Circular RNAs (circRNAs) are a novel and unique class of noncoding RNAs that are back-spliced from pre-mRNAs. It has been confirmed that circRNAs are involved in various malignant behaviors of hepatocellular carcinoma (HCC). However, the role of circRNA in the regulation of ferroptosis and the underlying mechanism remain unknown. Here, cIARS (hsa_circ_0008367) was found to be the most highly expressed circRNA after sorafenib (SF) treatment in HCC cells. Small interfering RNA against cIARS (si-cIARS) significantly suppressed the cellular sensitivity to SF or Erastin through inactivating ferroptosis, which may be partially attributed to the inhibition of autophagy and ferritinophagy. Prediction analysis and mechanistic identification revealed that cIARS physically interacted with RNA binding protein (RBP) ALKBH5, which was a negative regulator of autophagic flux in HCC. The dissociation of BCL-2/BECN1 complex, mediated by ALKBH5 silencing was effectively blocked by si-cIARS. Furthermore, the inhibition of ferroptotic events, autophagic flux and ferritinophagy resulted from si-cIARS, were significantly rescued by ALKBH5 downregulation. Overall, cIARS may be an important circRNA, positively regulating SF-induced ferroptosis through suppressing the ALKBH5-mediated autophagy inhibition.

Emerging studies have shown that circular RNAs could be ideal biomarkers and even potential therapeutic targets for some tumors, including bladder cancer. However, only a few studies have investigated the circular RNAs in human bladder cancer. The key circular RNA molecules are closely related to bladder cancer and their roles remain largely unknown. Here, we investigated a novel circular RNA molecule, hsa-circ-0003221(circPTK2), which is differentially expressed in bladder carcinoma. Significant differential expression levels of circPTK2 were confirmed with quantitative PCR in 40 pairs of tissue and blood samples from patients with bladder carcinoma. Moreover, circPTK2 levels both in tissue and blood were significantly correlated with several clinicopathologic characteristics, including poor differentiation (P = 0.0103 in tissue, P = 0.024 in blood), N2-N3 lymph node metastasis (P = 0.0065 in tissue, P = 0.016 in blood), and T(II-III-IV) stage (P = 0.008 in tissue, P = 0.0003 in blood). Quantitative PCR results confirmed that circPTK2 is highly expressed in migrated cells separated by Transwell assay and in metastatic lymph nodes of tumors transplanted in nude mice. In vitro silence of circPTK2 by small interfering RNA inhibited the proliferation and migration of bladder cancer cells. On the contrary, circPTK2 overexpression promoted proliferation and migration. This study showed that circPTK2 promotes proliferation and migration of cells and may be a novel potential biomarker and therapeutic target for bladder cancer diagnosis and therapy.

Hepatocellular carcinoma (HCC) is a highly malignant disease with a poor prognosis and high mortality due to a low early diagnosis rate, resistance to systemic treatments and progression to late-stage liver disease. Owing to limitations in the detection of HCC and the lack of awareness of healthcare systems, fewer than 40% of HCC patients are eligible for surgery due to advanced stages of the disease at the time of diagnosis and the occurrence of multiple lesions in the cirrhotic or fibrotic liver. At present, the updated American Association for the Study of Liver Disease (AASLD) guidelines no longer recommend alpha-fetoprotein (AFP) testing as a part of diagnostic evaluation. Thus, it is imperative to establish a novel diagnostic strategy with high sensitivity and reliability to monitor risk factors to detect HCC at an early stage. In recent years, “liquid biopsy,” (including circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA)), has emerged as a technique for the characterization of circulating cells, providing a strong basis for the individualized treatment of patients. As a noninvasive detection method, liquid biopsy is expected to play an important role in the early diagnosis, dynamic monitoring of cancer patients and drug screening. In this review, we will focus on the clinical applications, recent studies and future prospects of liquid biopsy, particularly focusing on HCC.