Targeted alpha immunotherapy of CD20-positive B-cell lymphoma model: dosimetry estimate of 225Ac-DOTA-rituximab using 64Cu-DOTA-rituximab

Evaluating 64Cu-DOTA-rituximab as a PET agent in patients with B-cell lymphoma: a head-to-head comparison with 18F-fluorodeoxyglucose PET/computed tomography

BACKGROUND

This study aimed to evaluate the biodistribution of 64Cu-DOTA-rituximab and its diagnostic feasibility for lymphoma using CD20-targeted 64Cu-DOTA-rituximab PET/computed tomography (PET/CT).

METHODS

A prospective study involving six patients diagnosed with lymphoma was conducted between January 2022 and January 2023. These patients underwent 18F-fluorodeoxyglucose (18F-FDG) and 64Cu-DOTA-rituximab PET/CT scans. 64Cu-DOTA-rituximab PET/CT images were acquired at 1, 24, and 48 h after administering 64Cu-DOTA-rituximab to assess the biodistribution and dosimetry over time. The observed lymph nodes were categorized into specific regions, including cervical and supraclavicular, axillary and infraclavicular, mediastinal, hilar, abdominal paraaortic and retroperitoneal, iliac, mesenteric, and inguinal regions, to compare the diagnostic ability of 18F-FDG and 64Cu-DOTA-rituximab PET/CT in detecting lymphoma lesions. Furthermore, the tumor-to-background ratio was calculated and compared with the maximum standardized uptake (SUVmax) of the tumors and the mean standardized uptake (SUVmean) of normal organs. Internal radiation dosimetry was determined using the OLINDA/EXM software.

RESULTS

64Cu-DOTA-rituximab uptake in lymph nodes associated with lymphoma progressively increased from 1 to 48 h after injection. In contrast, 64Cu-DOTA-rituximab uptake in normal organs, such as blood, lung, kidney, bladder, muscle, bone, and brain, decreased over time, whereas it increased in the liver and spleen. When it comes to the comparison between 64Cu-DOTA-rituximab and 18F-FDG, the SUVmax of tumors was higher on 64Cu-DOTA-rituximab PET/CT (18.1 ± 8.3) than on 18F-FDG PET/CT (5.2 ± 1.5). Additionally, the tumor-to-background ratio, measured using the SUVmean of normal muscles, was higher on 64Cu-DOTA-rituximab PET/CT (55.7 ± 31.0) than on 18F-FDG PET/CT (8.6 ± 2.8). No adverse events related to 64Cu-DOTA-rituximab injection were reported.

CONCLUSION

The results of this study demonstrate the feasibility of using 64Cu-DOTA-rituximab PET/CT to evaluate the CD20 expression. The increased 64Cu-DOTA-rituximab uptake in lymph nodes associated with tumors, higher SUVmax, and tumor-to-muscle ratios observed with 64Cu-DOTA-rituximab PET/CT compared with 18F-FDG PET/CT, highlight the diagnostic potential of this imaging modality.

Recent preclinical and clinical advances in radioimmunotherapy for non-Hodgkin's lymphoma

Radioimmunotherapy (RIT) is a therapy that combines a radioactive nucleotide with a monoclonal antibody (mAb). RIT enhances the therapeutic effect of mAb and reduces toxicity compared with conventional treatment. The purpose of this review is to summarize the current progress of RIT for treating non-Hodgkin's lymphoma (NHL) based on recent preclinical and clinical studies. The efficacy of RIT targeting the B-lymphocyte antigen cluster of differentiation 20 (CD20) has been demonstrated in clinical trials. Two radioimmunoconjugates targeting CD20, yttrium-90 (90Y)-ibritumomab-tiuxetan (Zevalin) and iodine-131 (131I)-tositumomab (Bexxar), have been approved in the USA Food and Drug Administration (FDA) for treating relapsed/refractory indolent or transformed NHL in 2002 and 2003, respectively. Although these two radioimmunoconjugates are effective and least toxic, they have not achieved popularity due to increasing access to novel therapies and the complexity of their delivery process. RIT is constantly evolving with the identification of novel targets and novel therapeutic strategies using newer radionuclides such as alpha-particle isotopes. Alpha-particles show very short path lengths and high linear energy transfer. These characteristics provide increased tumor cell-killing activities and reduced non-specific bystander responses on normal tissue. This review also discusses reviewed pre-targeted RIT (PRIT) and immuno-positron emission tomography (PET). PRIT potentially increases the dose of radionuclide delivered to tumors while toxicities to normal tissues are limited. Immuno-PET is a molecular imaging tracer that combines the high sensitivity of PET with the specific targeting capability of mAb. Immuno-PET strategies targeting CD20 and other antigens are currently being developed. The theragnostic approach by immuno-PET will be useful in monitoring the treatment response.

64 Cu-DOTA-Rituximab PET/CT of B-Cell Non-Hodgkin Lymphoma for Imaging the CD20 Expression

ABSTRACT

64 Cu-DOTA-rituximab PET/CT was performed on a 62-year-old and a 71-year-old men diagnosed with B-cell non-Hodgkin lymphoma. Compared with 18 F-FDG PET/CT, lesions could be detected more sensitively, and it was confirmed that there was no discernible 64 Cu-DOTA-rituximab uptake in the tumor other than lymphoma. 64 Cu-DOTA-rituximab PET/CT could be a powerful tool for the diagnosis and monitoring treatment response of lymphoma because of imaging the CD20 expression.

Prostate specific membrane antigen binding radiopharmaceuticals: Current data and new concepts

Prostate specific membrane antigen (PSMA) represents a validated target for prostate cancer therapeutics. The phase III VISION study with ¹⁷⁷lutetium (¹⁷⁷Lu)-PSMA-617 represented a pivotal step forward and the FDA has now approved this agent in advanced metastatic castrate-resistant prostate cancer (mCRPC). A number of other PSMA targeted radiopharmaceuticals are now under development. Some of these agents are targeted to PSMA via monoclonal antibodies such as J591 and TLX591. Others are targeted to PSMA via small molecules such as PSMA-617, PSMA I&T, MIP-1095, etc. In addition to the use of various ligands, multiple isotopes are now in clinical trials. Beta emitters in development include ¹⁷⁷Lu, ¹³¹iodide (¹³¹I), and ⁶⁷copper (⁶⁷Cu). Targeted alpha emitters potentially include ²²⁵actinium (²²⁵Ac), ²²⁷thorium (²²⁷Th), and ²¹²lead (²¹²Pb). Phase III trials are underway with both ¹⁷⁷Lu-PSMA-617 and ¹⁷⁷Lu-PSMA I&T in mCRPC. Single dose phase I trials are complete with ²²⁵Ac-J591 but additional data are need to launch a phase III. Data are promising with ²²⁵Ac-PSMA-617 but concerns remain over salivary and renal toxicity. Tandem therapies are also considered combining both beta and alpha-targeted therapy. Taken together the field of PSMA targeted radiopharmaceuticals is rapidly developing. The targeted alpha therapies are particularly promising and several developmental paths forward are being considered in the near future.

Improved Therapy of B-Cell Non-Hodgkin Lymphoma by Obinutuzumab-Dianthin Conjugates in Combination with the Endosomal Escape Enhancer SO1861

Immunotoxins do not only bind to cancer-specific receptors to mediate the elimination of tumor cells through the innate immune system, but also increase target cytotoxicity by the intrinsic toxin activity. The plant glycoside SO1861 was previously reported to enhance the endolysosomal escape of antibody-toxin conjugates in non-hematopoietic cells, thus increasing their cytotoxicity manifold. Here we tested this technology for the first time in a lymphoma in vivo model. First, the therapeutic CD20 antibody obinutuzumab was chemically conjugated to the ribosome-inactivating protein dianthin. The cytotoxicity of obinutuzumab-dianthin (ObiDi) was evaluated on human B-lymphocyte Burkitt’s lymphoma Raji cells and compared to human T-cell leukemia off-target Jurkat cells. When tested in combination with SO1861, the cytotoxicity for target cells was 131-fold greater than for off-target cells. In vivo imaging in a xenograft model of B-cell lymphoma in mice revealed that ObiDi/SO1861 efficiently prevents tumor growth (51.4% response rate) compared to the monotherapy with ObiDi (25.9%) and non-conjugated obinutuzumab (20.7%). The reduction of tumor volume and overall survival was also improved. Taken together, our results substantially contribute to the development of a combination therapy with SO1861 as a platform technology to enhance the efficacy of therapeutic antibody-toxin conjugates in lymphoma and leukemia.

Targeting C3b/C4b and VEGF with a bispecific fusion protein optimized for neovascular age-related macular degeneration therapy

Antiangiogenesis therapies targeting vascular endothelial growth factor (VEGF) have revolutionized the treatment of neovascular ocular diseases, including neovascular age-related macular degeneration (nAMD). Compelling evidence has implicated the vital role of complement system dysregulation in AMD pathogenesis, implying it as a potential therapeutic strategy for geographic atrophy in dry AMD and to enhance the efficacy of anti-VEGF monotherapies in nAMD. This study reports the preclinical assessment and phase 1 clinical outcomes of a bispecific fusion protein, efdamrofusp alfa (code: IBI302), which is capable of neutralizing both VEGF isoforms and C3b/C4b. Efdamrofusp alfa showed superior efficacy over anti-VEGF monotherapy in a mouse laser-induced choroidal neovascularization (CNV) model after intravitreal delivery. Dual inhibition of VEGF and the complement activation was found to further inhibit macrophage infiltration and M2 macrophage polarization. Intravitreal efdamrofusp alfa demonstrated favorable safety profiles and exhibited antiangiogenetic efficacy in a nonhuman primate laser-induced CNV model. A phase 1 dose-escalating clinical trial (NCT03814291) was thus conducted on the basis of the preclinical data. Preliminary results showed that efdamrofusp alfa was well tolerated in patients with nAMD. These data suggest that efdamrofusp alfa might be effective for treating nAMD and possibly other complement-related ocular conditions.

Dosimetry in targeted alpha therapy. A systematic review: current findings and what is needed

Objective. A systematic review of dosimetry in Targeted Alpha Therapy (TAT) has been performed, identifying the common issues. Approach. The systematic review was performed in accordance with the PRISMA guidelines, and the literature was searched using the Scopus and PubMed databases. Main results. From the systematic review, three key points should be considered when performing dosimetry in TAT. (1) Biodistribution/Biokinetics: the accuracy of the biodistribution data is a limit to accurate dosimetry in TAT. The biodistribution of alpha-emitting radionuclides throughout the body is difficult to image directly, with surrogate radionuclide imaging, blood/faecal sampling, and animal studies able to provide information. (2) Daughter radionuclides: the decay energy of the alpha-emissions is sufficient to break the bond to the targeting vector, resulting in a release of free daughter radionuclides in the body. Accounting for daughter radionuclide migration is essential. (3) Small-scale dosimetry and microdosimetry: due to the short path length and heterogeneous distribution of alpha-emitters at the target site, small-scale/microdosimetry are important to account for the non-uniform dose distribution in a target region, organ or cell and for assessing the biological effect of alpha-particle radiation. Significance. TAT is a form of cancer treatment capable of delivering a highly localised dose to the tumour environment while sparing the surrounding healthy tissue. Dosimetry is an important part of treatment planning and follow up. Being able to accurately predict the radiation dose to the target region and healthy organs could guide the optimal prescribed activity. Detailed dosimetry models accounting for the three points mentioned above will help give confidence in and guide the clinical application of alpha-emitting radionuclides in targeted cancer therapy.