- 16 minutes, which was 59% shorter than the imaging time in the IP injection group of 82 +/- 48 minutes (p < 0.001). No uptake into internal mammary nodes was seen in either group.

CONCLUSIONS

Moving the site of injection ofunfiltered Tc-99m-SC to the subareolar lymphatic plexus (SA injection) increased the success rate of preoperative lymphoscintigraphy to 90%, compared with 50% using IP injections. Preoperative SA lymphoscintigraphy resulted in the rapid visualization of axillary sentinel nodes within 30 minutes of SA injection, enabling a visual determination of the approximate number of sentinel nodes and their relative locations within the axilla. We conclude SA injection of unfiltered Tc-99m-SC is superior to IP injections when performing preoperative breast lymphoscintigraphy and is a visually useful aid to lymphatic mapping for breast cancer.

The correlation of axillary ultrasonography with histologic breast cancer downstaging after induction chemotherapy

BACKGROUND

The goal of this study was to examine the role of ultrasonography in detecting axillary lymph node metastases in stage II breast cancer patients after induction chemotherapy (IC).

METHODS

Of 172 consecutive patients with T1-3, N0-1, M0 breast cancer registered in a prospective IC trial, a subset of 130 evaluable patients were chosen, with (1) both physical and ultrasonographic examinations of the axilla before and after IC; (2) exactly four cycles of IC; (3) no presurgical radiation therapy; and (4) an axillary lymph node dissection.

RESULTS

Before IC, 32 patients (25%) were negative for axillary involvement by both physical and ultrasonographic examinations. After IC, this number increased to 64 (49%). Of these, 31 (48%) were positive by pathology examination. In most cases, however, the residual tumor was minimal.

CONCLUSIONS

Stage II breast cancer patients who were or became node negative by both ultrasonographic and physical examinations after IC had a 48% incidence of nodal metastases. Because the residual tumor was minimal, irradiation may be sufficient for adequate local control of the axilla.

Absorption of liposome-encapsulated tetracaine versus nonliposome-encapsulated tetracaine from open wounds in rabbits

The plasma tetracaine concentration versus time profiles for liposome-encapsulated tetracaine (LET) versus nonliposome-encapsulated tetracaine (NLET) were determined after topical application to open wounds in six rabbits (three in LET and three in NLET). H3-tetracaine preparations of LET or NLET were applied randomly to uniform dermal lacerations in anesthetized rabbits. Plasma tetracaine concentrations (ng/mL) of arterial blood samples obtained were measured at predetermined intervals (0.25, 0.5, 1.0, 2.0, and 24 hours) by isotope tracer assay. Results (mean +/- standard deviation) showed the peak plasma tetracaine concentration (Cmax) and the time to Cmax were 40.8 +/- 5.1 ng/mL and 40.1 +/- 7.3 minutes for LET, and 117.8 +/- 9.7 ng/mL and 49.1 +/- 50.2 minutes for NLET. Plasma tetracaine concentrations at all samples times were significantly lower for LET versus NLET. Liposome encapsulation of topically applied tetracaine significantly decreases both the peak and overall plasma tetracaine concentrations compared with the nonencapsulated form. The data suggest that liposome encapsulation of topically applied local anesthetics such as a solution of tetracaine, adrenaline, and cocaine, might reduce the potential systemic toxicity caused by rapid absorption of these compounds.

Progress in the assessment of lymphatic spread in rectal cancer. Rectal endoscopic lymphoscintigraphy

Rectal endoscopic lymphoscintigraphy was performed in 10 control subjects and in a series of 85 patients with adenocarcinoma of the rectum as a prospective study to evaluate lymphatic drainage of the rectum and lymphatic spread in rectal cancer. Complete cranial drainage was demonstrated in all control subjects, and internal iliac nodes were also visible in 50 percent of cases. Results were correlated with histologic node examination in all patients operated upon for rectal cancer. Rectal endoscopic lymphoscintigraphy was assessed for sensitivity (85 percent), specificity (68 percent), overall accuracy (76 percent), positive predictive value (71 percent), and negative predictive value (83 percent). False-negative and false-positive results are discussed. Rectal endoscopic lymphoscintigraphy represents the only method currently available for evaluation of lymphatic spread in rectal cancer.

A possible role for ultrasound of the axilla in staging primary breast cancer

The axillae of 30 patients with primary breast cancer (Stage I and II) were prospectively examined in this pilot study using ultrasound. No patient had palpable axillary lymph nodes on clinical examination. Treatment had involved wide local excision, but no prior form of surgical dissection had been performed on the axilla. Using the contralateral axilla as an internal control, lymph nodes were observed in the ipsilateral axilla alone on ultrasound in 8/30 patients (27%). Following radical irradiation of the breast and local lymph drainage areas, 2/8 patients of the group with observed lymph nodes have relapsed, one with systemic disease and the other with local recurrence in the breast, after a minimum follow-up of 12 months. No patient without observed nodes has recurred. This difference does not reach statistical significance. This technique merits further investigation as an adjunct to current staging procedures for early breast cancer.

Breast scintigraphy with 99mTc-diethylene triamine penta-acetic acid for the detection of malignant disease

A single-blind prospective study of 99mTc-diethylene triamine penta-acetic acid (DTPA) breast scintigraphy was performed on 160 women who presented at the outpatient clinic with suspected breast tumour. The sensitivity of scintigraphy in establishing the diagnosis of breast cancer was 75 per cent. The specificity of scintigraphy in excluding the presence of breast cancer was 91 per cent. The diagnostic value of DTPA breast scintigraphy is at present too low in comparison with mammography to be clinically useful.

Lymph node localization of non-specific antibody-coated liposomes

Subcutaneously injected small unilamellar liposomes are drained into the lymphatics and localized in the regional lymph nodes, and thus they can be used for the detection of metastatic spread in breast cancer patients and for delivery of drugs to diseased lymph nodes (1-8). An aqueous phase marker, [125I]-polyvinylpyrrolidone, and a lipid phase marker, [3H]-cholesterol, were used to study the lymph node localization of IgG-coated liposomes injected subcutaneously into mouse and rat footpads. The results show that human immunoglobulin G (IgG) coated liposomes are rapidly removed from the site of injection and are localized in the regional lymph nodes to a greater extent than control liposomes (i.e. liposomes without IgG). Free IgG was found to inhibit the uptake of IgG-coated liposomes by the lymph nodes. The localization of IgG-coated liposomes in the regional lymph nodes is influenced by charge of the liposomes. The results presented here suggest that antibody-coated liposomes may provide a more efficient way of delivering therapeutic agents to the lymph nodes in the treatment of diseases such as breast cancer with lymph node involvement. Similarly, monoclonal antibody-coated liposomes containing lymphoscintigraphic material may improve the detection of lymph node metastases.

Potential and limitations of drug targeting: an overview

Potential and limitations of current efforts in drug targeting are discussed in terms of the criterion that targeting strategies must ultimately be gauged by their success in producing selectivity of pharmacological response thereby reducing or eliminating side effects which are not mechanism-related. A wide variety of approaches are considered, including: local drug administration, differential metabolism, carriers and vehicles, macromolecular recognition, site-specific activation and molecular specificity. Each approach is briefly assessed for its potential to be developed as a realistic candidate for human health care.

An evaluation of pelvic lymphoscintigraphy in the staging of colorectal carcinoma

Lymphoscintigraphy was used to delineate the lymphatic drainage of the rectum and distal colon in 18 patients with carcinoma of the rectum or sigmoid colon, in four with inflammatory disease of the large bowel and in 20 controls without colorectal pathology. Abdominal imaging was performed after submucosal injection of either 4 mCi 99mTc-antimony sulphide colloid or 0.5 mCi 99mTc-dextran into the rectum through a proctoscope. In nine patients with colorectal carcinoma, abdominal imaging was performed immediately pre-operatively and the excised specimen of large bowel was also imaged in vitro immediately postoperatively. The presence or absence of nodal uptake of radionuclide on abdominal scanning did not discriminate between normal and diseased large bowel, and the extent of nodal uptake demonstrated either by abdominal scans or by in vitro scans of excised specimens bore no relationship to the presence or absence of nodal metastases demonstrated histologically in the cancer patients. Pelvic lymphoscintigraphy as performed in this study has no demonstrable value in the diagnosis or staging of colorectal cancer.

Assessment of the potential uses of liposomes for lymphoscintigraphy and lymphatic drug delivery. Failure of 99m-technetium marker to represent intact liposomes in lymph nodes

The in vivo fate of subcutaneously injected neutral SUV liposomes in rats was examined using a membrane marker, 99mTc, and an aqueous marker, 125I-labelled poly(vinyl pyrrolidone). Liposomes with entrapped 125I-labelled poly(vinyl pyrrolidone) were labelled with 99mTc by the SnCl2 method. 99mTc-radioactivity was localized several-fold more in the primary and secondary regional lymph nodes than 125I-labelled poly(vinyl pyrrolidone)-radioactivity. Similarly, 99mTc-radioactivity appeared and was subsequently cleared from the circulation much more rapidly than 125I-labelled poly(vinyl pyrrolidone). The gel chromatography of the lymph node homogenate revealed that 60-70% of 125I-labelled poly(vinyl pyrrolidone)-radioactivity was in the liposome fractions, whereas only 3% of 99mTc-radioactivity was co-eluted with the liposomes. Thus, the two markers have different fates in the lymphatics, and the presence of all 99mTc-radioactivity does not represent the 60-70% of intact liposomes present in lymph nodes. Using the aqueous marker 125I-labelled poly(vinyl pyrrolidone), the lymph node localization of positive, negative and neutral small unilamellar vesicles was studied, and it was found that 125I-radioactivity was more localized from negative liposomes than from positive liposomes, which in turn was more localized than that from neutral liposomes. Thus, these findings differ from those reported earlier, where the authors used 99mTc as a liposomal marker. In vitro studies showed that liposomes of preparations containing 20 mol% cholesterol became 'leaky' to low-molecular-weight drugs, for example, methotrexate (Mr 454) to a much greater extent than with a large-molecular-weight substance, 125I-labelled poly(vinyl pyrrolidone) (Mr 30 000-40 000), when incubated with rat lymph at 37 degrees C. Using the two markers 99mTc and 125I-labelled poly(vinyl pyrrolidone) it was found that the localization of both radioactivities was reduced in lymph nodes draining lambda-carrageenan-treated footpads. In conclusion, it is suggested that liposomes can be used for the delivery of drugs to diseased lymph nodes, and it would be worthwhile examining the possibilities of using alternative methods of labelling liposomes with 99mTc rather than using the SnCl2 technique, or using other radionuclides as markers for gamma-scan imaging.

Rectal lymphoscintigraphy

Regional lymph nodes of the rectum are not demonstrable by pedal lymphoscintigraphy. We have evaluated the technique of rectal lymphoscintigraphy, using a technique similar to that which has been used in the assessment of lymph nodes in breast and prostatic cancer. Thirty-five patients were studied: ten normal subjects and 25 patients with rectal cancer. In normal subjects, the lymph nodes accompanying the superior hemorrhoidal artery and the inferior mesenteric artery are demonstrable in succession; after three hours the aortic lymph nodes are demonstrable. The 25 patients with rectal cancer underwent resection of their primary tumor and the stage was defined according to Dukes (1932). In five patients (stage A) no alteration was demonstrable. In 11 patients (stage B) the demonstration of regional lymph nodes was delayed vs. the control group. In nine cases (stage C) the demonstration of regional lymph nodes was delayed and defective versus the control group.