44Sc-DOTA-BN[2-14]NH2 in comparison to 68Ga-DOTA-BN[2-14]NH2 in pre-clinical investigation. Is 44Sc a potential radionuclide for PET?

AIM: In the present study we demonstrate the in vitro and in vivo comparison of the (44)Sc and (68)Ga labeled DOTA-BN[2-14]NH(2). (44)Sc is a positron emitter with a half life of 3.92 h. Hence it could be used for PET imaging with ligands requiring longer observation time than in the case of (68)Ga. METHODS: The binding affinity of (nat)Sc-DOTA-BN[2-14]NH(2) and (nat)Ga-DOTA-BN[2-14]NH(2) to GRP receptors was studied in competition to [(125)I-Tyr(4)]-Bombesin in the human prostate cancer cell line PC-3. A preliminary biodistribution in normal rats was performed, while first microPET images were assessed in male Copenhagen rats bearing the androgen-independent Dunning R-3327-AT-1 prostate cancer tumor. RESULTS: The affinity to GRP receptors in the PC-3 cell line was higher for (nat)Ga-DOTA-BN[2-14]NH(2) (IC(50)(nM)=0.85 ± 0.06) than that of (nat)Sc-DOTA-BN[2-14]NH(2) (IC(50) (nM)=6.49 ± 0.13). The internalization rate of (68)Ga labeled DOTA-BN[2-14]NH(2) was slower than that of (44)Sc, but their final internalization percents were comparable. (68)Ga-DOTA-BN[2-14]NH(2) was externalized faster than (44)Sc-DOTA-BN[2-14]NH(2). The biodistribution of (44)Sc-DOTA-BN[2-14]NH(2) and (68)Ga-DOTA-BN[2-14]NH(2) in normal rats revealed a higher uptake in target organs and tissues of the first one while both excreted mainly through urinary tract. In microPET images both tracers were accumulated in the tumor with similar uptake patterns. CONCLUSIONS: Despite the differences in the receptor affinity both the (68)Ga- and the (44)Sc-labeled DOTA-BN[2-14]NH(2) tracers showed comparable distribution and similar time constants of uptake and elimination. Moreover no differences in tumor accumulation (neither in the overall uptake nor in the dynamics) were observed from the microPet imaging. From that perspective the use of either (44)Sc or (68)Ga for detecting tumors with GRP receptors is equivalent.

Alzheimer's disease: spect and pet tracers for beta-amyloid imaging.

The definite diagnosis of Alzheimer's disease (AD) is based on the detection of beta amyloid (Aß) plaques and neurofibrillary tangles (NFTs) - which are the pathological hallmarks of the disease- in the postmortem brains. Although regional Cerebral Blood Flow (rCBF) and Cerebral Glucose Metabolism (CGM) abnormalities have already been studied in AD patients with Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET), the development of specific imaging agents for direct mapping of Aß plaques in the living brain, is a great challenge. Aß probes could significantly contribute to the early diagnosis of AD, the elucidation of the underlying neuropathological processes and the evaluation of anti-amyloid therapies which are currently under investigation. The development of SPECT and PET tracers for Aß imaging represents an active area in radiopharmaceutical design. A substantial number of potential Aß imaging radioligands have been designed and used in-vitro. They are either monoclonal antibodies to Aß and radiolabeled Aß peptides, or derivatives of histopathological stains such as Congo red (CR), chrysamine-G (CG) and Thioflavin T (TT). Though, only few of them, that display high binding affinity to Aß as well as sufficient brain penetration, have been used primarily in in-vivo studies and to a smaller degree on human subjects. Since Aß plaques are not homogenous and contain multiple binding sites that can accommodate structurally diverse compounds, they offer flexibility in designing various different probes, as potential amyloid imaging agents.

Study of the labeling of two novel RGD-peptidic derivatives with the precursor [99mTc(H2O)3(CO)3]+ and evaluation for early angiogenesis detection in cancer.

In the initial stages of tumor formation, overexpression of integrins identifying the RGD sequence (Arg-Gly-Asp) is observed. The aim of the present study was the synthesis and labeling of two novel RGD derivatives, via the precursor [99mTc(H2O)3(CO)3]+, as well as the radiochemical and radiopharmacological evaluation of the labeled products. The labeling led to the formation of a single product in each case (>98%), with noteworthy in vitro stability, fast blood clearance and elimination by the hepatobiliary and the urinary systems.

Fast cancer uptake of 99mTc-labelled bombesin (99mTc BN1).

In human blood, breakdown of gastrin-releasing peptide and other bombesin-related peptides occurs in less than 15 min. This quick enzymatic cleavage might impair the diagnostic use of labelled bombesin (BN). 99mTc-labelled bombesin (99mTc BN1) was injected intravenously and dynamic uptake data were acquired for diagnosing 26 cancers of different origin: 15 breast, 3 prostate, 5 colo-rectal, 1 pancreas, 2 small cell lung cancers and 1 gastrinoma. Background subtracted tumour uptake data were plotted against time and fitted with known mathematical functions. Twenty-three out of 26 cancers showed rapid increase of radioactivity followed by a radioactivity plateau, with some oscillations around the average plateau value. The time to 80% of max activity (T80) was the reference parameter to measure and to compare the uptake speeds. The slowest T80 was 7 min in one T1b breast cancer, gastrinoma reached T80 in 5 min and node-positive prostate cancers in 2 min. N+ breast cancers showed T80 at 3.62 +/- 0.75 min, N- breast cancers at 5.5 +/- 0.88 min (p < 0.02). When all the tumours were considered, N+ tumours showed T80 at 2.68 +/- 1.03 min and N- cancers at 5.5 +/- 0.82 min. In all the cancer types, the uptake of 99mTc BN was faster than 10 min. This result shows the ability of 99mTc BN to image tumours. The faster uptake by N+ versus N- cancers probably depends on the higher blood flow in N+ cancers.

Samarium-153 and technetium-99m-labeled monoclonal antibodies in angiogenesis for tumor visualization and inhibition.

BACKGROUND: Angiogenesis is the development of new blood vessels from pre-existing ones. Vascular endothelial growth factor (VEGF) is one of the most important angiogenic activators. Our studies are focused on the detection of VEGF by use of radiolabeled anti-endothelial monoclonal antibodies, which have the ability to localize in newly-formed vasculature of a cancerous origin. MATERIALS AND METHODS: The anti-endothelial monoclonal antibody VG76e was labeled with Samarium-153 and Technetium-99m. Biodistribution of the radiolabeled species was assessed in normal female Swiss mice, while tumor uptake was also evaluated. RESULTS: VG76e was labeled with 99mTc and 153Sm, resulting in a single product with a labeling yield of over 95%. Biodistribution studies showed non-specific uptake in any organ, with elimination via the hepatobiliary system. Finally, satisfactory tumor uptake was observed for both radiolabeled derivatives. CONCLUSION: Monoclonal antibodies raised against epithelial growth factors or their receptors, when labeled with appropriate radionuclides, may be a useful tool for early tumor detection and eventually for therapy.

A 3D high-resolution gamma camera for radiopharmaceutical studies with small animals.

The results of studies conducted with a small field of view tomographic gamma camera based on a Position Sensitive Photomultiplier Tube are reported. The system has been used for the evaluation of radiopharmaceuticals in small animals. Phantom studies have shown a spatial resolution of 2mm in planar and 2-3mm in tomographic imaging. Imaging studies in mice have been carried out both in 2D and 3D. Conventional radiopharmaceuticals have been used and the results have been compared with images from a clinically used system.

Improving spatial resolution in SPECT with the combination of PSPMT based detector and iterative reconstruction algorithms.

This paper investigates the possibility of developing a SPECT system that combines the high spatial resolution of position sensitive photomultiplier tubes (PSPMTs) with the excellent performance of iterative reconstruction algorithms. A small field of view (FOV) camera based on a PSPMT and a pixelized scintillation crystal made of CsI(Tl) have been used for the acquisition of the projections. With the use of maximum likelihood expectation maximization (ML-EM) and ordered subsets expectation maximization (OSEM) slices of the object are obtained while three-dimensional (3D) reconstruction of the object is carried out using a modified marching cubes (MMC) algorithm. The spatial resolution of tomographic images obtained with the system was 2-3mm. The spatial resolution of a conventional system that uses filtered backprojection (FBP) for slices reconstruction was more than 9 mm.

Labeling of monoclonal antibodies with 153Sm for potential use in radioimmunotherapy.

The labeling of a monoclonal (anti-CEA) and a polyclonal (IgG) antibody with 153Sm has been investigated, using the bicyclic anhydride of DTPA (cDTPAa) as the chelating agent. The radiochemical study was performed using a combination of radioanalytical techniques (gel filtration, HPLC, ITLC-SG and SDS-PAGE). Optimization of factors affecting labeling (pH, Ab, Ab-DTPA concentration, etc.) leads to a labeling yield higher than 90%. Biodistribution studies in normal mice showed slow blood clearance and high uptake into the liver, kidney and lungs.

Phase I trial of technetium [Leu13] bombesin as cancer seeking agent: possible scintigraphic guide for surgery?

AIMS AND BACKGROUND: Bombesin-like neuropeptides work as neurotransmitters and growth factors at the same time. Several human cancers show overexpression of three receptors for mammalian counterparts of amphibia bombesins (ABNs), ie gastrin-releasing peptide (GRP), neuromedin B (NMB) and possibly another peptide. ABNs in turn are able to bind to mammalian and human receptors in vitro, and it is therefore interesting to study radioisotope-labeled bombesin (BN) and BN-like peptides as cancer seeking agents. METHODS AND STUDY DESIGN: Starting from the amino acid sequence of [Leu13] ABN, the Demokritos Institute has synthesized and labeled with technetium a new BN-like peptide that has the same biological characteristics as the amphibian peptide; changes were made only in the N-terminal part of the tetradecapeptide. After having obtained satisfactory results with 99mTc BN in a preclinical study, we started a phase I trial involving cancer patients as well as normal volunteers in Tomsk. Three normal volunteers, one patient with small cell lung cancer and one patient with primary prostate cancer were studied after iv injection of 185 MBq, corresponding to 0.7 micrograms of 99mTc BN. Dynamic images of the tumors were acquired for 20 mins, followed by SPET. Total body images were acquired in patients and normal volunteers 1 and 3 h after 99mTc BN acquisition. In addition, 99mTc sestamibi scintigraphy was performed in the patient with small cell lung carcinoma. RESULTS: No relevant side effects were observed. Both tumors were well visualized on early 1-2 mins images with planar as well as tomographic imaging. Total body images showed radioactivity in the liver, kidneys and thyroid gland. The stomach and spleen were ever imaged. Radioactivity was found in the urinary bladder 4 mins after injection in the patient with prostate cancer. Three-hour total body scans showed radioactivity in the duodenum. In the patient in whom also 99mTc sestamibi scintigraphy was performed, thyroid uptake was much higher with sestamibi than with 99mTc BN, whereas the uptake of small cell lung carcinoma was higher with 99mTc BN than with sestamibi. CONCLUSIONS: 99mTc BN is able to clearly image tumors with BN receptor overexpression. Our first impression is that in the future this radiopharmaceutical may serve as a cancer seeking agent and, due to its high tumoral uptake, also as a radiotracer for radioisotope-guided surgery.

Breast cancer takes up 99mTc bombesin. A preliminary report.

BACKGROUND: Several tumors including lung, prostate, ovarian, colon, and exocrine pancreatic cancer show receptors for the amphibian neurotransmitter and growth factor bombesin (BN) and its mammalian counterparts gastrin-releasing peptide and neuromedin B. Also breast cancer has been reported to show such receptors: the presence of BN receptors in primary breast cancer has been demonstrated on cultured cells and by autoradiography on breast tissue samples. Authors who have studied BN receptors in breast cancer do not agree on their frequency in primary cancer, but indicate that 100% of metastatic breast cancers show such receptors. METHODS: We examined three primary breast cancer patients with 99mTc BN and 99mTc sestamibi one week before surgery. One of them showed axillary node invasion. The same acquisition technique was used for breast and chest imaging with both radiopharmaceuticals, whereas total body images were acquired only with 99mTc BN. Also the administered radioactivity was different: 20 mCi of 99mTc sestamibi and 5-8 mCi of 99mTc BN. Dynamic images were acquired for 20 mins after iv injection with the patient in ventral decubitus and the gamma camera positioned in a lateral view, as is generally done in Khakhali's prone scintimammography. Anterior chest images were acquired for 30 mins. Prone scintimammography was performed one hour after administration of both tracers. ROIs were drawn on tumors and surrounding breast with the same technique in order to calculate the tumor to breast ratio (T/B). In addition, total body scan was performed one hour and three hours after 99mTc BN administration. All three patients underwent breast conserving surgery with lymphadenectomy. Postoperative pathologic assessment showed the following T and N stages in the three patients: T1bN0, T1c-N0, and T1cN1. RESULTS: All three cancers were imaged with both tracers. The T/B of 99mTc BN was always higher than that of 99mTc sestamibi. Chest uptake was always much higher with 99mTc sestamibi than with 99mTc BN. Comparison between 99mTc BN and 99mTc sestamibi images gave other intriguing results: in the N1 patient both tracers clearly imaged the invaded node, but on the 99mTc BM image the primary tumor was larger than on the 99mTc sestamibi image and the node was smaller. It is known that 99mTc BN is not taken up by vessels and inflammatory tissue. The time activity curves of the two tracers were significantly different in all patients, with an increase in 99mTc BN uptake in the first three to five minutes, followed by a less sharp uprise of the curve, quite similar to a plateau. CONCLUSIONS: Our first impression is that 99mTc BN is a useful breast cancer seeking agent and very promising for lymph node staging.

Synthesis, chemical, radiochemical and radiobiological evaluation of a new 99mTc-labelled bombesin-like peptide.

A new pentadecapeptide bombesin analogue was prepared by Fmoc synthesis, purified by HPLC and identified by electron ionization mass spectrometry. The biological activity of the new peptide was tested on isolated human colonic muscle cells and compared to native bombesin. Labelling of the new biomolecule with Tc-99m yielded a single radioactive species which remained stable at room temperature for eight hours. In a binding assay, the radiolabelled peptide showed high affinity for oat-cell carcinoma (Kd = 9.8 nM) and colorectal adenocarcinoma (Kd = 27.2 nM). Biodistribution studies, performed in normal rodents, indicated uptake by organs that normally express bombesin receptors, such as liver, intestines and kidneys. Scintigraphic studies, performed in nude mice transplanted with small cell lung carcinoma and colon cancer cells, showed significant tumor uptake two hours p.i. The new synthetic pentadecapeptide appears to have promise for several malignancies, including oat-cell lung carcinoma, colorectal cancer and gastroenteropancreatic (GEP) tumors.

Technetium labeled bombesin-like peptide: preliminary report on breast cancer uptake in patients.

Bombesin-like peptides are neurotransmitters and cancer growth factors. Several tumors, breast cancer among them, show one or more than one of the three known bombesin receptors. We have synthesized and labeled with technetium 99m a new pentadecapeptide, analogue to the leu13 amphibian bombesin (99mTc BN). Labeling yield was 83 +/- 4%. Prone Scintimammography was performed on five patients affected by breast cancers (T categorization: two T1b and three T1c), after injecting 0.7 mg, 185 to 296 MBq (5 to 8 mCi) of the peptide. Total body scan did not show free technetium biodistribution. No adverse reaction was observed. Prone Scintimammography with 99mTc Sestamibi (99mTc SM) was also performed few days later. 99mTc BN detected all 5 cancers, whereas 99mTc SM only four: all the T1c and one T1b cancer. Two of them showed axillary node invasion that was detected by both the radiotracers. A fibroadenoma present on contralateral breast to the one with cancer, was not detected neither by 99mTc SM nor by 99mTc BN. Tumor/breast normal tissue ratio (T/B) was constantly higher with 99mTc BN than with 99mTc SM. Maximal T/B was measured as 1.79 with 99mTc SM and 2.25 with 99mTc BN 5 min after fast i.v. administration. In conclusion our 99mTc BN is taken up by primary breast cancer showing higher T/B than 99mTc SM (p < 0.01). In our limited scale, 99mTc BN appears to be safe and, in our limited scale, even more accurate than 99mTc SM for detecting breast cancer.

High intratumoural accumulation of stealth liposomal doxorubicin (Caelyx) in glioblastomas and in metastatic brain tumours.

The blood-brain barrier is a major obstacle for the chemotherapeutic drugs to effectively reach primary or secondary brain tumours. Stealth liposomal drugs are highly accumulated in tumoural tissues. In the present study we investigated the relative accumulation of(99m)Tc-DTPA radiolabelled stealth liposomal doxorubicin (Caelyx) in 10 patients with metastatic brain tumours and five patients with brain glioblastoma undergoing radiotherapy. Patients with metastatic brain lesions were treated with 10 consecutive fractions of radiotherapy (whole brain, 3 Gy/fraction, day 1-12) followed by a booster dose of 9 Gy (3 Gy/fraction, day 21-23). Caelyx, at a dose of 25 mg mg(-2)was given on day 1 and on day 21. Radiolabelled Caelyx accumulation was 13-19 times higher in the glioblastomas and 7-13 times higher in the metastatic lesions, as compared to the normal brain. The drug accumulation in the tumoural areas was 40-60% of the accumulation in the bone marrow of the skull bones. The normal brain radioactivity was <4% of the bone marrow, confirming an important shielding effect of the blood-brain barrier in the normal but not in the tumoural tissue. Four of 10 patients with metastatic lesions showed a complete response in CT-scan performed 2 months following therapy. There was no severe toxicity related to radiotherapy or to chemotherapy noted. It is concluded that stealth liposomal drugs selectively overcome the blood-brain barrier in the tumoural areas. The clinical importance of this observation is now under investigation.

High intratumoral accumulation of stealth liposomal doxorubicin in sarcomas--rationale for combination with radiotherapy.

Sarcomas are radioresistant tumors, the only curative therapy being radical surgical resection. Stealth liposomal doxorubicin (Caelyx) is a novel drug formulation that allows prolonged circulation and high intratumoral concentration. This study investigates the concurrent use of radiotherapy with Caelyx in a cohort of 7 patients with locally advanced or recurrent sarcoma. Radiotherapy was given as a standard fractionation regimen to a total dose of 70 Gy. Caelyx was given as a 30-min infusion at a dose of 25 mg/m2 every 2 weeks. Scintigraphic imaging with Caelyx-99mTc-DTPA showed an increased (2.8 +/- 0.9 times higher) intratumoral drug accumulation compared to the surrounding healthy tissue. The regimen was well tolerated without any severe hematological or systemic toxicity. 'In field' radiation toxicity was not increased. Complete response was observed in 4/7 cases. It is concluded that combined chemo-radiotherapy with stealth liposomal doxorubicin for locally advanced sarcomas is feasible and promising, the benefit expected from the unique ability of the stealth liposomes to accumulate selectively in the tumoral tissue.

Radioimmunoscintigraphy and radioimmunotherapy in cancer: principles and application.

Radioimmunoscintigraphy (RIS) and radioimmunotherapy (RIT) are recent approaches in the diagnosis and treatment of cancer. They take advantage of the antibody specificity of tumor surface antigens and of the emitted radiation from suitable radioisotopes, as a means of imaging (RIS) or therapy (RIT). Research into RIS and RIT radiolabelled agents remains an ongoing process. Principles governing the choice of radionuclides, labelling protocols, antibody suitability, and optimization of "tumor to normal tissue ratios" are the same for both RIS and RIT. The investigational stages of the labelled product, prior to clinical application, are also the same. These stages include radiochemical and radiobiological evaluation as well as determination of immunoreactivity. Furthermore, RIS may be considered as the first stage in development, before progressing on to RIT. Differences between RIS and RIT are associated with the application of each technique, that is, the type of radiation emitted by the isotope, dosage regimens, haematopoetic toxicity and the appearance of human antimurine antibody response (HAMA). RIS has found widespread clinical application, detecting a variety of tumors. However, its potential lies in patient management and in detecting metastases. On the other hand RIT is still in its infancy. It appears promising, and for the moment is used as a complementary technique to surgery and/or chemotherapy in clinical trials on cancer treatment. Finally, incorporation of these basic principles arising from past experiences, into the design of RIT trials improve responses.

Liposomal doxorubicin and conventionally fractionated radiotherapy in the treatment of locally advanced non-small-cell lung cancer and head and neck cancer.

PURPOSE: Stealth (ALZA Corporation, Palo Alto, CA) liposomal drug formulation allows a higher intratumoral accumulation and a prolonged plasma half-life of the encapsulated drugs. In the study presented here, we evaluated the feasibility of Stealth liposomal doxorubicin (Caelyx; ALZA Corporation) administered concurrently with conventionally fractionated radiotherapy in the treatment of non-small-cell lung cancer (NSCLC) and head and neck cancer (HNC). PATIENTS AND METHODS: Fifteen patients with NSCLC and 15 with squamous-cell HNC were recruited in two phase I dose-escalation trials. The starting dose of Caelyx was 10 mg/m(2) every 2 weeks (for three cycles during radiotherapy) and was increased by 5 mg/m(2) dose increments for every three patients. RESULTS: The maximum tolerated dose of Caelyx was 20 mg/m(2) for HNC and 25 mg/m(2) in NSCLC patients. Oral/pharyngeal mucositis was the dose-limiting toxicity for HNC patients. "In field" radiation skin toxicity was slightly increased. Hematologic toxicity was minimal. Single photon emission computed tomographic evaluation of Caelyx distribution, using technetium-99m-diethylenetriamine pentaacetic acid labeling, revealed a high intratumoral accumulation of the drug. The tumor to thoracic vessel area count ratio in the NSCLC cases ranged from 0.6 to 1.6 (mean +/- SD, 1.01 +/- 0.29), whereas this ratio was higher (0.8 to 1.85; mean +/- SD, 1.35 +/- 0.39) in HNC cases (P =.049). The complete response rate was 21% in the NSCLC cases and 75% in the HNC cases. NSCLC cases with higher Caelyx tumor accumulation responded better to the regimen. The tumor microvessel density assessed with the anti-CD31 monoclonal antibody directly correlated with the degree of the Caelyx accumulation (P =.007; r =. 92). CONCLUSION: We conclude that combination of radiotherapy with Stealth liposomal doxorubicin is feasible. The potential role of such a regimen in the treatment of highly angiogenic tumors requires further investigation.

Technetium-99m labelling of human immunoglobulin and preliminary clinical evaluation in tumour patients.

In the present investigation we have human immunoglobulin labelled with 99Tc(m), applying two different systems. The radiochemical characteristics of the labelled antibody were studied by conventional, radioanalytical methods. Further on, pharmacokinetics of this 99Tc(m)-labelled biomolecule were investigated, by i.v. administration in women, checked for tumours of the ovaries, uterus and cervix. Scintigraphic findings were compared to the results of other imaging techniques (CT, US, X rays), as well as to surgical findings. Our studies indicated that 99Tc(m)-human immunoglobuline can be applied successfully for the scintigraphic detection of several malignant and benign tumours of the female genital system. Tumour accumulation is probably due to the activation of particular cells, as macrophages and lymphocytes, responsible for inflammatory and immunological responses.

Radiochemical and radioimmunological data of 99Tcm-anti-CEA labelled by two diverse methods.

The aim of this study was to make a comparative evaluation of a direct and an indirect method for the labelling of anti-CEA with technetium-99m (99Tcm). With the direct method, disulphide bridges were cleaved by the use of 2-mercaptoethanol as reductant, whereas with the indirect method, the antibody was coupled to 2-iminothiolane. In both cases, a preformed intermediate chelate was used for 99Tcm exchange. The radiochemical and radiobiological behaviour of the 99Tcm-labelled species were studied. Furthermore, the influence of the labelling systems on the integrity of monoclonal antibodies, as well as the ability of 99Tcm-anti-CEA to tag onto human cancer cells, was investigated for the two labelling systems. Both methods showed a high labelling yield and resulted in immunoreactive and stable derivatives. However, detailed electrophoretical and radiochemical data, as well as the cysteine challenge trial, indicated relatively greater stability for the 2-mercaptoethanol reduction procedure.

Immunolocalization of transitional cell carcinoma of the bladder with intravesically administered technetium-99m labelled HMFG1 monoclonal antibody.

The aim of this study was the immunolocalization of transitional cell carcinoma of the bladder with a radiolabelled murine tumour-associated monoclonal antibody and the measurement of the absolute uptake of the antibody by the tumour. Fourteen patients with transitional cell carcinoma of the bladder received 3-6 mCi (111-222 MBq) of technetium-99m labelled HMFG1 monoclonal antibody intravesically and one patient, 2 mCi (74 MBq) of iodine-131 labelled 11.4.1, which is a non-tumour-specific monoclonal antibody. Four of the 15 patients were evaluated with single-photon emission tomography (SPET) 1 1/2 to 2 h post administration. All patients underwent transurethral resection of the bladder tumour within 12-20 h following intravesical administration of the radiolabelled antibody. The radioactivity of biopsy specimens from normal urothelium and tumour areas were counted in a gamma counter. The mean uptake of the radiolabelled antibodies from normal and tumour sites was expressed as a percentage of the administered dose per kilogram of tissue. Conventional histology and immunohistochemistry using HMFG1 monoclonal antibody were performed on paraffin sections of the biopsy specimens. Although our results are preliminary, it can be concluded that: (a) bladder tumours are well imaged by SPET when using 99mTc-HMFG1; (b) intravesically administered radiolabelled antibody remains on the bladder tissue and does not escape into the systemic circulation; (c) the wide range of tumour uptake values (0%-9.3% administered dose/kg) observed probably can be attributed to heterogeneity of the antigenic expression of the tumour; (d) values of 99mTc-HMFG1 monoclonal antibody uptake by the tumour do not justify future attempts at radioimmunotherapy.

Immunotargeting of urothelial cell carcinoma with intravesically administered Tc-99m labeled HMFG1 monoclonal antibody.

Ten patients with transitional cell carcinoma (TCC) of the bladder received 3-6 mCi of HMFG1 monoclonal antibody (MAb) intravesically. The antibody was labeled with Tc-99m using the 2-Iminothiolane method. All patients underwent transurethral resection of the bladder tumor within 12-20 h following intravesical administration of 99m-Tc-HMFG1. The presence of the radiolabeled MAb in the circulation was studied by measuring the radioactivity in the serum for a period up to 20 h. Three of 10 patients underwent immunoscintigraphy (SPECT) 2-3 h postadministration and cancerous areas could be easily localized. Biopsies were taken from the tumor sites as well as from normal bladder mucosa. Absolute uptake of the administered MAb expressed as percent administered dose/kg of tissue could be evaluated only in eight patients. Multiple specimen taken from various tumor sites in every patient gave a wide range of uptake values ranging from 0 to 9.29% adm. dose/kg, whereas normal tissue uptake values ranged from 0 to 1.63, respectively.