Abstract 3459: Water extract from Euglena gracilis prevents lung carcinoma growth in mice via attenuation of myeloid-derived suppressor cells and granulocytes

Abstract

Phytochemicals have been developed into treatments against many diseases, including various cancers. Euglena is a genus of single-cell flagellate eukaryotes having features of both animals and plants. These organisms, which are found in both fresh and salt water, have been used as a dietary supplement for their rich nutrient content. Although recent studies suggest that Euglena extracts have anti-tumor properties, the mechanism is yet to be clarified. Accordingly, the anti-tumor and immunomodulatory effects of partially purified water extract from Euglena gracilis (EWE) was evaluated in cell culture and a mouse orthotopic lung carcinoma allograft model. The EWE was prepared by a PBS extraction at 37°C for 30 min, centrifugation at 2,000 g for 20 min, and filtration through a membrane filter (0.22 μm pore size). Primary components of this extract are water soluble materials and exclude mature paramylons, intact chloroplasts, and oil droplets. In two-dimensional cell culture, the EWE treatment inhibited cell growth of both murine Lewis lung carcinoma (LLC) and human lung carcinoma cells (A549 and H1299) in a dose (1-100 μg/ml) and time (24-72 h)-dependent manner. In contrast, the growth of mouse bone marrow cells (BMCs), but not mouse splenocytes (SPLs) were dose (1-100 μg/ml) and time (24-72 h)-dependently stimulated by the treatment with EWE. In three-dimensional spheroid culture, spheroid growth of LLC cells was significantly attenuated by EWE treatment. Flow cytometry revealed that the EWE treatment attenuated granulocytic myeloid-derived suppressor cells in BMCs. In a mouse LLC orthotopic allograft model, pretreatment with EWE (100-200 mg/kg/day, via drinking water) three weeks prior to LLC cell inoculation significantly attenuated the growth of LLC tumors in the lungs of immunocompetent syngeneic mice. However, this attenuation was not seen for EWE treatment initiated after LLC cell inoculation. The tumor growth attenuation by EWE pretreatment coincided with a significant decrease of myeloid-derived cells, primarily neutrophils. EWE pretreatment appears to inhibit lung carcinoma growth mainly by stimulating host anti-tumor immunity via an attenuation of the host myeloid-derived immune suppressor cells. Hence, the present study suggests that the partially purified extract derived from Euglena gracilis contains bioactive materials that prevent lung carcinoma growth. This study was supported by 2016EUGLENA-RC1 (MT), 2017EUGLENA-RC2 (MT and JC), a Kansas State University College of Veterinary Medicine SMILE award (MT and JC), and NIH grant P20 RR017686 (MT). Citation Format: Susumu Ishiguro, Deepa Upreti, Nicole Robben, Page Cote, Riley Burghart, Damilola Ogun, Tran Le, Jennifer Delzeit, Jayson Carswell, Arashi Nakashima, Ayaka Nakashima, Kengo Suzuki, Jeffrey Comer, Masaaki Tamura. Water extract from Euglena gracilis prevents lung carcinoma growth in mice via attenuation of myeloid-derived suppressor cells and granulocytes [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3459.