Persistent Oxidative Stress in Vestibular Schwannomas After Stereotactic Radiation Therapy

Thiol oxidative stress-dependent degradation of transglutaminase2 via protein S-glutathionylation sensitizes 5-fluorouracil therapy in 5-fluorouracil-resistant colorectal cancer cells

5-Fluorouracil (5-Fu) is a first-line drug for colorectal cancer (CRC) therapy. However, the development of 5-Fu resistance limits its chemotherapeutic effectiveness and often leads to poor prognoses of CRC. Transglutaminase 2 (TGM2), a member of the transglutaminase family, is considered to be associated with chemoresistance through apoptotic prevention in various cancers including CRC. TGM2 was found to be overexpressed in two 5-Fu-resistant CRC cell lines and down-regulated by increased thiol oxidative stress induced by inhibition of glutathione reductase (GR). The present study aimed to explore the role of TGM2 in 5-Fu-resistant CRC and the mechanism of action by which the elevated thiol oxidative stress down-regulates TGM2 protein level. The results revealed that 5-Fu-resistance induced by overexpression of TGM2 in CRC cells was reversed through up-regulation of thiol oxidative stress. Knockdown of TGM2 increased the chemosensitivity of CRC cells to 5-Fu. Thiol oxidative stress potentially enhanced the therapeutic effect of 5-Fu in the resistant CRC cells by promotion of 5-Fu-induced apoptosis through down-regulation of TGM2. The elevated thiol oxidative stress increased the S-glutathionylation of TGM2 and led to proteasomal degradation of TGM2. Furthermore, Cys193 was identified as the S-glutathionylation site in TGM2, and its mutation resulted in thiol oxidative stress-mediated CRC cell apoptotic resistance. TGM2-induced EMT was also suppressed by the elevated thiol oxidative stress. A xenograft tumor model confirmed the effect of thiol oxidative stress in the reversal of 5-Fu resistance in CRC cells in vivo. TGM2 protein expression level was found to be significantly higher in human CRC specimens than in non-cancerous colorectal tissues. Taken together, the present data suggest an important role of TGM2 in 5-Fu resistance in CRC cells. Up-regulation of thiol oxidative stress could be a potential therapeutic approach for treating 5-Fu-resistant CRC and TGM2 may serve as a potential therapeutic target of thiol oxidative stress.

Reregulated mitochondrial dysfunction reverses cisplatin resistance microenvironment in colorectal cancer

Chemotherapy is one of the most basic and important treatments for malignant tumors. However, most chemotherapeutic drugs suffer from the resistance of tumor cells and lead to chemotherapy failure. Multidrug resistance (MDR) of tumor cells is the main obstacle to chemotherapy failure. The generation of MDR is not only the result of the performance of tumor cells, but the tumor microenvironment (TEM) also plays an important role in this process. The simultaneous dual intervention of cancer cells and the TEM has the potential to provide surprising results in overcoming MDR tumor therapy. Therefore, in this study, we designed a folate acid ligand-modified nanoparticle (FA-NPs) with a size of about 145 nm targeting multidrug-resistant colorectal cancer and successfully co-loaded cisplatin and Tris(2-chloroisopropyl) phosphate (TCPP). FA-NPs can enrich tumor sites through receptor-mediated endocytosis. In vitro mechanism studies have shown that nanoparticles can reverse cisplatin resistance mainly by further increasing the level of reactive oxygen species in tumor cells, breaking the homeostasis of the internal environment, then trigging mitochondrial stress, regulating drug resistance-related pathways, and improving the tumor drug resistance microenvironment; finally, the cisplatin recovers the antitumor effect with assistance from TCPP.

The biological underpinnings of radiation therapy for vestibular schwannomas: Review of the literature

OBJECTIVE

Radiation therapy is a mainstay in the treatment of numerous neoplasms. Numerous publications have reported good clinical outcomes for primary radiation therapy for Vestibular Schwannomas (VS). However, there are relatively few pathologic specimens of VSs available to evaluate post-radiation, which has led to a relative dearth in research on the cellular mechanisms underlying the effects of radiation therapy on VSs.

METHODS

Here we review the latest literature on the complex biological effects of radiation therapy on these benign tumors-including resistance to oxidative stress, mechanisms of DNA damage repair, alterations in normal growth factor pathways, changes in surrounding vasculature, and alterations in immune responses following radiation.

RESULTS

Although VSs are highly radioresistant, radiotherapy is often successful in arresting their growth.

CONCLUSION

By better understanding the mechanisms underlying these effects, we could potentially harness such mechanisms in the future to potentiate the clinical effects of radiotherapy on VSs.

LEVEL OF EVIDENCE

N/A.