Bevacizumab radioimmunotherapy in triple-negative breast cancer xenograft

Objectives: Radioimmunotherapy (RIT) has been investigated for serval years. But slow blood clearance of antibody can cause severe hematological side-effects. Because bevacizumab (a clinically used anti-VEGF antibody) has an even longer terminal biological half-life compared to other antibodies, a blood clearance enhancement strategy is necessary for the application of bevacizumab RIT in clinical settings. Three steps pretargeting strategy using avidin-biotin system might solve this problem. In this study, we performed three steps pretargeting RIT with bevacizumab for treatment triple negative breast cancer (TNBC).

Methods: MDA-MB-231 (TNBC cell line) was selected for preparing xenografts mice. In our pretargeting strategy, biotinylated bevacizumab was injected intravenously into tumor-bearing mice. After 24 hours, a clearing agent (avidin) was administered. Lastly, 3 hours after injection of clearing agent, radiolabeled streptavidin or succinylated streptavidin (succ-streptavidin) was administered. To obtain the optimal therapeutic efficiency, we did pretargeting biodistribution study by labeled Indium-111 to streptavidin with and without succinylation for evaluating the kidney and the tumor uptake. For dose escalating and therapy study, we used the same pretargeting method but labeled Yttrium-90 to succ-streptavidin. In the therapeutic study, all mice were divided into 4 groups; 300 µCi (group1), 250 µCi (group2), 200 µCi (gourp3) and no treatment for the last group (group4). The observation was terminated when the tumor volume exceeded 2000 mm³ or the mice were dead.

Results: ¹¹¹In-succ-streptavidin comparing to without succinylated one has successfully decreased the kidney uptake for prevention the renal toxicity. The kidney uptake was 6.91 ± 0.98 vs 21.38± 2.43 (1 h p<0.0001) and 4.52± 0.40 vs 73.85 ± 6.74 (24 h p<0.0001). While, there was no significant difference in tumor accumulation levels between the ¹¹¹In-succ-streptavidin and ¹¹¹In-streptavidin, as well as the avidin-biotin system was rapidly increased the blood clearance. The tumor to blood ratio was 0.103 ± 0.015 vs 0.110 ± 0.035 (1 h, p=0.84) and 2.48 ± 0.67 vs 1.03 ± 0.12 (24 h, p<0.05). The escalating study revealed that 300 µCi was considered as the maximum tolerated dose. At day 10, tumor growth was significantly suppressed in all treatment groups compared to that of the no-treatment group (p<0.05). The mean tumor volume in group1, group2, group3 and group4 was 392.3 ± 65.7, 468.4 ± 159.7, 526.8 ± 154.0 and 945.0 ± 474.5, respectively.

Conclusions: Our pretargeting strategy using avidin-biotin system and succinylated streptavidin achieved fast blood clearance and low kidney uptake. In addition, enough therapeutic effect was observed. Therefore, this approach could increase the maximum tolerate dose for treatment and minimize the radiation exposure to bone marrow and kidney. These results indicated that our pretargeting treatment may effective for human TNBC treatment.