IN VIVO A NT IT U MOR A C T I V I T Y O F L O C O R E G I O N A L ² ¹ ¹ A T-T R A S T U Z U M AB I N THE TREATMENTOF PERITON EAL M ETA S TA S I S O F GAS TR I C C A N C E R I N M I C E
AUTHORSHuizi Keiko Li1,2,3, Yukie Morokoshi1, Kotaro Nagatsu4, Tadashi Kamada2,5, andSumitaka Hasegawa1 (2017)
1.Radiation and Cancer Biology Team, National Institutes for Quantum andRadiological Science and Technology; 2.Graduate School of Medical andPharmaceutical Sciences, Chiba University, Chiba; 3.Japan Society for the
Promotion of Science, Tokyo; 4.Targetry and Target Chemistry Team;
5.Clinical Research Cluster, National Institutes for Quantum and Radiological
Science and Technology, Chiba, JapanINTRODUCTION
Gastric cancer (GC) is one of the leading causes of cancer-related deathworldwide. Recent advances identified reliable predictive biomarkers such as
human epidermal growth factor receptor (HER2), thus introducing moleculartargeted drug therapy. GC’s HER2-positive, when amplified or over expressed,
play an important role in the development and progression of certain
aggressive types of breast cancer. Trastuzumab, an anti-HER2 mAb(monoclonal antibody), has been used previously as a targeted therapy for
HER2-positive GC. It induces an immune-mediated response that causesinternalization and downregulation of HER2 and yields excellent treatment
outcomes. Radioimmunotherapy (RIT) is a targeted radioisotope treatment

method that uses an antibody as a carrier of therapeutic radioisotopes. The
selective targeting of radioisotopes to the tumor using a radiolabeled cancerspecific antibody enables the delivery of a high dose of radiation directly tocancer cells while minimizing the exposure of normal cells. 211At is ofparticular interest because it emits highly cytotoxic α -particles that can kill atarget cell, making it one of the most potent cell-killing agents available.
Astatine-211 is therefore particularly suited to the targeted killing ofdisseminated or micrometastatic solid tumors that are usually resistant.

OBJECTIVE
Astatine-211-labeled trastuzumab (211At-trastuzumab or 211At-tras)
emitting highly cytotoxic α -particles could be a potent agent for the targeted
ablation of HER2-positive PMGC. This study thus investigated thetherapeutic efficacy of a-RIT using 211At-tras in preclinical mouse models of
HER2-positive peritoneal metastasis of gastric cancer.

MATERIAL & METHODSRadioimmunotherapy in PMGC mice. The PMGC mouse models were
established by i.p. injecting luciferase-transfected N87/Luc cells (3x105) into

5-week-old B17/Icr-scid/scidJcl (homo) female mice 1 week before theexperiment. These PMGC model mice then underwent RIT at 1 week aftercell inoculation. Mice received a single i.p. injection of PBS, trastuzumab,
non-carrier 211At (1 MBq), or 211At-trastuzumab (0.1 or 1 MBq). Tumor growthin the PMGC mice was monitored every week using an in vivo
bioluminescence imaging Fusion system (Vilber Lourmat, France).
Bioluminescence from PMGC was captured for 10 s at 10 min after theinjection of luciferin (10 mg/mL in PBS, 300 µL/mouse). The totalbioluminescence intensity in the abdominal region was quantified using Bio1D software (Vilber Lourmat).

Figure 1.

Luminescence
65 000PBS (Control)

RESULTS
Figure 1. Locoregional therapy with astatine-211 labeledtrastuzumab (211At-tras) in a mouse model of peritoneal metastasisof gastric cancer (PMGC) and tumor monitoring.
Representative bioluminescence images of tumor growth in themouse model treated with PBS (control), unlabeled Tras, 211At (1 MBq),or 211At-tras (0.1 or 1 MBq) 8 days after N87/Luc implantation Images
were captured on the day before treatment at Day 0 then at 3, 5 and 7
weeks after treatment. The color scale indicates the luminescenceintensity per pixel. The tumor growth was monitored longitudinally ineach group by the in vivo bioluminescence imaging Fusion system(Vilber Lourmat, France). Tumor growth was obvious in the PMGC
mice injected with PBS, unlabeled Tras, free 211At 1mBq, and 0.1 MBq
211At-tras. In contrast, a single injection of 1 MBq 211At-trastuzumab
reduced the tumor burden at 3 weeks after injection, with the tumors
becoming undetectable at 5–7 weeks after treatment. Tras and PBS
injections had little to no effect on tumor growth in the PMGC model.

CONCLUSION
In the current study, it has been demonstrated that 211At-trastuzumabspecifically targets HER2-positive GC cells in vivo and thus
successfully inhibits tumor growth and improves survival in PMGC
model mice with time. These results demonstrate the abilities of theFusion FX7 (Vilber Lourmat, France) in imaging targeted therapy andits biodistribution pattern in the treatment of peritoneal metastasis ofgastric cancer in mice.

Tras
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5 weeks

7 weeks