Anti-CD45 radioimmunotherapy with 90Y but not 177Lu is effective treatment in a syngeneic murine leukemia model.

Radioimmunotherapy (RIT) for treatment of hematologic malignancies has primarily employed monoclonal antibodies (Ab) labeled with 131I or 90Y which have limitations, and alternative radionuclides are needed to facilitate wider adoption of RIT. We therefore compared the relative therapeutic efficacy and toxicity of anti-CD45 RIT employing 90Y and 177Lu in a syngeneic, disseminated murine myeloid leukemia (B6SJLF1/J) model. Biodistribution studies showed that both 90Y- and 177Lu-anti-murine CD45 Ab conjugates (DOTA-30F11) targeted hematologic tissues, as at 24 hours 48.8 ± 21.2 and 156 ± 14.6% injected dose per gram of tissue (% ID/g) of 90Y-DOTA-30F11 and 54.2 ± 9.5 and 199 ± 11.7% ID/g of 177Lu-DOTA-30F11 accumulated in bone marrow (BM) and spleen, respectively. However, 90Y-DOTA-30F11 RIT demonstrated a dose-dependent survival benefit: 60% of mice treated with 300 µCi 90Y-DOTA-30F11 lived over 180 days after therapy, and mice treated with 100 µCi 90Y-DOTA-30F11 had a median survival 66 days. 90Y-anti-CD45 RIT was associated with transient, mild myelotoxicity without hepatic or renal toxicity. Conversely, 177Lu- anti-CD45 RIT yielded no long-term survivors. Thus, 90Y was more effective than 177Lu for anti-CD45 RIT of AML in this murine leukemia model

Comparative Analysis of Bispecific Antibody and Streptavidin-Targeted Radioimmunotherapy for B-cell Cancers

Streptavidin (SA)-biotin pretargeted radioimmunotherapy (PRIT) that targets CD20 in non-Hodgkin lymphoma (NHL) exhibits remarkable efficacy in model systems, but SA immunogenicity and interference by endogenous biotin may complicate clinical translation of this approach. In this study, we engineered a bispecific fusion protein (FP) that evades the limitations imposed by this system. Briefly, one arm of the FP was an anti-human CD20 antibody (2H7), with the other arm of the FP an anti-chelated radiometal trap for a radiolabeled ligand (yttrium[Y]-DOTA) captured by a very high-affinity anti-Y-DOTA scFv antibody (C825). Head-to-head biodistribution experiments comparing SA-biotin and bispecific FP (2H7-Fc-C825) PRIT in murine subjects bearing human lymphoma xenografts demonstrated nearly identical tumor targeting by each modality at 24 hours. However, residual radioactivity in the blood and normal organs was consistently higher following administration of 1F5-SA compared with 2H7-Fc-C825. Consequently, tumor-to-normal tissue ratios of distribution were superior for 2H7-Fc-C825 (P < 0.0001). Therapy studies in subjects bearing either Ramos or Granta subcutaneous lymphomas demonstrated that 2H7-Fc-C825 PRIT is highly effective and significantly less myelosuppressive than 1F5-SA (P < 0.0001). All animals receiving optimal doses of 2H7-Fc-C825 followed by 90Y-DOTA were cured by 150 days, whereas the growth of tumors in control animals progressed rapidly with complete morbidity by 25 days. In addition to demonstrating reduced risk of immunogenicity and an absence of endogenous biotin interference, our findings offer a preclinical proof of concept for the preferred use of bispecific PRIT in future clinical trials, due to a slightly superior biodistribution profile, less myelosuppression, and superior efficacy

Cerenkov Imaging.

<p>Five female athymic mice per imaging group were injected with either <b>A</b>) 0.3 mCi of ⁹⁰Y-DOTA-30F11 or <b>B</b>) 0.3 mCi ¹⁷⁷Lu-DOTA-30F11 and imaged 24 hours after injection, using a Xenogen IVIS Spectrum imaging platform under 2.5% isoflurane. Differences in the intensity of splenic activity between the mice that received the two isotopes may be attributed to differences in the decay energies of their emitted β⁻ particles; note the different scales used in each image.</p

¹⁷⁷Lu- and ⁹⁰Y-DOTA-30F11 Biodistribution.

<p>Five mice per group received 10⁵ syngeneic leukemic cells <i>i.v.</i> two days before radiolabeled anti-CD45 DOTA-Ab. Mice were euthanized at <b>A</b>) 6, <b>B</b>) 24, and <b>C</b>) 48 hours after injection of (▪) ⁹⁰Y- or (□) ¹⁷⁷Lu- DOTA-30F11. Organs were harvested and counts measured to calculate % ID/g.</p

Target-to-Normal Organ Ratios.

<p>Mean ratios of radioactivity uptake for ⁹⁰Y-DOTA-30F11 (▪) and ¹⁷⁷Lu-DOTA-30F11 (□) delivered to BM (<b>A</b> and <b>B</b>) or spleen (<b>C</b> and <b>D</b>) compared to normal organs at 24 and 48 hours.</p

Survival from anti-CD45 RIT using ⁹⁰Y or ¹⁷⁷Lu.

<p>Ten mice per group were given 10⁵ syngeneic leukemic cells on day -2, and then injected with <b>A</b>) ⁹⁰Y-(∇) or ¹⁷⁷Lu-(□)-DOTA-30F11, at 300 µCi (filled), or 100 µCi (unfilled); or <b>B</b>) isotype control Ab ⁹⁰Y-(▾)- or ¹⁷⁷Lu-(▪) DOTA-rat IgG at 300 µCi, on day 0, and monitored for death, extensive weight loss or lethargy, in which case they were euthanized. Untreated leukemic mice (--) served as a control group.</p

Calculated absorbed dose (cGy)/µCi administered.

<p>Calculated absorbed dose (cGy)/µCi administered.</p

Hematologic, renal and hepatic toxicity.

<p>Five mice per group were bled at baseline (day -19), 1, 2, 3, 4, and 8 weeks after injection of radiolabeled anti-CD45 Ab at time 0 [300 µCi ⁹⁰Y-DOTA-30F11 (▾), 300 µCi ¹⁷⁷Lu-DOTA-30F11 (▪), or liver ⁹⁰Y-DOTA-30F11 equivalent dose of 665 µCi ¹⁷⁷Lu-DOTA-30F11 (□)]. Blood was analyzed for <b>A</b>) WBC, <b>B</b>) Hg, <b>C</b>) platelets, <b>D</b>) BUN concentrations, <b>E</b>) Cr, <b>F</b>) AST, <b>G</b>) ALT, and <b>H</b>) ALP, and values were compared to values from age-matched untreated control mice ().</p

Comparative Analysis of Bispecific Antibody and Streptavidin-Targeted Radioimmunotherapy for B-cell Cancers

Streptavidin (SA)-biotin pretargeted radioimmunotherapy (PRIT) that targets CD20 in non-Hodgkin lymphoma (NHL) exhibits remarkable efficacy in model systems, but SA immunogenicity and interference by endogenous biotin may complicate clinical translation of this approach. In this study, we engineered a bispecific fusion protein (FP) that evades the limitations imposed by this system. Briefly, one arm of the FP was an anti-human CD20 antibody (2H7) with the other arm of the FP an anti-chelated radiometal trap for a radiolabeled ligand (yttrium[Y]-DOTA) captured by a very high-affinity anti-Y-DOTA scFv antibody (C825). Head-to-head biodistribution experiments comparing SA-biotin and bispecific FP (2H7-Fc-C825) PRIT in murine subjects bearing human lymphoma xenografts demonstrated nearly identical tumor targeting by each modality at 24 hrs. However, residual radioactivity in the blood and normal organs was consistently higher following administration of 1F5-SA compared to 2H7-Fc-C825. Consequently, tumor-to-normal tissue ratios of distribution were superior for 2H7-Fc-C825 (p<0.0001). Therapy studies in subjects bearing either Ramos or Granta subcutaneous lymphomas demonstrated that 2H7-Fc-C825 PRIT is highly effective and significantly less myelosuppressive than 1F5-SA (p<0.0001). All animals receiving optimal doses of 2H7-Fc-C825 followed by (90)Y-DOTA were cured by 150 days, whereas the growth of tumors in control animals progressed rapidly with complete morbidity by 25 days. In addition to demonstrating reduced risk of immunogenicity and an absence of endogenous biotin interference, our findings offer a preclinical proof of concept for the preferred use of bispecific PRIT in future clinical trials, due to a slightly superior biodistribution profile, less myelosuppression and superior efficacy