New insights into the mechanisms of action of radioimmunotherapy in lymphoma

The bone marrow niche and hematopoietic system are distinctly remodeled by CD45-targeted astatine-211 radioimmunotherapy

Radioimmunotherapy (RIT) is used to treat patients with hematological malignancies known to infiltrate the bone marrow (BM) microenvironment. RIT uses target-specific monoclonal antibodies stably conjugated to radionuclides to deliver cytotoxic radiation to cells of interest. While RIT is effective at delivering radiation to cancer cells, normal tissue is also exposed to radiation upon RIT, the consequences of which are largely unknown. Here, we studied the cellular and molecular effects of CD45-targeted astatine-211 ( 211 At) RIT, IgG non-targeted 211 At RIT, and Cesium-137 total-body irradiation (TBI) on hematopoietic cells and their BM niche in wild-type immunocompetent mice. Relative to non-targeted RIT or TBI, CD45-targeted RIT significantly delayed hematopoietic regeneration overall in the peripheral blood and BM and reduced hematopoietic stem/progenitor cell recovery and colony-forming ability. While BM endothelial cells (ECs) do not express the CD45 antigen, CD45-targeted RIT significantly depleted BM ECs compared to non-targeted RIT or TBI. RNA sequence analysis revealed significantly different transcriptomic profiles of BM ECs from CD45-RIT-treated mice compared to non- targeted RIT or TBI. ECs from CD45-RIT-treated mice, but not TBI or IgG-RIT-treated mice, were transcriptionally enriched for TGFβ, NOTCH, and IFNα signaling pathways compared to untreated mice. Collectively, our study indicates that CD45-targeted RIT severely impacts hematopoietic and EC niche recovery compared to non- targeted approaches. Future studies are required to determine the long-term consequences of such RIT-driven effects on BM niche physiology and how BM niche reprogramming by RIT affects cancer cells.

KEY POINTS

CD45-targeted radioimmunotherapy more effectively suppresses the hematopoietic system than non- targeted radiation delivery.The bone marrow vascular niche is differentially reprogrammed by CD45-targeted radioimmunotherapy compared to non-targeted radiation delivery.

Tumour targeting and radiation dose of radioimmunotherapy with (90)Y-rituximab in CD20+ B-cell lymphoma as predicted by (89)Zr-rituximab immuno-PET: impact of preloading with unlabelled rituximab

Purpose

To compare using immuno-PET/CT the distribution of ⁸⁹Zr-labelled rituximab without and with a preload of unlabelled rituximab to assess the impact of preloading with unlabelled rituximab on tumour targeting and radiation dose of subsequent radioimmunotherapy with ⁹⁰Y-labelled rituximab in CD20+ B-cell lymphoma.

Methods

Five patients with CD20+ B-cell lymphoma and progressive disease were prospectively enrolled. All patients underwent three study phases: initial dosimetric phase with baseline ⁸⁹Zr-rituximab PET/CT imaging without a cold preload, followed 3 weeks later by a second dosimetric phase with administration of a standard preload (250 mg/m²) of unlabelled rituximab followed by injection of ⁸⁹Zr-rituximab, and a therapeutic phase 1 week later with administration of unlabelled rituximab followed by ⁹⁰Y-rituximab. PET/CT imaging and tracer uptake by organs and lesions were assessed.

Results

With a cold rituximab preload, the calculated whole-body dose of ⁹⁰Y-rituximab was similar (mean 0.87 mSv/MBq, range 0.82–0.99 mSv/MBq) in all patients. Without a preload, an increase in whole-body dose of 59 % and 87 % was noted in two patients with preserved circulating CD20+ B cells. This increase in radiation dose was primarily due to a 12.4-fold to 15-fold higher dose to the spleen without a preload. No significant change in whole-body dose was noted in the three other patients with B-cell depletion. Without a preload, consistently higher tumour uptake was noticed in patients with B-cell depletion.

Conclusion

Administration of the standard preload of unlabelled rituximab impairs radioconjugate tumour targeting in the majority of patients eligible for radioimmunotherapy, that is patients previously treated with rituximab-containing therapeutic regimens. This common practice may need to be reconsidered and further evaluated as the rationale for this high preload has its origin in the “prerituximab era”.

Clinical Trial Application: CTA 2011-005474-38

Trial Registry: EudraCT

Electronic supplementary material

The online version of this article (doi:10.1007/s00259-015-3025-6) contains supplementary material, which is available to authorized users.

Improving the treatment of non-Hodgkin lymphoma with antibody-targeted radionuclides

Radioimmunotherapy of non-Hodgkin lymphoma comprises a (90)Y- or (131)I-labeled murine anti-CD20 IgG, but both agents also include a substantial dose of unlabeled anti-CD20 IgG given immediately before the radioconjugate to reduce its uptake in the spleen (primary normal B-cell antigen sink); this extends its plasma half-life and improves tumor visualization. Thus, these treatments combine an effective anti-CD20 radioconjugate with an unconjugated anti-CD20 antibody that is also therapeutically active, but the large anti-CD20 IgG predose ( approximately 900 mg) may diminish the tumor localization of the radioimmunoconjugate (eg, 10-35 mg). We have examined alternative approaches that enhance radionuclide targeting and improve antitumor responses. One uses a (90)Y-labeled anti-CD22 IgG (epratuzumab) combined with an antibody therapy regimen of a humanized anti-CD20 IgG (veltuzumab). Pretargeted radionuclide therapy using a trivalent, humanized, recombinant bispecific anti-CD20 antibody with a (90)Y-hapten-peptide is another highly effective method that is also less toxic than directly radiolabeled IgG. Finally, all approaches benefit from the addition of a consolidation-dosing regimen of the anti-CD20 IgG antibody. This article reviews these various options and discusses how some fundamental changes could potentially enhance the response and duration from radionuclide-targeted therapy.