To live or let die: Unclear task of autophagy in the radiosensitization battle

Role of autophagy in modulating tumor cell radiosensitivity: Exploring pharmacological interventions for glioblastoma multiforme treatment

Autophagy is an innate cellular process characterized by self-digestion, wherein cells degrade or recycle aged proteins, misfolded proteins, and damaged organelles via lysosomal pathways. Its crucial role in maintaining cellular homeostasis, ensuring development and survival is well established. In the context of cancer therapy, autophagy's importance is firmly recognized, given its critical impact on treatment efficacy. Following radiotherapy, several factors can modulate autophagy including parameters related to radiation type and delivery methods. The concomitant use of chemotherapy with radiotherapy further influences autophagy, potentially either enhancing radiosensitivity or promoting radioresistance. This review article discusses some pharmacological agents and drugs capable of modulating autophagy levels in conjunction with radiation in tumor cells, with a focus on those identified as potential radiosensitizers in glioblastoma multiforme treatment.

Blocking ACSL6 Compromises Autophagy via FLI1-Mediated Downregulation of COLs to Radiosensitize Lung Cancer

Lung cancer (LC) is the leading cause of cancer-related mortality worldwide. Radiotherapy is the main component of LC treatment; however, its efficacy is often limited by radioresistance development, resulting in unsatisfactory clinical outcomes. Here, we found that LC radiosensitivity is up-regulated by decreased expression of long-chain acyl-CoA synthase 6 (ACSL6) after irradiation. Deletion of ACSL6 results in significant elevation of Friend leukemia integration 1 transcription factor (FLI1) and a marked decline of collagens (COLs). Blocking of ACSL6 impairs the tumor growth and upregulates FLI1, which reduces the levels of COLs and compromises irradiation-induced autophagy, leading to considerable therapeutic benefits during radiotherapy. Moreover, the direct interaction between ACSL6 and FLI1 and engagement between FLI1 and COLs indicates the involvement of the ACSL6-FLI1-COL axis. Finally, the potently adjusted autophagy flux reduces its otherwise contributive capability in surviving irradiation stress and leads to satisfactory radiosensitization for LC radiotherapy. These results demonstrate that enhanced ACSL6 expression promotes the aggressive performance of irradiated LC through increased FLI1-COL-mediated autophagy flux. Thus, the ACSL6-FLI1-Col-autophagy axis may be targeted to enhance the radiosensitivity of LC and improve the management of LC in radiotherapy.

Enhancing autophagy leads to increased cell death in radiation-treated cervical cancer cells

This study was carried out to determine the effect of autophagy modulation in radiation treatment of cervical cancer cells. HeLa and CaSki cells were irradiated with γ-rays (2 Gy/min) after treatment with an autophagy inducer (rapamycin) and inhibitor (3-MA). Expression of LC3 and cell death in two cell preparations were examined. In addition, expression of Caspase-3 and PARP were examined after radiation alone and with autophagy inhibitor treatment. A notable increment of LC3 expression was detected after radiation in both cell lines. Cell viability was observed to decrease in 3-MA-treated cells compared to radiation alone, and even further in rapamycin-treated cells. Apoptosis was confirmed to occur later than autophagy in radiation treatment, and inhibition of autophagy derived a decrease in apoptosis. In conclusion, radiation-induced autophagy may be regulated by modulators, and autophagy augmentation yields an increase in cervical cancer cell death under radiation.Impact statementWhat is already known on this subject? Autophagy is known to contribute both to tumour cell survival and death against radiation therapy. The effect of induction or inhibition of radiation-induced autophagy on cervical cancer cell death is not clear.What the results of this study add? Cell viability was observed to decrease in 3-MA-treated cells compared to radiation alone, and even further in rapamycin-treated cells. Apoptosis occurred later than autophagy in radiation treatment, and inhibition of autophagy derived a decrease in apoptosis.What the implications are of these findings for clinical practice and/or further research? Our results suggest that radiation-induced autophagy may be regulated by modulators, and autophagy augmentation yields an increase in cervical cancer cell death under radiation.

Oligodendrocyte Progenitors Display Enhanced Proliferation and Autophagy after Space Flight

Intracranial hypertension (ICP) and visual impairment intracranial pressure (VIIP) are some of the consequences of long-term space missions. Here we examined the behavior of oligodendrocyte progenitors (OLPs) after space flight using time-lapse microscopy. We show that most OLPs divided more than ground control (GC) counterparts did. Nonetheless, a subpopulation of OLPs flown to space presented a significant increase in autophagic cell death. Examination of the proteomic profile of the secretome of space flown OLPs (SPC-OLPs) revealed that the stress protein heat shock protein-90 beta "HSP-90β" was the 5th most enriched (6.8 times) and the secreted protein acidic and rich in cysteine "SPARC" was the 7th most enriched (5.2 times), with respect to ground control cells. SPARC induces endoplasmic reticulum stress, which leads to autophagy. Given the roles and importance of these two proteins in mammalian cells' metabolism, their upregulation may hold the key to modulating cell proliferation and autophagy, in order to mitigate ICP and VIIP during and after space missions.

Mechanisms of radioresistance and the underlying signaling pathways in colorectal cancer cells

Radiotherapy is one of the most common modalities for the treatment of a wide range of tumors, including colorectal cancer (CRC); however, radioresistance of cancer cells remains a major limitation for this treatment. Following radiotherapy, the activities of various cellular mechanisms and cell signaling pathways are altered, resulting in the development of radioresistance, which leads to therapeutic failure and poor prognosis in patients with cancer. Furthermore, even though several inhibitors have been developed to target tumor resistance, these molecules can induce side effects in nontumor cells due to low specificity and efficiency. However, the role of these mechanisms in CRC has not been extensively studied. This review discusses recent studies regarding the relationship between radioresistance and the alterations in a series of cellular mechanisms and cell signaling pathways that lead to therapeutic failure and tumor recurrence. Our review also presents recent advances in the in vitro/in vivo study models aimed at investigating the radioresistance mechanism in CRC. Furthermore, it provides a relevant biochemical basis in theory, which can be useful to improve radiotherapy sensitivity and prolong patient survival.

Association of ATG16L1 rs2241880 and TP53 rs1042522 with characteristics and course of diffuse large B-cell lymphoma

BACKGROUND

Diffuse large B-cell lymphoma (DLBCL) represents the most frequent lymphoma in adults. Prognosis for DLBCL patients may be evaluated through the most prominent clinical/laboratory parameters or pattern of gene expression. In order to improve prognostic/prediction scores or provide new therapeutic targets, novel genetic markers are needed. This study evaluates the association of ATG16L1 rs2241880 and TP53 rs1042522 with clinical characteristics and course of DLBCL.

METHODS

The study included 108 DLCBL patients treated with R-CHOP. Of these, 44 patients were subjected to stem cell transplantation and 55 to radiotherapy. Genotyping was performed by TaqMan genotyping assays.

RESULTS

Amongst analyzed characteristics and prognostic scores, genotypes were associated with clinical stage (TP53 CG+CC vs GG p = 0.06), extranodal disease (ATG16L1 AG vs AA p = 0.07; AG vs GG p = 0.04), lymphocyte-to-monocyte ratio (LMR) (ATG16L1 AA vs AG+GG, p = 0.052; AA vs GG, p = 0.054) and neutrophils-to-lymphocytes ratio (NLR) (ATG16L1 AA vs AG+GG, p = 0.033; AA vs GG, p = 0.003). Analyzed genotypes didn't impact response to therapy, relapse and therapy-related complications. Considering outcome, patients with ATG16L1 AA had higher survival rate than GG carriers (p = 0.04). In all patients, duration of overall survival (OS) and relapse free survival (RFS) was not affected by analyzed genotypes. When subjected to radiotherapy, patients with ATG16L1 A allele (p = 0.05) or AA genotype (p = 0.03) had superior OS.

CONCLUSION

Our results demonstrated the association of TP53 rs1042522 with clinical stage and ATG16L1 rs2241880 with extranodal disease, LMR and NLR. The impact of ATG16L1 genotypes on OS in patients subjected to radiotherapy, indicates significance of individual single nucleotide polymorphisms (SNPs) in particular subgroups of DLBCL.

Hypoxia-Induced Cancer Cell Responses Driving Radioresistance of Hypoxic Tumors: Approaches to Targeting and Radiosensitizing

Simple Summary

Some regions of aggressive malignancies experience hypoxia due to inadequate blood supply. Cancer cells adapting to hypoxic conditions somehow become more resistant to radiation exposure and this decreases the efficacy of radiotherapy toward hypoxic tumors. The present review article helps clarify two intriguing points: why hypoxia-adapted cancer cells turn out radioresistant and how they can be rendered more radiosensitive. The critical molecular targets associated with intratumoral hypoxia and various approaches are here discussed which may be used for sensitizing hypoxic tumors to radiotherapy.

Abstract

Within aggressive malignancies, there usually are the “hypoxic zones”—poorly vascularized regions where tumor cells undergo oxygen deficiency through inadequate blood supply. Besides, hypoxia may arise in tumors as a result of antiangiogenic therapy or transarterial embolization. Adapting to hypoxia, tumor cells acquire a hypoxia-resistant phenotype with the characteristic alterations in signaling, gene expression and metabolism. Both the lack of oxygen by itself and the hypoxia-responsive phenotypic modulations render tumor cells more radioresistant, so that hypoxic tumors are a serious challenge for radiotherapy. An understanding of causes of the radioresistance of hypoxic tumors would help to develop novel ways for overcoming this challenge. Molecular targets for and various approaches to radiosensitizing hypoxic tumors are considered in the present review. It is here analyzed how the hypoxia-induced cellular responses involving hypoxia-inducible factor-1, heat shock transcription factor 1, heat shock proteins, glucose-regulated proteins, epigenetic regulators, autophagy, energy metabolism reprogramming, epithelial–mesenchymal transition and exosome generation contribute to the radioresistance of hypoxic tumors or may be inhibited for attenuating this radioresistance. The pretreatments with a multitarget inhibition of the cancer cell adaptation to hypoxia seem to be a promising approach to sensitizing hypoxic carcinomas, gliomas, lymphomas, sarcomas to radiotherapy and, also, liver tumors to radioembolization.

Lys05 - A Promising Autophagy Inhibitor in the Radiosensitization Battle: Phosphoproteomic Perspective

BACKGROUND

Autophagy is a crucial factor contributing to radioresistance during radiotherapy. Although Lys05 has proven its ability to improve the results of radiotherapy through the inhibition of autophagy, molecular mechanisms of this inhibition remain elusive. We aimed to describe the molecular mechanisms involved in Lys05-induced inhibition of autophagy.

MATERIALS AND METHODS

Radioresistant human non-small cell lung carcinoma cells (H1299, p53-negative) and methods of quantitative phosphoproteomics were employed to define the molecular mechanisms involved in Lys05-induced inhibition of autophagy.

RESULTS

We confirmed that at an early stage after irradiation, autophagy was induced, whereas at a later stage after irradiation, it was inhibited. The early-stage induction of autophagy was characterized mainly by the activation of biosynthetic and metabolic processes through up- or down-regulation of the critical autophagic regulatory proteins Sequestosome-1 (SQSTM1) and proline-rich AKT1 substrate 1 (AKT1S1). The late-stage inhibition of autophagy was attributed mainly to down-regulation of Unc-51 like autophagy-activating kinase 1 (ULK1) through phosphorylation at Ser638.

CONCLUSION

This work contributes to emerging phosphoproteomic insights into autophagy-mediated global signaling in lung cancer cells, which might consequently facilitate the development of precision medicine therapeutics.

Ubiquitin-specific protease 14 promotes radio-resistance and suppresses autophagy in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is a common malignant tumor in the world. Radiotherapy is one of the standard therapies for patients with OSCC, but its clinical efficiency is limited due to radioresistance. In this study, we identified a mechanism of such resistance regulated by Ubiquitin-specific protease 14 (USP14). USP14 expression was significantly increased in clinical OSCC tissue samples and cell lines, and OSCC patients with high USP14 expression predicted poor overall survival rate. Additionally, a negative correlation between USP14 and LC3B was observed in patients with OSCC. We then found that irradiation (IR)-reduced cell survival of OSCC cells lines was further decreased when USP14 was knocked down. However, USP14 over-expression significantly promoted the cell viability of OSCC cells after IR treatment. Colony formation analysis confirmed thatafter IR treatment,USP14 knockdown markedly decreased the proliferation of OSCC cells, but over-expressing USP14 significantly up-regulated the proliferative activity of OSCC cells. Furthermore, DNA damage caused by IR was enhanced by USP14 knockdown, while been suppressed in OSCC cells with USP14 over-expression. Additionally, IR-inducedapoptosis was further promoted by USP14 knockdown in OSCC cells, which was, however, significantly abolished by USP14 over-expression.Moreover, our in vivo studies showed that IR-reduced tumor growth and tumor weight were further enhanced by USP14 knockdown in OSCC tumor-bearing nude mice. Finally, we found that USP14 knockdown could promote IR-induced autophagy by increasing LC3BII and γH2AX expression levels in IR-treated OSCC cells. However, this event was markedly abolished by ATG5 knockdown, subsequently restoring the cell proliferation in IR-incubated OSCC cells.Finally, we found that USP14-mediated apoptosis was autophagy-dependent in IR-treated OSCC cells. Taken together, these findings suggested that suppressing USP14 could alleviateradioresistancein OSCC both in vitro and in vivo by inducing apoptosis and autophagy, and thus could be served as a promising therapeutic strategy for OSCC treatment.

Effect of autophagy on irradiation‑induced damage in osteoblast‑like MC3T3‑E1 cells

Autophagy is activated under radiation stress, which serves an important role in maintaining bone homeostasis. However, the underlying mechanisms of irradiation-induced autophagy in bone homeostasis is not well understood. The present study aimed to determine the effects of radiation-activated autophagy on pre-osteoblastic MC3T3-E1 cells. X-ray irradiation activated autophagy in a dose-dependent manner, with an increased fluorescence intensity of monodansylcadaverine staining, increased ratio of microtubule-associated protein 1 light chain 3β (LC3)-II/LC3-I, decreased p62 expression, and increased ATG5 and beclin-1 expression levels in MC3T3-E1 cells 72 h after irradiation compared with those in non-irradiated MC3T3-E1 cells. Irradiation reduced colony formation and mineralization in a dose-dependent manner in MC3T3-E1 cells at 2 and 3 weeks after irradiation, respectively. Decreased levels of alkaline phosphatase activity and runt-related transcription factor 2 expression were observed at 72 h post-irradiation. In addition, irradiation-induced apoptosis was accompanied by a decreased ratio of Bcl-2/BAX protein and increased the activity of caspase-3. By contrast, doxycycline (DOX)-inhibited autophagy attenuated the decreased colony formation and mineralization, and aggravated the increased cell apoptosis in irradiated MC3T3-E1 cells. Furthermore, the ratio of phosphorylated P38/P38 was observed to be higher following DOX treatment within 1 week of irradiation, which was reversed 2 weeks post-irradiation. In conclusion, DOX-inhibited autophagy aggravated X-ray irradiation-induced apoptosis at an early stage, but maintained cell proliferation and mineralization at a late stage in irradiated MC3T3-E1 cells.

Linc-RA1 inhibits autophagy and promotes radioresistance by preventing H2Bub1/USP44 combination in glioma cells

Radiotherapy is one of the standard treatments for glioma patients; however, its clinical efficacy is limited by radioresistance. We identified a mechanism of such resistance mediated by linc-RA1 (radioresistance-associated long intergenic noncoding RNA 1). Linc-RA1 was upregulated in radioresistant glioma cells and glioma tissue samples, compared with radiosensitive cells and nontumor tissues. Linc-RA1 was associated with inferior overall survival and advanced clinical stage of glioma. Linc-RA1 promoted glioma radioresistance in vitro and in vivo. Mechanistically, linc-RA1 stabilized the level of H2B K120 monoubiquitination (H2Bub1) by combining with H2B and inhibiting the interaction between H2Bub1 and ubiquitin-specific protease 44 (USP44), which inhibited autophagy, thus contributing to glioma radioresistance. These results reveal that linc-RA1-mediated autophagy is a key mechanism of radioresistance and is an actionable target for improving radiotherapy efficacy in patients with glioma.

FGFR Inhibition Enhances Sensitivity to Radiation in Non-Small Cell Lung Cancer

FGFRs are commonly altered in non-small cell lung cancer (NSCLC). FGFRs activate multiple pathways including RAS/RAF/MAPK, PI3K/AKT, and STAT, which may play a role in the cellular response to radiation. We investigated the effects of combining the selective FGFR 1-3 tyrosine kinase inhibitor AZD4547 with radiation in cell line and xenograft models of NSCLC. NSCLC cell lines were assessed with proliferation, clonogenic survival, apoptosis, autophagy, cell cycle, and DNA damage signaling and repair assays. In vivo xenografts and IHC were used to confirm in vitro results. NSCLC cell lines demonstrated varying degrees of FGFR protein and mRNA expression. In vitro clonogenic survival assays showed radiosensitization with AZD4547 in two NSCLC cell lines. In these two cell lines, an increase in apoptosis and autophagy was observed with combined radiation and AZD4547. The addition of AZD4547 to radiation did not significantly affect γH2AX foci formation. Enhanced xenograft tumor growth delay was observed with the combination of radiation and AZD4547 compared with radiation or drug alone. IHC results revealed inhibition of pMAPK and pS6 and demonstrated an increase in apoptosis in the radiation plus AZD4547 group. This study demonstrates that FGFR inhibition by AZD4547 enhances the response of radiation in FGFR-expressing NSCLC in vitro and in vivo model systems. These results support further investigation of combining FGFR inhibition with radiation as a clinical therapeutic strategy.

Fibroblast Growth Factor Receptors as Targets for Radiosensitization in Head and Neck Squamous Cell Carcinomas

PURPOSE

We examined the capacity of the pan-fibroblast growth factor receptor (FGFR) inhibitor AZD4547 to augment radiation response across a panel of head and neck squamous cell carcinoma (HNSCC) cell lines and xenografts.

METHODS AND MATERIALS

FGFR1, FGFR2, and FGFR3 RNA in situ hybridization expression was assessed in a cohort of HNSCC patient samples, cell lines, and patient-derived xenografts (PDXs). In vitro effects of AZD4547 and radiation on cell survival, FGFR signaling, apoptosis, autophagy, cell cycle, and DNA damage repair were evaluated. Reverse phase protein array was used to identify differentially phosphorylated proteins in cells treated with AZD4547. In vivo tumor responses were evaluated in cell lines and PDX models.

RESULTS

FGFR1, FGFR2, and FGFR3 RNA in situ hybridization were expressed in 41%, 81%, and 89% of 107 oropharynx patient samples. Sensitivity to AZD4547 did not directly correlate with FGFR protein or RNA expression. In sensitive cell lines, AZD4547 inhibited p-MAPK in a time-dependent manner. Significant radiosensitization with AZD4547 was observed in cell lines that were sensitive to AZD4547. The mechanism underlying these effects appears to be multifactorial, involving inhibition of the MTOR pathway and subsequent enhancement of autophagy and activation of apoptotic pathways. Significant tumor growth delay was observed when AZD4547 was combined with radiation compared with radiation or drug alone in an FGFR-expressing HNSCC cell line xenograft and PDX.

CONCLUSIONS

These findings suggest that AZD4547 can augment the response of radiation in FGFR-expressing HNSCC in vivo model systems. FGFR1 and FGFR2 may prove worthy targets for radiosensitization in HNSCC clinical investigations.

The role of Atg7-mediated autophagy in ionizing radiation-induced neural stem cell damage

Impairment of neurogenesis is thought to be one of the important mechanisms underlying radiation-induced cognitive decline. Self-renewal and differentiation of neural stem cells (NSCs) are important components of neurogenesis. It has been well established that autophagy plays an important role in neurodegenerative conditions, however, its role in radiation-induced cognitive decline remains unclear. Our previous studies have found that ionizing radiation (IR) induces autophagy in mouse neurons, and minocycline, an antibiotic that can cross the blood-brain barrier, protects neurons from radiation-induced apoptosis through promoting autophagy, thus may contribute to the improvement of mouse cognitive performance after whole-brain irradiation. In the present study, we investigated whether autophagy is involved in radiation-induced damage in self-renewal and differentiation of NSCs. We found that NSCs were extremely sensitive to IR. Irradiation induced autophagy in NSCs in a dose-dependent manner. Atg7 knockdown significantly decreased autophagy, thus increased the apoptosis levels in irradiated NSCs, suggesting that autophagy protected NSCs from radiation-induced apoptosis. Moreover, compared with the negative control NSCs, the neurosphere size was significantly reduced and the neuronal differentiation was notably inhibited in Atg7-deficient NSCs after irradiation, indicating that autophagy defect could exacerbate radiation-induced reduction in NSC self-renewal and differentiation potential. In conclusion, down-regulating autophagy by selective Atg7 knockdown in NSCs enhanced radiation-induced NSC damage, suggesting an important protective role of autophagy in maintaining neurogenesis. Along with the protective effect of autophagy on irradiated neurons, our results on NSCs not only shed the light on the involvement of autophagy in the development of radiation-induced cognitive decline, but also provided a potential target for preventing cognitive impairment after cranial radiation exposure.

A Potent Autophagy Inhibitor (Lys05) Enhances the Impact of Ionizing Radiation on Human Lung Cancer Cells H1299

Autophagy inhibition through small-molecule inhibitors is one of the approaches to increase the efficiency of radiotherapy in oncological patients. A new inhibitor-Lys05-with the potential to accumulate within lysosomes and to block autophagy was discovered a few years ago. Several studies have addressed its chemosensitizing effects but nothing is known about its impact in the context of ionizing radiation (IR). To describe its role in radiosensitization, we employed radioresistant human non-small cell lung carcinoma cells (H1299, p53-negative). Combined treatment of H1299 cells by Lys05 together with IR decreased cell survival in the clonogenic assay and real-time monitoring of cell growth more than either Lys05 or IR alone. Immunodetection of LC3 and p62/SQSTM1 indicated that autophagy was inhibited, which correlated with increased SQSTM1 and decreased BNIP3 gene expression determined by qRT-PCR. Fluorescence microscopy and flow cytometry uncovered an accumulation of lysosomes. Similarly, transmission electron microscopy demonstrated the accumulation of autophagosomes confirming the ability of Lys05 to potentiate autophagy inhibition in H1299 cells. We report here for the first time that Lys05 could be utilized in combination with IR as a promising future strategy in the eradication of lung cancer cells.

Dual effects of gossypol on human hepatocellular carcinoma via endoplasmic reticulum stress and autophagy

Treatment outcomes for hepatocellular carcinoma (HCC) remain unsatisfactory, and effective new therapeutic methods are urgently needed. Gossypol has been shown to have an anti-HCC effect, but the underlying mechanism requires further study. In this study, we found gossypol inhibited HCC cells in vitro and in vivo. Typical apoptosis was induced in HCC cells. Dilated ER and autophagosomes were observed by electron microscopy, and the activation of the unfolded protein response and autophagy markers suggested that gossypol induced both ER stress and autophagy. C/EBP homologous protein was the key factor that led to apoptotic cell death, whereas inositol-requiring enzyme 1α and eukaryotic initiation factor 2α played a protective role. Autophagy protected the cells from ER stress-related apoptosis. Both in vitro and in vivo studies indicated that inhibition of autophagy enhanced the anti-HCC effect of gossypol. Taken together, ER stress is the molecular mechanism underlying gossypol-induced apoptosis and autophagy. Gossypol exhibits anti-HCC activity primarily through the activation of apoptosis. However, gossypol-induced autophagy protects HCC cells from ER stress. Therefore, a combination therapy of gossypol and autophagy inhibitors may lead to an enhanced anti-HCC effect.

Targeting autophagy in thyroid cancers

Thyroid cancer is one of the most common endocrine malignancies. Although the prognosis for the majority of thyroid cancers is relatively good, patients with metastatic, radioiodine-refractory or anaplastic thyroid cancers have an unfavorable outcome. With the gradual understanding of the oncogenic events in thyroid cancers, molecularly targeted therapy using tyrosine kinase inhibitors (TKIs) is greatly changing the therapeutic landscape of radioiodine-refractory differentiated thyroid cancers (RR-DTCs), but intrinsic and acquired drug resistance, as well as adverse effects, may limit their clinical efficacy and use. In this setting, development of synergistic treatment options is of clinical significance, which may enhance the therapeutic effect of current TKIs and further overcome the resultant drug resistance. Autophagy is a critical cellular process involved not only in protecting cells and organisms from stressors but also in the maintenance and development of various kinds of cancers. Substantial studies have explored the complex role of autophagy in thyroid cancers. Specifically, autophagy plays important roles in mediating the drug resistance of small-molecular therapeutics, in regulating the dedifferentiation process of thyroid cancers and also in affecting the treatment outcome of radioiodine therapy. Exploring how autophagy intertwines in the development and dedifferentiation process of thyroid cancers is essential, which will enable a more profound understanding of the physiopathology of thyroid cancers. More importantly, these advances may fuel future development of autophagy-targeted therapeutic strategies for patients with thyroid cancers. Herein, we summarize the most recent evidence uncovering the role of autophagy in thyroid cancers and highlight future research perspectives in this regard.

Rationale for combination of radiation therapy and immune checkpoint blockers to improve cancer treatment

Radiation therapy for cancer is considered to be immunosuppressive. However, the cellular response after radiation therapy may stimulate or suppress an immune response. The effect may vary with the tumor type and occasionally tumor regressions have been observed outside the irradiated volume, both in animal studies and in the clinic. A renewed interest in the role of immunity for the observed effect of radiation came with the current recognized role of immune checkpoint blockers (ICBs) for control of selected cancer types. We therefore here review preclinical studies and clinical reports on the interaction of ICBs and radiation as a basis for further clinical trials. Some tumor types where the combination of these modalities seems especially promising are also proposed.

Radio-sensitizing effects of VE-821 and beyond: Distinct phosphoproteomic and metabolomic changes after ATR inhibition in irradiated MOLT-4 cells

Current anti-cancer strategy takes advantage of tumour specific abnormalities in DNA damage response to radio- or chemo-therapy. Inhibition of the ATR/Chk1 pathway has been shown to be synthetically lethal in cells with high levels of oncogene-induced replication stress and in p53- or ATM- deficient cells. In the presented study, we aimed to elucidate molecular mechanisms underlying radiosensitization of T-lymphocyte leukemic MOLT-4 cells by VE-821, a higly potent and specific inhibitor of ATR. We combined multiple approaches: cell biology techniques to reveal the inhibitor-induced phenotypes, and quantitative proteomics, phosphoproteomics, and metabolomics to comprehensively describe drug-induced changes in irradiated cells. VE-821 radiosensitized MOLT-4 cells, and furthermore 10 μM VE-821 significantly affected proliferation of sham-irradiated MOLT-4 cells. We detected 623 differentially regulated phosphorylation sites. We revealed changes not only in DDR-related pathways and kinases, but also in pathways and kinases involved in maintaining cellular metabolism. Notably, we found downregulation of mTOR, the main regulator of cellular metabolism, which was most likely caused by an off-target effect of the inhibitor, and we propose that mTOR inhibition could be one of the factors contributing to the phenotype observed after treating MOLT-4 cells with 10 μM VE-821. In the metabolomic analysis, 206 intermediary metabolites were detected. The data indicated that VE-821 potentiated metabolic disruption induced by irradiation and affected the response to irradiation-induced oxidative stress. Upon irradiation, recovery of damaged deoxynucleotides might be affected by VE-821, hampering DNA repair by their deficiency. Taken together, this is the first study describing a complex scenario of cellular events that might be ATR-dependent or triggered by ATR inhibition in irradiated MOLT-4 cells. Data are available via ProteomeXchange with identifier PXD008925.

Autophagy-regulating microRNAs: potential targets for improving radiotherapy

BACKGROUND

Radiotherapy (RT) is one of the most important therapeutic strategies against cancer. However, resistance of cancer cells to radiation remains a major challenge for RT. Thus, novel strategies to overcome cancer cell radioresistance are urgent. Macroautophagy (hereafter referred to as autophagy) is a biological process by which damaged cell components can be removed and accordingly represent a cytoprotective mechanism. Because radiation-induced autophagy is associated with either cell death or radioresistance of cancer cells, a deeper understanding of the autophagy mechanism triggered by radiation will expedite a development of strategies improving the efficacy of RT. MicroRNAs (miRNAs) are involved in many biological processes. Mounting evidence indicates that many miRNAs are involved in regulation of the autophagic process induced by radiation insult, but the underlying mechanisms remain obscure. Therefore, a deep understanding of the mechanisms of miRNAs in regulating autophagy and radioresistance will provide a new perspective for RT against cancer.

METHODS

We summarized the recent pertinent literature from various electronic databases, including PubMed. We reviewed the radiation-induced autophagy response and its association of the role, function and regulation of miRNAs, and discussed the feasibility of targeting autophagy-related miRNAs to improve the efficacy of RT.

CONCLUSION

The beneficial or harmful effect of autophagy may depend on the types of cancer and stress. The cytoprotective role of autophagy plays a dominant role in cancer RT. For most tumor cells, reducing radiation-induced autophagy can improve the efficacy of RT. MiRNAs have been confirmed to take part in the autophagy regulatory network of cancer RT, the autophagy-regulating miRNAs therefore could be developed as potential targets for improving RT.

Insulin-like growth factor-1 receptor knockdown enhances radiosensitivity via the HIF-1α pathway and attenuates ATM/H2AX/53BP1 DNA repair activation in human lung squamous carcinoma cells

Insulin-like growth factor-1 receptor (IGF-1R) is a cell membrane receptor involved in cell proliferation and apoptosis, which is highly expressed in lung squamous cell carcinoma (SCC). The present study aimed to observe the influence of IGF-1R silencing on the radiosensitivity of SCC and investigate the potential mechanisms involved. Human lung SCC H520 cells with relatively high expression of IGF-1R were used. IGF-1R expression was silenced using short hairpin RNA. The influence of IGF-1R silencing on radiosensitivity and apoptosis was assessed using a clone formation assay and flow cytometry. The expression levels of proteins relevant in DNA damage repair and hypoxic signaling pathways were analyzed using western blotting. Decreased expression of IGF-1R led to an increase in the sensitivity of H520 cells to irradiation. Molecular analysis showed that the reduced expression of IGF-1R decreased the protein expression of ataxia-telangiectasia mutated (ATM), H2A histone family member X (H2AX) and p53 binding protein 1 (53BP1), which are associated with the DNA repair pathway. Furthermore, 53BP1 is also known to be involved in apoptosis. Proteins involved in the hypoxic pathway, including hypoxia inducible factor 1 α (HIF-1α), matrix metallopeptidase 9 (MMP-9) and vascular endothelial growth factor A (VEGFA) were also involved in the radiosensitivity. In conclusion, decreased expression of IGF-1R leads to improved radiosensitivity of SCC cells, and the underlying mechanism may be associated with the decreased expression of proteins involved in ATM/H2AX/53BP1 DNA damage repair and the HIF-1α/MMP-9 hypoxic pathway, which results in the induction of apoptosis and increased radiosensitivity. These findings suggest that targeting of IGF-1R may represent a novel approach for lung SCC radiation treatment.

Radiosensitization by Marine Sponge Agelas sp. Extracts in Hepatocellular Carcinoma Cells with Autophagy Induction

Although radiation therapy is an effective treatment modality in many cancers, there is an urgent need to develop therapeutic drugs capable of overcoming radioresistance or minimizing normal tissue toxicity. A wide variety of marine-derived bioactive compounds have been screened for anti-cancer drug discovery, but little is known regarding radiation therapy applications. In this study, six different extracts of marine sponges collected from the Micronesian sea were screened for anti-cancer and radiosensitizing activity. Two extracts derived from Agelas sponges collected off the coast of Kosrae and Chuuk, the Federated States of Micronesia significantly decreased clonogenic survival of hepatocellular carcinoma (HCC) cells after exposure to ionizing radiation (IR). The Agelas extracts augmented IR-induced apoptosis and accumulation of reactive oxygen species (ROS). Endoplasmic reticulum (ER) stress was increased via unfolded protein response stimulation, which induced autophagy. N-acetylcysteine, a ROS scavenger, diminished ER stress and autophagy induction effects. This result indicated that Agelas extracts may sensitize HCC cells to IR via ROS overproduction in vitro. Our findings suggest that the Agelas sp. may have potential utility in radiosensitizer development.

The Role of the Mammalian Target of Rapamycin (mTOR) in Pulmonary Fibrosis

The phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR)-dependent pathway is one of the most integral pathways linked to cell metabolism, proliferation, differentiation, and survival. This pathway is dysregulated in a variety of diseases, including neoplasia, immune-mediated diseases, and fibroproliferative diseases such as pulmonary fibrosis. The mTOR kinase is frequently referred to as the master regulator of this pathway. Alterations in mTOR signaling are closely associated with dysregulation of autophagy, inflammation, and cell growth and survival, leading to the development of lung fibrosis. Inhibitors of mTOR have been widely studied in cancer therapy, as they may sensitize cancer cells to radiation therapy. Studies also suggest that mTOR inhibitors are promising modulators of fibroproliferative diseases such as idiopathic pulmonary fibrosis (IPF) and radiation-induced pulmonary fibrosis (RIPF). Therefore, mTOR represents an attractive and unique therapeutic target in pulmonary fibrosis. In this review, we discuss the pathological role of mTOR kinase in pulmonary fibrosis and examine how mTOR inhibitors may mitigate fibrotic progression.

Metal-based NanoEnhancers for Future Radiotherapy: Radiosensitizing and Synergistic Effects on Tumor Cells

Radiotherapy is one of the major therapeutic strategies for cancer treatment. In the past decade, there has been growing interest in using high Z (atomic number) elements (materials) as radiosensitizers. New strategies in nanomedicine could help to improve cancer diagnosis and therapy at cellular and molecular levels. Metal-based nanoparticles usually exhibit chemical inertness in cellular and subcellular systems and may play a role in radiosensitization and synergistic cell-killing effects for radiation therapy. This review summarizes the efficacy of metal-based NanoEnhancers against cancers in both in vitro and in vivo systems for a range of ionizing radiations including gamma-rays, X-rays, and charged particles. The potential of translating preclinical studies on metal-based nanoparticles-enhanced radiation therapy into clinical practice is also discussed using examples of several metal-based NanoEnhancers (such as CYT-6091, AGuIX, and NBTXR3). Also, a few general examples of theranostic multimetallic nanocomposites are presented, and the related biological mechanisms are discussed.

The inhibitory effect of minocycline on radiation-induced neuronal apoptosis via AMPKα1 signaling-mediated autophagy

Due to an increasing concern about radiation-induced cognitive deficits for brain tumor patients receiving radiation therapy, developing and evaluating countermeasures has become inevitable. Our previous study has found that minocycline, a clinical available antibiotics that can easily cross the blood brain barrier, mitigates radiation-induced long-term memory loss in rats, accompanied by decreased hippocampal neuron apoptosis. Thus, in the present study, we report an unknown mechanism underlying the neuroprotective effect of minocycline. We demonstrated that minocycline prevented primary neurons from radiation-induced apoptosis and promoted radiation-induced autophagy in vitro. Moreover, using an immortalized mouse hippocampal neuronal cell line, HT22 cells, we found that the protective effect of minocycline on irradiated HT22 cells was not related to DNA damage repair since minocycline did not facilitate DNA DSB repair in irradiated HT22 cells. Further investigation showed that minocycline significantly enhanced X-irradiation-induced AMPKα1 activation and autophagy, thus resulting in decreased apoptosis. Additionally, although the antioxidant potential of minocycline might contribute to its apoptosis-inhibitory effect, it was not involved in its enhancive effect on radiation-induced AMPKα1-mediated autophagy. Taken together, we have revealed a novel mechanism for the protective effect of minocycline on irradiated neurons, e.g. minocycline protects neurons from radiation-induced apoptosis via enhancing radiation-induced AMPKα1-mediated autophagy.

Stress and the nonsense-mediated RNA decay pathway

Cells respond to internal and external cellular stressors by activating stress-response pathways that re-establish homeostasis. If homeostasis is not achieved in a timely manner, stress pathways trigger programmed cell death (apoptosis) to preserve organism integrity. A highly conserved stress pathway is the unfolded protein response (UPR), which senses excessive amounts of unfolded proteins in the ER. While a physiologically beneficial pathway, the UPR requires tight regulation to provide a beneficial outcome and avoid deleterious consequences. Recent work has demonstrated that a conserved and highly selective RNA degradation pathway-nonsense-mediated RNA decay (NMD)-serves as a major regulator of the UPR pathway. NMD degrades mRNAs encoding UPR components to prevent UPR activation in response to innocuous ER stress. In response to strong ER stress, NMD is inhibited by the UPR to allow for a full-magnitude UPR response. Recent studies have indicated that NMD also has other stress-related functions, including promoting the timely termination of the UPR to avoid apoptosis; NMD also regulates responses to non-ER stressors, including hypoxia, amino-acid deprivation, and pathogen infection. NMD regulates stress responses in species across the phylogenetic scale, suggesting that it has conserved roles in shaping stress responses. Stress pathways are frequently constitutively activated or dysregulated in human disease, raising the possibility that "NMD therapy" may provide clinical benefit by downmodulating stress responses.

Influence of autophagy on the efficacy of radiotherapy

Autophagy is an important catabolic process in which cells digest and recycle their own cytoplasmic contents for maintaining cellular homeostasis. Interestingly, autophagy could play both pro-death and pro-survival roles in influencing the development of cancer via various signal pathways. As radiotherapy is one of the main treatment modalities for cancer, we reviewed the effect of autophagy modulations on radiosensitivity and radiotherapy efficacy in various cancer types. The future development of autophagy modifications for improving radiotherapy efficacy and cancer prognosis will also be discussed.

The Role of Autophagy in Cancer

Autophagy is a highly conserved and regulated process that targets proteins and damaged organelles for lysosomal degradation to maintain cell metabolism, genomic integrity, and cell survival. The role of autophagy in cancer is dynamic and depends, in part, on tumor type and stage. Although autophagy constrains tumor initiation in normal tissue, some tumors rely on autophagy for tumor promotion and maintenance. Studies in genetically engineered mouse models support the idea that autophagy can constrain tumor initiation by regulating DNA damage and oxidative stress. In established tumors, autophagy can also be required for tumor maintenance, allowing tumors to survive environmental stress and providing intermediates for cell metabolism. Autophagy can also be induced in response to chemotherapeutics, acting as a drug-resistance mechanism. Therefore, targeting autophagy is an attractive cancer therapeutic option currently undergoing validation in clinical trials.

Egr-1 regulates irradiation-induced autophagy through Atg4B to promote radioresistance in hepatocellular carcinoma cells

Although hepatocellular carcinoma (HCC) is usually response to radiation therapy, radioresistance is still the major obstacle that limits the efficacy of radiotherapy for HCC patients. Therefore, further investigation of underlying mechanisms in radioresistant HCC cells is warranted. In this study, we determined the effect of early growth response factor (Egr-1) on irradiation-induced autophagy and radioresistance in HCC cell lines SMMC-7721 and HepG2. We showed that autophagy-related gene 4B (Atg4B) is induced by Egr-1 upon ionizing radiation (IR) in HCC cells. Luciferase reporter assays and chromatin immunoprecipitation (ChIP) revealed that Egr-1 binds to the Atg4B promoter to upregulate its expression in HCC cells. Suppression of Egr-1 function by dominant-negative Egr-1 dampens IR-induced autophagy, cell migration, and increases cell sensitivity to radiotherapy. Together, these results suggest that Egr-1 contributes to HCC radioresistance through directly upregulating target gene Atg4B, which may serve as a protective mechanism by preferential activation of the autophagy.

The Traditional Chinese Medicine DangguiBuxue Tang Sensitizes Colorectal Cancer Cells to Chemoradiotherapy

Chemotherapy is an important treatment modality for colon cancer, and concurrent chemoradiation therapy (CCRT) is the preferred treatment route for patients with stage II and III rectal cancer. We examined whether DangguiBuxue Tang (DBT), a traditional Chinese herbal extract, sensitizes colorectal cancer cells to anticancer treatments. The polysaccharide-depleted fraction of DBT (DBT-PD) contains greater amounts of astragaloside IV (312.626 µg/g) and ferulic acid (1.404 µg/g) than does the original formula. Treatment of the murine colon carcinoma cell line (CT26) with DBT-PD inhibits growth, whereas treatment with comparable amounts of purified astragaloside IV and ferulic acid showed no significant effect. Concurrent treatment with DBT-PD increases the growth inhibitory effect of 5-fluorouracil up to 4.39-fold. DBT-PD enhances the effect of radiation therapy (RT) with a sensitizer enhancement ratio (SER) of up to 1.3. It also increases the therapeutic effect of CCRT on CT26 cells. Cells treated with DBP-PD showed ultrastructural changes characteristic of autophagy, including multiple cytoplasmic vacuoles with double-layered membranes, vacuoles containing remnants of degraded organelles, marked swelling and vacuolization of mitochondria, and autolysosome-like vacuoles. We conclude that DBT-PD induces autophagy-associated cell death in CT26 cells, and may have potential as a chemotherapy or radiotherapy sensitizer in colorectal cancer treatment.

The Challenge of Developing Autophagy Inhibition as a Therapeutic Strategy

The finding that cancer chemotherapeutic drugs and ionizing radiation often promote autophagy has provided the foundation for clinical trials combining autophagy-blocking agents with antitumor drugs and radiation. The premise driving these trials is that therapy-induced autophagy is cytoprotective; consequently, inhibition of autophagy is anticipated to sensitize malignancies to therapy. However, it is well-established that autophagy may also mediate the toxicity of antitumor drugs while evidence also exists for a nonprotective function of autophagy. Consequently, given that it cannot be predicted what form autophagy will take upon treatment with chemotherapy or radiation, the current ongoing clinical trials are likely to generate contradictory or inconsistent results, with the potential consequence that autophagy inhibition could be dismissed as therapeutic strategy based on what are essentially false-negative outcomes. Appropriate interpretation of the outcomes of these trials would require knowledge as to whether the drugs or radiation used promote the cytoprotective form of autophagy in the tumor cells as well as whether the chloroquine or hydroxychloroquine actually inhibit the autophagy. Ultimately, it will be necessary to identify those patients for whom the strategy of autophagy inhibition would be anticipated to improve the response to therapy. However, this is currently not feasible in the absence of appropriate bioassays or predictive markers for characterization of the autophagy or the effectiveness of pharmacologic approaches for autophagy inhibition in the clinic. Cancer Res; 76(19); 5610-4. ©2016 AACR.

Enhanced inhibition of clonogenic survival of human medulloblastoma cells by multimodal treatment with ionizing irradiation, epigenetic modifiers, and differentiation-inducing drugs

Background

Medulloblastoma (MB) is the most common pediatric brain tumor. Current treatment regimes consisting of primary surgery followed by radio- and chemotherapy, achieve 5-year overall survival rates of only about 60 %. Therapy-induced endocrine and neurocognitive deficits are common late adverse effects. Thus, improved antitumor strategies are urgently needed. In this study, we combined irradiation (IR) together with epigenetic modifiers and differentiation inducers in a multimodal approach to enhance the efficiency of tumor therapy in MB and also assessed possible late adverse effects on neurogenesis.

Methods

In three human MB cell lines (DAOY, MEB-Med8a, D283-Med) short-time survival (trypan blue exclusion assay), apoptosis, autophagy, cell cycle distribution, formation of gH2AX foci, and long-term reproductive survival (clonogenic assay) were analyzed after treatment with 5-aza-2′-deoxycytidine (5-azadC), valproic acid (VPA), suberanilohydroxamic acid (SAHA), abacavir (ABC), all-trans retinoic acid (ATRA) and resveratrol (RES) alone or combined with 5-aza-dC and/or IR. Effects of combinatorial treatments on neurogenesis were evaluated in cultured murine hippocampal slices from transgenic nestin-CFPnuc C57BL/J6 mice. Life imaging of nestin-positive neural stem cells was conducted at distinct time points for up to 28 days after treatment start.

Results

All tested drugs showed a radiosynergistic action on overall clonogenic survival at least in two-outof-three MB cell lines. This effect was pronounced in multimodal treatments combining IR, 5-aza-dC and a second drug. Hereby, ABC and RES induced the strongest reduction of clongenic survival in all three MB cell lines and led to the induction of apoptosis (RES, ABC) and/or autophagy (ABC). Additionally, 5-aza-dC, RES, and ABC increased the S phase cell fraction and induced the formation of gH2AX foci at least in oneout-of-three cell lines. Thereby, the multimodal treatment with 5-aza-dC, IR, and RES or ABC did not change the number of normal neural progenitor cells in murine slice cultures.

Conclusion

In conclusion, the radiosensitizing capacities of epigenetic and differentiation-inducing drugs presented here suggest that their adjuvant administration might improve MB therapy. Thereby, the combination of 5-aza-dC/IR with ABC and RES seemed to be the most promising to enhance tumor control without affecting the normal neural precursor cells.

Autophagy is not uniformly cytoprotective: a personalized medicine approach for autophagy inhibition as a therapeutic strategy in non-small cell lung cancer

BACKGROUND

Lung cancer is the leading cause of cancer-related death worldwide. In addition to surgical resection, which is considered first-line treatment at early stages of the disease, chemotherapy and radiation are widely used when the disease is advanced. Of multiple responses that may occur in the tumor cells in response to cancer therapy, the functional importance of autophagy remains equivocal; this is likely to restrict current efforts to sensitize this malignancy to chemotherapy and/or radiation by pharmacological interference with the autophagic response.

SCOPE OF REVIEW

In this review, we attempt to summarize the current state of knowledge based on studies that evaluated the function of autophagy in non-small cell lung cancer (NSCLC) cells in response to radiation and the most commonly used chemotherapeutic agents.

MAJOR CONCLUSIONS

In addition to the expected prosurvival function of autophagy, where autophagy inhibition enhances the response to therapy, autophagy appears also to have a "non-cytoprotective" function, where autophagy blockade does not affect cell viability, clonogenicity or tumor volume in response to therapy. In other cases, autophagy may actually mediate drug action via expression of its cytotoxic function.

GENERAL SIGNIFICANCE

These observations emphasize the complexity of autophagy function when examined in different tumor cell lines and in response to different chemotherapeutic agents. A more in-depth understanding of the conditions that promote the unique functions of autophagy is required in order to translate preclinical findings of autophagy inhibition to the clinic for the purpose of improving patient response to chemotherapy and radiation.