Abstract 2588: Oral administration of water extract from Euglena gracilis prevents lung carcinoma growth in mice by alteration of intestinal microbiota

Euglena gracilis, a single-celled alga, is rich in nutrients and thus, used as a nutritional dietary supplement. This alga can be found in both fresh and saltwater and possesses characteristics of both plants and animals. Euglena gracilis extracts have a wide range of medicinal properties including stimulation of anticancer immunity against multiple types of cancers; however, the anticancer mechanism has not yet been fully elucidated. Therefore, a water extract from Euglena gracilis devoid of water-insoluble mature paramylons was evaluated as an anticancer agent against lung carcinoma. Two different extracts were prepared using dried powder from whole Euglena gracilis. First, partially purified water extract (EWE) was prepared by suspending dry powder in PBS and centrifugation at 10,000g for 20 min followed by a filtration using a 0.22µm pore size membrane. Second, boiled EWE (bEWE) was prepared by immersing unfiltered EWE in boiling water for 12 min followed by centrifugation at 10,000g for 10 min and filtration using 0.22µm pore size membrane. Both EWE and bEWE treatments inhibited the growth of lung carcinoma cells in vitro in a dose- and time-dependent manner. Furthermore, both extracts significantly inhibited the three-dimensional growth of Lewis Lung Carcinoma (LLC) cells. Flow cytometry analysis showed that the EWE treatment attenuates granulocytic myeloid-derived suppressor cells (MDSCs) in bone marrow cell cultures. The in vivo study was conducted using a mouse LLC orthotopic allograft model. Oral administration of EWE and bEWE (100-200 mg/kg/day) three weeks prior to LLC cell inoculation attenuated the tumor growth in the lungs of immunocompetent mice while decreasing the peripheral granulocytes. However, this attenuation was not seen for the extract treatment initiated after LLC cell inoculation. The tumor growth attenuation was more efficient with the bEWE treatment than with EWE treatment. The fecal microbiomes of the mice were analyzed by 16s rRNA gene amplicon sequencing which revealed that alpha diversity in three groups (EWE, bEWE, and PBS control) was similar, however, the microbial compositions of the EWE- and bEWE-treated mouse groups were more diversified than in the PBS group. Specifically, an increase in the ratio of Bacteroidetes to Firmicutes was observed, and a significant increase in Akkermansia and Muribaculum was detected in EWE- and bEWE- treated mice compared to PBS treated mice. These studies suggest that oral administration of partially purified water extracts from Euglena gracilis altered the intestinal microbiome and the alteration may attenuate host MDSCs, thereby preventing lung carcinoma growth. This study was supported by 2016EUGLENA-RC1 (MT), 2017EUGLENA-RC2 (MT and JC), Kansas State University College of Veterinary Medicine SMILE award (MT and JC), and NIH grant P20 RR017686 (MT). Citation Format: Deepa Upreti, Susumu Ishiguro, Mayme Loyd, Nicole Robben, Paige Cote, Morgan Phillips, Ayaka Nakashima, Kengo Suzuki, Jeffrey Comer, Masaaki Tamura. Oral administration of water extract from Euglena gracilis prevents lung carcinoma growth in mice by alteration of intestinal microbiota [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2588.