Tumor immunotargeting using innovative radionuclides.

This paper reviews some aspects and recent developments in the use of antibodies to target radionuclides for tumor imaging and therapy. While radiolabeled antibodies have been considered for many years in this context, only a few have reached the level of routine clinical use. However, alternative radionuclides, with more appropriate physical properties, such as lutetium-177 or copper-67, as well as alpha-emitting radionuclides, including astatine-211, bismuth-213, actinium-225, and others are currently reviving hopes in cancer treatments, both in hematological diseases and solid tumors. At the same time, PET imaging, with short-lived radionuclides, such as gallium-68, fluorine-18 or copper-64, or long half-life ones, particularly iodine-124 and zirconium-89 now offers new perspectives in immuno-specific phenotype tumor imaging. New antibody analogues and pretargeting strategies have also considerably improved the performances of tumor immunotargeting and completely renewed the interest in these approaches for imaging and therapy by providing theranostics, companion diagnostics and news tools to make personalized medicine a reality.

¹8F-FDG PET predicts survival after pretargeted radioimmunotherapy in patients with progressive metastatic medullary thyroid carcinoma.

PURPOSE: PET is a powerful tool for assessing targeted therapy. Since (18)F-FDG shows a potential prognostic value in medullary thyroid carcinoma (MTC), this study evaluated (18)F-FDG PET alone and combined with morphological and biomarker evaluations as a surrogate marker of overall survival (OS) in patients with progressive metastatic MTC treated with pretargeted anti-CEA radioimmunotherapy (pRAIT) in a phase II clinical trial. METHODS: Patients underwent PET associated with morphological imaging (CT and MRI) and biomarker evaluations, before and 3 and 6 months, and then every 6 months, after pRAIT for 36 months. A combined evaluation was performed using anatomic, metabolic and biomarker methods. The prognostic value of the PET response was compared with demographic parameters at inclusion including age, sex, RET mutation, time from initial diagnosis, calcitonin and CEA concentrations and doubling times (DT), SUVmax, location of disease and bone marrow involvement, and with response using RECIST, biomarker concentration variation, impact on DT, and combined methods. RESULTS: Enrolled in the study were 25 men and 17 women with disease progression. The median OS from pRAIT was 3.7 years (0.2 to 6.5 years) and from MTC diagnosis 10.9 years (1.7 to 31.5 years). After pRAIT, PET/CT showed 1 patient with a complete response, 4 with a partial response and 24 with disease stabilization. The combined evaluation showed 20 responses. For OS from pRAIT, univariate analysis showed the prognostic value of biomarker DT (P = 0.011) and SUVmax (P = 0.038) calculated before pRAIT and impact on DT (P = 0.034), RECIST (P = 0.009), PET (P = 0.009), and combined response (P = 0.004) measured after pRAIT. PET had the highest predictive value with the lowest Akaike information criterion (AIC 74.26) as compared to RECIST (AIC 78.06), biomarker variation (AIC 81.94) and impact on DT (AIC 79.22). No benefit was obtained by combining the methods (AIC 78.75). This result was confirmed by the analysis of OS from MTC diagnosis. CONCLUSION: (18)F-FDG PET appeared as the most potent and simplest prognostic method to predict survival in patients with progressive MTC treated with pRAIT. Biomarker DT before pRAIT also appeared as an independent prognostic factor, but no benefit was found by adding morphological and biomarker evaluation to PET assessment.

Pretargeted radioimmunotherapy (pRAIT) in medullary thyroid cancer (MTC).

Prognosis of medullary thyroid carcinoma (MTC) varies from long- to short-term survival, based on prognostic factors, such as serum calcitonin doubling time (Ct DT). Pretargeted radioimmunotherapy (pRAIT) is a novel targeted radionuclide therapy, using a bispecific monoclonal antibody (BsMAb) and a radiolabeled bivalent hapten, designed to improve the therapeutic index and to deliver increased tumor-absorbed doses to relatively radioresistant solid tumors. Pretargeting has demonstrated a more favorable therapeutic index and clinical efficacy than directly labeled anti-carcinoembryonic antigen (CEA) MAb in preclinical MTC models. Moreover, two phase I/II clinical trials assessing anti-CEA × anti-DTPA-indium BsMAb (murine F6x734 and chimeric hMN14x734) with (131)I-di-DTPA-indium showed encouraging therapeutic results in progressive, metastatic, MTC patients, with an improved survival in intermediate- and high-risk (pre-pRAIT Ct DT, <2 years) patients, as compared to contemporaneous untreated patients (median overall survival, 110 months vs 61 months; P < 0.030). pRAIT efficacy has been recently confirmed in a prospective multicenter phase II study assessing hMN14x734 and (131)I-di-DTPA-indium in rapidly progressive MTC patients. New pRAIT compounds are now available with fully humanized, recombinant, trivalent BsMAb (anti-CEA TF2) and histamine-succinyl-glutamine (HSG) peptides. The HSG peptide allows easy and stable labeling with different radiometals, such as (177)Lu or (90)Y beta-emitters having favorable physical features for pRAIT or (68)Ga and (18)F positron-emitters, allowing the development of a highly sensitive and specific immuno-positron emission tomography method in MTC or other CEA-positive tumors.

[Radiolabeled antibodies for cancer treatment]. / Les anticorps radiomarqués pour le traitement des cancers.

The first treatment ever by radio-immunotherapy (RIT) was performed by William H. Beierwaltes in 1951 and was a success. Fifty years later, the main question is to find ways of extending the success of radiolabelled anti-CD20 antibodies in indolent non-Hodgkin's lymphoma to other forms of cancer. Solid tumours are much more radioresistant than lymphomas, but they respond to RIT if the lesions are small. Clinical situations of residual or minimal disease are thus the most likely to benefit from RIT in the adjuvant or consolidation settings. For disseminated disease, like leukemias or myelomas, the problem is different: beta- particles emitted by the radioactive atoms classically used for cancer treatment (iodine-131 or yttrium-90) disperse their energy in large volumes (ranges 1 mm to 1 cm) and are not very effective against isolated cells. Advances in RIT progress in two directions. One is the development of pretargeting strategies in which the antibody is not labelled but used to provide binding sites to small molecular weight radioactivity vectors (biotin, haptens). These techniques have been shown to increase tumour to non-target uptake ratios and anti-tumour efficacy has been demonstrated in the clinic. The other approach is the use of radionuclides adapted to the various clinical situations. Lutetium-177 or copper-67, because of the lower energy of their emission, their relatively long half-life and good gamma emission, may significantly improve RIT efficacy and acceptability. Beyond that, radionuclides emitting particles such as alpha particles or Auger electrons, much more efficient to kill isolated tumour cells, are being tested for RIT in the clinic. Finally, RIT should be integrated with other cancer treatment approaches in multimodality protocols. Thus RIT, now a mature technology, should enter a phase of well designed and focused clinical developments that may be expected to afford significant therapeutic advances.

Sensitivity and prognostic value of positron emission tomography with F-18-fluorodeoxyglucose and sensitivity of immunoscintigraphy in patients with medullary thyroid carcinoma treated with anticarcinoembryonic antigen-targeted radioimmunotherapy.

CONTEXT: Patients with progressive medullary thyroid carcinoma (MTC) undergo multiple imaging procedures for diagnosis of relapse and staging. OBJECTIVE: Our objective was to assess the sensitivity and prognostic value of 18F-2-fluoro-2-deoxy-d-glucose (FDG) positron emission tomography (PET)/computed tomography (CT), and the imaging sensitivity of pretargeted iodine-131-radioimmunotherapy (RIT) in patients with progressive MTC. DESIGN/SETTING/PATIENTS: We performed a prospective multicenter study in high-risk patients with rapidly progressing MTC enrolled in a phase-II pretargeted RIT study, as documented by short serum calcitonin (Ct) or carcinoembryonic antigen (CEA) doubling time (DT). INTERVENTIONS/MAIN OUTCOME MEASURES: Patients underwent neck-thoracic-abdominal CT, spine and pelvic magnetic resonance imaging, whole-body post-RIT immunoscintigraphy (IS) with iodine-131, and whole-body 18F-FDG-PET/CT imaging. Imaging sensitivity and the correlation between FDG uptake and biomarkers DT were evaluated. RESULTS: A total of 33 patients with mean CEA and Ct DTs of 1.90 yr (range 0.21-8.50) and 1.52 yr (range 0.09-6.01), respectively, were evaluated. Sensitivity of FDG-PET/CT was 83% for neck, 85% for mediastinal, 75% for lung, 60% for liver, and 67% for bone metastases; overall sensitivity was 76%. Median standardized uptake value (SUVmax) was 5.23 (2.06-13.90). SUVmax correlated significantly with Ct DT (P = 0.011) and minimal DT (minimal value between CEA DT and Ct DT) (P = 0.027). Overall sensitivity of post-RIT IS, CT, and bone magnetic resonance imaging were 94, 74, and 85%, respectively. CONCLUSIONS: These results demonstrate the value of FDG-PET/CT for staging of patients with progressive MTC, especially in the neck and mediastinum, with possible prognostication by SUV quantification. Post-RIT IS was the most sensitive of the imaging modalities studied prospectively.

Gemcitabine radiosensitizes multiple myeloma cells to low let, but not high let, irradiation.

The radiosensitizing properties of gemcitabine in relation to low Linear Energy Transfer (LET) particles (Cobalt 60) and high-LET particles (alpha-RIT (213)Bi-radiolabeled CHX-DTPA-B-B4) were analyzed. Three multiple myeloma cell lines (LP1, RPMI 8226, U266) were irradiated with or without 10 nM gemcitabine 24 h prior to radiation. Gemcitabine led to radiosensitization of LP1 and U266 cells with low-LET (Radiation Enhancement Ratio: 1.55 and 1.49, respectively) but did not radiosensitize any cell line when combined with high-LET.

Targeting, toxicity, and efficacy of 2-step, pretargeted radioimmunotherapy using a chimeric bispecific antibody and 131I-labeled bivalent hapten in a phase I optimization clinical trial.

UNLABELLED: Safety, targeting, and antitumor efficacy of pretargeted radioimmunotherapy using anti-carcinoembryonic antigen (CEA) hMN-14 x m734 bispecific antibody (BsmAb) and 131I-di-diethylenetriamine pentaacetic acid (DTPA)-indium hapten were evaluated in a phase I study performed on patients with CEA-expressing tumors. METHODS: Twenty-two patients with nonmedullary thyroid carcinoma (non-MTC) (group I, 13 patients) or medullary thyroid carcinoma (MTC) (group II, 9 patients) were enrolled. These patients received a 75 mg/m2 (11 patients) or 40 mg/m2 (11 patients) dose of BsmAb and escalating activities of (131)I-di-DTPA-indium 5 d later. Toxicity and tumor response were assessed in 20 patients who received a therapeutic (>2.2 GBq) hapten dose of radioactivity. RESULTS: The percentage of lesions detected by immunoscintigraphy after injection of the therapeutic dose of hapten was 70% on an anatomic-site basis. High bone uptake was relatively frequent. A transient grade I or II hepatic toxicity was observed in 5 patients (45%) injected with 75 mg/m2 of BsmAb and in 1 patient (11%) injected with 40 mg/m2. No other nonhematologic toxicity was observed. With 75 mg/m2 of BsmAb, hematologic toxicity was high: 5 cases of grade III or IV leukopenia (45%) and 5 cases of grade III or IV thrombopenia (45%). With a 40 mg/m2 dose of BsmAb, hematologic toxicity was reduced significantly: 3 cases of grade III or IV leukopenia (33%) and 1 case of grade III or IV thrombopenia (11%) (P = 0.02). Toxicity was significantly higher in MTC patients than in non-MTC patients (P = 0.019). Nine cases of tumor stabilization of 3 mo to more than 12 mo were observed (45%), 6 in the MTC group and 3 in the non-MTC group. The rate of disease stabilization was significantly higher with 75 mg/m2 of BsmAb (64%) than with 40 mg/m2 (22%) (P = 0.04). Human antimouse antibody elevation was observed in 1 patient (8%) and human antihuman antibody in 4 (33%). CONCLUSION: A BsmAb dose of 40 mg/m2 and a 5-d interval appeared to be a better dose/schedule regimen, with acceptable toxicity. Under these conditions, the maximal tolerated activity was 3 GBq of 131I-di-DTPA-indium in MTC patients. In non-MTC patients, dose escalation should continue.

Mechanisms of cell sensitization to alpha radioimmunotherapy by doxorubicin or paclitaxel in multiple myeloma cell lines.

PURPOSE: The purpose of this study was to analyze different mechanisms (cell cycle synchronization, DNA damage, and apoptosis) that might underlie potential synergy between chemotherapy (paclitaxel or doxorubicin) and radioimmunotherapy with alpha radionuclides. EXPERIMENTAL DESIGN: Three multiple myeloma cell lines (LP1, RMI 8226, and U266) were treated with 213Bi-radiolabeled B-B4, a monoclonal antibody that recognizes syndecan-1 (CD138) 24 hours after paclitaxel (1 nmol/L) or doxorubicin (10 nmol/L) treatment. Cell survival was assessed using a clonogenic survival assay. Cell cycle modifications were assessed by propidium iodide staining and DNA strand breaks by the comet assay. Level of apoptosis was determined by Apo 2.7 staining. RESULTS: Radiation enhancement ratio showed that paclitaxel and doxorubicin were synergistic with alpha radioimmunotherapy. After a 24-hour incubation, paclitaxel and doxorubicin arrested all cell lines in the G2-M phase of the cell cycle. Doxorubicin combined with alpha radioimmunotherapy increased tail DNA in the RPMI 8226 cell line but not the LP1 or U266 cell lines compared with doxorubicin alone or alpha radioimmunotherapy alone. Neither doxorubicin nor paclitaxel combined with alpha radioimmunotherapy increased the level of apoptosis induced by either drug alone or alpha radioimmunotherapy alone. CONCLUSION: Both cell cycle arrest in the G2-M phase and an increase in DNA double-strand breaks could lead to radiosensitization of cells by doxorubicin or paclitaxel, but apoptosis would not be involved in radiosensitization mechanisms.

Prognostic impact of serum calcitonin and carcinoembryonic antigen doubling-times in patients with medullary thyroid carcinoma.

CONTEXT: After unsuccessful surgery, medullary thyroid carcinoma (MTC) may be fatal or remain stable for decades, and precise survival predictors are needed. OBJECTIVE: This study assesses the prognostic value of calcitonin and carcinoembryonic antigen (CEA) doubling-times (DT). DESIGN: This is a retrospective study on 65 MTC patients from 2.9-29.5 yr after surgery. SETTING: Data registered in the database of the French Neuroendocrine Tumor Group were analyzed anonymously. PATIENTS: All patients had abnormal calcitonin levels after total thyroidectomy and bilateral lymph node dissection. INTERVENTION: Calcitonin and CEA serum levels were measured during routine disease follow-up. MAIN OUTCOME MEASURE: To assess DT as prognostic factors, a patient population was extracted from the database. RESULTS: When calcitonin DT was less than 6 months, 5- and 10-yr survivals were three of 12 (25%) and one of 12 (8%), respectively; when between 6 months and 2 yr, 5- and 10-yr survivals were 11 of 12 (92%) and three of eight (37%), whereas all 41 patients with calcitonin DT greater than 2 yr were alive at the end of the study. Tumor-Node-Metastasis (TNM) stage, European Organization for Research and Treatment of Cancer (EORTC) score, and calcitonin DT were significant predictors of survival by univariate analysis, but only calcitonin DT remained an independent predictor of survival by multivariate analysis (P = 0.002) with a proportion of variance explained (PVE) of 37.4%. Calcitonin DT was a better predictor than CEA (PVE 63.3% and 47.0%, respectively). Calcitonin DT calculated using only the first four measurements was also an independent predictor of survival (P < 0.000001; PVE 40.4%). CONCLUSION: Calcitonin DT may be superior to initial clinical staging and among the most powerful prognostic indicators in MTC.

Pharmacokinetics and dosimetry studies for optimization of anti-carcinoembryonic antigen x anti-hapten bispecific antibody-mediated pretargeting of Iodine-131-labeled hapten in a phase I radioimmunotherapy trial.

PURPOSE: Pharmacokinetics and dosimetry of hMN-14 x m734 bispecific monoclonal antibody (BsMAb) and (131)I-labeled di-diethylenetriaminepentaacetic acid-indium ((131)I-hapten) were studied to optimize pretargeted radioimmunotherapy. EXPERIMENTAL DESIGN: Thirty-five patients with carcinoembryonic antigen-expressing tumors were included. In a first group of 12 patients, (131)I-trace-labeled BsMAb doses were escalated from 10 to 100 mg/m(2), and 3.7 GBq of (131)I-hapten were administered 7 days later. In a second group, 12 patients received 75 mg/m(2) BsMAb and 2.6-4.2 GBq of (131)I-hapten 5 days later. The BsMAb dose was then reduced to 40 mg/m(2), and 10 patients received 1.9-5.5 GBq of (131)I-hapten. Blood samples were collected. Biodistribution was monitored by quantitative scintigraphy. RESULTS: Directly labeled BsMAb pharmacokinetics was described by two exponentials: half-lives were 8.1 h (2.0-18.1 h) and 48.2 h (22.8-79.4 h); blood clearance was 123 ml/h (64-195 ml/h). With a 7-day interval, 10 or 30 mg/m(2) BsMAb resulted in fast elimination and very low tumor uptake of hapten, whereas 50 or 100 mg/m(2) resulted in favorable tumor accretion. With 75 mg/m(2) BsMAb and a 5-day interval, hapten clearance was 152 ml/h (81-298 ml/h). Calculated radiation dose to tumor was 3.9 Gy/GBq (0.4-22.4 Gy/GBq) for the hapten, compared with 2.0 Gy/GBq (0.3-3.8 Gy/GBq) for the BsMAb, but hematological toxicity prevented dose escalation. Reduction of the BsMAb dose to 40 mg/m(2) accelerated hapten clearance to 492 ml/h (113-2544 ml/h) and reduced hematological toxicity without compromising tumor uptake [5.2 Gy/GBq (0.5-12.6 Gy/GBq)]. CONCLUSIONS: Optimized BsMAb doses and time interval will allow for the administration of higher, tumoricidal, activity doses.

[Radiation therapy with 131I-MIBG is still relevant for metastatic carcinoid tumors]. / Tumeur carcinoïde au stade métastatique: intérêt toujours d'actualité de la thérapie à la mIBG-I131.

We report different treatment options (currently used and on trial) for a patient with a gastrointestinal carcinoid tumor and metastases in the liver, and discuss the advantages of using internal radiotherapy with 131I-MIBG rather than other treatments. According to the literature, this pathology has a poor prognosis, and considering the significant efficacy of this radiopharmaceutical treatment on symptoms, tumor reduction, and biochemical parameters, it seems to be under used. There are currently no standard treatment options. We present a management strategy for gastrointestinal carcinoid tumors with 131I-MIBG.

Enhanced antitumor activity of combined pretargeted radioimmunotherapy and paclitaxel in medullary thyroid cancer xenograft.

A significant antitumor effect associated with moderate toxicity was obtained previously with anticarcinoembryonic antigen x antidiethylene-triaminepentaacetic acid (DTPA)-indium F6-734 bispecific antibody and iodine-131-labeled DTPA-indium bivalent hapten in an animal model of medullary thyroid cancer (MTC). The purpose of this study was to determine whether the cytotoxic agents doxorubicin and paclitaxel, also known as radiosensitizers, improve efficacy of pretargeted radioimmunotherapy (RIT) in experimental MTC. Nude mice bearing TT MTC xenograft were treated with F6-734 and iodine-131-labeled DTPA-indium bivalent hapten injected 48 h apart with or without doxorubicin or paclitaxel. The maximum tolerated dose (MTD) of RIT was 92.5 MBq (as determined previously) and that of doxorubicin and paclitaxel 200 and 1000 micrograms, respectively. A control group received no treatment. Animal weight, hematotoxicity, tumor volume, and serum calcitonin were monitored for 5 months. Tumor growth inhibition induced by drugs alone, RIT alone, or combined therapy was characterized by measuring relative tumor volume 20, 40, and 60 days after treatment to detect additivity or synergism. Mean tumor volume doubling time (MTVDT) was 13 +/- 4 days in the control group, 15 +/- 8 days in the group treated with the MTD of doxorubicin, and 32 +/- 13 days in the group treated with the MTD of paclitaxel. After RIT alone at 92.5 MBq, MTVDT was 86 +/- 22 days. After RIT at 74 MBq (80% of MTD), MTVDT was 56 +/- 10 days. MTVDT was not significantly different from this value after RIT plus doxorubicin, 60 +/- 16 days (65 and 100% of the respective single-agent MTDs). Combination of RIT with paclitaxel (65 and 100% of the respective single-agent MTDs) prolonged the suppression of tumor growth. One complete response was observed, and MTVDT was 114 +/- 44 days. This value was significantly longer than the value obtained with RIT alone at 74 MBq (P < 0.05) or with RIT combined with doxorubicin (P < 0.02). The change in serum calcitonin levels paralleled those in tumor volume. Analysis of dose-response curves at days 20 and 40 showed additivity between RIT and paclitaxel, and analysis at day 60 suggested a synergistic effect. In conclusion, addition of doxorubicin did not improve RIT efficacy, whereas paclitaxel improved RIT efficacy significantly without increasing toxicity.

Molecular advances in pretargeting radioimunotherapy with bispecific antibodies.

The use of antibodies against tumor-associated cell surface antigens for the targeted delivery of radionuclides was introduced >20 years ago. Although encouraging results have been achieved with radiolabeled antibodies in the management of hematopoietic malignancies, there remains a need for successfully treating solid tumors with this modality. One promising approach involving pretargeted delivery of radionuclides has been shown to be capable of significantly increasing the radioactive uptake in tumor relative to normal organs, thereby potentially improving the efficacy of both detection and therapy of cancer. Uncoupling of the radionuclide from the tumor-targeting antibody allows the relatively slow process of antibody localization and clearance to occur before a very rapid and highly specific delivery of the radioactive payload carried on a small molecule, such as a peptide. This minireview discusses the various strategies and advancements made since the concept of pretargeting was proposed in the mid-1980s, with emphasis on those comprising bispecific antibodies for cancer therapy. Critical aspects of these pretargeting systems for achieving higher tumor:nontumor ratios are considered. In addition, both preclinical and clinical results obtained from a pretargeting method known as the Affinity Enhancement System are presented. Future directions of pretargeting technology are also suggested.

Story of Rubidium-82 and Advantages for Myocardial Perfusion PET Imaging.

Rubidium-82 has a long story, starting in 1954. After preclinical studies in dogs showing that myocardial uptake of this radionuclide was directly proportional to myocardial blood flow (MBF), clinical studies were performed in the 80s leading to an approval in the USA in 1989. From that time, thousands of patients have been tested and their results have been reported in three meta-analyses. Pooled patient-based sensitivity and specificity were, respectively, 0.91 and 0.90. By comparison with (99m)Tc-SPECT, (82)Rb PET had a much better diagnostic accuracy, especially in obese patients with body mass index ≥30 kg/m(2) (85 versus 67% with SPECT) and in women with large breasts. A great advantage of (82)Rb PET is its capacity to accurately quantify MBF. Quite importantly, it has been recently shown that coronary flow reserve is associated with adverse cardiovascular events independently of luminal angiographic severity. Moreover, coronary flow reserve is a functional parameter particularly useful in the estimate of microvascular dysfunction, such as in diabetes mellitus. Due to the very short half-life of rubidium-82, the effective dose calculated for a rest/stress test is roughly equivalent to the annual natural exposure and even less when stress-only is performed with a low activity compatible with a good image quality with the last generation 3D PET scanners. There is still some debate on the relative advantages of (82)Rb PET with regard to (99m)Tc-SPECT. For the last 10 years, great technological advances substantially improved performances of SPECT with its accuracy getting closer to this of (82)Rb/PET. Currently, the main advantages of PET are its capacity to accurately quantify MBF and to deliver a low radiation exposure.