Abstract 1766: Dinutuximab targets GD2+ breast cancer stem cells and inhibits TNBC tumor growth
Authors: Battula Venkata Lokesh , Nguyen Khoa , Somanchi Anitha , Mu Hong , Ueno Naoto T. , Lee Dean , Andreeff Michael 
Published: August 2018

Abstract
Breast cancer stem-like cells (BCSCs), also known as breast cancer initiating cells, are a fraction of cells in the primary tumor that are highly tumorigenic, chemotherapy resistant, and are able to cause metastases. Therefore, targeting BCSCs is an important strategy that could complement standard chemotherapy for breast cancer. We have identified that ganglioside GD2 as an important maker for BCSCs and that ST8SIA1 (GD3-synthase) is an enzyme that regulates GD2 expression in BCSCs (Battula et al., JCI, 2012). GD2 is over expressed in triple negative breast cancer (TNBC) compared to non-TNBC. Inhibition of GD2 expression by knockdown of ST8SIA1 completely inhibited tumor growth and metastases in xenograft models. Therefore, we hypothesize that targeting GD2+ BCSCs will inhibit TNBC tumor growth. To test our hypothesis, we used the chimeric anti-GD2 monoclonal antibody (Dinutuximab) that has been FDA approved for the treatment of neuroblastoma in children. The main mode of action for dinutuximab is antibody dependent cell-mediated cytotoxicity (ADCC). To test the activity of dinutuximab against GD2+ BCSCs, we treated MDA-MB-231 and SUM159 breast cancer cells with dinutuximab alone at different concentrations (1, 12.5, 25, 50, and 100µg/ml) for 24, 48, and, 72hrs or in combination with IL-21 activated NK cells. As control, cells were treated with rituximab (anti-CD20 antibody) and NK cells. Although only a moderate effect was observed on GD2+ cells when treated with dinutuximab alone, we found a dramatic decrease in the number of live (annexin-vneg and DAPIneg) GD2+ cells when treated with dinutuximab in combination with NK-cells. This combination decreased the percentage of GD2+ cells from 20.1±0.3% to 5.8±0.2% (p&lt;0.001). No significant effect on GD2+ cells was observed in the rituximab + NK cell group, indicating that the dinutuximab + NK-cell combination is most affective in inducing cytolysis of GD2+ cells. Next, to investigate the effect of dinutuximab on in-vivo tumor growth, we implanted firefly luciferase expressing MDA-MB-231 cells into nude mice (these mice were chosen because of the presence of NK cells). When palpable tumors were formed (tumor volume 25-30mm3), the mice were treated with dinutuximab or rituximab at 1.4mg/kg twice a week for 6 weeks. Tumor growth was measured weekly by bioluminescence imaging as well as by calipers. We found a &gt;10 fold decrease in tumor growth in mice treated with dinutuximab compared to control. In contrast, tumor volumes reached up to 250mm3 within 10 weeks of tumor implantation in the rituximab treated group (p&lt;0.001). Conclusion: Our data suggest that dinutuximab targets GD2+ BCSCs with the help of NK cells by ADCC and inhibits tumor growth. We are currently in the process of developing a phase I/II clinical trial using dinutuximab in patients with TNBC. In addition, preclinical testing of dinutuximab in combination with NK cells using TNBC PDX models is underway.
Citation Format: Venkata Lokesh Battula, Khoa Nguyen, Anitha Somanchi, Hong Mu, Naoto T. Ueno, Dean Lee, Michael Andreeff. Dinutuximab targets GD2+ breast cancer stem cells and inhibits TNBC tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1766.