The reoccurrence of androgen-dependent prostate cancer after anti-androgen therapy mainly depends on prostate cancer stem-like cells. To reduce the risk, it is important to delete the cancer stem-like cells. Furthermore, to induce differentiation of cancer stem-like cells is critical to abrogate stemness of the cells. Therefore, we tried to investigate a possibility on the establishment of a new effective therapy to eradicate the cancer stemlike cells via the induction of differentiation in this study. Prostate cancer stem-like cells from an androgen-dependent prostate cancer cell line (LNCaP cell) had severe resistance against an anti-androgen therapeutic agent. We selected Bowman-Birk inhibitor (BBI) from soybeans reported as a chemopreventive agent in prostate cancer to differentiate the caner stem-like cells and a-tocopheryl succinate (TOS) known as a mitocan to induce effectively cytotoxic effect against the cancer stem-like cells. In fact, only TOS treatment had cytotoxic effect against the cancer stem-like cells, but the addition of BBI treatment to the cells treated with TOS reinforced TOS-mediated cytotoxicity in the cancer stem-like cells. This reinforcement coincided with the combination-enhanced apoptosis in the stem-like cells. Also, we confirmed caspase9-caspase3 cascade mainly contributed to the enhancement of the cytotoxicity in the stem-like cells caused by the combination, indicating that the reinforcement of BBI on TOS-mediated apoptosis via mitochondria related to the enhancing cytotoxic effect of the combination on the prostate cancer stem-like cells. Overall, it seems that the combination is an effective new approach to reduce the reoccurrence of prostate cancer targeting prostate cancer stem cells.

CD146 (MCAM) expressed on not only vascular endothelial and smooth muscle cells but also various malignant tumor cells. It has been shown that overexpression of CD146 predicts poor prognosis of solid tumor. Several reports by using transfectants or gene silencing technique have shown that CD146 is involved in cell adhesion and inflammatory cell migration. However, contribution of CD146 in tumor metastasis and antitumor immunity are still unknown. To investigate the effect of CD146 on tumor metastatic properties, we establish two subclones from DLD-1 (human colon adenocarcinoma cells) expressing CD146 or not. Both cell lines express epithelial tumor marker EpCAM and TROP2 equally, while CD146 (+) DLD-1 could only express CD44 variant v8–v10 and EphA2. Using metabolic assay, we found enhanced metabolism and decreased lactate production in CD146 (+) DLD-1. Consist with the morphological changes to mesenchymal features CD146 (+) DLD-1, the expression of E-cadherin and claudin-3 in tight junction were decreased in CD146 (+) DLD-1. In addition, CD146 (+) DLD-1 significantly increased the production of VEGF and the induction of various genes (slug, twist and zeb1) which are involved in epithelial to mesenchymal transition (EMT). Interestingly, the expression of immune checkpoint molecules including B7-H1, B7-DC (both PD-1 ligands), CD155 and IDO were up-regulated in CD146 (+) DLD-1 inducing the resistance of cytotoxic effect of activated lymphocytes. These results indicate that CD146 (+) DLD-1 strongly induces immune escape mechanism, thus demonstrating a new relationship between CD146 and EMT and anti-tumor immunity, which would be a new treatment and diagnostic target for immunotherapy.

Nobiletin is a citrus polymethoxy flavonoid that suppresses cell proliferation, angiogenesis and metastatic properties in various cancer cells. In this study, we investigated the combined effects of nobiletin and various chemotherapeutic agents on the cytotoxicity of human colon and esophageal cancer cells. We cultured cancer cells at serial dilution of chemotherapeutic agents with or without nobiletin and assessed cell cytotoxicity at 5 days after drug treatment. The addition of a suboptimal dose of nobiletin did not alter the growth of cancer cells, however cytotoxic effect of antimetabolites (gemcitabine and 5-FU) and DNA-platinating agent (cisplatin) were markedly attenuated by nobiletin. By contrast, nobiletin markedly enhanced antitumor effect of antimicrotubule agents such as docetaxel, paclitaxel, vincristine and MMAE. Moreover, enhanced cytotoxicity by nobiletin was also verified in the combination with MMAE- or DM1-conjugated antibodies to EpCAM and EphA2. We found the inhibition of phosphorylation and nuclear translocation of Pin1 (peptidyl-prolyl isomerase) by nobiletin, suggesting a rational molecular target of nobiletin is Pin1. Overall, these data suggest that nobiletin might useful for the chemotherapeutic treatment of microtubule inhibitors. Citation Format: Kazunori Kato, Takumi Yamazaki, Masaaki Honma. Nobiletin synergizes cytotoxicity of antimicrotubule agents by inhibiting Pin1 pathway [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1054. doi:10.1158/1538-7445.AM2017-1054