The acquired radioresistance in HeLa cells under conditions mimicking hypoxia was attenuated by a decreased expression of HIF subunit genes induced by RNA interference

Disturbance in the regulation of miR 17-92 cluster on HIF-1-α expression contributes to clinically relevant radioresistant cells: an in vitro study

Cellular radioresistance is one of the major obstacles to the effectiveness of cancer radiotherapy. In an attempt to elucidate the implication of HIF-1α and miR-17-92 expressions in refractory radioresistant cells and also in order to study the potential applications of these molecules as novel therapeutic modalities to overcome radioresistant cancers, the current study was conducted. Clinically relevant radioresistant (CRR) cells from human cancer cell lines were established by exposing to long-term fractionated radiation of X-rays. Correspondingly, microarray analysis and real time RT-PCR were performed to find miRNA involved in the CRR phenotype. HIF-1α was down-regulated and miR17-92 cluster was overexpressed in CRR cells by transfection. The expression of miR 17-3p was inhibited by specific inhibitors and miR 19a was enforced by mimics, respectively in parental cells. Overexpression of HIF-1α in parental cells or down regulation of HIF-1α in CRR cells were not involved in radioresistance. However, when HIF-1α was genetically modified to constitutively express under normoxia condition, it was rendered for protection to cells. Exogenous overexpression of miR 17-92 cluster in CRR cells resulted in abolition of HIF-1α expression and restored sensitizations to ionizing radiation. Attenuated expression of miR-17-3p in parental cells protected them from irradiation. Overall, fine-tune deregulation of miR 17-92 cluster in CRR cells might account for the accumulation of HIF-1α in the CRR cells following exposure to irradiation.

Functional Interaction of Hypoxia-Inducible Factor 2-Alpha and Autophagy Mediates Drug Resistance in Colon Cancer Cells

Hypoxia and the accumulation of hypoxia-inducible factors (HIFs) in tumors have been associated with therapeutic resistance and with autophagy establishment. We examined the effects of stable knockdown of HIF-1α or HIF-2α expression on autophagy and drug resistance in colon cancer cells. We found that under normoxic conditions, malignant cells exhibit increased basal levels of autophagy, compared with non-malignant cells, in addition to the previously reported coexpression of HIF-1α and HIF-2α. Knockdown of HIF-1α or HIF-2α expression resulted in increased autophagic and apoptotic cell death, indicating that the survival of cells is HIF-dependent. Cytotoxic-induced cell death was significantly increased by knockdown of HIFs but not by autophagy inhibition. Strikingly, although malignancy-resistant cells were sensitized to death by nutrient stress, the combination with HIF-2α depletion, but not with HIF-1α depletion, induced severe cell death. Oxidative stress levels were significantly increased as a result of HIF-2α specific inhibition or silencing suggesting that this may contribute to sensitize cells to death. The in vitro results were confirmed in vivo using a xenograft mouse model. We found that coordinated autophagy and mTOR inhibition enhanced cell death and induced tumor remission only in HIF-2α-silenced cells. Finally, using a specific HIF-2α inhibitor alone or in combination with drugs in patient-derived primary colon cancer cells, overcame their resistance to 5-FU or CCI-779, thus emphasizing the crucial role played by HIF-2α in promoting resistance and cell survival.

Role of metabolism in cancer cell radioresistance and radiosensitization methods

BACKGROUND

Radioresistance is a major factor leading to the failure of radiotherapy and poor prognosis in tumor patients. Following the application of radiotherapy, the activity of various metabolic pathways considerably changes, which may result in the development of resistance to radiation.

MAIN BODY

Here, we discussed the relationships between radioresistance and mitochondrial and glucose metabolic pathways, aiming to elucidate the interplay between the tumor cell metabolism and radiotherapy resistance. In this review, we additionally summarized the potential therapeutic targets in the metabolic pathways.

SHORT CONCLUSION

The aim of this review was to provide a theoretical basis and relevant references, which may lead to the improvement of the sensitivity of radiotherapy and prolong the survival of cancer patients.