Cure of Micrometastatic B-Cell Lymphoma in a SCID Mouse Model Using 213Bi-Anti-CD20 Monoclonal Antibody

We studied the feasibility of using the α-emitting ²¹³Bi-anti-CD20 therapy with direct bioluminescent tracking of micrometastatic human B-cell lymphoma in a SCID mouse model. Methods: A highly lethal SCID mouse model of minimal-tumor-burden disseminated non-Hodgkin lymphoma (NHL) was established using human Raji lymphoma cells transfected to express the luciferase reporter. In vitro and in vivo radioimmunotherapy experiments were conducted. Single- and multiple-dose regimens were explored, and results with ²¹³Bi-rituximab were compared with various controls, including no treatment, free ²¹³Bi radiometal, unlabeled rituximab, and ²¹³Bi-labeled anti-HER2/neu (non-CD20-specific antibody). ²¹³Bi-rituximab was also compared in vivo with the low-energy β-emitter ¹³¹I-tositumomab and the high-energy β-emitter ⁹⁰Y-rituximab. Results: In vitro studies showed dose-dependent target-specific killing of lymphoma cells with ²¹³Bi-rituximab. Multiple in vivo studies showed significant and specific tumor growth delays with ²¹³Bi-rituximab versus free ²¹³Bi, ²¹³Bi-labeled control antibody, or unlabeled rituximab. Redosing of ²¹³Bi-rituximab was more effective than single dosing. With a single dose of therapy given 4 d after intravenous tumor inoculation, disease in all untreated controls, and in all mice in the 925-kBq ⁹⁰Y-rituximab group, progressed. With 3,700 kBq of ²¹³Bi-rituximab, 75% of the mice survived and all but 1 survivor was cured. With 2,035 kBq of ¹³¹I-tositumomab, 75% of the mice were tumor-free by bioluminescent imaging and 62.5% survived. Conclusion: Cure of micrometastatic NHL is achieved in most animals treated 4 d after intravenous tumor inoculation using either ²¹³Bi-rituximab or ¹³¹I-tositumomab, in contrast to the lack of cures with unlabeled rituximab or ⁹⁰Y-rituximab or if there was a high tumor burden before radioimmunotherapy. α-emitter-labeled anti-CD20 antibodies are promising therapeutics for NHL, although a longer-lived α-emitter may be of greater efficacy.

Radiation Exposure to the Nuclear Medicine Personnel During Preparation and Handling of 213Bi-Radiopharmaceuticals

Because of the excellent ability of α-particles to transfer a high amount of energy over a short tissue range, targeted α-therapy has been attracting rising numbers of nuclear medicine centers. In this study, we estimated the radiation exposure to the occupational workers with pocket dosimeters during handling of the α-emitter ²¹³Bi, used for targeted α-therapy of neuroendocrine tumor and castration-resistant prostate cancer patients. The dose rates from patients at different distances and time points after injection of the therapy were also evaluated. Methods: This prospective study was done in the Department of Nuclear Medicine at Fortis Memorial Research Institute, Gurgaon, India. Twelve patients with neuroendocrine tumors or castration-resistant prostate cancer were enrolled to receive ²¹³Bi-DOTATOC or ²¹³Bi-prostate-specific membrane antigen therapy, respectively. Each patient received 2-3 intravenous injections of ²¹³Bi-peptide, 266-362 MBq (7.2-9.8 mCi) in a single cycle over 2-3 d. The radiation exposure to nuclear medicine personnel at the chest and extremity levels was assessed for tasks such as elution, dispensing, injecting, and collecting blood samples. Radiation levels were measured at distances of 1 cm and 1 m from patients immediately after, and at 1, 2, and 4 h after, the administration of ²¹³Bi-peptide. Results: The external dose incurred at the chest level by radiopharmacists during synthesis, by physicians during injection, by technologists during imaging, and by nurses during sample collection was 2-7 μSv/procedure. The extremity dose was 1-14 μSv/procedure. The dose rate at 1 m from patients immediately after ²¹³Bi-radiopharmaceutical injection was 0.02-0.03 μSv/MBq⋅h. Conclusion: The external radiation doses received by occupational workers involved in various procedures were far below the limit prescribed by the regulatory authority (20 mSv/y).

NorthStar Perspectives for Actinium-225 Production at Commercial Scale

OBJECTIVE

Actinium-225, and its daughter Bismuth-213, have great promise in Alpha Immuno Therapy (AIT) for treatment of various disease modalities. Unfortunately, current production levels of actinium-225 do not support broad use of either actinium-225 or bismuth-213 in development or use for disease treatment. Further, the current cost per millicurie is much too high to be sustainable long term. Resolution of both supply and cost issues allows clinical research to proceed through clinical trials and potentially produce one or more effective therapies for cancer or infectious diseases that could benefit the public.

METHODS

NorthStar Medical Technologies, LLC, has investigated several routes that could lead to commercial scale production of actinium-225.

RESULTS

This article will discuss those efforts and results to date.

CONCLUSION

The outlook for future supplies of actinium-225 from multiple sources to support clinical needs is encouraging.

Targeted α-therapy of prostate cancer using radiolabeled PSMA inhibitors: a game changer in nuclear medicine

Prostate cancer (PCa) is one of the most common malignancies in men and is a major contributor to cancer related deaths worldwide. Metastatic spread and disease progression under androgen deprivation therapy signify the onset of metastatic castration resistant prostate cancer (mCRPCa)-the lethal form of the disease, which severely deteriorates the quality of life of patients. Over the last decade, tremendous progress has been made toward identifying appropriate molecular targets that could enable efficient in vivo targeting for non-invasive imaging and therapy of mCPRCa. In this context, a promising enzymatic target is prostate specific membrane antigen (PSMA), which is overexpressed on PCa cells, in proportion to the stage and grade of the tumor progression. This is especially relevant for mCRPCa, which has significant overexpression of PSMA. For therapy of mCRPCa, several nuclear medicine clinics all over the world have confirmed that 177Lu-labeled-PSMA enzyme inhibitors (177Lu-PSMA-617 and 177Lu-PSMA I&T) have a favorable dosimetry and convincing therapeutic response. However, ~30% of patients were found to be short or non-responders and dose escalation was severely limited by chronic hematological toxicity. Such limitations could be better overcome by targeted alpha therapy (TAT) which has the potential to bring a paradigm shift in treatment of mCRPCa patients. This concise review presents an overview of the successes and challenges currently faced in TAT of mCRPCa using radiolabeled PSMA inhibitors. The preclinical and clinical data reported to date are quite promising, and it is expected that this therapeutic modality will play a pivotal role in advanced stage PCa management in the foreseeable future.

A Radiolabeled Fully Human Antibody to Human Aspartyl (Asparaginyl) β-Hydroxylase Is a Promising Agent for Imaging and Therapy of Metastatic Breast Cancer

There is a need for novel effective and safe therapies for metastatic breast cancer based on targeting tumor-specific molecular markers of cancer. Human aspartyl (asparaginyl) β-hydroxylase (HAAH) is a highly conserved enzyme that hydroxylates epidermal growth factor-like domains in transformation-associated proteins and is overexpressed in a variety of cancers, including breast cancer. A fully human monoclonal antibody (mAb) PAN-622 has been developed to HAAH. In this study, they describe the development of PAN-622 mAb as an agent for imaging and radioimmunotherapy of metastatic breast cancer. PAN-622 was conjugated to several ligands such as DOTA, CHXA″, and DTPA to enable subsequent radiolabeling and its immunoreactivity was evaluated by an HAAH-specific enzyme-linked immunosorbent assay and binding to the HAAH-positive cells. As a result, DTPA-PAN-622 was chosen to investigate biodistribution in healthy CD-1 female mice and 4T1 mammary tumor-bearing BALB/c mice. The ¹¹¹In-DTPA-pan622 mAb concentrated in the primary tumors and to some degree in lung metastases as shown by SPECT/CT and Cherenkov imaging. A pilot therapy study with ²¹³Bi-DTPA-PAN-622 demonstrated a significant effect on the primary tumor. The authors concluded that human mAb PAN-622 to HAAH is a promising reagent for development of imaging and possible therapeutic agents for the treatment of metastatic breast cancer.

Molecular targeted α-particle therapy for oncologic applications

OBJECTIVE

A significant challenge facing traditional cancer therapies is their propensity to significantly harm normal tissue. The recent clinical success of targeting therapies by attaching them to antibodies that are specific to tumor-restricted biomarkers marks a new era of cancer treatments.

CONCLUSION

In this article, we highlight the recent developments in α-particle therapy that have enabled investigators to exploit this highly potent form of therapy by targeting tumor-restricted molecular biomarkers.