Frank Bruchertseifer

225Ac-PSMA-617 for PSMA-Targeted α-Radiation Therapy of Metastatic Castration-Resistant Prostate Cancer

Prostate-specific membrane antigen (PSMA) is a promising target in prostate cancer. Recently, we started the first-in-human treatment with an α-radionuclide–labeled PSMA ligand. Although the case series is still ongoing, we here report in advance about two patients in highly challenging clinical situations who showed a complete response to 225Ac-PSMA-617 therapy. Methods: 68Ga-PSMA-11 PET/CT validated the presence of the PSMA-positive tumor phenotype. A 100-kBq activity of 225Ac-PSMA-617 per kilogram of body weight was administered bimonthly. Prostate-specific antigen response and hematologic toxicity were measured at least every 4 wk. Restaging was performed with 68Ga-PSMA-11 PET/CT. Results: Both patients experienced a prostate-specific antigen decline to below the measurable level and showed a complete response on imaging. No relevant hematologic toxicity was observed. Xerostomia was the only mentionable clinical side effect. Conclusion: Targeted α-therapy with 225Ac-PSMA-617, although still experimental, obviously has strong potential to significantly benefit advanced-stage prostate cancer patients.

Alpha- versus Beta-Particle Radiopeptide Therapy in a Human Prostate Cancer Model (213Bi-DOTA-PESIN and 213Bi-AMBA versus177Lu-DOTA-PESIN)

Recurrent prostate cancer presents a challenge to conventional treatment, particularly so to address micrometastatic and small-volume disease. Use of α-radionuclide therapy is considered as a highly effective treatment in such applications due to the shorter range and exquisite cytotoxicity of α-particles as compared with β-particles. (213)Bi is considered an α-emitter with high clinical potential, due to its short half-life (45.6 minutes) being well matched for use in peptide-receptor radionuclide α-therapy; however, there is limited knowledge available within this context of use. In this study, two novel (213)Bi-labeled peptides, DOTA-PEG(4)-bombesin (DOTA-PESIN) and DO3A-CH(2)CO-8-aminooctanoyl-Q-W-A-V-G-H-L-M-NH(2) (AMBA), were compared with (177)Lu (β-emitter)-labeled DOTA-PESIN in a human androgen-independent prostate carcinoma xenograft model (PC-3 tumor). Animals were injected with (177)Lu-DOTA-PESIN, (213)Bi-DOTA-PESIN, or (213)Bi-AMBA to determine the maximum tolerated dose (MTD), biodistribution, and dosimetry of each agent; controls were left untreated or were given nonradioactive (175)Lu-DOTA-PESIN. The MTD of (213)Bi-DOTA-PESIN and (213)Bi-AMBA was 25 MBq (0.68 mCi) whereas (177)Lu-DOTA-PESIN showed an MTD of 112 MBq (3 mCi). At these dose levels, (213)Bi-DOTA-PESIN and (213)Bi-AMBA were significantly more effective than (177)Lu-DOTA-PESIN. At the same time, (177)Lu-DOTA-PESIN showed minimal, (213)Bi-DOTA-PESIN slight, and (213)Bi-AMBA marked kidney damage 20 to 30 weeks posttreatment. These preclinical data indicate that α-therapy with (213)Bi-DOTA-PESIN or (213)Bi-AMBA is more efficacious than β-therapy. Furthermore, (213)Bi-DOTA-PESIN has a better safety profile than (213)Bi-AMBA, and represents a possible new approach for use in peptide-receptor radionuclide α-therapy treating recurrent prostate cancer.

An Improved Method for the Production of Ac‐225/Bi‐213 from Th‐229 for Targeted Alpha Therapy

Abstract This work describes an improved method for radium/actinium separation as part of a process for the production of Ac‐225 from a Th‐229 source for targeted alpha therapy of cancer. The separation method is based on the use of a newly developed extraction chromatographic resin containing the diglycolamide (DGA) class of molecules. The weight distribution ratios of Ac(III) on the extraction chromatographic resins N,N,N′N′ tetraoctyldiglycolamide (TODGA) and N,N,N′N′ tetrakis‐2‐ethylhexyldiglycolamide (TEHDGA) (both Eichrom Inc.) were determined at varying nitric and hydrochloric acid concentrations by batch experiments to optimize conditions for the separation of Ac(III) from Ra(II). Consequently, a robust and rapid procedure based on the use of TEHDGA resin was developed yielding a carrier‐free, clinical‐grade Ac‐225 with an overall yield exceeding 98%.

Spectroscopic study of the interaction of U(VI) with transferrin and albumin for speciation of U(VI) under blood serum conditions

The quantitative description of the interactions of uranium with blood serum components is of high relevance for a rational design of molecules suitable for in vivo chelation of uranium. We have determined the stability constants for the complexation of U(VI) with human serum transferrin and albumin by time-resolved laser-induced fluorescence spectroscopy and difference ultraviolet spectroscopy. Both proteins interact strongly with U(VI), forming ternary complexes with carbonate acting as a synergistic anion. Together with literature data describing the interaction of U(VI) with low molecular weight inorganic and organic serum components, the speciation of U(VI) in blood serum was calculated. In agreement with published experimental data, the model calculation shows that complexation with proteins and carbonate ion governs U(VI) speciation; 35% of U(VI) is bound to proteins and 65% to carbonate. Among the protein pool, albumin is the main protein interacting with U(VI). In addition, the results show that Ca(II) must be considered in the model as a competitive metal ion with respect to U(VI) for binding to albumin surface sites. Based on these findings several promising molecules for in vivo chelation of (230)U could be identified.

Bismuth-213 and Actinium-225 – Generator Performance and Evolving Therapeutic Applications of Two Generator-Derived Alpha-Emitting Radioisotopes

The alpha emitters (225)Ac and (213)Bi are promising therapeutic radionuclides for application in targeted alpha therapy of cancer and infectious diseases. Both alpha emitters are available with high specific activity from established radionuclide generators. Their favourable chemical and physical properties have led to the conduction of a large number of preclinical studies and several clinical trials, demonstrating the feasibility, safety and therapeutic efficacy of targeted alpha therapy with (225)Ac and (213)Bi. This review describes methods for the production of (225)Ac and (213)Bi and gives an overview of (225)Ac/(213)Bi radionuclide generator systems. Selected preclinical studies are highlighted and the current clinical experience with (225)Ac and (213)Bi is summarized.

Analysis of patient survival in a Phase I trial of systemic targeted α-therapy for metastatic melanoma.

Targeted α-therapy is an experimental approach to the management of cancer. Short range α-particle radiation from a radioisotope attached to a targeting monoclonal antibody kills targeted cancer cells. Survival results are analyzed from a previously reported Phase I study of systemic targeted α-therapy for patients with stage IV metastatic melanoma or in-transit metastases. Following intravenous administration of 46-925 MBq of the α-immunoconjugate, (213)Bi-cDTPA-9.2.27, 38 patients were followed to observe response and toxicity. Responses were measured by physical examination, computed tomography at 8 weeks and blood sampling. Toxicity was monitored by blood pathology, urine analysis, glomerular filtration rate and human antimouse antibody response. The maximum tolerance dose was not achieved as there were no adverse events of any type or level. However, an objective partial response rate of 10% was observed, with 40% stable disease at 8 weeks and a median survival of 8.9 months. These results were unexpected because of the short half-life of the (213)Bi and short range of the α-radiation. Survival analysis demonstrated melanoma-inhibitory activity, disease stage, lactate dehydrogenase and treatment effects to be significant prognostic indicators for survival.

213Bi Radioimmunotherapy with an Anti-mCD138 Monoclonal Antibody in a Murine Model of Multiple Myeloma

New multiple myeloma (MM) treatments—such as high-dose melphalan therapy plus autologous stem cell transplantation or regimens incorporating bortezomide, thalidomide, and lenalidomide—substantially increase the rate of complete response that is associated with longer patient survival. Thus, maintaining the complete response status by improving the minimal residual disease after induction therapy is a key goal for MM management. Here, we address the question of radioimmunotherapy efficacy in MM minimal residual disease treatment in mice with a low tumor burden. α-emitters are particularly well adapted to this approach because the short range of α-particles enables localized irradiation of tumor cells within the bone marrow and a cytotoxic effect on isolated cells due to the high LET (linear energy transfer) of α-particles. The CD138 antigen was used as a target because of its strong expression on myeloma cells in 100% of patients. Method: Intravenous injection of 106 5T33 mouse myeloma cells into the Syngeneic mouse strain C57BL/KaLwRij resulted in a rapid invasion of the marrow and limb paralysis, as illustrated by bioluminescence imaging with luciferase-transfected 5T33 cells. Radioimmunotherapy was performed 10 d after 5T33 cell engraftment with an intravenous injection of an antimouse CD138 antibody radiolabeled with 213Bi at activities of 1.85, 3.7, 7.4, and 11.1 MBq. A blood cell count was performed weekly to monitor hematologic toxicity. The levels of blood Flt3 ligand were also measured to evaluate the radioimmunotherapy-related myelotoxicity. Disease progression was monitored by titrating the monoclonal IgG2b antibody produced by 5T33 cells. Results: The groups treated with 3.7 and 7.4 MBq exhibited a median survival greater than 300 and 227 d, respectively, compared with 45.5 d in the control untreated group. The highest activity (11.1 MBq) showed short-term toxicity whereas the lowest activity (1.85 MBq) gave results similar to those of the controls. With activities of 3.7 and 7.4 MBq, mice exhibited a transient hematologic toxicity whereas only temporary and moderate myelotoxicity was observed with 7.4 MBq. Conclusion: This study demonstrates promising therapeutic efficacy of 213Bi-labeled anti-mCD138 for the treatment of residual disease in the case of MM, with only moderate and transient toxicity.

Anti-prostate-specific membrane antigen liposomes loaded with 225Ac for potential targeted antivascular α-particle therapy of cancer.

This study evaluates targeted liposomes loaded with the α-particle generator 225Ac to selectively kill prostate-specific membrane antigen (PSMA)–expressing cells with the aim to assess their potential for targeted antivascular radiotherapy. Methods: In this study, PEGylated liposomes were loaded with 225Ac and labeled with the mouse antihuman PSMA J591 antibody or with the A10 PSMA aptamer. The targeting selectivity, extent of internalization, and killing efficacy of liposomes were evaluated on monolayers of prostate cancer cells intrinsically expressing PSMA (human LNCaP and rat Mat-Lu cells) and on monolayers of HUVEC induced to express PSMA (induced HUVEC). Results: The loading efficiency of 225Ac into preformed liposomes ranged from 58.0% ± 4.6% to 85.6% ± 11.7% of introduced radioactivity. The conjugation reactions resulted in approximately 17 ± 2 J591 antibodies and 9 ± 2 A10 aptamers per liposome. The average size of liposomes, 107 ± 2 nm in diameter, was not affected by conjugation or loading. LNCaP cells exhibit 2:1:0.5 relative PSMA expression, compared with MatLu and induced HUVEC, respectively, based on flow cytometry detecting association of the J591 antibody. J591-labeled liposomes display higher levels of total specific binding to all cell lines than A10 aptamer-labeled liposomes. Specific cell association of targeted liposomes increases with incubation time. Cytotoxicity studies demonstrate that radiolabeled J591-labeled liposomes are most cytotoxic, with median lethal dose values, after 24 h of incubation, equal to 1.96 (5.3 × 10−5), 2.92 × 102 (7.9 × 10−3), and 2.33 × 101 Bq/mL (6.3 × 10−4 μCi/mL) for LNCaP, Mat-Lu, and induced HUVEC, respectively, which are comparable to the values for the radiolabeled J591 antibody. For A10 aptamer–labeled liposomes, the corresponding values are 3.70 × 101 (1.0 × 10−3), 1.85 × 103 (5.0 × 10−2), and 4.07 × 103 Bq/mL (1.1 × 10−1 μCi/mL), respectively. Conclusion: Our studies demonstrate that anti-PSMA–targeted liposomes loaded with 225Ac selectively bind, become internalized, and kill PSMA-expressing cells including endothelial cells induced to express PSMA. These findings—combined with the unique ability of liposomes to be easily tuned, in terms of size and surface modification, for optimizing biodistributions—suggest the potential of PSMA-targeting liposomes encapsulating α-particle emitters for selective antivascular α radiotherapy.

Intravesical α-Radioimmunotherapy with 213Bi-Anti-EGFR-mAb Defeats Human Bladder Carcinoma in Xenografted Nude Mice

Transurethral resection of urothelial carcinoma often results in tumor recurrence due to disseminated tumor cells. Therefore, new therapeutic strategies are urgently needed. The aim of this study was to establish an orthotopic human bladder carcinoma mouse model using the epidermal growth factor receptor (EGFR)–overexpressing bladder carcinoma cell line EJ28 and to compare therapeutic efficacy of intravesically instilled α-particle–emitting 213Bi-anti-EGFR-monoclonal antibody (mAb) with mitomycin C. Methods: Female Swiss nu/nu mice were intravesically inoculated with luciferase-transfected EJ28 human bladder carcinoma cells after the induction of urothelial lesions by electrocautery. At different time points after cell inoculation, mice were treated intravesically with 213Bi-anti-EGFR-mAb, mitomycin C, or unlabeled anti-EGFR-mAb. Tumor development and therapeutic response were evaluated via bioluminescence imaging. Results: Mice without therapy and those treated with unlabeled anti-EGFR-mAb reached a median survival of 41 d and 89 d, respectively. Mice that underwent therapy with 0.925 MBq of 213Bi-anti-EGFR-mAb 1 h, 7 d, or 14 d after cell instillation survived more than 300 d in 90%, 80%, and 40% of the cases, respectively. Therapy with 0.37 MBq 1 h or 7 d after tumor cell inoculation resulted in survival of more than 300 d in 90% and 50% of mice, respectively. Mitomycin C treatment after 1 h and 7 d prolonged survival to more than 300 d in 40% and 50%, respectively; however, treatment turned out to be nephrotoxic. In contrast, no signs of nephrotoxicity could be observed after 213Bi-anti-EGFR-mAb treatment. Conclusion: The study suggests that radioimmunotherapy using intravesically instilled 213Bi-anti-EGFR-mAb is a promising option for treatment of bladder cancer in patients.

Treatment of Peritoneal Carcinomatosis by Targeted Delivery of the Radio-Labeled Tumor Homing Peptide 213Bi-DTPA-[F3]2 into the Nucleus of Tumor Cells

Background α-particle emitting isotopes are effective novel tools in cancer therapy, but targeted delivery into tumors is a prerequisite of their application to avoid toxic side effects. Peritoneal carcinomatosis is a widespread dissemination of tumors throughout the peritoneal cavity. As peritoneal carcinomatosis is fatal in most cases, novel therapies are needed. F3 is a tumor homing peptide which is internalized into the nucleus of tumor cells upon binding to nucleolin on the cell surface. Therefore, F3 may be an appropriate carrier for α-particle emitting isotopes facilitating selective tumor therapies. Principal Findings A dimer of the vascular tumor homing peptide F3 was chemically coupled to the α-emitter 213Bi (213Bi-DTPA-[F3]2). We found 213Bi-DTPA-[F3]2 to accumulate in the nucleus of tumor cells in vitro and in intraperitoneally growing tumors in vivo. To study the anti-tumor activity of 213Bi-DTPA-[F3]2 we treated mice bearing intraperitoneally growing xenograft tumors with 213Bi-DTPA-[F3]2. In a tumor prevention study between the days 4–14 after inoculation of tumor cells 6×1.85 MBq (50 µCi) of 213Bi-DTPA-[F3]2 were injected. In a tumor reduction study between the days 16–26 after inoculation of tumor cells 6×1.85 MBq of 213Bi-DTPA-[F3]2 were injected. The survival time of the animals was increased from 51 to 93.5 days in the prevention study and from 57 days to 78 days in the tumor reduction study. No toxicity of the treatment was observed. In bio-distribution studies we found 213Bi-DTPA-[F3]2 to accumulate in tumors but only low activities were found in control organs except for the kidneys, where 213Bi-DTPA-[F3]2 is found due to renal excretion. Conclusions/Significance In conclusion we report that 213Bi-DTPA-[F3]2 is a novel tool for the targeted delivery of α-emitters into the nucleus of tumor cells that effectively controls peritoneal carcinomatosis in preclinical models and may also be useful in oncology.