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Recent studies that have emerged on the diversity of RNA modification in tumors suggest their eligibility as bona fide targets in diagnosis and drug discovery. N6-methyladenosine (m6A) was first reported and is most common in epitranscriptome modification of various RNAs. The YT521-B homology (YTH) domain family are representative m6A-binding proteins, but how the YTH domain family is involved in cancer remains to be clearly understood. Given that clinical sequence data in colorectal cancer indicate that overexpression of YTHDF1 is outstanding among other family members, we studied the role of Ythdf1 and the transcriptional control of YTHDF1. Immunostaining of Ythdf1 showed that its expression was associated with various malignant tumor behaviors, such as depth, lymph node metastasis, and poorer cancer stages. The study of patient survival indicated that patients with high Ythdf1 expression had significantly poorer overall survival. The results indicated that Ythdf1 expression is an independent prognostic factor of patients. The in vitro study showed that the knockdown of YTHDF1 resulted in the suppression of cancer proliferation and sensitization to the exposure of anticancer drugs such as fluorouracil and oxaliplatin. Importantly, the study upstream of the YTHDF1 gene indicated that an oncogenic transcription factor c-Myc was associated with YTHDF1 in both expression and chromatin immunoprecipitation data. Moreover, the knockdown experiments of c-Myc showed the inhibition of YTHDF1, supporting a notion of c-Myc-driven YTHDF1 axis significance. These data suggest that m6A reader Ythdf1 plays a significant role in colorectal cancer progression.

BACKGROUND: OncoBEAM TM RAS CRC kit using BEAMing technology is a circulating tumour DNA (ctDNA) test for detecting plasma RAS mutational status in metastatic colorectal cancer (mCRC). We conducted a multicentre, prospective study to investigate the concordance of the RAS mutational status between plasma ctDNA and tumour tissue DNA. METHODS: mCRC patients without prior anti-EGFR antibodies or regorafenib treatment were enroled. Plasma-and tissue-based RAS mutational status were determined by BEAMing, respectively. RESULTS: A total of 280 patients from eight institutions were eligible. The overall agreement between plasma-and tissue-based analyses was 86.4%, with a positive percent agreement of 82.1% and negative percent agreement of 90.4%. From logistic regression analysis, lung metastasis alone indicated the most significant factor associated with discordance. The agreement between plasma-and tissue-based analyses was 64.5% in patients with lung metastasis alone (n = 31) indicating lower amount of ctDNA. Among the cases with lung metastasis alone, all plasma-and tissue-based analyses were perfectly concordant in cases with ≥20 mm of maximum lesion diameter or ≥10 lesions. CONCLUSION: The clinical validity of OncoBEAM TM RAS CRC kit was confirmed. Careful attention should be paid for mCRC patients with lung metastases alone having fewer metastases or smaller diameter lesions.

Cancer stem cells (CSCs) are known to influence chemoresistance, survival, relapse and metastasis. Aldehyde dehydrogenase (ALDH) functions as an epithelial CSC marker. In the present study, we investigated the involvement of ALDH in gastric CSC maintenance, chemoresistance and survival. Following screening for eight candidate markers (CD13, CD26, CD44, CD90, CD117, CD133, EpCAM and ALDH), five gastric cancer cell lines were found to contain small subpopulations of high ALDH activity (ALDH(high) cells). We also examined the involvement of ALDH(high) cell populations in human primary tumor samples. Immunodeficient NOD/SCID mice were inoculated with tumor tissues obtained from surgical specimens. ALDH(high) cells were found to persist in the xenotransplanted primary tumor samples. in the immunodeficient mice, ALDH(high) cells exhibited a greater sphere‑forming ability in vitro and tumorigenic potential in vivo, compared with subpopulations of low ALDH activity (ALDH(low) cells). Cell cultures treated with 5-fluoro-uracil and cisplatin exhibited higher numbers of ALDH(high) cells. Notch1 and Sonic hedgehog (Shh) expression was also found to increase in ALDH(high) cells compared with ALDH(low) cells. Therefore, it can be concluded that ALDH generates chemoresistance in gastric cancer cells through Notch1 and Shh signaling, suggesting novel treatment targets.

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