Division of Cancer Differentiation

Koji Okamoto, Daisuke Shiokawa, Hirokazu Ohata, Toshiaki Miyazaki, Kaoru Yamawaki, Nupur Nigam, Ai Sato, Hiroaki Sakai, Seiko Ogawa, Manami Miura, Kenta Takahashi, Rie Uchino, Wakako Hara, Taichi Iijima, Katsuya Yokoyama, Mayu Fukami

Introduction

Cancer stem cells (CSCs) are initially identified in hematologic cancer, and the following researches indicated that they also exist in many solid tumors. It has been proposed that CSCs are responsible for the refractory nature of solid tumors, i.e. the capability for generation of metastatic foci and for chemoresistance. Our group focuses on studying CSCs from solid tumor, especially those from colon cancer and ovarian cancer. We have established the in vitro 3D culture of colon and ovarian CSCs, and aim to find out weakness of CSCs that can be exploited for clinical purposes. For that purpose, we also use the established CSCs to generate patient-derived xenograft tumor in order to understand the mechanisms of chemoresistance. In addition, by combining sensitivity data for chemotherapy compounds with data from genomic and gene expression analyses and clinical information, we are in the process of establishing a comprehensive panel of the 3D culture of these cancers, which will be instrumental for stratifying the clinical cases and devise the strategy for the personalized medicine.

Our team and what we do

We are performing basic and translational research to understand the refractory nature of cancer and to devise the effective diagnosis and therapy. For that purpose, we mainly use the 3D culture system of solid tumors.

Research activities

1.Biological characterization of cancer stem cells in vitro from human refractory cancer

Using the in vitro 3D culture (spheroid culture) from human colon cancer and serous ovarian cancer, we have isolated and expanded CSCs. Using the cultivated CSCs, we demonstrated that activation of mTORC1 by reactive oxygen species (ROS) is crucial for the proliferation and maintenance of colon CSCs, and that ROS is produced by NADPH oxidase. In addition to colon CSCs, we examined regulatory pathways of ovarian CSCs, and showed that ALDH1 expression is functionally important for the proliferation of ovarian CSCs. Furthermore, we performed metabolome analyses of the spheroid culture from different clinical samples, and identified some metabolites that are abundant in CSCs from liver metastasis.

2.PDX models of colon and ovarian cancer

Through the transplantation of the in vitro cultivated CSCs into immuno-compromized NOG mice, we established in vivo models of colon and ovarian cancer (PDX models). In addition, we established models to study chemoresistance by treating tumor-transplanted mice with chemotherapeutic compounds. By applying single-cell gene expression analyses, cellular heterogeneity of xenograft tumors and identity of chemo-resistant cells were examined. A similar approach to study cellular heterogeneity of cancer was applied for mouse models of inflammation-associated colon cancer in ApcMin/+ mice.

Education

Teaching students (two undergraduate students, five graduate students)

Future prospects

We will aim to translate the acquired knowledge for CSCs into clinical practice by performing further characterization of CSCs derived from refractory cancer.