FZD10-targeted α-radioimmunotherapy with 225 Ac-labeled OTSA101 achieves complete remission in a synovial sarcoma model.

Synovial sarcomas are rare tumors arising in adolescents and young adults. The prognosis for advanced disease is poor, with an overall survival of 12-18 months. Frizzled homolog 10 (FZD10) is overexpressed in most synovial sarcomas, making it a promising therapeutic target. The results of a phase 1 trial of ß-radioimmunotherapy (RIT) with the 90 Y-labeled anti-FZD10 antibody OTSA101 revealed a need for improved efficacy. The present study evaluated the potential of α-RIT with OTSA101 labeled with the α-emitter 225 Ac. Competitive inhibition and cell binding assays showed that specific binding of 225 Ac-labeled OTSA101 to SYO-1 synovial sarcoma cells was comparable to that of the imaging agent 111 In-labeled OTSA101. Biodistribution studies showed high uptake in SYO-1 tumors and low uptake in normal organs, except for blood. Dosimetric studies showed that the biologically effective dose (BED) of 225 Ac-labeled OTSA101 for tumors was 7.8 Bd higher than that of 90 Y-labeled OTSA101. 90 Y- and 225 Ac-labeled OTSA101 decreased tumor volume and prolonged survival. 225 Ac-labeled OTSA101 achieved a complete response in 60% of mice, and no recurrence was observed. 225 Ac-labeled OTSA101 induced a larger amount of necrosis and apoptosis than 90 Y-labeled OTSA101, although the cell proliferation decrease was comparable. The BED for normal organs and tissues was tolerable; no treatment-related mortality or obvious toxicity, except for temporary body weight loss, was observed. 225 Ac-labeled OTSA101 provided a high BED for tumors and achieved a 60% complete response in the synovial sarcoma mouse model SYO-1. RIT with 225 Ac-labeled OTSA101 is a promising therapeutic option for synovial sarcoma.

Positron Emission Intensity in the Decay of 86gY for Use in Dosimetry Studies.

The ß+-emitting radionuclide 86gY (t1/2 = 14.7 h) forms a matched-pair with the ß--emitting therapeutic radionuclide 90Y (t1/2 = 2.7 d) for theranostic application in medicine. This approach demands a precise knowledge of the positron emission probability of the PET nuclide which was until recently rather uncertain for 86gY. In this work, an 86gY source of high radionuclidic purity was prepared and a direct measurement of the positron emission intensity per 100 decay of the parent (hereafter "positron emission intensity") was performed using high-resolution HPGe detector γ-ray spectroscopy. The electron capture intensity was also determined as an additional check by measuring the Kα and Kß X-rays of energies 14.1 and 15.8 keV, respectively, using a low energy HPGe detector. From those measurements, normalized values of 27.2 ± 2.0% for ß+-emission and 72.8 ± 2.0% for EC were obtained. These results are in excellent agreement with values recently reported in the literature based on a detailed decay scheme study.

Lung shunt and lung dose calculation methods for radioembolization treatment planning.

Radioembolization, also known as selective internal radiation therapy (SIRT), is firmly established in the management of patients with unresectable liver cancers. Advances in normal and tumor liver dosimetry and new knowledge about tumor dose response relationships have helped promote the safe use of higher prescribed doses, consequently transitioning radioembolization from palliative to curative therapy. The lungs are considered a critical organ of risk for radioembolization treatment planning. Unfortunately, lung dosimetry has not achieved similar advances in dose calculation methodology as liver dosimetry. Current estimations of lung dose are dependent on a number of parameters associated with data acquisition and processing algorithms, leading to poor accuracy and precision. Therefore, the efficacy of curative radioembolization may be compromised in patients for whom the lung dose derived using currently available methods unnecessarily limits the desired administered activity to the liver. We present a systematic review of the various methods of determining the lung shunt fraction (LSF) and lung mean dose (LD). This review encompasses pretherapy estimations and post-therapy assessments of the LSF and LD using both 2D planar and 3D SPECT/CT based calculations. The advantages and limitations of each of these methods are deliberated with a focus on accuracy and practical considerations. We conclude the review by presenting a lexicon to precisely describe the methodology used for the estimation of LSF and LD; specifically, category, agent, modality, contour and algorithm, in order to aid in their interpretation and standardization in routine clinical practice.

90Y-microsphere radioembolization: The method, clinical evidence and perspective.

The current review unfolds the procedural steps and the clinical evidence for yttrium-90 (90Y)-microspheres radioembolization. Radioembolization is part of the loco-regional therapeutic spectrum for liver malignancy and involves the invasive, intra-arterial delivery of microspheres carrying ß-emitter isotopes in order to destroy cancerous tissue via ionizing radiation. The main steps of the therapeutic process are selection of eligible patients, angiographic workup, simulation scintigraphy, pre-treatment dosimetry, actual treatment and post-treatment imaging/dosimetry. Radioembolization is routinely applied in advanced stage hepatocellular carcinoma (HCC), yet its role is being investigated even in earlier stages. Prospective, randomized controlled trials did not verify increased overall survival of radioembolization over systemic treatment with sorafenib in HCC; however, it showed survival benefit in certain sub-groups and a favorable toxicity profile with fewer adverse events. Radioembolization is also applied in metastatic colon cancer showing tumoral liver responses, which however did not translate into an overall survival benefit. Data regarding applications of this method in other neoplasms, such as neuroendocrine tumors, breast cancer and melanoma are also presented. There are ongoing clinical trials to define the role of radioembolization within recent treatments algorithms, to determine optimal combinations of this treatment with systemic and targeted therapies and to decide the patients' sub-groups, who will benefit the most.

Yttrium-86 Is a Positron Emitting Surrogate of Gadolinium for Noninvasive Quantification of Whole-Body Distribution of Gadolinium-Based Contrast Agents.

Gadolinium-based contrast agents (GBCAs) are used to provide diagnostic information in clinical magnetic resonance (MR) examinations. Gadolinium (Gd) has been detected in the brain, bone and skin of patients, months and years following GBCA administration, raising concerns about long term toxicity. Despite increased scrutiny, the concentration, chemical form and fate of the retained gadolinium species remain unknown. Importantly, the whole body biodistribution and organ clearance of GBCAs is poorly understood in humans. Gadolinium lacks suitable isotopes for nuclear imaging. We demonstrate that the yttrium-86 isotope can be used as a gadolinium surrogate. We show that Gd and their analogous Y complexes have similar properties both in solution and in vivo, and that yttrium-86 PET can be used to track the biodistribution of GBCAs over a two-day period.

Therapeutic efficacy evaluation of radioimmunotherapy with 90 Y-labeled anti-podoplanin antibody NZ-12 for mesothelioma.

Podoplanin is a type I transmembrane sialomucin-like glycoprotein that is highly expressed in malignant mesothelioma. The rat-human chimeric antibody NZ-12 has high affinity for human podoplanin and antibody-dependent cellular cytotoxicity and is applicable for radioimmunotherapy (RIT) to enhance the antitumor effect. In the present study, we evaluated the in vivo and in vitro properties of radiolabeled NZ-12 and the antitumor effect of RIT with 90 Y-labeled NZ-12 in an NCI-H226 (H226) malignant mesothelioma xenograft mouse model. 111 In-labeled NZ-12 bound specifically to H226 cells with high affinity, and accumulation was high in H226 tumors but low in major organs. RIT with 90 Y-labeled NZ-12 significantly suppressed tumor growth and prolonged survival without body weight loss and obvious adverse effects. Higher podoplanin expression levels were observed in human mesothelioma specimens, suggesting higher tumor accumulation of 90 Y-labeled NZ-12 in patients compared with the H226 tumor xenografts. Our findings suggest that 90 Y-labeled NZ-12 is a promising RIT agent as a new therapeutic option for malignant mesothelioma that warrants further clinical studies to evaluate the dosimetry and efficacy in patients.

Yttrium-90 glass microspheres radioembolization (RE) for biliary tract cancer: a large single-center experience.

PURPOSE: Radioembolization (RE) is a promising treatment option for biliary tract cancers (BTC). We report here the largest series to date using this treatment modality. METHODS: We retrospectively studied data from 64 patients treated outside prospective clinical trial at our institution. We studied baseline characteristics as potential prognostic factors. We studied dose delivered to the tumor as predictive factors of outcomes in patients not receiving concomitant chemotherapy. RESULTS: The Progression-Free Survival and Overall Survival (OS) were 7.6 months [95% Confidence Interval (CI): 4.6-10.6] and 16.4 months [95% CI: 7.8-25.0] in the whole cohort. The factors independently associated with OS in multivariable analysis were the primary localization of ICC (HR = 0.27, 95% CI: 0.11-0.68, p = 0.005) and a PS > 0 (HR = 2.21, 95% CI: 1.11-4.38, p = 0.024). During follow-up, 12 patients (19%) underwent surgery following downstaging, with a median OS of 51.9 months. In patients not treated with concomitant chemotherapy (n = 31), OS was significantly higher in patients with a dose delivered to the tumor 260Gy or higher than in patients with a dose delivered to the tumor lower than 260Gy (median 28.2 vs 11.4 months, log-rank p = 0.019). CONCLUSION: Our results confirm that RE is a promising treatment modality in BTC. A high proportion of patients could be downstaged to surgery, with promising long-term survival. Dose delivered to the tumor correlated with clinical outcomes when chemotherapy was not used concomitantly.

Single Low-Dose Injection of Evans Blue Modified PSMA-617 Radioligand Therapy Eliminates Prostate-Specific Membrane Antigen Positive Tumors.

Prostate cancer is the most frequently diagnosed malignant tumor in men worldwide. Prostate-specific membrane antigen (PSMA) is a surface molecule specifically expressed by prostate tumors that has been shown to be a valid target for internal radionuclide therapy in both preclinical and clinical settings. The most common radiotherapeutic agent is the small molecule 177Lu-PSMA-617, which is under clinical evaluation in multiple countries. Nevertheless, its efficacy in causing tumor regression is still suboptimal, even when administered in several cycles per patient, perhaps due to poor pharmacokinetics (PK), which limits uptake by the tumor cells. We postulated that the addition of the Evans blue (EB) moiety to PSMA-617 would improve the PK by extending circulation half-life, which would increase tumor uptake and improve radiotherapeutic efficacy. PSMA-617 was modified by conjugation of a 2-thiol acetate group onto the primary amine and thereafter reacted with a maleimide functional group of an EB derivative, to give EB-PSMA-617. The PK and radiotherapeutic efficacy of 90Y- or 177Lu-EB-PSMA-617 was compared to the clinically used radiopharmaceutical 90Y- or 177Lu- PSMA-617 in PC3-PIP tumor-bearing mice. EB-PSMA-617 retained binding to serum albumin as well as a high internalization rate by tumor cells. Upon injection, metal-labeled EB-PSMA-617 demonstrated an extended blood half-life compared to PSMA-617 and, thereby, prolonged the time window for binding to PSMA. The improved PK of EB-PSMA-617 resulted in significantly higher accumulation in PSMA+ tumors and highly effective radiotherapeutic efficacy. Remarkably, a single dose of 1.85 MBq of 90Y- or 177Lu-EB-PSMA-617 was sufficient to eradicate established PMSA+ tumors in mice. No significant body weight loss was observed, suggesting little to no gross toxicity. The construct described here, EB-PSMA-617, may improve the radiotherapeutic efficacy for patients with PSMA-positive tumors by reducing both the amount of activity needed for therapy as well as the frequency of administration, as compared to PSMA-617.

Radioembolization with 90Y glass microspheres for hepatocellular carcinoma: significance of pretreatment 11C-acetate and 18F-FDG PET/CT and posttreatment 90Y PET/CT in individualized dose prescription.

PURPOSE: The aim of this study was to establish an algorithm for the prescription of 90Y glass microsphere radioembolization (90Y-GMRE) of HCC in individual patients based on the relationship between tumour dose (TD) and response validated by 90Y PET/CT dosimetry and dual-tracer PET/CT metabolic parameters. METHODS: The study group comprised 62 HCC patients prospectively recruited for 90Y-GMRE who underwent pretreatment dual-tracer (11C-acetate and 18F-FDG) PET/CT as surrogate markers of HCC cellular differentiation. Pretreatment tumour-to-nontumour ratio on 99mTc-MAA SPECT/CT (T/NTMAA) was correlated with posttreatment 90Y PET/CT T/NT90Y after quantification validation. The TD-response relationship for HCC of different tracer groups was assessed on follow-up PET/CT 2 months after treatment. RESULTS: 90Y PET/CT was accurate in the measurement of recovery of injected 90Y activity (81.9-99.9%, median 94.8%). Pretreatment SPECT/CT T/NTMAA was strongly correlated with posttreatment 90Y PET/CT T/NT90Y (5.6 ± 3.2 versus 5.9 ± 3.5, T/NT90Y 1.01 × T/NTMAA + 0.161, r = 0.918, P < 0.05). The response rates were 72.4% (21/29), 70.6% (12/17) and 25% (4/16) for well, moderately and poorly differentiated HCC, respectively. The cut-off TD for a good response was significantly different between poorly differentiated and well/moderately differentiated HCC (262 Gy versus 152/174 Gy) with 89.2% sensitivity and 88% specificity. At a limiting tolerated liver dose of 70 Gy, the T/NTMAA thresholds for predicting a good response in poorly differentiated and well/moderately differentiated HCC were 3.5 and 2.0/2.3. Disregarding HCC cellular differentiation, the cut-off TD became 170 Gy, with lower sensitivity (70.3%) and specificity (76%). CONCLUSION: 90Y PET/CT can provide accurate dosimetry for 90Y-GMRE. Pretreatment T/NTMAA predicts posttreatment T/NT90Y. The TD thresholds for a good response are tracer-dependent, with a strong correlation between HCC radiosensitivity and cellular differentiation and other PET-based parameters. These cytokinetic factors improve treatment efficacy while minimizing organ damage for the prescription of personalized 90Y-GMRE.

Bevacizumab Radioimmunotherapy (RIT) with Accelerated Blood Clearance Using the Avidin Chase.

The overexpression of vascular endothelial growth factor (VEGF) in varying types of solid tumor renders radioimmunotherapy (RIT) with the anti-VEGF antibody bevacizumab (BV) a promising treatment. However, the slow blood clearance of BV, which may increase the occurrence risk of hematotoxicity, hinders the application of BV-RIT. Using the avidin chase is a long-known blood clearance enhancement strategy for biotinylated-mAb. To enhance RIT efficacy by increasing the radioactivity dose, we evaluated the ability of avidin to accelerate the blood clearance of yttrium-90 (90Y)-labeled biotinylated BV (90Y-Bt-BV) in a xenograft mouse model of triple-negative breast cancer (TNBC). The biodistribution study in the TNBC xenograft mice confirmed the high and specific tumor accumulation of the indium-111 (111In)-BV. The blood clearance enhancement effect of the avidin chase was demonstrated in the normal mouse studies with 111In-Bt-BV. In the subsequent biodistribution studies with the tumor-bearing mice, an optimized dose of avidin injection subsequent to 111In-Bt-BV with an appropriate biotin valency successfully accelerated the blood clearance of 111In-Bt-BV without impairing its tumor accumulation level. The avidin chase enabled an increase in the maximum tolerated dose of 90Y-Bt-BV to twice as much as that of 90Y-BV in tumor-bearing mice and thereby significantly improved the therapeutic effect of 90Y-Bt-BV compared to 90Y-BV ( p < 0.05). These results underscored the potential usefulness of 90Y-bevacizumab-RIT with the avidin chase for the treatment of VEGF-positive tumors.

86/90Y-Based Theranostics Targeting Angiogenesis in a Murine Breast Cancer Model.

Angiogenesis is widely recognized as one of the hallmarks of cancer. Therefore, imaging and therapeutic agents targeted to angiogenic vessels may be widely applicable in many types of cancer. To this end, the theranostic isotope pair, 86Y and 90Y, were used to create a pair of agents for targeted imaging and therapy of neovasculature in murine breast cancer models using a chimeric anti-CD105 antibody, TRC105. Serial positron emission tomography imaging with 86Y-DTPA-TRC105 demonstrated high uptake in 4T1 tumors, peaking at 9.6 ± 0.3%ID/g, verified through ex vivo studies. Additionally, promising results were obtained in therapeutic studies with 90Y-DTPA-TRC105, wherein significantly ( p < 0.05) decreased tumor volumes were observed for the targeted treatment group over all control groups near the end of the study. Dosimetric extrapolation and tissue histological analysis corroborated trends found in vivo. Overall, this study demonstrated the potential of the pair 86/90Y for theranostics, enabling personalized treatments for cancer.

90Y-daclizumab, an anti-CD25 monoclonal antibody, provided responses in 50% of patients with relapsed Hodgkin's lymphoma.

Despite significant advances in the treatment of Hodgkin's lymphoma (HL), a significant proportion of patients will not respond or will subsequently relapse. We identified CD25, the IL-2 receptor alpha subunit, as a favorable target for systemic radioimmunotherapy of HL. The scientific basis for the clinical trial was that, although most normal cells with exception of Treg cells do not express CD25, it is expressed by a minority of Reed-Sternberg cells and by most polyclonal T cells rosetting around Reed-Sternberg cells. Forty-six patients with refractory and relapsed HL were evaluated with up to seven i.v. infusions of the radiolabeled anti-CD25 antibody (90)Y-daclizumab. (90)Y provides strong ß emissions that kill tumor cells at a distance by a crossfire effect. In 46 evaluable HL patients treated with (90)Y-daclizumab there were 14 complete responses and nine partial responses; 14 patients had stable disease, and nine progressed. Responses were observed both in patients whose Reed-Sternberg cells expressed CD25 and in those whose neoplastic cells were CD25(-) provided that associated rosetting T cells expressed CD25. As assessed using phosphorylated H2AX (γ-H2AX) as a bioindicator of the effects of radiation exposure, predominantly nonmalignant cells in the tumor microenvironment manifested DNA damage, as reflected by increased expression of γ-H2AX. Toxicities were transient bone-marrow suppression and myelodysplastic syndrome in six patients who had not been evaluated with bone-marrow karyotype analyses before therapy. In conclusion, repeated (90)Y-daclizumab infusions directed predominantly toward nonmalignant T cells rosetting around Reed-Sternberg cells provided meaningful therapy for select HL patients.

Efficacy Evaluation of Combination Treatment Using Gemcitabine and Radioimmunotherapy with 90Y-Labeled Fully Human Anti-CD147 Monoclonal Antibody 059-053 in a BxPC-3 Xenograft Mouse Model of Refractory Pancreatic Cancer.

The poor prognosis of pancreatic cancer requires the development of more effective therapy. CD147 expresses in pancreatic cancer with high incidence and has a crucial role in invasion and metastasis. We developed a fully human monoclonal antibody (059-053) with high affinity for CD147. Here we evaluated the efficacy of combined treatment using radioimmunotherapy (RIT) with 90Y-labeled 059-053 and gemcitabine in a BxPC-3 xenograft mouse model. Expression of CD147 and matrix metalloproteinase-2 (MMP2) in BxPC-3 tumors was evaluated. In vitro and in vivo properties of 059-053 were evaluated using 111In-labeled 059-053 and a pancreatic cancer model BxPC-3. Tumor volume and body weight were periodically measured in mice receiving gemcitabine, RIT, and both RIT and gemcitabine (one cycle and two cycles). High expression of CD147 and MMP2 was observed in BxPC-3 tumors and suppressed by 059-053 injection. Radiolabeled 059-053 bound specifically to BxPC-3 cells and accumulated highly in BxPC-3 tumors but low in major organs. Combined treatment using RIT with gemcitabine (one cycle) significantly suppressed tumor growth and prolonged survival with tolerable toxicity. The two-cycle regimen had the highest anti-tumor effect, but was not tolerable. Combined treatment with 90Y-labeled 059-053 and gemcitabine is a promising therapeutic option for pancreatic cancer.

Clinical feasibility of 90Y digital PET/CT for imaging microsphere biodistribution following radioembolization.

PURPOSE: The purpose of this study was to evaluate the clinical feasibility of next generation solid-state digital photon counting PET/CT (dPET/CT) technology and imaging findings in patients following 90Y microsphere radioembolization in comparison with standard of care (SOC) bremsstrahlung SPECT/CT (bSPECT/CT). METHODS: Five patients underwent SOC 90Y bremsstrahlung imaging immediately following routine radioembolization with 3.5 ± 1.7 GBq of 90Y-labeled glass microspheres. All patients also underwent dPET/CT imaging at 29 ± 11 h following radioembolization. Matched pairs comparison was used to compare image quality, image contrast and 90Y biodistribution between dPET/CT and bSPECT/CT images. Volumetric assessments of 90Y activity using different isocontour thresholds on dPET/CT and bSPECT/CT images were also compared. RESULTS: Digital PET/CT consistently provided better visual image quality and 90Y-to-background image contrast while depicting 90Y biodistribution than bSPECT/CT. Isocontour volumetric assessment using a 1% threshold precisely outlined 90Y activity and the treatment volume on dPET/CT images, whereas a more restrictive 20% threshold on bSPECT/CT images was needed to obtain comparable treatment volumes. The use of a less restrictive 10% threshold isocontour on bSPECT/CT images grossly overestimated the treatment volume when compared with the 1% threshold on dPET/CT images. CONCLUSIONS: Digital PET/CT is clinically feasible for the assessment of 90Y microsphere biodistribution following radioembolization, and provides better visual image quality and image contrast than routine bSPECT/CT with comparable acquisition times. With further optimization and clinical validation, dPET technology may allow faster and more accurate imaging-based assessment of 90Y microsphere biodistribution.

Pyclen Tri-n-butylphosphonate Ester as Potential Chelator for Targeted Radiotherapy: From Yttrium(III) Complexation to (90)Y Radiolabeling.

The Y(3+) complex of PCTMB, the tri-n-butyl phosphonate ester of pyclen (3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene), was synthesized as well as its Ho(3+) and Lu(3+) analogues. X-ray diffraction analyses revealed isomorphous dimeric M2(PCTMB)2·9H2O (M = Y, Ho, Lu) structures that crystallize in the centrosymmetric P1̅ triclinic space group. (1)H NMR and UV studies in aqueous solutions indicated that Y(3+) complexation is fast, being quantitative in 167 min at pH 3.8 and in 13 min at pH 5.5 (25 °C, acetate buffer, I = 0.150 M, [Y(3+)] = [PCTMB] = 0.2 mM). (1)H NMR DOSY and photon correlation spectroscopy experiments evidenced the formation of aggregates in chloroform with a bimodal distribution that changes slightly with concentration (11-24 and 240-258 nm). The behavior of the acid-assisted dissociation of the complex of Y(3+) with PCTMB was studied under pseudo-first-order conditions, and the half-life of the [Y(PCTMB)] complex in 0.5 M HCl at 25 °C was found to be 37 min, a value that decreases to 2.6 min in 5 M HCl. The Y(3+) complex of PCTMB is thermodynamically very stable, with a stability constant of log KY-PCTMB = 19.49 and pY = 16.7 measured by potentiometry. (90)Y complexation studies revealed fast radiolabeling kinetics; optimal radiolabeling conditions were obtained for (90)Y in acetate medium, PCTMB at 10(-4) to 10(-2) M in acetate buffer pH = 4.75, 15 min at 45-60 °C. In vitro stability studies in human serum showed that [(90)Y(PCTMB)] is quite stable, with about 90% of the activity still in the form of the radiotracer at 24 h and 80% from 48 h to 72 h. A comparison with other ligands such as PCTA, DOTA, and DTPA already used for in vivo application shows that [(90)Y(PCTMB)] is an interesting lipophilic and neutral analogue of these reference chelates for therapeutic applications in aqueous and nonaqueous media.

(90) Y/(177) Lu-labelled Cetuximab immunoconjugates: radiochemistry optimization to clinical dose formulation.

Radiolabelled monoclonal antibodies (mAbs) are increasingly being utilized in cancer theranostics, which is a significant move toward tailored treatment for individual patients. Cetuximab is a recombinant, human-mouse chimeric IgG1 mAb that binds to the epidermal growth factor receptor with high affinity. We have optimized a protocol for formulation of clinically relevant doses (~2.22 GBq) of (90) Y-labelled Cetuximab and (177) Lu-labelled Cetuximab by conjugation of the mAb with a suitable bifunctional chelator, N-[(R)-2-amino-3-(paraisothiocyanato-phenyl)propyl]-trans-(S,S)-cyclohexane-1,2-diamine-N,N,N',N″,N″-pentaacetic acid (CHX-A″-DTPA). The radioimmunoconjugates demonstrated reasonably high specific activity (1.26 ± 0.27 GBq/mg for (90) Y-CHX-A″-DTPA-Cetuximab and 1.14 ± 0.15 GBq/mg for (177) Lu-CHX-A″-DTPA-Cetuximab), high radiochemical purity (>95%) and appreciable in vitro stability under physiological conditions. Preliminary biodistribution studies with both (90) Y-CHX-A″-DTPA-Cetuximab and (177) Lu-CHX-A″-DTPA-Cetuximab in Swiss mice bearing fibrosarcoma tumours demonstrated significant tumour uptake at 24-h post-injection (p.i.) (~16%ID/g) with good tumour-to-background contrast. The results of the biodistribution studies were further corroborated by ex vivo Cerenkov luminescence imaging after administration of (90) Y-CHX-A″-DTPA-Cetuximab in tumour-bearing mice. The tumour uptake at 24 h p.i. was significantly reduced with excess unlabelled Cetuximab, suggesting that the uptake was receptor mediated. The results of this study hold promise, and this strategy should be further explored for clinical translation.

Yttrium-90 ibritumomab tiuxetan followed by rituximab maintenance as treatment for patients with diffuse large B-cell lymphoma are not candidates for autologous stem cell transplant.

BACKGROUND: Not all patients with diffuse large B-cell lymphoma (DLBCL) are candidates for aggressive regimens. (90)Y ibritumomab tiuxetan ((90)Y-IT), an anti-CD20 radionuclide-conjugated antibody, has demonstrated clinical efficacy in DLBCL with a favorable toxicity profile. METHODS: This phase II trial investigated the overall response rate (ORR), event-free survival (EFS), overall survival (OS) and toxicity of treatment with (90)Y-IT (0.4 or 0.3 mCi (90)Y/kg based on platelets) followed by rituximab maintenance therapy in patients with DLBCL not candidates for transplant. RESULTS: 25 patients were enrolled. At best response 8 patients obtained a complete response (CR) and 1 a partial response (ORR 36%). Median EFS was 2.5 months and OS 8.1 months. No patient who obtained CR later relapsed systemically. Two patients were free of disease at the 61- and 100-month follow-ups; 65% had grade 3/4 thrombocytopenia, but no significant bleeding was observed. Grade 3 nonhematologic toxicity occurred in 36%. Patients who had progressed through a rituximab-containing regimen responded poorly. CONCLUSION: The ORR of 36% with (90)Y-IT as salvage therapy for DLBCL while inferior to more aggressive regimens is significant with acceptable toxicity. For a subset of patients not candidates for salvage with autologous transplant, this treatment strategy can produce a durable, long-lasting remission.

Potential of a Cetuximab-based radioimmunotherapy combined with external irradiation manifests in a 3-D cell assay.

Targeting epidermal growth factor receptor (EGFR)-overexpressing tumors with radiolabeled anti-EGFR antibodies is a promising strategy for combination with external radiotherapy. In this study, we evaluated the potential of external plus internal irradiation by [(90) Y]Y-CHX-A″-DTPA-C225 (Y-90-C225) in a 3-D environment using FaDu and SAS head and neck squamous cell carcinoma (HNSCC) spheroid models and clinically relevant endpoints such as spheroid control probability (SCP) and spheroid control dose 50% (SCD50 , external irradiation dose inducing 50% loss of spheroid regrowth). Spheroids were cultured using a standardized platform. Therapy response after treatment with C225, CHX-A"-DTPA-C225 (DTPA-C225), [(90) Y]Y-CHX-A"-DTPA (Y-90-DTPA) and Y-90-C225 alone or in combination with X-ray was evaluated by long-term monitoring (60 days) of spheroid integrity and volume growth. Penetration kinetics into spheroids and EGFR binding capacities on spheroid cells were identical for unconjugated C225 and Y-90-C225. Spheroid-associated radioactivity upon exposure to the antibody-free control conjugate Y-90-DTPA was negligible. Determination of the SCD50 demonstrated higher intrinsic radiosensitivity of FaDu as compared with SAS spheroids. Treatment with unconjugated C225 alone did not affect spheroid growth and cell viability. Also, C225 treatment after external irradiation showed no additive effect. However, the combination of external irradiation with Y-90-C225 (1 µg/ml, 24 hr) resulted in a considerable benefit as reflected by a pronounced reduction of the SCD50 from 16 Gy to 9 Gy for SAS spheroids and a complete loss of regrowth for FaDu spheroids due to the pronounced accumulation of internal dose caused by the continuous exposure to cell-bound radionuclide upon Y-90-C225-EGFR interaction.

A systematic comparative evaluation of 90Y-labeled bifunctional chelators for their use in targeted therapy.

This paper describes a systematic comparative evaluation of five commonly used bifunctional chelators, namely,p-isothiocyanato benzyl derivatives of diethylenetriaminepentacetic acid (DTPA-NCS), trans-cyclohexyl diethylenetriaminepentaceticacid (CHX-A″-DTPA-NCS), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA-NCS), 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA-NCS), and 3,6,9,15-tetraazabicyclo [9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (PCTA-NCS), on the basis of their ability to complex 90Y at room temperature, in vitro and in vivo stability and clearance pattern in biological system. The results of the experiments carried out revealed that CHX-A″-DTPA-NCS was the most promising option as it could be radiolabeled with 90Y at room temperature with highest specific activity and demonstrated high in vitro stability in human serum and in presence of challenging metal ions commonly present inhuman plasma. The clearance pattern in Swiss mice revealed that 90Y-CHX- A″-DTPA-NCS cleared through the kidneys with minimum retention in any other major organ. Thus, the use of cyclohexyl-DTPA based bifunctional chelators would increase the scope of making 90Y-labeled agents suitable for targeted therapy.