Background: The tumor microenvironment (TME) including stromal cells and immune cells is considered to be a crucial factor in clinical field. TME support cancer cells and contributes to tumor stemness and heterogeneity that cause treatment resistance. Platelet-derived growth factor (PDGF) is a well-known growth factor and it was reported to be involved in cancer growth and migration through PDGF receptors (PDGFRs). PDGFRs are cell surface type III tyrosine kinase receptors and two subtypes are known as PDGFRA and PDGFRB. We previously reported that the high PDGFR beta (PDGFRB) expression was an independent predictor of recurrence of colorectal cancer (CRC), and the inhibition of PDGFRB by PDGFR inhibitor, crenolanib, suppressed tumor growth and migration of CRC in vitro. However, PDGFRB is expressed not only in cancer cells but also in surrounding stromal cells that consist TME. In this study we revealed the interaction between cancer cells and tumor stromal cells via PDGFR, and examined the effectiveness of PDGFR inhibition in CRC treatment.

Results: The effects of PDGFR inhibition were examined in four CRC cell lines (RKO, HCT116, HT29, and DLD1) and six primary cultured CRC cells (724iCC, 821iCC, 25DiCC, 603iCC, 602iCC, 622iCC, and 1M29FiCC) using crenolanib. Primary cultured CRC cells named 2D organoid (2DO) were established from surgically resected specimen according to the method we previously reported (AACR Annual Meeting 2018, 2019. BBRC, 2019). In CRC cells, crenolanib showed additive and synergistic effects with other anticancer drugs, and suppressed expression of stem cell markers including octamer-binding transcription factor 4 (Oct4). Exposure to cancer exosomes increased PDGFRB expression of fibroblasts and promoted transforming growth factor β (TGF-β) secretion, and they were suppressed by crenolanib. Co-culture with fibroblasts enhanced the expression of PDGFRB in cancer cells and promoted stemness and epithelial-mesenchymal transition (EMT) via TGFB signaling, which were suppressed by crenolanib. Among stem cell markers, we focused on Oct4. We previously reported that Oct4 promoted distant metastasis of CRC. Oct4 expression was significantly higher in 2DOs compared with cell lines. Oct4+ cells of 2DO were resistant to treatment and a single Oct4+ cell reproduced tumor heterogeneity. Oct4+ cells were supported by TGF-β, and suppressed by crenolanib. Oct4 expression was correlated with PDGFRB expression in clinical specimen, and patients with high expression of both PDGFRB and Oct4 had a worse prognosis than patients with either or both.

Conclusions: PDGFR inhibition by crenolanib regulates stemness and of EMT in CRC via suppression of TGF-β signaling of tumor and TME. RDGFR could be a new therapeutic target to supress EMT and stem cells of CRC.

Citation Format: Shiki Fujino, Norikatsu Miyoshi, Aya Ito, Masaru Sasaki, Takasyuki Ogino, Hidekazu Takahashi, Mamoru Uemura, Chu Matsuda, Tsunekazu Mizushima, Yuichiro Doki. PDGFR is a key factor to regulate stemness and epithelial mesenchymal transition of colorectal cancer with suppression of tumor microenvironment [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 4000.