New radiopharmaceutical agents for the treatment of castration-resistant prostate cancer.

Prostate cancer (PCa) is the fourth most common cancer worldwide in terms of incidence and third among male, but is becoming the most common cancer in developed countries. In many patients the disease will progress despite of castration levels of testosterone, to become castration-resistant PCa (CRPC). Nearly all patients with CRPC show bone metastases. The treatment of patients with bony metastases has dramatically changed during the past three years because of new therapeutic approaches addressed to obtain pain control, reduced skeletal morbidity, and most importantly, increased survival rate. A possible therapy can be based also on the use of radiopharmaceuticals systemically administered to slow or reverse the bone metastatic progression. In facts bone-homing radiopharmaceuticals are taken up in areas of high bone turnover, including areas with high osteoblastic activity. Recently, a bone targeting radiopharmaceutical, Radium-223 dichloride was added to this group of drugs clearly representing a new generation of radiopharmaceutical in bone therapy. Clinical trials had shown that the treatment with Ra-223 allowed the reduction of the risk of death respect to placebo. No other radiometabolic treatment achieved such result, evidentiating the disease-modifying properties of this bone-homing radiopharmaceutical. In an effort to treat patients with disseminated PCa, who became resistant to hormonal therapy, molecular targets have been recently identified. Prostate specific membrane antigen (PSMA) is one attractive target for diagnosis and therapy of metastasized PCa since its expression levels are directly correlated to androgen independence, metastasis, and progression. Gastrin-releasing peptide receptors (GRPr) are also highly overexpressed in PCa. Numerous studies suggest the possibility of a high PCa-specific signal with radiolabeled bombesin analogs targeting GRPr. Low molecular weight peptides directed against these molecular targets have been radiolabeled with positron emitting radionuclides such as 68Ga in order to improve sensitivity and specificity for detecting primary, metastatic, and recurrent PCa by PET/CT over conventional imaging techniques. Although peptide radionuclide ligand therapy studies have just initiated, the diagnostic relevance of 68Ga labeled specific tracers has already been established its clinical utility and represents a valid tool against this common and deadly cancer.

Yttrium-90 -- current status, expected availability and applications of a high beta energy emitter.

Yttrium-90 ((90)Y, T(1/2) 64.14 h) is a key example of a high beta energy-emitting radionuclide which is available from the strontium-90 ((90)Sr)/(90)Y radionuclide generator system. Clinical uses of (90)Y-labeled radiopharmaceutical agents have been pursued for many years and many applications have proven to be clinical effective. These most notably include the application of 90Y-labeled antibodies for a variety of applications such as for effective treatment of non-Hodgkin's lymphoma. One of the major advantages for use of (90)Y is ready availability from the very long-lived (90)Sr parent (T(1/2) 28.78 y). Because of the importance of maintaining generator performance and minimizing parent breakthrough, this paper describes development, use and quality control of both high capacity cation adsorption-type and electrochemical generator systems. In addition, the preparation and targeting to tumors in mice of DOTA-conjugated Nimotuzamab (h-R3) antibody which recognizes the external domain of the EPFR antibody radiolabeled with (90)Y obtained from the electrochemical generator is also described. As a key example for clinical applications of (90)Y, the use of (90)Y-labeled biotin for intra-operative pre-targeting for radionuclide therapy (IART®) of breast cancer is also described.

Testing of microbial contamination during the preparation of the radiocompound [9°Y]DOTATOC for clinical trials: a process validation study by Media Fill approach.

AIM: Radioisotopes used in nuclear radiopharmacy possess short half-lives, not allowing enough time to wait for completion of sterility tests. Moreover, carrying out sterility tests on highly radioactive solutions inside the hospital microbiology laboratory arises concerns about radioprotection. Therefore, the release of radiopharmaceuticals for injection is allowed in microbial analysis. For this reason, the effectiveness of the aseptic procedures has to be continuously assessed in order to guarantee the safety of the drug. The aim of this study was to validate the sterile preparation of [9°Y]DOTATOC by means of media fill test. METHODS: In order to validate the process, a simulation test was used: the media fill test. To apply this method, operators simulated each step of the process using culture medium (Triptic Soy Broth, TSB) instead of actual radiopharmaceutical product. Media fill test procedure has been subdivided into 5 phases, from the simulation of reagent preparation through the dispensing operations up to ward delivery. After every step, the processed medium was incubated at 35 °C for 14 days. If the compounding procedures are adequately performed, no growth of microorganisms will be detected. RESULTS: Microbiological analyses, carried out on all vials obtained at the end of each step, showed no microbial growth. For this reason, sterility tests were considered satisfactory. CONCLUSION: Application of media-fill test allowed both to validate operative modality used for [9°Y]-DOTATOC handling and to attest the ability of operators who worked on it. Additionally, a correct quality control of the radiopharmaceutical i.v. preparations allows clinic infections control and prevention.

Improved radiotracing of oxytocin receptor-expressing tumours using the new [111In]-DOTA-Lys8-deamino-vasotocin analogue.

Oxytocin receptors (OTR) have been described in a number of tumours of different origin, and represent a new target for specific radiolabelled oxytocin (OT) analogues in cancer diagnosis and therapy. By linking the DOTA chelating agent to position 8 of the deamino derivative of Lys(8)-vasotocin (dLVT), we obtained a new compound (DOTA-dLVT) with the following characteristics: (1) it forms a monomeric and stable compound that binds to OTR with an affinity comparable to that of the endogenous OT ligand; (2) it is characterised by a very good selectivity profile for the human OTR, with a low affinity binding to the closely related V1a, V1b and V2 vasopressin receptor subtypes; (3) it induces rapid and persistent receptor internalisation and (4) when radiolabelled, [(111)In]-DOTA-dLVT is efficiently and selectively taken up by OTR-positive tumours grown in mice. These features makes radiolabelled DOTA-dLVT a very good candidate for the radiotargeting of OTR-expressing tumours.

Novel antitenascin antibody with increased tumour localisation for Pretargeted Antibody-Guided RadioImmunoTherapy (PAGRIT).

The Pretargeted Antibody-Guided RadioImmunoTherapy (PAGRIT) method is based on intravenous, sequential administration of a biotinylated antibody, avidin/streptavidin and (90)Y-labelled biotin. The hybridoma clone producing the monoclonal antitenascin antibody BC4, previously used for clinical applications, was found not suitable for further development because of the production of an additional, nonfunctional light chain. In order to solve this problem, the new cST2146 hybridoma clone was generated. The monoclonal antibody ST2146, produced by this hybridoma, having the same specificity as BC4 but lacking the nonfunctional light chain, was characterised. ST2146 was found able to bind human tenascin at an epitope strictly related, if not identical, to the antigenic epitope of BC4. It showed, compared to BC4, higher affinity and immunoreactivity and similar selectivity by immunohistochemistry. Biodistribution studies of biotinylated ST2146 and three other monoclonal antitenascin antibodies showed for ST2146 the highest and more specific tumour localisation in HT29-grafted nude mice. On the overall, ST2146 appears to be a good alternative to BC4 for further clinical development of PAGRIT.

Pretargeted adjuvant radioimmunotherapy with yttrium-90-biotin in malignant glioma patients: a pilot study.

In a previous study we applied a three-step avidin-biotin pretargeting approach to target 90Y-biotin to the tumour in patients with recurrent high grade glioma. The encouraging results obtained in this phase I-II study prompted us to apply the same approach in an adjuvant setting, to evaluate (i) time to relapse and (ii) overall survival. We enrolled 37 high grade glioma patients, 17 with grade III glioma and 20 with glioblastoma, in a controlled open non-randomized study. All patients received surgery and radiotherapy and were disease-free by neuroradiological examinations. Nineteen patients (treated) received adjuvant treatment with radioimmunotherapy. In the treated glioblastoma patients, median disease-free interval was 28 months (range=9-59); median survival was 33.5 months and one patient is still without evidence of disease. All 12 control glioblastoma patients died after a median survival from diagnosis of 8 months. In the treated grade III glioma patients median disease-free interval was 56 months (range=15-60) and survival cannot be calculated as only two, within this group, died. Three-step radioimmunotherapy promises to have an important role as adjuvant treatment in high grade gliomas, particularly in glioblastoma where it impedes progression, prolonging time to relapse and overall survival. A further randomized trial is justified.

90Y-DOTA-D-Phe1-Try3-octreotide in therapy of neuroendocrine malignancies.

Somatostatin receptors type 2 (sst(2)) are expressed in high concentration on numerous neudoendocrine tumors. The successful use of radiolabeled somatostatin analogs in imaging promoted further studies in utilizing them in radiopeptide therapy. The somatostatin analog [(90)Y-DOTA-D-Phe(1)-Try3]octreotide (DOTATOC) (DOTA: 1,4,7,10-tetraazacyclododecane-N,N',N'',N'''-tetraacetic acid) possesses favorable characteristic for its therapeutic use; shows high affinity for sst(2), moderately high affinity for sst(5), and intermediate affinity for sst(3); high hydrophilicity; stable and facile labeling with (111) In and (90) Y. In this article we report our experience with (90)Y-DOTATOC in neuroendocrine tumors. Eighty-seven patients with neuroendocrine tumors were treated with a cumulated activity ranging from 7.4 to 20.2 GBq. Most patients responded with stabilization of disease (48%); however, objective responses were observed in 28% of patients (5% complete response). No major acute reactions were observed up to the activity of 5.55 GBq per cycle. The dose limiting was bone marrow toxicity and the maximal tolerated dose was defined as 5.18 GBq.

The humoral immune response to macrocyclic chelating agent DOTA depends on the carrier molecule.

UNLABELLED: The chelating agent 1,4,7,10-tetraazacyclododecane-N,N', N",N"'-tetraacetic acid (DOTA) is used to label monoclonal antibodies (mAbs) and peptides with (90)Y. DOTA allows the generation of clinically useful stable metallic radioconjugates for the treatment of a variety of tumors, but its immunogenicity has remained controversial. In this study, we evaluated the immune response to DOTA in a preclinical mouse model and in patients entered in a clinical trial. METHODS: Sera were obtained from BALB/c mice injected intraperitoneally or subcutaneously with different doses and formulations of syngeneic and xenogeneic mAbs or peptide (murine mAb Mov19 [mM19]; its chimeric version; murine V/human C ChiMov19 [cM19]; or Tyr(3)-octreotide)-DOTA conjugates. Sera from patients with neuroendocrine tumors, enrolled in a protocol for somatostatin receptor-mediated radionuclide therapy with (90)Y-DOTA-D-Phe(1)-Tyr(3)-octreotide (DOTATOC), were also collected before and after each treatment. Levels and specificity of antibody response to relevant (Mov19, ChiMov19, or Tyr(3)-octreotide) and nonrelevant (human serum albumin) DOTA targets were tested by enzyme-linked immunosorbent assay and competition assays. An anti-DOTA mAb (IgG1) derived from a ChiMov19-DOTA immunized mouse was used, in a competitive radioimmunoassay, to determine the efficiency of DOTA presentation on the different carriers. RESULTS: Depending on the immunogenicity and dosage of the mAb, a specific anti-DOTA response was revealed in the preclinical system. However, DOTA-peptide conjugate induced no immune-detectable response against either chelator or carrier. DOTA was poorly presented on small peptides, as determined using the anti-DOTA mAb. CONCLUSION: A humoral response against DOTA is possible, but only as a consequence of the response elicited against the carrier. Octreotide was not immunogenic. Thus, (90)Y-DOTATOC can be considered a safe and useful tool for receptor-mediated radionuclide therapy of somatostatin receptor-overexpressing tumors.

Pre-targeted locoregional radioimmunotherapy with 90Y-biotin in glioma patients: phase I study and preliminary therapeutic results.

The aim of this study was to determine the maximum-tolerated dose, of a pre-targeting three-step (3-S) method employing 90Y-biotin in the locoregional radioimmunotherapy (RIT) of recurrent high grade glioma, and to investigate the antitumor efficacy of this new treatment. Twenty-four patients with recurrent glioma underwent second surgical debulking and implantation of a catheter into the surgical resection cavity (SRC), in order to introduce the radioimmunotherapeutic agents [biotinylated monoclonal antibody (MoAb), avidin and 90Y-biotin]. Eight patients with anaplastic astrocytoma (AA) and 16 patients with glioblastoma (GBM) were injected with biotinylated anti-tenascin MoAb (2 mg), then with avidin (10 mg; 24 h later) and finally 90Y-biotin (18 h later). Each patient received two of these treatments 8-10 weeks apart. The injected activity ranged from 0.555 to 1.110 GBq (15-30 mCi). Dosage was escalated by 0.185 GBq (5 mCi) in four consecutive groups. The treatment was well tolerated without acute side effects up to 0.740 GBq (20 mCi). The maximum tolerated activity was 1.110 GBq (30 mCi) limited by neurological toxicity. None of the patients developed hematologic toxicity. In three patients infection occurred around the catheter. The average absorbed dose to the normal brain was minimal compared with that received at the SRC interface. At first control (after 2 months), partial (PR) and minor (MR) responses were observed in three GBM (1 PR; 2 MR) and three AA patients (1 PR; 2 MR) with an overall objective response rate of 25%. Stable disease (SD) was achieved in seven GBM and five AA patients (50%). There was disease progression in six GBM patients (25%), but in none of the AA patients. At the dosage of 0.7-0.9 GBq per cycle, locoregional 3-S-RIT was safe and produced an objective response in 25% of patients. Based on these encouraging results, phase II studies employing 3-S-RIT soon after first debulking are justified.

111In-labeled 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid-lys(8)-vasotocin: a new powerful radioligand for oxytocin receptor-expressing tumors.

We developed a radioactive ligand for tumors expressing oxytocin receptors (OTRs) by linking the chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) to Lys(8)-vasotocin (LVT), an analogue of oxytocin with high affinity for OTRs. The new reagent (DOTA-LVT) retained high affinity for human OTRs, as proved by in vitro affinity binding to cells endogenously expressing OTRs, such as MCF7 breast carcinoma and MOG-U-V-W glioblastoma cells lines, as well as to transiently transfected COS7 cells. In in vivo experiments, DOTA-LVT carrying (111)In showed specific binding activity to OTR-positive TS/A mouse mammary tumors. The present study opens new perspectives for imaging and, possibly, therapy of OTR-positive human tumors such as breast and endometrial carcinomas, neuroblastomas, and glioblastomas.

Receptor-mediated radiotherapy with 90Y-DOTA-D-Phe1-Tyr3-octreotide.

A newly developed somatostatin radioligand, DOTA-[D-Phe1-Tyr3]-octreotide (DOTATOC), has been synthesised for therapeutic purposes, because of its stable and easy labelling with yttrium-90. The aim of this study was to determine the dosage, safety profile and therapeutic efficacy of 90Y-DOTATOC in patients with cancers expressing somatostatin receptors. We recruited 30 patients with histologically confirmed cancer. The main inclusion criterion was the presence of somatostatin receptors as documented by 111In-DOTATOC scintigraphy. 90Y-DOTATOC was injected intravenously using a horizontal protocol: patients received equivalent-activity doses in each of three cycles over 6 months. The first six patients received 1.11 GBq per cycle and the four successive groups of six patients received doses increasing in 0.37-GBq steps. Toxicity was evaluated according to WHO criteria. No patient had acute or delayed adverse reactions up to 2.59 GBq 90Y-DOTATOC per cycle (total 7.77 GBq). After a total dose of 3.33 GBq, one patient developed grade II renal toxicity 6 months later. The maximum tolerated dose per cycle has not yet been reached, although transient lymphocytopenia has been observed. Total injectable activity is limited by the fact that the maximum dose tolerated by the kidneys has been estimated at 20-25 Gy. Complete or partial tumour mass reduction occurred in 23% of patients; 64% had stable and 13% progressive disease. It is concluded that high activities of 90Y-DOTATOC can be administered with a low risk of myelotoxicity, although the cumulative radiation dose to the kidneys is a limiting factor and requires careful evaluation. Objective therapeutic responses have been observed.

Adoptive immunotherapy by avidin-driven cytotoxic T lymphocyte-tumor bridging.

We have shown previously that T cells, tagged with biotinylated anti-CD3 antibody fragments, can exert avidin-dependent cytolytic activity on suitably biotinylated tumor cells in vitro. In this study, we demonstrate that avidin-driven CTL-tumor bridging in vivo leads to growth inhibition of murine tumors WEHI-164 fibrosarcoma and RMA lymphoma. The biodistribution of biotin-tagged 111In-labeled T cells demonstrated a selective avidin-dependent and time-dependent accumulation of radioactivity at tumor sites. The specificity of lymphocyte tumor localization was demonstrated by the concurrent time-dependent decrease of radioactivity in the blood and in all other organs. Furthermore, we documented a therapeutic effect of the adoptively transferred T cells, i.e., a significant delay of tumor growth at early stages. All of the experiments included a control group of mice, which received all of the reagents, except avidin. These avidin-minus mice showed no specific localization and no delay in tumor growth, indicating that avidin bridging was essential for T-cell activity at tumor sites.

Sentinel node localization by lymphoscintigraphy: a reliable technique with widespread applications.

The concept of the sentinel lymph node (SN) represents an important contribution to guide appropriate surgery of cancer. Diagnostic non-invasive or minimally invasive procedures that provide accurate preoperative staging of the lymph node status are badly needed. The technique of SN biopsy, first developed with the purpose to select melanoma patients for regional node dissection, has been extended to other malignancies. Initial studies in breast carcinoma, conducted with vital blue dye, showed that the SN concept was biologically valid, although SN was missed in up to 30%-40% of cases. If a radioactive tracer is injected close to the tumor, then the SN can be identified by lymphoscintigraphy (LS), and a gamma ray detecting probe (GDP) can be used to locate the skin projection of SN and assist biopsy. These techniques are already used successfully in melanoma and breast carcinoma where the various parameters involved, such as the size of the radioactive particles, the injection site and injection volume, have recently been optimized. In a large series of breast cancer patients, the overall predictive value of the SNs biopsy guided by LS and GDP was 96.8%; in patients with small carcinomas (< 1.2 cm diameter), the concordance between SN and axillary status was 98.6%. In patients with melanoma, LS combined with GDP showed itself to be superior to the blue dye mapping. LS associated with GDP allowed the detection of SN in 98% of cases and 72 SNs in 54 basins were localized. Using blue dye instead, SN was stained only in 80% of patients (50 SNs in 40 basins). Lymphoscintigraphic techniques have shown promising results also in tumors such as vulva and tongue. In conclusion, LS is a simple nuclear medicine technique, relatively inexpensive and well accepted by patients. SN biopsy guided by a GDP is becoming widely adopted for a variety of neoplasms, contributing significantly to the search for less aggressive treatments in patients with early stages of cancer.

Dosimetry in radionuclide therapies with 90Y-conjugates: the IEO experience.

The basis for a successful radionuclide therapy is a high and stable uptake of the radiopharmaceutical in the target tissue along with low activity concentration in other normal organs. The contribution of dosimetry in radionuclide therapy is to predict before the treatment the absorbed doses in tumor and normal organs, to identify the critical organs, to minimize any possible toxicity and to evaluate the maximum tolerated dose. We report our experience concerning pharmacokinetics and dosimetry of two 90Y-therapeutic protocols: 3-step pretargeting radioimmunotherapy (RIT) according to the biotin-avidin system and receptor mediated radionuclide therapy with the somatostatin analogue [DOTA-D-Phe1-Tyr3] octreotide named DOTATOC. For the dosimetric analysis, analogous approaches for the two radiolabeled compounds due to the similar pharmacokinetic characteristics were adopted; the MIRD formalism was applied, taking into account both the physical and the biological characteristics of the radioconjugate and patients' metabolism. In order to determine biological clearance, serial blood samples and complete urine collection were obtained up to 48 hours after injection; to evaluate biodistribution, several whole body scans were acquired. Both therapies showed the advantageous characteristics of a fast blood clearance and a predominantly renal excretion of the radiopharmaceuticals thus lowering the irradiation of the total body. Although pharmacokinetic characteristis were similar, different critical organs were found for the two therapies; in particular, some considerations regarding red marrow, spleen and kidneys were required. The results of our studies indicate that high activities of 90Y-biotin (3-step RIT) and 90Y-DOTATOC can be administered with acceptable radiation doses to normal organs.

Radiation protection in radioguided surgery of breast cancer.

The protocols for sentinel lymph node biopsy and radioguided occult lesion localization could potentially be of great value in the management of breast cancer patients. Both involve the injection of a 99Tcm-labelled radiopharmaceutical close to or into the lesion, localization of the sentinel lymph node or occult lesion by scintigraphy, and surgical removal with the aid of a hand-held gamma-ray detector. We present dosimetric data on patients and hospital personnel involved in these procedures. For evaluation of radiation protection, we measured the absorbed dose and air kerma rate. Activity levels in excised tissues and surgical instruments were also determined. For patients, the mean absorbed dose to the abdomen was 0.45 mGy, which is low compared to doses received from other diagnostic examinations. For surgeons after 100 operations, the mean absorbed dose to the hands was 0.45 mGy and the mean effective dose 0.09 mSv. Absorbed doses to all hospital personnel involved in the procedures were very low compared to recommended annual limits stipulated by the International Commission on Radiological Protection. We conclude that these procedures, performed according to protocols laid down by the European Institute of Oncology, Milan, are safe from the point of view of radiological protection and that only routine precautions are necessary.

Biokinetics and dosimetry in patients administered with (111)In-DOTA-Tyr(3)-octreotide: implications for internal radiotherapy with (90)Y-DOTATOC.

Recent advances in receptor-mediated tumour imaging have resulted in the development of a new somatostatin analogue, DOTA-dPhe(1)-Tyr(3)-octreotide. This new compound, named DOTATOC, has shown high affinity for somatostatin receptors, ease of labelling and stability with yttrium-90 and favourable biodistribution in animal models. The aim of this work was to evaluate the biodistribution and dosimetry of DOTATOC radiolabelled with indium-111, in anticipation of therapy trials with (90)Y-DOTATOC in patients. Eighteen patients were injected with DOTATOC (10 microg), labelled with 150-185 MBq of (111)In. Blood and urine samples were collected throughout the duration of the study (0-2 days). Planar and single-photon emission tomography images were acquired at 0.5, 3-4, 24 and 48 h and time-activity curves were obtained for organs and tumours. A compartmental model was used to determine the kinetic parameters for each organ. Dose calculations were performed according to the MIRD formalism. Specific activities of >37 GBq/ micromol were routinely achieved. Patients showed no acute or delayed adverse reactions. The residence time for (111)In-DOTATOC in blood was 0.9+/-0.4 h. The injected activity excreted in the urine in the first 24 h was 73%+/-11%. The agent localized primarily in spleen, kidneys and liver. The residence times in source organs were: 2.2+/-1.8 h in spleen, 1.7+/-1.2 h in kidneys, 2.4+/-1.9 h in liver, 1.5+/-0.3 h in urinary bladder and 9. 4+/-5.5 h in the remainder of the body; the mean residence time in tumour was 0.47 h (range: 0.03-6.50 h). Based on our findings, the predicted absorbed doses for (90)Y-DOTATOC would be 7.6+/-6.3 (spleen), 3.3+/-2.2 (kidneys), 0.7+/-0.6 (liver), 2.2+/-0.3 (bladder), 0.03+/-0.01 (red marrow) and 10.1 (range: 1.4-31.0) (tumour) mGy/MBq. These results indicate that high activities of (90)Y-DOTATOC can be administered with low risk of myelotoxicity, although with potentially high radiation doses to the spleen and kidneys. Tumour doses were high enough in most cases to make it likely that the desired therapeutic response desired would be obtained.

Clinical validation of the avidin/indium-111 biotin approach for imaging infection/inflammation in orthopaedic patients.

We report here the results of a validation study of the avidin/indium-111 biotin approach in patients with skeletal lesions. This study involved 54 patients with orthopaedic conditions: 20 patients with intermediate suspected osteomyelitis of the trunk, 19 patients with infection/inflammation of prosthetic joint replacements, and 15 patients with suspected osteomyelitis of appendicular bones. Avidin (3 mg) was injected as an i.v. bolus, followed 4 h later by 111In-biotin; imaging was acquired 30 min and 16-18 h after administration of 111In-biotin. Technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO)-labelled leucocyte scintigraphy was performed in 39/54 patients. The overall sensitivity of the avidin/111In-biotin scan was 97.7% (versus 88.9% for 99mTc-HMPAO leucocyte scintigraphy). While the diagnostic performance of avidin/111In-biotin scintigraphy was similar to that of 99mTc-HMPAO leucocyte scintigraphy in patients with prosthetic joint replacements or osteomyelitis of appendicular bones, the avidin/111In-biotin approach clearly performed better than 99mTc-HMPAO leucocyte scintigraphy in patients with suspected osteomyelitis of the trunk (100% sensitivity, specificity and accuracy versus 50% sensitivity, 100% specificity and 66.7% accuracy for 99mTc-HMPAO-leucocyte scintigraphy). These results demonstrate the feasibility of the avidin/111In-biotin approach for imaging sites of infection/inflammation in the clinical setting. Although no systematic advantages of avidin/111In-biotin scintigraphy were found versus 99mTc-HMPAO leucocyte scintigraphy, the newer scintigraphic method is more practicable and involves lower biological risk for the operators.

Antibody-guided three-step therapy for high grade glioma with yttrium-90 biotin.

While the incidence of brain tumours seems to be increasing, median survival in patients with glioblastoma remains less than 1 year, despite improved diagnostic imaging and neurosurgical techniques, and innovations in treatment. We have developed an avidin-biotin pre-targeting approach for delivering therapeutic radionuclides to gliomas, using anti-tenascin monoclonal antibodies, which seems potentially effective for treating these tumours. We treated 48 eligible patients with histologically confirmed grade III or IV glioma and documented residual disease or recurrence after conventional treatment. Three-step radionuclide therapy was performed by intravenous administration of 35 mg/m2 of biotinylated anti-tenascin monoclonal antibody (1st step), followed 36 h later by 30 mg of avidin and 50 mg of streptavidin (2nd step), and 18-24 h later by 1-2 mg of yttrium-90-labelled biotin (3rd step). 90Y doses of 2.22-2.96 GBq/m2 were administered; maximum tolerated dose (MTD) was determined at 2.96 GBq/m2. Tumour mass reduction (>25%-100%), documented by computed tomography or magnetic resonance imaging, occurred in 12/48 patients (25%), with 8/48 having a duration of response of at least 12 months. At present, 12 patients are still in remission, comprising four with a complete response, two with a parital response, two with a minor response and four with stable disease. Median survival from 90Y treatment is 11 months for grade IV glioblastoma and 19 months for grade III anaplastic gliomas. Avidin-biotin based three-step radionuclide therapy is well tolerated at the dose of 2.2 GBq/m2, allowing the injection of 90Y-biotin without bone marrow transplantation. This new approach interferes with the progression of high-grade glioma and may produce tumour regression in patients no longer responsive to other therapies.

Three-step radioimmunotherapy with yttrium-90 biotin: dosimetry and pharmacokinetics in cancer patients.

A three-step avidin-biotin approach has been applied as a pretargeting system in radioimmunotherapy (RIT) as an alternative to conventional RIT with directly labelled monoclonal antibodies (MoAbs). Although dosimetric and toxicity studies following conventional RIT have been reported, these aspects have not previously been evaluated in a three-step RIT protocol. This report presents the results of pharmacokinetic and dosimetric studies performed in 24 patients with different tumours. Special consideration was given to the dose delivered to the red marrow and to the haematological toxicity. The possible additive dose to red marrow due to the release of unbound yttrium-90 was investigated. The protocol consisted in the injection of biotinylated MoAbs (first step) followed 1 day later by the combined administration of avidin and streptavidin (second step). After 24 h, biotin radiolabelled with 1.85-2.97 GBq/m2 of 90Y was injected (third step). Two different chelating agents, DTPA and DOTA, coupled to biotin, were used in these studies. Indium-111 biotin was used as a tracer of 90Y to follow the biodistribution during therapy. Serial blood samples and complete urine collection were obtained over 3 days. Whole-body and single-photon emission tomography images were acquired at 1, 16, 24 and 40 h after injection. The sequence of images was used to extrapolate 90Y-biotin time-activity curves. Numerical fitting and compartmental modelling were used to calculate the residence time values (tau) for critical organs and tumour, and results were compared; the absorbed doses were estimated using the MIRDOSE3.1 software. The residence times obtained by the numerical and compartmental models showed no relevant differences (<10%); the compartmental model seemed to be more appropriate, giving a more accurate representation of the exchange between organs. The mean value for the tau in blood was 2.0+/-1.1 h; the mean urinary excretion in the first 24 h was 82.5%+/-10.8%. Without considering any contribution of free 90Y, kidneys, liver, bladder and red marrow mean absorbed doses were 1.62+/-1.14, 0.27+/-0.23, 3.61+/-0.70 and 0. 11+/-0.05 mGy/MBq, respectively; the effective dose was 0.32+/-0.06 mSv/MBq, while the dose to the tumour ranged from 0.62 to 15.05 mGy/MBq. The amount of free 90Y released after the injection proved to be negligible in the case of 90Y-DOTA-biotin, but noteworthy in the case of 90Y-DTPA-biotin (mean value: 5.6%+/-2.5% of injected dose), giving an additive dose to red marrow of 0.18+/-0.08 mGy per MBq of injected 90Y-DTPA-biotin. Small fractions of free 90Y originating from incomplete radiolabelling can contribute significantly to the red marrow dose (3.26 mGy per MBq of free 90Y) and may explain some of the high levels of haematological toxicity observed. These results indicate that pretargeted three-step RIT allows the administraton of high 90Y activities capable of delivering a high dose to the tumour and sparing red marrow and other normal organs. Although 90Y-biotin clears rapidly from circulation, the use of DOTA-biotin conjugate for a stable chelation of 90Y is strongly recommended, considering that small amounts of free 90Y contribute significantly in increasing the red marrow dose.