A covalent conjugate (NR-LU-10͞SA) was prepared between streptavidin (SA) and NR-LU-10, a mAb that binds an antigen expressed on the surface of most human carcinomas. NR-LU-10͞SA was injected into nude mice bearing human tumor xenografts. Injection of biotinylated galactosyl-human serum albumin reduced the circulating levels of conjugate by 95%. Subsequent administration of 90 Y-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-biotin achieved peak uptake at the tumor within 2 hr while >80% of the radioactivity was eliminated in the urine. A single dose of 600 -800 Ci of 90 Y-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-biotin produced cures in 10͞10 mice with established (>200 mm 3 ) s.c. human small cell lung or colon cancer xenografts and 8͞10 cures in mice with human breast cancer xenografts without significant toxicity.

Purpose: The therapeutic efficacy of a unique melanoma-targeting peptide conjugated with an in vivo generated a-particle-emitting radionuclide was evaluated in the B16/F1mouse melanoma animal model. a-Radiation is densely ionizing, resulting in high concentrations of destructive radicals and irreparable DNA double-strand breaks. This high linear energy transfer overcomes radiation-resistant tumor cells and oxygen effects resulting in potentially high therapeutic indices in tumors such as melanoma.

No abstract

Pretargeted radioimmunotherapy (PRIT) has demonstrated remarkable efficacy targeting tumor antigens, but immunogenicity and endogenous biotin blocking may limit clinical translation. We describe a new PRIT approach for the treatment of multiple myeloma (MM) and other B-cell malignancies, for which we developed an anti-CD38-bispecific fusion protein that eliminates endogenous biotin interference and immunogenic elements. In murine xenograft models of MM and non-Hodgkin lymphoma (NHL), the CD38-bispecific construct demonstrated excellent blood clearance and tumor targeting. Dosimetry calculations showed a tumor-absorbed dose of 43.8 Gy per millicurie injected dose of Y, with tumor-to-normal organ dose ratios of 7:1 for liver and 15:1 for lung and kidney. In therapy studies, CD38-bispecific PRIT resulted in 100% complete remissions by day 12 in MM and NHL xenograft models, ultimately curing 80% of mice at optimal doses. In direct comparisons, efficacy of the CD38 bispecific proved equal or superior to streptavidin (SA)-biotin-based CD38-SA PRIT. Each approach cured at least 75% of mice at the highest radiation dose tested (1200 µCi), whereas at 600- and 1000-µCi doses, the bispecific outperformed the SA approach, curing 35% more mice overall ( < .004). The high efficacy of bispecific PRIT, combined with its reduced risk of immunogenicity and endogenous biotin interference, make the CD38 bispecific an attractive candidate for clinical translation. Critically, CD38 PRIT may benefit patients with unresponsive, high-risk disease because refractory disease typically retains radiation sensitivity. We posit that PRIT might not only prolong survival, but possibly cure MM and treatment-refractory NHL patients.

α-Emitting radionuclides deposit a large amount of energy within a few cell diameters and may be particularly effective for radioimmunotherapy targeting minimal residual disease (MRD). To evaluate this hypothesis, (211)At-labeled 1F5 monoclonal antibody (mAb) (anti-CD20) was studied in both bulky lymphoma tumor xenograft and MRD animal models. Superior treatment responses to (211)At-labeled 1F5 mAb were evident in the MRD setting. Lymphoma xenograft tumor-bearing animals treated with doses of up to 48 µCi of (211)At-labeled anti-CD20 mAb ([(211)At]1F5-B10) experienced modest responses (0% cures but two- to threefold prolongation of survival compared with negative controls). In contrast, 70% of animals in the MRD lymphoma model demonstrated complete eradication of disease when treated with (211)At-B10-1F5 at a radiation dose that was less than one-third (15 µCi) of the highest dose given to xenograft animals. Tumor progression among untreated control animals in both models was uniformly lethal. After 130 days, no significant renal or hepatic toxicity was observed in the cured animals receiving 15 µCi of [(211)At]1F5-B10. These findings suggest that α-emitters are highly efficacious in MRD settings, where isolated cells and small tumor clusters prevail.