This review addresses the majority of assays that have been published thus far, including the enrichment and detection steps and the markers used in these assays, accompanied by some biological issues of CTC and the results of clinical application harvested.

Rationale: Colorectal cancer (CRC) is a common malignant tumor of the digestive system. However, the efficacy of surgery and chemotherapy is limited. Ferroptosis is an iron-and reactive oxygen species (ROS)-dependent form of regulated cell death (RCD) and plays a vital role in tumor suppression. Ferroptosis inducing agents have been studied extensively as a novel promising way to fight against therapy resistant cancers. The aim of this study is to investigate the mechanism of action of tagitinin C (TC), a natural product, as a novel ferroptosis inducer in tumor suppression. Methods: The response of CRC cells to tagitinin C was assessed by cell viability assay, clonogenic assay, transwell migration assay, cell cycle assay and apoptosis assay. Molecular approaches including Western blot, RNA sequencing, quantitative real-time PCR and immunofluorescence were employed as well. Results: Tagitinin C, a sesquiterpene lactone isolated from Tithonia diversifolia, inhibits the growth of colorectal cancer cells including HCT116 cells, and induced an oxidative cellular microenvironment resulting in ferroptosis of HCT116 cells. Tagitinin C-induced ferroptosis was accompanied with the attenuation of glutathione (GSH) levels and increased in lipid peroxidation. Mechanistically, tagitinin C induced endoplasmic reticulum (ER) stress and oxidative stress, thus activating nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf2). As a downstream gene (effector) of Nrf2, heme oxygenase-1 (HO-1) expression increased significantly with the treatment of tagitinin C. Upregulated HO-1 led to the increase in the labile iron pool, which promoted lipid peroxidation, meanwhile tagitinin C showed synergistic anti-tumor effect together with erastin. Conclusion:In summary, we provided the evidence that tagitinin C induces ferroptosis in colorectal cancer cells and has synergistic effect together with erastin. Mechanistically, tagitinin C induces ferroptosis through ER stress-mediated activation of PERK-Nrf2-HO-1 signaling pathway. Tagitinin C, identified as a novel ferroptosis inducer, may be effective chemosensitizer that can expand the efficacy and range of chemotherapeutic agents.

Hypoxia inducible factors (HIFs) are activated in many tumors and show either promoter or suppressor activity depending on the tumor cell biology and background. However, the role of HIF member HIF-2α remains unclear in hepatocellular carcinoma (HCC). Here, HIF-2α expression was measured in HCC and paired peritumoral tissues by qRT-PCR, western blot analysis, and immunofluorescence assays, and the clinical significance was explored in 246 HCC patients. In cell culture, HIF-2α levels were over-expressed or knocked-down by use of expression or short hairpin RNA recombinant plasmid respectively. Cells were analyzed by immunoblot, chromatin immunoprecipitation coupled with microarray, co-immunoprecipitation, and histochemical staining. In vivo tumor growth was analyzed in nude mice. We found that the average expression of HIF-2α was relatively low in HCC tissues, and the decreased level was associated with lower overall survival (p=0.006). High HIF-2α expression in HCC cells induced higher levels of apoptosis and expression of pro-apoptotic proteins, and it inhibited cell and tumor growth. Furthermore, HIF-2α inhibited expression of the novel target gene transcription factor dimerization partner 3 (TFDP3). TFDP3 protein was found to bind with E2F transcription factor 1 (E2F1) and inhibit its transcriptional activity through both p53-dependent and -independent pathways. Re-introduction of TFDP3 expression reversed HIF-2α-induced apoptosis. Conclusions Data gathered from cell lines, tumorigenicity studies, and primary HCC samples demonstrate a negative role of HIF-2α in tumors, which is mediated by the TFDP3/E2F1 pathway. Our study provides evidence supporting a possible tumor suppressor role for HIF-2α and has uncovered a mechanism that links HIF-2α to a fundamental biological regulator, E2F1.