Abstract P2-04-23: A monoclonal antibody against hypo-glycosylated bone sialoprotein II has application for diagnostic purposes in samples of breast cancer patients and for treatment of skeletal metastasis caused by MDA-MB-231 breast cancer cells in rats
Authors: Berger MR , Zepp M , Westphal G , Berger I , Armbruster FP 
Published: March 2017

The SIBLING protein bone sialoprotein II (BSP) has been implicated in lytic skeletal metastasis as it is expressed in a subset of primary breast cancers and can be detected at elevated levels in the serum of patients with increased risk to develop skeletal metastasis. The aim of this study was to investigate the potential application of a rat monoclonal antibody against hypo-glycosylated BSP (IDK1) for diagnostic and therapeutic purposes.

The diagnostic part of this study was based on breast cancer specimens from the biobank / repository of the Institute of Pathology of the Municipal Hospital Kassel, Germany. Immune-histochemical analyses were performed with IDK1 for comparing BSP expression between ten human primary breast tumor sections and their corresponding bone metastatic tissue samples. The therapeutic part of this study was based on a model in nude rats, in which the rats were implanted with human MDA-MB-231 breast cancer cells for selective and orthotopic appearance of osteolytic skeletal lesions. Tumor bearing rats were treated with IDK1 starting at two or four weeks after tumor cell inoculation into the femoral artery of one hind leg. Tumor growth was monitored by light emission, caused by luciferase mediated metabolism of luciferin. Photon emission was recorded at regular intervals by a Xenogen IVIS 100 imaging system. After sacrifice, samples of lesions and apparently healthy tissues were investigated by H&E staining as well as by immune-histological staining for BSP.

BSP staining was found within the cytoplasm of tumor cells. Increased expression of BSP was also detected in healthy bone cells, e.g. osteoblasts, as soon as breast tumor cells invaded bone tissue. An elevation of BSP expression near necrotic centers was also found. Expression of BSP in primary breast tumors was positively correlated with BSP expression in bone metastases. Furthermore, bone metastases showed higher and more intensive expression of BSP than their respective primary breast tumors (p&lt;0.0039).

In the experimental treatment part, all but one untreated tumor bearing rats showed rapid tumor growth accompanied with lytic destruction of femur and tibia of the respective hind leg (18/19; tumor take rate 95%). In contrast, rats treated with the anti-BSP antibody did not show a significant increase in light emission nor a clinical deterioration. In fact, 8 of 10 rats receiving the antibody at a dose of 10 mg/kg/week starting at two weeks after tumor implantation did not show any light emission after 4 to 6 weeks (p = 0.01 versus control) as well as 6 of 10 rats receiving the antibody at the same dose starting at four weeks after tumor implantation (p &lt; 0.05). Radiological and histological examination confirmed that animals without light emission were free of tumor growth, corresponding to a complete remission.

In conclusion, the rat monoclonal antibody directed against BSP is a powerful tool with potential for diagnostic and therapeutic applications in breast cancer skeletal metastasis and warrants further development.

Citation Format: Berger MR, Zepp M, Westphal G, Berger I, Armbruster FP. A monoclonal antibody against hypo-glycosylated bone sialoprotein II has application for diagnostic purposes in samples of breast cancer patients and for treatment of skeletal metastasis caused by MDA-MB-231 breast cancer cells in rats [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-04-23.