Inhibition of mammalian target of rapamycin by rapamycin increases the radiosensitivity of esophageal carcinoma Eca109 cells

Potential Molecular Targets in the Setting of Chemoradiation for Esophageal Malignancies

Although the development of effective combined chemoradiation regimens for esophageal cancers has resulted in statistically significant survival benefits, the majority of patients treated with curative intent develop locoregional and/or distant relapse. Further improvements in disease control and survival will require the development of individualized therapy based on the knowledge of host and tumor genomics and potentially harnessing the host immune system. Although there are a number of gene targets that are amplified and proteins that are overexpressed in esophageal cancers, attempts to target several of these have not proven successful in unselected patients. Herein, we review our current state of knowledge regarding the molecular pathways implicated in esophageal carcinoma, and the available agents for targeting these pathways that may rationally be combined with standard chemoradiation, with the hope that this commentary will guide future efforts of novel combinations of therapy.

The future potential of Annona muricata L. extract and its bioactive compounds as radiation sensitizing agent: proposed mechanisms based on a systematic review

Despite technological advances in cancer treatment, especially in radiotherapy, many efforts are being made in improving cancer cell radio-sensitivity to increase therapeutic ratio and overcome cancer cell radio-resistance. In the present review, we evaluated the anticancer mechanism of Annona muricata L. (AM) leaves extract and its bioactive compounds such as annonaceous acetogenins, annomuricin, annonacin, or curcumin; and further correlated them with the potential of the mechanism to increase or to reduce cancer cells radio-sensitivity based on literature investigation. We see that AM has a promising future potential as a radio-sensitizer agent.

lncRNA KLF3-AS1 Suppresses Cell Migration and Invasion in ESCC by Impairing miR-185-5p-Targeted KLF3 Inhibition

Esophageal squamous cell carcinoma (ESCC) is a common cancer occurring in males and females worldwide. Accumulating evidence continues to highlight the crucial roles of long non-coding RNAs (lncRNAs) in the process of tumorigenesis. However, the regulatory mechanism of lncRNAs in ESCC remains unclear. The aim of this study is to elucidate the role of lncRNA Krüppel-like factor 3 antisense RNA 1 (KLF3-AS1) in ESCC by regulating miR-185-5p and KLF3. Initially, ESCC cell spheres with stem cell-like properties were prepared by suspension culture, and subsequently characterized by assessing colony formation ability and stem cell markers. LncRNA KLF3-AS1 was found to be poorly expressed in ESCC and could upregulate the expression of KLF3 by binding to miR-185-5p. lncRNA KLF3-AS1 upregulation was observed to inhibit miR-185-5p, thereby contributing to decreased expression of SOX2 and Oct4 (octamer-binding transcription factor 4). Furthermore, enhancement of lncRNA KLF3-AS1 resulted in reduced colony formation ability, cell invasion and migration, and tumor volume in vivo while promoting cell apoptosis in ESCC through downregulation of miR-185-5p. Collectively, this study indicated that lncRNA KLF3-AS1 inhibited ESCC cell invasion and migration by impairing miR-185-5p-mediated inhibition of KLF3, highlighting a promising novel potential target for ESCC treatment.

mTOR-Mediated Antioxidant Activation in Solid Tumor Radioresistance

Radiotherapy is widely used for the treatment of cancer patients, but tumor radioresistance presents serious therapy challenges. Tumor radioresistance is closely related to high levels of mTOR signaling in tumor tissues. Therefore, targeting the mTOR pathway might be a strategy to promote solid tumor sensitivity to ionizing radiation. Radioresistance is associated with enhanced antioxidant mechanisms in cancer cells. Therefore, examination of the relationship between mTOR signaling and antioxidant mechanism-linked radioresistance is required for effective radiotherapy. In particular, the effect of mTOR signaling on antioxidant glutathione induction by the Keap1-NRF2-xCT pathway is described in this review. This review is expected to assist in the identification of therapeutic adjuvants to increase the efficacy of radiotherapy.

Enhancement of mTOR signaling contributes to acquired X-ray and C-ion resistance in mouse squamous carcinoma cell line

Our aim was to evaluate whether repetition of C‐ion (carbon ion beam) irradiation induces radioresistance as well as repeated X‐ray irradiation in cancer cell lines, and to find the key molecular pathway for radioresistance by comparing radioresistant cancer cells with their parental cells. A mouse squamous cell carcinoma cell line, NR‐S1, and radioresistant cancer cells, NR‐S1‐C30 (C30) and NR‐S1‐X60 (X60), established by repetition of C‐ion and X‐ray irradiation, respectively, were used. X‐ray and C‐ion sensitivity, changes in lysosome, mitochondria, intracellular ATP and reactive oxygen species (ROS) level, and mechanistic target of rapamycin (mTOR) signaling were evaluated. Moreover, the effect of rapamycin on radioresistance was also assessed. X‐ray and C‐ion resistance of C30 cells was moderate, and the resistance of X60 cells was the highest in this study. In X60 cells, the amount of lysosome, mitochondria, intracellular ATP and ROS level were significantly increased, and mTOR and p70S6K (ribosomal protein S6 kinase p70) phosphorylation were enhanced compared with C30 and NR‐S1 cells. The inhibition of mTOR signaling was effective for X‐ray and C‐ion radiosensitization in both cell lines, especially in X60 cells in which X‐ray and C‐ion resistance was decreased to the same level as that in NR‐S1 cells. Our results indicated that the contribution to generate X‐ray and C‐ion resistance was less for repeated C‐ion irradiations compared with repeated X‐ray irradiation. Moreover, we found that activated mTOR signaling contributes to X‐ray and C‐ion resistance in the X60 cancer cells.

Crosstalk between autophagy and intracellular radiation response (Review)

Autophagy induced by radiation is critical to cell fate decision. Evidence now sheds light on the importance of autophagy induced by cancer radiotherapy. Traditional view considers radiation can directly or indirectly damage DNA which can activate DNA damage the repair signaling pathway, a large number of proteins participating in DNA damage repair signaling pathway such as p53, ATM, PARP1, FOXO3a, mTOR and SIRT1 involved in autophagy regulation. However, emerging recent evidence suggests radiation can also cause injury to extranuclear targets such as plasma membrane, mitochondria and endoplasmic reticulum (ER) and induce accumulation of ceramide, ROS, and Ca2+ concentration which activate many signaling pathways to modulate autophagy. Herein we review the role of autophagy in radiation therapy and the potent intracellular autophagic triggers induced by radiation. We aim to provide a more theoretical basis of radiation-induced autophagy, and provide novel targets for developing cytotoxic drugs to increase radiosensitivity.

Inhibition of mTOR enhances radiosensitivity of lung cancer cells and protects normal lung cells against radiation

Radiotherapy has been used for a long time as a standard therapy for cancer; however, there have been no recent research breakthroughs. Radioresistance and various side-effects lead to the unexpected outcomes of radiation therapy. Specific and accurate targeting as well as reduction of radioresistance have been major challenges for irradiation therapy. Recent studies have shown that rapamycin shows promise for inhibiting tumorigenesis by suppressing mammalian target of rapamycin (mTOR). We found that the combination of rapamycin with irradiation significantly diminished cell viability and colony formation, and increased cell apoptosis, as compared with irradiation alone in lung cancer cell line A549, suggesting that rapamycin can enhance the effectiveness of radiation therapy by sensitizing cancer cells to irradiation. Importantly, we observed that the adverse effects of irradiation on a healthy lung cell line (WI-38) were also offset. No enhanced protein expression of mTOR signaling was observed in WI-38 cells, which is normally elevated in lung cancer cells. Moreover, DNA damage was significantly less with the combination therapy than with irradiation therapy alone. Our data suggest that the incorporation of rapamycin during radiation therapy could be a potent way to improve the sensitivity and effectiveness of radiation therapy as well as to protect normal cells from being damaged by irradiation.

Chemoradiation in oesophageal cancer

Oesophageal cancer is the 8th most common cancer worldwide, and has significant mortality and morbidity rates. The two most common histological types, squamous cell carcinoma and adenocarcinoma, have different localizations, distinctive risk factors, and molecular mechanisms. Survival for patients with locoregional oesophageal cancer is poor when treated with surgery only, with 5-year survival less than 10-15%. Radiation therapy has limited efficacy when given alone. Concurrent chemoradiation improves local-regional control and facilitates margin-free resection when delivered preoperatively. Chemoradiation prolongs survival when given as definitive treatment or combined with surgery. Neoadjuvant chemoradiation also reduces risk of distant recurrence. To date, there is no data supporting the addition of targeted therapy to concurrent chemoradiation. Understanding molecular pathways regulating both radiosensitivity and tumorigenesis/invasion may lead to the discovery of new targeted agents, improving outcome of chemoradiation in terms of both locoregional and systemic control, ultimately resulting in prolonged survival.