Radiosensitivity Of Colorectal Cancer Research Articles

Abstract 314: A novel MDM2-p53 antagonist APG-115 induces p53-mediated apoptosis and enhances radiosensitivity in colorectal cancer

Abstract Background: Colorectal carcinoma is the third leading cause of cancer-related mortality in China. MDM2-p53 inhibitor APG-115 is a novel potential anticancer agent. We aim to investigate the anticancer effect and radiosensitivity enhancement of APG-115 in colorectal cancer. Materials and methods: Human colorectal cancer cell lines (LOVO, HCT116, RKO, HT29, SW480 and SW620) were treated with the APG-115 alone or with radiation (0-8Gy). Transwell, clonogenic survival assays, CCK-8, flow cytometry, RT-qPCR, Western blot were used to assay cell invasion, cell survival, cell cycle progression, quantification of mRNA expression and DNA damage repair. In vivo, xenograft mouse models (RKO Cell line) were established to analyze the anticancer effect and radiosensitivity enhancement of APG-115. Results: In vitro, APG-115 not only inhibited invasion and proliferation of colorectal cell lines, but also induced cell-cycle arrest in G1/S phase. Meanwhile, APG-115 increased the mRNA and protein expression of p53 downstream targets dependent on MDM2-p53 signal pathway. The combination of APG-115 and radiation caused cells to accumulate in G2/M and resulted in the accumulation of H2AX-related DNA damage, indicating an increasing of radiosensitivity. In xenograft mouse models, single therapy with either radiation or APG-115 was equivalent in delaying tumor growth, although APG-115 slightly outperforming therapy with radiation alone. Combination therapy delayed tumor growth more significantly compared with either single agent therapy. By analyzing proliferation marker Ki67 in xenograft tumor specimens, we found that the number of proliferating cells significantly decreased in tumors receiving combination treatment of APG-115 and radiation compared with tumors receiving single agent treatment. These results strongly confirmed the enhanced antitumor capacity of APG-115 when combined with radiation. Conclusions: Our data strongly suggest that MDM2-p53 inhibitor APG-115 may serve not only as a stand-alone therapy, but also as an effective adjunct to current radiotherapeutic regimens for treating colorectal cancer dependent on MDM2-p53 axis. Citation Format: Han-Jie Yi, Xiang-Lei Yan, Qiu-Yun Luo, Luping Yuan, Baoxia Li, Wentao Pan, Lin Zhang, Miao-Zhen Qiu, Guangfeng Wang, Yifan Zhai, Da-Jun Yang. A novel MDM2-p53 antagonist APG-115 induces p53-mediated apoptosis and enhances radiosensitivity in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 314.

Inhibition of ATG12-mediated autophagy by miR-214 enhances radiosensitivity in colorectal cancer

Radioresistance hampers success in the treatment of patients with advanced colorectal cancer (CRC). Improving our understanding of the underlying mechanisms of radioresistance could increase patients’ response to irradiation (IR). MicroRNAs are a class of small RNAs involved in tumor therapy response to radiation. Here we found that miR-214 was markedly decreased in CRC cell lines and blood of CRC patients after IR exposure. Meanwhile, autophagy was enhanced in irradiated CRC cells. Mechanically, ATG12 was predicted and identified as a direct target of miR-214 by dual luciferase assay, qPCR, and Western blot. In vitro and in vivo experiments showed that miR-214 promoted radiosensitivity by inhibiting IR-induced autophagy. Restoration of ATG12 attenuated miR-214-mediated inhibition of cell growth and survival in response to IR. Importantly, miR-214 was highly expressed in radiosensitive CRC specimens and negatively correlated with plasma level of CEA. Moreover, ATG12 and LC3 expressions were increased in radioresistant CRC specimens. Our study elucidates that miR-214 promotes radiosensitivity by inhibition of ATG12-mediated autophagy in CRC. Importantly, miR-214 is a determinant of CRC irradiation response and may serve as a potential therapeutic target in CRC treatment.

MiR-29a Regulates Radiosensitivity in Human Intestinal Cells by Targeting PTEN Gene.

Two major challenges encountered during radiotherapy for colorectal cancer (CRC) are radioresistance of tumor cells and damage to normal cells. An understanding of the mechanisms of radioresistance in CRC may lead to new strategies for overcoming obstacles to affective clinical therapy. In this study, the miR-29a expression was compared among four cell lines: the normal human intestinal epithelial crypt cell line, HIEC and three CRC cell lines, HT29, DLD-1 and HCT116. The roles of miR-29a in regulating cellular radiosensitivity were then investigated. The findings from this study showed that miR-29a mimic enhanced radioresistance in HIEC, HT29 and DLD-1 cells with low levels of intrinsic miR-29a. On the other hand, a miR-29a inhibitor significantly sensitized HCT116 cells with high levels of miR-29a after irradiation. Further studies indicated that PTEN was the direct functional target of miR-29a and was involved in radiosensitivity. MiR-29a could activate the PI3K/Akt signaling pathway through negatively regulated PTEN expression. In conclusion, miR-29a may regulate the radiosensitivity of intestinal cell lines by targeting the PTEN gene, which indicates miR-29a might serve as a novel approach to enhance radiosensitivity in CRC.

The interactions between polo-like kinase 1 (PLK1), microsatellite instability (MSI) and radiosensitivity of colorectal cancer (CRC)

The interactions between polo-like kinase 1 (PLK1), microsatellite instability (MSI) and radiosensitivity of colorectal cancer (CRC)

Knockdown of long non-coding RNA HOTAIR inhibits proliferation and invasiveness and improves radiosensitivity in colorectal cancer.

Colorectal cancer (CRC) is still one of the most important neoplasias causing human death. Multidisciplinary therapy has won consensus in the management of CRC, of which, radiotherapy occupies an important position. However, radioresistance is still a major obstacle in local control of CRC. Overexpression of long non-coding RNA HOTAIR has been found to correlate with tumorigenesis and poor prognosis in several types of cancer. In the present study, we analyzed HOTAIR expression levels of 53 CRC patients in tumor and adjacent normal tissue by real-time quantitative PCR. Knockdown of HOTAIR by RNA interference was performed to explore its roles in cell proliferation, migration, invasion, apoptosis and radiosensitivity. Results showed that CRC patients had higher HOTAIR expression in tumor tissues compared with adjacent normal tissues. In vitro, downregulation of HOTAIR reduced proliferation, migration and invasiveness while enhanced apoptosis and radio-sensitivity of CRC cells. Taken together, our findings suggest that long non-coding RNA HOTAIR expression is closely associated with tumor invasion and radiosensitivity, indicating the potential role in diagnostics and therapeutics of CRC.

Novel Epigenetic CREB-miR-630 Signaling Axis Regulates Radiosensitivity in Colorectal Cancer.

BackgroundmiR-630 has been reported to be a modulator of several cancers, but the mechanism by which is it influences radioresistance remains unknown. We aimed to identify the molecular function of miR-630 and its regulatory mechanism in colorectal cancer (CRC) cell lines.MethodologyOverexpression and loss-of-function analyses of miR-630 were performed in CRC cell lines by measuring their levels of growth and apoptosis after ionic radiation (IR). Target genes were detected via a dual-luciferase assay and Western blot. Chromatin immunoprecipitation assay was carried out to identify the transcription factor regulating miR-630, and a demethylation experiment was also conducted.ResultsmiR-630 expression was found to be positively correlated with radiosensitivity in CRC cell lines (p<0.05). After IR treatment, miR-630 induced apoptosis in cells; however, the opposite was observed when miR-630 was downregulated (p<0.05). BCL2L2 and TP53RK were identified as the target genes of miR-630, and the function of miR-630 was found to depend on these two genes (p<0.05). In addition, evidence showed that CREB regulates the level of miR-630, and demethylation can elevate miR-630 levels (p<0.05).ConclusionCREB–miR-630–BCL2L2 and TP53RK comprise a novel signaling cascade regulating radiosensitivity in CRC cell lines by inducing cell apoptosis and death.

Effects of heterochromatin in colorectal cancer stem cells on radiosensitivity

Radiotherapy (RT) is a major non-surgical modality in the comprehensive treatment for colorectal adenocarcinoma. The radioresistance of cancer stem cells (CSCs) is a key factor that influences therapeutic effectiveness. This study was to investigate the effects of specific chromosome structure and histone modification in CSCs in colorectal adenocarcinoma radioresistance. Samples were collected from resected human colorectal adenocarcinomas. Subcutaneous colorectal cancer model was established in nude mice. Immunohistochemistry showed that xenografts generated from bulk colorectal cancer cells resembled the original tumor specimen. Flow cytometry was performed to sort CSCs (CD133+) and non-CSCs (CD133-) from both resected samples of colorectal adenocarcinoma and xenograft before and after high single-dose radiation. The markers labeling heterochromatin (H3K9me3, HP1-alpha and H3K4me1) and euchromatin (H3K4me3) in CD133+ and CD133- nucleus were detected by immunofluorescence. There was distinct difference in chromatin structure between colorectal CSCs (CD133+) and non-CSCs (CD133-). The chromatin displayed compact patches in CD133+ nucleus, but loosely latticed structure in CD133- nucleus; immunofluorescence verified that the compact patches existing in CSCs was generated from heterochromatin construction. In addition, the vacuole-like defect in heterochromatin regions of CSCs was observed within 24 h after exposure to 10 gray (Gy) single-dose RT. Interestingly, this phenomenon was repaired from 96 h, and recovered to dense plaque structure in heterochromatin regions of CSCs after 144 h. However, no significant difference in non-CSCs was observed after RT exception for a loose chromatin structure. CSCs play a role in radiosensitivity in colorectal cancer. The mechanism may be related to heterochromatin formation and histone methylation.

372 POSTER Radiosensitivity in colorectal cancer: Any association with nuclear factor-kappaB?

372 POSTER Radiosensitivity in colorectal cancer: Any association with nuclear factor-kappaB?