New PSMA-Targeting Ligands: Transformation from Diagnosis (Ga-68) to Radionuclide Therapy (Lu-177).

Prostate-specific membrane antigen (PSMA) is a promising target for the diagnosis and radionuclide therapy of prostate cancer. This study reports conversion of a previously reported 68Ga-imaging agent, [68Ga]Ga-P16-093, to a Lu-177 radionuclide therapeutic agent. Substitution of the HBED-CC metal chelating group with DOTA(GA)2 led to P17-087 (4) and P17-088 (7). Both agents showed excellent PSMA binding affinity (IC50 = 10-30 nM) comparable to that of recently FDA-approved [177Lu]Lu-PSMA-617 (Pluvicto). Biodistribution studies in PSMA expressing tumor bearing mice showed that [177Lu]Lu-4 exhibited very high tumor uptake and a fast blood clearance similar to those of [177Lu]Lu-PSMA-617. Conversely, [177Lu]Lu-7, containing an albumin binder, extended its blood half-life and exhibited significantly higher uptake and longer tumor residence time than [177Lu]Lu-4 and [177Lu]Lu-PSMA-617. The switch from chelator HBED-CC to DOTA(GA)2 and the switch from the imaging isotope gallium-68 to the therapeutic isotope lutetium-177 have successfully transformed a PSMA-targeting agent from diagnosis to promising radionuclide therapeutic agents.

177Lu-doxycycline as potential radiopharmaceutical: electrochemical characterization, radiolabeling, and biodistribution in tumor-bearing mice.

PURPOSE: Recent studies with doxycycline as adjuvant therapy to conventional chemotherapy have shown promising results in cancer therapy. The current study aimed to examine the capability of 177Lu-labeled tetracycline ligand, doxycycline hyclate, to use as an anticancer agent. MATERIALS AND METHODS: Doxycycline was radiolabeled with beta-emitting radioisotope 177Lu. Complex formation and its interaction with DNA were investigated electrochemically. Binding of 177Lu-doxycycline to CT 26 cell line was done. Biodistribution of 177Lu-doxycycline was examined in healthy Wistar rats and CT26 colon carcinoma tumor-bearing mice by i.v. and i.p. administration, respectively. RESULTS: Doxycycline hyclate was successfully radiolabeled with 177Lu in high radiolabeling yield (>99%). The radiolabeled complex was stable in vitro in saline and human serum over 72 h. Non-radioactive Lu-doxycycline complex formation was demonstrated electrochemically as well. Intercalative interactions of the doxycycline and Lu-doxycycline with DNA were proved using simultaneously spectrophotometric and electrochemical methods. The binding of the radiolabeled complex with plasma proteins was 4.0 ± 0.4%. The partition coefficient showed the lipophilic nature of the complex similar to the free ligand. The binding curve demonstrates binding from 0.1 nM concentrations of 177Lu-doxycycline, with half-binding estimated ∼100 nM. Biodistribution studies of 177Lu-doxycycline in CT26 colon tumor-bearing mice showed a satisfactory accumulation rate in the tumor (2.88 ± 0.85% ID/g) 3 h after intraperitoneal injection. Both the hepatobiliary system and the urinary system were prominent as excretory routes of the radiolabeled complex. CONCLUSION: Considering obtained results, 177Lu-doxycycline complex, due to its excellent electrochemical and biological characteristics, with emphasis on the binding ability to DNA via intercalative interaction as well as significant accumulation in the tumor, is suitable for further in vivo studies to investigate its potential use in cancer treatment.

High-Specific-Activity-131I-MIBG versus 177Lu-DOTATATE Targeted Radionuclide Therapy for Metastatic Pheochromocytoma and Paraganglioma.

Targeted radionuclide therapies (TRT) using 131I-metaiodobenzylguanidine (131I-MIBG) and peptide receptor radionuclide therapy (177Lu or 90Y) represent several of the therapeutic options in the management of metastatic/inoperable pheochromocytoma/paraganglioma. Recently, high-specific-activity-131I-MIBG therapy was approved by the FDA and both 177Lu-DOTATATE and 131I-MIBG therapy were recommended by the National Comprehensive Cancer Network guidelines for the treatment of metastatic pheochromocytoma/paraganglioma. However, a clinical dilemma often arises in the selection of TRT, especially when a patient can be treated with either type of therapy based on eligibility by MIBG and somatostatin receptor imaging. To address this problem, we assembled a group of international experts, including oncologists, endocrinologists, and nuclear medicine physicians, with substantial experience in treating neuroendocrine tumors with TRTs to develop consensus and provide expert recommendations and perspectives on how to select between these two therapeutic options for metastatic/inoperable pheochromocytoma/paraganglioma. This article aims to summarize the survival outcomes of the available TRTs; discuss personalized treatment strategies based on functional imaging scans; address practical issues, including regulatory approvals; and compare toxicities and risk factors across treatments. Furthermore, it discusses the emerging TRTs.

Examining Absorbed Doses of Indigenously Developed 177Lu-PSMA-617 in Metastatic Castration-Resistant Prostate Cancer Patients at Baseline and During Course of Peptide Receptor Radioligand Therapy.

Aim: The objective of this study was to estimate the absorbed doses to the normal organs and tumor lesions in metastatic castration-resistant prostate cancer (mCRPC) patients treated with indigenously developed 177Lu-PSMA-617 that could establish optimal treatment protocol with minimum risk to the dose-limiting organs. Furthermore, attempt was also made to compare radiation absorbed doses for normal organs and tumor lesions in subsequent cycles of 177Lu-PSMA-617 peptide receptor radioligand therapy (PRLT) in the same group of patients during the course of treatment. Methods: A total of 30 patients of proven mCRPC were enrolled for this prospective study. These patients received up to 5 cycles of treatment with 177Lu-PSMA-617 PRLT (1 cycle for 13 patients, 2 cycles for 9 patients, 3 cycles for 3 patients, and 5 cycles for 5 patients), at 11-12-week intervals between the two successive therapies. The patients underwent postadministration whole-body scintigraphy at five time points: 0.5 (prevoid), 2, 12, 24, and 72/96 h (postvoid). From time-activity curves generated by drawing regions of interests on the images, number of disintegrations was determined. Tumor masses were estimated from pretherapeutic 68Ga-PSMA-11 positron emission tomography-computed tomography images. Absorbed doses for organs and tumors were calculated using OLINDA 2.0 software. Results: The average activity of 177Lu-PSMA-617 (mean ± SD) administered per patient per cycle was 4.94 ± 0.45 GBq. The mean absorbed organ doses (mean ± SD) from first therapy cycle in Gy/GBq were as follows: kidneys 0.52 ± 0.16, spleen 0.17 ± 0.07, liver 0.08 ± 0.05, salivary glands 0.53 ± 0.30, lacrimal glands 1.45 ± 0.85, nasal mucosa membrane 0.46 ± 0.19, urinary bladder 0.23 ± 0.02, and bone marrow 0.04 ± 0.03. The mean effective dose for whole body from first therapy cycle was 0.05 ± 0.03 Sv/GBq. Among all the normal organs, lacrimal glands received the highest absorbed dose. The median dose for all lesions, bone lesions, lymph nodes, primary site, liver lesion, lung lesion, and soft tissue deposit from first therapy cycle was determined to be 4.17, 4.23, 3.96, 4.36, 10.27, 0.78, and 4.68 Gy/GBq respectively. Absorbed doses received by the normal organs in five consecutive cycles follow three different trends, (a) for kidneys, salivary glands, and nasal mucous membrane, absorbed doses increased from first therapy cycle to second therapy cycle and then slowly decreased in subsequently therapy cycles; (b) for spleen, liver, and lacrimal glands, absorbed doses decreased with the successive therapy cycles; and (c) in case of bone marrow, bladder, and whole body, mean absorbed dose almost remained constant in each therapy cycle. Absorbed doses to the lesions gradually decreased with increase of the number of therapy cycles. Conclusions: The organ and tumor absorbed doses of 177Lu-PSMA-617 in mCRPC patients were found to be comparable to the data reported in the literature. The highest absorbed organ dose was observed in lacrimal glands and being a dose limiting organ, a cumulative activity up to 32.5 GBq (878 mCi) of 177Lu-PSMA-617 in 4-5 therapy cycles appears safe and feasible to achieve full therapeutic window.

Comparison of Dual-Tracer PET and CT Features to Conventional Risk Categories in Assessing Response to 177Lu-PSMA-617 Therapy for Metastatic Prostate Adenocarcinoma with Urinary Bladder Involvement.

The present communication details the imaging characteristics, peculiarities, and response to 177Lu-labeled prostate-specific membrane antigen (PSMA)-617-targeted radioligand therapy (PRLT) in accordance with Gleason score and use of dual-tracer PET (68Ga-PSMA-11 and 18F-FDG) in patients with urinary bladder invasion or metastasis by prostate cancer, including the prognostic value of 18F-FDG PET in predicting response to treatment. The CT attenuation units (Hounsfield units) correlated with the prostate primary in the case of direct tumor extension from the prostate, whereas in hematogenous metastatic seeding the Hounsfield units were lower than in the primary prostatic tumor. A favorable outcome to 177Lu-PSMA-617 PRLT was observed in patients with low or no baseline 18F-FDG uptake despite a high Gleason score and a high-risk National Comprehensive Cancer Network prognostic category and did not correlate with the latter alone, whereas a high SUVmax on 18F-FDG PET/CT was associated with an adverse outcome. These findings suggest a promising role for 18F-FDG PET/CT in predicting therapeutic outcomes more confidently, and hence the concept of dual-tracer PET appears to hold good in prostate adenocarcinoma theranostics.

Efficacy and Safety of 177Lu-PSMA-617 Radioligand Therapy in Metastatic Castration-Resistant Prostate Cancer Patients.

PURPOSE: The aim of this study was to evaluate the efficacy and safety of Lu-PSMA-617 radioligand therapy in metastatic castration-resistant prostate cancer (mCRPC). METHODS: In this prospective, single-arm, single-institutional study, 90 mCRPC patients with progressive disease (PD) on second-line hormonal therapy and/or docetaxel chemotherapy were recruited for the study. All patients underwent diagnostic Ga-PSMA-HBED-CC PET/CT, prior to inclusion for therapy. Included patients underwent Lu-PSMA-617 therapy at 8- to 12-weekly intervals. The primary end point was to assess the overall survival. The secondary and cosecondary end points included biochemical response assessment as per the Prostate Cancer Working Group 3 criteria, progression-free survival, radiological and molecular response criteria, clinical response, safety profile, and disease control rates. All the outcome parameters were evaluated in 90 patients except for the radiographic and molecular response, which was evaluated in 69 patients. RESULTS: The median age of patients was 66.5 years (range, 30-88 years). The median activity administered per cycle was 3.7 to 8 GBq ranging from 1 to 7 cycles, and patients were followed up over a median duration of 28 months. At 2- to 3-month interval after the first therapy and the end of the assessment, greater than 50% decline in prostate-specific antigen was observed in 32.2% and 45.5%, respectively. Univariate analysis did not reveal any variables such as prior therapies, laboratory parameters, concomitant hormonal therapy, and SUV patient parameters associated with prostate-specific antigen decline. Radiographic response by diagnostic CT revealed partial remission in 23% (16/69), stable disease in 54% (37/69), and PD in 23% (16/69) of patients. Molecular tumor response by PET Response Criteria in Solid Tumor 1 criteria revealed 19 (27.5%) of 69 patients with partial remission, 30 (43.5%) of 69 with stable disease, and 20 (29%) of 69 with PD. The disease control rates according to the radiographic and molecular response were 77% and 71%, respectively. The median overall survival and median progression-free survivals were 14 and 11.8 months, respectively. Toxicities related to radioligand therapy were low and transient with no serious adverse effects. CONCLUSIONS: Lu-PSMA-617 radionuclide therapy is a safe and effective approach to the treatment of mCRPC patients.

Determination of whole-body tumour burden on [68Ga]PSMA-11 PET/CT for response assessment of [177Lu]PSMA-617 radioligand therapy: a retrospective analysis of serum PSA level and imaging derived parameters before and after two cycles of therapy.

AIM: In patients with metastasized castration-resistant prostate cancer a reliable imaging-based therapy response assessment in addition to PSA kinetics is desirable. Recently, measurements of whole-body tumour burden by [68Ga]PSMA-11 PET/CT have been reported for response assessment in oligometastasic patients. The present study investigated the association of PSMA PET derived parameters and serum PSA level before and after [177Lu]PSMA-617 radioligand therapy (RLT). METHODS: This retrospective study assessed whole-body PSMA tumour volume (PSMA-TV) in 10 patients with multifocal to diffuse metastases before and after 2 cycles of RLT using volume of interest (VOI) analysis. A standardized uptake value (SUV) threshold-based approach was used to semi-automatically delineate all voxels with a SUV ≥ 2.0 g/ml using the software ROVER® (ABX Radeberg, Germany). Voxels with physiological tracer uptake (e. g. kidneys) were excluded manually. Correlations between PSMA-TV and serum PSA level before and after two cycles of RLT as well as changes thereof (ΔPSMA-TV and ΔPSA, respectively) were calculated. RESULTS: Changes of ΔPSMA-TV and ΔPSA were concordant in 7 of 10 patients. Whereas a good correlation was found between PSMA-TV and PSA before RLT (ρ = 0.81, p = 0.0049), this correlation was attenuated after RLT (ρ = 0.64, p = 0.0479). Consequently, no association was found between ΔPSMA-TV and ΔPSA (ρ = 0.39, p = 0.26). CONCLUSION: The attenuation of the correlation of PSA and PSMA-TV after RLT suggests that in patients with advanced disease the comparison of imaging based parameters such as PSMA-TV and PSA level might be useful for an adequate monitoring of treatment response.

Targeting of prostate-specific membrane antigen for radio-ligand therapy of triple-negative breast cancer.

BACKGROUND: Triple-negative breast cancer has extremely high risk of relapse due to the lack of targeted therapies, intra- and inter-tumoral heterogeneity, and the inherent and acquired resistance to therapies. In this study, we evaluate the potential of prostate-specific membrane antigen (PSMA) as target for radio-ligand therapy (RLT). METHODS: Tube formation was investigated after incubation of endothelial HUVEC cells in tumor-conditioned media and monitored after staining using microscopy. A binding study with 68Ga-labeled PSMA-addressing ligand was used to indicate targeting potential of PSMA on tumor-conditioned HUVEC cells. For mimicking of the therapeutic application, tube formation potential and vitality of tumor-conditioned HUVEC cells were assessed following an incubation with radiolabeled PSMA-addressing ligand [177Lu]-PSMA-617. For in vivo experiments, NUDE mice were xenografted with triple-negative breast cancer cells MDA-MB231 or estrogen receptor expressing breast cancer cells MCF-7. Biodistribution and binding behavior of [68Ga]-PSMA-11 was investigated in both tumor models at 30 min post injection using µPET. PSMA- and CD31-specific staining was conducted to visualize PSMA expression and neovascularization in tumor tissue ex vivo. RESULTS: The triple-negative breast cancer cells MDA-MB231 showed a high pro-angiogenetic potential on tube formation of endothelial HUVEC cells. The induced endothelial expression of PSMA was efficiently addressed by radiolabeled PSMA-specific ligands. 177Lu-labeled PSMA-617 strongly impaired the vitality and angiogenic potential of HUVEC cells. In vivo, as visualized by µPET, radiolabeled PSMA-ligand accumulated specifically in the triple-negative breast cancer xenograft MDA-MB231 (T/B ratio of 43.3 ± 0.9), while no [68Ga]-PSMA-11 was detected in the estrogen-sensitive MCF-7 xenograft (T/B ratio of 1.1 ± 0.1). An ex vivo immunofluorescence analysis confirmed the localization of PSMA on MDA-MB231 xenograft-associated endothelial cells and also on TNBC cells. CONCLUSIONS: Here we demonstrate PSMA as promising target for two-compartment endogenous radio-ligand therapy of triple-negative breast cancer.

99mTc-, 90Y-, and 177Lu-Labeled Iron Oxide Nanoflowers Designed for Potential Use in Dual Magnetic Hyperthermia/Radionuclide Cancer Therapy and Diagnosis.

Development of a complex based on iron oxide nanoparticles (IONPs) for diagnosis and dual magnetic hyperthermia/radionuclide cancer therapy accomplishing high yields of radiolabeling and great magnetic heat induction is still a challenge. We report here the synthesis of citric acid, poly(acrylic acid) (PAA) and poly(ethylene glycol) coated IONPs and their labeling with three radionuclides, namely, technetium (99mTc), yttrium (90Y), and lutetium (177Lu), aiming at potential use in cancer diagnosis and therapy. Polyol-synthesized IONPs are a flowerlike structure with 13.5 nm spherically shaped cores and 24.8 nm diameter. PAA-coated nanoparticles (PAA@IONP) showed the best characteristics such as easy radiolabeling with very high yields (>97.5%) with all three radionuclides, and excellent in vitro stabilities with less than 10% of radionuclides detaching after 24 h. Heating ability of PAA@IONP in an alternating external magnetic field showed intrinsic loss power value of 7.3 nH m2/kg, which is one of higher reported values. Additionally, PAA@IONP itself presented no significant cytotoxicity to the CT-26 cancer cells, reaching IC50 at 60 µg/mL. However, under the external magnetic field, they show hyperthermia-mediated cells killing, which correlated with the magnetic field strength and time of exposure. Since PAA@IONP are easy to prepare, biocompatible, and with excellent magnetic heat induction, these nanoparticles radiolabeled with high-energy beta emitters 90Y and 177Lu have valuable potential as agent for dual magnetic hyperthermia/radionuclide therapy, while radiolabeled with 99mTc could be used in diagnostic imaging.

Preparation and in vitro evaluation of radiolabeled HA-PLGA nanoparticles as novel MTX delivery system for local treatment of rheumatoid arthritis.

Radiosynovectomy is a technique used to decrease inflammation of the synovial tissue by intraarticular injection of a ß-emitting radionuclide, such as 177Lu, which is suitable for radiotherapy due to its decay characteristics. Drug-encapsulating nanoparticles based on poly lactic­co­glycolic acid (PLGA) polymer are a suitable option to treat several arthritic diseases, used as anti-inflammatory drugs transporters of such as methotrexate (MTX), which has been widely used in the arthritis treatment (RA), and hyaluronic acid (HA), which specifically binds the CD44 and hyaluronan receptors overexpressed on the inflamed synovial tissue cells. The 1,4,7,10­Tetraazacyclododecane­1,4,7,10­tetraacetic acid (DOTA) was used as complexing agent of Lutetium-177 for radiotherapy porpoises. The aim of this research was to synthesize 177Lu-DOTA-HA-PLGA(MTX) as a novel, smart drug delivery system with target-specific recognition, potentially useful in radiosynovectomy for local treatment of rheumatoid arthritis. The polymeric nanoparticle system was prepared and chemically characterized. The MTX encapsulation and radiolabelling were performed with suitable characteristics for its in vitro evaluation. The HA-PLGA(MTX) nanoparticle mean diameter was 167.6 nm ±â€¯57.4 with a monomodal and narrow distribution. Spectroscopic techniques demonstrated the effective conjugation of HA and chelating agent DOTA to the polymeric nanosystem. The MTX encapsulation was 95.2% and the loading efficiency was 6%. The radiochemical purity was 96 ±â€¯2%, determined by ITLC. Conclusion: 177Lu-DOTA-HA-PLGA(MTX) was prepared as a biocompatible polymeric PLGA nanoparticle conjugated to HA for specific targeting. The therapeutic nanosystem is based on bi-modal mechanisms using MTX as a disease-modifying antirheumatic drug (DMARD) and 177Lu as a radiotherapeutic component. The 177Lu-DOTA-HA-PLGA(MTX) nanoparticles showed properties suitable for radiosynovectomy and further specific targeted anti-rheumatic therapy.

Combination of 177 Lu-lilotomab with rituximab significantly improves the therapeutic outcome in preclinical models of non-Hodgkin's lymphoma.

OBJECTIVES: To investigate the therapeutic potential of the next-generation anti-CD37 radioimmunoconjugate 177 Lu-lilotomab satetraxetan (177 Lu-lilotomab) in combination with the anti-CD20 antibody rituximab for treatment of mice with non-Hodgkin's lymphoma (NHL) xenografts. METHODS: Nude mice with subcutaneous (s.c.) Burkitt's lymphoma Daudi xenografts and SCID mice intravenously (i.v.) injected with Mantle cell lymphoma Rec-1 cells were treated with either 177 Lu-lilotomab or rituximab alone or with the combination of both treatments. Tumour volume, body weight, blood counts and clinical status were monitored. CD20 expression was measured using flow cytometry with fluorescence-labelled rituximab. RESULTS: The combination of 177 Lu-lilotomab and rituximab was synergistic for treatment of nude mice with s.c. Daudi xenografts while it was additive for treatment of SCID mice with i.v. injected Rec-1 cells. Binding of rituximab to NHL cells in-vitro was increased by pretreatment with 177 Lu-lilotomab. CONCLUSIONS: Treatment of mice with NHL xenografts with 177 Lu-lilotomab synergistically increased tumour suppression of subsequent anti-CD20 immunotherapy and improved survival. If the same effect is confirmed in a recently started clinical study, it could change the way radioimmunotherapy and CD20 immunotherapy would be used in the future.

Relevant tumor sink effect in prostate cancer patients receiving 177Lu-PSMA-617 radioligand therapy.

AIM: In metastatic prostate cancer patients PSMA targeting radioligands have gained significant impact as theranostic probes. In this study a correlation between total tumor volume (TTV) and measured kidney dose as well as salivary glands (SG) uptake in 177Lu-PSMA-617 therapy was evaluated. METHODS: Eleven consecutive prostate cancer patients receiving a first cylcle of 177Lu-PSMA-617 (administered activity of approximately 6GBq) were included. The 68Ga-PSMA-11 PET/CT scan previous to therapy was used to determine TTV and SG uptake (glandulae submandibularis) employing PMOD version 3.403 with different 68Ga-PSMA-11 thresholds based on the standardized uptake value (SUV).The kidney dose was estimated with the software ULMDOS using planar whole-body scintigrams. RESULTS: Kidney dose and SG uptake was inversely correlated to TTV, indicating high kidney dose and high SG uptake in case of low tumor load and low kidney dose and low SG uptake in case of high tumor load. CONCLUSION: Our data support the hypothesis that in 177Lu-PSMA-617 therapy an individualized treatment activity based on total tumor volume could be beneficiary.

Unusual Case of Diffuse Penile Metastasis of Prostate Cancer on 68Ga PSMA PET/CT Imaging and 177Lu PSMA Posttherapy Scintigraphy.

An 85-year-old man with prostate cancer for metastatic workup underwent Gallium Prostate-Specific Membrane Antigen (Ga-PSMA) PET/CT (Ga-PSMA PET/CT), which revealed unusual tracer uptake in the shaft and glans of penis as well as multiple systemic metastases in liver, skeletal, and lymph nodes. The penile lesion was proved to be metastatic adenocarcinoma from prostate on fine needle aspiration cytology. The patient underwent Lutetium (Lu)-labeled PSMA radioligand therapy, which also revealed diffuse tracer uptake in the penile shaft as well as other metastatic sites.

Value of post-therapy 177Lu-PSMA images for accurate interpretation of therapy response with 68Ga-PSMA PET/CT. / Valor de las imágenes de 177Lu-PSMA post-terapia para una interpretación precisa de la respuesta a la terapia con PET/TC con 68Ga-PSMA.

A 54-year-old man with progressive prostate cancer underwent a 68Ga-PSMA PET/CT, which showed lymph node and bone metastases. After 2-cycles of 177Lu-PSMA therapy, the repeated 68Ga-PSMA PET/CT showed decreased radiotracer uptake in lymph node and bones metastases, but there were new lesions which may be compatible with progression or tumour sink-effect. A review of 177Lu-PSMA-therapy images revealed that new lesions in the second PET/CT were the metastatic lesions that progressed after the first PET/CT, and subsequently showed a good response. The patient received additional cycles of 177Lu-PSMA therapy, and the disease regressed further, with a PSA of 0.06ng/ml. Response evaluation of new therapeutic diagnostics (theranostic) agents needs a review of not only diagnostic PET/CT images, but also post-therapy images and laboratory results.

Targeting angiogenesis for radioimmunotherapy with a 177Lu-labeled antibody.

PURPOSE: Increased angiogenesis is a marker of aggressiveness in many cancers. Targeted radionuclide therapy of these cancers with angiogenesis-targeting agents may curtail this increased blood vessel formation and slow the growth of tumors, both primary and metastatic. CD105, or endoglin, has a primary role in angiogenesis in a number of cancers, making this a widely applicable target for targeted radioimmunotherapy. METHODS: The anti-CD105 antibody, TRC105 (TRACON Pharmaceuticals), was conjugated with DTPA for radiolabeling with 177Lu (t 1/2 6.65 days). Balb/c mice were implanted with 4T1 mammary carcinoma cells, and five study groups were used: 177Lu only, TRC105 only, 177Lu-DTPA-IgG (a nonspecific antibody), 177Lu-DTPA-TRC105 low-dose, and 177Lu-DTPA-TRC105 high-dose. Toxicity of the agent was monitored by body weight measurements and analysis of blood markers. Biodistribution studies of 177Lu-DTPA-TRC105 were also performed at 1 and 7 days after injection. Ex vivo histology studies of various tissues were conducted at 1, 7, and 30 days after injection of high-dose 177Lu-DTPA-TRC105. RESULTS: Biodistribution studies indicated steady uptake of 177Lu-DTPA-TRC105 in 4T1 tumors between 1 and 7 days after injection (14.3 ± 2.3%ID/g and 11.6 ± 6.1%ID/g, respectively; n = 3) and gradual clearance from other organs. Significant inhibition of tumor growth was observed in the high-dose group, with a corresponding significant increase in survival (p < 0.001, all groups). In most study groups (all except the nonspecific IgG group), the body weights of the mice did not decrease by more than 10%, indicating the safety of the injected agents. Serum alanine transaminase levels remained nearly constant indicating no damage to the liver (a primary clearance organ of the agent), and this was confirmed by ex vivo histological analyses. CONCLUSION: 177Lu-DTPA-TRC105, when administered at a sufficient dose, is able to curtail tumor growth and provide a significant survival benefit without off-target toxicity. Thus, this targeted agent could be used in combination with other treatment options to slow tumor growth allowing the other agents to be more effective.

Open-field mouse brain PET: design optimisation and detector characterisation.

'Open-field' PET, in which an animal is free to move within an enclosed space during imaging, is a very promising advance for neuroscientific research. It provides a key advantage over conventional imaging under anesthesia by enabling functional changes in the brain to be correlated with an animal's behavioural response to environmental or pharmacologic stimuli. Previously we have demonstrated the feasibility of open-field imaging of rats using motion compensation techniques applied to a commercially available PET scanner. However, this approach of 'retro-fitting' motion compensation techniques to an existing system is limited by the inherent geometric and performance constraints of the system. The goal of this project is to develop a purpose-built PET scanner with geometry, motion tracking and imaging performance tailored and optimised for open-field imaging of the mouse brain. The design concept is a rail-based sliding tomograph which moves according to the animal's motion. Our specific aim in this work was to evaluate candidate scanner designs and characterise the performance of a depth-of-interaction detector module for the open-field system. We performed Monte Carlo simulations to estimate and compare the sensitivity and spatial resolution performance of four scanner geometries: a ring, parallel plate, and two box variants. Each system was based on a detector block consisting of a 23 × 23 array of 0.785 × 0.785 × 20 mm3 LSO crystals (overall dim. 19.6 × 19.6 × 20 mm). We found that a DoI resolution capability of 3 mm was necessary to achieve approximately uniform sub-millimetre spatial resolution throughout the FoV for all scanners except the parallel-plate geometry. With this DoI performance, the sensitivity advantage afforded by the box geometry with overlapping panels (16% peak absolute sensitivity, a 36% improvement over the ring design) suggests this unconventional design is best suited for imaging the mouse brain. We also built and characterised the block detector modelled in the simulations, including a dual-ended readout based on 6 × 6 arrays of through-silicon-via silicon photomultipliers (active area 84%) for DoI estimation. Identification of individual crystals in the flood map was excellent, energy resolution varied from 12.4% ± 0.6% near the centre to 24.4% ± 3.4% at the ends of the crystal, and the average DoI resolution was 2.8 mm ± 0.35 mm near the central depth (10 mm) and 3.5 mm ± 1.0 mm near the ends. Timing resolution was 1.4 ± 0.14 ns. Therefore, the DoI detector module meets the target specifications for the application and will be used as the basis for a prototype open-field mouse PET scanner.

DNA-assisted upconversion nanoplatform for imaging-guided synergistic therapy and laser-switchable drug detoxification.

The side effects of chemotherapy bring significant physical and psychological suffering to patients. To solve this urgent medical problem, Yb3+ and Er3+ co-doped NaLuF4 upconversion nanoparticles (UCNPs) were constructed for upconversion luminescence (UCL)-labeled diagnosis under 980 nm laser irradiation. The UCNPs were then modified layer by layer with polypyrrole and a special programming DNA segment as photothermal conversion agents and controllable drug carriers, respectively. The nanoplatform was successfully used for imaging-guided synergistic therapy (photothermal therapy and chemotherapy) at a safe power density (300 mW cm-2), and DNA-assisted detoxification at lower temperature in cancer cells when the laser off. The synergistic therapy of the nanoplatform achieved a higher therapeutic index (∼85%) than chemotherapy only (∼44%) and photothermal therapy only (∼25%) in vitro. In vivo experiments also suggested that the nanoplatform had a higher therapeutic effect and lower side effects. The toxicity study was also evaluated, indicating the nanoplatform is low toxic to living system. This multifunctional upconversion nanoplatform provided an innovative method for imaging-guided photothermal-chemotherapy and laser-switchable drug detoxification.

The 68Ga/177Lu theragnostic concept in PSMA targeting of castration-resistant prostate cancer: correlation of SUVmax values and absorbed dose estimates.

INTRODUCTION: A targeted theragnostic approach based on increased expression of prostate-specific membrane antigen (PSMA) on PC cells is an attractive treatment option for patients with metastatic castration-resistant prostate cancer (mCRPC). METHODS: Ten consecutive mCRPC patients were selected for 177Lu-PSMA617 therapy on the basis of PSMA-targeted 68Ga-PSMA-HBED-CC PET/CT diagnosis showing extensive and progressive tumour load. Following dosimetry along with the first therapy cycle restaging (68Ga-PSMA-HBED-CC and 18F-NaF PET/CT) was performed after 2 and 3 therapy cycles (each 6.1 ± 0.3 GBq, range 5.4-6.5 GBq) given intravenously over 30 minutes, 9 ± 1 weeks apart. PET/CT scans were compared to 177Lu-PSMA617 24-hour whole-body scans and contrast-enhanced dual-phase CT. Detailed comparison of SUVmax values and absorbed tumour doses was performed. RESULTS: 177Lu-PSMA617 dosimetry indicated high tumour doses for skeletal (3.4 ± 1.9 Gy/GBq; range 1.1-7.2 Gy/GBq), lymph node (2.6 ± 0.4 Gy/GBq; range 2.3-2.9 Gy/GBq) as well as liver (2.4 ± 0.8 Gy/GBq; range 1.7-3.3 Gy/GBq) metastases whereas the dose for tissues/organs was acceptable in all patients for an intention-to-treat activity of 18 ± 0.3 GBq. Three patients showed partial remission, three mixed response, one stable and three progressive disease. Decreased 177Lu-PSMA617 and 68Ga-PSMA-HBED-CC uptake (mean SUVmax values 20.2 before and 15.0 after 2 cycles and 11.5 after 3 cycles, p < 0.05) was found in 41/54 skeletal lesions, 12/13 lymph node metastases, 3/5 visceral metastases and 4/4 primary PC lesions. CONCLUSION: Due to substantial individual variance, dosimetry is mandatory for a patient-specific approach following 177Lu-PSMA617 therapy. Higher activities and/or shorter treatment intervals should be applied in a larger prospective study.

Excellent Response to 177Lu-PSMA-617 Radioligand Therapy in a Patient With Advanced Metastatic Castration Resistant Prostate Cancer Evaluated by 68Ga-PSMA PET/CT.

Recently radiolabeled ligands targeting prostate specific membrane antigen (PSMA) have been introduced for diagnostics and treatment of prostate cancer. Labeled with Lutetium, PSMA radioligand therapy (RLT) is one of the most promising new treatments of metastatic castration refractory prostate cancer. We present images of Ga-PSMA PET/CT and parameters of response of a 75-year-old heavily pretreated metastatic castration refractory prostate cancer patient with extended bone metastases, showing an extraordinary biochemical response in PSA-levels concordant to SUV decline in bone metastases. Furthermore, this case shows that CT is of no use in assessing response in bone metastases of prostate cancer.